Fourth Generation and Dark Matter - University of Arizonashufang/talk/ppp9_4th.pdf ·...

S. Su

Fourth Generation and Dark Matter

In collaboration with J. Alwall, J.L. Feng, J. KumararXiv: 1002.3366; 110x.xxxx.

Shufang Su • U. of Arizona

Saturday, June 4, 2011

S. Su

Not the usual 4th generation ...CDF: b’

Selection2 like-signed leptons 2 jets (1 flavor tag)Missing transverse energy Sample2.7/fb

CDF t’

t’

t’qq

100

101

102

103

even

ts/2

5 G

eV

10-1

diffe

renc

e

0

+20

-20

0 100 200 300 500400Mreco (GeV)

CDF Run 2 (4.6 fb-1)Preliminary

QCDW+jets, EWtt_

Observedt’t’

_


S. Su

Exotic 4th Generation Quarks


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chiral under SM gauge group


S. Su


chiral under SM gauge group

charge under hidden symmetry


S. Su 4

Outline -

Motivation: general / specific

Constraints

Simulations and cut analysis Exclusion and discovery reach

Conclusion


S. Su 5

Dark matter motivation: general-

Dark Matter: long-lived on cosmological time scale Charge under a new unbroken symmetry ⇒ absolutely stable

๏ have only gravitational interaction with the SMcan not be discovered at colliders

๏ couple to SM through connector Y YY production with y → f X

DM

X Y f

connector SM


S. Su 5





DM

X Y f

connector SM

SM charge & dark charge


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DM

X Y f

connector SM

SUSY neutralino squark quark R-parity

ExD KK gauge boson KK quark quark KK-parity

Our study DM(no SM charge) exotic quark quark dark charge

SM charge & dark charge


S. Su 6

-

WIMPless model (discrete symmetry)

V = λ�XQ�

LqL + XB�RbR + XT �

RtR�

Q�L :

�3, 2, 1

6

�

T �R :

�3, 1, 2

3

�

B�R :

�3, 1,− 1

3

�.

Dark matter motivation: WIMPless modelJ.L. Feng and J. Kumar, PRL 101, 231301 (2008)


S. Su 6

-


V = λ�XQ�


RtR�

Q�L :

�3, 2, 1

6

�

T �R :

�3, 1, 2

3

�

B�R :

�3, 1,− 1

3

�.

not chiralityopposite chiralityof SM quark



S. Su 6

-


V = λ�XQ�


RtR�

Q�L :

�3, 2, 1

6

�

T �R :

�3, 1, 2

3

�

B�R :

�3, 1,− 1

3

�.


Exotic 4th-generationmirror quarks



S. Su 6

-


V = λ�XQ�


RtR�

Q�L :

�3, 2, 1

6

�

T �R :

�3, 1, 2

3

�

B�R :

�3, 1,− 1

3

�.




2

FIG. 1: Sectors of the model. SUSY breaking is mediated bygauge interactions to the MSSM and the hidden sector, whichcontains the dark matter particle X. An optional connectorsector contains fields Y , charged under both MSSM and hid-den sector gauge groups, which induce signals in direct andindirect searches and at colliders. There may also be otherhidden sectors with their own dark matter particles, leadingto multi-component dark matter.

models of Ref. [3] to include one hidden sector. Our re-sults will not depend on hidden sector details, but toaid in drawing intuition from well-known results, we as-sume that the hidden sector has the same matter andgauge groups as the MSSM, but with di!erent gauge andYukawa couplings, as discussed below. SUSY breakinggives vacuum expectation values to a chiral field S, with!S" = M + !2F . We couple S to MSSM messenger fields" and " and hidden sector messenger fields "X and "X

through the superpotential W = ""S" + "X"XS"X .These couplings generate messenger F -terms Fm = "Fand FmX = "XF and induce SUSY-breaking masses inthe MSSM and hidden sectors at the messenger massscales Mm = "M and MmX = "XM , respectively.

Relic Density. Neglecting subleading e!ects and O(1)factors, the MSSM superpartner masses are

m #g2

16#2

Fm

Mm

=g2

16#2

F

M, (2)

where g is the largest relevant gauge coupling. Since malso determines the electroweak symmetry breaking scale,m # mweak. The hidden sector superpartner masses are

mX #g2

X

16#2

FmX

MmX=

g2X

16#2

F

M. (3)

As a result,

mX

g2X

#m

g2#

F

16#2M; (4)

that is, mX/g2X is determined solely by the SUSY-

breaking sector. As this is exactly the combination ofparameters that determines the thermal relic density ofEq. (1), the hidden sector automatically includes a darkmatter candidate that has the desired thermal relic den-sity, irrespective of its mass. (In this example, the su-perpartner masses are independent of " and "X ; this

will not hold generally. However, given typical couplings" # "X # O(1), one expects the messenger F -terms andmasses to be approximately the same as those appearingin !S", and Eq. (4) remains valid.)

This analysis assumes that these thermal relics are sta-ble. Of course, this is not the case in the MSSM sector,where thermal relics decay to gravitinos. This is a majordrawback for GMSB, especially because its classic darkmatter candidate, the thermal gravitino [5], is now toohot to be compatible with standard cosmology [6]. So-lutions to the dark matter problem in GMSB includemessenger sneutrinos [7], late entropy production [8], de-caying singlets [9], and gravitino production in late de-cays [10], but all of these bring complications, and onlythe last one makes use of the WIMP miracle.

The problem exists in the MSSM, however, only be-cause of an accident: the stable particles of the MSSM (p,e, $, %, G) have masses which are not set by the SUSY-breaking scale. Indeed, in the cases of the proton andelectron, this accident results from extremely suppressedYukawa couplings, which remain unexplained. There isno reason for the hidden sector to su!er from this unfor-tunate malady. Very generally, since mX is the only massscale in the hidden sector, we expect all hidden particlesto have mass # mX or be essentially massless, if en-forced by a symmetry. We assume that the thermal relichas mass around mX , and that discrete or global sym-metries make this particle stable. At the same time, theparticles that are essentially massless at freeze out pro-vide the thermal bath required for the validity of Eq. (1).An example of a viable hidden sector is one with MSSM-like particle content, but with di!erent gauge couplings,3rd generation quark flavor conserved by a discrete orglobal symmetry, and hidden t, b, t, and b masses all# mX . The lightest of these hidden particles will bestable. They will combine with other particles to formneutral bound states, properly seed structure formation,and, in the absence of constraints on anomalous isotopesin hidden sea water, be excellent dark matter candidates.

To summarize so far: GMSB models with hidden sec-tors provide dark matter candidates that are not WIMPsbut nevertheless naturally have the correct thermal relicdensity. These candidates have masses and gauge cou-plings satisfying mX/g2

X # mweak/g2weak, and

10!3 <# gX

<# 3

10 MeV <# mX

<# 10 TeV , (5)

where the upper limits from perturbativity nearly satu-rate the unitarity bound [11], and the lower limits arerough estimates from requiring the thermal relic to benon-relativistic at freeze out so that Eq. (1) is valid.

Detection. If the hidden sector is not directly coupledto the SM, then the corresponding dark matter candidateinteracts with the known particles only through gravity.These candidates are cold dark matter, and their prop-erties could be probed through their impact on structure

2





m #g2

16#2

Fm

Mm

=g2

16#2

F

M, (2)


mX #g2

X

16#2

FmX

MmX=

g2X

16#2

F

M. (3)

As a result,

mX

g2X

#m

g2#

F

16#2M; (4)








10!3 <# gX

<# 3

10 MeV <# mX

<# 10 TeV , (5)



arX

iv:0

803.4

196v2 [h

ep-p

h]

1 M

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008

UCI-TR-2008-10

The WIMPless Miracle

Jonathan L. Feng and Jason KumarDepartment of Physics and Astronomy, University of California, Irvine, CA 92697, USA

We propose that dark matter is composed of particles that naturally have the correct thermalrelic density, but have neither weak-scale masses nor weak interactions. These WIMPless modelsemerge naturally from gauge-mediated supersymmetry breaking, where they elegantly solve thedark matter problem. The framework accommodates single or multiple component dark matter,dark matter masses from 10 MeV to 10 TeV, and interaction strengths from gravitational to strong.These candidates enhance many direct and indirect signals relative to WIMPs and have qualitativelynew implications for dark matter searches and cosmological implications for colliders.

PACS numbers: 95.35.+d, 04.65.+e, 12.60.Jv

Introduction. Cosmological observations require darkmatter that cannot be composed of any of the knownparticles. At the same time, attempts to understandthe weak force also invariably require new states. Thesetypically include weakly-interacting massive particles(WIMPs) with masses around the weak scale mweak !100 GeV " 1 TeV and weak interactions with couplinggweak # 0.65. An appealing possibility is that one of theparticles motivated by particle physics simultaneouslysatisfies the needs of cosmology. This idea is motivatednot only by Ockham’s razor, but by a striking quanti-tative fact, the “WIMP miracle”: WIMPs are naturallyproduced as thermal relics of the Big Bang with the den-sities required for dark matter. The WIMP miracle con-nects physics at the largest and smallest length scales,drives most of the international program of dark mattersearches, and is the leading reason to expect cosmologicalinsights when the Large Hadron Collider (LHC) beginsoperation in the coming year.

We show here, however, that the WIMP miracle doesnot necessarily imply the existence of WIMPs. More pre-cisely, we present well-motivated particle physics mod-els in which particles naturally have the desired ther-mal relic density, but have neither weak-scale masses norweak force interactions. In these models, dark mattermay interact only gravitationally or it may couple morestrongly to known particles. The latter possibility impliesthat prospects for some dark matter experiments may begreatly enhanced relative to WIMPs, with implicationsfor searches that di!er radically from those of WIMPs.

Quite generally, a particle’s thermal relic density is [1]

"X $1

%!v&!

m2X

g4X

, (1)

where %!v& is its thermally-averaged annihilation crosssection, mX and gX are the characteristic mass scaleand coupling entering this cross section, and the laststep follows from dimensional analysis. In the mod-els discussed here, mX will be the dark matter parti-cle’s mass. The WIMP miracle is the statement that,for (mX , gX) ! (mweak, gweak), the relic density is typi-cally within an order of magnitude of the observed value,

"X ' 0.24. Equation (1) makes clear, however, thatthe thermal relic density fixes only one combination ofthe dark matter’s mass and coupling. This observationalone might be considered adequate motivation to con-sider other values of (mX , gX) that give the correct "X .Here, however, we further show that simple models withlow-energy supersymmetry (SUSY) predict exactly thecombinations of (mX , gX) that give the correct "X . Inthese models, mX is a free parameter. For mX (= mweak,these models are WIMPless, but for all mX they containdark matter with the desired thermal relic density.

Models. The models we consider are SUSY mod-els with gauge-mediated SUSY breaking (GMSB) [2, 3].These models have several sectors, as shown in Fig. 1.The MSSM sector includes the fields of the minimal su-persymmetric standard model. The SUSY-breaking sec-tor includes the fields that break SUSY dynamically andmediate this breaking to the MSSM through gauge in-teractions. There are also one or more additional sectorswhich have SUSY breaking gauge-mediated to them, andthese sectors contain the dark matter particles. Thesesectors may not be particularly well-hidden, dependingon the presence of connector sectors to be discussed be-low, but we follow precedent and refer to them as “hid-den” sectors throughout this work. For other recent in-vestigations of hidden dark matter, see Refs. [4].

Independent of cosmology, this is a well-motivated sce-nario for new physics. GMSB models feature many ofthe well-known virtues of SUSY, while at the same timeelegantly solving the flavor problems that genericallyplague proposals for new weak-scale physics. In addi-tion, in SUSY models that attempt to unite the standardmodel (SM) with quantum gravity, such as those arisingfrom string theory, hidden sectors are ubiquitous. Fromthis point of view, it is likely that such sectors are notmerely an unmotivated contrivance, but a requirement ofthe consistency of quantum gravity. Moreover, in largeclasses of string models, such as intersecting brane mod-els, SUSY breaking in one sector will naturally be medi-ated by gauge interactions to every other sector, produc-ing exactly the framework we have described.

As a concrete example, we extend the canonical GMSB


S. Su 6

-


V = λ�XQ�


RtR�

Q�L :

�3, 2, 1

6

�

T �R :

�3, 1, 2

3

�

B�R :

�3, 1,− 1

3

�.




๏ indirect detection XX → ff, YY

๏ direct detection Xf → Xf

๏ collider: 4th generation fermions

2





m #g2

16#2

Fm

Mm

=g2

16#2

F

M, (2)


mX #g2

X

16#2

FmX

MmX=

g2X

16#2

F

M. (3)

As a result,

mX

g2X

#m

g2#

F

16#2M; (4)








10!3 <# gX

<# 3

10 MeV <# mX

<# 10 TeV , (5)



2





m #g2

16#2

Fm

Mm

=g2

16#2

F

M, (2)


mX #g2

X

16#2

FmX

MmX=

g2X

16#2

F

M. (3)

As a result,

mX

g2X

#m

g2#

F

16#2M; (4)








10!3 <# gX

<# 3

10 MeV <# mX

<# 10 TeV , (5)



arX

iv:0

803.4

196v2 [h

ep-p

h]

1 M

ay 2

008

UCI-TR-2008-10

The WIMPless Miracle

Jonathan L. Feng and Jason KumarDepartment of Physics and Astronomy, University of California, Irvine, CA 92697, USA

We propose that dark matter is composed of particles that naturally have the correct thermalrelic density, but have neither weak-scale masses nor weak interactions. These WIMPless modelsemerge naturally from gauge-mediated supersymmetry breaking, where they elegantly solve thedark matter problem. The framework accommodates single or multiple component dark matter,dark matter masses from 10 MeV to 10 TeV, and interaction strengths from gravitational to strong.These candidates enhance many direct and indirect signals relative to WIMPs and have qualitativelynew implications for dark matter searches and cosmological implications for colliders.

PACS numbers: 95.35.+d, 04.65.+e, 12.60.Jv

Introduction. Cosmological observations require darkmatter that cannot be composed of any of the knownparticles. At the same time, attempts to understandthe weak force also invariably require new states. Thesetypically include weakly-interacting massive particles(WIMPs) with masses around the weak scale mweak !100 GeV " 1 TeV and weak interactions with couplinggweak # 0.65. An appealing possibility is that one of theparticles motivated by particle physics simultaneouslysatisfies the needs of cosmology. This idea is motivatednot only by Ockham’s razor, but by a striking quanti-tative fact, the “WIMP miracle”: WIMPs are naturallyproduced as thermal relics of the Big Bang with the den-sities required for dark matter. The WIMP miracle con-nects physics at the largest and smallest length scales,drives most of the international program of dark mattersearches, and is the leading reason to expect cosmologicalinsights when the Large Hadron Collider (LHC) beginsoperation in the coming year.

We show here, however, that the WIMP miracle doesnot necessarily imply the existence of WIMPs. More pre-cisely, we present well-motivated particle physics mod-els in which particles naturally have the desired ther-mal relic density, but have neither weak-scale masses norweak force interactions. In these models, dark mattermay interact only gravitationally or it may couple morestrongly to known particles. The latter possibility impliesthat prospects for some dark matter experiments may begreatly enhanced relative to WIMPs, with implicationsfor searches that di!er radically from those of WIMPs.

Quite generally, a particle’s thermal relic density is [1]

"X $1

%!v&!

m2X

g4X

, (1)

where %!v& is its thermally-averaged annihilation crosssection, mX and gX are the characteristic mass scaleand coupling entering this cross section, and the laststep follows from dimensional analysis. In the mod-els discussed here, mX will be the dark matter parti-cle’s mass. The WIMP miracle is the statement that,for (mX , gX) ! (mweak, gweak), the relic density is typi-cally within an order of magnitude of the observed value,

"X ' 0.24. Equation (1) makes clear, however, thatthe thermal relic density fixes only one combination ofthe dark matter’s mass and coupling. This observationalone might be considered adequate motivation to con-sider other values of (mX , gX) that give the correct "X .Here, however, we further show that simple models withlow-energy supersymmetry (SUSY) predict exactly thecombinations of (mX , gX) that give the correct "X . Inthese models, mX is a free parameter. For mX (= mweak,these models are WIMPless, but for all mX they containdark matter with the desired thermal relic density.

Models. The models we consider are SUSY mod-els with gauge-mediated SUSY breaking (GMSB) [2, 3].These models have several sectors, as shown in Fig. 1.The MSSM sector includes the fields of the minimal su-persymmetric standard model. The SUSY-breaking sec-tor includes the fields that break SUSY dynamically andmediate this breaking to the MSSM through gauge in-teractions. There are also one or more additional sectorswhich have SUSY breaking gauge-mediated to them, andthese sectors contain the dark matter particles. Thesesectors may not be particularly well-hidden, dependingon the presence of connector sectors to be discussed be-low, but we follow precedent and refer to them as “hid-den” sectors throughout this work. For other recent in-vestigations of hidden dark matter, see Refs. [4].

Independent of cosmology, this is a well-motivated sce-nario for new physics. GMSB models feature many ofthe well-known virtues of SUSY, while at the same timeelegantly solving the flavor problems that genericallyplague proposals for new weak-scale physics. In addi-tion, in SUSY models that attempt to unite the standardmodel (SM) with quantum gravity, such as those arisingfrom string theory, hidden sectors are ubiquitous. Fromthis point of view, it is likely that such sectors are notmerely an unmotivated contrivance, but a requirement ofthe consistency of quantum gravity. Moreover, in largeclasses of string models, such as intersecting brane mod-els, SUSY breaking in one sector will naturally be medi-ated by gauge interactions to every other sector, produc-ing exactly the framework we have described.

As a concrete example, we extend the canonical GMSB


S. Su 7

3rd generation vs. the first two-

๏ first two generations, tree level scattering ⇒ λ ~ 0.03

๏ third generation- loop level scattering, λ ~ 0.3-1, more natural

- less constrained by FCNC

X

q

Q!

X

q

X X

g g

Q!

q

q q

M. A. Shifman, A. I. Vainshtein and V. I. Zakharov, Phys. Lett. B 78, 443 (1978).

X

q

Q!

X

q

X X

g g

Q!

q

q q


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Collider Signature: exotic quarks-

Y particle appears as exotic 4th generation mirror quarks Q’

p

p

Qʼ

Qʼ

DM

qDM

q

Collider Signal T’T’→ttXX, B’B’ →bbXX

๏ differ from SUSY searches: cascade decay ๏ differ from usual 4th generation quark T’ → Wb, B’ → Wt


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Collider Signature: exotic quarks-

Collider Signal: T’T’→ttXX, B’B’ →bbXX

๏ appears in a general set of new physics scenarios- asymmetric dark matter - little Higgs with T-parity- baryon and lepton number as gauge symmetry- ...

๏ Connection to solution for Hierarchy problem- need top partner - the lighter, the more natural- decay straight to invisible particles- bottom partner

P. Fileviez Perez and M. B. Wise, arXiv: 1002.1754

H.C. Cheng and I. Low, JHEP 0408, 061 (2004)

B. Dutta and J. Kumar, arXiv: 1012.1341


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Constraints-

๏ perturbativity constraints: mQ’ = yQ’ v, mQ’ ≤ 600 GeV (if through Yukawa)๏ precision electroweak data: |mT’-mB’| ~ 50 GeV (for SU(2) doublet)๏ direct searches limits

B’B’→bbXX, similar to sbottom pair production with b→ bχ01

7

Leptoquark Mass (GeV)

150 200 250 300

(p

b)

2B!

"

-110

1

-1D0, L=5.2 fb (a)

LQ NLO cross section, )=1#b$3

BF(LQ%B

LQ NLO cross section, spF!B=1 - 0.5

Observed limits

Expected limits


150 200 250 300

(p

b)

2B!

"

-110

1

Bottom Squark Mass (GeV)

0 50 100 150 200 250

Neu

tralin

o M

ass (

GeV

)

0

20

40

60

80

100

120


0 50 100 150 200 250

Neu

tralin

o M

ass (

GeV

)

0

20

40

60

80

100

120


0 50 100 150 200 250

Neu

tralin

o M

ass (

GeV

)

0

20

40

60

80

100

120

Observed

Expected

-1D0, L=5.2 fb (b)

D0Run I

-192 pb

CDFRun I

-188 pb

CDFRun II

-1295 pb

D0Run II

-1310 pb

D0 Run II-15.2 fb

=208 G

eV

s

LE

P

1

0&'

+ m

b

= m

1b~m


0 50 100 150 200 250

Neu

tralin

o M

ass (

GeV

)

0

20

40

60

80

100

120

FIG. 3: (color online). (a) The 95% C.L. expected (dashed line) and observed (points plus solid line) limits on ! ! B2 asa function of mLQ for the pair production of third-generation leptoquarks where B is the branching fraction to b". Thetheory band is shown in grey with an uncertainty range as discussed in the text. The long-dashed line indicates the expectedsuppression of ! ! B2 above the t# threshold for equal b" and t# couplings. (b) The 95% C.L. exclusion contour in the(mb1

,m!01) plane. Also shown are results from previous searches at LEP [23] and the Tevatron [7, 24].

expected from known SM processes. We set limits onthe cross section multiplied by square of the branchingfraction B to the b! final state as a function of lepto-quark mass. These results are interpreted as mass limitsand give a limit of 247 GeV for B = 1 for the produc-tion of charge-1/3 third-generation scalar leptoquarks.We also exclude the production of bottom squarks fora range of values in the (mb1

,m!01) mass plane such as

mb1> 247 GeV for m!0

1= 0 and m!0

1> 110 GeV for

160 < mb1< 200 GeV. These limits significantly extend

previous results.We thank the sta!s at Fermilab and collaborating

institutions, and acknowledge support from the DOEand NSF (USA); CEA and CNRS/IN2P3 (France);FASI, Rosatom and RFBR (Russia); CNPq, FAPERJ,FAPESP and FUNDUNESP (Brazil); DAE and DST (In-dia); Colciencias (Colombia); CONACyT (Mexico); KRFand KOSEF (Korea); CONICET and UBACyT (Ar-gentina); FOM (The Netherlands); STFC and the RoyalSociety (United Kingdom); MSMT and GACR (CzechRepublic); CRC Program and NSERC (Canada); BMBFand DFG (Germany); SFI (Ireland); The Swedish Re-search Council (Sweden); and CAS and CNSF (China).

[1] H.E. Haber and G.L. Kane, Phys. Rep. 117, 75 (1985); S.P. Martin, arXiv:hep-ph/9709356 and references therein.

[2] P. Fayet, Phys. Rev. Lett. 69, 489 (1977).[3] D. E. Acosta and S. K. Blessing, Ann. Rev. Nucl. Part.

Sci. 49, 389 (1999) and references therein; C. Amsler etal., Phys. Lett. B 667, 1 (2008).

[4] V.M. Abazov et al. (D0 Collaboration), Phys. Rev. Lett.104, 071801 (2010).

[5] W. Beenaakker et al., Nucl. Phys. B515, 3 (1998);www.thphys.uni-heidelberg.de/"plehn/prospino/. Thecalculation used a gluino mass of 609 GeV.

[6] M. Kramer, T. Plehn, M. Spira, and P. M. Zerwas, Phys.Rev. Lett. 79, 341 (1997).

[7] V.M. Abazov et al. (D0 Collaboration), Phys. Rev. Lett.97, 171806 (2006); V.M. Abazov et al. (D0 Collabora-tion), Phys. Rev. D 60, R031101 (1999).

[8] V.M. Abazov et al. (D0 Collaboration), Phys. Rev. Lett.99, 061801 (2007). Charge-2/3 and 4/3 third-generation

leptoquarks have been excluded for mLQ < 210 GeVassuming a 100% branching fraction into the b# mode,V.M. Abazov et al. (D0 Collaboration), Phys. Rev. Lett.101, 241802 (2008).

[9] V.M. Abazov et al. (D0 Collaboration), Nucl. Instrum.Methods in Phys. Res. A 565, 463 (2006); M. Abolinset al., Nucl. Instrum. Methods in Phys. Res. A 584, 75(2008); R. Angstadt et al., arXiv.org:0911.2522 [phys.ins-det], submitted to Nucl. Instrum. Methods in Phys.Res. A.

[10] G.C. Blazey et al., arXiv:hep-ex/0005012.[11] T. Sjostrand, S. Mrenna, and P. Skands, J. High Energy

Phys. 05, 026 (2006). We use version 6.323.[12] J.M. Campbell and R.K. Ellis, Phys.Rev. D 60, 113006

(1999); J.M. Campbell and R.K. Ellis, Phys.Rev. D 62,114012 (2000).

[13] M. Cacciari et al., J. High Energy Phys. 4, 068 (2004);N. Kidonakis and R. Vogt, Phys. Rev. D 68, 114014

V. M. Abazov et al. [D0 Collaboration], 1005.2222

msb>247 GeV (95% C.L.)D0


S. Su 10

Constraints-

๏ perturbativity constraints: mQ’ = yQ’ v, mQ’ ≤ 600 GeV (if through Yukawa)๏ precision electroweak data: |mT’-mB’| ~ 50 GeV (for SU(2) doublet)๏ direct searches limits

B’B’→bbXX, similar to sbottom pair production with b→ bχ01

7


150 200 250 300

(p

b)

2B!

"

-110

1

-1D0, L=5.2 fb (a)

LQ NLO cross section, )=1#b$3

BF(LQ%B

LQ NLO cross section, spF!B=1 - 0.5

Observed limits

Expected limits


150 200 250 300

(p

b)

2B!

"

-110

1


0 50 100 150 200 250

Neu

tralin

o M

ass (

GeV

)

0

20

40

60

80

100

120


0 50 100 150 200 250

Neu

tralin

o M

ass (

GeV

)

0

20

40

60

80

100

120


0 50 100 150 200 250

Neu

tralin

o M

ass (

GeV

)

0

20

40

60

80

100

120

Observed

Expected

-1D0, L=5.2 fb (b)

D0Run I

-192 pb

CDFRun I

-188 pb

CDFRun II

-1295 pb

D0Run II

-1310 pb

D0 Run II-15.2 fb

=208 G

eV

s

LE

P

1

0&'

+ m

b

= m

1b~m


0 50 100 150 200 250

Neu

tralin

o M

ass (

GeV

)

0

20

40

60

80

100

120

FIG. 3: (color online). (a) The 95% C.L. expected (dashed line) and observed (points plus solid line) limits on ! ! B2 asa function of mLQ for the pair production of third-generation leptoquarks where B is the branching fraction to b". Thetheory band is shown in grey with an uncertainty range as discussed in the text. The long-dashed line indicates the expectedsuppression of ! ! B2 above the t# threshold for equal b" and t# couplings. (b) The 95% C.L. exclusion contour in the(mb1

,m!01) plane. Also shown are results from previous searches at LEP [23] and the Tevatron [7, 24].

expected from known SM processes. We set limits onthe cross section multiplied by square of the branchingfraction B to the b! final state as a function of lepto-quark mass. These results are interpreted as mass limitsand give a limit of 247 GeV for B = 1 for the produc-tion of charge-1/3 third-generation scalar leptoquarks.We also exclude the production of bottom squarks fora range of values in the (mb1

,m!01) mass plane such as

mb1> 247 GeV for m!0

1= 0 and m!0

1> 110 GeV for

160 < mb1< 200 GeV. These limits significantly extend

previous results.We thank the sta!s at Fermilab and collaborating

institutions, and acknowledge support from the DOEand NSF (USA); CEA and CNRS/IN2P3 (France);FASI, Rosatom and RFBR (Russia); CNPq, FAPERJ,FAPESP and FUNDUNESP (Brazil); DAE and DST (In-dia); Colciencias (Colombia); CONACyT (Mexico); KRFand KOSEF (Korea); CONICET and UBACyT (Ar-gentina); FOM (The Netherlands); STFC and the RoyalSociety (United Kingdom); MSMT and GACR (CzechRepublic); CRC Program and NSERC (Canada); BMBFand DFG (Germany); SFI (Ireland); The Swedish Re-search Council (Sweden); and CAS and CNSF (China).

[1] H.E. Haber and G.L. Kane, Phys. Rep. 117, 75 (1985); S.P. Martin, arXiv:hep-ph/9709356 and references therein.

[2] P. Fayet, Phys. Rev. Lett. 69, 489 (1977).[3] D. E. Acosta and S. K. Blessing, Ann. Rev. Nucl. Part.

Sci. 49, 389 (1999) and references therein; C. Amsler etal., Phys. Lett. B 667, 1 (2008).

[4] V.M. Abazov et al. (D0 Collaboration), Phys. Rev. Lett.104, 071801 (2010).

[5] W. Beenaakker et al., Nucl. Phys. B515, 3 (1998);www.thphys.uni-heidelberg.de/"plehn/prospino/. Thecalculation used a gluino mass of 609 GeV.

[6] M. Kramer, T. Plehn, M. Spira, and P. M. Zerwas, Phys.Rev. Lett. 79, 341 (1997).

[7] V.M. Abazov et al. (D0 Collaboration), Phys. Rev. Lett.97, 171806 (2006); V.M. Abazov et al. (D0 Collabora-tion), Phys. Rev. D 60, R031101 (1999).

[8] V.M. Abazov et al. (D0 Collaboration), Phys. Rev. Lett.99, 061801 (2007). Charge-2/3 and 4/3 third-generation

leptoquarks have been excluded for mLQ < 210 GeVassuming a 100% branching fraction into the b# mode,V.M. Abazov et al. (D0 Collaboration), Phys. Rev. Lett.101, 241802 (2008).

[9] V.M. Abazov et al. (D0 Collaboration), Nucl. Instrum.Methods in Phys. Res. A 565, 463 (2006); M. Abolinset al., Nucl. Instrum. Methods in Phys. Res. A 584, 75(2008); R. Angstadt et al., arXiv.org:0911.2522 [phys.ins-det], submitted to Nucl. Instrum. Methods in Phys.Res. A.

[10] G.C. Blazey et al., arXiv:hep-ex/0005012.[11] T. Sjostrand, S. Mrenna, and P. Skands, J. High Energy

Phys. 05, 026 (2006). We use version 6.323.[12] J.M. Campbell and R.K. Ellis, Phys.Rev. D 60, 113006

(1999); J.M. Campbell and R.K. Ellis, Phys.Rev. D 62,114012 (2000).

[13] M. Cacciari et al., J. High Energy Phys. 4, 068 (2004);N. Kidonakis and R. Vogt, Phys. Rev. D 68, 114014

V. M. Abazov et al. [D0 Collaboration], 1005.2222

msb>247 GeV (95% C.L.)

msb > 247 GeV ⇒ mB’ > 365 (440) GeV

D0


S. Su 11

Constraints: direct search-

CDF, Run II, 2.5 fb-1, gluino pair production, g → bb b→ bχ01

T. Aaltonen et al. [CDF Collaboration], PRL 102, 221801 (2009).

two or more jets, large MET, 2b-tagging

]2Gluino Mass [GeV/c200 250 300 350 400

]2

Sbot

tom

Mas

s [G

eV/c

100

150

200

250

300

350

]2Gluino Mass [GeV/c200 250 300 350 400

]2

Sbot

tom

Mas

s [G

eV/c

100

150

200

250

300

350

CDF Run I excluded

kinem

atica

lly for

bidde

n

b~ b g~

2) = 60 GeV/c0m(2) = 500 GeV/cq~m(

-1CDF Run II 156 pbExcluded Region

-1D0 Run II 310 pbSbottom Pair ProductionExcluded Region

]2Gluino Mass [GeV/c200 250 300 350 400

]2

Sbot

tom

Mas

s [G

eV/c

100

150

200

250

300

350 )-1CDF Run II (2.5 fb95% CL limitExpected limit

b (100% BR)b~ g~

(100% BR)0 b b~

]2) [GeV/cg~m(250 300 350 400

Cro

ss S

ectio

n [p

b]

-210

-110

1

]2) [GeV/cg~m(250 300 350 400

Cro

ss S

ectio

n [p

b]

-210

-110

1

PROSPINO NLO (CTEQ6M)

=1.96 GeVs at g~g~ pp

)g~= m(Fµ= Rµ2)=500 GeV/cq~m( 2)=60 GeV/c0m(

)2]=250 GeV/cb~95% CL limit (m[Expected limit


)-1 CDF Run II (2.5 fb

b (100% BR)b~ g~

(100% BR)0 b b~


S. Su 11


CDF, Run II, 2.5 fb-1, gluino pair production, g → bb b→ bχ01

T. Aaltonen et al. [CDF Collaboration], PRL 102, 221801 (2009).

two or more jets, large MET, 2b-tagging

]2Gluino Mass [GeV/c200 250 300 350 400

]2

Sbot

tom

Mas

s [G

eV/c

100

150

200

250

300

350

]2Gluino Mass [GeV/c200 250 300 350 400

]2

Sbot

tom

Mas

s [G

eV/c

100

150

200

250

300

350

CDF Run I excluded

kinem

atica

lly for

bidde

n

b~ b g~

2) = 60 GeV/c0m(2) = 500 GeV/cq~m(

-1CDF Run II 156 pbExcluded Region

-1D0 Run II 310 pbSbottom Pair ProductionExcluded Region

]2Gluino Mass [GeV/c200 250 300 350 400

]2

Sbot

tom

Mas

s [G

eV/c

100

150

200

250

300

350 )-1CDF Run II (2.5 fb95% CL limitExpected limit

b (100% BR)b~ g~

(100% BR)0 b b~

]2) [GeV/cg~m(250 300 350 400

Cro

ss S

ectio

n [p

b]

-210

-110

1

]2) [GeV/cg~m(250 300 350 400

Cro

ss S

ectio

n [p

b]

-210

-110

1

PROSPINO NLO (CTEQ6M)

=1.96 GeVs at g~g~ pp

)g~= m(Fµ= Rµ2)=500 GeV/cq~m( 2)=60 GeV/c0m(



)-1 CDF Run II (2.5 fb

b (100% BR)b~ g~

(100% BR)0 b b~mgluino > 340 GeV for Δm ~ 20 GeV ⇒ mB’ > 370 GeV


S. Su 12


mgluino > 590 GeV

ATLAS Collaboration: 1103.4344

0-lepton 1-lepton 1-leptonMonte Carlo data-driven

tt and single top 12.2± 5.0 12.3± 4.0 14.7± 3.7W and Z 6.0± 2.0 0.8± 0.4 -QCD 1.4± 1.0 0.4± 0.4 0+0.4

!0.0

Total SM 19.6± 6.9 13.5± 4.1 14.7± 3.7Data 15 9 9

Table 2: Summary of the expected and observed event yields. TheQCD prediction for the zero-lepton channel is based on the semi-data-driven method described in the text. For the one-lepton chan-nel, the results for both the Monte Carlo and the data-driven ap-proach are given. Since the data-driven technique does not distin-guish between top and W/Z backgrounds the total background es-timate is shown in the top row. The errors are systematic for theexpected Monte Carlo prediction and statistical for the data-driventechnique.

tive values of the stop mass. Gluino masses below 520 GeVare excluded for stop masses in the range between 130 and300 GeV.Finally, the results of both analyses were used to calcu-

late 95% C.L. exclusion limits in the MSUGRA/CMSSMframework with large tan!. Figure 4 shows the observedand expected limits in the (m0,m1/2) plane, assumingtan! = 40, and fixing µ >0 and A0 = 0. The largestsensitivity is found for the zero-lepton analysis. Thecombination of the two analyses, which takes account ofcorrelations between systematic uncertainties of the twochannels, is also shown. Sbottom and stop masses be-low 550 GeV and 470 GeV are excluded across the plane,respectively. Due to the MSUGRA/CMSSM constraints,this interpretation is also sensitive to first and second gen-eration squarks. From the present analysis, masses of thesesquarks below 600 GeV are excluded for mg ! mq. Gluinomasses below 500 GeV are excluded for the m0 range be-tween 100 GeV and 1 TeV, independently on the squarkmasses. Changing the A0 value from 0 to "500 GeV leadto significant variations in third generation squark mixing.Across the (m0,m1/2) parameter space, sbottom and stop

masses decrease by about 10% and 30%, respectively, ifA0 is changed from 0 to "500 GeV. The exclusion regionof the one-lepton analysis, mostly sensitive to stop finalstates, extends the zero-lepton reach by about 20 GeV inm1/2 for m0 <600 GeV.

8. Conclusions

The ATLAS collaboration has presented a first searchfor supersymmetry in final states with missing transversemomentum and at least one b-jet candidate in proton-proton collisions at 7 TeV. The results are based on datacorresponding to an integrated luminosity of 35 pb!1 col-lected during 2010. These searches are sensitive to thegluino-mediated and direct production of sbottoms andstops, the supersymmetric partners of the third genera-tion quarks, which, due to mixing e!ects, might be the

[GeV]g~

m100 200 300 400 500 600 700

[G

eV

]1

b~m

200

300

400

500

600

700

0

1!" b+#

1b~

+b , 1

b~ # g~ production,

1b~

-1

b~

+ g~-g~

= 7 TeVs, -1

L dt = 35 pb$b-jet channel, 0-lepton, 3 jets

ATLAS

Reference point

)g~) >> m(1,2

q~) = 60 GeV , m(0

1!"m(

+b forb

idden

1b~

# g~

obs. limit 95% C.L.

exp. limit 95% C.L.

-1 2.65 fb1

b~

1b~

CDF

-1 5.2 fb1

b~

1b~

D0

-1+b 2.5 fb1

b~ # g~, g~g~CDF

Figure 2: Observed and expected 95% C.L. exclusion limits, as ob-tained with the zero-lepton channel, in the (mg ,mb

1

) plane. The

neutralino mass is assumed to be 60 GeV and the NLO cross sectionsare calculated using PROSPINO in the hypothesis of mq

1,2

! mg. The

result is compared to previous results from CDF searches which as-sume the same gluino-sbottom decays hypotheses, a neutralino massof 60 GeV and mq

1,2

= 500 GeV (! mg for the Tevatron kinematic

range). Exclusion limits from the CDF and D0 experiments on directsbottom pair production [8, 9] are also reported.

400 450 500 550 600

Cro

ss s

ectio

n [

pb

]

10

210b-jet channel, 1-lepton, 2 jets

)0

1!" 2 m(%)

±

1!") = 60 GeV , m(

0

1!"m(

)g~) >> m(1,2

q~ m(

= 210 GeV1t~m

NLO Prospino

obs. limit 95% C.L.

exp. limit 95% C.L.

[GeV]g~

m400 450 500 550 600

10

210

= 180 GeV1t~m

ATLAS = 7 TeVs , -1

L dt = 35 pb$

±

1!" b+# 1t

~+t , 1t

~ # g~ production, 1t

~-1t

~ + g~-g~

Figure 3: Observed and expected 95% C.L. upper limits, as obtainedwith the one-lepton analysis, on the gluino-mediated and stop pairproduction cross section as a function of the gluino mass for twoassumed values of the stop mass and BR(t1 " b!±

1) = 1. The

chargino is assumed to have twice the mass of the neutralino (=60 GeV) and NLO cross sections are calculated using PROSPINO inthe hypothesis of mq

1,2

! mg. Theoretical uncertainties on the

NLO cross sections are included in the limit calculation.

lightest squarks.

Since no excess above the expectations from StandardModel processes was found, the results are used to excludeparameter regions in various R-parity conserving SUSYmodels. Under the assumption that the lightest squark b1is produced via gluino-mediated processes or direct pairproduction and decays exclusively via b1 # b"0

1, gluino

7

0 lepton, 3 j (1b)

ATLAS, 35 pb-1, gluino+sbottom pair production


S. Su 12


mgluino > 590 GeV

ATLAS Collaboration: 1103.4344

0-lepton 1-lepton 1-leptonMonte Carlo data-driven

tt and single top 12.2± 5.0 12.3± 4.0 14.7± 3.7W and Z 6.0± 2.0 0.8± 0.4 -QCD 1.4± 1.0 0.4± 0.4 0+0.4

!0.0

Total SM 19.6± 6.9 13.5± 4.1 14.7± 3.7Data 15 9 9

Table 2: Summary of the expected and observed event yields. TheQCD prediction for the zero-lepton channel is based on the semi-data-driven method described in the text. For the one-lepton chan-nel, the results for both the Monte Carlo and the data-driven ap-proach are given. Since the data-driven technique does not distin-guish between top and W/Z backgrounds the total background es-timate is shown in the top row. The errors are systematic for theexpected Monte Carlo prediction and statistical for the data-driventechnique.

tive values of the stop mass. Gluino masses below 520 GeVare excluded for stop masses in the range between 130 and300 GeV.Finally, the results of both analyses were used to calcu-

late 95% C.L. exclusion limits in the MSUGRA/CMSSMframework with large tan!. Figure 4 shows the observedand expected limits in the (m0,m1/2) plane, assumingtan! = 40, and fixing µ >0 and A0 = 0. The largestsensitivity is found for the zero-lepton analysis. Thecombination of the two analyses, which takes account ofcorrelations between systematic uncertainties of the twochannels, is also shown. Sbottom and stop masses be-low 550 GeV and 470 GeV are excluded across the plane,respectively. Due to the MSUGRA/CMSSM constraints,this interpretation is also sensitive to first and second gen-eration squarks. From the present analysis, masses of thesesquarks below 600 GeV are excluded for mg ! mq. Gluinomasses below 500 GeV are excluded for the m0 range be-tween 100 GeV and 1 TeV, independently on the squarkmasses. Changing the A0 value from 0 to "500 GeV leadto significant variations in third generation squark mixing.Across the (m0,m1/2) parameter space, sbottom and stop

masses decrease by about 10% and 30%, respectively, ifA0 is changed from 0 to "500 GeV. The exclusion regionof the one-lepton analysis, mostly sensitive to stop finalstates, extends the zero-lepton reach by about 20 GeV inm1/2 for m0 <600 GeV.

8. Conclusions

The ATLAS collaboration has presented a first searchfor supersymmetry in final states with missing transversemomentum and at least one b-jet candidate in proton-proton collisions at 7 TeV. The results are based on datacorresponding to an integrated luminosity of 35 pb!1 col-lected during 2010. These searches are sensitive to thegluino-mediated and direct production of sbottoms andstops, the supersymmetric partners of the third genera-tion quarks, which, due to mixing e!ects, might be the

[GeV]g~

m100 200 300 400 500 600 700

[G

eV

]1

b~m

200

300

400

500

600

700

0

1!" b+#

1b~

+b , 1

b~ # g~ production,

1b~

-1

b~

+ g~-g~

= 7 TeVs, -1

L dt = 35 pb$b-jet channel, 0-lepton, 3 jets

ATLAS

Reference point

)g~) >> m(1,2

q~) = 60 GeV , m(0

1!"m(

+b forb

idden

1b~

# g~

obs. limit 95% C.L.

exp. limit 95% C.L.

-1 2.65 fb1

b~

1b~

CDF

-1 5.2 fb1

b~

1b~

D0

-1+b 2.5 fb1

b~ # g~, g~g~CDF

Figure 2: Observed and expected 95% C.L. exclusion limits, as ob-tained with the zero-lepton channel, in the (mg ,mb

1

) plane. The

neutralino mass is assumed to be 60 GeV and the NLO cross sectionsare calculated using PROSPINO in the hypothesis of mq

1,2

! mg. The

result is compared to previous results from CDF searches which as-sume the same gluino-sbottom decays hypotheses, a neutralino massof 60 GeV and mq

1,2

= 500 GeV (! mg for the Tevatron kinematic

range). Exclusion limits from the CDF and D0 experiments on directsbottom pair production [8, 9] are also reported.

400 450 500 550 600

Cro

ss s

ectio

n [

pb

]

10

210b-jet channel, 1-lepton, 2 jets

)0

1!" 2 m(%)

±

1!") = 60 GeV , m(

0

1!"m(

)g~) >> m(1,2

q~ m(

= 210 GeV1t~m

NLO Prospino

obs. limit 95% C.L.

exp. limit 95% C.L.

[GeV]g~

m400 450 500 550 600

10

210

= 180 GeV1t~m

ATLAS = 7 TeVs , -1

L dt = 35 pb$

±

1!" b+# 1t

~+t , 1t

~ # g~ production, 1t

~-1t

~ + g~-g~

Figure 3: Observed and expected 95% C.L. upper limits, as obtainedwith the one-lepton analysis, on the gluino-mediated and stop pairproduction cross section as a function of the gluino mass for twoassumed values of the stop mass and BR(t1 " b!±

1) = 1. The

chargino is assumed to have twice the mass of the neutralino (=60 GeV) and NLO cross sections are calculated using PROSPINO inthe hypothesis of mq

1,2

! mg. Theoretical uncertainties on the

NLO cross sections are included in the limit calculation.

lightest squarks.

Since no excess above the expectations from StandardModel processes was found, the results are used to excludeparameter regions in various R-parity conserving SUSYmodels. Under the assumption that the lightest squark b1is produced via gluino-mediated processes or direct pairproduction and decays exclusively via b1 # b"0

1, gluino

7

0 lepton, 3 j (1b)

ATLAS, 35 pb-1, gluino+sbottom pair production

limits translated to B’B’ →bbXX is weak


S. Su 13


CDF, Run II, 2.7 fb-1, stop pair production,

mst > 150 - 185 GeV, weaker than sbottom limit

t1 → bχ±1 → bχ01lν

A. G. Ivanov [CDF Collaboration], arXiv:0811.0788 [hep-ex].

2) GeV/c1

t~

M(120 130 140 150 160 170 180

2)

GeV

/c0 1!"

M(

45

50

55

60

65

70

75

80

85 2)=105.8 GeV/c±

1!"M(

b)=11

±!"#1t

~BR(

Observed 95% CL)-1CDF Run II Preliminary (2.7 fb

l)=0.25$1

0!"#

1

±!"(2BR

l)=0.50$1

0!"#

1

±!"(2BR

l)=1.0$1

0!"#

1

±!"(2BR

Excluded by LEP

2) GeV/c1

t~

M(135 140 145 150 155 160 165 170 175 180 185

2)

Ge

V/c

0 1!"

M(

45

50

55

60

65

70

75

80

85 2)=125.8 GeV/c±

1!"M(

b)=11

±!"#1t

~BR(

Observed 95% CL)-1CDF Run II Preliminary (2.7 fb

l)=0.25$1

0!"#

1

±!"(2BR

l)=0.50$1

0!"#

1

±!"(2BR

l)=1.0$1

0!"#

1

±!"(2BR

Excluded by LEP


S. Su 14


ATLAS-CONF-2011-036

ATLAS, 35 pb-1, ttbar+MET , 1 lepton, >=4 j , + MET

[GeV]Tm

150 200 250 300 350 400

Events

per

20 G

eV

0

2

4

6

8

10

[GeV]Tm

150 200 250 300 350 400

Events

per

20 G

eV

0

2

4

6

8

10

>80 GeVmiss

T4, E!

jetN

)-1Data (35 pb

QCD

(Single-Lepton)tt

(Dilepton)tt

Single Top

Z + jets

W + jets

Diboson

275, 50 [GeV]TT

300, 10 [GeV]TT

ATLASPreliminary

(a) mT

[GeV]missTE

80 100 120 140 160 180 200 220 240E

vents

per

10 G

eV

1

2

3

4

5

6

7

8

9

[GeV]missTE

80 100 120 140 160 180 200 220 240E

vents

per

10 G

eV

1

2

3

4

5

6

7

8

9 >120 GeVT

4, m!jet

N

)-1Data (35 pb

QCD

(Single-Lepton)tt

(Dilepton)tt

Single Top

Z + jets

W + jets

Diboson

275, 50 [GeV]TT

300, 10 [GeV]TT

ATLAS Preliminary

(b) EmissT

Figure 3: mT and EmissT in the signal region. The dotted and dashed lines show the expected distributions

for two of the excluded signal mass points stacked on the backgrounds, and the numbers in the legend

correspond to m(T ) and m(A0). The last bin in each plot includes the overflow.

8 Summary and Conclusions

We have presented a first search for anomalous EmissT in the tt single-lepton final state. In 35 pb!1 of pp

collisions at center-of-mass energy 7 TeV, we see no sign of an excess of events above those predicted

by the Standard Model. Using the simple model of pair-produced quark-like objects decaying to a top

quark and a heavy neutral particle, we exclude with more than 95% confidence m(T )=300 GeV for aneutral particle mass less than 10 GeV and m(T )=275 GeV for a neutral particle mass less than 50 GeV.

This limit can be interpreted quite broadly for a number of new physics scenarios, though more

integrated luminosity is required for exclusions on models with low cross section.

References

[1] CDF Collaboration, Public note 10185.


[3] J. Alwall, J. L. Feng, J. Kumar et al., Phys. Rev. D81, 114027 (2010). [arXiv:1002.3366 [hep-ph]].

[4] T. Han, R. Mahbubani, D. G. E. Walker and L. T. E. Wang, JHEP 0905, 117 (2009)

[arXiv:0803.3820 [hep-ph]].

[5] N. Arkani-Hamed, A. G. Cohen and H. Georgi, Phys. Lett. B 513, 232 (2001) [arXiv:hep-

ph/0105239].

[6] H. C. Cheng and I. Low, JHEP 0309, 051 (2003) [arXiv:hep-ph/0308199].


[8] H. C. Cheng, I. Low and L. T. Wang, Phys. Rev. D 74, 055001 (2006) [arXiv:hep-ph/0510225].

[9] T. Appelquist, H. C. Cheng and B. A. Dobrescu, Phys. Rev. D 64, 035002 (2001) [arXiv:hep-

ph/0012100].

9


S. Su 14


ATLAS-CONF-2011-036

ATLAS, 35 pb-1, ttbar+MET , 1 lepton, >=4 j , + MET

[GeV]Tm

150 200 250 300 350 400

Events

per

20 G

eV

0

2

4

6

8

10

[GeV]Tm

150 200 250 300 350 400

Events

per

20 G

eV

0

2

4

6

8

10

>80 GeVmiss

T4, E!

jetN

)-1Data (35 pb

QCD

(Single-Lepton)tt

(Dilepton)tt

Single Top

Z + jets

W + jets

Diboson

275, 50 [GeV]TT

300, 10 [GeV]TT

ATLASPreliminary

(a) mT

[GeV]missTE

80 100 120 140 160 180 200 220 240E

vents

per

10 G

eV

1

2

3

4

5

6

7

8

9

[GeV]missTE

80 100 120 140 160 180 200 220 240E

vents

per

10 G

eV

1

2

3

4

5

6

7

8

9 >120 GeVT

4, m!jet

N

)-1Data (35 pb

QCD

(Single-Lepton)tt

(Dilepton)tt

Single Top

Z + jets

W + jets

Diboson

275, 50 [GeV]TT

300, 10 [GeV]TT

ATLAS Preliminary

(b) EmissT

Figure 3: mT and EmissT in the signal region. The dotted and dashed lines show the expected distributions

for two of the excluded signal mass points stacked on the backgrounds, and the numbers in the legend

correspond to m(T ) and m(A0). The last bin in each plot includes the overflow.

8 Summary and Conclusions

We have presented a first search for anomalous EmissT in the tt single-lepton final state. In 35 pb!1 of pp

collisions at center-of-mass energy 7 TeV, we see no sign of an excess of events above those predicted

by the Standard Model. Using the simple model of pair-produced quark-like objects decaying to a top

quark and a heavy neutral particle, we exclude with more than 95% confidence m(T )=300 GeV for aneutral particle mass less than 10 GeV and m(T )=275 GeV for a neutral particle mass less than 50 GeV.

This limit can be interpreted quite broadly for a number of new physics scenarios, though more

integrated luminosity is required for exclusions on models with low cross section.

References



[3] J. Alwall, J. L. Feng, J. Kumar et al., Phys. Rev. D81, 114027 (2010). [arXiv:1002.3366 [hep-ph]].

[4] T. Han, R. Mahbubani, D. G. E. Walker and L. T. E. Wang, JHEP 0905, 117 (2009)

[arXiv:0803.3820 [hep-ph]].

[5] N. Arkani-Hamed, A. G. Cohen and H. Georgi, Phys. Lett. B 513, 232 (2001) [arXiv:hep-

ph/0105239].



[8] H. C. Cheng, I. Low and L. T. Wang, Phys. Rev. D 74, 055001 (2006) [arXiv:hep-ph/0510225].

[9] T. Appelquist, H. C. Cheng and B. A. Dobrescu, Phys. Rev. D 64, 035002 (2001) [arXiv:hep-

ph/0012100].

9

mT’ > 275 GeV for mX<50 GeV

mT’ > 300 GeV for mX<10 GeV


S. Su 15

Simulation-

MadGraph - Pythia - PGS

Signal:

๏ hadronic channel: large cross section- SM backgrounds, tt, W, have MET with lepton- irreducible background: Z→ νν + jets

๏ semi-leptonic channel: isolated lepton, suppress QCD background๏ purely leptonic channel: suppressed cross section

T. Han, R. Mahbubani, D. G. E. Walker and L. T. E. Wang, JHEP 0905, 117 (2009)

T �T � → t(∗)Xt(∗)X → bW+XbW−X

Similar analyses in the literature•semileptonic mode, high mass, large luminosity

•hadronic mode, spin and mass determinationP. Meade and M. Reece, Phys. Rev. D 74, 015010 (2006).


S. Su 16

Semileptonic channel: precuts-

๏ large MET

๏ large mTW

(GeV)T

Missing E0 100 200 300 400 500

Cro

ss s

ectio

n / b

in (p

b)

-310

-210

-110

1

10

0 100 200 300 400 500

-310

-210

-110

1

10

=300,1X

,mT’m=400,1

X,mT’m

=500,1X

,mT’mW+jets

)µ (2e/tt) (1tt

)µ (1e/tt

(GeV)WTM

0 50 100 150 200 250 300 350 400

Cro

ss s

ectio

n / b

in (p

b)

-210

-110

1

0 50 100 150 200 250 300 350 400

-210

-110

1

=300,1X

,mT’m=400,1

X,mT’m

=500,1X

,mT’mW+jets

)µ (2e/tt) (1tt

)µ (1e/tt

๏ one isolated electron or muon

Precuts

Signal:T’T’ → ttXX → bbjj l + MET

mWT ≡ mT (pl

T , �pT )

=�

2|plT || �pT | cos(∆φ(pl

T , � pT ))

LHC10LHC10


S. Su 16


๏ large MET

๏ large mTW

(GeV)T

Missing E0 100 200 300 400 500

Cro

ss s

ectio

n / b

in (p

b)

-310

-210

-110

1

10

0 100 200 300 400 500

-310

-210

-110

1

10

=300,1X

,mT’m=400,1

X,mT’m

=500,1X

,mT’mW+jets

)µ (2e/tt) (1tt

)µ (1e/tt

(GeV)WTM

0 50 100 150 200 250 300 350 400

Cro

ss s

ectio

n / b

in (p

b)

-210

-110

1

0 50 100 150 200 250 300 350 400

-210

-110

1

=300,1X

,mT’m=400,1

X,mT’m

=500,1X

,mT’mW+jets

)µ (2e/tt) (1tt

)µ (1e/tt

๏ one isolated electron or muon

Precuts

Signal:T’T’ → ttXX → bbjj l + MET

mWT ≡ mT (pl

T , �pT )

=�

2|plT || �pT | cos(∆φ(pl

T , � pT ))

LHC10LHC10

SM bg peak around mW


S. Su 17


๏ Njet ≥ 4

๏ second, hadronically decay W

N(jets)0 1 2 3 4 5 6 7 8 9

Cro

ss s

ectio

n / b

in (p

b)

-310

-210

-110

0 1 2 3 4 5 6 7 8 9

-310

-210

-110

=300,1X

,mT’m=400,1

X,mT’m

=500,1X

,mT’mW+jets

)µ (2e/tt) (1tt

)µ (1e/tt

(GeV)jjm60 80 100 120 140 160 180

Cro

ss s

ectio

n / b

in (p

b)

-310

-210

60 80 100 120 140 160 180

-310

-210

=300,1X

,mT’m=400,1

X,mT’m

=500,1X

,mT’mW+jets

)µ (2e/tt) (1tt

)µ (1e/tt

LHC10

LHC10


S. Su 18

Semileptonic channel: Tevatron-

TABLE I: Signal and background cross sections in fb after cuts for the semi-leptonic channel at

the Tevatron. The signal examples are for mX = 1 GeV and mT ! = 300, 400, and 500 GeV asindicated. The W cross sections in parentheses were simulated with a cut on /ET > 80 GeV and atleast 3 jets in the parton-level generation.

Cut T ! (300) T ! (400) T ! (500) tt W+jets

No cut 203.2 16.33 1.11 5619 (5179)

1 µ/e, no ! 36.1 2.88 0.194 1041 (2060)

/ET > 100 GeV 17.7 2.00 0.157 107.2 (728.8)

mWT > 100 GeV 10.7 1.38 0.114 22.6 (36.62)

! 4 jets 4.81 0.64 0.062 2.6 0.30

|mjj " mW | < 10 GeV 4.13 0.51 0.049 2.2 0.19

All precuts 4.13 0.51 0.049 2.19 0.19

mWT > 150 GeV 1.93 0.325 0.036 0.62 0.035

/ET > 150 GeV 1.75 0.367 0.041 0.281 0.035

HT > 300 GeV 1.93 0.353 0.042 1.18 0.07

/ET > 150, HT > 300 1.04 0.279 0.037 0.056 0.017

TABLE II: As in Table I, but for the semi-leptonic channel at the 10 TeV LHC and with crosssections in pb.

Cut T ! (300) T ! (400) T ! (500) tt (1 e/µ) tt (1 !) tt (2 e/µ) W+jets

No cut 14.89 3.16 0.922 66.67 43.96 10.62 (42.28)

1 µ/e, no ! 3.2 0.669 0.193 36.45 8.15 3.18 (15.74)

/ET > 100 GeV 1.92 0.52 0.165 5.05 2.07 0.888 (10.33)

mWT > 100 GeV 1.1 0.342 0.116 0.134 0.638 0.471 (0.235)

! 4 jets 0.357 0.116 0.043 0.056 0.091 0.062 0.028

|mjj " mW | < 10 GeV 0.165 0.049 0.016 0.026 0.03 0.014 0.01

All precuts 0.165 0.049 0.016 0.027 0.031 0.014 0.01

mWT > 150 GeV 0.081 0.033 0.012 0.001 0.015 0.006 0.002

mWT > 200 GeV 0.032 0.019 0.008 0 0.006 0.003 0.001

/ET > 150 GeV 0.099 0.036 0.014 0.005 0.012 0.005 0.004

/ET > 200 GeV 0.040 0.025 0.010 0.001 0.004 0.001 0.002

/ET > 250 GeV 0.016 0.013 0.007 0 0.002 0.001 0.002

HT > 400 GeV 0.107 0.035 0.013 0.018 0.022 0.008 0.007

HT > 500 GeV 0.059 0.021 0.009 0.011 0.014 0.004 0.005

/ET > 150, HT > 400 0.067 0.027 0.012 0.004 0.01 0.004 0.003

/ET > 150, HT > 500 0.037 0.016 0.008 0.003 0.007 0.002 0.002

/ET > 200, HT > 400 0.032 0.02 0.009 0.001 0.004 0.001 0.002

/ET > 200, HT > 500 0.02 0.013 0.007 0 0.004 0.001 0.002

/ET > 250, HT > 400 0.014 0.012 0.006 0 0.002 0.001 0.002

/ET > 250, HT > 500 0.009 0.008 0.005 0 0.002 0.001 0.001

17

Tevatron: semileptonic

Additional cuts: MET, mTW, HT

2.4 fb


S. Su 19

-

TABLE I: Signal and background cross sections in fb after cuts for the semi-leptonic channel at

the Tevatron. The signal examples are for mX = 1 GeV and mT ! = 300, 400, and 500 GeV asindicated. The W cross sections in parentheses were simulated with a cut on /ET > 80 GeV and atleast 3 jets in the parton-level generation.

Cut T ! (300) T ! (400) T ! (500) tt W+jets

No cut 203.2 16.33 1.11 5619 (5179)

1 µ/e, no ! 36.1 2.88 0.194 1041 (2060)

/ET > 100 GeV 17.7 2.00 0.157 107.2 (728.8)

mWT > 100 GeV 10.7 1.38 0.114 22.6 (36.62)

! 4 jets 4.81 0.64 0.062 2.6 0.30

|mjj " mW | < 10 GeV 4.13 0.51 0.049 2.2 0.19

All precuts 4.13 0.51 0.049 2.19 0.19

mWT > 150 GeV 1.93 0.325 0.036 0.62 0.035

/ET > 150 GeV 1.75 0.367 0.041 0.281 0.035

HT > 300 GeV 1.93 0.353 0.042 1.18 0.07

/ET > 150, HT > 300 1.04 0.279 0.037 0.056 0.017

TABLE II: As in Table I, but for the semi-leptonic channel at the 10 TeV LHC and with crosssections in pb.

Cut T ! (300) T ! (400) T ! (500) tt (1 e/µ) tt (1 !) tt (2 e/µ) W+jets

No cut 14.89 3.16 0.922 66.67 43.96 10.62 (42.28)

1 µ/e, no ! 3.2 0.669 0.193 36.45 8.15 3.18 (15.74)

/ET > 100 GeV 1.92 0.52 0.165 5.05 2.07 0.888 (10.33)

mWT > 100 GeV 1.1 0.342 0.116 0.134 0.638 0.471 (0.235)

! 4 jets 0.357 0.116 0.043 0.056 0.091 0.062 0.028

|mjj " mW | < 10 GeV 0.165 0.049 0.016 0.026 0.03 0.014 0.01

All precuts 0.165 0.049 0.016 0.027 0.031 0.014 0.01

mWT > 150 GeV 0.081 0.033 0.012 0.001 0.015 0.006 0.002

mWT > 200 GeV 0.032 0.019 0.008 0 0.006 0.003 0.001

/ET > 150 GeV 0.099 0.036 0.014 0.005 0.012 0.005 0.004

/ET > 200 GeV 0.040 0.025 0.010 0.001 0.004 0.001 0.002

/ET > 250 GeV 0.016 0.013 0.007 0 0.002 0.001 0.002

HT > 400 GeV 0.107 0.035 0.013 0.018 0.022 0.008 0.007

HT > 500 GeV 0.059 0.021 0.009 0.011 0.014 0.004 0.005

/ET > 150, HT > 400 0.067 0.027 0.012 0.004 0.01 0.004 0.003

/ET > 150, HT > 500 0.037 0.016 0.008 0.003 0.007 0.002 0.002

/ET > 200, HT > 400 0.032 0.02 0.009 0.001 0.004 0.001 0.002

/ET > 200, HT > 500 0.02 0.013 0.007 0 0.004 0.001 0.002

/ET > 250, HT > 400 0.014 0.012 0.006 0 0.002 0.001 0.002

/ET > 250, HT > 500 0.009 0.008 0.005 0 0.002 0.001 0.001

17

• Additional mWT cut: m

WT > 150, 200 GeV

• Additional �ET cuts: �ET > 150, 200, 250 GeV.• HT =

�4i=1 |pj

T |i + |plT | cuts: HT > 400, 500 GeV.

• Combinations of the cuts above.

Semileptonic channel: LHC10

LHC10: semileptonic

Additional cuts: MET, mTW, HT

82 fb


S. Su 20

Tevatron exclusion-

๏ optimal cuts (after precuts)๏ S/B > 0.1, more than 2 events๏ Poisson statistics

(GeV)T’m

300 320 340 360 380 400 420 440 460 480 500

(G

eV

)X

m

0

20

40

60

80

100

120

140

160

180

200

-12 fb

-15 fb

-110 fb

-120 fb

t + mX = mT’m

Semileptonic channel

X at the Tevatront t X ! T’Exclusion for T’

(GeV)T’m

300 320 340 360 380 400 420 440 460 480 500

(G

eV

)X

m

0

20

40

60

80

100

120

140

160

180

200

-12 fb

-15 fb

-110 fb

-120 fb

t + mX = mT’m

Hadronic channel


FIG. 3: 95% CL Tevatron exclusion contours for the semi-leptonic channel (left) and the hadronicchannel (right) for integrated luminosities 2, 5, 10, and 20 fb!1. For each point in parameter space,the cut with the best significance has been chosen.

luminosity of 20 fb!1 at the end of Tevatron running, a reach of up to 455 GeV for thehadronic channel can be achieved.

The reach in mT ! is almost independent of mX for small to medium mX . However, whenmX approaches the on-shell decay threshold of mT ! ! mt, the reach is limited since the topand X are produced nearly at rest in the T " rest frame, and the T "T " system therefore needsa transverse boost for the X particles to produce large missing transverse momentum. Thisleads to the dip in the exclusion curves at mX close to mT ! ! mt, and indeed there is noexclusion reach at the Tevatron for mT ! ! mt ! mX

<" 15 GeV. For 20 fb!1 integratedluminosity and mT ! between 370 and 390 GeV, mX could be excluded up to 160 GeV at95% CL using the hadronic mode. For smaller mT ! , the reach in mX is decreased due to thesoftness of the X particle distributions, while for larger mT ! , it is decreased because of thesmall T "T " production cross section.

Figure 4 shows the 3! (Gaussian equivalent2) Tevatron discovery contours for both thesemi-leptonic and hadronic channels for integrated luminosities of 2, 5, 10, and 20 fb!1. A3! signal could be observed for mT ! < 360 GeV and mX

<" 110 GeV in the semi-leptonicchannel with 20 fb!1 integrated luminosity. The hadronic channel is more promising. With5 fb!1 integrated luminosity, a reach in mT ! up to 360 GeV could be achieved when mX isnot too large. With 20 fb!1 integrated luminosity, the reach is extended to 400 GeV for mX

up to about 80 GeV. For larger mX , the reach in mT ! decreases.Figure 5 shows the 95% CL exclusion contours for a 10 TeV early LHC run, in the semi-

leptonic and hadronic channels for integrated luminosities 100, 200, and 300 pb!1. With just100 pb!1, the LHC exclusion reach for mT ! exceeds the Tevatron exclusion reach with 20 fb!1

luminosity. Exclusions of mT ! up to 490, 520, and 535 GeV could be achieved with 100,

2 By Gaussian equivalent, we mean that we have converted the one-sided Poisson probability into the

equivalent ! deviation in a two-sided Gaussian distribution, which is more commonly used in the literature.

12

95% C.L. 95% C.L.


S. Su 20

Tevatron exclusion-


(GeV)T’m

300 320 340 360 380 400 420 440 460 480 500

(G

eV

)X

m

0

20

40

60

80

100

120

140

160

180

200

-12 fb

-15 fb

-110 fb

-120 fb

t + mX = mT’m



(GeV)T’m

300 320 340 360 380 400 420 440 460 480 500

(G

eV

)X

m

0

20

40

60

80

100

120

140

160

180

200

-12 fb

-15 fb

-110 fb

-120 fb

t + mX = mT’m

Hadronic channel


FIG. 3: 95% CL Tevatron exclusion contours for the semi-leptonic channel (left) and the hadronicchannel (right) for integrated luminosities 2, 5, 10, and 20 fb!1. For each point in parameter space,the cut with the best significance has been chosen.

luminosity of 20 fb!1 at the end of Tevatron running, a reach of up to 455 GeV for thehadronic channel can be achieved.

The reach in mT ! is almost independent of mX for small to medium mX . However, whenmX approaches the on-shell decay threshold of mT ! ! mt, the reach is limited since the topand X are produced nearly at rest in the T " rest frame, and the T "T " system therefore needsa transverse boost for the X particles to produce large missing transverse momentum. Thisleads to the dip in the exclusion curves at mX close to mT ! ! mt, and indeed there is noexclusion reach at the Tevatron for mT ! ! mt ! mX

<" 15 GeV. For 20 fb!1 integratedluminosity and mT ! between 370 and 390 GeV, mX could be excluded up to 160 GeV at95% CL using the hadronic mode. For smaller mT ! , the reach in mX is decreased due to thesoftness of the X particle distributions, while for larger mT ! , it is decreased because of thesmall T "T " production cross section.

Figure 4 shows the 3! (Gaussian equivalent2) Tevatron discovery contours for both thesemi-leptonic and hadronic channels for integrated luminosities of 2, 5, 10, and 20 fb!1. A3! signal could be observed for mT ! < 360 GeV and mX

<" 110 GeV in the semi-leptonicchannel with 20 fb!1 integrated luminosity. The hadronic channel is more promising. With5 fb!1 integrated luminosity, a reach in mT ! up to 360 GeV could be achieved when mX isnot too large. With 20 fb!1 integrated luminosity, the reach is extended to 400 GeV for mX

up to about 80 GeV. For larger mX , the reach in mT ! decreases.Figure 5 shows the 95% CL exclusion contours for a 10 TeV early LHC run, in the semi-

leptonic and hadronic channels for integrated luminosities 100, 200, and 300 pb!1. With just100 pb!1, the LHC exclusion reach for mT ! exceeds the Tevatron exclusion reach with 20 fb!1

luminosity. Exclusions of mT ! up to 490, 520, and 535 GeV could be achieved with 100,

2 By Gaussian equivalent, we mean that we have converted the one-sided Poisson probability into the

equivalent ! deviation in a two-sided Gaussian distribution, which is more commonly used in the literature.

12

95% C.L. 95% C.L.

soft decay products


S. Su 21

Tevatron searches (CDF)-

arX

iv:1

103.

2482

v1 [

hep-

ex]

12 M

ar 2

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K.R. Bland,5 B. Blumenfeld,24 A. Bocci,15 A. Bodek,48 D. Bortoletto,47 J. Boudreau,46 A. Boveia,12

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M. Cavalli-Sforza,4 A. Cerrif ,27 L. Cerritoq,29 Y.C. Chen,1 M. Chertok,7 G. Chiarelli,45 G. Chlachidze,16

F. Chlebana,16 K. Cho,26 D. Chokheli,14 J.P. Chou,21 W.H. Chung,59 Y.S. Chung,48 C.I. Ciobanu,43

M.A. Cioccidd,45 A. Clark,19 G. Compostellabb,42 M.E. Convery,16 J. Conway,7 M.Corbo,43 M. Cordelli,18

C.A. Cox,7 D.J. Cox,7 F. Cresciolicc,45 C. Cuenca Almenar,60 J. Cuevasw,10 R. Culbertson,16 D. Dagenhart,16

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L. Demortier,49 J. Dengc,15 M. Deninno,6 F. Devoto,22 M. d’Erricobb,42 A. Di Cantocc,45 B. Di Ruzza,45

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T. Aaltonen et al. [CDF Collaboration], arXiV:1103.2482

6

theoretical cross section by generating ensembles of sim-ulated experiments that describe expected fluctuationsof statistical and systematic uncertainties on both sig-nal and backgrounds. The observed limits are consistentwith expectation in the background-only hypothesis, for afew example signal mass points we tabulate the expectedand observed limits(see Table II). We convert the ob-served upper limits on the pair-production cross sectionsto an exclusion curve in mass parameter space for thedark matter model involving fourth generation quarks,see Fig. 3.

TABLE II: Expected 95% CL upper limit on T !T !

production cross-section, !exp, the range of expectedlimits which includes 68% of pseudoexperiments, and

the observed limit, !obs, for representative signal pointsin (mT ! ,mX).

mT ! ,mX

(GeV/c2)!exp [pb] +34% !34% !obs [pb].

200,1 1.31 1.86 0.83 1.21220,40 1.40 2.17 0.93 1.20260,1 0.23 0.40 0.14 0.20280,1 0.16 0.27 0.09 0.15280,20 0.18 0.29 0.11 0.17280,40 0.17 0.27 0.11 0.12

mT ! ,mX

(GeV/c2)!exp [pb] +34% !34% !obs [pb].

300,100 0.34 0.51 0.24 0.39310,90 0.19 0.29 0.11 0.21320,80 0.15 0.24 0.08 0.12350,50 0.07 0.10 0.04 0.02360,110 0.09 0.19 0.05 0.09370,1 0.06 0.10 0.04 0.05

]2 [ GeV/c T’m200 220 240 260 280 300 320 340 360

]2 [

GeV

/c

Xm

20

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100

Cros

s sec

tion

uppe

r lim

it [fb

]

1

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310Expected exclusion Observed exclusion

X-mT’=mtm

FIG. 3: Observed versus expected exclusion in(mT ! ,mX) along with the cross section upper limits.

In conclusion, we have searched for new physics parti-cles T ! decaying to top quarks with invisible particles Xwith a detector signature of tt + /Et. We calculate up-per limits on the cross section of such events and exclude

a dark matter model involving exotic fourth generationquark up to mT ! = 360 GeV/c2. Our cross section limitson the generic decay, T ! ! t+X , may be applied to themany other models that predict the production of a heavyparticle T ! decaying to top quarks and invisible particlesX , such as the supersymmetric process t ! t + "0. Asimilar search performed at the LHC, given its higher en-ergy regime, would be able to provide limits on such asupersymmetric decay.

We thank the Fermilab sta! and the technical sta!s ofthe participating institutions for their vital contributions.This work was supported by the U.S. Department of En-ergy and National Science Foundation; the Italian Isti-tuto Nazionale di Fisica Nucleare; the Ministry of Edu-cation, Culture, Sports, Science and Technology of Japan;the Natural Sciences and Engineering Research Councilof Canada; the National Science Council of the Repub-lic of China; the Swiss National Science Foundation; theA.P. Sloan Foundation; the Bundesministerium fur Bil-dung und Forschung, Germany; the World Class Univer-sity Program, the National Research Foundation of Ko-rea; the Science and Technology Facilities Council andthe Royal Society, UK; the Institut National de PhysiqueNucleaire et Physique des Particules/CNRS; the RussianFoundation for Basic Research; the Ministerio de Cien-cia e Innovacion, and Programa Consolider-Ingenio 2010,Spain; the Slovak R&D Agency; and the Academy of Fin-land.

[1] J. Feng, arXiv:1003.0904v2 [astro-ph.CO](2010).[2] J. Feng et al. , arXiv:1002.3366 [hep-ph](2010).[3] H. C. Cheng and I. Low, JHEP 0408, 061

[arXiv:hep-ph/0405243](2004)[4] P. Fileviez Perez and M. B. Wise, arXiv:1002.1754 [hep-

ph](2010).[5] M. Drees, R. Godbole, and P. Roy, Hackensack, USA:

World Scientific (2004) 555 p.[6] D. Acosta et al. (The CDF Collaboration), Phys. Rev. D

71, 032001 (2005).[7] A. Abulencia et al. (The CDF Collaboration), Phys. Rev.

Lett. 97, 082004 (2006); D. Acosta et al. (The CDF Col-laboration), Phys. Rev. Lett. 94, 091803 (2005).

[8] CDF uses a cylindrical coordinate system with the zaxis along the proton beam axis. Pseudorapidity is " "! ln(tan(#/2)), where # is the polar angle relative to theproton beam direction, and $ is the azimuthal angle whilepT = |p| sin #, ET = E sin #.

[9] F. Abe et al (The CDF Collaboration) , Phys. Rev. D 45,001448 (1992).

[10] A. Bhatti et al., Nucl. Instrum. Methods 566, 375 (2006).[11] Missing transverse momentum, #ET , is defined as the mag-

nitude of the vector !!

iEi

T%ni where EiT are the magni-

tudes of transverse energy contained in each calorimetertower i, and %ni is the unit vector from the interactionvertex to the tower in the transverse (x, y) plane.

[12] J. Alwall et al. J. High Energy Phys. 0709 (2007) 028,

95% C.L.4.8 fb-1Semileptonic


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X at the Tevatront t X ! T’Discovery of T’

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FIG. 4: 3! (Gaussian equivalent) Tevatron discovery contours for the semi-leptonic channel (left)and the hadronic channel (right) for integrated luminosities 2, 5, 10, and 20 fb!1. For each pointin parameter space, the cut with the best significance has been chosen.

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FIG. 5: 95% CL exclusion contours for a 10 TeV LHC run in the semi-leptonic channel (left) andthe hadronic mode (right), for integrated luminosities 100, 200, and 300 pb!1. For each point inparameter space, the cut with the best significance has been chosen.

200, and 300 pb!1 integrated luminosity for the semi-leptonic channel. The exclusion regionfor the hadronic channel covers almost the entire interesting mass parameter space with300 pb!1 luminosity. Note that at the LHC, we could tolerate much smaller mT ! ! mX ; inparticular, we start probing the o!-shell decay region T " " t#X " bWX for mT !!mX < mt.

Figure 6 shows the 3! (Gaussian equivalent) discovery contours for a 10 TeV LHC run, inthe semi-leptonic and hadronic channels for integrated luminosities 100, 200, and 300 pb!1.Although the reach in both mT ! and mX is limited for the semi-leptonic mode, the hadronic

13

95% C.L. 95% C.L.


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LHC 10 exclusion-

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off-shell top


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LHC10 discovery-

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X at 10 TeV LHCt t X ! T’Discovery for T’

FIG. 6: 3! (Gaussian equivalent) discovery contours for a 10 TeV LHC run, in the semi-leptonicchannel (left) and the hadronic channel (right), for integrated luminosities 100, 200, and 300 pb!1.For each point in parameter space, the cut with the best significance has been chosen.

channel could provide a 3! signal for mT !<! 490 GeV and mX

<! 170 GeV with 300 pb!1

luminosity. We might also observe a positive signal for mX up to about 170 GeV in theo!-shell decay region (mT ! " mX < mt) for mT !

<! 330 GeV.It is clear from the discovery and exclusion contours, both for the Tevatron and the

LHC, that the fully hadronic channel has considerably larger reach than the semi-leptonicchannel, for reasons enumerated in Sec. IV. In this channel, the full, currently viable, regionin parameter space can be excluded at a 10 TeV LHC run.3 In case both channels are visible,they can be used to distinguish between di!erent model and mass hypotheses.

VI. CONCLUSIONS

We have considered the prospects for hadron colliders to pair produce new exotic quarksthat decay directly to a pair of dark matter particles and SM particles. Although we have aparticular interest in the WIMPless dark matter scenario [7] (including a specific example [8]that can potentially explain the DAMA annual modulation result), this scenario is motivatedon quite general grounds, and, with minor modifications, our analysis applies to many otherdark matter scenarios and other new physics models.

We have focused on the up-type exotic quark T ". T " pair production leads to T "T " #ttXX, and we have then analyzed the semi-leptonic and fully hadronic channels. The fullyhadronic channel (vetoing events with leptons) seems to be the most e"cient, because of

3 The results obtained here can be readily translated to an LHC run at 7 TeV, by multiplying the integrated

luminosities needed by roughly a factor of 3. This approximation accounts for the di!erence in cross

sections at di!erent center of mass energies, assuming that the cut e"ciencies for both the signal and

backgrounds do not change significantly.

14

LHC @7TeV, multiply lumonisity by a factor of 3.

3 σ 3 σ


S. Su 25

Tevatron search-

Signal: B’B’ →bbXX

๏ no lepton๏ 2 or 3 jets, with |ηj|<2.5, PTj > 20 GeV๏ αj1j2 < 164o

๏ MET ≥ 40 GeV, MET/GeV > 80 - 40XΔϕmin (MET, jets)๏ ≥ 2 b-jets, including leading jet๏Δϕ(MET, jets) > 0.6, A=(MET-MHT)/(MET+MHT), -0.1 < A < 0.2๏Xjj = (PTj1+PTj2)/HT, Xjj > 0.75๏ HT > 60 GeV

Precuts

๏ PTj1, MET, Xjj, HT

Additional cuts

Bg: W(lν)jj, Z(νν) jj,WZ, ttbar, single top.


S. Su 26

Tevatron reach-


Preliminary results for B’B’ →bbXX

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95% C.L. 3 σPREL

IMiNAR

Y

PREL

IMiNAR

Y


S. Su 27

Tevatron cross section reach-

(GeV)B’m100 150 200 250 300 350 400 450 500

Cro

ss s

ectio

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b)

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’)B(B’

-1L=5 fb

-1L=20 fb

X at Tevatronb bX Cross section limits for pp discovery limit5

discovery limit3

95% exclusion limit

PREL

IMiNAR

Y


S. Su 28

LHC7 search-

Signal: B’B’ →bbXX

๏ no lepton๏ 2 or 3 jets, with |ηj|<2.5, PTj > 100, 40 (40) GeV๏ MET ≥ 80 GeV ๏ f=MET/Meff, f>0.3 for 2 jets, f>0.25 for 3 jets๏Δϕ(MET, jets) > 0.2 ๏Sphericity ST>0.2๏ ≥ 1 b-jets, including leading jet

Precuts

๏ PTj1, MET, Meff, additional btag

Additional cuts

Bg: W(lν)jj, Z(νν) jj,WZ, ttbar, single top.


S. Su 29

LHC reach-


Preliminary results for B’B’ →bbXX

(GeV)B’m100 200 300 400 500 600 700 800 900 1000

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eV

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m

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X at 7 TeV LHCb b X ! B’Exclusion for B’

(GeV)B’m100 200 300 400 500 600 700 800 900 1000

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eV

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b + mX = mB’m

X at 7 TeV LHCb b X ! B’Discovery for B’

95% C.L.3 σ

PREL

IMiN

ARY

PREL

IMiN

ARY


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LHC7 cross section reach-

(GeV)B’m100 200 300 400 500 600 700 800 900 1000

Cro

ss s

ectio

n (p

b)

-210

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1

10

210’)B(B’

-1L=100 pb

-1L=10 fb

X at 7 TeV LHCb bX Cross section limits for pp discovery limit5

discovery limit3

95% exclusion limit

PREL

IMiNAR

Y


S. Su 31

Conclusions

Pair production of exotic quarks → DM + SM particles

DM motivated, e.g., WIMPless scenario

T’T’ →ttXX semileptonic mode and hadronic mode

Current CDF exclusion (4.8 fb-1): 360 GeV

Exclusion: LHC @ 10 TeV, 300 pb-1

Discovery: ๏ mX<130 GeV, mT’ < 405 GeV for Tevatron 20 fb-1

๏ mX<170 GeV, mT’ < 490 GeV for LHC10 300 pb-1

B’B’ →bbXX

๏ current exclusion (5.2 fb-1, D0): 440 GeV

๏ Tevatron 20 fb-1, exclusion, 470 GeV

๏ LHC @ 7 TeV, 1 fb-1, discovery: 545 GeV

-


S. Su 32

Conclusions

identify signal as T’, B’ production,comparing with SUSY

complementary between collider studies and DM searches

๏ small λ, DM searches unsuccessful

๏ displaced vertex at collider

-


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