From Jet Scaling to Jet Vetos - uni-heidelberg.deplehn/includes/talks/2012/cms_12.pdf · New...

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics From Jet Scaling to Jet Vetos

Tilman Plehn

Heidelberg

CMS week, 2/2012

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Jet counting

Why count jets

– complete event reconstruction crucial at LHC [Higgs plus 0,1,2 jets; jets plus /~pT ]

– utilize tagging and recoil jets in Higgs searches

– identify decay jets in BSM searches

– reduce t t and gg backgrounds

⇒ dσ/dnjets just another distribution to cut on (?)

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Jet counting

Why count jets






Why not [intro: arXiv:0910.4182, Springer Lecture Notes]

– remember qg → qZ

– collinear divergence from g → qq splitting [overlapping with soft divergence]Z pmaxT

pminT

dp2T

Cp2

T

= 2Z pmax

T

pminT

dpT pTCp2

T

' 2CZ pmax

T

pminT

dpT1

pT= 2C log

pmaxT

pminT

universal form following factorization

σn+1 =

Zσn

dp2a

p2a

dzαs

2πP(z)

– universally divergent, fixed order poorly defined

– find object to ‘renormalize’ [i.e. absorbe universal divergence]

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Jet counting

Why count jets






DGLAP equation and jet-inclusive rates

– re-organize perturbation series [sum collinear logs]

σn+1(x, µ) ∼1n!

1

2πb0log

αs(µ20)

αs(µ2)

!n Z 1

x0

dxn

xnP„

xxn

«· · ·Z 1

x0

dx1

x1P„

x2

x1

«σ1(x1, µ0)

– DGLAP equivalent to ‘infrared RGE’

– factorization scale as inclusive momentum cutoff [vanishing at all orders]

σtot(µ) =

Z 1

0dx1

Z 1

0dx2

Xij

fi (x1, µ) fj (x2, µ) σij (x1x2S, µ)

– collinear jets automatically included

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Poisson scaling

Theory: soft gluon radiation [Peskin & Schroeder Ch 6]

– example: photons off hard electrononly abelian diagrams, successive radiation

– eikonal approximation

Mn+1 = gsT aε∗µ(k) u(q)

qµ +O( /k)

(qk) +O(k2)Mn

– factorization of ‘hard process’ and soft radiation factors

– Poisson distribution [normalized pdf for n if n expected]

σn =nne−n

n!⇐⇒ R(n+1)/n =

σn+1

σn=

nn + 1

Ingredients of Poisson distribution

1– radiation matrix element nn:abelian fine, non-abelian a little tricky [ISR-FSR, see Ioffe, Fadin, Lipatov]

2– phase space factor 1/n!:only combinatorics, matrix element ordered [angular ordering, color suppression]

3– normalization factor e−n

– similar to parton shower for collinear regimes

s

s

1/pT

1/pT

1/pT

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Staircase scaling

Experiment: from UA1 to ATLAS/CMS [Steve Ellis, Kleiss, Stirling]

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Staircase scaling


– W/Z+jets production– many equivalent descriptions

R(n+1)/n =σn+1

σn= const

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Staircase scaling



R(n+1)/n =σn+1

σn= const

– same for inclusive and exclusive rates [Blackhat-Sherpa]

R incl(n+1)/n =

P∞j=n+1 σ

(excl)j

σ(excl)n +

P∞j=n+1 σ

(excl)j

= Rexcl(n+1)/n

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Staircase scaling



R(n+1)/n =σn+1

σn= const


R incl(n+1)/n =

P∞j=n+1 σ

(excl)j

σ(excl)n +

P∞j=n+1 σ

(excl)j

= Rexcl(n+1)/n

– confirmed by CMS

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Staircase scaling



R(n+1)/n =σn+1

σn= const


R incl(n+1)/n =

P∞j=n+1 σ

(excl)j

σ(excl)n +

P∞j=n+1 σ

(excl)j

= Rexcl(n+1)/n


Theoretical studies [Englert, TP, Schichtel, Schumann]

– CKKW/MLM merging [we used Sherpa]

– phase space effects? → moderate

– αs uncertainties? → small

– scale uncertainties? → tuning parameter?jetsn

2 3 4 5 6

jets

dndN

210

310

410

510

610

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

W+jets

µW+jets, 1/4

µW+jets, 4

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

W+jets

µW+jets, 1/4

µW+jets, 4

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

W+jets

µW+jets, 1/4

µW+jets, 4

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

W+jets

µW+jets, 1/4

µW+jets, 4

jetsn2 3 4 5 6

jets

dndN

210

310

410

510

610

jetsn2 3 4 5 6

var

iati

onsα

0.5

1

1.5 theoretical uncertainty

statistical uncertainty

jetsn2 3 4 5 6

var

iati

onsα

0.5

1

1.5

jetsn2 3 4 5 6

var

iati

onµ

1

10

jetsn2 3 4 5 6

var

iati

onµ

1

10

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Staircase scaling



R(n+1)/n =σn+1

σn= const


R incl(n+1)/n =

P∞j=n+1 σ

(excl)j

σ(excl)n +

P∞j=n+1 σ

(excl)j

= Rexcl(n+1)/n


Theoretical studies [Englert, TP, Schichtel, Schumann]

– CKKW/MLM merging [we used Sherpa]

– phase space effects? → moderate

– αs uncertainties? → small

– scale uncertainties? → tuning parameter?

– same for QCD jets

– correctly described by ME-PS merging!?

jetsn2 3 4 5 6

jets

dndN

410

510

610

710

810

910

1010

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

QCD

µQCD, 1/4

µQCD, 4

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

QCD

µQCD, 1/4

µQCD, 4

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

QCD

µQCD, 1/4

µQCD, 4

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

QCD

µQCD, 1/4

µQCD, 4

jetsn2 3 4 5 6

jets

dndN

410

510

610

710

810

910

1010

jetsn2 3 4 5 6

var

iati

onsα 0.8

1



jetsn2 3 4 5 6

var

iati

onsα 0.8

1

1.2

jetsn2 3 4 5 6

var

iati

onµ 1

10

210

jetsn2 3 4 5 6

var

iati

onµ 1

10

210

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Interpolating scaling patterns

Scaling for photon plus jets [Englert, TP, Schichtel, Schumann]

– naively, no scaling at all [Alex Tapper, private complaint]

– after appropriate cuts, great playground

1– staircasedemocratic γ and jet acceptancelarge γ-jet separation [m or ∆R, no large logs]

no reason for ordered emission [1/n! in Poisson form]

dominant: non-abelian splitting of ISR gluonhelping: pdf effect shifting to high-njets

2/1 3/2 4/3 5/4 6/5 7/6

nn+

1R

0

0.1

0.2

0.3

0.4

0.5

=-0.0064dndR

=0.15970R> 70 GeV, ,jγm

=-0.0007dndR

=0.14880R> 90 GeV, ,jγm

=0.0029dndR

=0.14070R>110 GeV, ,jγm

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Interpolating scaling patterns

Scaling for photon plus jets [Englert, TP, Schichtel, Schumann]

– naively, no scaling at all [Alex Tapper, private complaint]

– after appropriate cuts, great playground

1– staircasedemocratic γ and jet acceptancelarge γ-jet separation [m or ∆R, no large logs]

no reason for ordered emission [1/n! in Poisson form]

dominant: non-abelian splitting of ISR gluonhelping: pdf effect shifting to high-njets

2/1 3/2 4/3 5/4 6/5 7/6

nn+

1R

0

0.1

0.2

0.3

0.4

0.5

=-0.0064dndR

=0.15970R> 70 GeV, ,jγm

=-0.0007dndR

=0.14880R> 90 GeV, ,jγm

=0.0029dndR

=0.14070R>110 GeV, ,jγm

2– Poissongenerate ‘hard process’ [m, pT ,∆R, ...]

lower general pminT for soft-collinear logarithm

rely on lot-enhanced radiation

dominant: successive ordered ISRremaining: high-n staircase tail

⇒ staircase–Poisson transition tunable!

2/1 3/2 4/3 5/4 6/5 7/6 8/7n

n+1

R0

0.5

1

1.5 =1.7138n

=0.01310R>100 GeV,

T,j1p

=2.361n

=-0.05090R>150 GeV,

T,j1p

=2.6287n

=-0.05360R>200 GeV,

T,j1p

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Jet veto in Higgs searches

Jet veto in Higgs analyses [Barger, Phillips, Zeppenfeld; Rainwater]

– particularly useful for WBF signals [remove t t and Z+jets backgrounds]

– veto central (semi-hard) jetsestimate Pvetoapply as ‘efficiency factor’

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics





– implicit in LHC Higgs searchesindividual searches for exclusive fixed njets

– problem in Higgs phenomenology

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics







In terms of jet counting [Gerwick, TP, Schumann]

– avoid Pveto as one number

– study exclusive njets distribution:1– understand basic features:

staircase for inclusive samplesPoisson for hard processes

2– predict from theory [including error]

3– validate simulation4– extrapolate to regimes/processes

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics







In terms of jet counting [Gerwick, TP, Schumann]

– avoid Pveto as one number

– study exclusive njets distribution:1– understand basic features:

staircase for inclusive samplesPoisson for hard processes

2– predict from theory [including error]

3– validate simulation4– extrapolate to regimes/processes

staircase scaling Poisson scaling

σn σ0 e−bn σtote−n nn

n!

Rexcl(n+1)/n e−b n

n + 1

Rincl(n+1)/n e−b

0@ (n + 1) e−n n−(n+1)

Γ(n + 1) − nΓ(n, n)+ 1

1A−1

〈njets〉1

2

1

cosh b − 1n

Pveto 1 − e−b e−n

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics


Example: WBF H → ττ [Gerwick, TP, Schumann]

– staircase scaling before WBF cuts [QCD and e-w processes]

– first emission sensitive to cuts

– e-w Zjj production with too many structures

1

n!/n+1!-1 0 1 2 3 4 5 6

) n!/

n+1

!R(

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Higgs gluon fusion

Z QCD

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

R(n

+1)

/n

n + 1

n

1/0 2/1 3/2 4/3 5/4 6/5

1

n!/n+1!-1 0 1 2 3 4 5 6

) n!/

n+1

!R(

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Higgs WBF

Z EW

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

R(n

+1)

/n

n + 1

n

1/0 2/1 3/2 4/3 5/4 6/5

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics






WBF cuts: two forward tagging jets

– count add’l jets to reduce backgrounds

pvetoT > 20 GeV min y1,2 < yveto

< max y1,2

– Poisson for QCD processes [‘radiation’ pattern]

1

n!/n+1!-1 0 1 2 3 4 5

) n!/

n+1

!R(

0

0.5

1

1.5

2

2.5

Higgs gluon fusion

Z QCD

n(Z QCD) = 1.42

n(Higgs gg fusion) = 1.80

0.5

1.0

1.5

2.0

2.5

R(n

+1)

/n

n + 1

n

1/0 2/1 3/2 4/3 5/4

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics






WBF cuts: two forward tagging jets

– count add’l jets to reduce backgrounds

pvetoT > 20 GeV min y1,2 < yveto

< max y1,2

– Poisson for QCD processes [‘radiation’ pattern]

– staircase-like for e-w processes [generic]

– features of njets distributions understood

⇒ cut on njets fine, your job now 1

n!/n+1!-1 0 1 2 3 4 5

) n!/

n+1

!R(

0

0.5

1

1.5

2

2.5

Higgs gluon fusion

Z QCD

n(Z QCD) = 1.42

n(Higgs gg fusion) = 1.80

0.5

1.0

1.5

2.0

2.5

R(n

+1)

/n

n + 1

n

1/0 2/1 3/2 4/3 5/4

1

n!/n+1!-1 0 1 2 3 4 5

) n!/

n+1

!R(

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Higgs WBF

Z EW

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

R(n

+1)

/n

n + 1

n

1/0 2/1 3/2 4/3 5/4

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics






Why we need the veto probabilities [SFitter: Lafaye, TP, Rauch, Zerwas]

– extraction of Higgs couplings [with error bars]

– including associated Higgs-jet channels [WBF eventually crucial]

– general fit of all couplings [Michael Rauch in Moriond 2012]

gjjH = gSMjjH`1 + ∆j

´

0

0.2

0.4

0.6

0.8

1

1.2

110 115 120 125 130 135 140 145 150

mH [GeV]

∆W∆Z∆t∆b∆

τ∆H

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

New physics

Effective mass [Englert, TP, Schichtel, Schumann]

– obviously sensitive to new physics massesbut awful variable, after theory uncertainty

– correlation meff ∼ 〈pT 〉 × njets

– use merged sample for meffestimate scale and αs uncertainties

[GeV]effm200 400 600 800

[1/

100

GeV

]ef

fdmdN 310

410

510

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

W+jets

µW+jets, 1/4

µW+jets, 4

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

W+jets

µW+jets, 1/4

µW+jets, 4

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

W+jets

µW+jets, 1/4

µW+jets, 4

2≥ jn

> 50 GeVT, j

p

-1L = 1 fb

W+jets

µW+jets, 1/4

µW+jets, 4

[GeV]effm200 400 600 800

[1/

100

GeV

]ef

fdmdN 310

410

510

[GeV]effm200 400 600 800

var

iati

onsα 0.9

1



[GeV]effm200 400 600 800

var

iati

onsα 0.9

1

1.1

[GeV]effm200 400 600 800

var

iati

onµ

1

10

[GeV]effm200 400 600 800

var

iati

onµ

1

10

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

New physics





– estimate SUSY significance as function of meff

[GeV]effm200 400 600 800 1000 1200 1400

[1/

100

GeV

]ef

fdmdN

-210

-1101

10

210

310

410

510 signalleptonictt

hadronicttW+jetsZ+jetsQCD

[GeV]effm200 400 600 800 1000 1200 1400

[1/

100

GeV

]ef

fdmdN

-210

-1101

10

210

310

410

510

[GeV]effm200 400 600 800 1000 1200 1400

BS+

B

0.5

1

1.5

2

2.5

3

= 2jn

-1L = 1 fb

[GeV]effm200 400 600 800 1000 1200 1400

BS+

B

0.5

1

1.5

2

2.5

3 [GeV]effm200 400 600 800 1000 1200 1400

[1/

100

GeV

]ef

fdmdN

-210

-1101

10

210

310

410

510 signalleptonictt

hadronicttW+jetsZ+jetsQCD

[GeV]effm200 400 600 800 1000 1200 1400

[1/

100

GeV

]ef

fdmdN

-210

-1101

10

210

310

410

510

[GeV]effm200 400 600 800 1000 1200 1400

BS+

B

0.5

1

1.5

2

2.5

3

= 3jn

-1L = 1 fb

[GeV]effm200 400 600 800 1000 1200 1400

BS+

B

0.5

1

1.5

2

2.5

3

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

New physics






– multijet studies establishing meff

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

New physics







Mass vs color charge

– now, significance as function of njets

jetsn2 3 4 5 6 7

jets

dndN

10

210

310

410

510

610signal

leptonictt

hadronicttZ+jetsW+jetsQCD

jetsn2 3 4 5 6 7

jets

dndN

10

210

310

410

510

610

jetsn2 3 4 5 6 7

BS+B

0.5

1

1.5

2

2.5-1L = 1 fb

jetsn2 3 4 5 6 7

BS+B

0.5

1

1.5

2

2.5

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

New physics







Mass vs color charge

– now, significance as function of njets

– representing new physics color charge [gluino does not decay via gluon]

– exclusive 2D likelihood including all information

2 3 4 5 6nj0.2

0.4

0.6

0.8

1.

1.2

1.4

1.6meffHTeVL

SPS1a, 1 inverse fb

0Σ

6Σ

2 3 4 5 6nj0.2

0.4

0.6

0.8

1.

1.2

1.4

1.6meffHTeVL

SPS1a, squarks+squarks, 1 inv. fb

0Σ

4Σ

2 3 4 5 6nj0.2

0.4

0.6

0.8

1.

1.2

1.4

1.6meffHTeVL

SPS1a, squarks+gluino, 1 inv. fb

0Σ

3.2Σ

2 3 4 5 6nj0.2

0.4

0.6

0.8

1.

1.2

1.4

1.6meffHTeVL

SPS1a, gluino+gluino, 1 inv. fb

0Σ

0.6Σ

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

Exclusive jet counting

staircase (non-abelian) vs Poisson (ordered)

– start by measuring dσ/dnjets

– test both regimes in photon+jets

– described by ME-PS merging [CKKW/MLM, unchanged by NLO]

– key to jet vetos

– key to SUSY searches

Understanding Jet Scaling and Jet Vetos in Higgs SearchesE Gerwick, TP, S SchumannPRL 108 (2012)

Establishing Jet Scaling Patterns with a PhotonC Englert, TP, P Schichtel, S SchumannarXiv:1108.5473, JHEP in print

Jets plus Missing Energy with an AutofocusC Englert, TP, P Schichtel, S SchumannPRD83 (2011)

Much of this work was funded by the BMBF Theorie-Verbund which is ideal for hard and relevant LHC work

Jet Scaling

Tilman Plehn

Counting jets

Poisson

Staircase

Interpolating

Jet veto

New physics

New physics at the LHCmissing

energy

(p.89)

cascade

decays

(p.91)

mono-

jets/photon

(p.15)

lepton

resnce

(p.109)

di-jet

resnce

(p.109)

top

resnce

(p.120)

WW/ZZ

resnce

(p.15)

W’

resnce

(p.93)

top

partner

(p.116)

charged

tracks

(p.123)

displ.

vertex

(p.123)

multi-

photons

(p.29)

spherical

events

(p.47,76)

SUSY (heavy grav.)

(p.17,26)XX XX X

SUSY (light grav.)

(p.17,27)X X X X X X

large extra dim

(p.39)XX XX X

universal extra dim

(p.47)XX XX X X X X X X

technicolor (vanilla)

(p.51)X X X X XX

topcolor/top seesaw

(p.53,54)X XX X

little Higgs (w/o T)

(p.55,58)X X X X X

little Higgs (w T)

(p.55,58)XX XX X X X X X X X

warped extra dim (IR SM)

(p.61,63)X X X X

warped extra dim (bulk SM)

(p.61,64)X X XX X X

Higgsless/comp. Higgs

(p.69,73)X X XX XX

hidden valleys

(p.75)X X X X X X X X X X X X X

[arXiv:0912.3259, Morrissey, TP, Tait]

From Jet Scaling to Jet Vetos - uni-heidelberg.deplehn/includes/talks/2012/cms_12.pdf · New...

Documents

Transcript of From Jet Scaling to Jet Vetos - uni-heidelberg.deplehn/includes/talks/2012/cms_12.pdf · New...