Post on 07-Jan-2016
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June_2004 E. Gallas - SUSY 2004 1
Searches for Extra Dimensions and
Heavy di-lepton Resonances at D0
Elizabeth Gallas Fermi National Accelerator Laboratory
Computing Division
12th International Conferenceon Supersymmetryand Unification of Fundamental InteractionsJune 17-23, 2004Epochal Tsukuba, Tsukuba, Japan.
June_2004 E. Gallas - SUSY 2004 2
Outline• 3-Space / Time:
– Fermilab Tevatron with Experiment DØ / mid Run 2 • What can Extra Dimensions (ED) do for you ?• Phenomenology (of interest for pp colliders)
– 2 particular ED models• Large Extra Dimensions
– ADD (Arkani-Hamed, Dimopoulos, Dvali)• TeV-1 ‘longitudinal’ Extra Dimensions
– DDG (Dienes, Dudas, Gherghetta)– DØ: A window into ‘Extra Dimensions’ (ED)
• DØ: Lepton/Photon Final state searches for :– Large Extra Dimensions (ED)– TeV-1 ‘longitudinal’ Extra Dimensions– Z’ boson
• Summary and Conclusions
–
June_2004 E. Gallas - SUSY 2004 3
Chicago
Tevatron
Main Injector & Recycler
DØCDF
p source
TEVATRON Run 2 Upgrade
• New Main Injector : 150 GeV– Store protons, shoot to
target for anti-proton production
• New recycler :– Magnet storage ring for anti-
proton
• Higher energy:– 1.96 TeV vs 1.8 TeV– Higher cross sections
(30 % for the SUSY)
• Higher antiproton intensity:– 6x6 36x36 bunches
(3.5 μs 396 ns)– Higher luminosity
• Run 1 : 2x1031 cm-2s-1
• Run 2 : 2x1032 cm-2s-1
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SMTSMT
SMT
DØ Run 2a UpgradeSolenoid (2T)
4-layer Silicon Vertex and 16-layer Fiber Trackers
Muon forward chamber (||<2 ), shielding
New preshower, upgrade Calorimeter electronics
Upgrade to Trigger and DAQ system
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What can Extra Dimensions do for you ?
…proposals dating at least back to 1920’s…
• Recent renaissance in the theory proposes:– unite all known forces (including gravity)
• known particles, electroweak and strong interactions– confined to a ‘brane’ - a hypersurface in the “bulk” of 4+n Dim
• gravity appears weak – diluted in extra dimensions.
– There is no “desert”– Offers alternative to the “hierarchy
problem”• only one important scale in nature --
may be accessible at Tevatron and LHC energies
– Lends practical aspects to string theory…
it’s not just a beautiful idea… we can test it !
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Large Extra Dimensions (LED)in the ADD Model
• ADD (Arkani-Hamed, Dimopoulos, Dvali) model assumes:– n Extra Dimensions of size R– SM particles and interactions are confined to 4D-world (brane)– Gravity propagates in 4+n Dimensional space
• Gravity appears weak – diluted in extra dimensions
– In this formulation:
• where MPl (apparent 4D Planck Scale):• Ms (fundamental Planck Scale) is brought to
the TeV range
• Constraints (cosmology, tabletop expts):– Extra dimensions ‘compactified’ (RC < 1 mm)– require n>1 (g forces at large distances)Collider experiments – only probe for ED for n3 !
nc
nSPl RMM 22
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LED Tevatron Search Modes
• Direct Searches (graviton escapes the brane)– look for JET recoiling against missing ET (next talk)
• Indirect Searches (this talk)– virtual graviton - contributions to l+l-, production
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Virtual Graviton Exchange
• The predicted cross section is described by:
where g = F/MS4 == (in TeV-4)
describes strength of gravity in the presence of LEDand F is a dimensionless parameter ~ 1 which depends on the formalism (for the effective Lagrangian):
GRW: F = 1HLZ: F = log(Ms
2/M2), n =2 F = 2/(n-2), n > 2Hewett F = 2/, =±1
• Experimentally, the process is defined by the – invariant mass of the di-boson or di-leptons (M)– cosine of the scattering angle, * (|cos *|).
2int
2
cosM GKKGSM fffdd
d
•SM term•interference term•direct gravity term
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Search for ED in ee/ channel
• Dataset 200 pb-1
• Use di-EM objects– both ee and
• SelectionsTwo EM with Et > 25 GeV
with tight quality cuts
Fiducial requirements:• central EM objects:
|eta| < 1.1
• central/forward objects:1.5 < |eta| < 2.4
LED signal MC for g =0.6
fakes
Bkg
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Highest mass Drell-Yan event
Invariant mass 475 GeV/c2, cos θ* = 0.01
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di-EM Mass,Cos θ* distributions
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• Uncertainties:
Uncertainties in G for di-EM sample
Source of Systematic Uncertainty
K-factor (NLO effects) 10%
Choice of p.d.f. 5%
Normalization x eff iciency 2%
ET dependence of eff iciency 5%
Total 12%
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LED: LED in at DØ -
MS > 880 GeV (95% CL)Run 2 Preliminary
•Luminosity = 100 pb-1
•Select events with2 muons PT> 15 GeVM > 50 GeV
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Summary: Limits on LED MS
for various formalisms F• No evidence for signatures in excess of high-mass dielectron,
diphoton or dimuon events over SM expectation, from coupling to Kaluza-Klein gravitons
• Fit (di-EM Mass,Cos θ*) distribution – Single parameter for ED effects: ηG = F/M4
S
• Translate ηG limits to 95% CL lower limits on Planck scale MS , in TeV, using different formalisms for F
• DiEM limits - combine Run I & Run 2 – best limits on LED to date• Di limits for Run 2 with more statistics -- in preparation
GRW HLZ for n=: 2 3 4 5 6 7
Hewett
diEM 1.43 1.67 1.70 1.43 1.29 1.20 1.14 1.28
diMU 0.88 0.68 0.95 0.79 0.72 0.67 0.63 0.71
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Dedicated ee Search for ‘longitudinal’ Extra Dimensions
• Another ED model (TeV-1 “longitudinal” EDs):– proposed by Dienes, Dudas, and Gherghetta (DDG)
– Fermions confined to 4D
– but SM gauge bosons propagate in TeV-1 ED of size:
R = 1/MC
– Predicts Kaluza-Klein states of gauge bosons (KK, WKK, ZKK, gKK)
• produced directly (with sufficient energy)
• produced indirectly (virtual exchange of KK modes)
• Lepton pair production cross section depends on
C = 2 / 3 MC2, where MC = ‘compactification’ scale of TeV-1 ED
• This analysis:– look for virtual exchanges of KK excitations of the Z and
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Jet mis-ID signal
C=5TeV-2
SM + fakes
Dedicated ee Search for TeV-1 Dimensions (DDG)
Predicts strong negative interference effects unlike LED discussed before
Use di-EM dataset (200 pb-1)– adding track match– fiducial requirements –
same as for LED analysis
Find upper limit on
C < 2.63 TeV
and thereby (lower limit):
Mc > 1.12 TeV (95% CL)
First search of this type
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Z Limits from ee: SM, E6
• Various models propose new neutral gauge bosons– SM couplings– variety of E6 GUT inspired
• Dataset 200 pb-1 – same as in ED analysis• Limits on Z’ mass in GeV/c2:SM couplings
Run I Run II 670 780
E6 couplings
ZI Zχ Zψ Zη 575 640 650 680
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Z’:
No evidence: Set limitsM(Z’) > 610 GeVRun 2 Preliminary
This is a previous result under revision with increased statistics:We used the same dimuon sample as used for LED search to look for heavy Z-like resonances
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Summary• No signal for new physics observed so far
– but some interesting events !
• New Limits from DØ: Extra Dimensions and Z’
* limits under revision with increased statistics
• improved limits on additional gauge bosons !• most sensitive collider search for ED’s to date!
– higher efficiency in widest acceptance– di-EM channels using 200 pb-1 integrated luminosity (now 300 pb-1 on tape)– first collider search for TeV-1 ‘longitudinal’ Extra Dimensions
Topic Prelim. Run 2
LED : ee and MS >1.43 TeV (Run 1&2)
LED : MS > 880 GeV *
TeV-1 ‘longitudinal’ ED: ee Mc > 1.12 TeV
Z’ : M(Z’) > 610 GeV *
Z’ : ee M(Z’) > 780 GeV