Search for new physics in dilepton and diphoton final states with CDF
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Transcript of Search for new physics in dilepton and diphoton final states with CDF
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Search for new physics in dilepton and diphoton final states with CDF
Xin Wu(University of Geneva, Switzerland)
On behalf of the CDF collaboration
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The Tevatron and CDF (run 2) pp collisions: Ecm = 1.96TeV
– Data on tape approaching 1 fb1 !
CDF detector performs well– Data taking efficiency ~90%– Analyses progress rapidly as
reconstructed and calibrated data become available
Muon System
COT
Plug Calorimeter
Time-of-Flight
Central Calorimeters
Solenoid
Silicon Tracker
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Search with high mass dilepton/diphoton
High mass dilepton and diphoton productions are well understood in SM
Leptons (especially e and ) and photons can be cleanly identified experimentally
New physics may show up as narrow resonances or deviations (‘contact interaction terms’)
CDF run 1 ee result
CDF run 2 d/dM result (207 pb1, hep-ex/0412050)
NLO (DIPHOX)
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Models of new physics in dilepton and diphoton
Phenomenologies are well developed for dilepton and diphoton final states at hadron colliders– SUSY models– Various models with Z’– Extra spatial dimensions (ADD and RS)– Lepton-quark compositeness– Technicolor, Leptoquarks, excited leptons, …
Searches strive to be model independent– Optimization on individual final state (signature based)– Generic cross section limit in case of negative result
Guidance from models are important– Use general features to calculate acceptance and to
optimize S/N for small signals– In case of negative results, set limits on model
parameters (feed back to model building)
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Analyses presented in this talk Search in ee and with 200 pb1
Search in ee using mass and angular distributions with 448 pb1
– Generic Z’ models with parametrization of Carena et al, PRD70:093009, 2004
Search in with 345 pb1
Search in with 190 pb1
More exclusive searches, if time permits– Search in +met with 202 pb1
– Search in and ET with 307 pb1 (hot off the press!)
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Selection– Isolated ee/, Et>25 Gev– Combination of triggers to
ensure full efficiency High mass data
M
(GeV/c2)
ee
Obs. Exp. Obs. Exp.
150 205 212.999.3 58 55.32.5
200 84 78.233.4 18 20.91.0
300 22 13.64.4 6 5.20.3
400 5 2.90.7 1 2.30.2
Background contributions– Drell-Yan– QCD, cosmic , tt, WW, WZ
14,799 ee and 7,775 Search in ee and with 200 pb1
Mee150
M150
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Cross section limit for Xee or
CL*Br limit: ~ 20 fb for all spins for Mll > 600 GeV
spin-2 (eg. G) Limit is spin dependant
– Acceptance depends on angular distribution of decaying particle
spin-0 (eg. sneutrino)
cross section limits turned into mass limits of given models
spin-1 (eg. Z’)
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(Selected) model dependents limits
Spin-0– R-parity violating sneutrinos
Spin-1– Z’ with SM coupling– Z’ in GUT E6 models
Spin-2– Gravitons in models with
warped extra dimensions (Randall-Sundrum)
’ 2*Br ee
0.01 680 665
730
0.005 620 590
665
Mass Limit, 95%CL (GeV/c2)~
Z’ mass limits 95%CL (in GeV/c2)
ee
Z’SM 770 740 825
Z 630 585 675
Z 645 605 690
Z 675 640 720
ZI 570 540 615
k/MPL ee
0.1 660 610 710
0.05 470 455 510
0.01 - 165 170
RS MG mass Limits, 95%CL (GeV/c2)
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New search in ee of 448 pb1
Mee still in very good agreement with SM– High mass region (M200 GeV/c2):
Data: 120 Exp.: 125 11stat
30,745 ee cadidates
Use angular distribution in high mass region to increase sensitivity for new physics
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Angular distribution (cos*) * : scattering angle in Collin-Soper frame
– Minimize ambiguity in the incoming quark Pt
p p
P =0Z-Axis
pp
lab frame
Observed angular distribution also agrees with SM
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Setting limits with ee of 448 pb1
Generic Z’ search: use classification scheme proposed by Carena et al (PRD70:093009,2004) – 4 model classes: B-xL, q+xu, 10+x5, d-xL– 3 parameters : MZ’, gZ’, x
Use 2-d CLs method (used for LEPII Higgs mass limits) to set limit– Test statistics build from Poisson probabilities for SM
and Z’ in (Mee, cos*) bins Test 40k model points in 4 classes
– Use acceptance matrix with same (Mee, cos*) bins
• Avoid undertaking full simulation for 40k points
binsN
jjiji NAn
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K*LO calculation for a given model point
Expectation for bin i
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Results from ee of 448 pb1
LEPIIg=0.10g=0.05g=0.03
Exclusion regions in (MZ’, gZ’, x) space for 4 model classes
– eg. d-xu models: improve on LEPII results
Easy to obtain limit on particular models
Model MZ’ 95%CL Limit (GeV/c2)
Z′SM 845
E6 Z 720
E6 Z 690
E6 Z 715
E6 ZI 625
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Search in with 345 pb1
M (GeV/c2) Obs. Exp.
100 87 96.8 21.6
300 1 4.21.0
350 1 1.50.5
Background– SM diphoton production
• Dominant at very high masses
– Fakes: -jet and jet-jet• Jet fragments into hard
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Selection– 2 central isolated , ET>15
GeV
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Limits from of 345 pb1
Virtual G exchange in warped extra dimension (RS) – 2 parameters: MG (1st graviton excitation state) and k/MPL
k/MPL ee/(200 pb-
1) (345 pb-1)
0.1 660/610 690
0.01 -/165 220
RS MG mass Limits, 95%CL (GeV/c2)
Br() =2Br(ee)
g,q
g,q
f,V
f,V
G
KKn
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Search in with 195 pb1
0.175 0.175
shrinking cone angle1/Et
Selection– 3 final states: eh, h, hh
– tau hadronic trigger used for hh
h idendification with “shrinking cone algorithm”
– ET 15(25) GeV for e, h (hh)
– Mvis = m(vis + vis + ET) 120 GeV/c2
• control: Mvis<120 GeV/c2
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Result of search in with 195 pb1
Control sample– obs. 90 vs. exp. 99.312.5
High mass– obs. 4 vs. exp. 2.80.5
Background– Z/*– fake h from W+jet, multi-
jet events
394 GeV/c2
Cross section limit– ~ 1500 fb at high mass
Mass limit on Z’SM
– MZ’ >394 GeV/c2
– ee/ (200 pb1): 620/605 First high mass
search
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Search in ET with 202 pb1
PRD 71, 031104(R) (2005)
Selection– 2 central isolated , ET>13
GeV0 event observed for ET>45
Gev0.30.1 background
expected
10 ~G~
m(±) > 167 GeV/c2
m(0) > 93 GeV/c2
NLSP LSP
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Search in and ET with 307 pb1
A priori selection, same as in run 1– Tight e or : ET
>25 GeV
– Loose e or : ET>20 GeV (plug electron ET>15 GeV)
– ET>25 GeV, ET>25 GeV
Data agrees with expectation– Run 1 (86 pb, 1.8 TeV) 2.7 excess in ET not
confirmed in exact repeat of the analysis with much more data
First public prestation yesterday (22/7/05) by A. Loginov, SUSY2005
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Conclusions Searches in dilepton (e, , ) and diphoton
final states with 200-400 pb-1 data from CDF run2 yields more stringent limits on production of new heavy particles– Excluded larger parameter space of many
models of new physics beyond SM Analyses continues with increasing statistics
and more sophisticated search techniques– Soon 1 fb-1 on tape and 4-8 fb-1 by 2009
The Tevatron still has a chance to steal the thunder from LHC