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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