Search for Narrow Search for Narrow Resonance Decaying to Resonance Decaying to Muon Pairs in 2.3 fbMuon Pairs in 2.3 fb-1-1

Ye Lion behalf of CDF Collaboration

University of Wisconsin-Madison

APS April Meeting, St. Louis - 14 April 2008 2Ye Li

MotivationMotivation Theory Driven

Standard Model successful but incompleteStrong discovery potential in dimuon

channelNew models predict narrow neutral

resonance, e.g. • Additional U(1) symmetry: Z’ • Extra space-time dimension: Randall-Sundrum

gravitonFocus on Z’ → channel

APS April Meeting, St. Louis - 14 April 2008 3Ye Li

MotivationMotivation Experiment Driven

Last Tevatron dimuon resonance searches performed with integrated luminosity 200 pb-1

→ Our search: L ≈ 2.3 fb-1 of CDF Run II dataSignificant increase of sensitivity to

dielectron and diphoton channelsExcellent tracking resolution (Central Outer

Tracker, Drift Chamber)

APS April Meeting, St. Louis - 14 April 2008 4Ye Li

MethodologyMethodology Model Drell-Yan background and

signal resonance with PYTHIA + detector simulation

Use Z region for normalization Remove uncertainty on luminosityEasy accounting

APS April Meeting, St. Louis - 14 April 2008 5Ye Li

MethodologyMethodology Inverse Mass (1/m) Scan

Excellent angular resolution → negligibleHigh PT track curvature (~1/PT) resolution

constant → constant 1/m resonance width

1/m ≈ 0.16/TeV

CDF Run II Preliminary

APS April Meeting, St. Louis - 14 April 2008 6Ye Li

MethodologyMethodology Fit for NZ’ (number of Z’ candidate)

Calculate Binned Poisson likelihood L(NZ’;MZ’) for region 1/m < 10/TeV

Construct the narrowest possible interval in NZ’ at 95% C.L.

Scan for resonanceSignificance determined by Monte-Carlo

pseudo-experiments

APS April Meeting, St. Louis - 14 April 2008 7Ye Li

Dataset & SelectionDataset & Selection Dataset from high PT muon trigger Dimuon event selection

Two opposite-sign tight muonsAt least one muon passing the trigger

CDF Run II Preliminary

APS April Meeting, St. Louis - 14 April 2008 8Ye Li

EfficiencyEfficiency Mass dependence

Track and muon-hit cuts independent of mass

Momentum dependence Normalization of background expectation

• Only consider P dependence• No P dependence of trigger eff. for PT > 30 GeV

Separate the sample into signal and normalization (Z-pole) regions

APS April Meeting, St. Louis - 14 April 2008 9Ye Li

AcceptanceAcceptance Comparison of muon in W →

data vs. simulation for two muon detector regions

0.6 < || < 1.0 (CMX)

|| < 0.6 (CMUP)

CDF Run II Preliminary

APS April Meeting, St. Louis - 14 April 2008 10Ye Li

AcceptanceAcceptance Mass-dependent Acceptance

Larger mass → Lower boost → More central events → Larger acceptance

CDF Run II Preliminary

APS April Meeting, St. Louis - 14 April 2008 11Ye Li

BackgroundBackground Drell-Yan */Z →

PYTHIA + Simulation WW and tt-bar

PYTHIA + Simulation Cosmic Rays

Identified Cosmic-ray samples QCD Jets and Decays-in-Flight

Data

APS April Meeting, St. Louis - 14 April 2008 12Ye Li

Drell-YanDrell-Yan Dominant source for background Dominant source for systematic

uncertainty Mass spectrum affected by higher-

order correctionsCalculate up to next-to-next-to leading order

(NNLO) correction → k-factorDifferent Calculations give different k-

factorsAverage k-factor; Difference as uncertainty

APS April Meeting, St. Louis - 14 April 2008 13Ye Li

Signal ScanSignal Scan Pseudo-experiment: MZ’ = 250 GeV

Most likely distribution of NZ’

CDF Run II Preliminary

APS April Meeting, St. Louis - 14 April 2008 14Ye Li

Signal ScanSignal Scan Expected limits on NZ’ from 1000

pseudo-experiments on 50 Z’ masses

Data: to be implemented …!

CDF Run II Preliminary

APS April Meeting, St. Louis - 14 April 2008 15Ye Li

SummarySummary Use 1/m distribution for constant

resolution to search for Z’ Fitter and Simulation in place to study

signal acceptance and identification efficiency

Systematic uncertainties to be determined Signal scan performed on pseudo-

experiments Ready to unblind the data soon