Search for Anomalous Production of Multi-lepton Events at CDF Alon Attal Outline  Motivation  R p V SUSY  CDF & lepton detection  Analysis  Results for the CDF collaboration

Oct. 31, 2006Alon Attal – DPF Hawaii2 Standard Model & Beyond The SM agrees extraordinarily well with detector measurements, but is there more? Many new physics models predict new particles at the electroweak scale (~100 GeV/c 2 ). For example, in Supersymmetry a new particle is predicted for every one in the SM with different mass and spin. Fermions Bosons

Oct. 31, 2006Alon Attal – DPF Hawaii3 Analysis Strategy Require a method to reduce backgrounds while preserving new physics signal. At the Tevatron, jet production rate >> lepton production rate. Search for events with ≥ 3 charged leptons. Complements searches for leptons + E T. Attempt to be as model independent as possible. Sensitive to R p V SUSY, and other new physics models.

Oct. 31, 2006Alon Attal – DPF Hawaii4 R-Parity (R p ) R p = (-1) [3(B-L) + 2S] +1 for SM particles -1 for particles B = baryon #, L = lepton #, S = spin If R p is conserved: Lightest SUSY particle (LSP) is stable, dark matter candidate. SUSY particles are pair produced. New quantum Number:

Oct. 31, 2006Alon Attal – DPF Hawaii5 R-Parity Violation (R p V) Choose only L i L j E k term ≠ 0, protecting proton lifetime. | | < 0.1, only LSP decays via RpV coupling. Violate lepton # Violates baryon # 3 additional couplings: lklk ijk lili  j

Oct. 31, 2006Alon Attal – DPF Hawaii6 2 LSPs ( ) 1 ~ R p V Decays 2 particles ≥ 4 Charged Leptons cascade decay R p V decay p Most sensitive to 121 and 122. 00

Oct. 31, 2006Alon Attal – DPF Hawaii7 Tevatron & Luminosity 346 pb -1 used Data taken from March 2002 – August 2004

Oct. 31, 2006Alon Attal – DPF Hawaii8 CDF Detector & Lepton ID Lepton ID important to analysis  Studied in data and MC  Efficient (~90%)  Probability that jets are misidentified as leptons is small (< 0.02%) Muon Detectors Drift ChamberCalorimeter Electrons  Track + Calorimeter Cluster  95% of energy in EM calorimeter  |η| < 2.0 Muons  Track plus “stub” in muon detector  Minimum ionizing  |η| < 1.0 η = 1.0 η = 2.0 η = 0 ~

Oct. 31, 2006Alon Attal – DPF Hawaii9 MC Signal Distributions muon coverage electron coverage M (GeV) 0.13  (pb) 0 A0A0 + sign  M (GeV) M (GeV) tanβM 1/2 (GeV) M 0 (GeV) ±± ~ 1 00 ~ 2 00 ~ 1 Analysis Reference Point:Using mSUGRA framework

Oct. 31, 2006Alon Attal – DPF Hawaii10 Basic Event Selection Luminosity = 346 pb -1 Use high-p T lepton triggers (p T > 18 GeV/c). Lepton p T s: 20, 8, 5, 5 GeV/c. Dominant background from DY, impose following cuts on opposite sign leptons:  Impose Z veto cut ( GeV/c 2 )  |  | < 160° cut. Require isolated leptons to reduce jet backgrounds. Low mass cut (> 15 GeV/c 2 ) to reduce heavy flavor, and low mass resonances. Before Event Selection Events with > 3 leptons very clean!

Oct. 31, 2006Alon Attal – DPF Hawaii11 Validation Control samples are crucial to understanding our procedure Validate lepton ID efficiencies Validate selection cuts Trilepton events that fail 1 or more cuts

Oct. 31, 2006Alon Attal – DPF Hawaii12 Control Sample Overview y = x 26 total control samples (summary on left)  By lepton type  Inside & outside Z window  Number of leptons  Pass/Fail  cut Analysis procedure is validated through agreement between data and MC prediction Each point corresponds to a single control sample w/ error bars = ± 1σ

Oct. 31, 2006Alon Attal – DPF Hawaii13 Signal Samples Signal events: 4 eee, 1ee , 1  e Probability of observing ≥ 5 events with 3.1 expected = 17% Trilepton Signal Samples Process λ 121 (e ll ) λ 122 (  ll ) Z/  +  2.1 ± ± 1.0 Z/  + W 0.2 ± ± 0.1 Fakes0.7 ± ± 0.3 Total Background3.1 ± ± 1.0 RpV SUSY ( 121 ) 3.8 ± RpV SUSY ( 122 ) ± 0.4 Data51 ≥ 4 Lepton Signal Sample ProcessSignal Z/  +  ± Z/  +  Z/  ± Fakes0.004 ± Total Background0.008 ± RpV SUSY ( 121 ) 1.5 ± 0.2 RpV SUSY ( 122 ) 1.5 ± 0.3 Data0 Very Clean Signature

Oct. 31, 2006Alon Attal – DPF Hawaii14 Event Distributions 4 of the 6 events appear to be Z +  events. 2 of the 6 events appear to have mis-ID jets. Consistent with background prediction. CDF Run II Preliminary, 346 pb -1

Oct. 31, 2006Alon Attal – DPF Hawaii15 Setting Limits Use Bayesian method to find σ obs, combining 3 and ≥4 lepton signal samples. Set limits for both signs of    and  .

Oct. 31, 2006Alon Attal – DPF Hawaii16 Results Set limits on chargino and neutralino masses   >   <   >   < 0 M (GeV/c 2 ) M (GeV/c 2 ) SUSY Scenario CDF Limits 00 ~ 1 ±± ~ 1

Oct. 31, 2006Alon Attal – DPF Hawaii17 Conclusions We completed a search for new physics in the multilepton channel. We used a minimal amount of cuts to try and limit model dependence. No significant evidence of physics beyond the SM was detected. Limits on the lightest neutralino and chargino masses were set using an R p V SUSY framework. The ≥ 4 lepton sample provides a promising new method to search for new physics with the higher luminosity currently being delivered to the Tevatron.

Oct. 31, 2006Alon Attal – DPF Hawaii18 Backup

Oct. 31, 2006Alon Attal – DPF Hawaii19 Trilepton Event Jet 16 GeV Leading M ee = 70 GeV/c 2 e- 50 GeV, e+ 30 GeV, e- 13 GeV e- 50 GeV e+ 30 GeV e- 13 GeV e+ 30 GeV e- 50 GeV e- 13 GeV Jet 16 GeV Jet 16 GeV E T = 1.5 GeV

Oct. 31, 2006Alon Attal – DPF Hawaii20 Limits SUSY Scenario M (GeV/c 2 ) M (GeV/c 2 ) expectedobservedexpectedobserved   >   <   >   < 00 ~ 1 ±± ~ 1

Oct. 31, 2006Alon Attal – DPF Hawaii21 DØ Limits on R p V SUSY   <   >   <   > 0 M (GeV/c 2 ) M (GeV/c 2 ) SUSY Scenario DØ Limits 00 ~ 1 ±± ~ 1