1. February 27, 2003APPI20031 Study of Chargino Production in e + e ‐ Collisions at Large tanβ Yukihiro Kato Kinki University Collaboration with K.Fujii (KEK), M.M.Nojiri (Kyoto), T.Kamon (Texas A&M)

2. February 27, 2003APPI20032 Contents Introduction Monte Carlo Study Results Summary

3. February 27, 2003APPI20033 Need to consider chargino study at large tanβ MSSM – Large tanβ Scenario – Particular mass hierarchy at large tanβ (generated via Yukawa coupling and mixing)  If chargino is gaugino-like, tanβ mass(GeV/c 2 ) tanβ= 50

4. February 27, 2003APPI20034 The reference SUSY point for study ・ tanβ= 50, μ= 400 GeV ・ M 0 = 200 GeV, M 1 = 87.8GeV → ・ is a next lightest SUSY particle and decays to ・ τpolarization is 0.026 MSSM Scenario

5. February 27, 2003APPI20035 Final state : Two τand large missing energy a) Can we measure the chargino mass by using the τjet? b) Can we measure the cross section of the chargino production ? We assume and are measured at lower-energy Linear colliders. Chargino pair Production

6. February 27, 2003APPI20036 Analysis Monte Carlo Simulation: Event generator HELAS + BASES/SPRING + TAUOLA + LUND 7.4 Detector Simulation ー JLC-I quick simulation ◆ Central drift chamber + Electromagnetic and Hadron calorimeter + Muon chambers ◆ The tracking and the calorimeter performances are described in Ref. KEK report 92-16. ◆ With initial state radiation, beam energy spread, and beamstrahlung ≧ 20K events are generated for each process.

7. February 27, 2003APPI20037 Linear Colliders σ(P(e)= － 0.9) = 322 fb σ (P(e)= + 0.9) = 15 fb √s (GeV) σ(pb) The LC’s parameters: √s = 400 GeV ∫Ldt = 200 fb -1 Polarized electron beam, P(e) → P(e) = － 0.9 (L.H.)

8. February 27, 2003APPI20038 Backgrounds (1) pair production (2) Standard model gauge boson production (3) Two photon process e + e － → e + e － +τ + τ －

9. February 27, 2003APPI20039 Event Selections (a) e/μ removal (b) Two good jets with E(j) ≧ 5 GeV by JADE algorithm (Y-cut ≧ 0.0025) (c) Jet angle cut: { － Q j ・ P z (j)} ／ E(j) < 0.8 (d) Jet mass cut: M jet ≦ 3 GeV/c 2 (e) Missing Pt cut: P t miss ≧ 20 GeV/c 2 (f) Angle between P vis and jet: reject event with cosθ(J 1, P vis ) ≧ 0.9 and cosθ(J 2, P vis ) ≦‐ 0.7 (g) Thrust ≦ 0.98 (h) Acoplanarity ≧ 30°

10. February 27, 2003APPI200310 Angle between P vis and jet Cut (f) is effective for W + W - production Rejected

11. February 27, 2003APPI200311 Event Selection Efficiency S/N = 2.9

12. February 27, 2003APPI200312 τjet energy distribution depends on τ jet Energy Distribution can be measured by this distribution

13. February 27, 2003APPI200313 Chargino Mass Measurement τ jet energy distribution depends on Fit to this distribution as a function of Compare the distributions of various and calculated Δχ 2 for the reference point. Estimate

14. February 27, 2003APPI200314 Δχ 2 of τjet energy distributions for the reference point ±0.7 GeV/c 2 Uncertainty of Chargino Mass estimate the uncertainty

15. February 27, 2003APPI200315 Uncertainties of and were assumed to be very small. (estimated by the other experiments) How much required when can be measured within 1σat reference point? But… calculateΔχ 2 various and fixed reference point

16. February 27, 2003APPI200316 Uncertainties of and within 1σ Uncertainty of in the plane require

17. February 27, 2003APPI200317 The efficiency weakly depends on the chargino mass. Event Selection Efficiencies for Different Chargino Masses

18. February 27, 2003APPI200318 Expected Uncertainty for the Production Cross Section Selection efficiency weakly depends on can be determined by uncertainties of ε, ∫Ldt, and N obs σ= 322±10 fb Δσ

19. February 27, 2003APPI200319 Study of chargino pair production at large tanβ is important for LC. τjet energy distribution is an effective tool for chargino mass measurement. ⇒ If the chargino mass is determined within 1σ, ±0.7 GeV/c 2, ⇒ required Event Selection efficiency of chargino pair production weakly depend on the chargino mass. ⇒ can be measured the production cross section. Summary