Study of Chargino Production in e + e ‐ Collisions at Large tanβ

1. 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) APPI2003

2. Contents • Introduction • Monte Carlo Study • Results • Summary APPI2003

3. MSSM – Large tanβ Scenario – Particular mass hierarchy at large tanβ mass(GeV/c2) (generated via Yukawa coupling and mixing) tanβ= 50  If chargino is gaugino-like, tanβ Need to consider chargino study at large tanβ APPI2003

4. MSSM Scenario The reference SUSY point for study ・ tanβ= 50, μ= 400 GeV ・ M0 = 200 GeV, M1 = 87.8GeV 　→ 　→　 ・ 　 is a next lightest SUSY particle and decays to ・ τpolarization is 0.026 APPI2003

5. Chargino pair Production 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. APPI2003

6. 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. APPI2003

7. Linear Colliders The LC’s parameters: • √s = 400 GeV ∫Ldt = 200 fb-1 • Polarized electron beam, P(e) σ(pb) σ(P(e)=－0.9) = 322 fb σ(P(e)= + 0.9) = 15 fb → P(e) = －0.9 (L.H.) √s (GeV) APPI2003

8. Backgrounds (1) pair production (2) Standard model gauge boson production (3) Two photon process e+ e－ →　e+ e－+τ+τ－ APPI2003

9. 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: {－Qj・Pz(j)}／E(j) < 0.8 (d) Jet mass cut: Mjet≦ 3 GeV/c2 (e) Missing Pt cut: Ptmiss ≧ 20 GeV/c2 (f) Angle between Pvis and jet: reject event with cosθ(J1, Pvis) ≧0.9 and cosθ(J2, Pvis)≦‐0.7 (g) Thrust ≦ 0.98 (h) Acoplanarity ≧ 30° APPI2003

10. Angle between Pvis and jet Rejected Cut (f) is effective for W+W- production APPI2003

11. Event Selection Efficiency S/N = 2.9 APPI2003

12. τ jet Energy Distribution τjet energy distribution depends on can be measured by this distribution APPI2003

13. Chargino Mass Measurement τ jet energy distribution depends on Fit to this distribution as a function of Compare the distributions of various and calculated Δχ2 for the reference point. Estimate APPI2003

14. Uncertainty of Chargino Mass Δχ2 of τjet energy distributions for the reference point estimate the uncertainty ±0.7 GeV/c2 APPI2003

15. Uncertainties of and were assumed to be very small. (estimated by the other experiments) But… How much required when can be measured within 1σat reference point? various and fixed reference point calculateΔχ2 APPI2003

16. Uncertainties of and Uncertainty of in the plane within 1σ require APPI2003

17. Event Selection Efficiencies for Different Chargino Masses The efficiency weakly depends on the chargino mass. APPI2003

18. Expected Uncertainty for the Production Cross Section Selection efficiency weakly depends on can be determined by uncertainties of ε, ∫Ldt, and Nobs Δσ σ= 322±10 fb APPI2003

19. Summary • 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/c2, ⇒required • Event Selection efficiency of chargino pair production weakly depend on the chargino mass. ⇒ can be measured the production cross section. APPI2003