1APPI2003February 27, 2003

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

Yukihiro Kato

Kinki University

Collaboration with K.Fujii (KEK), M.M.Nojiri (Kyoto), T.Kamon (Texas A&M)

February 27, 2003 APPI2003 2

ContentsContents

• Introduction

• Monte Carlo Study

• Results

• Summary

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0111

~~~~χτχ

MMMM

Need to consider chargino Need to consider chargino study at large tanβstudy at large tanβ

MSSM – Large tanβ Scenario –MSSM – Large tanβ Scenario –

Particular mass hierarchy at large tanβ

(generated via Yukawacoupling and mixing)

If chargino is gaugino-like,

%~~~ 1000

111 )Br( νχτντχtanβ

mas

s(G

eV/c

2 )

tanβ= 50

February 27, 2003 APPI2003 4

22 GeV/c152.7GeV/c86.4 1

01 τ~χ~ M,M

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

2GeV/c171.01χ

~M

MSSM ScenarioMSSM Scenario

1τ~

τ~ ＋01χ

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Final state : Two τand large missing energya) Can we measure the chargino mass by using the τje

t?b) Can we measure the cross section of the chargino p

roduction?

We assume and are measured at lower-energy

Linear colliders.

Chargino pair ProductionChargino pair Production

0

1χ~τ

ντ~ντ~~~ χχee 110

1χ~τ

1τ~M01χ~M

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AnalysisAnalysisMonte 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.

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Linear CollidersLinear Colliders

)χ~χ~ee( 11

σ(P(e)= － 0.9) = 322 fbσ(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) = P(e) = －－ 0.9 (L.H.)0.9 (L.H.)

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BackgroundsBackgrounds

(1) pair production

(2) Standard model gauge boson production

(3) Two photon process e+ e － →　 e+ e － +τ+τ －

0

1

0

111 χτχτττ ~~~~ 1τ~

ν)τ,μ,e, decays(ZννZ andeeZ

ντ,μ,e,(ZZ

WW

000

00 ）

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Event SelectionsEvent 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/c≦ 2

(e) Missing Pt cut: Ptmiss 20 GeV/c≧ 2

(f) Angle between Pvis and jet: reject event with

cosθ(J1, Pvis) 0.9 and cosθ(J≧ 2, Pvis) ‐0.7 ≦

(g) Thrust 0.98≦(h) Acoplanarity 30°≧

)2,1(,),(cos

iPP

PPPJ

visi

visivisi

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Angle between PAngle between Pvisvis and jet and jet

Cut (f) is effective for W+W- production

Rejected

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Event Selection EfficiencyEvent Selection Efficiency

S/N = 2.9

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τjet energy distribution depends on

τ jet Energy Distributionτ jet Energy Distribution

１χ~M

fixedareand 011 χτ ~~ MM

can be measured

by this distribution

１χ~M

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Chargino Mass MeasurementChargino Mass Measurement

τ jet energy distribution depends on １χ~M

)fixedareand( 011 χτ ~~ MM

Fit to this distribution as a function of １χ~M

Compare the distributions of various

and calculated Δχ2 for the reference point.

１χ~M

Estimate １χ~M

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Δχ2 of τjet energy distributions for the reference point

±0.7 GeV/c2

isχ １

~M

Uncertainty of Chargino MassUncertainty of Chargino Mass

estimate theuncertainty

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Uncertainties of and Uncertainties of and

were assumed to be very small.

(estimated by the other experiments)011 χτ and ~~ MM ΔΔ

How much required when

can be measured within 1σat reference point?

011 χτ and ~~ MM ΔΔ

１χ~M

But…

calculateΔχ2011 χτ and ~~ MMvarious

and fixed １χ~M

referencepoint

01χ~M

1τ~M

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Uncertainties of and Uncertainties of and

1

01 τχ ~~ MM

within 1σ１χ~M

2χ GeV/cΔ 0

141.M~

2τ GeV/cΔ

161.M~

Uncertainty of in the plane

１χ~M

require

1τ~M 01χ~M

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The efficiency weakly depends on the chargino mass.

Event Selection Efficiencies for DiEvent Selection Efficiencies for Different Chargino Massesfferent Chargino Masses

)c/GeV4.86M,c/GeV7.152M( 2~

2~ 0

11

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Expected Uncertainty for the Expected Uncertainty for the Production Cross SectionProduction Cross Section

Selection efficiency weakly depends on

１χ~M

)~~ee( 11 χχ

can be determined by uncertainties of ε, ∫Ldt, and Nobs

σ= 322±10 fb

Δσ

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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 product

ion weakly depend on the chargino mass. ⇒ can be measured the production cross section.

2GeV/c701

.M~

2

2τ

GeV/cGeV/c

1

4161

01

.M.M

~

~

SummarySummary