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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)
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February 27, 2003 APPI2003 2
ContentsContents
• Introduction
• Monte Carlo Study
• Results
• Summary
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February 27, 2003 APPI2003 3
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
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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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February 27, 2003 APPI2003 5
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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February 27, 2003 APPI2003 7
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