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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). Contents. Introduction Monte Carlo Study Results Summary. MSSM – Large tanβ Scenario –. - PowerPoint PPT Presentation
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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)
February 27, 2003 APPI2003 2
ContentsContents
• Introduction
• Monte Carlo Study
• Results
• Summary
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
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
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
February 27, 2003 APPI2003 6
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.
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.)
February 27, 2003 APPI2003 8
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 )
February 27, 2003 APPI2003 9
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
February 27, 2003 APPI2003 10
Angle between PAngle between Pvisvis and jet and jet
Cut (f) is effective for W+W- production
Rejected
February 27, 2003 APPI2003 11
Event Selection EfficiencyEvent Selection Efficiency
S/N = 2.9
February 27, 2003 APPI2003 12
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
February 27, 2003 APPI2003 13
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
February 27, 2003 APPI2003 14
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
February 27, 2003 APPI2003 15
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
February 27, 2003 APPI2003 16
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
February 27, 2003 APPI2003 17
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
February 27, 2003 APPI2003 18
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
February 27, 2003 APPI2003 19
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