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The Studying very light gravitino using ILD detector simulation

Ryo Katayama (Tokyo)

Collaborators:T.Suehara(ICEPP) , T.Tanabe(ICEPP), Y.Satoru(ICEPP) , M.Sigeki(IPMU) ,

M.Takeo(IPMU) , F.Keisuke(KEK)

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Introduction• In the case of Gauge mediated SUSY breaking (GMSB), the

gravitino appears as the lightest supersymmetric particle(LSP)• The O(1 eV) very light gravitino is very attractive from view of

Cosmology

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NLSP stau

• By measuring the NLSP mass and lifetime, gravitino mass be determined

For example, the following value give a stau life time of mLSP =6.5eV , mNLSP 　 =120GeV ct = 100 mm For comparison , the tau lifetime is ct = 87.11 mm

~

e+

τ−

τ+

τ−

~Z ＊ , γ*

e-

~

~

τ+

[arXiv:1104.3624]

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The measurement of stau lifetime

• The impact parameter is defined as the shortest length between track and IP.

• By using the impact parameter distribution ,we can measure the stau lifetime.

• The stau decay to cascade products.The impact parameter enhance.

• We do not use the impact parameter in the z direction because of the large uncertainty of the primary vertex in that direction. We use the d0 component (projection onto the x-y plane).

1st layer

Gravitinostau

t

Hadronic decay (π±, K±, etc.)

Impactparameter d

16mmIP

Leptonic decay (e±, μ±, ν.)

Decayproducts

~

e+

τ−

τ+

τ−

~Z ＊ , γ*

e-

~

~

τ+

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Signal and BackgroundSignal & Background processes

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Condition•stau mass :120GeV•decay life time :cτ = 100μm•Center of mass energy : 500GeV,

Integrated luminosity : 500fb-1,Beam polarization : (Pe-,Pe+)=(+0.8,-0.3)• τ decay mode :1-prong ~ 85％• Selection: 1-prong+1-prong event

[PDG]

<The decay ratio 1-prong mode >

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Cutstau-stau tt gg -> tt WW, ZZ ->

lnlnNo cut 68077 630805 1.861e+9 158091

Track=2 45636 306454 8.516e+8 75261

pT> 5 GeV for each track 38823 261667 7.393e+6 69519

|cos qmiss| < 0.9 35861 149527 1.856e+6 40099

Evis> 20 GeV 35632 149408 615414 40067

|cos q|< 0.8 for each track 29147 116303 378763 15090

Acoplanarity > -0.93 19226 11745 0 8398

q12 / Evis > 3.0/400(stau lifetime)

18594 804 0 5652

|d0|/s(d0) > 2.0 for each track(stau mass)

16728 455 0 565

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stau mass accuracy (preliminary)• From fitting track energy upper

limit, the stau mass can be determined from kinematic relation.

• By running Poisson statics fluctuation to high statistics track energy distribution samples, we make a experiment (Toy MC).

• By running Toy MC 10,000 times,the mass fit distribution can be acquired.

• From the error estimation from the mass fit distribution, we acquired following result.

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stau lifetime accuracy1(preliminary)• The do distribution reflect

the lifetime stau->tau.• High statistics sample

was prepared for ct = 90 mm , 100 mm, 110 mm (Template samples).

• By using for ct = 100 mm, the do distribution was created from Toy MC.

注 )右上二段目のBackground分布は ct ~ 100mmのデータを使用

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stau lifetime accuracy2(preliminary)• At first, we compute the

reduced chi2 between Toy MC sample and template sample.

• The chi2 minimum indicates the most probable value of the lifetime given by the fit.

• By Evaluating the error from Toy MC 10,000 times, we obtained following result.

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Gravitino mass accuracy (preliminary)• The NLSP lifetime and mass substitute to the

following gravitino mass accuracy formula

• The relative accuracy of gravitino mass can was determined about 3%.

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open issues•The Cross Section of Bhabha scattering and gg->ll have order ~ nb ,event number~O(109).

•Since MC statistics is insufficient , preselected samples should be prepared.

•If Bhabha is found to be problematic, we may choose to drop theelectron channel.

•Estimate the accuracy of the stau mass by using the threshold scan

•Changing stau mass and lifetime, evaluate the accuracy of gravitino mass.

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Summary•In the case that stau mass is 120GeV and

lifetime is ct = 100mm , using ILD detector simulation ,

we acquired the following result: •From track energy fit , the accuracy of stau

mass is 1.1%•From template fit , the accuracy of stau

lifetime is 1.4%•Combiding above results , the accuracy of

gravitino mass is estimeted to be about 3%.

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Back Up

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Constraint from cosmology

Acoplanarity(with all other cuts applied)

Visible Energy(with all other cuts applied)

Transverse momentum(with all other cuts applied)

|cos qmis|(with all other cuts applied)

|cos q|(with all other cuts applied)

q12/Evis(with all other cuts applied)

Transverse momentun(after only 2-prong)注 )ただしシグナルは無偏極である

Visible energy ( after only 2-prong )注 )ただしシグナルは無偏極である

|cos q| (after only 2-prong)注 )ただしシグナルは無偏極である

Acoplanarity (After only 2-prong)注 )ただしシグナルは無偏極である

track energy(GeV) d0/d0errorYellow:Signal Red:Tau pair Blue:AA->tautau Green:WW+ZZ