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Measurement of Very Light Gravitino Mass via Stau Lifetime Using ILD Detector Simulation

This study investigates the very light gravitino as the lightest supersymmetric particle in the context of Gauge Mediated SUSY Breaking (GMSB). Utilizing the ILD detector simulation, we measure the lifetime of the next-to-lightest supersymmetric particle (NLSP), stau, with a mass of 120 GeV and a decay length of approximately 100 μm. We analyze decay channels, impact parameters, and implement a fitting procedure to determine stau and gravitino masses. Preliminary results indicate a gravitino mass accuracy of about 3%. This research holds significance in cosmology and supersymmetry.

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Measurement of Very Light Gravitino Mass via Stau Lifetime Using ILD Detector Simulation

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  1. 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)

  2. Introduction • In the case of Gauge mediated SUSY breaking (GMSB), the gravitino appears as the lightest supersymmetricparticle(LSP) • The O(1 eV) very lightgravitinois very attractive from view of Cosmology

  3. NLSP stau By measuring the NLSPmass and lifetime, gravitino mass be determined τ− e- ~ τ− ~ ~ Z＊, γ* ~ τ+ e+ For example, the following value give a stau life time of mLSP=6.5eV , mNLSP=120GeV  ct =100 mm τ+ For comparison ,the tau lifetime is  ct =87.11 mm [arXiv:1104.3624]

  4. The measurement of stau lifetime Leptonic decay (e±, μ±, ν.) Hadronic decay (π±, K±, etc.) Decay products • The impact parameterisdefined as the shortest length between track and IP. • By using the impact parameter distribution ,we can measure the staulifetime. • The staudecay 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). t stau Gravitino IP 16mm Impact parameter d 1st layer τ− e- ~ τ− ~ ~ Z＊, γ* ~ τ+ e+ τ+

  5. Signal and Background Signal & Background processes

  6. 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 <The decay ratio 1-prong mode > [PDG]

  7. Cut

  8. stau mass accuracy (preliminary) • From fitting track energy upper limit, the stau mass can be determined from kinematic relation. • By running Poissonstatics fluctuationto 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.

  9. stau lifetime accuracy1(preliminary) • The do distribution reflect the lifetime stau->tau. • High statistics samplewasprepared for ct = 90 mm , 100 mm, 110 mm (Template samples). • By using for ct = 100 mm, the do distributionwascreated from Toy MC. 注)右上二段目のBackground分布はct ~ 100mmのデータを使用

  10. stau lifetime accuracy2(preliminary) • At first, we compute the reduced chi2between 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 obtainedfollowing result.

  11. Gravitino mass accuracy (preliminary) • The NLSP lifetime and mass substitute to the following gravitino mass accuracy formula • The relative accuracy of gravitino mass canwasdetermined about 3%.

  12. 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.

  13. 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% • Combidingabove results , the accuracy of gravitino mass isestimeted to be about 3%.

  14. Back Up

  15. Constraint from cosmology

  16. Acoplanarity(with all other cuts applied)

  17. Visible Energy(with all other cuts applied)

  18. Transverse momentum(with all other cuts applied)

  19. |cosqmis|(with all other cuts applied)

  20. |cosq|(with all other cuts applied)

  21. q12/Evis(with all other cuts applied)

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

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

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

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

  26. d0/d0error • track energy(GeV) • Yellow:SignalRed:Tau pair Blue:AA->tautauGreen:WW+ZZ

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