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Studying Very Light Gravitino at ILC

Studying Very Light Gravitino at ILC. Ryo Katayama (Tokyo). Collaborators: Shigeki Matsumoto ( IPMU ) , T . Moroi ( Tokyo ) , K. Fujii (KEK) , T. Suehara (ICEPP), T. Tanabe ( ICEPP ) , S . Yamashita (ICEPP). Motivation.

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Studying Very Light Gravitino at ILC

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  1. Studying Very Light Gravitino at ILC Ryo Katayama (Tokyo) Collaborators: • Shigeki Matsumoto (IPMU) , T. Moroi (Tokyo), K. Fujii (KEK), T. Suehara (ICEPP),T. Tanabe (ICEPP) , S . Yamashita (ICEPP)

  2. Motivation • very light gravitino (~O(10eV)) is quite attractive from the view of point cosmology. • The lifetime of the next lightest supersymmetryparticle (NLSP) directly gives the gravitino mass. • We will focus on the case that the NLSP is stau. • It is difficult to measure the NLSP lifetime at LHC. • Itshould bepossible to determine the NLSP lifetime at ILC. [arXiv:1104.3624]

  3. NLSP : Stau τ− • From the stau mass and lifetime, we can get the gravitino mass. • Estimating the gravitino mass precision is our goal. e- ~ τ− ~ g ~ g Z＊, γ* ~ τ+ e+ τ+ NLSP lifetime example.  t～ 100 x Mpl2 x m3/22/mNLSP5～ O(10–13 ) sec.  ct～ 100 mm Tau lepton lifetime.  ct ～ 80 mm

  4. Impact Parameter • Long lifetime means large impact parameter. • Thus, by observing the impact parameter distribution of the tau decay products, we can measure the stau lifetime. Leptonic decay (e±, μ±, ν.) Hadronic decay (π±, K±, etc.) t Stau 1st layer Stau IP Gravitino 16mm Impact parameter d

  5. Background Signal & Background processes ~ ~ (+ ISR) [gg-BG] e+e– e+ e–gg e+ e–t+t– (+ ISR) • First, evaluate the tau pair background. • Tau is reconstructed in the following 1-prong modes: [Signal] e+e–t+t– [PDG]

  6. Resultofpreceding study Kinematical Cuts ① ② (Evis = Total energy of charged particles.) ③ (q = Scattering angle of the t-jet.) ④ (f = Azimuthal angle of the t-jet.) ⑤ ( is the momentum of isolated g (> 30 GeV)) Stau Mass = 120 GeV Luminosity = 100 fb-1 CM Energy = 500 GeV Two ts and isolated g in [tt-BG] should be on one plane.

  7. ResultofFull simulation(1/2) • The analysis assumes an integrated luminosityof 500fb-1; only consider 1-prong decayfor both taus, beam polarization of (-0.8, +0.3) • Check the cut efficiency of preceding page. • The cut efficiency from the result of full simulation is shown in thefollowing table and in the next slides. • <feature> • The number of AA->tautaubackground is 102times more than the number of signal. • Thenumber ofsignalis comparable to the sum of tau pair and WW & ZZ background. • Therefore, we need to develop better analysis strategy.

  8. ResultofFull simulation(2/2) • the result of full simulation is shown in the figure below.

  9. Cut table-Combined all cut • The effect and purpose of these cuts are explained in the following slides.

  10. Cut 1-require transverse momentum<5GeVfor both tracks • <result> • <feature> • Because AA->tautau is a t-channel process, the transverse momentum suppresses it well. • More statistics of AA->tautau is needed for a more accurate estimate (the weight is about 5000)

  11. Transverse momentum (Only 2-prong)

  12. Transverse momentum (with all other cuts applied)

  13. Cut2 –Minimum visible energy=20GeV • <result> • <feature>

  14. Visible energy ( Only 2-prong )

  15. Visible energy(with all other cuts applied)

  16. Cut3-|cos[Theta_z]|<0.8 (Theta_z : angle from beam axis) • <result> • <feature> • This cut prepares rejection of Bhabha scattering events.

  17. |cos[Theta_z]| (2-prong)

  18. |cos[Theta_z]|(with all other cuts applied)

  19. Cut4--0.85<cos(Phi[0]-Phi[1])(Phi: Azimuthal angle) • <result> • The decay product of tau pair BG is almost back-to-back because tau is light. • Though ISR effect distorts kinematical geometry, the geometry be conserved on x-y plane. • <feature>

  20. cos(Phi[0]-Phi[1]) (Only 2-prong) • Give the distribution to following figure.

  21. cos(Phi[0]-Phi[1]) (with all other cuts applied) • Give the distribution to following figure.

  22. Cut 5 –Angle/Energy>3.0/400(Angle is defined as 3D) • <result> • Though the tau pair background can begin to generate from merely 5GeV, but signal from240GeV. • Therefore, the tau pair creation easy to be distorted kinematical geometry constrain, on the other hand, the stau pair creation is not. • <feature>

  23. Angle : Visble energy( Only 2-prong) • Note: the following figure distribution is not normalize by luminosity. • Give the distributionto following figure.

  24. Angle : Visble energy(with all other cuts applied) • Note: the following figure distribution is not normalize by luminosity. • Give the distribution to following figure.

  25. Cut table-Combined all cut

  26. Cut table- Cut excepted for self condition

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

  28. Mass fit2 (Preliminary) • Count • track energy(GeV) • Yellow:SignalRed:Tau pair Blue:AA->tautauGreen:WW+ZZ

  29. summary • The number of AA->tautau background can be reduced O(109) to 5000. • The AA background result have problem that fluctuation is too enhanced. • The ratio the signal to the sum of tau pair and WW and ZZ background is improved about 1:1 to 3:1. • Next steps: mass measurement by fitting, lifetime measurement

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