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Studying Very Light Gravitino at ILC

Shigeki Matsumoto (IPMU). Studying Very Light Gravitino at ILC. Collaborators: T . Moroi ( Tokyo ) [for basic idea: arXiv:1104.3624] & K. Fujii (KEK), T. Moroi (Tokyo), T. Suehara (ICEPP) [for realistic evaluations.].

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Studying Very Light Gravitino at ILC

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  1. Shigeki Matsumoto (IPMU) Studying Very Light Gravitino at ILC Collaborators: T. Moroi (Tokyo) [for basic idea: arXiv:1104.3624] & K. Fujii (KEK), T. Moroi (Tokyo), T. Suehara (ICEPP) [for realistic evaluations.] Q. Is it possible to study the property of the very light gravitino (～ O(10) eV) at the ILC? • A. Yes it is by observing the distribution ofthe impact parameter, which is obtainedby the decay products of the stau NLSP!

  2. 1/6 Gravitino = Super partner of Graviton! Its spin is 3/2! Gravitino Mass = <F>/Mpl/31/2, & <F> = SUSY breaking scale! Its interactions are suppressed by 1/<F> ～ 1/(Mpl m3/2) The Gravitino LSP Structure Formation of Universe Vacuum Stability LEP, SN cooling 10 –7 10 –13 10 –11 10 –9 10 –12 10 –10 10 –8 T. Moroi, hep-ph/9503210 Very Light Gravitino, whose mass is O(1)-O(10) eV, is quite attractive from the viewpoint of Cosmology!

  3. 2/6 Next Lightest Supersymmetric Particle (NLSP) is living long! How long?  t～ 100 x Mpl2 x m3/22/mNLSP5～ O(10–13 ) sec.  ct～ 100 mm !!! (Decay length is not long!) What happens at the ILC? We focus on the casethat the NLSP is Stau! Decay! Prod. 1st layer NLSP 16mm e+ e– Stau pair

  4. 3/6 Hadronic decay (p±, K±, etc.) Impact parameter d is one of convenient quantities to measure the lifetime of the NLSP in such a circumstance. t Stau Stau Impact Parameter d Gravitino Impact parameter d Signal & Background processes ~ ~ (+ ISR) [Signal] e+e–t+t– [gg-BG] e+e– e+ e–gg e+ e–t+t– (+ ISR)

  5. 4/6 ① 100% efficiency for tagging and no contamination assumed. ② (Evis = Total energy of charged particles.) Kinematical Cuts To reduce gg-BG. Tagging forward e± will also be useful. ③ (q = Scattering angle of the t-jet.) t, W, and Z in BG are likely to be produced with high rapidity. ④ (f = Azimuthal angle of the t-jet.) (L-lim.) Two ts in [tt-BG] are almost back-to-back even w/ ISR. (U-lim.) To reduce t leptons from the Z boson decay. ⑤ ( is the momentum of isolated g (> 30 GeV)) Two ts and isolated g in [tt-BG] should be on one plane. Stau Mass = 120 GeV Luminosity = 100 fb-1 CM Energy = 500 GeV

  6. 5/6 Stau Mass = 120 GeV CME = 500 GeV Results Stau Mass = 120 GeV CME = 500 GeV Lum = 100 fb-1 BG Bin size = 20 mm (0mm < d < 2mm) & &

  7. 6/6 It is possible to study the lightgravitino with the mass of O(10) eV at the ILC. When the lifetime is longer than ～10-14 sec, the lifetime can measured accurately. Information of the lifetime translated to the scale of the SUSY breaking <F>. CME = 500 GeV Lum = 100 fb-1 Summary & Discussions Stau Mass = 120 GeV • How can be large the efficiency of the t-tagging? • Polarization of the incident e± can reduce the BG? • Is there the effect of the magnetic field to detect the signal? • Changing the CME increases the significance to detect the signal? • 3-prong decay of t can be used to detect the decay point?  Go to a full simulation with realistic detector setup.

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