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 supersymmetry particle (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. It should be possible to determine the NLSP lifetime at ILC. [arXiv:1104.3624]

3. NLSP : Stau From the stau mass and lifetime, we can get the gravitino mass. Estimating the gravitino mass precision is our goal. ~ e+e+ τ−τ− τ+τ+ τ−τ− ~ Z ＊, γ* e-e- g NLSP lifetime example.   ～ 100 x M pl 2 x m 3/2 2 /m NLSP 5 ～ O(10 –13 ) sec.  c  ～ 100  m Tau lepton lifetime.  c  ～ 80  m g ~ ~ τ+τ+

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. 1st layer Gravitino Stau  Hadronic decay (π ±, K ±, etc.) Impact parameter  16mm IP Leptonic decay (e ±, μ ±, ν.)

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

6. Result of preceding study ① (E vis = Total energy of charged particles.) ② (  = Scattering angle of the  -jet.) ③ (  = Azimuthal angle of the  -jet.) ④ ( is the momentum of isolated  (> 30 GeV)) Two  s and isolated  in [  -BG] should be on one plane. ⑤ Kinematical Cuts Stau Mass = 120 GeV Luminosity = 100 fb -1 CM Energy = 500 GeV

7. Result of Full simulation(1/2) Check the cut efficiency of preceding page. The cut efficiency from the result of full simulation is shown in the following table and in the next slides. condition\eventSignaltau pair BGAA>tautauWW or ZZ->lnulnu No cut68077.66308051.86169e+09158091 All cut16966.271111.06925e+079385.81 The analysis assumes an integrated luminosity of 500fb - 1 ; only consider 1-prong decay for both taus, beam polarization of (-0.8, +0.3) 1.The number of AA->tautau background is 10 2 times more than the number of signal. 2.The number of signal is comparable to the sum of tau pair and WW & ZZ background. Therefore, we need to develop better analysis strategy.

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

9. Cut table- Combined all cut condition\nameSignalTau pair BGAA->tautauWW+ZZ->lnulnu No cut68077.66308051.86169e+09158091 Only 2-prong (cut0)458093064548.51622e+0875260.6 Transverse momentum >5GeV with tracks(cut1) 39023.82616677.39323e+0669519.2 Visible energy>20GeV (cut2) 38791.12615125.11885e+0669485.5 |cos[theta]|<0.8 (cut3) (theta : scattering angle) 30771.91271471.13901e+0616615.1 cos[Phi[0]-Phi[1]]>-0.9 (cut4) (Phi : azimuthal angle ) 15187.811984.720115.26925.15 +Angle/Evis>3.0/400(cut 5) 14527.7808.6795057.54079.5 The effect and purpose of these cuts are explained in the following slides.

10. Cut 1- require transverse momentum<5GeV for both tracks condition\eventSignaltau pair BGAA>tautauWW or ZZ->tautau No cut68077.66308051.86169e+09158091 Only 2-prong (Cut0) 458093064548.51622e+0875260.6 Only 2-prong +Pt<5 GeV 39023.82616677.39323e+0669651.9 Cut0 ->Cut0+…+Cut1 45809 ->39023.8 306454 ->261667 8.51622e+08 ->7.39323e+06 75260.6 ->69651.9 Except for oneself /All Cut 16511.2 /14527.7 1081.78 /808.679 5.59882e+06 /5057.5 4399.63 /4079.5 1.Because AA->tautau is a t-channel process, the transverse momentum suppresses it well. 2.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 condition\eventSignaltau pair BGAA>tautauWW or ZZ->tautau No cut68077.66308051.86169e+09158091 Only 2-prong (Cut0) 458093064548.51622e+0875260.6 Only 2-prong +Evis>20 GeV 44656.13041071.19237e+0874931.4 Cut0+Cut1 ->Cut0+…+Cut2 39023.8 ->38791.1 261667 ->261512 7.39323e+06 ->5.11885e+06 69651.9 ->69485.5 All other cuts /All Cuts 14680.6 /14527.7 815.163 /808.679 60530.8 /5057.5 4100.35 /4079.5

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) condition\eventSignaltau pair BGAA>tautauWW or ZZ->tautau No cut68077.66308051.86169e+09158091 Only 2-prong (Cut0) 458093064548.51622e+0875260.6 Only 2-prong +|cos[Theta_z]| 35002.91356362.18259e+0817516.8 Cut0+...+Cut2 ->Cut0+…+Cut3 38791.1 ->30771.9 261512 ->127147 5.11885e+06 ->1.13901e+06 69485.5 ->16615.1 Except for oneself /All Cut 19626.3 /14527.7 2171.76 /808.679 80513.6 /5057.5 22467.7 /4079.5 This cut prepares rejection of Bhabha scattering events.

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

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

19. condition\eventSignaltau pair BGAA>tautauWW or ZZ->tautau No cut68077.66308051.86169e+09158091 Only 2-prong (Cut 0) 45809.33077808.52527e+0875393.4 Only 2-prong +cos[Phi] cut 22325.521311.93.9419e+0834053.7 Cut0+...+Cut3 ->Cut0+…+Cut4 30771.9 ->15187.8 127147 ->11984.7 1.13901e+06 ->20115.2 16615.1 ->6925.15 Except for oneself /All Cut 30037.7 /14527.7 103881 /808.679 1.09883e+06 /5057.5 12109.8 /4079.5 Cut4- -0.85<cos(Phi[0]-Phi[1]) (Phi: Azimuthal angle) 1.The decay product of tau pair BG is almost back- to-back because tau is light. 2.Though ISR effect distorts kinematical geometry, the geometry be conserved on x-y plane.

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) condition\eventSignaltau pair BGAA>tautauWW or ZZ->tautau No cut68077.66308051.86169e+09158091 Only 2-prong (Cut0) 458093064548.51622e+0875260.6 Only 2-prong +Angle cut 436671902786.22424e+0847132.7 Cut0+...+Cut4 ->Cut0+…+Cut5 15187.8 ->14527.7 11984.7 ->808.679 20115.2 ->5057.5 6925.15 ->4079.5 Except for oneself /All cut 15187.8 /14527.7 11984.7 /808.679 20115.2 /5057.5 6925.15 /4079.5 1.Though the tau pair background can begin to generate from merely 5GeV, but signal from240GeV. 2.Therefore, the tau pair creation easy to be distorted kinematical geometry constrain, on the other hand, the stau pair creation is not.

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

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

25. Cut table- Combined all cut condition\nameSignalTau pair BGAA->tautauWW+ZZ->lnulnu No cut68077.66308051.86169e+09158091 Only 2-prong (cut0)458093064548.51622e+0875260.6 Transverse momentum >5GeV with tracks(cut1) 39023.82616677.39323e+0669519.2 Visible energy>20GeV (cut2) 38791.12615125.11885e+0669485.5 |cos[theta]|<0.8 (cut3) (theta : scattering angle) 30771.91271471.13901e+0616615.1 cos[Phi[0]-Phi[1]]>-0.9 (cut4) (Phi : azimuthal angle ) 15187.811984.720115.26925.15 +Angle/Evis>3.0/400(cut 5) 14527.7808.6795057.54079.5

26. Cut table- Cut excepted for self condition condition\nameSignalTau pair BGAA->tautauWW+ZZ->lnulnu All Cut14527.7808.6795057.54079.5 Except for Transverse momentum >5GeV with tracks(cut1) 16511.21081.785.59882e+064399.63 Except for visible energy>20GeV (cut2) 14680.6815.16360530.84100.35 Except for |cos[theta_z]|<0.8 (cut3) 19626.32171.7680513.622467.7 Except for cos[Phi[0]-Phi[1]]>-0.9 (cut4) 30037.71038811.09883e+0612109.8 Except for Angle/Evis>3.0/400(cut5) 15187.89150.6220115.26891.78

27. Mass fit (Preliminary) track energy(GeV) d0/d0error Yellow:Signal Red:Tau pair Blue:AA->tautau Green:WW+ZZ

28. Mass fit2 (Preliminary) track energy(GeV) Count Yellow:Signal Red:Tau pair Blue:AA->tautau Green:WW+ZZ

29. summary The number of AA->tautau background can be reduced O(10 9 ) 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