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• 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]

NLSP : Stau• From the stau mass and lifetime,

we can get the gravitino mass.• Estimating the gravitino mass

precision is our goal.

~

e+

τ−

τ+

τ−

~Z ＊ , γ*

e-

g

NLSP lifetime example.

t ～ 100 x Mpl2 x m3/2

2/mNLSP5 ～ O(10–13 )

sec. ct ～ 100 mm Tau lepton lifetime.

ct ～ 80 mm

g~

~

τ+

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 layerGravitino

Stau

t

Stau

Hadronic decay (π±, K±, etc.)

Impactparameter d

16mm

IP

Leptonic decay (e±, μ±, ν.)

BackgroundSignal & Background processes

[Signal] e+ e– t+ t –

[gg-BG] e+ e– e+ e– gg e+ e– t+ t –

(+ ISR)

(+ ISR)

~ ~

First, evaluate the tau pair background.Tau is reconstructed in the following 1-prong modes:

[PDG]

Result of preceding study

①(Evis = Total energy of charged particles.)②

(q = Scattering angle of the t-jet.)③

(f = Azimuthal angle of the t-jet.)④

( is the momentum of isolated g (> 30 GeV))Two ts and isolated g in [tt-BG] should be on one plane.⑤

Kinematical Cuts

Stau Mass = 120 GeV

Luminosity = 100 fb-1

CM Energy = 500 GeV

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\event Signal tau pair BG AA>tautau WW or ZZ->lnulnu

No cut 68077.6 630805 1.86169e+09 158091

All cut 16966.2 7111 1.06925e+07 9385.81

• 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 102 times more than the number of signal.

2. The number of signal is comparable to the sum of tau pair and WW & ZZ background.

<feature>

Therefore, we need to develop better analysis strategy.

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

Cut table-Combined all cut

condition\name Signal Tau pair BG AA->tautau WW+ZZ->lnulnu

No cut 68077.6 630805 1.86169e+09 158091

Only 2-prong (cut0) 45809 306454 8.51622e+08 75260.6

Transverse momentum >5GeV with tracks(cut1)

39023.8 261667 7.39323e+06 69519.2

Visible energy>20GeV (cut2)

38791.1 261512 5.11885e+06 69485.5

|cos[theta]|<0.8 (cut3) (theta : scattering angle)

30771.9 127147 1.13901e+06 16615.1

cos[Phi[0]-Phi[1]]>-0.9 (cut4) (Phi : azimuthal angle)

15187.8 11984.7 20115.2 6925.15

+Angle/Evis>3.0/400(cut5)

14527.7 808.679 5057.5 4079.5

The effect and purpose of these cuts are explained in the following slides.

Cut 1-require transverse momentum<5GeV for both tracks

condition\event Signal tau pair BG AA>tautau WW or ZZ->tautauNo cut 68077.6 630805 1.86169e+09 158091Only 2-prong(Cut0)

45809 306454 8.51622e+08 75260.6

Only 2-prong+Pt<5 GeV

39023.8 261667 7.39323e+06 69651.9

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

<result>

<feature> 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)

Transverse momentum (Only 2-prong)

Transverse momentum (with all other cuts applied)

Cut2 –Minimum visible energy=20GeV

<result>condition\event Signal tau pair BG AA>tautau WW or ZZ->tautauNo cut 68077.6 630805 1.86169e+09 158091Only 2-prong(Cut0)

45809 306454 8.51622e+08 75260.6

Only 2-prong+Evis>20 GeV

44656.1 304107 1.19237e+08 74931.4

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

<feature>

Visible energy ( Only 2-prong )

Visible energy(with all other cuts applied)

Cut3-|cos[Theta_z]|<0.8 (Theta_z : angle from beam axis)


45809 306454 8.51622e+08 75260.6

Only 2-prong+|cos[Theta_z]|

35002.9 135636 2.18259e+08 17516.8

Cut0+...+Cut2->Cut0+…+Cut3

38791.1->30771.9

261512->127147

5.11885e+06->1.13901e+06

69485.5->16615.1


19626.3/14527.7

2171.76/808.679

80513.6/5057.5

22467.7/4079.5

<result>

This cut prepares rejection of Bhabha scattering events.

<feature>

|cos[Theta_z]| (2-prong)

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

<result>condition\event Signal tau pair BG AA>tautau WW or ZZ->tautauNo cut 68077.6 630805 1.86169e+09 158091Only 2-prong(Cut 0)

45809.3 307780 8.52527e+08 75393.4

Only 2-prong+cos[Phi] cut

22325.5 21311.9 3.9419e+08 34053.7


30771.9->15187.8

127147->11984.7

1.13901e+06->20115.2

16615.1->6925.15


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.

<feature>

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

cos(Phi[0]-Phi[1]) (with all other cuts applied)

• Give the distribution to following figure.

Cut 5 –Angle/Energy>3.0/400(Angle is defined as 3D) <result>


45809 306454 8.51622e+08 75260.6

Only 2-prong+Angle cut

43667 190278 6.22424e+08 47132.7


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.

<feature>

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

Angle : Visble energy(with all other cuts applied)

• Give the distribution to following figure.

Note: the following figure distribution is not normalize by luminosity.

Cut table-Combined all cut


No cut 68077.6 630805 1.86169e+09 158091

Only 2-prong (cut0) 45809 306454 8.51622e+08 75260.6

Transverse momentum >5GeV with tracks(cut1)

39023.8 261667 7.39323e+06 69519.2

Visible energy>20GeV (cut2)

38791.1 261512 5.11885e+06 69485.5

|cos[theta]|<0.8 (cut3) (theta : scattering angle)

30771.9 127147 1.13901e+06 16615.1

cos[Phi[0]-Phi[1]]>-0.9 (cut4) (Phi : azimuthal angle)

15187.8 11984.7 20115.2 6925.15

+Angle/Evis>3.0/400(cut5)

14527.7 808.679 5057.5 4079.5

Cut table-Cut excepted for self condition


All Cut 14527.7 808.679 5057.5 4079.5

Except for Transverse momentum >5GeV with tracks(cut1)

16511.2 1081.78 5.59882e+06 4399.63

Except for visible energy>20GeV (cut2)

14680.6 815.163 60530.8 4100.35

Except for |cos[theta_z]|<0.8 (cut3)

19626.3 2171.76 80513.6 22467.7

Except for cos[Phi[0]-Phi[1]]>-0.9 (cut4)

30037.7 103881 1.09883e+06 12109.8

Except for Angle/Evis>3.0/400(cut5)

15187.8 9150.62 20115.2 6891.78

Mass fit (Preliminary)

track energy(GeV) d0/d0error

Yellow:Signal Red:Tau pair Blue:AA->tautau Green:WW+ZZ

Mass fit2 (Preliminary)

track energy(GeV)

Count

Yellow:Signal Red:Tau pair Blue:AA->tautau Green:WW+ZZ

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

Documents

Studying Very Light Gravitino at ILC