STAU SEARCHES @ CLIC

Ilkay Turk Cakir

Turkish Atomic Energy Authority

with co-authors O. Cakir, J. Ellis, Z. Kirca

with the contributions from A. De Roeck, D. Schulte

CLIC WORKSHOP CERN, 16-18 October 2007

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• LSP and NLSP in SUSY• mSUGRA points + point • production cross sections

– optimization for the threshold

• relevant SUSY processes • detection of stau• conclusion

Outline

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• most interesting possibility offered by quantum field theory

– relating to fermions to bosons

• unification with gravity• unification of gauge couplings• solution of the hierarchy problem• dark matter in the Universe• ...

Supersymmetry (SUSY)

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• GraMSB: gravity-mediation– SUSY breaking scale ~ 1011 GeV– sparticle masses ~ (GeV-TeV)– CMSSM & GUT unification mSUGRA

mSUGRA parameters:

• GMSB: gauge-mediated– SUSY breaking scale ~ 105 GeV– LSP = Gravitino mass (~ eV-GeV)

Most interesting:gravitino LSP, stau NLSP

Experimental constraint on NLSP stau: > 87.6 GeV (pair production) –Abbiendi 04

1~m

SUGRA Model

m1/2 = common gaugino mass m0 = common scalar mass

A0= trilinear coupling tan β = ratio of VEVs

sign() = sign of Higgs mixing parameter

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- consistent with present data from particle physics and BBN constraints -astrophysics and cosmology constrain metastable particles such as staus-comparison between calculated and observed abundance of light elements - NLSP stau has long lifetime ~ 104 – 106 s- LSP gravitino, mG ~ m0 or mG ~ 0.2 m0

Points:Points: - low m0, low m1/2, low tan - high m0, high m1/2, high tan - low m0, high m1/2, high tan - high m0, high m1/2, low tan

A. De Roeck et al. 05

O. Cakir et al. 07

in some certain parameter space of

mSUGRA, good agreement between BBN calculations and observed

6,7Li abundances

mSUGRA Benchmark Points

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mSUGRA with gravitino LSP and stau NLSP: benchmark points , , and the point

Agreement between BBN calculations and the observed Li abundances

Three benchmark points with astrophysical constraints

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The lighter (heavier) stau mass eigenstate is a linear combination of left and right-handed eigenstates

Stau decay rate is given by

In large regions of mSUGRA parameters space, the lighter stau is the NLSP ending with an LSP

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stau NLSP life-time, decay width, lenght

t 6.58x10-25s/(GeV)

L1.97x10-16m/(GeV)

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Point :

t=2.9x106s = 33.7 day

Point :

t=1.7x106s = 19.4 day

Point :

t=6.4x104s =0.7 day

Point :

t=1.35x103s

The benchmark points of mSUGRA

These points could be probed at

LHC and CLIC

This point could be probed only at

CLIC

This point could be

probed at LHC, ILC and

CLIC

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SUSY R-parity conservation pair production at colliders

Stau pair production

S. Kraml

hep-ph/9903257

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unpolarized cross-sections with statistical errors

12Red: e- (%90), e+ (%60) ; blue: e- (%90); green: unpolarized

polarized cross-sections polarized cross-sections

13Errors on the mixing (cos~0.6) and stau mass (m)

Polarization

e- %90

e+ %60

accuracies on the measurements: )cos,( ~~

1 m

(0.7, 0.005) for

(2.4, 0.01) for ,

at Ecm=1000 GeV;

(8, 0.02) for

at Ecm=3000 GeV

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The total cross section in pb calculated using PYTHIA with the full ISASUGRA spectrum [Baer et al. 00], including both initial and final state radiation (ISR+FSR)

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1

10

100

1000

10000

eps zeta eta theta

500

1000

3000

5000

# e

ven

tsNumber of stau pairs produced at:

Ecm = 500, 1000 GeV with L=200 fb-1

Ecm = 3000, 5000 GeV with L=400 fb-1

Ecm(GeV)

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distribution

with simulated CLIC

energy spectrum

(optimize total luminosity)

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Stau pair production at benchmark points and optimal energies for slow-staus with

<0.4

optimal center of mass energies for the constraint <0.4 :

330 GeV for

730 GeV for

700 GeV for

2500 GeV for

18The cross sections for pair-production of supersymmetric particles in the benchmark scenarios ,, and , as functions of s. (eReR)=8.5x10-4 pb,

(RR)=7.3x10-4pb at 3000 GeV for point

SUSY processes: cascades ending with an NLSP stau

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Significant decay modes and branching ratios of SUSY particles

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The coresponding values of for staus stopping in different detector parts for the benchmark points , ,

and

Martyn, 06

c1 = 2.087, c2 = 3.22 for steel

Detection of stau

Rossi, 52

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The number of stau pairs with < 0.4, stopped in GLCD

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CONCLUSIONS

Many “staus” at CLIC

•Discussed the choice of cm energy that would maximize the for prod. slow moving stau with < 0.4 in a CLIC det.

•Presented metastable staus produced in the cascade decays of heavier sparticles, so that optimal cm energies for trapping staus higher than stau pair-prod. threshold

•If stau (for point ,,) found by the LHC, one would know optimal energy and optimal number of stopping staus

•6,7Li friendly point features relatively heavy sparticles beyond the reach of either the LHC or the ILC, but within the kinematic reach of CLIC

•Even if there are some light sparticles, the heavier sparticles beyond the reach of LHC and ILC can be discovered and measured precisely at a high energy linear collider CLIC