Measuring lepton flavor violation at LHC with
a long-lived slepton in the coannihilation regionJoe Sato (Saitama University )
Collaborators
Satoru Kaneko,Takashi Shimomura, Masato Yamanaka,Oscar Vives
Physical review D 78, 116013 (2008)arXiv:1002.????
1, Introduction
1, Introduction
In Standard Model (SM)
Lepton Flavour Violation (LFV) through the neutrino oscillation
But … Forever invisible
Detection of the LFV signalOne of the evidence for beyond the
SM
1, Introduction
One of the candidates for beyond the SM Supersymmetric (SUSY)
modelSupersymmetry
Lepton SleptonGauge boson
Gaugino
Symmetry between boson and fermion
Stability of Higgs mass, dark matter, gauge coupling unification, hierarchy problem, and so on
Why SUSY models ??
1, Introduction
In Supersymmetric (SUSY) models
Enhancement of LFV through the slepton mixingDetectable at future
experiments
Understanding the structure of slepton mixing
Observational results of LFV search experiments
Possible to confirm the SUSY model !
1, Introduction
Purpose in this workUnderstanding the structure of
slepton mixing
Large Hadron Collider (LHC) experiment
Where is the stage ?
What is the key ingredient ?Long-lived stau
2, Long-lived stau
Setup in the work
Framework Minimal Supersymmetric Standard Model (MSSM)Lightest supersymmetric particle (LSP)Lightest neutralino
Next Lightest Supersymmetric Particle (NLSP)Lighter stau
Dark matter ∴R-parity
Coannihilation scenario[ K. Griest and D. Seckel PRD 43 (1991) ]
Enough to reduce DM densityProviding DM abundance consistent with WMAP
LSP DM and NLSP stau decouple from thermal bath
Requirement for coannihilation scenario
At around the same time
Long-lived stau in the coannihilation scenario
Can not decay into two body
Phase space suppression Long lifetime
Attractive parameter region in coannihilation scenariodm ≡ NLSP mass － LSP mass < tau
mass (1.77GeV)
Long-lived stau
At the LHC, the long-lived stau would be producedAvailable for investigating the slepton
mixing
Stau lifetime (s)
Without slepton mixing
Phys. Rev. D73:055009-1-8, 2006
Furthermore it can offer a solution to Lithium
Problem in Standard Big-Bang Nucleosynthesis
Phys.Rev.D76:125023,2007Phys.Rev.D78:055007,2008arXiv:1001.1217
3, Slepton mixing as a source of LFV
With or without slepton mixing
Without slepton mixing
With slepton mixing
Decay rate of stau ( Slepton mixing )
Impossible to decay into two bodyLong-lived and would escape from detector
Decay into two body opens !~ 2
Measurements of the stau lifetimeStrong sensitibity to slepton mixing
parameter
Decay with slepton mixing
Slepton mixing parameter
Decay process with LFV
Slepton mass matrix
Decay with slepton mixing
Decay rate
Effective coupling
Slepton mixing parameter
Decay process with LFV
Bounds on slepton mixing parameter
Slepton mixing parameter
Bounds on slepton mixing parameterFor stau mass 300GeV
⋍
More strict constraint on mixing parameter !
L. Calibbi, J. Jones-Perez, and O. Vives, Phys. Rev. D 78,075007 (2008).
Stau lifetime with LFV
Stau lifetime (s)
With slepton mixing
Stau lifetime with LFV
Stau lifetime (s)
With slepton mixing
Stau decay into tau and neutralinoInsensitive to slepton mixing
parameter
Stau lifetime with LFV
With slepton mixing
Competition between LFV decay and 3(4) body decayVery good sensitivity to small slepton mixing
parameter
Stau lifetime (s)
4, LHC phenomenology
Looking for stau and that decay at the ATLAS
One of the LHC detectorATLAS
Production rate of SUSY particles [ P.Z. Skands, Eur. Phys. J. C 23, 173
(2002) ]For stau mass 300GeV
⋍
Produced number of stau
Expected number of stau decay at the ATLAS
Decay probability
Expected number of decay
Lorentz factor
In the following discussion
Constraint on slepton mixing parameter at ATLASExpected number of LFV stau
decay
All of the staus decay before they reach detectorsNo signals of heavy charged
particle
Constraint on slepton mixing parameter at ATLAS
Expected number of LFV stau decay
All of the staus decay before they reach detectorsNo signals of heavy charged
particleLower bound on slepton mixing parameters
Stau lifetime (s)
Constraint on slepton mixing parameter at ATLASExpected number of LFV stau
decay
Staus decay inside detectors
Constraint on slepton mixing parameter at ATLASExpected number of LFV stau
decayStau lifetime (s)
Staus decay inside detectorsSlepton mixing parameters are strictly
constrained
Constraint on slepton mixing parameter at ATLASExpected number of LFV stau
decay
All of staus leave detectors Lower bound on stau
lifetime
Constraint on slepton mixing parameter at ATLAS
Expected number of LFV stau decay
Stau lifetime (s)
All of staus leave detectors Stringent upper bounds on slepton mixing
parametersLet’s construct bigger detector !!
For further study on LFV
5, Summary and discussion
Slepton mass matrix includes off-diagonal elements, and it leads to Lepton Flavour Violation (LFV)
Stau lifetime is sensitive to the slepton mixing
Summary
Stau lifetime > 10 (s)
-12
Strict lower bound on slepton mixing parameter
Stau lifetime > 10 (s)
-5
Strict upper bound on slepton mixing parameter
10 (s) < lifetime < 10 (s)
-10 -8
LHC provides a very good opportunity to study LFV !!
Important to understand slepton mixing structure for study LFV
In the MSSM coannihilation scenario, NLSP stau can be long-lived
Discussion
What is the source of slepton mixing ??
SUSY seesaw models with right-handed neutrinos
Energy scale
LFV source in the neutrino Yukawa matrix
Energy scale
Renormalization Group Evolution (RGE)
Slepton mixing in slepton mass matrix
Slepton mixing parameter
Discussion
What is the source of slepton mixing ??
SUSY seesaw models with right-handed neutrinos
Energy scale
LFV source in the neutrino Yukawa matrix
Energy scale
Renormalization Group Evolution (RGE)
Slepton mixing in slepton mass matrix
For large mixing (MNS-like)
An element of MNS matrix
Discussion
What is the source of slepton mixing ??
SUSY seesaw models with right-handed neutrinos
Energy scale
LFV source in the neutrino Yukawa matrix
Energy scale
Renormalization Group Evolution (RGE)
Slepton mixing in slepton mass matrix
For small mixing (CKM-like)
Example in MSSM with RH neutrino
Appendix
Pair annihilation rate of DM decides DM relic abundance
Too week to reduce DM density sufficiently
Decouple species : DM only
On the stage of DM freeze-out
DM over abundance !!
Original thermal relic scenario
Coannihilation scenario
Annihilation rates of DM and NLSP decide DM relic abundance
Decouple species : DM and NLSP
On the stage of DM freeze-out
Enough to reduce DM densityProviding DM abundance consistent with WMAP
[ K. Griest and D. Seckel PRD 43 (1991) ]
Requirement for coannihilation
Requirement for coannihilation mechanism
Two species decoupling at around the same time
mass of decoupling particle
For the coannihilation process
Ingredient of the decoupling point
Total abundance of stau and neutralino
