joe sato (saitama university ) collaborators satoru kaneko,takashi shimomura, masato yamanaka,oscar...

Measuring lepton flavor violation at LHC with

a long-lived slepton in the coannihilation region

Joe 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 produced

Available 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 body

Long-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


Decay process with LFV

Bounds on 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 (s)

With slepton mixing

Stau decay into tau and neutralino

Insensitive to slepton mixing parameter


With slepton mixing

Competition between LFV decay and 3(4) body decay

Very 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 ATLAS

Expected number of LFV stau decay

All of the staus decay before they reach detectorsNo signals of heavy charged

particle



All of the staus decay before they reach detectorsNo signals of heavy charged

particleLower bound on slepton mixing parameters

Stau lifetime (s)



Staus decay inside detectors



Stau lifetime (s)

Staus decay inside detectorsSlepton mixing parameters are strictly

constrained



All of staus leave detectors Lower bound on stau

lifetime



Stau lifetime (s)

All of staus leave detectors Stringent upper bounds on slepton mixing

parameters

Let’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


Discussion



Energy scale


Energy scale



For large mixing (MNS-like)

An element of MNS matrix

Discussion



Energy scale


Energy scale



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

joe sato (saitama university ) collaborators satoru kaneko,takashi shimomura, masato yamanaka,oscar...

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