Impact of squark generation mixing on the search for squarks and gluinos at LHC

Impact of squark generation mixing on the search for squarks and gluinos at LHC

K. HidakaTokyo Gakugei University

In collaboration withA. Bartl, H. Eberl, B. Herrmann, W. Majerotto , W. Porod

(Phys. Lett. B679 (2009) 260; arXiv:0905.0132[hep-ph])

ICHEP2010, 23 July 2010, Paris

Contents1. Introduction

2. MSSM with Quark Flavor Violation (QFV)

3. Constraints on the MSSM

4. QFV Benchmark Scenario

5. Impact of squark generation mixing on squark and gluino decays

6. Impact on gluino signatures at LHC

7. Impact on squark signatures at LHC

8. Conclusion

• Discovery of all SUSY partners and study of their properties are essential for testing the MSSM.

• Here we focus on SUSY partners of quraks and gluons (i.e. squarks and gluinos).

• With the start of the Large Hadron Collider (LHC) at CERN a new era of particle physics has begun.

• If weak scale SUSY is realized in nature, squarks and gluinos will have high production rates for masses up to O(1) TeV at LHC.

• The main decay modes of squarks and gluinos are usually assumed to be quark-flavor conserving (QFC).

• However, the squarks are not necessarily quark-flavor eigenstates. The flavor mixing in the squark sector may be stronger than that in the quark sector. In

this case quark-flavor violating (QFV) decays of squarks and gluinos could occur with a significant rate.

• Here we study the effect of the mixing of charm-squark and top-squark on the production and decays of squarks and gluinos.

1. Introduction(1) Motivation;

(2)Purpose of this work;

• In this work we study the effect of scharm-stop mixing on the squark and gluino decays at LHC in the general MSSM. • We show that due to the mixing effect the branching ratios of QFV squark and gluino decays can be very large in a significant region of the QFV parameters despite the very strong experimental constraints on QFV from B meson observables.

• This could have an important impact on the search for squarks and gluinos and the MSSM parameter determination at LHC.

2. MSSM with QFV• The basic parameters of the MSSM with QFV:

tantanmA ,MM11MM22mgluino ,MM22QQMM22

UU M M22DDTTUUTTDD

at weak at weak scalescale((u, c, t or d, s, u, c, t or d, s, b)b)

tantan ratio of VEV of the two Higgs doublets <Hratio of VEV of the two Higgs doublets <H00 22>/<H>/<H0011>>

mA : CP odd Higgs boson mass

MM1,1, M M22: : 　　 U(1), SU(2) gaugino massU(1), SU(2) gaugino mass

mgluino : gluino mass: gluino mass

higgsino mass parameterhiggsino mass parameter

MM22QQleft squarkleft squarksoft mass matrixsoft mass matrix

MM22UU right up-type squark right up-type squarksoft mass matrixsoft mass matrix

MM22DD right down-type squark right down-type squarksoft mass matrixsoft mass matrix

TTUUtrilinear coupling matrix of up-type squark and Higgs bosontrilinear coupling matrix of up-type squark and Higgs boson

TTDD trilinear coupling matrix of down-type squark and Higgs bosontrilinear coupling matrix of down-type squark and Higgs boson

• Here we study 　　　　　 mixing case.

　　 LFV parameters in our study are:

　　　　 : 　　　　　　　 mixing term 　（　　　　　　　　　 mixing term)

　　　　　 : 　　　　　　　　 mixing term

　　　　　 : 　　　　　　　　 mixing term

　　　　 : 　　　　　　　　 mixing term

• (note) We assume that all the basic parameters are real.

• (note) The basic parameters determine all of the physics here.

2,23LM

2

,23EM

23A

32A

L L

R R

L R

R L

• Here we study 　　　　　 mixing effect.　　 QFV parameters in our study are:

MM22Q,Q, 　 : 　　　　　　　 mixing term 　（　　　　　　

mixing term)

MM22UU 　　 : 　　　　　　　　 mixing term

TTUU 　　 : 　　　　　　　　 mixing term

TTUU 　　 : 　　　　　　　　 mixing term

(Note) We work in the super-CKM basis of squarks: .

In this basis we have due to the SU(2) symmetry,

where is the soft mass matrix of left up-type squarks

is the soft mass matrix of left down-type squarks and

K is the CKM matrix.

(Note) We have as .

tc ~~

LL tc ~~ LL bs~~

RR tc ~~ RL tc ~~ LR tc ~~

)~

,~,~

,~

,~,~

(),~,~,~,~,~,~( RRRLLLRRRLLL bsdbsdtcutcu122 KMKM QQu

2

uQM

2QM

22QQ MM

u 1K

The following constraints are imposed in our analysis in order to respect experimental and theoretical constraints:

(a) Constraints from the B-physics experiments :

(b) LEP and Tevatron limits on sparticle masses

(ex) etc.

(c) The experimental limit on SUSY contributions to the electroweak parameter:

(d) Vacuum stability conditions on trilinear couplings (see J.A. Casas and S. Dimopoulos, Phys. Lett. B 387 (1996) 107 [hep-ph/9606237].)

(ex) etc.

3. Constraints on the MSSM

)(|| 22

233

222

2223 mMMhT UQtU u

22122222

2 cos)sin( ZWZHmmmm

GeVm 1031

~

0012.0)( SUSY

2009)Photon (Lepton CL) (95% 10 4.22 < ) s B(b 102.92 -4-4 BABAR)(BELLE, CL) (95% )or e=(with 10 2.60 < ) s B(b <100.60 -6--6

(CDF) CL) (95% 10 4.3 < ) B(B -8-s

BABAR) (BELLE, CL) (68% 10 0.35) (1.73 = ) B(B -4u

(CDF) CL) (68% ps 0.12 17.77 =M -1Bs

GeVmg 308~

(Note) These constraints are very important:

and data => strongly constrain the QFV squark parameters

Vacuum stability conditions => strongly constrain QFV trilinear couplings TU

data => strongly constrain

sBM) s B(b

) B(Bu )tan,( Hm

(Note) We use the public code SPheno v3.0 in the calculation of the B-physics observables.

4. QFV Benchmark Scenario

We take the following scharm-stop mixing scenario as a QFV benchmark scenario:

mixing termLL tc ~~

mixing termRR tc ~~

< up-squark sector > < down-squark sector >

QFV Benchmark Scenario

Rtm~

Rum~

Rcm~

gm~

Lum~

Lcm~

Ltm~

Rbm~

Rdm~

Rsm~

gm~

Ldm~

Lsm~

Lbm~

RR tc ~~

In this scenario, gluino can decay only into strong mixtures of and !Rc~ Rt~

RR tcu ~69.0~73.0~1 RR tcu ~73.0~69.0~

2

• We study the effect of squark generation mixing on the squark and gluino

decays at LHC.

• In case of mixing, squarks and gluino could decay as follows:


RR tc ~~

g~

2,1~u

c

t0

1~

g~

2,1~u

t

c

01

~

In our scenario we have:

(Note) ,

• Gluino decay branching ratios in our scenario:

RR tcu ~69.0~73.0~1 RR tcu ~73.0~69.0~

2

QFV

QFC

QFC

We have very large QFV gluino decay branching ratio!

Contour plots of Contour plots of QFVQFV BR in our BR in our scenario

contours

)~~( 01ctgB

mixing parameterRR tc ~~ mixing parameterLL tc ~~

The QFV decay branching ratio can be very large in a significant part of

the plane allowed by all of the constraints.

)~~( 01ctgB

uRRuLL

2323

This can lead to large QFV effects at LHC!

　　　　　contours

410) s B(b

our benchmark scenario

mixing parameterRR tc ~~ mixing parameterLL tc ~~

Contour plots of Contour plots of QFVQFV BR in our BR in our scenario

contours

)~~( 01ctgB

excluded by data) s B(b

The QFV decay branching ratio can be very large in a significant part of

the plane allowed by all of the constraints.

)~~( 01ctgB

uRRuLL

2323


dependences of gluino decay BR’s in our scenario uRL

23

mixing parameterLR tc ~~

The QFV decay branching ratio can be very large (~30 - 50%) in a

wide allowed range of mixing parameter .

)~~( 01ctgB

uRL

23LR tc ~~

dependences of squark decay BR’s in our scenario uRR

23

mixing parameterRR tc ~~

The QFV decay branching ratios and can be very

large simultaneously in a wide allowed range of the mixing parameter

.

uRR

23RR tc ~~

)~~( 012,1 cuB )~~( 0

12,1 tuB



01

~~ ctg

The signature of the QFV gluino decay at LHC:

' top-quark + jet + missing-energy'

Large mixing RR tc ~~

Large QFV BR )~~( 01ctgB

01

~~ ctg

g~ c

t

01

~

Example of QFV gluino signature at LHC

Example of QFV gluino decay signature at LHC :

XctXgpp 01

01

01

~~~~

‘top-quark + jet + missing-ET + beam-jets‘


01

~


c

p p

qqq~

t

g~

01

~

jetbeam jetbeam

QFV gluino decay

Single top-quark production




p pqq

tc

(Note) Single top–quark production could be a SM BG.

However the cross section of this process would be very small because it is a weak process.XbtXZWpp 0""

Invariant mass distribution of two quarks from gluino decay in our benchmark scenario

Impact on invariant mass distribution

We have remarkable multi-edge structures in the invariant mass distribution of charm and top quarks!

This edge structure is due to the intermediate squark effect.

g~

2,1~u

c

t0

1~

Large rate of QFV squark signature at LHC :

7. Impact on squark signatures at LHC

XctXuupp )~)(~(~~ 01

012,12,1


Large mixing RR tc ~~

Large QFV BR’s ,)~~( 012,1 cuB )~~( 0

12,1 tuB



p p

gg

g

t

2,1~u2,1

~u

c

01

~0

1~

jetbeam jetbeam

QFV squark decay



p pgg

tc

(Note) Single top–quark production could be a SM BG.

However the cross section of this process would be very small because it is a weak process.XbtXZWpp 0""

dependences of QFV cross sections at LHC in our benchmark scenario

uRR

23

The QFV cross sections can be very large in a wide allowed range of the mixing parameter .

uRR

23

RR tc ~~


)14)(~~)(~~( 01

0111

11 TeVEXcttcXuupp cmct )14)(~~)(~~( 01

0122

22 TeVEXcttcXuupp cmct

(Note) We have obtained similar results for the QFV cross sections in a QFV scenario based on the mSUGRA scenario SPS1a’.

Our analyses suggest the following:

• One should take into account the possibility of significant contributions

from QFV decays in the squark and gluino search at LHC.

• Moreover one should also include QFV squark parameters (i.e. squark generation

mixing parameters) in the determination of the basic SUSY parameters at LHC.

•Detailed Monte Carlo studies including background processes and detector effects are

necessary to identify the parameter region where the proposed QFV squark and gluino

signals are observable with sufficient significance, e.g. the so-called "5 discovery

region".

Impact on squark and gluino search at LHC

8. Conclusion

• We have studied production and decays of squarks and gluinos in the MSSM with

squark generation mixing, especially mixing.

• We have shown that QFV squark and gluino decay branching ratios such as

, , can be very large (up to ~50%) due to the

mixing in a significant region of the QFV parameters despite the very strong

constraints on QFV from experimental data on B mesons .

• This can result in remarkable QFV squark and gluino signal events such as

‘ + beam-jets' with a significant rate at LHC.

• We have also studied the effect of the squark generation mixing on the invariant mass

distributions of the two quarks from the gluino decay at LHC. We have found that it

can result in novel and characteristic edge structures in the distributions. In particular,

multiple-edge (3- or 4-edge) structures can appear in the charm-top quark mass

distribution.

LRLR tc //~~

)~~( 01ctgB

RR tc ~~

)~~( 012,1 cuB )~~( 0

12,1 tuB

misTEctpp

• These could have an important impact on the search for squarks and gluinos and the MSSM parameter determination at LHC.

Backup Slides

• We study the effect of squark generation mixing on the squark and gluino

decays at LHC.

• In case of mixing, gluino and squarks could decay as follows:

• Possible two-body decays of the gluino and squarks are:


g~

2,1~u

c

t0

1~

RR tc ~~

dependences of gluino decay BR’s in our scenario uRR

23


The QFV decay branching ratio increases quickly with increase of the

mixing parameter and can be very large in a wide allowed range

of .

uRR

23

uRR

23

)~~( 01ctgB

RR tc ~~

dependences of gluino and squark two-body decay BR’suRR

23

Gluino two-body decay BR’s

Squark two-body decay BR’s mixing parameterRR tc ~~


01

~~ ctg Gluino pair production and the QFV gluino decay lead to

QFV gluino signature at LHC :

XctctXggpp )~)(~(~~ 01

01

01

~~ ctg

blbWt

‘top-quark + top-quark + 2 jets + missing-ET + beam-jets‘

‘isolated same sign dilepton + 4 jets + missing-ET + beam-jets‘

isolated same sign dilepton


c

p p

gg

g

t

g~g~

tc

01

~0

1~

b bW

l

W

'l

jetbeam jetbeam

QFV gluino decay


p pgg

c

isolated same sign dilepton

l 'l


c

b b

Impact of squark generation mixing on the search for squarks and gluinos at LHC

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