Detection of slepton non-universality effects at LHC

references:

hep-ph/0405052, A. Barr

hep-ph/0406317, Goto, Kawagoe, Nojiri

Electron/muon efficiency

• It has aplication whenever exclusive studies

and leptonic signatures/endpoints are analysed, like for exmaple in the left squark cascade decay:

when we study ll, llq and lq endpoints and apply

subtraction:

01

02

~ ~ ~ ~ lqlllqqq RL

eee )( )( 2

Correction factors for different efficiencies

Outline

• Left squark decay

• Charge asymmetry

• Left/right slepton mixing

• Left squark decay, general case

• Influence of mixings on charge asymmetry

Left squark decay,charge asymmetry

when slepton is purely right handed

Left squark decay

, ,,,

~ ~ ~ ~ 0

102

elcsduq

llqllqqq nearRL

Final state: l+, l- , q, missing energy

First emitted lepton (near)

Decays of squark and slepton are spherically symmetric.

Due to neutralino spin 1/2, if decay into followed

by , the lepton favours going in the opposite

direction to for ( and going in the same

drection for the ). Angular distribution is not symmetric

Invariant mass M(qlnear) is charge asymmetric.

(decays to left and decays to right slepton have opposite

asymmetries. ). If we can measure this asymmetry it is

direct proof of neutralino spin.

Lq~ 0

2~

ll~ ~0

202

~ Rl~

~Ll

Spin effects on M(qlnear)

No spin correlations,no charge asymmetry,identical distributions

of M(ql+) and M(ql-)

Spin correlations taken

into account, M(ql+)

Spin correlations taken

into account, M(ql-)

M(ql)

Eve

nts

M(ql+)

M(ql-)

Ideal distributions

Charge asymmetry

)(s

qlmd

d

ss

ssA

Selected mSUGRA point – LHCC 5

(now excluded by LEP): mm00 =100 GeV m =100 GeV m1/21/2 =300 GeV A =300 GeV A00 =300 GeV =300 GeV

tan(tan(ββ) =2.1 sign() =2.1 sign(μμ)=+)=+

--second neutralino do not decay to left sleptonsecond neutralino do not decay to left slepton

-right squark never decay to second neutralino-right squark never decay to second neutralino

Monte Carlo

• ISAJET, HERWIG, ATLFAST• Choice of parton distribution function is crucial• Necessary to include spin effects in HERWIG

P. Richardson JHEP 11 (2001) 029 • Selection cuts to isolate left squark decay applied

Asymmetry M(qlnear)

Parton level distributions , can’t be measured by experiment

ql+

ql- ql+

ql-

quark antiquark

Asymmetry M(qlfar)

Parton level distributions, can’t be measured by experiment

quark antiquark

ql+

ql- ql+ ql-

Problems

• We do not know which is the first and which is the second emitted squark

• Quark and antiquark are experimentally

indistinguishable and have opposite asymmetries

Solution

• Study of M(l-q) and M(l+q) distributions• Each distribution contain contribution from

both near and far lepton and contribution from both quark and antiquark

LHC is pp collider → more quarks then antiquarks is going to be produced and asymmetry can be measured

Asymmetry M(ql)Parton level distributions

ql+ql-

Asymmetryafter event selection and detector simulation

No spin correlations

After selection

Parton level x 0.6

M(ql) asymmetry

ql+

ql-

L=500 fb-1 L=500 fb-1

asymmetry M(ll)L=150 fb-1

Left squark decay andcharge asymmetry

general case

Left/right slepton mixings• SELECTRONS: L/R mixing is negligible.

Selectron mass eigenstates:

• SMUONS: Smuon mass eigenstates:

For large values tg(β) mixing can be observed

• STAUS: Mixing is significant. Stau mass eigenstates:

For “typical” mSUGRA point M1≈ 0.5 M2 , wino components

dominate , bino component dominates , lighter

slepton is dominantly , and the heavier one is

dominantly

~ , ~LR ee

~ , ~LR

~ , ~21

21~ , ~

02

~ 01

~1

~l

2

~lRl

~

Ll~

Decay of second neutralinodepend on the mSUGRA point

llR ~~0

2 llL ~~0

2 ll

~~2

02 ll

~~1

02

DominantAllowed for some points,when m(0

2) > m(l2).

~ , ~ , e~ ~

~ ~ ~ ~

1,21,21,22,1

012,1

02

l

llqllqqqL

Left squark decaygeneral case

Effects of left/right mixings

Left/right mixing affect

- the charge asymmetry

- decay width for l=µ,

• SELECTRONS: maximal asymmetry A(e) ≈ -1.• SMUONS: asymmetry smaller then in selectron case if there is

L/R mixing significant.

• STAUS: asymmetry opposite to selectron case

l l~ ~0

2

)~~()~~()~~( 1021

021

02 ee

• Very important to choose point with:

- large BR for left squark cascade decay

in order to have large available statistics

with small luminosity

- large values of tg(β) if we want to study

smuon mixing

Some examples1. If smuon mixing is not significant and decay of

is open, then we have asymmetries from

2. If smuon mixing is not significant and both decays of

are open, then we have

asymmetries from

llR ~~0

2

~ , ~~02 RR ee ~~

102

, ~~0

2 llR llR ~~0

2

~ , ~~02 RR ee

~ , ~~02 LL ee

~~1

02

~~2

02

SPS1a:

mm00 =100 GeV m =100 GeV m1/21/2 =250 GeV A =250 GeV A00 =-100 GeV =-100 GeV

sign(sign(μμ)=+ )=+ tg(β)=10, 15, 20

SPS3:mm00 =90 GeV m =90 GeV m1/21/2 =400 GeV A =400 GeV A00 =0 GeV =0 GeV

sign(sign(μμ)=+ )=+ tg(β)=10

Decay is also open, and should show

opposite charge asymmetry to that of

Modified point effect of smuon mixing is significant

~ ~0

2 llL

Rl~

SPS1a ( tg(β) = 10 )

SPS3

theory

theory

Plans

• Start studies with SU3 point. All the necessary effects to be included in HERWIG and start private production.

• First step would be to measure charge asymmetry, what would confirm neutralino spin. (Efficiencies would be included in mass distributions.)

• Flavour workshop, CERN, 3-7 November