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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