Transcript Weak Production SUSY Search

Weak Production SUSY Search
In LHC
Bai Yu
IHEP, Beijing
2014-01-23 , @USTC
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Outline
• Introduction to super symmetry(SUSY)
• SUSY at LHC
• Search in ATLAS
– 2-lepton(2L) Search
– 3-lepton (3L) Search
– 2-tau (hadronic decay)
• Search in CMS
– 3-lepton search
– 4-lepton search (in GMSB scenario)
• Summary
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SUSY : A Brief Introduction
An Maximum Extension to
Poincare Symmetry
Standard Model
SUSY Partners
• A solution to the hierarchy
problem
• Provide candidate to Dark
Matter
• A clue of unification
• incorporate the gravity
SM particles and their super partner
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SUSY Breaking and Parameters
Why SUSY is broken?
NO SUSY PARTNER FOUND YET!
SUSY Breaking Mechanism:
• GMSB (gauge mediated)
• SUGRA (gravity mediated)
• AMSB (anomaly mediated)
•….
MSSM-124 :
• Minimum SUSY extension to
SM
• Most of parameter are from
symmetry broken
• Not all the parameter space is
physical
• Usually simplified for
experment intepretation
• Gaugino
• Chargino: Mixed wino and charged higgsino
•
,
,
• Neutralino: Mixed bino and netrual
•
, , , ,
• R-Parity Conserved
Process
– LSP : netrual massive
susuy particle
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SUSY Symmetry in TeV Scale
• “Naturalness ” requires
SUSY breaking parameter
not higher than a few TeV
• Need to probe in electroweak scale
We can do it here!
Over 20/fb 8-TeV collision data collected in 2012
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SUSY in Weak Production
• Might be the dominant SUSY production in LHC if gluino and squark are
heavy
• Interaction Vertex :
• Process :
• Decay process determined by mass spectrum of gaugino and slepton
– Enssential to Analyis Strategy
– Final state : 2-3 leptons , large Missing transverse energy(MET), low jet
activity
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Electro-Weak SUSY Search in
ATLAS Experiment with
2L(e/mu) Final States
ATLAS-CONF-2013-049
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Scenarios and Signal Regions
• 4 scenarios explored
1.
Slepton pair production
• Mass of gaugions(except LSP) set to 2.5 GeV, slepton at least 30 GeV hevier than LSP, varying
between 90-370 GeV
2.
Chargino to slepton
• Mass set the mean of LSP and chargino mass. Chargino mass in 100-450 GeV
3.
Chargino to W
• Chargino mass at least 80 GeV greater than LSP mass, scan LSP mass from 0 GeV
4.
GMSB
• NLSP chargino 1 mass set to be 110 GeV, most sensitive signal grid
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Background Estimation
• Main background
– Same flavor
• ZV, ttbar, WW
– Different flavor
• ttbar, WW
• Strategy
– Define control region for each signal region
– For each SR,
– Implementing simultaneous fit to these CR and
SR(Standard method in ATLAS SUSY WG)
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Results from the Simultaneous Fit
SRWWa
e+e- in SR mt2 90
μ+μ- in SR mt2 90
SRWWb
eμ in SR mt2 90
SRWWc
• Data and MC
agrees
reasonably
• Fit results used
as inputs for
exclusion limit
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Interpretation
Right handed sleptonn pair Left handed sleptonn pair
Mass degenerate
• No discovery
• Set exclusion limit
for the first 2
scenario
• Set upper limit for
the last 2 scenario
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Electro-Weak SUSY Search in
ATLAS Experiment with at Least
2 hadronically decaying taus in
Final States
ATLAS-CONF-2013-028
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Scenarios and Signal Regions
C1C1 production
C1N2 production
Simplified model
• Minimum particle contents necessary
• Parametrized directly in terms of the
sparticle masses
• C1 and N2 are mass-degenerate
• stau and tau sneutrino are massdegenerate
• SUSY particle other than stau/stau
neutrino, C1, N1 and N2 are assumed to
be heavy
Direct stau production
pMSSM model
• Squark and gluino
are heavy
• tan β = 50(large)
• M1 = 50 GeV
• M2 and μ vary
between 100-500 GeV
• Ligtest stau mass 95
GeV
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Background Estimation in Tau
Channel
• Backgrounds
ABCD method
– Fake tau backgrounds QCD
and W+jets, estimated by
Data Driven Method
– Z+jets, top, diboson
estimated from MC(Directly
or ABCD-like MC driven
method)
• Two orthogonal
variables: tau-id
and MT2
• Extrapolate
from CR-A to SR
• Validate in other
regions
Good agreement
between data and
MC
Simultaneous fit
applied for both
QCD-CR and SR
SR OS-mt2
SR OS-mt2 nobjet
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Interpretation
Exclusion limit for C1N2
production
Exclusion limit for
C1C1 production
Exclusion limit for
pMSSM
•
No discovery. 95% CL exclusion limit was set
•
For C1C1 production, chargino mass are excluded up to 350 GeV for light neutralino
mass
•
For C1N2 production, charigno mass are excluded up to 300 (330) GeVwith neutralino
mass 50(100) GeV
•
For pMSSM, region with high M2(corresponding to stau production) are excluded
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On-going Work on tau Analysis
• Aming publishment in 2014
• New SR definition
– 5 signal regions defined now, including SR for
direct stau production
• New background estimation
– Use large statistic W+jets sample
– Define W control region, implemented in
simultaneous fit
• Try to be approved in SUSY WG no later than
end of February
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Electro-Weak SUSY Search in
ATLAS Experiment with
3L(e/mu) Final States
ATLAS-CONF-2013-035
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Scenarios and Signal Regions
• Same C1 and N2 decay brach
ratio for each flavor
• Slepton and lepton sneutrino
mass degenerate, set as mean
value of C1 mass and N1 mass
• Slepton and sneutrino assumed
to be very heavy
• Branch ratio decay to higgs set
to be 0
SR Definition
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Background Estimation
• Reducible Backgrounds
– ttbar, Z+jets, W+jets, single top
– Include fake leptons, Estimated by Matrix
Method
• Irreducible Backgrounds
– WZ, tri-boson, ttW/Z
– Control region for background WZ selected,
simultaneous fit applied to both WZ-CR and SR
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Interpretation
Decay via sleptons
Decay via gauge bosons
• Null results, exclusion limit set with context of simplified model C1N2
decay
• With assumption C1N2 decay via slepton, the C1 and N2 mass have been
rejected up to 600 GeV for large mass difference with C1
• With assumption C1N2 decay via gauge boson, , the C1 and N2 mass have
been rejected up to 315 GeV for large mass difference with C1
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Electro-Weak SUSY Search in
CMS Experiment with 2L Final
States
SUS-13-006
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Scenarios and Analysis Strategy
• OS 2-lepton search (non-resonant), slepton pair
production or chargino decay slepton
• SS 2-lepton search:
• Flavor Democratic : C1 and N2
decay to different flavor slepton
with same BR,
• τ-enriched : C1 decay to tau,
N2 decay democratically
• τ -dominant : both C1 and N2
decay to tau
– One of the 3 lepton from C1N2 elude from detection
• OS Analysis strategy : fit the data with
template
• SS Analysis strategy : directly from MC (with
rejection to OSSF lepton pair)
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Result of Template Fit in OS Analysis
Opposite flavor channel
Same flavor channel
Extrapolation from Low to High
Region
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Results of Background Estimation in
SS Analysis
• Reasonable agreement between
data and MC in MET distribution
• Results with/without 3rd lepton
rejection listed, interpretation
only use that with 3rd lepton veto
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Interpretation-1, Flavor Dem
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Intepretation-2, tau-enriched and
tau dominant
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Electro-Weak SUSY Search in
CMS Experiment with 3L Final
States
SUS-13-006
Scenario much the same as that in ATLAS
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Interpretation of 3L Analysis
WZ + MET
C1 pair production
Slepton pair production
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Summary
EWK SUSY limit in ATLAS
EWK SUSY Limit in CMS
• All the study give null results, exclusion or upper
limit set in parameter space
• Need to continue probing with high energy
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Thank you!
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