1. Weak Production SUSY Search In LHC
Bai Yu
IHEP, Beijing

2. 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

3. SUSY : A Brief Introduction
Standard Model
SUSY Partners
An Maximum Extension to Poincare Symmetry
A solution to the hierarchy problem
Provide candidate to Dark Matter
A clue of unification
incorporate the gravity
SM particles and their super partner

4. SUSY Breaking and Parameters
Why SUSY is broken?
NO SUSY PARTNER FOUND YET!
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
SUSY Breaking Mechanism:
GMSB (gauge mediated)
SUGRA (gravity mediated)
AMSB (anomaly mediated) ….
Gaugino
Chargino: Mixed wino and charged higgsino
, ,
Neutralino: Mixed bino and netrual
, , , ,
R-Parity Conserved Process
LSP : netrual massive susuy particle

5. SUSY Symmetry in TeV Scale
“Naturalness ” requires SUSY breaking parameter not higher than a few TeV
Need to probe in electro-weak scale
We can do it here!
Over 20/fb 8-TeV collision data collected in 2012

6. 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

7. Electro-Weak SUSY Search in ATLAS Experiment with 2L(e/mu) Final States
ATLAS-CONF

8. Scenarios and Signal Regions
4 scenarios explored
Slepton pair production
Mass of gaugions(except LSP) set to 2.5 GeV, slepton at least 30 GeV hevier than LSP, varying between GeV
Chargino to slepton
Mass set the mean of LSP and chargino mass. Chargino mass in GeV
Chargino to W
Chargino mass at least 80 GeV greater than LSP mass, scan LSP mass from 0 GeV
GMSB
NLSP chargino 1 mass set to be 110 GeV, most sensitive signal grid

9. 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)

10. Results from the Simultaneous Fit
SRWWa
SRWWb
SRWWc
e+e- in SR mt2 90
μ+μ- in SR mt2 90
eμ in SR mt2 90
Data and MC agrees reasonably
Fit results used as inputs for exclusion limit

11. Interpretation No discovery
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

12. Electro-Weak SUSY Search in ATLAS Experiment with at Least 2 hadronically decaying taus in Final States
ATLAS-CONF

13. Scenarios and Signal Regions
C1C1 production
C1N2 production
Direct stau 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 mass-degenerate
SUSY particle other than stau/stau neutrino, C1, N1 and N2 are assumed to be heavy
pMSSM model
Squark and gluino are heavy
tan β = 50(large)
M1 = 50 GeV
M2 and μ vary between GeV
Ligtest stau mass 95 GeV

14. Background Estimation in Tau Channel
ABCD method
Backgrounds
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

15. 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

16. 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

17. Electro-Weak SUSY Search in ATLAS Experiment with 3L(e/mu) Final States
ATLAS-CONF

18. 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

19. 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

20. 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

21. Electro-Weak SUSY Search in CMS Experiment with 2L Final States

22. Scenarios and Analysis Strategy
OS 2-lepton search (non-resonant), slepton pair production or chargino decay slepton
SS 2-lepton search:
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)
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

23. Result of Template Fit in OS Analysis
Opposite flavor channel
Same flavor channel
Extrapolation from Low to High Region

24. 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

25. Interpretation-1, Flavor Dem

26. Intepretation-2, tau-enriched and tau dominant

27. Electro-Weak SUSY Search in CMS Experiment with 3L Final States
Scenario much the same as that in ATLAS

28. Interpretation of 3L Analysis
WZ + MET
C1 pair production
Slepton pair production

29. 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

30. Thank you!