1. SUSY searches @ LHC Alan Barr University of Oxford A perspective
UK HEP Forum th September 2011

2. Motivational arguments…
8 Sept 2011
Alan Barr, University of Oxford

3. Motivational arguments…
8 Sept 2011
Alan Barr, University of Oxford

4. Alan Barr, University of Oxford
What sort of searches?
Lepton(s) [taus]
Proton
Jet(s) [b-jets]
Photon(s)
Proton
Invisible(s)
Signature driven.
“Measure what you can measure.”
(Some signatures arguably better motivated…)
8 Sept 2011
Alan Barr, University of Oxford

5. Alan Barr, University of Oxford
What sort of searches?
Strongly interacting particles produced  Decay to WIMP candidate…
[ Lepton(s) ]
Proton
Jet(s)
Proton
Invisible(s)
8 Sept 2011
Alan Barr, University of Oxford

6. A discovery could have come (very) early…
8 Sept 2011
Alan Barr, University of Oxford

7. Alan Barr, University of Oxford
Jets + pTmiss
June 2010
Pileup
8 Sept 2011
Alan Barr, University of Oxford

8. Alan Barr, University of Oxford
ICHEP, July 2010
ATLAS and CMS show “commissioning” & “early search” plots
Plenary speakers talk about first top quarks…
8 Sept 2011
Alan Barr, University of Oxford

9. Alan Barr, University of Oxford
interpretation paper…
ATLAS was “already surpassing Tevatron’s reach” for compressed SUSY
8 Sept 2011
Alan Barr, University of Oxford

10. Alan Barr, University of Oxford
ATLAS July/Aug 2010
Early SUSY searches with Etmiss and b-jets
08/2010 7
0.3
ATLAS-CONF
Background to long-lived stopped particle searches
07/2010
0.07
ATLAS-CONF
Early SUSY searches with >=1 isolated leptons, jets and Etmiss
ATLAS-CONF
Early SUSY searches with jets and Etmiss
ATLAS-CONF
8 Sept 2011
Alan Barr, University of Oxford

11. Alan Barr, University of Oxford
CMS: first 2010 paper
Use jets only – not pTmiss
8 Sept 2011
Alan Barr, University of Oxford

12. First papers from ATLAS
Lepton + jets + pTmiss
Jets + pTmiss
8 Sept 2011
Alan Barr, University of Oxford

13. Alan Barr, University of Oxford
And limits from ATLAS…
PRL 106 (2011)
PLB 701 (2011) 186
8 Sept 2011
Alan Barr, University of Oxford

14. Observations on first papers
Data-driven background techniques
PTmiss resolutions & tails from data
State of the art Monte Carlos:
Alpgen, Herwig++, …
In-situ measurements of:
non-collision backgrounds
pTmiss smearing
Use of new variables: (mT2, T, …) as well as old favourites (meff, hT, …)
Full statistical analysis
Limits in mSUGRA/CMSSM and for simplified models
Fiducial  to allow reinterpretation
8 Sept 2011
Alan Barr, University of Oxford

15. Observations on first measurements
Experiments performed much better than (I) expected
8 Sept 2011
Alan Barr, University of Oxford

16. Observations on first measurements
Experiments performed much better than (I) expected
Monte Carlo generators performed much better than (I) expected
8 Sept 2011
Alan Barr, University of Oxford

17. Observations on first measurements
Experiments performed much better than (I) expected
Monte Carlo generators performed much better than (I) expected
Writing papers with thousands of co-authors is both extremely helpful and mind-blowingly frustrating(!)
8 Sept 2011
Alan Barr, University of Oxford

18. Alan Barr, University of Oxford
Summer 2011
(Much) more luminosity:
Improved BG determination (control region stats)
Improved signal reach
New channels become tractable
Efficient update/development of existing analyses
Branch out in new directions
8 Sept 2011
Alan Barr, University of Oxford

19. Alan Barr, University of Oxford
Bruneliere: Implications of LHC physics
8 Sept 2011
Alan Barr, University of Oxford

20. Alan Barr, University of Oxford
Bruneliere: Implications of LHC physics
8 Sept 2011
Alan Barr, University of Oxford

21. Alan Barr, University of Oxford
8 Sept 2011
Alan Barr, University of Oxford

22. Alan Barr, University of Oxford
8 Sept 2011
Alan Barr, University of Oxford

23. Alan Barr, University of Oxford
Paper imminent
8 Sept 2011
Alan Barr, University of Oxford

24. Alan Barr, University of Oxford
8 Sept 2011
Alan Barr, University of Oxford

25. Alan Barr, University of Oxford
8 Sept 2011
Alan Barr, University of Oxford

26. Recent highlights: 3rd generation
ATLAS-CONF
Recent highlights: 3rd generation
8 Sept 2011
Alan Barr, University of Oxford

27. Recent highlights: 3rd generation
ATLAS-CONF

28. Lepton + (B-)jets + ptmiss
8 Sept 2011
Alan Barr, University of Oxford

29. Recent highlights: CMS mT2
PAS-SUS
8 Sept 2011
Alan Barr, University of Oxford

30. Recent highlights: ATLAS multijets
SUSY 2011 conference
8 Sept 2011
Alan Barr, University of Oxford

31. ATLAS Multijets - results
Paper imminent…
8 Sept 2011
Alan Barr, University of Oxford

32. UK groups are centrally involved…
Particularly:
Liverpool: susy with b-jets, photons
Oxford: pile-up, large jet multiplicities
Sheffield: jet smearing & QCD BGs
Cambridge: dilepton, VB + jets
Imperial: alpha T, early searches
Sussex: multi-lepton searches
8 Sept 2011
Alan Barr, University of Oxford

33. Alan Barr, University of Oxford
Where next – short term?
~10 x factor in lumi at 7 TeV
Limited improvement in existing channels/models
Getting systematics limited
Can improve BG determinations but getting tougher…
Raising cuts slightly will increase reach slightly.
Many more channels/interpretations open up:
Compressed models
Lower cross-section models
EW production
3rd generation – Stops and Taus
Large lepton multiplicities
Z + ptmiss
Higgs + ptmiss?
Kinks, stubs, exotics…
8 Sept 2011
Alan Barr, University of Oxford

34. The game starts again at 14 TeV
Where next longer term?
The game starts again at 14 TeV
8 Sept 2011
Alan Barr, University of Oxford

35. Alan Barr, University of Oxford
Multi-lepton SUSY
Multi-lepton SUSY
≥ 3 leptons (electron or muon)
Expect:
Observe no events
Charginos and neutralino cascade decays
≥ 3 leptons (electron or muon) pT > {20, 20, 20(e) or 10 (mu)} GeV
≥ 2 jets with pT > 50 GeV and |η| < 2.5
ETmiss > 50 GeV
mll (ossf) Z mass veto (within 5 GeV of mZ)
mll (ossf) photon veto (< 20 GeV)
Top dominates after Z veto
Also phenomenological limits: see…
8 Sept 2011
Alan Barr, University of Oxford

36. Alan Barr, University of Oxford
Dilepton SUSY
Di-lepton SUSY
1) Opposite sign and same sign 2) Charge asymmetry analysis
Two papers in the pipeline
8 Sept 2011
Alan Barr, University of Oxford

37. Stable charged particle search
R-hadrons
Two independent detector subsystems
dE/dx: pixels (Time over threshold)
β: tile (ToF resolution ≈ns)
The 2-dimensional distribution of mass estimates as reconstructed in the tile calorimeter and pixel detector. Data and signal predictions for a gluino R-hadron of mass 500 GeV are displayed. The distributions are shown following the selection dE/dx > 1.8 MeV g^{-1} cm^{2} (pixel), beta < 1 (tile) and pT > 50 GeV.
Cross-section limits at 95% CL as a function of sparticle mass. Since some candidate events are observed for the mass windows used for the 100 GeV mass hypotheses, the mass points between 100 and 200 GeV are connected with a dotted line. This indicates that fluctuations in the excluded cross-section will occur. The mass limits quoted in the text are inferred by comparing the cross-section limits with the model predictions. Systematic uncertainties from the choice of PDF and the choice of renormalisation and factorisation scales are represented as a band in the cross-section curves. Previous mass limits are indicated by shaded vertical lines for sbottom (ALEPH), stop (CDF) and gluino 
95% confidence limits:
Stable gluino > 586 GeV
Stable stop > 309 GeV
Stable sbottom 294 GeV
8 Sept 2011
Alan Barr, University of Oxford

38. Alan Barr, University of Oxford
Electroweak symmetry breaking
Hierarchy problem?
WIMPs?
What is the physics at the TeV-scale?
8 Sept 2011
Alan Barr, University of Oxford

39. Alan Barr, University of Oxford
Analysis of the 2010 data
8 Sept 2011
Alan Barr, University of Oxford

40. Alan Barr, University of Oxford
Other searches?
Lepton(s) [taus]
Proton
Jet(s) [b-jets]
Photon(s)
Proton
Invisible(s)
Signature driven.
“Measure what you can measure.”
(Some signatures arguably better motivated…)
8 Sept 2011
Alan Barr, University of Oxford

41. Example Supersymmetry search
Mass (GeV)
“Typical” SUSY spectrum
Assume R-parity
Look for:
Jets from squark & gluino decays
Leptons from gaugino & slepton decays
Missing energy from (stable) LSPs
8 Sept 2011
Alan Barr, University of Oxford

42. Alan Barr, University of Oxford
8 Sept 2011
Alan Barr, University of Oxford

43. Alan Barr, University of Oxford
ATLAS-CONF
all the squarks are heavier than the gluino, which decays exclusively (via virtual stop) into three-body final states ( t + tbar + LSP)
8 Sept 2011
Alan Barr, University of Oxford