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New physics @ ATLAS. Alan Barr University of Oxford. Kings College London 23 rd March 2011. Electroweak symmetry breaking. Hierarchy problem?. WIMPs?. What is the physics at the TeV -scale?. End of 2010 run. 22 July ICHEP. - PowerPoint PPT Presentation
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New physics @ ATLAS
Alan BarrUniversity of Oxford
Kings College London 23rd March 2011
Alan Barr, University of Oxford 223/03/2011
Electroweak symmetry breaking
Hierarchy problem?
What is the physics at the TeV-scale?
WIMPs?
Alan Barr, University of Oxford 323/03/2011
22 July ICHEP
End of 2010 run
Alan Barr, University of Oxford 4
Parton-parton luminosity
23/03/2011
Alan Barr, University of Oxford 523/03/2011
Alan Barr, University of Oxford 6
SUSY & BSM strategy• Precision reliable hermetic detector• Basic kinematics• Understand detector and SM• Look at final states with:
23/03/2011
Proton
Proton
Lepton(s)
Jet(s)
Invisible(s)
Photon(s)
Examples given
Alan Barr, University of Oxford 7
Basic kinematics
23/03/2011
Transverse mass mT =
Transverse momenta, pT
Scalar sums of transverse momenta: HT, meff = HT + ETmiss
Missing transverse momentum, ETmiss
“Stransverse” mass (generalisation of mT to 2 parent particles)
Azimuthal angle differences Δφ
Pseudorapidity, η = - ln tan θ/2
8
1-lepton + Jets + ETmiss
1-lepton SUSY
1 electron or muon pT>20 GeV3 jets pT > {60, 30, 30} GeVET
miss > 125 GeVET
miss > 0.25 * meff
mT > 100 GeVmeff > 500 GeVSelection based heavily on pre data-takingMC studies e.g. arXiv:0901.0512
First ATLAS SUSY paperarXiv:1102.2357 accepted by PRL
Lepton reduces QCD BGExpect leptons in SUSY cascade decays
Alan Barr, University of Oxford 9
Control regions – some examples
23/03/2011
Multiple redundant control regionsQCD background separately
Systematics include (not only) JES, JER, lumi, lepton efficiency, CR stats, extrapolation, … Top C/R distinguished from
W+jets using b-tagging
1-lepton SUSY
Great care with BG for all analyses presented
Alan Barr, University of Oxford 10
1-lepton results
23/03/2011
1-lepton SUSY
Likelihood ratio as a function of signal strengthToy MCs for p-valuesProfile likelihood for nuisance parameters (conservative systematics)Fully simulated backgrounds, signal pointsIncludes systematic uncertainties on signal strength
Alan Barr, University of Oxford 11
SUSY: Jets + ETmiss
23/03/2011
0-lepton SUSY
Squark decays Gluino decays
Conceptually simple search for squarks and gluinosSeveral overlapping signal regions:
ArXiV:1102.5290
Alan Barr, University of Oxford 12
Robust background determinations
23/03/2011
• 2-4 measurement methods per background
• Examples:– Reversal of cuts & kinematic control
regions– Fully data-driven inc. jet transfer functions– Tau re-decay, smear– Z νν from:
Z ee, Z μμW eν, W μν
0-lepton SUSY
Alan Barr, University of Oxford 1323/03/2011
0-lepton SUSY
Exclude non-SM effective cross sections (σ x BR x Acc x Eff):A: 1.3 pb B: 0.35 pb C: 1.1 pb D: 0.11 pb
Squark, Gluino interpretations
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/susy-0lepton_01/
Alan Barr, University of Oxford 14
Multi-lepton SUSY
23/03/2011
Multi-lepton SUSY
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2011-039/
Also phenomenological limits: see…
Expect:
Observe no events
Top dominates after Z veto
≥ 3 leptons (electron or muon)
Alan Barr, University of Oxford 15
SUSY with b-jets
23/03/2011
SUSY with b jets
Done for both 1-lepton, 0-lepton channels
Paper in the pipeline…
Sensitive to Stop, Sbottom, Gluinoproduction
Top background dominates after b-jet requirementData-driven QCD background determination
Alan Barr, University of Oxford 16
Stable charged particle search
23/03/2011
95% confidence limits:
Stable gluino > 586 GeVStable stop > 309 GeV Stable sbottom 294 GeV
R-hadrons
Two independent detector subsystemsdE/dx: pixels (Time over threshold)β: tile (ToF resolution ≈ns)
Alan Barr, University of Oxford 17
W’ searches
23/03/2011
Electrons Muons
arxiv:1103.1391
Electron pT > 25 GeV, |η| < 1.37 or 1.52 < |η| < 2.40Muon pT > 25 GeV, |η| < 1.05ET
miss > 25 GeVM(W’SSM) > 1.49 TeV
Alan Barr, University of Oxford 18
Z’ searches…
23/03/2011
Electrons Muons
M(Z’SSM) > 1.05 TeV
Alan Barr, University of Oxford 19
Dijet inv. mass, angular distributions
23/03/2011
http://arxiv.org/abs/1103.3864Compositeness scale, Λ > 9.6 TeV
Alan Barr, University of Oxford 20
Diphoton resonances
23/03/2011
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2011-044/
Alan Barr, University of Oxford 21
Diphoton + ETmiss
23/03/2011
Interpret in context of Universal Extra DimensionsΛR = 20
Alan Barr, University of Oxford 22
Fourth generation Q search• Di-leptonic channel
23/03/2011
Approximate mass reconstruction on varying Δη, Δφ
Excludes m(Q) < 270 GeV (@95% CL)
Preliminary conclusions• Excellent operation of LHC and ATLAS• Commissioned physics objects:
Jets, e, mu, ETmiss , photons, b-jets, (tau)
• Wide variety of such final states studied• Also exotics… R-hadrons, multi-charged
particles, stopped gluinos…• Many limits well beyond previous colliders
23/03/2011
Alan Barr, University of Oxford 24
EXTRASA few little
23/03/2011
Alan Barr, University of Oxford 25
Papers and CONF notes 1/3:SUSY papers and notes
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults23/03/2011
Alan Barr, University of Oxford 26
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/ExoticsPublicResults
23/03/2011
Papers and CONF notes 2/3:Exotics papers
Alan Barr, University of Oxford 27
Papers and CONF notes 3/3Exotics Conf notes
23/03/2011
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/ExoticsPublicResults
Alan Barr, University of Oxford 2823/03/2011
0-lepton SUSY
Missing transverse momentum
Alan Barr, University of Oxford 29
meff distributions
23/03/2011
0-lepton SUSY
Cuts shown on mass-sensitive variable in final selection
Alan Barr, University of Oxford 30
BG example: ETmiss tails
23/03/2011
0-lepton SUSY
One example of very, very, very many background studies
Alan Barr, University of Oxford 3123/03/2011
1-lepton SUSY
Alan Barr, University of Oxford 32
1-lepton + Jets + ETmiss
23/03/2011
arXiv:1102.2357 1-lepton SUSY
Alan Barr, University of Oxford 33
1-lepton results
23/03/2011
1-lepton SUSY
Alan Barr, University of Oxford 34
Profile likelihood
• Hatted quantities maximise likelihood• Double hatted quantities maximise L for given
value of s• s and s-hat constrained to be non-negative• Likelihood ratio is the test statistic used to
calculate the p-value
23/03/2011
Alan Barr, University of Oxford 35
Kinematic distributions
23/03/2011
1-lepton SUSY
Electron channel Muon channel
Alan Barr, University of Oxford 36
Di-photon + ETmiss
• S
23/03/2011
arxiv:1012.4272
Alan Barr, University of Oxford 37
Jets, Electrons, Muons, ETmiss
• 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• ET
miss > 50 GeV
• mll (ossf) Z mass veto (within 5 GeV of mZ)• mll (ossf) photon veto (< 20 GeV)
23/03/2011
Multi-lepton SUSY
SM: Observe no events
Top dominates after Z veto
38
SM: H→γγ• Mass range: 110 GeV - 140 GeV• Data-driven estimation of all background components
– γγ, γj, jj• Inclusive
– only discriminant diphoton inv. mass
Sensitivity close to the current Tevatron limits.
ATLAS-CONF-2011-025
39
Z →ττmu + had
e + had
e + mu
ATLAS-CONF-2011-010ATLAS-CONF-2011-045
Alan Barr, University of Oxford 40
Stable massive particle search• Two independent detector
subsystems• dE/dx: pixels
(Time over threshold)• β: tile
(ToF resolution ≈ns)
• ETmiss > 40 GeV (trigger)
• pT > 50 GeV
23/03/2011
http://arxiv.org/abs/1103.1984
R-hadrons
Alan Barr, University of Oxford 41
0-lepton results0-lepton SUSY
Conservative systematicsJet energy scale (~7%)Luminosity (11%)Control region statisticsLepton vetoDifferent MCb-jet fractionMC statisticsHigher orders… more …
Alan Barr, University of Oxford 42
Dilepton SUSY
23/03/2011
Di-lepton SUSY
