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New physics @ ATLAS
Alan BarrUniversity of Oxford
Freiburg 11th May 2011
British press reportthe turn on of the LHC…
December 2008:
Alan Barr, University of Oxford 323/03/2011
Did you hear about the ATLAS di-photon
distribution?
April 2011:
Alan Barr, University of Oxford 4
This talk
• Why a Large Hadron Collider?• Accelerator and detector status• 100 years of discovery in 10 months• The energy-frontier measurements
– Supersymmetry– Exotics
• Prospects for the future (inc. Higgs)
11/05/2011
Alan Barr, University of Oxford 523/03/2011
Electroweak symmetry breaking
Hierarchy problem?
Physics at the TeV-scale?
WIMPs?
6
CMS
LHCb ATLAS
ALICE
Proton - ProtonControlled environmentCM energy = 7 TeV (14)~ 109 collision / second~ decade of operation
Alan Barr, University of Oxford 7
Semiconductor Tracker @ Oxford
11/05/2011
Alan Barr, University of Oxford 823/03/2011
UPDATE ME
Alan Barr, University of Oxford 923/03/2011
22 July ICHEP2010 to same vertical scale
35 pb-1
Alan Barr, University of Oxford 10
Parton-parton luminosity
23/03/2011
Event rate at the unitary limit as a function of CM energy
Exciting!
11
Top candidate event
12 12
pT(μ)= 48 GeV pT(e)=23 GeVET
miss=77 GeV, HT=196 GeVpT (b-tagged jet) = 57 GeVSecondary vertex: -- distance from primary: 3.8 mm -- 3 tracks pT > 1 GeV -- mass=1.56 GeV
pT (tracks) > 1 GeV
Alan Barr, University of Oxford 1323/03/2011
Top quark σ
WW
Inelastic cross-section
J/Ψ suppression in Pb-Pb
Interesting things I won’t discuss…
Alan Barr, University of Oxford 1423/03/2011
Measurement of the WW cross section in sqrt(s) = 7 TeV pp collisions with ATLAS Inspire record, Plots
Submitted to PRL (27 April 2011)
Measurement of the differential cross-sections of inclusive, prompt and non-prompt J/psi production in proton-proton collisions at √s = 7 TeV
Inspire record, Plots
Submitted to Nuclear Physics B (15 April 2011)
Measurement of the Inelastic Proton-Proton Cross-Section at √s=7 TeV with the ATLAS Detector
Inspire record, Plots
Submitted to Nature Comm (2 April 2011)
Measurement of the Muon Charge Asymmetry from W Bosons Produced in pp Collisions at sqrt(s) = 7 TeV with the ATLAS detector
Inspire record, Plots
submitted to PLB (15 Mar 2011)
Measurements of underlying event properties using neutral and charged particles in p-p collisions at 900 GeV and 7 TeV with the ATLAS detector at the LHC
Inspire record, Plots
submitted to EPJC (9 Mar 2011)
Measurement of Dijet Azimuthal Decorrelations in pp Collisions at √s=7 TeV Inspire record, Plots
Phys. Rev. Lett. 106, 172002 (2011) (14 Feb 2011)
Luminosity Determination in pp Collisions at √(s)=7 TeV Using the ATLAS Detector at the LHC
Inspire record, Plots
EPJC 71 (2011) , 1630 (11 Jan 2011)
Study of Jet Shapes in Inclusive Jet Production in pp Collisions at √s = 7 TeV using the ATLAS Detector
Inspire record, Plots
Phys. Rev. D 83, 052003 (2011) (30 Dec 2010)
Measurement of the centrality dependence of J/Psi yields and observation of Z production in lead-lead collisions with the ATLAS detector at the LHC
Inspire record, Plots
Phys Lett. B697 (2011) 294-312 (24 Dec 2010)
Measurement of the production cross section for W-bosons in association with jets in pp collisions at √s = 7 TeV with the ATLAS detector
Inspire record, Plots
Phys. Lett. B698 (2011) 325-345 (23 Dec 2010)
Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC
Inspire record, Plots
accepted by New J Phys (submitted 22 Dec 2010)
Measurement of the inclusive isolated prompt photon cross section in pp collisions at √s = 7 TeV with the ATLAS detector
Inspire record, Plots
Phys. Rev. D 83, 052005 (2011) (20 Dec 2010)
Measurement of the top quark-pair production cross section with ATLAS in pp collisions at √s=7 TeV
Inspire record, Plots
EPJC 71 (2011) 1577 (8 Dec 2010)
Measurement of underlying event characteristics using charged particles in pp collisions at √s = 900 GeV and 7 TeV with the ATLAS detector
Inspire record, Plots
accepted by Phys Rev D (submitted 3 Dec 2010)
Measurement of the W -> lnu and Z/gamma* -> ll production cross sections in proton-proton collisions at √s = 7 TeV with the ATLAS detector
Inspire record, Plots
JHEP 12 (2010) 060 (11 Oct 2010)
Measurement of inclusive jet and dijet cross sections in proton-proton collisions at 7 TeV centre-of-mass energy with the ATLAS detector
Inspire record, Plots, Data points
EPJC 71 (2011) 1-59 (30 Sep 2010)
See: https://twiki.cern.ch/twiki/bin/view/AtlasPublic
‘Sta
ndard
Model’ p
ap
ers
Lots of other very interesting things not covered ...
Alan Barr, University of Oxford 15
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
23/03/2011 Alan Barr, University of Oxford 16
Why Supersymmetry?
top
Δm2(h) Λ2cutoff
higgs higgs
stop?
higgs higgs
λλλ λ
Alan Barr, University of Oxford 17
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 mT2
(generalisation of mT to 2 parent particles)
Azimuthal angle differences Δφ
Pseudorapidity, η = - ln tan θ/2
Alan Barr, University of Oxford 1811/05/2011
Final states ReferenceLepton + Jets + ET
miss Phys. Rev. Lett. 106, 131802 (2011)
Jets + ETmiss arXiv:1102.5290
(submitted to PLB)
≥ 3 leptons + jets + ETmiss ATLAS-CONF-2011-039
≥ 1 b-jet + jets (± leptons) + ET
miss arXiv:1103.4344 (submitted to PLB)
Identical flavours.................Either sign combination.......
arXiv:1103.6208arXiv:1103.6214
Statistical combination(0-lep + 1-lep)
ATLAS-CONF-2011-064
1-lepton SUSY
0-lepton SUSY
Multi-lepton SUSY
SUSY with b jets
Di-lepton SUSY
For all public papers see:https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults
1-lepton SUSY0-lepton SUSY
19
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 20
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 21
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 22
SUSY: Jets + ETmiss
23/03/2011
0-lepton SUSY
Squark decays Gluino decays more jets
Conceptually simple search for squarks and gluinosSeveral overlapping signal regions:
Four overlapping signal regions
Alan Barr, University of Oxford 23
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
Only a couple of very many data-driven checks/BG determinations
Alan Barr, University of Oxford 2423/03/2011
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
Auxiliary plots (Acc x Eff) allow reinterpretation in a variety of models
Alan Barr, University of Oxford 25
Multi-lepton SUSY
23/03/2011
Multi-lepton SUSY
Expect:
Observe no events
Top dominates after Z veto
≥ 3 leptons (electron or muon)
Charginos and neutralino cascade decays
Alan Barr, University of Oxford 26
SUSY with b-jets
23/03/2011
SUSY with b jets
Done for both 1-lepton, 0-lepton channels
Sensitive to Stop, Sbottom, Gluinoproduction
Top background dominates after b-jet requirementData-driven QCD background determination
Alan Barr, University of Oxford 27
Dilepton SUSY
23/03/2011
Di-lepton SUSY
Two papers: 1) Opposite sign and same sign 2) Charge asymmetry analysis
Majorana nature of gluinos, neutralino same sign dilepton eventsLepton number carried by sleptons flavour correlations
Alan Barr, University of Oxford 28
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 subsystems:dE/dx: pixels (Time over threshold)β: tile (ToF resolution ~ns)
Alan Barr, University of Oxford 29
Combined exclusion
11/05/2011
1-lepton SUSY0-lepton SUSY
Statistical combination fromproduct of likelihoods
Alan Barr, University of Oxford 30
Wider interpretation...
23/03/2011
http://arxiv.org/abs/1103.0969
Allanach, Khoo, Lester, Williams
Cassel, Ghilencea, Kraml, Lessa, Rosshttp://arxiv.org/abs/1101.4664
Points sampled from fits to global dataGlobal CMSSM fits
Regions with low fine tuning
ATLAS 0/1 leptonCMS αT
Excluded by ATLAS0-lepton search
Alan Barr, University of Oxford 31
A RACE THROUGH SOME EXOTIC SIGNATURES…
Not only Supersymmetry...
11/05/2011
Alan Barr, University of Oxford 32
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 33
Z’ searches…
23/03/2011
Electrons Muons
M(Z’SSM) > 1.05 TeV
Alan Barr, University of Oxford 34
Dijet inv. mass, angular distributions
23/03/2011
http://arxiv.org/abs/1103.3864Compositeness scale, Λ > 9.6 TeV
Alan Barr, University of Oxford 35
Diphoton resonances
23/03/2011
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2011-044/
Limits on RS graviton: 545 GeV (920 GeV), for k/MPl = 0.02 (0.1)
Alan Barr, University of Oxford 36
Diphoton + ETmiss
23/03/2011
Interpret in context of Universal Extra DimensionsVary size of extra dimension with constant ΛR = 20
Alan Barr, University of Oxford 37
Fourth generation Q search• Di-leptonic channel
23/03/2011
Approximate mass reconstruction on varying Δη, Δφ
Excludes m(Q) < 270 GeV (@95% CL)
Alan Barr, University of Oxford 38
(e,mu) resonance search
• Limits on RPV sneutrino e mu• Limits on flavour violating Z’
23/03/2011
Paper in the pipeline
Story so far• Excellent operation of LHC and ATLAS• Commissioned physics objects:
Jets, e, mu, ETmiss , photons, b-jets, (tau)
• Monte Carlo doing very well• Data-driven backgrounds proven• Wide variety of 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 40
Higgs -> WW
23/03/2011
41
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
Alan Barr, University of Oxford 42
Physics prospects: Higgs
23/03/2011
Alan Barr, University of Oxford 43
Current h ττ
23/03/2011https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2011-024/
Alan Barr, University of Oxford 44
EXPLORING NEW WORLDS...Launch is complete
11/05/2011
Alan Barr, University of Oxford 45
EXTRASA few little
23/03/2011
Alan Barr, University of Oxford 46
Exotics conf notes
23/03/2011
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/ExoticsPublicResults
Alan Barr, University of Oxford 4723/03/2011
0-lepton SUSY
Missing transverse momentum
Alan Barr, University of Oxford 48
meff distributions
23/03/2011
0-lepton SUSY
Cuts shown on mass-sensitive variable in final selection
Alan Barr, University of Oxford 49
BG example: ETmiss tails
23/03/2011
0-lepton SUSY
One example of very, very, very many background studies
Alan Barr, University of Oxford 5023/03/2011
1-lepton SUSY
Alan Barr, University of Oxford 51
1-lepton results
23/03/2011
1-lepton SUSY
Alan Barr, University of Oxford 52
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 53
Kinematic distributions
23/03/2011
1-lepton SUSY
Electron channel Muon channel
Alan Barr, University of Oxford 54
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
• ETmiss > 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
55
Z →ττmu + had
e + had
e + mu
ATLAS-CONF-2011-010ATLAS-CONF-2011-045
Alan Barr, University of Oxford 56
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 57
0-lepton results0-lepton SUSY
Conservative systematicsJet energy scale (~7%)Luminosity (11%)Control region statisticsLepton vetoDifferent MCb-jet fractionMC statisticsHigher orders… more …
