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ATLAS Review and Main ResultsRyszard StroynowskiSouthern Methodist University On behalf of theATLAS Collaboration

2Standard Model Matter is made of quarks and leptonsTheir interactions are governed by Gauge theories SU(2)L U(1) Electroweak & SU(3): StrongThe forces are transmitted by Gauge bosons: g, W, Z0: Electroweak Gluon : Strong Particles receive mass through interaction with the Higgs boson

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Standard Model Lagrangian3The problem of the origin of mass The problem of mass scalesDark matterEvolution of the universeParticle-antiparticle asymmetry in the universeUnification of gravity with the other forces4 What is the origin of the electroweak symmetry breaking Loop corrections blow up at high energies Where is the Higgs boson ?

The problems with the Standard Model

Expect new physics at the energy of ~ 1 TeV

5Dark Side of the Universe: Dark Matter

Dark MatterGaseous Matter

Dark (invisible) matter!Dark Matter appears to be weakly interacting massive particleLightest SUSY particle has these properties !5WIMPs ?556Why High Energy Accelerators?

Reproducible results Large mass E=mc2 Spatial resolution =h/p Elementary particles may be a sourceof dark matter

ATLASALICECMSLHCbLarge Hadron Collider7

ATLAS Detector2T solenoid, toroid system Tracking to ||=2.5, calorimetry to ||= 4.9

Electronisolated track with matching em cluster, from tracking, energy from calorimeter Muonisolated, combined track (ID and muon spectrometer) Photonisolated em cluster (no track) pointing to the vertex 2 tracks conversion: 2 electrons fitted to separated vertex 1 track conversion: 1 TRT track with with high ionization Tau (hadronic) tracking + calorimeter signal shape Jet energy deposits in calorimeters anti-kT algorithm, pT(jet) > 25 GeV b-jetjet with displaced vertex, L / (L) > 5.7 ETmiss energy imbalance in transverse plane from topological clusters in the calorimeters

ATLAS Experimental observables14

electronphotonb-jetmuonSignatures

0DetectorIn time LAr pileupmultiple (4-12) interactions per bunch crossingrequirements: precise vertex determination, photon pointing, spatial isolation of electron and photonsOut of time pileupcalorimeter signal collection time spans up to 8 bunch crossingssignal shape matching with expectationsPhoton conversionsabout 60% of photons converts in the tracker material before reaching calorimeterearly conversions reconstructed from 2 tracks, energy measured in the calorimeterlate conversions reconstructed from single tracks in TRTCosmic muonsremoved by the vertex and timing constraintsCalorimeter calibrationelectrons-Use calibration signals + Geant4 simulations based on test beam results + tag and probe signals from J/psi + Z photons-use Geant4 simulation + fudge factors to fix shower shapemuons- simulations + J/psi and Z signalsjets-simulationsmissing ET-simulationsDetailsData Collection Superb LHC performanceData collection efficiency >95%2010 46 pb-1 March 295 pb-1 July 1.50 fb-1 August 19 2.50 fb-1

Luminosity measured with calorimeters + several dedicated detectors. Calibrated with the Van der Meer beam-beam scans.

L/L = 3.4% (2010)L/L = 3.7% (2011, preliminary)

Nev = Ldt A =95.3%

=95.3%

Trigger and pileupPrimary triggersInclusive electrons pT > 20 GeV 22 GeVInclusive muons pT > 18 GeVInclusive jets pT > 180 GeVMissing energy ETmiss > 60 GeVDiphotons pT > 20 GeV + several additional and monitoring triggersPileup 5-14 interactions per beam crossing

7 verticesPhysics resultsImpossible to discuss all recent results. Within last 18 months ATLAS Collaboration produced 61 journal papers and 217 conference notes. The following are selected recent highlights only.Top results - Ido Mussche; Higgs Craig Wiglesworth;Tau physics Mogens Dam

General method of searching for new physics is to look for deviations from the expectations and to interpret the results within a specific model.

First step is to verify that we understand well the known physics:multiplicity, particle spectra, jet distributions, vector boson production, t tbar production,

QCD and the Standard Model

from N. Varelas, EPC2011time

QCD - particle and jet production

Impressive agreement of data with QCD Monte Carlo predictions over many (up to 12) orders of magnitude.diphotons

multiplicityParticles within jets, ptjets, fragmentationJets, ptarXiv1107.331122

Dijet mass cross section Comparison to NLO + non-perturbative correctionsATLAS-CONF-2011-047Gauge bosons

Theory - NLO or higher

Z e e

W

No deviations from SMTriple gauge couplingCross sections24SUPERSYMMETRYExtension of the Standard Model (SM) - solves many theoretical problems unification of gauge couplings, cancellation of fermion and boson contributions to Higgs mass (hierarchy problem),.

Each SM particle has a partner with spin that differs by .

If R parity is conserved R = (-1)2j+3B+L SUSY particles are produced in pairs and lightest one is stable.

The minimal extension of the SM (MSSM) introduces 105 new parameters. SUSY is predictive about spins and couplings but says nothing about the masses.

Large number of models with additional assumptions that reduce the numbers of free parameters (e.g., mSUGRA, CMSSM have 5 parameters). For most of the models a typical decay chain has lowest mass supersymmetric neutral particle that escapes the detection missing energy (ETmiss). Bonus: dark matter candidate

SUSYExample: squark decaySignature ETmiss + leptons + 3 jets

Electron with pT > 25 GeV and at least 3 jets with pT > 60, 25, 25 GeV.

Observed and expected 95% CL exclusion limits

ATLAS-CONF-2011-090Missing ETuniversal scalar massgaugino mass

Missing ETEvents with one lepton + jetsATLAS-CONF-2011-090

Search for squarks and gluinosEvents with jets and no leptonsATLAS-CONF-2011-086SUSY cont.Missing Transverse Energy, ETmiss

SM - W n: Missing transverse energy spectrum.No sign of deviation from known processes

ATLAS-CONF-2011-098Observed and expected 95% CL exclusion Limits in the mass sbottom-gluino planeMore SUSY exclusion limitsModels with large mixing of right handed and left-handed squarks expect large cross section For heavy quark jets. Signature: b-jets, no leptons and and large missing ET.ATLAS-CONF-2011-098

95% CL upper cross section limits in pbfor gluino masses > 200 GeVBump hunting

Method

Compare the invariant mass distribution with an expected signal from a newresonance of a fixed mass. For a given distribution, simulate signal and vary the mass to obtain the limit. Include probability of statistical fluctuations for both signal and background to compare the measured limit with an expected one.

Lepton pairs search for Z Lepton + ETmisssearch for WDi-photonHiggs, search for gravitons, extra dimensions,Di-jet search for W, Z, squarks, gluinos, excited quarks, . e search for exotic statesZZ, WWHiggs, exotic states,..

Search for sequential SM-like bosonsMZ > 1.83 TeV @ 95% CL for SSMMZ > 1.50 1.64 TeV @ 95%CL for E6 MW > 2.15 TeV @ 95% CL observedMW > 2.23 TeV @ 95% CL expected

Search in transverse massZW

Di-muon massarXiv:1108.1316, 1582, 31 Search for di-jet resonances

Enhancement in the mjet-jet spectrumInterpretation: excited quarks, axigluons, color octet scalars

95% CL limits in TeVmodelexpectedobservedq* 2.77 2.91 axigluon 3.02 3.21 color octet 1.71 1.91

Generic limit onresonance Search for di-jet resonances associated with W

Generic limit onresonance

Signal: 2 jets + lepton + neutrino electron: ET > 25 GeV, || < 2.47, R = 0.3 muon: pT > 20 GeV, || < 2.4 , R = 0.2 jet: anti-kT algorithm, R = 0.4, mT > 40 GeV ETmiss > 25 GeV

No evidence for CDF bump but the WW/WZ associated production rate is smallATLAS-CONF-2011-0972-jet invariant massSignal/background ratioSearch for exotics in lepton pairs

Same sign di-lepton mass sources: Majorana neutrinos universal extra dimensions 4th generation down-like quarks

Opposite charge e resonance sources: sneutrions R-parity violating SUSY models Z with lepton violating interactionsSame charge pairsOpposite charge pairsarXiv:1108.0366ATLAS-CONF-2011-109

35SM Higgs searchesOne of the main motivation for building LHC and ATLASImportant results see talk by Craig WiglesworthATLAS searches in many channels:H ggH ZZ* llll, llnn, llqq (l = e, m)H WW* lnln, lqq H ..

Combined constraints (EPS)ATLAS excludes at 95%CL 146 < mH < 232 GeV 256 < mH < 282 GeV 296 < mH < 466 GeV

Summary Limits for new physics ~ >1 TeV (>3 TeV for some exotic models).

No evidence for Supersymmetry so far.

Search for SM Higgs boson narrowed its possible mass range.

About a factor of 2 of data collected since EPS but not yet analyzed.

LHC works better than expected. ATLAS performance is excellent. Wealth of data allows for new ideas to be tested.

Exciting times. Backup slidesExotic Monojets

Monojet high ET jet + ETmissStandard Model process: single jet + Z with Z Ahmed-Arkani, Dimopulos, Dvali model with extra dimensionsmonojet pT is balanced by graviton that does not interact with detector. Model is characterized by MD a 4 + n-dimensional Planck scale

No excess above SM processesCross section limitsfor 2 and 4 extra dimensions

Methodology

What our Universe is made of ? A new set of particles, known as Supersymmetric particles, could explain the dark matter (but NOT the dark energy!)41Search for squarks and gluinos

Signature ETmiss + jets

Jet: anti-KT, R=0.4 pT>20 GeV, || 0.25