We present searches for generic SUSY models with R-parity conservation in the ATLAS detector at the LHC, based on signatures including missing transverse momentum from undetected neutralinos, multiple jets and leptons or b- and tau-jets. We also show the techniques developed to reconstruct the decays of SUSY particles. We concentrate on strategies to be applied to the first fb^(-1) of ATLAS data

Consonni, M

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Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsProspects for SUSY Discovery and Measurementswith the ATLAS Detector at the LHCMichele Consonni, on behalf of the ATLAS CollaborationRadboud University Nijmegen/NikhefPANIC08 - Eilat, Israel - 11 November 20081 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsOutline1 Introduction2 Inclusive searches of EmissT signatures3 Exclusive measurements4 Long-lived heavy particles5 Conclusions2 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsSupersymmetrySymmetry: bosons ←→ fermionsConsider minimal extension of SMAt LHC: production of stronglyinteracting SUSY particlesCross-section mostly dependent onparticle massesDecay chains model dependentTopics covered:R-parity conserving scenarios onlyEmissT signaturesLong-lived heavy particlesBenchmark models:mSUGRANUHMGMSB3 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsSUSY signaturesq˜Lχ˜01q˜Rq qχ˜02ℓ˜∓ℓ±χ˜01ℓ∓ppEmission of hard jets and leptonsIf the lightest SUSY particle is neutraland weakly interacting⇒ Missing energy in the detectorMain backgrounds:Z/W + jetstt¯QCD events4 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsEmissT signatures: zero- and one-lepton modesEffective Mass [GeV]0 500 1000 1500 2000 2500 3000 3500 4000-1events / 200 GeV / 1fb110210310410SU1SU2SU3SU4SU6SU8.1SM BGATLAS PreliminaryEffective Mass [GeV]500 1000 1500 2000 2500 3000-1events / 200 GeV / 1fb-110110210310 SU1SU2SU3SU4SU6SU8.1SM BGATLAS PreliminaryEmissT > 100 GeV + 4 jets + 0 (left) or 1 (right) leptonEffective Mass =∑jets,ℓ pT + EmissTLepton requirement to bring background down to manageablelevels5 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsEmissT signatures: other modesBroad spectrum of EmissT signatures (not covered here):Two and three leptons + jetsτ -jets + jetsb-jets + jetsMulti leptons (No requirements on the number of jets)=⇒ Direct production of χ˜0 and χ˜±Photons + jets=⇒ χ˜01 → G˜γAll signals and backgrounds studied with fully detailedGeant 4 simulations6 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsBackground estimation from dataPrecise estimate of background relies on both MC and dataControl samples needed for data driven estimatesExample: reverse one selection cutSignal region MT ≡ ~pT ,ℓ · ~EmissT > 100 GeVControl region MT ≡ ~pT ,ℓ · ~EmissT < 100 GeVEffective Mass [GeV]500 1000 1500 2000 2500 3000 / 200GeV−1Events / 1fb−110110210estimated BGSM BGttWZsingle topATLAS PreliminaryBackground shape fromcontrol sampleNormalize to number ofevents in signal sample in aregion where SUSYcontribution is small(EmissT < 200 GeV)7 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsSystematic effectsDetector response challengesLepton identification efficiencyJet energy scale and jet response tailsMissing ET shapeTheoretical uncertaintiesParton Density FunctionsNormalization of backgroundEW and QCD corrections at NLOSUSY contamination in control samples8 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsDiscovery reach [GeV]0m0 500 1000 1500 2000 2500 3000 [GeV]1/2m020040060080010004 jets 0 lepton4 jets 1 lepton4 jets 2 leptons OS1 jet 3 leptons (0.5 TeV)q~ (1.0 TeV)q~ (1.5 TeV)q~ (2.0 TeV)q~ (2.5 TeV)q~ (0.5 TeV)g~ (1.0 TeV)g~ (1.5 TeV)g~ (2.0 TeV)g~ATLAS Preliminary discoveryσ5  = 10 βMSUGRA tan NO EWSB LSP1τ∼ (103 GeV)+1χ∼ [TeV]Λ10 20 30 40 50 60 70 80βtan 51015202530354045 4 jets 2 lepton (OS)1 jet 3 lepton  (0.5 TeV)q~  (1.0 TeV)q~  (1.5 TeV)q~  (2.0 TeV)q~ (1.0 TeV)g~  (1.5 TeV)g~  (2.0 TeV)g~ATLAS Preliminary discoveryσ5 GMSBTACHYONICmSUGRA and GMSB scan1 fb−1 ∼ 1 year of LHC operationReach up to gluino and squark masses ∼ O(1 TeV)Stat. and syst. uncertainty on background included9 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsEndpoint measurementsMass spectrum informations from cascade kinematicq˜L → χ˜02q → (ℓ˜∓ℓ±q)→ χ˜01ℓ−ℓ+qEndpoints in invariant mass distributionsℓ+ + ℓ−ℓ+ + ℓ− + qℓ± + qFor instanceMedgeℓℓ = mχ˜02√√√√1− m2ℓ˜m2χ˜02√√√√1−m2χ˜01m2ℓ˜10 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsLeptonic signaturesm(ll) [GeV]0 20 40 60 80 100 120 140 160 180 200-1Entries/ 4 GeV / 0.5 fb020406080100120140160180SU4 OSSFBKG OSSFSU4 OSDFBKG OSDFATLAS Preliminarym(ll) [GeV]0 20 40 60 80 100 120 140 160 180 200-1Entries/4 GeV/ 0.5 fb-40-20020406080100120 / ndf 2χ   10.5 / 16Prob   0.839Norm      8.971± 70.07 M1+M2     8.267± 67.71 M2-M1     2.439± 52.68 ATLAS PreliminaryBackground significantly reduced by subtracting e±µ∓Medgeℓℓ = 52.7 ± 2.4 (stat) ± 0.2 (syst) GeVConsistent with true value 53.6 GeV11 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsOther signaturesτ+τ− invariant mass [GeV]ττM0 20 40 60 80 100 120 140 160 180-1entries / 10GeV/ 1fb-505101520ATLAS PreliminaryL− R mixing may enhanceτ+τ− with respect to ℓ+ℓ−No sharp edge because ofneutrino presenceHiggs to bb¯ in SUSY events (GeV)bbM0 50 100 150 200 250 300 350 400)-1Events (1/8 GeV/10 fb0102030405060708090 ATLAS Preliminary SignalComb BGSusy BGStandard Model BGGauss+Pol2EmissT requirementsuppresses QCD backgroundCompetitive with SMchannels12 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsLong-lived heavy particles: trigger issuesAssume the lightest SUSY particle is charged or stronglyinteractingPenetrating charged track ⇐⇒ “heavy slow muons”For β ∼ 0.8 ⇒ Time of flight 15 ns longer than muonsATLAS muon system provides excellent time of flightresolution (0.7 ns)⇒ Precise mass reconstruction and muon rejectionBut very high LHC bunch-crossing rate (25 ns)Particle could be assigned to the wrong bunch crossing andnot read outAppropriate triggering scheme is critical13 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsLong-lived heavy particles: discovery reachStable sleptonsreconstructed mass (GeV)0 20 40 60 80 100 120 140 160 180 200events/bin0100200300400500600700800ATLAS PreliminaryExample: 100 GeV sleptonDiscovery largelyindependent of the modelcharacteristicsR-hadronsSample Events/fb−1300 GeV gluino 6.4× 1031 TeV gluino 10.71.6 TeV gluino 0.1300 GeV stop 70.0600 GeV stop 3.91 TeV stop 0.1QCD events . 1Z → µµ . 1Characteristic “heavy slowmuon” signatureMay also undergo chargeflipping in the calorimeter14 / 15Introduction Inclusive searches of EmissT signatures Exclusive measurements Long-lived heavy particles ConclusionsConclusionsNew physics expected to appear at the TeV scaleR-parity conserving SUSY scenarios are well motivatedExtensive studies of signatures:With EmissTWith long-lived heavy particles⇒ Reach up to gluino and squark masses ∼ O(1 TeV) for 1 fb−1Discovery relies on good knowledge of backgroundsInterplay between MC and data-driven estimations15 / 15

Prospects for SUSY Discovery and Measurements with the ATLAS Detector at the LHC

We present searches for generic SUSY models with R-parity conservation in the ATLAS detector at the LHC, based on signatures including missing transverse energy from undetected neutralinos, multiple jets and leptons or tau- and b-jets. We also show the techniques developed to reconstruct the decays of SUSY particles. We concentrate on strategies to be applied to the first inverse fb of ATLAS data

ATL-PHYS-PROC-2008-08117December2008Prospects for SUSY Discovery and Measurements withthe ATLAS Detector at the LHCMichele Consonni, on behalf of the ATLAS CollaborationRadboud University Nijmegen/NIKHEF, Department of Experimental High Energy Physics,Toernooiveld 1, NL-6525 ED Nijmegen, NetherlandsAbstractWe present searches for generic SUSY models with R-parity conservation in the ATLAS de-tector at the LHC, based on signatures including missing transverse energy from undetectedneutralinos, multiple jets and leptons or τ - and b-jets. We also show the techniques developedto reconstruct the decays of SUSY particles. We concentrate on strategies to be applied to thefirst fb−1 of ATLAS data.Key words: SUSY, ATLAS, LHCPACS: 29.85.Fj, 14.80.Ly1. IntroductionSupersymmetric (SUSY) extensions of the Standard Model (SM) [1,2] are among thebest motivated models of new physics and predict a large spectrum of new, unobservedparticles with mass at the TeV scale, which are therefore expected to be produced at theLHC.The Minimal Supersymmetric Standard Model (MSSM) contains the minimal possibleaddition of particles. It associates to each SM particle a partner with spin differing byhalf a unit. Moreover, in order to avoid couplings that lead to a rapid proton decay, a newdiscrete symmetry, R-parity, is introduced. It turns out that all the ordinary SM particlesand the Higgs bosons have positive R-parity, while their supersymmetric partners haveR = −1. Three important phenomenological implications follow: in collider experiments,SUSY particles are produced in even number; each SUSY particle can decay only into astate containing an odd number of SUSY particles; the lightest SUSY particle (LSP) isstable.The experimental signature of supersymmetry at collider detectors is different depend-ing on the nature of the LSP. In this work, we will concentrate on models wih neutral andPreprint submitted to Elsevier 17 December 2008 [GeV]0m0 500 1000 1500 2000 2500 3000 [GeV]1/2m020040060080010004 jets 0 lepton4 jets 1 lepton4 jets 2 leptons OS1 jet 3 leptons (0.5 TeV)q~ (1.0 TeV)q~ (1.5 TeV)q~ (2.0 TeV)q~ (2.5 TeV)q~ (0.5 TeV)g~ (1.0 TeV)g~ (1.5 TeV)g~ (2.0 TeV)g~ATLAS Preliminary discoveryσ5  = 10 βMSUGRA tan NO EWSB LSP1τ∼ (103 GeV)+1χ∼Fig. 1. Left: effective mass distribution for a set of benchmark scenarios and for the SM background, inthe 1-lepton and 4-jet channel. Right: discovery contours in the Minimal Supergravity parameter space,for different search channels and for an integrated luminosity of 1 fb−1.weakly interacting LSP’s, that escape the detector without leaving any trace or energydeposit. However, thanks to the hermetic coverage of the ATLAS detector, an imbalanceof the total transverse energy measured, called missing transverse energy (EmissT ), canbe reconstructed.2. Inclusive searchesStrongly interacting SUSY particles, such as squarks and gluinos, will dominate theSUSY production at the LHC if their mass is in the TeV range. Their decay products willcontain two LSP’s and a number of SM particles, in particular highly energetic quarksand gluons. Typical SUSY signatures are therefore based on large missing transverseenergy and hard jets. Detailed studies have been carried out for a wide range of channels,including 0-, 1-, multi-lepton modes, as well as signatures involving τ - and b-jets. Selectioncuts are discussed in [3]. After applying a set of selection cuts, SUSY production isevident in the distribution of the effective mass, defined as the scalar sum of EmissT andthe transverse momentum of each of the requested particles.Figure 1 shows such distribution for a set of benchmark scenarios and for the SMbackground in the 1-lepton and 4-jet channel. In most of the cases, a noticeable excessof events is observable at high effective mass values already with 1 fb−1 of integratedluminosity, an amount of data that is expected to be collected within the first one or twoyears of LHC running.The right plot of Figure 1 shows the discovery contours for the same luminosity inthe (m0,m1/2) parameter space of the Minimal Supergravity model [2]. The remainingparameters are fixed to tanβ = 10, A0 = 0 GeV and positive µ. Squark and gluinomasses of the order of up to 1 TeV can be reached.3. Exclusive measurementsSince the cascade chain of SUSY particles always ends up with an LSP that escapesdetection, no invariant mass peak of supersymmetric particles can be reconstructed at2m(ll) [GeV]0 20 40 60 80 100 120 140 160 180 200-1Entries/4 GeV/ 0.5 fb-40-20020406080100120 / ndf 2χ   10.5 / 16Prob   0.839Norm      8.971± 70.07 M1+M2     8.267± 67.71 M2-M1     2.439± 52.68 ATLAS Preliminary (GeV)bbM0 50 100 150 200 250 300 350 400)-1Events (1/8 GeV/10 fb0102030405060708090 ATLAS Preliminary SignalComb BGSusy BGStandard Model BGGauss+Pol2Fig. 2. Left: reconstructed ℓ+ℓ− invariant mass distribution for a benchmark scenario and after back-ground subtraction. Right: reconstructed bb¯ invariant mass distribution for a benchmark scenario andfor the SM background.the LHC. Invariant masses of two or more particles coming from the same cascade may,however, show structures, such as thresholds and edges, that can provide informationabout the mass spectrum of the model.The cleaner, thus more powerful, channel is the di-leptonic signature. Figure 1 showsthe reconstructed ℓ+ℓ− invariant mass distribution for a benchmark scenario and afterbackground subtraction. The endpoint corresponds in this case to the mass differencebetween the lightest and the next-to-lightest neutralino. With 1 fb−1 of data, its valuecan be measured with an uncertainty of less than 3 GeV, dominated by statistical effects.Similar investigations have been performed for channels containing leptons plus jets ora pair of τ -jets.A particularly interesting signature arises from the emission of a Higgs boson duringthe cascade decay of a SUSY particle. In this case, the missing transverse energy producedin association with the Higgs boson can be exploited to reduce the background, makingit possible to study the dominant decay h→ bb¯, otherwise hidden by the enormous QCDcontinuum. The reconstructed bb¯ invariant mass distribution for a benchmark scenario isreported in the right plot of Figure 2. For 10 fb−1, the Higgs resonance peak is clearlyvisible over the background.4. ConclusionsSupersymmetry with R-parity conservation with particle masses below the TeV scaleshould be accessible by the ATLAS experiment with a few years of running. A broadspectrum of search channels have been investigated to cover many different SUSY sig-natures. Once a signal is established, kinematic endpoints in specific SUSY decay chainscan be exploited to reconstruct the mass spectrum of the model.References[1] H.P. Nilles, Phys. Rept. 110 (1984) 1.[2] S.P. Martin, (1997), hep-ph/9709356.[3] ATLAS Collaboration, CERN-OPEN-2008-020, Geneva, to appear.3

Prospects for SUSY Discovery and Measurements with the ATLAS Detector at the LHC

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