Searches for supersymmetry with the ATLAS detector Nikola Makovec GDR Terascale 23 april 2012

Searches designed around expected signatures: ATLAS strategy Strong production: Large production cross section 1st/2nd squarks and gluinos production Rich phenomenology of final states to explore Cascade decays Stops and sbottoms in gluino decays 3rd squark direct production: Expected to be the lightest squarks Extremely challenging: Small cross-section Difficult to disentangle from bkg Multiple decay scenarios to cover Electroweak chargino/neutralino production Very low cross-section Relevant when colored spartners are too heavy Good sensitivity in multi-leptons channels Non-”canonical” scenarios: R-parity violation LSP decays Semi-stable SUSY particles … Searches designed around expected signatures: Jet+MET+N lepton(s), b-tagged jets, multileptons final, tau final states, photon final states, resonances, displaced vertex, disappearing track, stable massive particles,…. Nikola Makovec

ATLAS results Papers Conference notes Nikola Makovec https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults Nikola Makovec

Limits, limits, limits Nikola Makovec

I will mainly focus on 4 analysis. Outline 0-lepton+MET+jets (5fb-1) Direct sbottom (2fb-1) Disappearing tracks (5fb-1) 3 leptons +MET (2fb-1) I will mainly focus on 4 analysis. Documentation for all ATLAS analysis can be found at: https://twiki.cern.ch/twiki/bin/view/AtlasPublic/SupersymmetryPublicResults Nikola Makovec

Non-collision background R-parity conservation Supersymmetric partnairs are pair produced The LSP is stable and escapes detector unseen  Large missing transverse energy (MET) Possible sources of “fake MET”: Electronic noise in calorimeters Cosmic rays (muons) Beam halo: muons produced by the proton beams interacting with the pipe The understanding and the cleaning of the MET tails is crucial for susy searches Nikola Makovec

Non-collision background Event display of a typical beam induced background event, where a muon travelling almost parallel to the beam axis leaves a substantial energy deposit in the LAr calorimeter. Nikola Makovec

Non-collision background Events are rejected if they contain any jets failing quality criteria designed to suppress non-collision backgrounds Many tools were developed to detect fake calorimeter energy deposition not coming from collisions Tracking information: Knowledge of the signal pulse shape at the cell level Prediction Measurement ADC ADC Ionization signal Noise time time Nikola Makovec

0lepton+jets+MET Total of 11 signal regions Small M Trigger Against Increasing jet multiplicity squarks gluinos/cascades Trigger Against QCD Mass scale Events with leptons are vetoed Signal/background discrimination based on the effective mass sensitive to the SUSY mass scale: Total of 11 signal regions Nikola Makovec

Background estimation strategy signal region Z+jets W+jets SuSy? QCD Top Similar kinematical cuts in CR and SR Nikola Makovec

Background estimation strategy photon control region Isolated photon +jets W control region 30<MT(l,MET)<100GeV No b-jet z control region MC signal region MC |Mll-mZ|<25GeV Z+jets W+jets MC SuSy? QCD Top MC QCD control region top control region Reversed (jet,met) cut 30<MT(l,MET)<100GeV b-tag Data driven Similar kinematical cuts in CR and SR Control regions for each significant BG Orthogonal event selection A global likelihood fit for the normalization of each background from the 5 control regions is simultaneously performed separately for each signal region. Background cross contamination in control regions automatically taken into account Smaller backgrounds, e.g. diboson: MC only Nikola Makovec

Z+jets background Irreducible background Two control regions Z(ll)+jets same process but low BR γ+jets higher statistics but slightly different process: massless boson, different couplings Theoretical uncertainties for γ+jets were carefully studied arXiv:1107.2803, arXiv:1106.1423 Theoretical uncertainties (scales and pdf) largely extent to cancel in the ratio smaller than 10%  Z +jets bkg estimation comes mainly from the γ+jets CR Z(ll)+jets +jets +jets Nikola Makovec

Results and interpretation SRA 2J SRD 5J No discrepancy with respect to SM predictions* The result is interpreted as a 95% CL exclusion limit on effective cross sections using a profile likelihood ratio approach following the CLs prescriptions. Systematic uncertainties: Correlated systematic uncertainties between the CR and SR largely cancel out in the transfer factor. Dominant systematic uncertainty: JES/JER, MC modeling (ISR,…) 95% CL exclusion limit include signal theoretical uncertainties (PDF, scale,…) *detailed numbers are in the backup slides Nikola Makovec

Results and interpretation Simplified gluino-squark neutralino model All masses set to 5 TeV except neutralino1, gluino, degenerated 1st & 2nd generation squarks Large mass splitting limit LSP mass set to 0. For each point, the SR with the best expected exclusion is used to evaluate whether the point is excluded or not. Results roughly unchanged for m(LSP) up to 200 GeV Nikola Makovec

Results and interpretation MSUGRA/CMSSM plane with tan = 10 ; A0 = 0 ; μ > 0 lepton can be produced in the cascade Nikola Makovec

Results and interpretation Zoom on the high m0 region decay chains can be long through several intermediate particles. The gluinos and squarks are expected to decay through a (possibly lengthy) cascade to lighter sparticles plus SM particles, until the decay chain terminates in the (stable) lightest SUSY particle (LSP) 0lepton+MET/HT+6-9jets Based on met significance Search for long decay chains without leptons ATLAS-CONF-2012-037 1lepton analysis Improved statistical method: simultaneous fit to multiple signal regions and to the shapes of distributions ATLAS-CONF-2012-041 Nikola Makovec

3rd generation Broad program of 3rd generation squark searches underway on ATLAS Gluino mediated sbottom/stop pair production Bjets + MET + 0/1 lepton: arXiv:1203.6193 Multijets: ATLAS-CONF-2012-037 2 same-sign leptons + jets + MET: arXiv:1203.5763 Direct sbottom/stop pair production stop pair production Effort ongoing but harder because numerous decay chains Cross-section is small, difficult to distinguish from top pairs sbottom pair production => 2 b-jets + MET If SUSY solves the hierarchy problem naturally, then 3rd generation squarks must be light Nikola Makovec

Direct sbottom Event signature: Exactly 2-b-tagged jets+MET SR defined with the boosted-corrected contransverse mass mCT Endpoint Sbottom: Top: 135 GeV JHEP 0804, 034 (2008) JHEP 1003, 030 (2010) Main Backgrounds : top, W+HF, Z+HF estimated using transfer factors from two control regions top,W+HF CR Z+HF CR Nikola Makovec

Direct sbottom Good agreement between data and SM prediction in the 3 signal regions : mCT > 100, 150, 200 GeV For each point, the SR with the best expected sensitivity is used to extract the limits msbottom < 390 GeV excluded for m(0) < 60 GeV Nikola Makovec

Long Lived Particles (LLP) signatures Signatures expected in several models R-hadrons, R-parity violation, very compressed spectra (AMSB),… Ex: RPV decays of LSP PLB 707 (2012) 478 Ex: AMSB model: neutralino and chargino are nearly mass degenerate ATLAS-CONF-2012-034 Ex: Long-lived sleptons or R-hadrons (gluino or squarks binding with other quarks) ATLAS-CONF-2012-022 PLB 703 (2011) 428 PLB 701 (2011) 1 Nikola Makovec

Disappearing tracks AMSB model: neutralino and chargino can be nearly mass degenerate Long Lived chargino Search for high-pt tracks that stop in outer TRT tracker in jets+MET events (strong production) Background: Nikola Makovec

Disappearing tracks AMSB model: neutralino and chargino can be nearly mass degenerate Long Lived chargino Search for high-pt tracks that stop in outer TRT tracker in jets+MET events (strong production) Background: Limit as function of lifetime for a 90.2 GeV chargino Nikola Makovec

Direct gauginos with leptons Weak gauginos are expected in ~100 GeV range (naturalness) Direct production may be the dominant SUSY process (favored in decoupling scenarios) arXiv:1201.5382 Weak gauginos can decay via gauge bosons, higgsinos, sleptons (daughters can be virtual) Look at leptonic decays to reject SM background 2 leptons (Phys. Lett. B709, 137 1fb-1) 3 leptons (ATLAS-CONF-2012-023 2fb-1) 4 leptons (ATLAS-CONF-2012-001 2fb-1) Nikola Makovec

3 leptons analysis SR1 Baseline signal region 2 signal regions Exactly 3 signal leptons PT > 10 GeV MET > 50 GeV At least one SFOS pair 2 signal regions SR1 Z depleted signal region Veto Zs with |MSFOS - MZ| < 10 GeV Veto B-jets SR2 Z enriched signal region Require |MSFOS - MZ| < 10 GeV Nikola Makovec

3 leptons analysis Irreducible background SR1 Reducible background: processes with 3 real, isolated leptons (WW,WZ,ttbar+V) derived from simulation with cross sections at NLO Reducible background: processes with fake leptons (mainly HF) Processes with 3 fake leptons are negligible Data driven estimation Background estimation checked in 2 validation regions Zdominated (VR1): 3 leptons, 30<MET<50GeV Top dominated (VR2): 3leptons, SFOS lepton pairs vetoed SR1 Nikola Makovec

3 leptons analysis pMSSM Simplified models M1=100GeV tan()=6 Heavy gluinos, squarks and heavy left handed sleptons Simplified models Nikola Makovec

Conclusion Many different searches for supersymmetric particles at ATLAS No excess above the SM expectation has been observed so far. Several analyses are in the process of being updated to the full 2011 dataset. We look forward to 8 TeV running this year. LHC already performing well!!! TO BE UPDATED Peak instantaneous: 5.12×1033 cm−2s−1 Nikola Makovec

Back up Nikola Makovec

2011 data taking Luminosity Trigger challenge: Pile-up challenge: Integrated : ~5fb-1 Peak instantaneous: 3.65×1033 cm−2s−1 Trigger challenge: main limitation for many analysis MET-only trigger threshold up to 180 GeV Pile-up challenge: Increase of average interactions per bunch crossing <> from 6 to 12 Significant in-time and out-of-time pileup Sizable impact on : Reconstruction CPU time Reconstructed vertices Calorimeter response (in-time and out-of-time pile-up) Jet energy scale and Etmiss resolution Lepton isolation … Nikola Makovec

+ Supersymmetry = 0 Symmetry that relates bosons and fermions Every SM particle has a superpartner differing by half a unit of spin Higgs sector extended to 5 Higgs But it must be a broken symmetry, since the superpartners of the SM particles have not been observed  superparticles should be heavier than the corresponding SM particles. Why supersymmetry is popular? Gauge Coupling Unification With the addition of minimal SUSY, joint convergence of the coupling constants is projected at approximately 1016 GeV Provide a candidate for the dark matter R-parity conserved scenario Elegant solution to the hierarchy problem The fermion and boson contribution to the Higgs mass cancel Only true if supersymmetry exists close to the TeV energy scale H f ~ + = 0 Nikola Makovec

Supersymmetric models New quantum number: R-parity MSSM: Minimal extension to the Standard Model that realizes supersymmetry with R-Parity conservation: SuSy particles are pair produced The LSP is stable and escapes detector unseen (DM candidate) Assumed to be the lightest neutralino MSSM introduces 105 new parameters Difficult to handle Need different approaches Top-down approaches Model of SUSY breaking: gravity mediated, gauge mediated... Assume GUT scale parameters (few) Predict phenomenology at the EWK scale (RGE) Ex: mSUGRA (a.k.a cMSSM): Supersymmetry breaking mediated via gravitational interaction Only 5 parameters: m0,m1/2,A0,tan,sign() Bottom-up approaches Phenomenological models Assume mass & hierarchy for SUSY particles Simplified models: Assume single decay chain (building block) Standard particles (R=+1) - 1 (SM) +1 (SUSY) SuSy particles (R=-1) Nikola Makovec

0lepton Nikola Makovec

Nikola Makovec

Nikola Makovec

Searches designed around expected signatures: ATLAS strategy Strong production: Large production cross section 1st/2nd squarks and gluinos production Rich phenomenology of final states to explore Cascade decays Stops and sbottoms in gluino decays … 3rd squark direct production: Expected to be the lightest squarks Extremely challenging: Small cross-section Difficult to disentangle from bkg Multiple decay scenarios to cover Electroweak chargino/neutralino production Very low cross-section Relevant when colored spartners are too heavy Good sensitivity in multi-leptons channels Non-”canonical” scenarios: R-parity violation LSP decays Semi-stable SUSY particles … Searches designed around expected signatures: Jet+MET+N lepton(s), b-tagged jets, multileptons final, tau final states, photon final states, resonances, displaced vertex, disappearing track, stable massive particles,…. Nikola Makovec