SUSY Search at CMS Jet+MET+0 lepton analysis Jet+MET+leptons analysis MET independent analysis Conclusions Anwar A Bhatti The Rockefeller University On behalf of CMS Collaboration LHC Dark Matter Workshop Michigan Center of Theoretical Physics January 6-10, 2009
SuperSymmetry A symmetry between fermions and bosons S=0 or S=1 S=½ Avoids fine-tuning of SM, can lead to GUTs Assume LSP is stable possible dark matter candidate SUSY breaking mechanism is unknown many parameters msugra: supergravity inspired model 5 free parameters: m 0, m ½, A 0, tan(β) and sign(µ) Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 2
Supersymmetry at CMS LM1 60,250 GeV Final state typically has multiple jets and large missing transverse energy. Cross sections depend on the SUSY parameters, specially masses of squarks and gluinos. Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 3
Benchmark Point LM1 m 0 =60 GeV, m ½ =250 GeV, tan(β)=10,a 0 =0,sign(µ)>0 Gluino mass = 600 GeV, squark mass =320 GeV Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 4
Inclusive Jet+MET Analysis Standrad Model Processes QCD W+jet (leptons) Z+jets (leptons) tt 10 10 pb 7x10 4 pb 7x10 3 pb 800 pb SUSY LM1 ~50 pb Require large MET and multi-jets to suppress the SM backgrounds. Use data-driven techniques to estimate backgrounds. Event Selection: Cleanup No leptons (no e,µ, isolated tracks, EM rich jets) Three leading jets with Pt>180, 110, 30 GeV HT = PtJet2+PtJet3+PtJet4+MET >500 GeV MET> 200 GeV Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 5
Missing Transverse Energy Cosmic Ray Muon Air Shower Cosmic Muon Energy: 250 GeV (ECAL) Event Cleanup 1 primary vertex Activity in Ecal, Hcal and tracker Halo Muons in CSCs and HB >0.175 > 0.1 Not a big issue as long as such events do not overlap with real pp collision. Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 6
Lepton Veto (remove W/Z/tt background) Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 7
QCD Background Events MET in QCD is due mis-measured jets and is in the same direction as the jet. R = ϕ + ( π ϕ ) > 0.5 1,2 2 1,2 2 1,2 where ϕ ϕ ϕ = jet1,jet2 1,2 MET QCD Even after these cuts, QCD is the largest background at LM1. SUSY@LM1 Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 8
Data-driven technique: Matrix Method For uncorrelated X,Y, background in C: C= D (B/A) Signal contamination in A,B,D should be small. Additional corrections if X and Y are correlated. Possible pair: MET and Δφ(Jet,Met) min Working on optimizing the procedure. Variable Y B Background A Background C Signal+BG D Background Variable X Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 9
Data Driven Technique: Jet Smearing MET in QCD events arises from the fluctuations in detector response to jets. The high MET tail in multi-jet events can be determined by smearing the jets in the low MET region using detector response functions. Response can be measured in wellunderstood data: multijet events dijet events photon-jet events Use response function to predict high MET region Response Function MET (GeV) Based on earlier ATLAS work PtCaloJet/PtParticleJet Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 10
Top Background MET Template: Events passing SUSY cuts but require a lepton and MT(lepton, MET) <100 GeV MET distribution same as the background except lepton. Normalize the MET template to the data in low MET region 100< MET<200 GeV. Works quite well if no SUSY contamination in normalization region. Effect of SUSY contamination in normalization region on the background estimate is under study. Semi-leptonic decays are dominant. not-identified Non-isolated Template Norm. Region Data Based on earlier ATLAS work MET MET Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 11
Irreducible Background: Z νν Data-driven Estimation I (Z+jets) Standard Candle: use Z µµ Replace leptons by neutrinos Total uncertainty ~20% for 1 fb -1 Statistically limited Br(Z µµ)= 1/6 Br(Z νν) Data-driven Estimation II (W,γ+jets) Gain in statistics: σ(z+2jet)=σ(w+2jet)/3=σ(γ+2jets)/0.8 Only Z µµ (ee) are usable. 3.3% Approximation: V+jets events at high p T have similar event shapes. Z νν background estimate (100 pb -1 ) MC-truth 35 From γ+jet 29±3(stat)±5(sys) From W+jets 35±10(stat)±8(sys)±3(theoy) More details in talk by James Lamb, later in the session. Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 12
Discovery Potential m g SUSY LM1 = 600GeV m =, q 520GeV SUSY LM1 discovery possible with < 10 pb -1 of data at s= 14 TeV. Acceptance ~13% Signal QCD Top pair Z(νν) W/Z Single top 6319 107 54 48 33 3 Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 13
Search for SUSY using leptonic decays g qq qqχ qqll qqllχ 0 0 2 1 Muon identification: Good track Good matching muon stub No additional track around the tracks No large energy deposit around muon track in calorimeter. Concentrating on muons: Relatively easy to identify Good momentum resolution Small SM backgrounds Low susy cross section but still good S/B and S/ B Sources of muons:(no particular order) b/c quarks (semi-leptonic decays) W/Z/top quark decays decay-in-flight τ-leptons cosmic rays mis-identified hadrons (punch through) new physics Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 14
Inclusive muon+met+jets analysis 1 muon with p T >30 GeV MET>130 GeV At least three jets: 440, 440, 50 GeV optimized η cuts cos[δφ(jet1,jet2)]<0.2 Cuts on Δφ(jet 1,2,3,MET) 5σ reach contour Excellent sensitivity to all LM benchmark points. Event Yield (1 fb -1 ) LM1: 300 events (efficiency=0.07%) BG: 3 events with uncertianty~20% Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 15
Same-sign Di-muon+MET+Jets Analysis Same sign muon (P T >10 GeV) 2 χ2 3, nhits 13, E E T miss 200 GeV 1 st Jet E T 175 GeV 2 nd Jet E T 130 GeV 3 rd Jet E T 55 GeV Expected events for 1 fb -1 @14 TeV Sample Events msugra LM1 17 tt µ µ Iso µ 1 µ 2 10 GeV, EIso 6 GeV 0.3 W/Z+jets 0.05 QCD 0.01 Tevatron 5σ reach contours A0=0, tan(β)=10, sign(µ)=+1 LEP g qqµ ± νχ q qµ ± νχ 0 1 0 1 Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 16
Dilepton+Jets+MET, mass edge Observation and measurement of χ 0 0 2 χ 1 ll SUSY di-lepton analysis in the talk by Oliver Gutsche Friday January 9th 2:00 pm Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 17
MET Independent Search Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 18
Dijet Search Signal: If, no cascade decays through gluinos Two jets uncorrelated in Pt and direction 0. 0 Mainly sensitive to q qχ0, q qχ2 qχνν 1,... 1 Backgrounds m q < m QCD dijets: back-to-back, similar p T s Z νν: Irreducible background W (e,µ) ν: MET when (e,µ) out of acceptance. g Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 19
MET-independent Dijet Search α(randal-tucker-smith) arxiv:0806.1049 Transverse α T QCD : back to back jets α(α T ) 0.5. SUSY: α (α T ) can be > 0.5. Analysis does not rely on missing transverse energy. Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 20
Event Selection HT>500 GeV Third jet veto pt< 50 GeV Δφ(MHT,jet 1,2,3 )>0.3 rad Lepton veto η(jet1) <2.5 H = p + p MHT = p + p T J1 J2 J1 J2 T T T T Δφ(jet1,jet2) α α T Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 21
Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 22
Expected Event Yield Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 23
Data-Driven Background Estimation Signal is in the central region. Use the ratio R= N( α > 0.55)/ N( α < 0.55) T in forward region to predict the background in the central region. R= C/D (assumed to be independent of η.) T Pre-selection (no η cut) + HT>500 GeV B( background) = A R α T 0.55 B(Signal+BG) A(BG+some signal) ~2 million QCD+~2K tt/w/z+~1k SUSY η of lead jet C(BG) D(BG) 0 2.5 4 Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 24
Background Estimation Simulated signal+bg α T >0.55 Estimated background α T >0.55 Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 25
Signal Topology: Two squarks decaying into two quarks+ two LPS. Squark-squark dominates Squark-gluino contributes when g qq Background: QCD :0, Z νν 57, W/Z 19, Total 86 Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 26
Summary The results from global run data look very good. Rate of events with large MET is low. The dijet analysis looks very promising. Ready to analyze the real collider data. Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 27
BACKUP
Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 29
CMS: Compact Muon Solenoid Total weight: 12,500 t Diameter: 15 m Overall Length: 22 m Magnetic field: 3.8 Tesla SUPERCONDUCTING COIL CALORIMETERS ECAL Scintillating PbWO4 crystals HCAL Plastic scintillator/brass sandwich IRON YOKE TRACKER Silicon Microstrips Pixels MUON BARREL Drift Tube Resistive Plate Chambers ( DT ) Chambers ( RPC ) MUON ENDCAPS Cathode Strip Chambers (CSC ) Resistive Plate Chambers (RPC) Muons: η <2.4 momentum resolution: dp T /p T ~1% (p T ~25 GeV) Calorimetry: Hadron η <5.0, δe/e ~ 70% / E + 8% EM η <3.0, δe/e ~ 2.8% / E + 0.3% + 12% / E Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 30
CDF limits tan(β)=5, A 0 =0 and μ<0. Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 31
Signal: If, no cascade decays through gluinos Two jets uncorrelated in Pt and direction 0. 0 Mainly sensitive to q qχ0, q qχ2 qχνν 1,... 1 Backgrounds m q < m QCD dijets: back-to-back, similar p T s Z νν: Irreducible background W (e,µ) ν: MET when (e,µ) out of acceptance. g Fraction of events passing selection cuts Process Pt of third jet (GeV) qq qg gg <30 <50 <70 80 61 51 18 34 44 1 3 5 Selection cuts described later. Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 32
Backgrounds Sources of background QCD: Seems to be under control but huge cross section Uncertainties due to higher order QCD effects missing in Monte Carlo Third jet veto should minimize higher order effects. W, Z, tops Z νν: Represents an irreducible background Two jets+ real missing E T Ideally, Z µµ events can be used but not enough statistics. Other control samples W+jets Photon+jets Jan 6-10, 2009 Anwar Bhatti LHCDM@MCTP 33