Search for Supersymmetry in ATLAS with Early LHC Data Natalia Panikashvili University of Michigan HEP seminar, USTC August 25, 2010, Hefei, China

Wednesday, March 16, Outline Introduction to SUSY The LHC and the ATLAS detector –Detector readiness –First ATLAS results SUSY searches with early data –Discovery Signatures –Strategy –jets + E T miss channel –jets + lepton(s) + E T miss channel –b-jet + lepton(s) + E T miss channel Summary

Wednesday, March 16, New Physics-one of the main motivations for the LHC Unexplained phenomena: Dark matter Neutrino oscillations Gravity From theoretical considerations: Hierarchy problem Gravity is not yet incorporated in the Standard Model The New Physics scenario: SUSY Extra dimensions Technicolor Little Higgs ………….. The Standard Model is a very successful gauge theory in particle physics, but it is incomplete!

Wednesday, March 16, Introduction to SUSY A symmetry which relates fermions & bosons –Q |fermion> ~ |boson>, Q |boson> ~ |fermion> SUSY requires at least two Higgs doublets to give masses to SM fermions SUSY doubles the particle spectrum –each particle has a superpartner with spin offset by ½ If R parity conservation is assumed - dark matter candidate –the lightest supersymmetric particle cannot decay Possible solution of the hierarchy problem Improves Unification of couplings

Wednesday, March 16, SUSY Challenges... If SUSY is unbroken - same mass for ordinary particles and superpartners. No superpartner observed to date SUSY must be broken! SUSY should be broken spontaneously in the hidden sector and the breaking is “mediated” to the observable sector Mediation results in soft terms Three proposals for mediations: –SUper GRAvity (SUGRA) –Gauge-Mediated Supersymmetry Breaking (GMSB) –Anomaly-Mediated Supersymmetry Breaking (AMSB) MSSM - Minimal Supersymmetric Standard Model

Wednesday, March 16, Predicted MSSM particles

Wednesday, March 16, mSUGRA benchmark points in ATLAS mSUGRA parameters: m 0 - the scalar masses m 1/2 - the gaugino mass A 0 - soft breaking trilinear coupling constant (higgs-sfermion-sfermion) tan  = / sign  - the sign of the Higgsino mass parameter SU4: A 0 =- 400GeV tan  = 10 SU3: A 0 =- 300GeV tan  = 6 SU1: A 0 = 0 tan  = 10 SU6: A 0 = 0 tan  = 50

Wednesday, March 16, SUSY Particle Production and Decays The most important consequence of the R parity is that all superpartners produced in pairs Example: gluino pair production and cascade decays Very rich experimental signature!

Wednesday, March 16, Large Hardon Collider pp collider Design beam energy7TeV Number of particles per bunch 1.15  Number of bunches2808 Bunch length7.55cm Luminosity10 34 cm -2 s -1

Wednesday, March 16, Cross section vs. center of mass energy 7TeV 14TeV7TeVreduction ttbar827pb160 pb5.1 SU4264pb36 pb7.4 SU318.9pb1.9pb9.4

Wednesday, March 16, Run Timeline Single beam splash First collisions observed at 900 GeV First collisions with stable beams  full detector on First collisions at 2.36 TeV First collisions at 7 TeV First W candidate observed First Z candidate observed

Wednesday, March 16, ATLAS online luminosity Collected 1.5 pb -1 so far with stable beams Peak luminosity ~ 4  cm -2 s -1

Wednesday, March 16, The ATLAS detector Length : ~ 46 m Radius : ~ 12 m Weight :~ 7000 tons ~10 8 electronic channels 3000 km of cables

Wednesday, March 16, The Inner Detector (ID) Pixel Detector (|  |<2.5) – 3 barrel layers, 2x3 end-cap discs –  (R  )~10  m,  (z)~115  m Semiconductor Tracker (SCT) (|  |<2.5) – 4 barrel layers, 2x9 end-cap discs –  (R  )~17 mm,  (z)~580 mm Transition Radiation Tracker (|  |<2.0) – dual purpose: tracking + e/  separation – 73 barrel straw layers and 2x160 end-cap radial layers –  (R  )~130 mm, 32 hits/track on average Insertion of SCT into TRT Installation of the Pixel Detector Installation of ID end-cap C

Wednesday, March 16, First results with stable beams at 900 GeV Hits on tracks for one of the first stable beam runs Pixel detector (5.05 < R < cm) Silicon strip detector (25.5 < R < 54.9 cm) Transition radiation tracker (55.4 < R < cm) ~ 98% live channels for all three subsystems

Wednesday, March 16, Long - lived particles reconstruction in ID Weak decay reconstruction provides a stringent test of tracking performance - reconstructed K s and Λ masses close to PDG value - width of the invariant mass peaks well reproduced by Monte Carlo K s   +  -  p p PDG m Ks =  MeV PDG m  =  MeV

Wednesday, March 16, Calorimeter Electromagnetic calorimeter –one barrel, two end-caps: LAr+Pb –4 longitudinal segmentations –Coverage: |  |<3.2 –170k channels Energy Resolution for EM Measure energy better than 1% at high energies Hadronic calorimeter –One barrel (|  |<1.7): Scintillator + Fe –Two end-caps (1.5<|  |<3.2): LAr + Cu –Two forwards (3.1<|  |<4.9): LAr + Cu –19k channels

Wednesday, March 16, First Z  e + e - Candidate

Wednesday, March 16, Jet reconstruction Jet reconstruction at R = 0.6 Not many high p T jets yet, but low energy p T spectrum is well produced by Monte Carlo

Wednesday, March 16, Missing transverse energy ( E T miss ) E T miss is a key to –SM physics (W, ttbar, …) –Higgs and SUSY searches E T miss distribution –well modeled –no significant tail E T miss resolution –well modeled by Monte Carlo events ● Data - MC

Wednesday, March 16, Muon Spectrometer 4 technologies: –Trigger chambers: TGC, RPC –Precision chambers: MDT, CSC Three stations in barrel (MDT, RPC) and end-cap (MDT,TGC,CSC) Muons cross 3 stations of precision chambers for sagitta measurement Trigger chambers are placed on both sides of middle precision layer Side View x y The Beam View

Wednesday, March 16, The Big Wheel Big wheels (and end-wall wheels): 400 MDT precision chambers 3600 TGC trigger chambers

Wednesday, March 16, Muon Spectrometer - barrel ~700 MDT precision chambers ~ 600 RPC trigger chambers

Wednesday, March 16, Magnets Barrel toroid length25m outer diameter20.1m peak field4T current20.5kA End-cap toroid length5m outer diameter10.7m peak field4T current20.5kA Solenoid length5.3m outer diameter1.2m peak field2T current7.6kA

Wednesday, March 16, Barrel toroid

Wednesday, March 16, First Z   +  - Candidate

Wednesday, March 16, J/ψ   +  - Candidates Integrated luminosity 9.5nb -1 : –M = ± GeV –N signal events = 592 ± 30 –  = ± GeV The invariant mass for all oppositely charged muon pairs passing vertexing Ratio of non-prompt to prompt J/ψ production cross-sections as a function of J/ψ transverse momentum

Wednesday, March 16, Inclusive W  ℓν at Hadron Colliders Using the first 17 nb −1 of data 46 W  eν candidates over 2.6 background events σ tot = 8.5 ± 1.3(stat) ± 0.7(sys) ± 0.9(lumi) nb 72 W  μν candidates over 5.3 background events σ tot = 10.3 ± 1.3(stat) ± 0.8(sys) ± 1.1(lumi) nb Agrees with SM expectation σ NNLO tot = ± 0.42 nb

Wednesday, March 16, Z/  * Cross Section Results Using the first 225 nb −1 of data 46 Z  ee candidates over 0.5 background events σ tot = 0.72 ± 0.11(stat) ± 0.10(sys) ± 0.08(lumi) nb 79 Z  μμ candidates over 0.2 background events σ tot = 0.89 ± 0.10(stat) ± 0.07(sys) ± 0.10(lumi) nb Agrees with SM expectation σ NNLO tot = 0.96 ± 0.04 nb

Wednesday, March 16, SUSY Discovery Signatures Large E T miss –Lightest SUSY Particle escaping detection High p T jets, High jet multiplicity –squark / gluinos production High p T leptons (>20GeV) –decays of charginos or neutralinos in cascade Spherical events –the initial heavy particles are usually produced approximately at rest in the detector and their cascade decays emit particles in many different directions Large effective mass –Meff = E T miss + p T (jets) + p T (leptons) –Total activity in the event

Wednesday, March 16, The simulated SUSY event Multiple jets Multiple leptons Large E T miss

Wednesday, March 16, Search Strategies Model independent approach is desirable! However it is impossible to cover all combinations Base our analysis on final states –which have large production cross – section –good S/B separation –in which we have good confidence in background estimation from data Final states: E T miss + N jets  3 gluino or/and squark production N jets ~ 2 squark production N jets = 0 direct neutralino production 0 leptons 1 leptons 2 leptons photons …… +=

Wednesday, March 16, Generic Searches E T miss > 80GeV, Δ  (jets, E T miss ) > 0.2, E T miss /M eff, S T > 0.2

Wednesday, March 16, Major Background (7TeV) Final statesMajor BG 0 lepton + 3 jetsQCD, top, W, Z 1 lepton + 3 jetsW, top, Z 2 leptons + 3 jetstop, di-bosons M eff = E T miss + p T (jets) + p T (leptons)

Wednesday, March 16, Discovery Reach – 7TeV 500pb -1 (tan  = 10) 0 leptons + 4 jets and 1 leptons + 4 jets – very promising final states (mass of squarks / gluino  600GeV)

Wednesday, March 16, Discovery Reach – 7TeV 1fb -1 (tan  = 10) 0 leptons + 4 jets and 1 leptons + 4 jets – very promising final states (mass of squarks / gluino  750GeV)

Wednesday, March 16, Discovery Reach – 7TeV 0.5/1fb -1 (tan  = 10) 0 leptons + 4 jets channel Discovery reach vs. the assumed systematic uncertainty

Wednesday, March 16, lepton + 2 jets channel – 70nb -1 We use this selection to define the normalization factor for QCD background: 0.61 Missing transverse energy Effective mass DataMC p T (jets) > 70GeV,30GeV  39824

Wednesday, March 16, lepton + 2 jets channel – 70nb -1 Data is in agreement with MC prediction MC prediction is dominated by the QCD processes Effective mass (E T miss > 40GeV) DataMC E T miss > 40GeV  225

Wednesday, March 16, QCD background: jet - E T miss correlations Select events with E T miss >100GeV and two back-to-back jets The source of the large E T miss in the QCD events – mis-measurement of the jet energy To reduce the QCD background – eliminate events in which the E T miss is closely associated with one of the leading jets QCD SU3

Wednesday, March 16, QCD background: jet - E T miss correlations Reject events with Δ  min < leptons + 2 jets channel (E T miss > 40GeV)

Wednesday, March 16, lepton + 2 jets channel – 70nb -1 DataMC E T miss > 40GeV  225 E T miss > 40GeV and Δ  >  128 E T miss > 40GeV, Δ  >0.2, E T miss /M eff >  3

Wednesday, March 16, lepton + 4 jets channel – 70nb -1 Missing transverse energy DataMC p T (jets) > 70,30,30,30GeV  2800

Wednesday, March 16, lepton + 4 jets channel – 70nb -1 M eff (E T miss > 40GeV) DataMC E T miss > 40GeV  54 E T miss > 40GeV, Δ  >  30 E T miss > 40GeV, Δ  >0.2, E T miss /M eff >  0.6 M eff (E T miss > 40GeV, Δ  >0.2,E T miss /M eff >0.2)

Wednesday, March 16, leptons + 4 jets channel M eff = 1.5 TeV M eff = 1.65 TeV (4 jets) E T miss = 100 GeV. All of the high energy jets are associated with the same primary vertex.

Wednesday, March 16, lepton + 2 jets channel – 70nb -1 Missing transverse energyTransverse mass Data is in agreement with MC prediction MC prediction is dominated by the QCD & W + jets processes

Wednesday, March 16, electron + 2 jets channel – 70nb -1 Effective mass E T miss > 30GeV E T miss > 30GeV, m T >100GeV DataMC p T (jets) > 30,30GeV, p T (l) > 20GeV  85 E T miss > 30GeV  7 M T >100GeV  1.6

Wednesday, March 16, muon + jets channel M eff = 915GeV E T miss = 118 GeV p T (  ) = 25 GeV  (  ) = 2.33 DataMC E T miss > 30GeV17 15  7 m T > 100GeV1 2.8  1.2

Wednesday, March 16, leptons + 2 jets channel – 70nb -1 Opposite signSame sign DataMC E T miss > 30GeV2 2.0  0.8

Wednesday, March 16, b – jets + E T miss channel sbottom pair production and sbottom decay into b - quark and neutralinos. gluino pair production and decay into ˜bb and ˜tt.

Wednesday, March 16, b – jets + 0 leptons + E T miss M eff (E T miss sig > 2GeV 1/2 )

Wednesday, March 16, b – jets + 1 leptons + E T miss

Wednesday, March 16, b – jets + E T miss channel 305 nb −1

Wednesday, March 16, GMSB search in ATLAS GMSB – Neutralino is NLSP (Bino-like, Higgsino- like) –  + E T miss,  Z + E T miss,ZZ + E T miss,  h + E T miss …

Wednesday, March 16, Summary ATLAS in the data taking mode – 7TeV Expected integrated luminosity – 100/200 pb -1 at 7TeV ATLAS is prepared for discovery with early data If masses of squarks and gluinos ~ 600 – 600 GeV we have a great potential to discover SUSY with first year data

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Wednesday, March 16, Production cross section and branching ration Higgsino – like neutralino model: M/Λ = 3, N=2,  = 0.75M 1, tan  = 3 (Phys. Rev. D62, , 2000) Neutralino Mass ( GeV )

Wednesday, March 16, Steps of Campaign at the LHC 1) Re-establish the SM process (standard candles: W, Z, top signals)

Wednesday, March 16, Unification of the gauge couplings It may also be taken as a strong hint in favor of a grand unified theory (GUT) or superstring models, both of which can naturally accommodate gauge coupling unification below MP

Wednesday, March 16, mSUGRA

Wednesday, March 16, b – jets + 0 leptons + E T miss Identification of jets originated from b-quarks (b-tagging) is based on the presence of a displaced vertex due to the decay of a b hadron inside the jet. signed decay length significance of the reconstructed secondary vertex L/  (L) > 6, p T > 30 GeV

Wednesday, March 16, b – jets + 0 leptons + E T miss M eff (E T miss sig > 2GeV 1/2 )