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Long lived LSPs

Long lived LSPs. SLAC ATLAS forum, 5 December 2007. Ignacio Aracena (SLAC) Keith Bechtol (Stanford) Dan Silverstein (Stanford) Claus Horn (SLAC). Content of this Talk. Motivation Signatures Reach studies Generator level studies Reconstruction Next steps.

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Long lived LSPs

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  1. Long lived LSPs SLAC ATLAS forum, 5 December 2007 Ignacio Aracena (SLAC) Keith Bechtol (Stanford) Dan Silverstein (Stanford) Claus Horn (SLAC)

  2. Content of this Talk • Motivation • Signatures • Reach studies • Generator level studies • Reconstruction • Next steps Working in collaboration with the ATLAS Hidden Valley group Claus Horn: Long-lived LSPs

  3. Motivation The general SUSY Lagrangian contains L and B violating terms: L number violating B number violating In RP conserving SUSY models these terms are neglected which ensures a stable LSP and, if neutral, a CDM candidate. However: • There are also RPV scenarios with dark matter candidates. • There are many other motivations for supersymmetry. • We have seen L violating effects in neutrino sector. • A HE theory should include B violation to explain baryon asymmetry. Should not exclude L / B violating effects a priori ! Advantage of RPV: Possibility to directly reconstruct sparticle masses. Striking signature: high pT DVs, no MET Claus Horn: Long-lived LSPs

  4. Existing limits on RPV couplings If couplings are small, we will not observe RPV in production, but displaced vertices! Claus Horn: Long-lived LSPs

  5. c q q q* l” q Signatures ‘Underlying SUSY event’ from main IP + Displaced vertex c LSP l Focusing on c LSP case l Superpotential Signature (cLSP) l* l l l+ l- + n l LLE c l l’ LQD 2 jets + l±/n q l* 3 jets l’’ UUD l’ q Other possible LSPs: (gravitino) sneutrino, slepton, squark (disfavoured by cosmology) Search for displaced vertices with 2jets+X or 2 leptons. Claus Horn: Long-lived LSPs

  6. d ~ ( )bg ml4 ac2 l2 mc5 Reach on RPV couplings LQD Decay length: Effective coupling ’ Decays in muon-spectrometer Decays in calorimeter b-tagging region Decays in inner detector Reach additionally extended due to ml and exp(d/d0) dependence. Covering 4 orders of magnitude; Largest region covered by ID Claus Horn: Long-lived LSPs

  7. Decay Regions Study decay region dependence on lifetime Decay probability for a single LSP Classifying displaced vertex position into 5 diff regions. ID=Decay in Inner detector MS=Decay in Muon-Spectrometer (ID includes b-tag) Considering 10K simulated events per t. x-axis t: decay length for b=1 Additional dependencies: • bg <-EKin<-m(c)-m(q) • Integrated lifetime distribution Claus Horn: Long-lived LSPs

  8. Combined Probability Two DV requirement may be important background discriminator. Both c decaying in ID Calculate combined probability: P2ID = PID2 PID+CAL = 2*PID*PCAL Ptot approaches 1 in end region. t[cm] Maximal 16% of events have two decays in the calorimeter for any lifetime. Both c decaying in calorimeter 5 decay regions (b-tagging, tracker, Calorimeter, MuonSpectrometer,ETmiss) -> In total 15 combinations. t[cm] Claus Horn: Long-lived LSPs

  9. Event Generation with Pythia Sparticle mass spectrum m( g ) = 5137 GeV m( dL,R ) ≈ 700 GeV m( uL,R ) ≈ 698 GeV m( t1,2,b1,2 ) ≈ 5000 GeV m( lL,R ) ≈ 5000 GeV m( c02 ) = 800 GeV m( c01 ) = 494 GeV • Setting sparticle masses by hand • Suppressing long decay chains • Allow long decay length of LSP in Pythia • Switch explicitly off neutrino decays • Suppress decays involving third generation quarks • Modified Pythia interface: • introduce new flags to select different RPV couplings • Resulting event: Squark pair production+ Claus Horn: Long-lived LSPs

  10. Generator level Studies pT eta Neutralino: Applying simple jet finder to construct jets out of tracks from DV: Jets: Claus Horn: Long-lived LSPs

  11. Dependence on Ec Electron pT for different Ec. Average deltaR of decay products Mean electron pT increases with increasing neutralino energy. Decay products are well separated even for high neutralino energies. Claus Horn: Long-lived LSPs

  12. Sample Production Generation in Pythia Simulation in Geant4 Using production transforms, run on the grid Digitization (-> RDO) Change tracking cuts, very slow Reconstruction (->ESD) Samples Create Track Selections 7mm 800 evts 100mm 50 evts 700mm 50 evts Conversion job (->AOD) Athena analysis (->AANT ntuple) ROOT analysis Claus Horn: Long-lived LSPs

  13. Experimental Handles Decays in the Inner Detector Main backgrounds High mass displaced vertices Secondary vertices within jets Material reactions Decays in the calorimeter Noise Pi0-jets Jets without tracks High em/had energy fraction Decays in the muon spectometer Clusters of muon ROIs Very high pT jets General Two DV decays in each event Common DV mass (neutralino) Missing ET to be studied Claus Horn: Long-lived LSPs

  14. Event Displays Shown are all stable truth particles Dashed line: electron Black: Underlying SUSY from IP Displaced Vertices: Red & blue Green: Neutalino (intermediate particles are not shown) Claus Horn: Long-lived LSPs

  15. ct = 7mm Stable truth particles x-y view y-z view Leptons and jets well seperated Claus Horn: Long-lived LSPs

  16. ct = 700 mm Example Claus Horn: Long-lived LSPs

  17. Reconstruction-Overview Many standard cuts have to be adjusted: Tracking Optimization for DV tracks ct=7mm Vertex finding Release constraints on vertex position Optimize for different regions Jet finding Match calorimeter clusters to DV tracks Lepton Reconstruction Match tracks to DV instead of IP ct=1m Optimize shower shape variables Claus Horn: Long-lived LSPs

  18. Reconstruction Strategy Vertexing methods: fitting tracks from one vertex/ topological • Track jets, on pre-selected tracks (cut on impact parameter) • Standard calorimeter jet finder (jets from IP) Pre-select all tracks within these jets (match at calo surface) Reject: Secondary vertices within jets Vertices within dead material map High vertex mass requirement Claus Horn: Long-lived LSPs

  19. Impact Parameter Red: QCD Blue: RPV (ct=7mm) Many track with d0 of order of cm -> Tails much wider for RPV sample Claus Horn: Long-lived LSPs

  20. Impact Parameter Significance Standard cuts Extended cuts QCD QCD SUSY RPV Impact parameter distribution indicates existence of DVs Claus Horn: Long-lived LSPs

  21. Jets in the 700 mm sample Running cone (0.4) tower jet finder on calorimeter clusters DeltaR Red: Truth, Black: Reconstructed Decays beyond the cal will lead to not reconstructed jets Next step: study efficiency as function of decay length Claus Horn: Long-lived LSPs

  22. Conclusions Exciting new analysis effort started. Small RPV couplings lead to striking signatures with disp. vertices. High pT displaced vertices may enable an early discovery. ATLAS covers a large region of unexplored RPV coupling space. Many adjustments are needed in reconstruction Claus Horn: Long-lived LSPs

  23. Backup slides Claus Horn: Long-lived LSPs

  24. Triggering Events may be triggered by jets/leptons from main IP Triggering on DV properties may extend trigger reach Introduction of specific triggers: Decays in calorimeter: low EEM/EHAD Decays in MuonSpectrometer: large # muon ROIs Claus Horn: Long-lived LSPs

  25. photons From IP From DV pions Claus Horn: Long-lived LSPs

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