Search for Charginos and Neutralinos with the DØ Detector

SUSY 006, 06/3/006 Marc Hohlfeld Search for Charginos and Neutralinos with the DØ Detector Marc Hohlfeld Laboratoire de l Accélérateur Linéaire, Orsay on behalf of the DØ Collaboration SUSY 006, 06/3/006

SUSY 006, 06/3/006 Marc Hohlfeld Outline Introduction Tevatron collider and DØ detector Signal and background Selection criteria Results Summary and outlook

SUSY 006, 06/3/006 Marc Hohlfeld Introduction msugra: five parameters m 0, m /, tan β, µ, A 0 R parity: R = ( ) 3(B L)+S Conserved LSP (neutralino) is stable R parity = + R parity = R parity = Particle Symbol Spin Particle Symbol Spin Particle Symbol Spin Lepton l Slepton ll, l R 0 Neutrino ν Sneutrino ν 0 Quark q Squark q L, q R 0 Gluon g Gluino g Photon γ Photino γ Z Boson Z Zino Z >= W Boson W ± Wino W± Neutralino χ 0 i Higgs H 0, H ± 0 Higgsino H0, H + Chargino χ ± j h 0, A 0 0 H >;, H 0 9 LEP limit for the chargino mass: m χ ± > 3.5 GeV

SUSY 006, 06/3/006 Marc Hohlfeld Tevatron and Data Taking p p collisions at center of mass energy of s =.96 TeV Update (006) PRL 95, 5805 (005) First DØ Run II Trilepton paper published in 005 ( Ldt 300 pb ) Now update with 3 4 times more data ( Ldt fb )

SUSY 006, 06/3/006 Marc Hohlfeld The DØ Detector Scintillators Proportional Drift Tubes (PDT) Central Preshower Detector (CPD) Superconducting Coil CFT CPS Central Fiber Tracker (CFT) Detector comprises several subdetectores NORTH SOUTH FPS Mini Drift Tubes (MDT) P Si Barrels F Disks H Disks P Forward Preshower Detector (FPD) Silicon Micro Tracker (SMT) Calorimeter Toroid Solenoid

SUSY 006, 06/3/006 Marc Hohlfeld The DØ Detector NORTH Mini Drift Tubes (MDT) P Scintillators Proportional Drift Tubes (PDT) Central Preshower Detector (CPD) Superconducting Coil Si Barrels F Disks CFT CPS SOUTH H Disks Central Fiber Tracker (CFT) P FPS Detector comprises several subdetectores Vertex and tracking detector Detection of vertices Measurement of the momentum of charged particles Measurement of the charge Forward Preshower Detector (FPD) Silicon Micro Tracker (SMT) Calorimeter Toroid Solenoid

SUSY 006, 06/3/006 Marc Hohlfeld The DØ Detector NORTH Mini Drift Tubes (MDT) P Scintillators Calorimeter Proportional Drift Tubes (PDT) Toroid Central Preshower Detector (CPD) Superconducting Coil Si Barrels Solenoid F Disks CFT CPS SOUTH H Disks Silicon Micro Tracker (SMT) Central Fiber Tracker (CFT) P FPS Forward Preshower Detector (FPD) Detector comprises several subdetectores Vertex and tracking detector Detection of vertices Measurement of the momentum of charged particles Measurement of the charge Calorimeter Detection of electrons, photons and jets Measurement of the energy Indirect detection of neutrinos using missing transverse energy

SUSY 006, 06/3/006 Marc Hohlfeld The DØ Detector NORTH Mini Drift Tubes (MDT) P Scintillators Calorimeter Proportional Drift Tubes (PDT) Toroid Central Preshower Detector (CPD) Superconducting Coil Si Barrels Solenoid F Disks CFT CPS SOUTH H Disks Silicon Micro Tracker (SMT) Central Fiber Tracker (CFT) P FPS Forward Preshower Detector (FPD) Detector comprises several subdetectores Vertex and tracking detector Detection of vertices Measurement of the momentum of charged particles Measurement of the charge Calorimeter Detection of electrons, photons and jets Measurement of the energy Indirect detection of neutrinos using missing transverse energy Muon spectrometer Detection of muons Standalone measurement of muon momentum

SUSY 006, 06/3/006 Marc Hohlfeld Search for Charginos and Neutralinos Associated production of charginos and neutralinos s channel: via W boson q t channel: squark exchange Destructive interference q W + χ~ 0 χ~+ Z W + χ~ 0 ~ 0 χ l + l l + ν q ~ χ~χ χ 0 + l 0 ~ ~ ~ l + q ~ + l ~ ~ χ + q ν Decay of chargino W bosons and lightest neutralino, W decays into lepton and neutrino Slepton and lepton, slepton decays into lightest neutralino and lepton Decay of neutralino Z bosons and lightest neutralino, Z decays into two leptons Slepton and neutrino, slepton decays into lightest neutralino and lepton Final state consists of Three charged leptons Two neutralinos (LSP) One neutrino χ 0 l + l + χ 0

SUSY 006, 06/3/006 Marc Hohlfeld Search for Charginos and Neutralinos () σ (pp χ χ, χ χ, χ χ, χ χ ) (pb) + o ± o o o o Trilepton channel is the golden mode for chargino/neutralino search Signature: three charged leptons plus missing transverse energy Challenges Leptons have low transverse momenta Small cross sections: σ BR < 0.5 pb 3 χ + χ χ ± χ o χ o χ o 53 80 5 9 σ (pp o o o o ± o + χ χ, χ χ, χ χ, χ χ ) (pb) pp ( s = TeV) : χ o 0 50 00 50 m(χ ±,χ o ) (GeV) arbitrary units 600 400 00 00 800 600 400 00 Four different analyses p T p T 3 p T 0 0 0 30 40 50 60 70 80 90 0 p T (GeV) Update summer 006 ee+track: Ldt. fb likesign µµ: Ldt 0.9 fb PRL 005 eµ+track: Ldt 30 pb µµ+track: Ldt 300 pb

SUSY 006, 06/3/006 Marc Hohlfeld Signal Monte Carlo Three reference points (Les Houches Accord) Heavy Medium Light m 0 (GeV) 98 88 m / (GeV) 9 8 tan β 3 3 3 µ > 0 > 0 > 0 A 0 0 0 0 m χ ± (Gev) 50 5 5 m χ 0 (GeV) 5 7 8 m χ 0 (GeV) 8 69 63 (GeV) m lr 53 9 9 σ BR (pb) 0.058 0.4 0. Mass of sleptons just above the neutralino masses: m lr m χ 0

SUSY 006, 06/3/006 Marc Hohlfeld Backgrounds Background components Vector boson pair production WW = leptons+e/ T WZ = 3 leptons+e/ T ZZ = leptons+e/ T or 4 leptons Vector boson production Z/γ ee, Z/γ µµ = leptons Z/γ ττ = leptons+e/ T W+jets/photon = lepton+e/ T Other components Multijet production = No isolated leptons t t = leptons+e/ T Υ ee, Υ µµ = leptons All backgrounds except QCD from Monte Carlo QCD contribution determined from data inverting some of the lepton ID criteria Events /.5 GeV Events / GeV 5 4 3 DØ RunII Preliminary. fb 5 0 5 30 35 40 45 50 55 60 M(e,e) [GeV] 4 3 3 DØ RunII Preliminary. fb Data Z ee Z tautau W e nu Y ee tt l b WW l + nu WZ 3l + nu ZZ 4l or l + nu 0 0 30 40 50 60 70 80 90 0 [GeV] E T QCD SUSY Data Z ee Z tautau W e nu Y ee tt l b WW l + nu WZ 3l + nu ZZ 4l or l + nu QCD SUSY

SUSY 006, 06/3/006 Marc Hohlfeld Selection Strategy. Dilepton+track analysis Require two reconstructed leptons (either e or µ) Require significant E/ T to account for escaping neutralinos/neutrinos Require one additional isolated high quality track Higher efficiency than reconstructed third lepton Efficient for e, µ and τ For some parameter points the third lepton has very low p T Dilepton+track analysis becomes inefficient. Likesign dilepton analysis Require two reconstructed leptons of the same charge Require significant E/ T to account for escaping neutralinos/neutrinos No requirement for a third object

SUSY 006, 06/3/006 Marc Hohlfeld ee + l Selection Preselection Two good reconstructed electrons p T > GeV and p T > 8 GeV Anti Z/γ ee cuts Small invariant mass 8 GeV < m ee < 60 GeV Not back to back φ ee <.9 Anti t t cut Reject events with large jet activity Sum of all jet momenta < 80 GeV Third isolated track Transverse momentum p l T > 4 GeV Isolated in tracker and calorimeter Events / GeV 3 DØ RunII Preliminary. fb 0 0 30 40 50 60 70 80 90 0 Transverse momentum [GeV] Data Z ee Z tautau W e nu Y ee tt l b WW l + nu WZ 3l + nu ZZ 4l or l + nu QCD SUSY

SUSY 006, 06/3/006 Marc Hohlfeld ee + l Selection () E/ T related cuts E/ T > GeV Transverse mass m T = p T E/ T ( Φ(e, E/ T )) > 0 GeV Significance of E/ T > 8 Events / GeV 4 3 DØ RunII Preliminary. fb Data Z ee Z tautau W e nu Y ee tt l b WW l + nu WZ 3l + nu ZZ 4l or l + nu QCD SUSY Events 4 3 DØ RunII Preliminary. fb Data Z ee Z tautau W e nu Y ee tt l b WW l + nu WZ 3l + nu ZZ 4l or l + nu QCD SUSY 3 3 0 0 30 40 50 60 70 80 90 0 min(mtr, Mtr ) [GeV] 0 0 40 60 80 0 0 40 60 80 00 Sig(E T )

SUSY 006, 06/3/006 Marc Hohlfeld ee + l Selection () E/ T related cuts E/ T > GeV Transverse mass m T = p T E/ T ( Φ(e, E/ T )) > 0 GeV Significance of E/ T > 8 E/ T and track Events / GeV ^ 3 DØ RunII Preliminary,. fb Data Z ee Z tautau W e nu Y ee tt l b WW l + nu WZ 3l + nu ZZ 4l or l + nu QCD SUSY Product of E/ T and track p T E/ T p T > 0 GeV 3 0 0 00 300 400 500 600 700 800 900 00 l3 MET X p [GeV ^] T

SUSY 006, 06/3/006 Marc Hohlfeld Likesign µµ Selection Preselection Two good muons of same charge p T > 5 GeV for both muons Not back to back φ µµ <.9 Anti Z/γ µµ cuts Small invariant mass for OS pairs 5 GeV < m µµ < 65 GeV Tightened p T cuts p T > 3 GeV and p T > 8 GeV events / GeV/c events / GeV/c 3 D0 Run II preliminary, 0.9 fb 0 0 40 60 80 0 0 40 m µ (GeV/c ) ± µ ± 3 D0 Run II preliminary, 0.9 fb 0 0 40 60 80 0 0 40 m µ (GeV/c ) + µ signal WZ WW ZZ W µν tt incl W+bb µν+x Z+bb µµ+x Z τ + τ Z µ + µ Υ s µ + µ QCD data signal WZ WW ZZ W µν tt incl W+bb µν+x Z+bb µµ+x Z τ + τ Z µ + µ Υ s µ + µ QCD data

SUSY 006, 06/3/006 Marc Hohlfeld Likesign µµ Selection () E/ T related cuts 5 GeV < m T < 65 GeV E/ T > GeV Significance of E/ T > E/ T p T of trailing muon > 60 GeV events / GeV/c 3 D0 Run II preliminary, 0.9 fb / events / GeV 3 signal WZ WW ZZ W µν tt incl W+bb µν+x Z+bb µµ+x Z τ + τ Z µ + µ Υ s µ + µ QCD data D0 Run II preliminary, 0.9 fb /c events / GeV 4 3signal WZ WW ZZ W µν tt incl W+bb µν+x Z+bb µµ+x Z τ + τ Z µ + µ Υ s µ + µ QCD data D0 Run II preliminary, 0.9 fb signal WZ WW ZZ W µν tt incl W+bb µν+x Z+bb µµ+x Z τ + τ Z µ + µ Υ s µ + µ QCD data 0 0 40 60 80 0 0 40 60 m T (E T,next to leading muon) (GeV/c ) 0 5 5 0 5 30 / Sig(E T ) (GeV ) 0 0 00 300 400 500 600 700 800 900 00 next to leading p (GeV /c) E T T

SUSY 006, 06/3/006 Marc Hohlfeld Final Event Numbers ee + l selection Expected: 0.76 ± 0.67 events Observed: 0 events Signal expectations:.69 ± 0.0 4.73 ± 0.0 events Dominant background: Diboson production, Z/γ ττ Likesign µµ selection Expected:. ± 0.4 events Observed: event Signal expectations: 0.6 ± 0.0 3.76 ± 0.5 events Dominant background: Diboson production, Z/γ µµ eµ + l selection Expected: 0.3 ± 0.5 events Observed: 0 events Signal expectations: 0.70 ± 0.03.45 ± 0.09 events Dominant background: Diboson production µµ + l selection Expected:.75 ± 0.57 events Observed: events Signal expectations: 0.47 ± 0.0.94 ± 0.08 events Dominant background: QCD, Z/γ production

SUSY 006, 06/3/006 Marc Hohlfeld Current Result Three reference scenarios ) BR(3l) (pb) χ 0 σ(χ ± 0.5 0.4 0.3 0. "3l max": Maximize leptonic BR of chargino and neutralino m χ 0 "Large m 0 ": Decays via W/Z bosons dominant Small leptonic BR "Heavy squarks": Relax scalar mass unification Increased production cross section LEP 0. heavysquarks 3lmax DØ Run II Preliminary, 0.3. fb ± 0 0 ~ M( χ ) M( χ ) M( χ ); M( l)>m( χ 0 ) tanβ=3, µ>0, no slepton mixing Observed Limit Expected Limit m l Mass limit for "3l max" scenario m χ ± > 40 GeV Mass limit from PRL m χ ± > 6 GeV largem 0 0 0 0 30 40 50 60 Chargino Mass (GeV)

SUSY 006, 06/3/006 Marc Hohlfeld Conclusion and Outlook Summary New search for charginos and neutralinos with fb of DØ data No evidence for signal Chargino mass limit of 40 GeV in scenario with enhanced leptonic BR Outlook Still room for lot of improvement Update µµ + l and eµ + l channels Include final states involving τ s

SUSY 006, 06/3/006 Marc Hohlfeld Conclusion and Outlook Summary New search for charginos and neutralinos with fb of DØ data No evidence for signal Chargino mass limit of 40 GeV in scenario with enhanced leptonic BR ) BR(3l) (pb) χ 0 σ(χ ± LEP 3lmax largem 0 Search for ±.0 fb.0 fb 0 χ χ 3l+X ± 0 ~ l)>m(χ 0 ) M(χ 0 M( χ ) M( χ ); M( tanβ=3, µ>0, no slepton mixing 4.0 fb ) 8.0 fb 0 0 40 60 80 00 0 40 Chargino Mass (GeV)