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Lepton pair production in ep collisions at HERA

Lepton pair production in ep collisions at HERA. Cristinel Diaconu CPP Marseille On behalf of H1 and ZEUS collaboration. Introduction. HERA e ± p collider  s=300-318 GeV HERA I : H1/ZEUS ~120 pb-1 HERA II 1fb -1

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Lepton pair production in ep collisions at HERA

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  1. Lepton pair production in ep collisions at HERA Cristinel Diaconu CPP Marseille On behalf of H1 and ZEUS collaboration C.Diaconu High Pt Multileptons at HERA

  2. Introduction • HERA e±p collider s=300-318 GeV • HERA I : H1/ZEUS ~120 pb-1 HERA II 1fb-1 • Di-lepton production in e-p collisions possible mainly trough gg collisions p(920 GeV) E(27.5 GeV) l+ l- Spectacular topology Precise SM prediction Interesting phase space for BSM signals (e+p  e-H++ e-l+l+ see J.Dingfelder talk in BSM) C.Diaconu High Pt Multileptons at HERA

  3. Standard Model Processes gg-inelastic gg-elastic Signal quasi-elastic qql+l- (Drell-Yan) (small @HERA) eel+l- (Cabibbo-Parisi) (small @HERA) g*/Zl+l- +Resonant/HQ production (low PT< 5 GeV) GRAPE (T.Abe et al.) : full diagram a+b+c (EW)+proton structure NC-DIS epeX fake 2nd electron from radiation or mis-id Compton: eg(p)e+photon(->fake 2nd e) Background e m Fake muons from hadrons (negligible) C.Diaconu High Pt Multileptons at HERA

  4. H1 and ZEUS : electron identification • Electron identified in calorimeters 5o<q<175o (isolated) • Central region: • H1 : 20o<q<150o • ZEUS: 17o<q<164o • calo-tracker redundancy exploited for background rejection: Good quality isolated track required Uranium ,6500 cells, precise timing, em:s(E)=18%/E 17o 164o 20o 150o LAr,44000 cells em:s(E)=12%/E Electrons ordered in PT: e1,e2,e3PT1>PT2>PT3 C.Diaconu High Pt Multileptons at HERA

  5. Multi-electron selection • Two central high PT electrons • H1 : PT(1)>10 GeV PT(2)>5 GeV 20o<q<150o • ZEUS: PT(1)>10 GeV E(2)>10 GeV17o<q<164o • + any other electron(3rd) identified in the calo 5o<q<175o Statistical and systematical errors Statistical errors C.Diaconu High Pt Multileptons at HERA

  6. Inclusive Distribution (H1) • Longitudinal momentum as expected for 2e and 3e • (E-Pz=2*Ee=55 GeV when all particles detected) • No high Ptmiss • Inelasticity spectrum well described 2e z 3e C.Diaconu High Pt Multileptons at HERA

  7. Electron transverse momenta (H1) 2e Steep spectra Good overall description Three 2e events @PT>50 GeV 3e C.Diaconu High Pt Multileptons at HERA

  8. Electron PT and polar angles (ZEUS) 2e+3e Good overall description PT1>30 GeV 8(Data)/7.1(SM) Two events with PTe1,2>50 GeV C.Diaconu High Pt Multileptons at HERA

  9. Mass distribution M12 H1 Mass of two highest PT electrons in the event 2e 2e+3e 3e Good overall agreement Several events at high mass M12>100 GeV C.Diaconu High Pt Multileptons at HERA

  10. Multi-electron events at high mass M12>100 GeV Statistical and systematical errors Statistical errors Reminder: H1/ZEUS different polar angle domains C.Diaconu High Pt Multileptons at HERA

  11. Example 2e event (ZEUS) M12=134 GeV PT=53 GeV PT=56 GeV C.Diaconu High Pt Multileptons at HERA

  12. Example 2e event (H1) M12=130GeV C.Diaconu High Pt Multileptons at HERA

  13. Example 3e event (H1) M12=118 GeV High mass from forward-backward topology C.Diaconu High Pt Multileptons at HERA

  14. H1: Cross section measurement epee+e-X + 2e Sample E-Pz<45 GeV , opposite charges PeT(1,2)>10,5 20o<q<150o y<0.82 Q2<1 GeV2 z Q2 - Data/MC: 41/48.3±6.1(1.9BG) Good agreement Inelastic process well described C.Diaconu High Pt Multileptons at HERA

  15. Multi-muon Events Muons identified in central tracker, mips in Calo and external muon chambers signals PT(m1,2)>2GeV 20o<qm<160o L=70pb-1 PT(m1,2)>5GeV 20o<qm<160o L=105pb-1 No events at high M12>100 H1: ~1ev expected from e-channel C.Diaconu High Pt Multileptons at HERA

  16. Example of di-muon event (H1) Mmm=80 GeV C.Diaconu High Pt Multileptons at HERA

  17. H1 Di-muon Cross Section Measurement Good agreement with SM Good description of inelasticity spectrum PT(m1,2)>2GeV 20o<qm<160o C.Diaconu High Pt Multileptons at HERA

  18. Summary • Multi-electron and multi-muon production has been measured in ep collision for • PT’s up to 50 GeV • M(ll) up to 100 GeV • Good overall agreement is found with the SM calculation. • Multi-electron events with M12> 100 GeV observed : • 2e : 3/0.25 (H1) 2/0.77 (ZEUS) • 3e : 3/0.23 (H1) 0/0.37 (ZEUS) • Promising for future investigation with 1fb-1 at HERA II C.Diaconu High Pt Multileptons at HERA

  19. Events at High Mass (H1) The 3 high mass pairs have also high PT 2e The 3 high mass pairs have a bwd-fwd topology 3e C.Diaconu High Pt Multileptons at HERA

  20. Isolated leptons event Not the same topology As high mass di-electrons High PT jet in the events C.Diaconu High Pt Multileptons at HERA

  21. Mass combinations for 3e events No other events with high mass combination C.Diaconu High Pt Multileptons at HERA

  22. High Mass Event (H1) M C.Diaconu High Pt Multileptons at HERA

  23. High Mass Event (H1) C.Diaconu High Pt Multileptons at HERA

  24. High Mass Event (H1) C.Diaconu High Pt Multileptons at HERA

  25. High Mass Event (H1) C.Diaconu High Pt Multileptons at HERA

  26. High Mass Event (H1) C.Diaconu High Pt Multileptons at HERA

  27. High Mass Event (H1) C.Diaconu High Pt Multileptons at HERA

  28. Control Analysis: photon conversions • Photon conversions studied with a clean Compton sample: two e.m. clusters and nothing else H1 innner detector tomography with high PT photons Good Description by the simulation, conversion @high PT under control C.Diaconu High Pt Multileptons at HERA

  29. Fake electrons : control analysis • Second e.m. cluster studied in a sample where a good isolated electron already identified Good description of fake electrons: under control Asking for a track greatly reduce the Compton component C.Diaconu High Pt Multileptons at HERA

  30. Tracking efficiency control • Track requirement efficiency has been calculated from an inclusive NC-DIS sample C.Diaconu High Pt Multileptons at HERA

  31. High Mass Events (ZEUS) M12=122 GeV C.Diaconu High Pt Multileptons at HERA

  32. High Mass Event (ZEUS) M12=94 GeV C.Diaconu High Pt Multileptons at HERA

  33. GRAPE/LPAIR comparison • Grape: full EW diagrams • Lpair: only gg • Increase of ~20% • Zee and gee contributions Grape/LPAIR LPAIR: Vermaseren calculation based on peripheral diagrams only Grape(“lpair”)/LPAIR C.Diaconu High Pt Multileptons at HERA

  34. H1 multi-e events 2e 2e 2/3 “2e” events have a third electron 2e 3e 3e 3e C.Diaconu High Pt Multileptons at HERA

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