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Measuring dileptons with HADES at 8 AGeV

Measuring dileptons with HADES at 8 AGeV. A.Kugler. Nuclear Physics Institute, 250 68 Rez, Czech Republic for HADES collaboration. Outline . Motivation HADES concept, components C+C reactions (hadrons, dileptons) Au+Au reactions (hadrons in RPC).

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Measuring dileptons with HADES at 8 AGeV

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  1. Measuring dileptons with HADES at 8 AGeV A.Kugler Nuclear Physics Institute, 250 68 Rez, Czech Republic for HADES collaboration

  2. Outline • Motivation • HADES concept, components • C+C reactions (hadrons, dileptons) • Au+Au reactions (hadrons in RPC)

  3. First generation of dilepton spectrometers DLS at Bevalac @1AGeV CERES at SPS @158AGeV rp<<rB rp>>rB Data: R.J. Porter et al.: PRL 79(97)1229 Model: E.L. Bratkovskaya et al.: NPA634(98)168, BUU, vacuum spectral function, folded with experimental resolution (DM/M ~ 10%)

  4. TOF SHOWER MDC RICH MAGNET HADES Detector • Features • 106 events / s • 45% geometrical acceptance (2p in f ,18 0< J < 85 0 ) • up to 200 charged particles • 1% mass resolution • Components • MOMENTUM RECONSTRUCTION& PARTICLE IDENTIFICATION • Mini Drift Chambers(MDC)in front and behind a superconducting toroid magnet • Time of Flight(TOF)wall • LEPTON ENHANCEMENT • Electromagnetic Showerdetector • LEPTON IDENTIFICATION • Hadron-blind Ring Imaging Cherenkov(RICH) detector

  5. PreShower Magnet Coils HADES real RICH MDC I RICH Back view

  6. TimeOfFlightdetector TOF wall covers >450: • 6 * 64 scint. Installed. • dt : 90 – 140 ps • dE/dx measurement • tracking TOFINO 180 <<450 • tof measurement t0.35 ns

  7. deuterons Tof [ns] protons Energy loss [MeV] MDC-Meta-hadron identification • Probability density functions for all kinds of particles calculated in individual pid algorithms • Probability density functions from individual pid algorithms for the same type of particle are combined MDC-Tofino MDC-TOF

  8. Simulations of HADES • event source: • UrQMD events • thermal source (Pluto++ event generator) • Separate production and analysis for each source of dileptons propagation of particles and detector response: Geant 3 based package HADES geometry and materials Digitization of simulated information to RAW DATA analysis: the same analysis steps as for real data keeping access to all information about particle

  9. Mesons yields in thermal model • Pluto event generator based on thermal model with boost • Parameter: Inverse slope • 2 A GeV - 89 MeV • 8 A GeV - 105 MeV • One dilepton per event • 50k dileptons per source Priv.comm. with A.Adronic • Multiplicities of pions, eta from TAPS • omega,rho,phi from mt scaling

  10. mT spectra – simulation T= 87± 1 Chi2/NDF=223/23 T= 86± 1 Chi2/NDF=257/23

  11. mT spectra – experiment T1= 48 ± 2 T2= 86 ± 2 Chi2/NDF=143/24 T1= 44 ± 2 T2= 85 ± 2 Chi2/NDF=57/24 Preliminary Preliminary T= 73 ± 1 Chi2/NDF=451/24 T= 75 ± 1 Chi2/NDF=401/24

  12. Single Lepton spectra CC 2AGeV November 2001 run Difference of Simulation and DATA < 20% CC 2.0 AGeV pT SIM- UrQMD - GEANT simulation with HADES geometry and detector response analyzed with the same cuts

  13. C+C, charged particle multiplicities in META(URQMD) 2AGeV 8AGeV META SHOWER TOF

  14. C+C, charged particle multiplicities,full simulation (GEANT, HYDRA) 2AGeV 8AGeV rec. track vs META hits META hits TOFINO hits TOF hits reconstructed tracks 0 20 0 20

  15. Hadrons (pt vs y) C+C, 2AGeV pi+ pi- p URQMD HYDRA DST Efficiency & acceptance

  16. Hadrons (pt vs y) C+C, 8AGeV pi+ pi- p URQMD HYDRA DST Efficiency & acceptance

  17. Leptons from eta Dalitz (theta) C+C, 2 AGeV e+ e- PLUTO HYDRA DST acceptance+efficiency 0.37 0.40

  18. Leptons from eta Dalitz (theta) C+C, 8 AGeV e+ e- PLUTO HYDRA DST acceptance+efficiency 0.30 0.37

  19. Leptons from omega (pt vs y) 2 A GeV • e+ • e- • Pluto • Geant & Hydra • Eff & acc

  20. Leptons from omega (pt vs y) 8 A GeV • e+ • e- • Pluto • Geant & Hydra • Eff & acc

  21. Dileptons for C+C

  22. Comparison of cocktails

  23. Dilepton yields 1.94e2 4.30e4

  24. Δy Tofino replacement by RPC

  25. UPSTREAM VIEW DOWNSTREAM VIEW RPC RPCs test setup at GSI, April 2003

  26. Rate behaviour of RPC

  27. Δy Charged hadrons, Au+Au Rate per cm2, minimum bias, Au+Au 8 AGeV

  28. Charged hadrons, rates and occupancy per slice

  29. Occupancy per slice, Au+Au, b=0-4 fm 8 AGeV 2 AGeV 0.3 0.7 30 60

  30. Conclusions and Outlook • C+C • similar charged hadrons spectra and multiplicities in META • pion acceptance is by 20-30% lower in 8 AGeV than 2AGeV • single lepton (from eta Dalitz) acceptance by 10-20% lower • dilepton acceptance by 20% lower • Dilepton yield from omega about two orders of magnitude higher Au+Au • Can higher count rate be managed by RPC? • High occupancy per slice >> subdivision of RPC ”rods” To be done • dilepton coctail in Au+Au, • “experimental trigger” in Au+Au • combinatorial background both in C+C and Au+Au

  31. Special thanks to: • Jan Novotný, NPI Řež • Diego Gonzales,USC/Santiago de Compostela • Marina Borisovna Golubeva, INR Moscow • Jaro Bielčik ( NPI Řež ), GSI Darmstadt and to • P.Tlustý, NPI Řež • Juan A. Garzón, USC/Santiago de Compostela • Fedor Guber, INR Moscow

  32. HADES Collaboration • Bratislava (SAS, PI) • Catania (INFN - LNS) • Coimbra (Univ.) • Cracow (Univ.) • Darmstadt (GSI) • Dresden (FZR) • Dubna (JINR) • Frankfurt (Univ.) • Giessen (Univ.) • Milano (INFN, Univ.) • Moscow (INR, ITEP,MEPhI) • Munich (Tech. Univ.) • Nicosia (Univ.) • Orsay (IPN) • Rez (NPI ASCR) • Santiago de Compostela (Univ.) • Valencia (Univ.) HADES spokeperson, Piotr Salabura, Cracow

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