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Mea surement of p 0 – induced single leptons in the HADES RICH

Mea surement of p 0 – induced single leptons in the HADES RICH. T. Eberl, T. Christ, L. Fabbietti, J. Friese, R. Gernhäuser, J. Homolka, H.-J. Körner, M. Münch, B. Sailer, and S. Winkler for the HADES collaboration. Motivation: Study of close e + e - - pairs RICH ring properties

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Mea surement of p 0 – induced single leptons in the HADES RICH

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  1. Measurement of p0 – induced single leptons in the HADES RICH T. Eberl, T. Christ, L. Fabbietti, J. Friese, R. Gernhäuser, J. Homolka, H.-J. Körner, M. Münch, B. Sailer,and S. Winkler for the HADES collaboration • Motivation: • Study of close e+e- - pairs • RICH ring properties • Comb. backgr. in e+e- - spectroscopy • Exp. Setup • HADES with low B-Field • Results • Opening angle distributions of identified close e+e- - pairs • Properties of Cherenkov Rings !!! T. Eberl, TU München

  2. Dilepton Spectroscopy HADES : Low mass e+e- pairs from p, p, A + A collisions Comb. Backgr. Suppression Close pair recognition !!!! & rejection 2 close rings in RICH 2 close tracks in MDC full scale HGEANT simulation T. Eberl, TU München

  3. Sources of Close Rings & Tracks Physics processes : p0 - Dalitz,p0 gg g - conversion, compt. scatt. Possible combinations P1 P2 RICH MDC e+ e- 1 1 e+ e- 1 2 e+ e- 2 2 e+ e- 2 1 fake ? e+ e- 2 3 ?? ........... e+/- 1 1 p 1 1 fake ! p+/- 1 1 fake ! ........... rare cases : p e+/- 1 2 p+/- e+/- 1 2 ........... < Q >~ 13 0 e+ g e- p0 Dalitz e- g interesting pair ??? e+ e- < Q>~ 20 Conversion in Target & Radiator T. Eberl, TU München

  4. Experimental Setup @ GSI, Darmstadt • HADES with RICH, MDC 1 / 2 , META , low B – field • optimized for e+/- with low p • full reconstr. of low mass pairs Deflection in B - field DQ = QMDC– QMETA ~ 1 / P DQ DQ standard T. Eberl, TU München

  5. HADES acceptance 3g-threshold of RICH Acceptance for p0-Dalitz leptons Simulation: p0-Dalitz decay T. Eberl, TU München

  6. C + C @ E = 1A GeV Experiment @ SIS - GSI Ibeam = 106 / s, Targ: stot = 5% Trig: MMeta > 3; s/stot ~ 0,7 Nexp = 9 * 106 evts. Numerical Experiment (Simulation) UrQMD + HGEANT Setup as in exp. Trig: MMeta > 3; included Nsim = 7 * 106 evts. • Analysis conditions: • Event selection: • MDC I/II : multiplicity Mtrack > 3 • RICH : min. 1 Ring corr. with MDC & META • Hit matching conditions: • before B- field : DQMDC-RICH < 2° ; DFMDC-RICH < 5° • after B- field : DQMDC-META : no ; DFMDC-META < 5° • no TOF cut !! T. Eberl, TU München

  7. e+/e- cand. for C + C @ 1A GeV Rings in RICH Defl. angles DQ = QMDC– QMETA of reconstructed tracks in RICH & MDC & META Single ?? e- e+ Double T. Eberl, TU München

  8. Measured RICH Rings C + C E = 1A GeV • Ring recognition: • Pattern Matrix • Hough-Transf. p0-Dalitz decay leptons ?! T. Eberl, TU München

  9. e+ e- pairs Opening angle distr. in MDC (before B – field)Reasonable agreement !!! C + C E = 1A GeV Exp Sim (total) Counts [a.u.] p0 – Dalitz Conversion Sim. normalised to Exp. Opening angle [deg] T. Eberl, TU München

  10. Ring selection for single electrons e+e- pairs with 1 track / ring Opening angle distr. In MDC (before B - field) Singlerings! e+ e- 2 MDC tracks 2 RICH rings T. Eberl, TU München

  11. e+ e- Rings for close tracks Opening angle distr. in MDC (before B - field) e+e- pairs with 2 tracks/ring Double rings ! e+ e- 2 MDC tracks 1 MDC track 1 RICH ring T. Eberl, TU München

  12. e+ e- e+ e- Sim Exp Ring properties: charge & pads Chargeperring Pads perring double double Counts [a.u.] Counts [a.u.] C + C E = 1A GeV single single Counts [a.u.] Counts [a.u.] Charge/ring [a.u.] Pads/ring T. Eberl, TU München

  13. e+ e- e+ e- Sim Exp Ring properties: cluster & quality Clusters perring Pattern Matrix sum double double Counts [a.u.] Counts [a.u.] C + C E = 1A GeV single single Counts [a.u.] Counts [a.u.] clusters/ring matrix sum [a.u.] T. Eberl, TU München

  14. Polar angle [deg] Momentum [MeV/c] Lepton recognition e- GEANT Simulation: p0 -Dalitz decay min 1 lepton required ! META MDC p0 RICH e+ RICH MDC META HADES reconstruction probability for a p0-Dalitz decay lepton C+C, E=1AGeV, low field setup, cons. param. set T. Eberl, TU München

  15. e- META MDC p0 RICH e+ Polar angle [deg] RICH MDC META Momentum [MeV/c] Pair recognition 2 leptons required ! GEANT Simulation: p0-Dalitz decay HADES reconstruction probability for a lepton from an identified p0-Dalitz lepton pair C+C, E=1AGeV, low field setup T. Eberl, TU München

  16. Summary • Dilepton spectroscopy with HADES : • Measurement of close pairs for low momentum e+e- • Good statistics of p0 – Dalitz and conversion leptons • Experimental data for comb. backgr. and eff. studies • Results from prel. analysis • Ident. of rings from fully reconstr. single leptons in RICH • Full scale simulation vs. experiment : ok • Simulation: single lepton reconstr. prob. for p0 – Dalitz • Meas. of key ring prop. for singles and doubles (for each sector) • Outlook: • Quantitative comb. backgr. studies • Efficiencies for single lepton identification T. Eberl, TU München

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