J/ ψ simulations: background studies and first results using a compact RICH detector

1. J/ψ simulations: background studies and first results using a compact RICH detector Alla Maevskaya INR RAS Moscow CBM Collaboration meeting September 2007

2. Outline Simulation environment J/ψ electrons identification by compact RICH J/ψ electrons identification by TRD Background suppression by compact RICH & TRD J/ψ reconstruction Background analysis J/ψ with target 25µm Ψ' simulation Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

3. Simulation&reconstruction environment • CBMROOT Release Aug07 • Gold target 250µm • Magnetic field: "ActiveField" • Full reconstruction STS & MVD • CA track finder • KF track fitter • Primary tracks only (χ2 at primary vertex < 3) • Compact RICH: ring finding, fitting, fake rejection, track matching • TRD 3 different routines for e-π separation • PID by RICH and TRD • Signal: J/ψ decayed to e+e- by PLUTO • HSD multiplicity: for central Au+Au@25GeV collision 1.92x10-5 • Background: superevent of 24K central Au+Au@25GeVUrQMD events Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

5. Comparison of standard and compact RICH for J/ψ reconstruction Can be optimised Standard RICH Compact rich Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

6. Electron identification by TRD π e π e e π Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

7. pion suppression by compact RICH & TRD 24000 Au+Au@25GeV all pions in CBM acceptance surveyed after cuts : • Pt>1GeV/c • RICH ring radius between 4.5 and 7 cm • satisfied all TRD PID criterion: wkn>11 & like>0.9 & ann>0.9 • mismatched electron's ring with wrong track Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

8. J/ψ's electron’s identification efficiency • all J/ψ's electrons accepted by CBM • after cuts P<11GeV/c and Pt>1GeV/c • identified by compact RICH: • neural network ring selection NN>-0.5 • Nhit per ring > 15 • Ring radius 4.5 – 6 cm • Distance between ring center • and track<1cm • identified by TRD • wkn>11 & like>0.9 & ann>0.9 Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

9. J/ψ phase space distribution March 07 Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

10. Invariant mass spectrum J/ψ + combinatorial background Superevent 6x108 central Au+Au@25GeV primary particles identified as electrons(p < 11 GeV/c, pt > 1 GeV) Signal/background =1.67 Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

11. Summary about using compact RICH for J/ψ reconstruction • compact RICH is good for J/ψ: • reconstruction efficiency and signal/background not worse than with “standard” RICH March07 Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

12. Background analysis of superevent 109 centralAu+Au@25GeV target 250µm target 25 µm γ number of -conversions vs target thickness π0 Dalitz π+π- PDG code of mother particles produced background in mass region >2.9 GeV Target 25µm thickness !!!!!!!!!!! Background sources: ~ 350π0 percentral Au+Au@25GeVdecayed in • γ γconversion on the target 98.8% • Dalitz decay : e+ e - γ • misidentified pions Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

13. Charmonium simulation with 25µm gold target Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

14. Simulation environment • cbmroot FEB07 • standard TRD and RICH on the end of May07 • fast tracking private version • superevent of 155000 Au+Au@25GeV central events (2.4x1010events), maximum possible statistics now • primary particles identified as electrons by RICH & TRD participated in combinatorial background Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

15. J/ψ invariant mass spectraparticles identified as electrons with P<11GeV/c for perfect RICH &TRD identification Pt>1GeV/c multiplicity 1.92x10-5 / central Au+Au@25GeV event dielectron branching ratio 0.06 32334 J/ψ correspond to superevent 2.4x1010 Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

16. Ψ' simulation • momentum and rapidity distribution from PLUTO • multiplicity according CBM TSR 2.56x10-7; • dielectron branching ratio 7.35x10-3 Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

17. Ψ’ Pt & Y distributions black histogram from PLUTO blue accepted by STS(5pionts) & TRD & RICH red "reconstructable" (P<11GeV/c) Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

18. Ψ' phase space distribution Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

19. Ψ' electron daughters : Pt momentum Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

20. Invariant mass spectra' + background2.4x1010 Au+Au@25GeVcentralevents, 45's Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

21. J/ψ & Ψ‘ & combinatorial background2.4x1010 Au+Au@25GeV Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

22. Summary Additional investigations should be done Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007