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

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

6. Electron identification by TRD Neural net method Output value (ann) >0.9 method method Output value (wkn) >11 Likelihood Output value (like) >0.9 Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007 π e π π e e

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

10. Invariant mass spectrum J/ψ + combinatorial background Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007 Superevent 6x10 8 central Au+Au@25GeV primary particles identified as electrons (p 1 GeV) Signal/background =1.67

11. Summary about using compact RICH for J/ψ reconstruction “standard” RICH&TRD “compact” RICH&TRD efficiency14%14% S/B1.71.67  compact RICH is good for J/ψ:  reconstruction efficiency and signal/background not worse than with “standard” RICH Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

12. Background analysis of superevent 10 9 central Au+Au@25GeV target 250µm target 25 µ m Background sources : ~ 350 π0 percentral Au+Au@25GeVdecayed in ~ 350 π0 per central Au+Au@25GeV decayed in γ γ conversion on the target 98.8% γ γ conversion on the target 98.8% Dalitz decay : e + e - γ Dalitz decay : e + e - γ misidentified pions misidentified pions Target 25µm thickness !!!!!!!!!!! Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007 number of -conversions vs target thickness γ π 0 Dalitz π+π-π+π-π+π-π+π- PDG code of mother particles produced background in mass region >2.9 GeV

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 (2.4x10 10 events), 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 spectra particles 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 2.4x10 10 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 all from PLUTO accepted by CBM reconstructable Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

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

20. Invariant mass spectra  ' + background 2.4x10 10 Au+Au@25GeV central events, 45  's all particles identified as electrons "expo" background fit +cut Pt>1GeV/c "Gaussian" background fit Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

21. J/ψ & Ψ‘ & combinatorial background 2.4x10 10 Au+Au@25GeV all particles identified as electrons by RICH & TRD (P<11GeV/c) + cut Pt>1GeV/c S/B J/ψ 178; Ψ' 1 S/B J/ψ 205; Ψ' 1.5 Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

22. Summary J/  →e+e- 1.92 ∙10 -5 14% 2002.1 ∙ 10 5  '→ e+e-2.56 ∙10 -7 15%(visible!)(3.4 ∙ 10 2 ) Additional investigations should be done Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007multiplicity total efficiency S/B yield/10 weeks