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Prospects to study the χ c production at CBM

Prospects to study the χ c production at CBM. Dmitry Goloubkov , Yuri Zaitsev ITEP, Moscow. We give preliminary considerations to the feasibility of χ c production study at CBM involving experience of

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Prospects to study the χ c production at CBM

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  1. Prospects to study theχc production at CBM Dmitry Goloubkov, Yuri Zaitsev ITEP, Moscow We give preliminary considerations to the feasibility of χc production study at CBM involving experience of an analogous measurement performed in proton-nucleus collisions at 920 GeV with the Hera-B detector

  2. Physical motivations forstudying χc in HI collisions • Additional charmonium probe and a “thermometer” for QGP dissociation temperature: Td(χ) ~ 1.1Tc, Td(J/ψ) ~ 2Tc [e.g. H. Satz, Nucl.Phys.A738 (2007) 249c] χcJ→J/ψγ, J=0,1,2 Large-size excited charmonium state sensitive probe for nuclear and QGP effects J/ψ→ l+l- D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  3. Physical motivations forstudying χc in HI collisions • Account for feed-down contribution to the J/ψ suppression by the normal nuclear matter: SJ/ψ = fJ/ψdirSJ/ψdir + fχSχ + fψ’Sψ’ [e.g. L. Gerland et al., Phys.Rev.Lett.81 (1998) 762] • Additional handle to the nonperturbative MEs of NRQCD D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  4. Muon Detector4 layers of gas pixel chambers (inner) and MWPC with cathode pad readout (outer), pad-coincidence pretrigger Top View Inner / Outer Tracker7 layers of GEM-MSGCs (inner) and honeycomb drift chambers (outer) Wire Target 2 stations, 4 wires each (C, Ti, W) 920 GeV/c Protons e+/e- beam Silicon Vertex Detector8 double-layers of double-sided Si-microstrips Magnet RICHC4F10 radiator, multianode PMT focal plane ECALW/Pb-scintillator sampling shashlik calorimeter, cluster pretrigger 20 m 10 m 0 m The Hera-B detector D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  5. 100 Hz Fourth Level Trigger (4LT):online reconstruction (and filtering) on PC farm, ca. 1500 rec. J/ψ per h The Hera-B dilepton trigger HERA-B detector: data is read out and buffered for 12s(proton bunches cross every 96 ns, 0.5 interactions/BX) 5 MHz • kjhkjhkjhkjh PreTriggers: ECAL cluster or muon hit coincidence as trigger seed (custom hardware) 3 MHz First Level Trigger (FLT): Track trigger in hardware using tracking detectors, seeding by pretriggers 20 kHz Second Level Trigger (SLT):FLT tracking confirmed, extrapolation to vertex detector, 2 track vertex fit (PC farm) 100 Hz D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  6. J/→ +- ~ 177,000 σ=44MeV/c2 J/→e+e- ~ 108,000 σ= 64MeV/c2 /  ~ 1600 (2S) ~3000(2S) Σi=1,2σ(χci)Br(χci→J/ψγ) Rχc = σ(J/ψ) σ(χc1)Br(χc1→J/ψγ) R12= σ(χc2)Br(χc2→J/ψγ) χcmeasurement at Hera-B Dilepton-trigger data sample • N ~ 15.000 χc • (largest statistics in pA) • Large photon detection • efficiency, εγ~ 40% • Both μ+μ- and e+e- channels D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  7. Selection criteria • J/ψ Selection • Track fit χ2 probability > 0.3% • Kaon RICH likelihood LK < 90% • Channel-specific PID cuts • μμ: muon likelihood Lμ > 5% • ee (values depend on the presence of bremsstrahlung radiated before the magnet): - geometrical matching of the track and the ECAL cluster, - E/p ratio • Dilepton vertex prob. > 1% • Reconstruction of χc • Mass difference ΔM=M(J/ψγ)-M(J/ψ) within mass window |Ml+l- - 3.1| < 2σ • Ncells > 2, Ecent/Eclus > 0.8 (suppress MIPs and hadronic showers) • Eγ > 0.3 GeV (remove noise, ensure good energy resolution) • EγT > 0.2 GeV (suppress soft background photons) • √(x2/4+y2) > 22cm (mask out high occupancy region around beam pipe) D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  8. HERA-B χc signal spectra ΔM=M(J/ψγ)-M(J/ψ) e+e- channel μ+μ- channel Nχc = 9630±550 Nχc = 5250±500 N1/N2 = 1.2±0.2 N1/N2 = 0.8±0.3 Reliable background subtraction is crucial !! D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  9. Background description • Main component of the background has combinatorial origin and is simulated by a mix-event method: Mix J/ψ’s and γ’s from events with same high energetic (Eclus > 5 GeV) neutral cluster multiplicity, and similar projections on the XY plane of the total vector momentum of all clusters observed by the ECAL • Procedure extensively tested with MC and real data • Applicable for differential studies of χc vs. xF and pT • Minimizes distortions due to residual correlations • Ensures energy-momentum conservation, accounts • for detector acceptance and real occupancy, etc. Contribution to: ΔM mix-events • Background from ψ(2S) → J/ψπ0π0 • in close vicinity of the χc signal • Bckg. scale factor incorporated in the fit of the ΔM spectrum (accounts for correlation between bckg. normalization and the χc peak parameters) D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  10. detector resolution M(χc2)-M(χc1) ~ () ET(γ) > 0.4 GeV background: mixed events entries/(1 MeV/c2) after background subtraction χc2 χc1 m(μ+μ-γ)-m(μ+μ-) [GeV/c2] χc1 - χc2 separation Necessary for R12, also important for Rχc since εγ(χc1)≠εγ(χc2), εJ/ψ(χc1)≠εJ/ψ(χc2) • Problem: • Possible solutions: • use γ-conversions to measure • the energy of the photon with • the tracker (lack of statistics) • significantly increase EγT cut • to improve energy resolution • constrain 2-G fit parameters The 2-Gaussian fit parameter χc1/χc2 is most sensitive to the absolute ECAL energy calibration:δEγ~ 2% => δM(χc1) ~ 8 MeV/c2 => δR12 ~ 35% D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  11. ~(19 ± 3)% (7.0±0.4)% (0.065±0.011)% σJ/ψdir = σJ/ψincl (1 - Rχc - Rψ’ - Rb ) χc ψ′ b J/ψ J/ψ J/ψ HERA-B χc Result arXiv:0807.2167 [hep-ex] Rχc ≈ 0.19 ± 0.03 (stat.+syst.) R12 ≈ 1.0 ± 0.4 (stat.+syst.) (excluding polarization systematics) • Results in both dilepton channels and • various target materials compatible with each other • Rχc lower than most published values • Additional systematic error due to possible polarization of J/ψ or χc => increase Rχc by as much as 20% and R12 by 16% at 95%C.L. ~ 73% of J/ψ’’s are produced directly D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  12. Simulation of Xc for CBM Xc pT Xc rapidity Black – generated Red - accepted Xc1,2→ J/ψ + γ and J/ψ → e+e- simulated by Pluto with thermodynamic spectrum, T = 170 MeV Assume ECAL energy resolution σE/E ~ 4%/√E + 1%, spatial resolution σXY ~ 5mm/√E + 1mm, apply mild cut on energy of the photon Eγ > 0.2GeV ECAL geometrical acceptance |X| > 84cm, |Y| > 84cm, |X| < 222cm, |Y| < 474cm D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  13. Electrons from J/ψ lepton pT lepton momentum Black – generated Red - accepted J/ψ mass Cut on pT(lepton) > 1GeV/c Momentum resolution dp/p ~ 2% neglect any background under J/ψ Aim: estimate the combinatorial (J/ψ + background photons) contribution to the ∆M(Xc) spectrum σ(M) ~ 43MeV D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  14. Photon from Xc spectra Photon energy Photon ET Black – generated Red - accepted ∆M Y vs X [geometrical] εγ ~60%, the higher ET from Xc induce effective cut E > ~1GeV σ(∆M) resolution ~15MeV/c2 , fully dominated by σE/E D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  15. J/ψ + background photons Photon ET Photon Energy Black – generated Red - accepted E > 0.2 Green – accepted E > 0.5 Blue - accepted E > 1.0 Cyan - accepted E > 1.5 Combinatorial background N photons per event For further analysis select Eγ > 1GeV J/ψ generated by Pluto with thermodynamic spectrum, T=170MeV Background photons taken from UrQMD central AuAu 25AGeV D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  16. Extrapolation to ~106J/ψ background simulated for 1M registered J/ψ ∆M for 200k generated Xc decays In principle, increasing statistics the signal extraction by background subtraction becomes possible D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

  17. Conclusions Production of excited charmonium states in HI collisions provide information complementary to J/ψ, important both in the QGP search and QCD studies of the standard nuclear effects Existing theoretical calculations of J/ψ suppression in HI collisions have to rely on the knowledge of fractions of fed-down J/ψ measured at different conditions in proton- and pion-induced interactions The newest precise measurement of Rχc was obtained by Hera-B in 920 GeV pA interactions. Hera-B has collected useful experience of χc measurement at relatively high combinatorial background. A generator MC study tells Rxc measurement might be possible with CBM (by increasing statistics or in periferal or lighter ion collisions) Further we plan to carry out a full-MC feasibility study of χc production measurement at CBM D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008

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