Prospects to study the χ c production at CBM We give preliminary considerations to the feasibility of χ c production study at CBM involving experience of an analogous measurement performed in proton-nucleus collisions at 920 GeV with the Hera-B detector Dmitry Goloubkov , Yuri Zaitsev ITEP, Moscow
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Prospects to study the χ c production at CBM We give preliminary considerations to the feasibility of χ c production study at CBM involving experience.
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Prospects to study theχc production at CBM
We give preliminary considerations to the feasibilityof χc production study at CBM involving experience of
an analogous measurement performed in proton-nucleus collisions at 920 GeV with the Hera-B detector
Dmitry Goloubkov, Yuri ZaitsevITEP, Moscow
D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008
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Physical motivations forstudying χc in HI collisions
Additional charmonium probe and a “thermometer” for QGP
Large-size excited charmonium statesensitive probe for nuclear and QGP effects
D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008
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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/ψ
dirSJ/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
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The Hera-B detector
10 m
Magnet
Muon Detector4 layers of gas pixel
chambers (inner) and MWPC with cathode pad
readout (outer), pad-coincidence pretrigger
0 m20 m
Top View
920 GeV/c Protons
Inner / Outer Tracker7 layers of GEM-MSGCs (inner) and honeycomb drift chambers (outer)
Wire Target 2 stations, 4 wires
each (C, Ti, W)
Silicon Vertex Detector
8 double-layers of double-sided Si-microstrips
RICHC4F10 radiator,
multianode PMT focal plane
ECALW/Pb-scintillator
sampling shashlik calorimeter, cluster
pretrigger
e+/e- beam
D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008
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• kjhkjhkjhkjh
HERA-B detector: data is read out and buffered for 12 s(proton bunches cross every 96 ns, 0.5 interactions/BX)
PreTriggers: ECAL cluster or muon hit coincidence as trigger seed (custom hardware)
5 MHz
First Level Trigger (FLT): Track trigger in hardware using tracking detectors, seeding by pretriggers
3 MHz
Second Level Trigger (SLT): FLT tracking confirmed, extrapolation to vertex detector, 2 track vertex fit (PC farm)
20 kHz
100 Hz
Fourth Level Trigger (4LT): online reconstruction (and filtering) on PC farm, ca. 1500 rec. J/ψ per h
100 Hz
The Hera-B dilepton trigger
D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008
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χc measurement at Hera-B
J/→e+e-
~ 108,000
σ = 64MeV/c2
/
J/ → +-
~ 177,000 σ=44MeV/c2
~3000(2S)
~ 1600 (2S)
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
Σi=1,2σ(χci)Br(χci→J/ψγ)Rχc = σ(J/ψ)
R12=σ(χc1)Br(χc1→J/ψγ)σ(χc2)Br(χc2→J/ψγ)
D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008
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Selection criteriaJ/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)• Eγ
T > 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
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HERA-B χc signal spectraΔM=M(J/ψγ)-M(J/ψ)
Reliable background subtraction is crucial !!
μ+μ-channel
e+e-channel
Nχc = 9630±550 Nχc = 5250±500
N1/N2 = 1.2±0.2 N1/N2 = 0.8±0.3
D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008
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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
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
• 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
for correlation between bckg. normalization and the χc peak parameters)
D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008
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Problem:
Possible solutions:• use γ-conversions to measure the energy of the photon with the tracker (lack of statistics)• significantly increase Eγ
T cut to improve energy resolution• constrain 2-G fit parameters
χc1 - χc2 separation
background: mixed events
after background subtraction
en
trie
s/(1
MeV
/c2)
m(μ+μ-γ)-m(μ+μ-) [GeV/c2]
ET(γ) > 0.4 GeV
χc2χc1
M(χc2)-M(χc1) ~ ( )detector resolution
Necessary for R12,also important for Rχc since
εγ(χc1)≠εγ(χc2), εJ/ψ(χc1)≠εJ/ψ(χc2)
The 2-Gaussian fit parameter χc1/χc2 is most sensitive to the absolute ECALenergy calibration: δEγ ~ 2% => δM(χc1) ~ 8 MeV/c2 => δR12 ~ 35%
D. Goloubkov, Yu. Zaitsev, CBM Meeting Dubna, 14 October 2008