Centrality, rapidity and transverse momentum dependence of J/ψ suppression in Pb-Pb collisions at √ s NN =2.76TeV ALICE Collaboration, May 2014 published in Physics Letters B 734 (2014) p.314 – 327 reported on Nov. 15 th during AEPSHEP 2014 – Puri, India by Discussion-group 4 (Cheng-Wei) : N. Alam, S. Bhowmik, I. Chakraborty, D. Das, R. Gouldouzian, C. Gupta , R. Koopman, F. Kuger , M. Moshin, R. Nishimura, D. Sahoo, T. Tomita, S. Zhang.
What happens during a heavy ion collision? Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 2 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
J/ψ production and suppression in QGP Prompt processes Non-prompt processes J/Ψ formation in the QGP. B-Meson and Bottomium (Υ) formation in the QGP. J/ Ψ b decay to J/Ψ outside QGP J/ Ψ Υ J/ Ψ Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 3 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
J/ψ production and suppression in QGP Prompt processes Non-prompt processes - Screening effect: - No screening for B Mesons J/ Ψ Density of color charges shields potential c-c bar pairs - J/Ψ emerging from b -quark suppressed (re-)combination conversion are not effected by (Debye screening length λ D ) QGP effects - Quenching in QGP: Interference with color charges B J/ Ψ while transversing the fireball J/ Ψ - And many more (Shadowing, Nuclear absorption, CNM…) Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 4 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
How to quantify the differences in J/ψ production between pp and PbPb collissions? ? Why not: N x (pp) ? R AA Nuclear modification factor # of observed J/ ψ events (signal) J/ ψ yield nuclear overlap function – > J/ ψ braching ratio detector derived from centrality class (PDG) acceptance ( η , ϕ ) J/ ψ pp cross section # of total events efficienies: – > results from pp collsions in (MB trigger) trigger, track reco., PHENIX, CDF and ALICE offline selection Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 5 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
Centrality, rapidity and transverse momentum distance between CMS Pb -Trajectories b unscattered nucleons are detected in the forward region (V0 and ZGC) b ‚ spectators ‘ are detected in V0 and ZGC Centrality classes (%) are defined and nuclear overlap function (T AA ) and <N part > resolved (Glauber models) Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 6 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
Centrality, rapidity and transverse momentum Rapidity y and Pseudo-rapidity η η defines inclination of the track towards the beamline. η = -0.9 Measured in terms of particle momentum Θ η = -2.5 in approximation of negligible particle masses η = -4.0 Transverse momentum p T p T describes the momentum in the plane perpendicular to the beam line. Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 7 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
ALICE - A Large Ion Collider Experiment Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 8 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
J/Ψ e + e - signal reconstruction Pair of opposite-sign(OS) electrons in the barrel region, satisfying - track quality cuts for track reconstruction in ITS and TPC (e.g. 1 of 2 hits in innermost IST layers reject γ conversion min. 70 (of 159) clusters in TPC, passing a χ 2 -based quality cut typical dE/dx in TPC electron identification / pion rejection) - momentum cut on p T > 0.85GeV (exp 1.5GeV in CMS J/Ψ ) - rapidity requirement |η|<0.8 4k signal-events N J/Ψ = N ee | 2.92<mee<3.16 GeV -Bkg Background obtained with data-driven mixed event technique in agreement within CR. Bremsstrahlung tail Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 9 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
J/Ψ µ + µ - signal reconstruction Muon tracks are reconstructed using the combined information of ITS and Muon Tracking Chambers: - tightend cut criteria compared to pp-collisions cope with larger background in Pb-Pb - accepted rapidity 2.5 < y < 4.0 (excluding events close to the MTC edges) 16k signal-events N J/Ψ is extracted in each centrality (9), kinematic (7) and rapidity (6) interval: Fit with and extended Crystal Ball. Signal-Bkg subtraction ( ME technique accordingly to e + e — channel) Both methods yield congruent results. Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 10 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
Centrality, rapidity and transverse momentum R AA (nuclear modification factor) dependence on centrality ( <N part >) is reported for: Mid rapidity region: | y |<0.8, e + e - -channel 3 centrality classes Forward rapidity region: 2.5< y <4.0 , µ + µ - -channel in 9 intervals. A clear suppression is observed at forward rapidity for <N part > >70, visible but less pronounced in mid- rapidity. In agreement with a saturation of screening effects at a threshold density of color charges at <N part > >70. Error estimation includes: Statistical uncertainties (error bars) Uncorrelated systematic uncertainties (boxes) Contradictory to PHENIX results (√ s NN =0.2TeV), Correlated systematic uncertainties (global syst.) exhibiting a suppression-factor >3! Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 11 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
Centrality, rapidity and transverse momentum R AA dependence on rapidity is evaluated in mid- and forward-rapidity region R AA -suppression of about 40% is observed within the forward region towards higher rapidity. ‘…The result from electron analysis is consistent with a constant or slightly increasing R AA towards mid rapidity.’ Error estimation includes: Statistical uncertainties (error bars) Uncorrelated systematic uncertainties (boxes) Correlated systematic uncertainties (global syst.) Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 12 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
Centrality, rapidity and transverse momentum R AA dependence on p T in the forward region for 0-90% centrality yields a >2 suppression. Similar results in 0-20% centrality (majority of J/ Ψ ) Observation is in agreement with CMS * (1.6<| y |<2.4, 0-100% centrality) results at same Pb-Pb collision conditions. Again ALICE results contradict previous results by PHENIX (Au- Au|√ sNN=0.2TeV, 1.2<| y |<2.2, 0-20% centrality) ‘results point to the presence of a new contribution to the J/ Ψ yield at low p T .‘ * CMS PT intervals 3<p T <30GeV and 6.5<p T <30GeV, thus dependent Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 13 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
Thank you for your attention! ? Questions are welcome (but might remain unresolved ) Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
‘Universal‘ Backup – Telephone Joker! Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 16 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
Backup - Systematic uncertainties Type I: Correlated uncertainties global uncertainty Type II: Uncorrelated uncertainties displayed on bin level Nov. 15 th 2014 Centrality, rapidity and transverse momentum dependence of 17 Puri, India J/ψ suppression in Pb – Pb collisions at √ sNN=2.76TeV
dE/dx in TPC for particle ID
Recommend
More recommend
