20.04.23
J/ψ Measurements with the ALICE Experiment at the LHC
Julian Book
28th Winter Workshop on Nuclear Dynamics
220.04.23
Outline
➤ Physics Motivation
➤ The ALICE Experiment
➤ Prompt and Non-Prompt J/ψ Measurements in pp Collisions
➤ Nuclear Modification in Heavy-Ion Collisions
➤ Summary
➤ Outlook
320.04.23
Motivation: J/ψ in Heavy-Ion Collisions
➤ Quark-Gluon Plasma (QGP): Deconfined state of strongly interacting matter➤ J/ψ suppression proposed as a signature [T.Matsui, H.Satz, Phys.Lett. B178(4),416-422 (1986)]
➤ QGP induced effects in AA➤ Melting due to Debye-screening➤ (Re)combination of uncorrelated ccbar➤ Thermal production (only at LHC)
➤ Suppression at SPS and RHIC (80,40%)
➤ Larger suppression at large rapidity
NA60, Nucl.Phys. A 830:345c-352c (2009)PHENIX, arXiv:1103.6269 (2011)
420.04.23
Motivation: J/ψ in pp Collisions
➤ Provide information on production models (CSM, NRQCD, CEM)➤ Elementary production not yet well understood➤ Crucial reference for nuclear modification in Pb-Pb
➤ Multi-Parton Interations on soft, soft-hard, hard scale?➤ Study pp collisions in different event classes, e.g. impact parameter multiplicity
520.04.23
Inclusive and Prompt J/ψ Measurements in ALICE
Down to pT = 0midrapidity |y|<0.9: ITS + TPC
forward rapidity 2.5 < y < 4.0: ITS + MUON
620.04.23
Proton-Proton Collisions
at
√s = 2.76 and 7 TeV
Energy LHC periodInt. Luminosity
J/ψ e+e- J/ψ μ+μ-
2.76 TeV
2011 1.1 nb-1 19.9 nb-1
7 TeV 2010 5.6 nb-1 15.6 nb-1
720.04.23
Invariant Mass Distributions
Midrapidity |y|<0.9 Forward rapidity 2.5<y<4.0
ALICE Coll., Phys.Lett. B704(2011)442
820.04.23
Inclusive Cross Sections: pT and y Dependence
ALICE Coll., Phys.Lett. B704(2011)442, arXiv:1203.3641
920.04.23
Model Comparison: pT and y Dependence
ALICE Coll., Phys.Lett. B704(2011)442, arXiv:1203.3641
1020.04.23
Contribution from B-hadrons
1.3 < pT < 7 GeV/c ; |y|<0.9
ATLAS: Nucl.Phys. B850 (2011) 387,LHCb: Eur.Phys.J. C71 (2011) 1645, CMS: Phys.J. C71, (2011) 1575
➤ fraction from B-hadron decays:0.137 +- 0.054(stat) + 0.025 -0.018 (syst) +0.022 -0.027 (syst polar.)
➤ Strongly pT dependent, rises up to 70% at 40 GeV/c
1120.04.23
Inclusive Cross Sections: Energy Dependence at midrapidity
➤ Strong energy dependence at midrapidity➤ Almost 2x(10x) larger cross sections than at Tevatron (RHIC)
compared to 7 TeV results
ALICE Coll., arXiv:1203.3641 (2012)
1220.04.23
First J/ψ Polarization Measurement at LHC
ALICE Coll., Phys.Rev.Lett. 108, 082001 (2012)M.Butenschoen, B.A. Kniehl arXiv:1201.3862 (2012)
€
W θ ,φ( ) ∝1
3+ λθ1+ λθ cos
2θ + λφ sin2θ cos2φ + λθφ sin2θ cosφ( )
1320.04.23
Charged Particle Multiplicity at Midrapidity
➤ Relative charged particle multiplicity
➤ Up to 5 times the mean multiplicity
➤ Similar significance of J/ψ signal in all intervals
€
dNch /dη = 6.01± 0.01(stat.)−0.12+0.2 (syst.)
ALICE Coll., Eur.Phys.J. C 68: 345–354 (2010)ALICE Coll., arXiv:1202.2816 (2012)(submitted to P.L. B)
1420.04.23
Invariant Mass Distributions
Midrapidity |y|<0.9 Forward rapidity 2.5<y<4.0
low
highmultiplicity
ALICE Coll., arXiv:1202.2816 (2012)(submitted to P.L. B)
1520.04.23
J/ψ Yield as a Function of Charged Particle Multiplicity
➤ Approximately linear increase with midrapidity dNch/dη➤ Similar behaviour in different rapidity regions➤ Enhancement relative to min. bias. yield up to 5(8) at forward (mid-) rapidity➤ PYTHIA shows an opposite trend
ALICE Coll., arXiv:1202.2816 (2012)(submitted to P.L. B)
1620.04.23
Pb-Pb Collisions
at
√sNN = 2.76 TeV
Energy LHC periodInt. Luminosity
J/ψ μ+μ-
2.76 TeV
2010 2.88 μb-1
1720.04.23
Signal in Pb-Pb Collisions at √sNN = 2.76 TeV
Forward rapidity 2.5<y<4.0
Double exponential (Background) + Crystal Ball function (Signals)
1820.04.23
RAA = 0.545 ± 0.032(stat.) ± 0.084(syst.)
➤Less supression at forward rapidity compared to lower √sNN
➤No significant centrality dependence
Nuclear Modification Factor
Centrality dependence
€
RAAi =
YJ /ψi
TAAi ×σ J /ψ
pp
ALICE Coll., arXiv:1202.1383 (2012)(submitted to P.R.L.)
1920.04.23
RAA = 0.545 ± 0.032(stat.) ± 0.084(syst.)
➤Less supression at forward rapidity compared to lower √sNN
➤No significant centrality dependence
➤Stat. Hadronization and transport models can describe the trend in data
Nuclear Modification Factor
Centrality dependence
€
RAAi =
YJ /ψi
TAAi ×σ J /ψ
pp
2020.04.23
➤ Current parametrizations for shadowing affect the RAA by max. 30%
➤ Need for pA measurements
➤ No explicit rapidity dependence
Nuclear Modification Factor
Rapidity dependence
€
RAAi =
YJ /ψi
TAAi ×σ J /ψ
pp
ALICE Coll., arXiv:1202.1383 (2012)(submitted to P.R.L.)
2120.04.23
Summary
➤ Inclusive J/ψ measurements in pp collisions at √s = 2.76 and 7 TeV
results covering a large rapidity area and pT = 0
➤ Polarization in pp collisions at √s = 7 TeV at LHC
in the forward region consistent with no polarization
➤ Fraction of non-prompt J/ψ production at √s = 7 TeV
~14% of J/ψ yield originates from B-hadron decays, strongly pT dependent
➤ Multiplicity dependence of relative J/ψ yields in pp collisions
linear increase of J/ψ yield with midrapidity dNch/dη
➤ Inclusive nuclear modification factor in Pb-Pb collisions at √s = 2.76 TeV
no significant centrality and rapidity dependence
less supression than at RHIC
less supression at low pT
2220.04.23
Outlook
➤ Pb-Pb collisions
➤ RAA in central rapidity
➤ Elliptic flow v2
➤ pA analysis (data end of 2012)
➤ pp collisions
➤ TRD trigger on electrons
Midrapidity |y|<0.9
2320.04.23
BACKUP
2420.04.23
Model Comparison
Direct J/ψ from Hard Processes in PYTHIA
String Interaction Model