We present the elliptic flow of inclusive J/$\psi$ measured in the
$\mu^{+}\mu^{-}$ channel at forward rapidity ($2.5<y<4.0$), down to zero
transverse momentum, in Pb-Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$
TeV with the ALICE muon spectrometer. The $p_{\mathrm T}$ dependence of
J/$\psi$ $v_2$ in non-central (20%-60%) Pb-Pb collisions at
$\sqrt{s_{_{\mathrm{NN}}}}=2.76$ TeV is compared with existing measurements at
RHIC and theoretical calculations. The centrality dependence of the
$p_{\mathrm{T}}$-integrated elliptic flow, as well as the $p_{\mathrm{T}}$
dependence in several finer centrality classes is presented.Comment: Quark Matter 2012 proceeding

Yang, Hongyan

English

arXiv

AbstractWe present the elliptic flow of inclusive J/ψ measured in the μ+μ− channel at forward rapidity (2.5<y<4.0), down to zero transverse momentum, in Pb–Pb collisions at sNN=2.76TeV with the ALICE muon spectrometer. The pT dependence of J/ψ v2 in non-central (20%–60%) Pb–Pb collisions at sNN=2.76TeV is compared with existing measurements at RHIC and theoretical calculations. The centrality dependence of the pT-integrated elliptic flow, as well as the pT dependence in several finer centrality classes is presented

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Elliptic flow of J/ψ at forward rapidity in Pb–Pb collisions at 2.76 TeV with the ALICE experiment 

We present the elliptic flow of inclusive J/$\psi$ measured in the $\mu^{+}\mu^{-}$ channel at forward rapidity ($2.5<y<4.0$), down to zero transverse momentum, in Pb-Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$ TeV with the ALICE muon spectrometer. The $p_{\mathrm T}$ dependence of J/$\psi$ $v_2$ in non-central (20%-60%) Pb-Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$ TeV is compared with existing measurements at RHIC and theoretical calculations. The centrality dependence of the $p_{\mathrm{T}}$-integrated elliptic flow, as well as the $p_{\mathrm{T}}$ dependence in several finer centrality classes is presented.We present the elliptic flow of inclusive J/@j measured in the @m^+@m^- channel at forward rapidity (2.5<y<4.0), down to zero transverse momentum, in Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76TeV with the ALICE muon spectrometer. The p_T dependence of J/@jv_2 in non-central (20%-60%) Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76TeV is compared with existing measurements at RHIC and theoretical calculations. The centrality dependence of the p_T-integrated elliptic flow, as well as the p_T dependence in several finer centrality classes is presented.We present the elliptic flow of inclusive J/ψ measured in the μ+μ− channel at forward rapidity ( 2.5<y<4.0 ), down to zero transverse momentum, in Pb–Pb collisions at sNN=2.76TeV with the ALICE muon spectrometer. The pT dependence of J/ψ v2 in non-central (20%–60%) Pb–Pb collisions at sNN=2.76TeV is compared with existing measurements at RHIC and theoretical calculations. The centrality dependence of the pT -integrated elliptic flow, as well as the pT dependence in several finer centrality classes is presented.We present the elliptic flow of inclusive J/$\psi$ measured in the $\mu^{+}\mu^{-}$ channel at forward rapidity ($2.5<y<4.0$), down to zero transverse momentum, in Pb-Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$ TeV with the ALICE muon spectrometer. The $p_{\mathrm T}$ dependence of J/$\psi$ $v_2$ in non-central (20%-60%) Pb-Pb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$ TeV is compared with existing measurements at RHIC and theoretical calculations. The centrality dependence of the $p_{\mathrm{T}}$-integrated elliptic flow, as well as the $p_{\mathrm{T}}$ dependence in several finer centrality classes is presented

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Elliptic flow of J/$\psi$ at forward rapidity in Pb-Pb collisions at 2.76 TeV with the ALICE experiment

1. Introduction
1A list of members of the ALICE Collaboration and acknowledgements can be found at the end of this issue.
The ALICE detector is described in [6]. At forward rapidity (2.5 < y < 4.0) the production
of quarkonium states is measured in the muon spectrometer down to pT = 0. The data sample
used for this analysis corresponds to 17 M dimuon unlike sign (MU) triggered Pb-Pb collisions
collected in 2011. It corresponds to an integrated luminosity Lint ≈ 70 μb−1. The event and muon
track selection are the same as described in [7], except for an additional requirement of the event
vertex position |Zvtx| < 10 cm to ensure a flat event plane distribution. J/ψ candidates are formed
by combining pairs of opposite-sign (OS) tracks reconstructed in the geometrical acceptance of
the muon spectrometer.
2. Data analysis and results
sNN = 200 GeV [5] consistent
with zero within uncertainties in the measured pT range (0-10 GeV/c). A non-zero measurement
of quarkonium elliptic flow is especially promising at the Large Hadron Collider (LHC) where
the high energy density of the medium and the large number of cc¯ pairs produced in Pb-Pb
collisions is expected to favor the flow development and regeneration scenarios.
Charmonium production in heavy ion collisions has been studied at diﬀerent energies and
with diﬀerent collision systems, ever since the J/ψ suppression induced by color screening of its
constituent quarks was proposed as a signature of the formation of a quark gluon plasma (QGP)
in heavy-ion collisions [1]. The recent measurement of the J/ψ production in Pb-Pb collisions at
forward rapidity performed by ALICE at the LHC [2] clearly showed less suppression compared
with SPS and RHIC results [3, 4]. At RHIC energies, the preliminary result from the STAR
collaboration showed a J/ψ elliptic flow in Au-Au collisions at √
Elliptic flow of J/ψ at forward rapidity in Pb-Pb collisions at
2.76 TeV with the ALICE experiment
Hongyan Yang (for the ALICE Collaboration)1
SPhN/Irfu, CEA-Saclay, Orme des Merisier, 91191 Gif-sur-Yvette, France
Abstract
sNN = 2.76 TeV is compared with existing measurements at RHIC and
theoretical calculations. The centrality dependence of the pT-integrated elliptic flow, as well as
the pT dependence in several finer centrality classes is presented.
sNN = 2.76 TeV
with the ALICE muon spectrometer. The pT dependence of J/ψ v2 in non-central (20%-60%)
Pb-Pb collisions at √
We present the elliptic flow of inclusive J/ψ measured in the μ+μ− channel at forward rapidity
(2.5 < y < 4.0), down to zero transverse momentum, in Pb-Pb collisions at √
Available online at www.sciencedirect.com
Nuclear Physics A 904–905 (2013) 673c–676c
0375-9474/ © 2013 CERN Published by Elsevier B.V. All rights reserved.
www.elsevier.com/locate/nuclphysa
http://dx.doi.org/10.1016/j.nuclphysa.2013.02.105
© CERN for the benefit of the ALICE Collaboration.
Figure 1: Left: v2 extraction with the event plane method in which the J/ψ raw yield is plotted as a function of Δϕ using
a fit to the data with dNJ/ψ/dΔϕ = A × (1 + 2vobs2 cos 2Δϕ). Right: Inclusive J/ψ v2 in the centrality bin 20%-60% as
a function of pT. A comparison to STAR results and to two parton transport model calculations [10, 11] are shown.
The vertical bars show the statistical uncertainties, and the boxes indicate the point-to-point uncorrelated systematic
uncertainties, which are dominated by the signal extraction.
The J/ψ v2 is measured using event plane based methods [8]. To make a direct comparison
with lower energy measurements, the inclusive J/ψ v2 (pT) was calculated in the same centrality
range 20%-60% as at RHIC [5], as discussed in detail in [9]. The v2 is extracted by fitting the J/ψ
raw yield as a function of Δϕ = φdimuon −ΨEP,2 with dNJ/ψ/dΔϕ = A× (1+2vobs2 cos 2Δϕ), where
A is a normalization constant (the standard event plane method), as shown in Fig. 1 (left panel).
At LHC, the event-plane-resolution-corrected v2 of J/ψ with 2 < pT < 4 GeV/c is diﬀerent from
the STAR preliminary measurement which is compatible with zero in all the measured pT range,
as shown in Fig. 1 (right panel). Two model calculations based on transport mechanism which
include a J/ψ regeneration component from deconfined charm quarks in the medium [10, 11]
are compared with data. These two models diﬀer mostly in the rate equation controlling the J/ψ
dissociation and regeneration. In both models about 50% of the produced J/ψ mesons originate
from regeneration in QGP in the most central collisions. On one hand, thermalized charm quarks
in the medium will transfer a significant elliptic flow to regenerated J/ψ. The maximum v2 at
pT ≈ 2.5 GeV/c results from a dominant contribution of regeneration at lower pT with respect to
the initial J/ψ component. Both models are able to qualitatively describe J/ψ v2(pT) data as both
were also able to describe the earlier RAA measurement [2].
Consistent results in the same centrality bin are obtained with an invariant mass fit technique,
in which we fit the v2 = 〈cos 2Δϕ〉 vs. invariant mass (mμμ) as described in [12]. The method
involves calculating the v2 of the OS dimuons as a function of mμμ and then fitting the resulting
v2 (mμμ) distribution using: v2(mμμ) = vsig2 α(mμμ) + v
bkg
2 (mμμ)[1 − α(mμμ)], where v
sig
2 is the J/ψ
elliptic flow and vbkg2 is the background flow (parametrized using a second order polynomial
function in this analysis). α(mμμ) = S/(S + B) is the ratio of the signal over the sum of the
signal plus background of the mμμ distributions. α(mμμ) is extracted from fits to the OS invariant
mass distribution in each pT and centrality class. The OS dimuon invariant mass distribution
was fitted with a Crystal Ball (CB) function to reproduce the J/ψ line shape, and either a third
order polynomial or a variable width gaussian to describe the underlying continuum. The CB
function connects a Gaussian core with a power-law tail [13] at low mass to account for energy
loss fluctuations and radiative decays. The combination of several CB and underlying continuum
H. Yang / Nuclear Physics A 904–905 (2013) 673c–676c674c
Figure 2: Left: 〈pT 〉uncor and v2 extraction with the fit invariant mass technique. Right: Event plane resolution corrected
J/ψ v2 as a function of centrality of J/ψ with pT ≥ 1.5 GeV/c. The vertical bars show the statistical uncertainties, and the
boxes indicate the point-to-point uncorrelated systematic uncertainties, which are dominated by the signal extraction.
parametrization were tested to assess the signal and the related systematic uncertainties. The J/ψ
v2 in each pT and centrality class was determined as the average of the vsig2 obtained by fitting
v2(mμμ) with various background shapes, while the corresponding systematic uncertainties were
defined as the r.m.s. of these results. A similar method is used to extract the uncorrected average
transverse momentum 〈pT〉uncor of the reconstructed J/ψ in each centrality and pT class. Fig. 2
(left panel) shows typical fits of the OS invariant mass distribution (top left), the 〈cos 2(φ−ΨEP,2)〉
(bottom left) and 〈pT〉uncor (middle left) as a function ofmμμ in the 20%-60% centrality class. The
obtained J/ψ 〈pT〉uncor is used to locate the ALICE points when plotted as a function of transverse
momentum.
Fig. 2 (top right) shows v2 for inclusive J/ψ with pT ≥ 1.5 GeV/c as a function of centrality.
The vertical bars show the statistical uncertainties while the boxes indicate the point-to-point
uncorrelated systematic uncertainties from the signal extraction. The measured v2 depends on
the pT distribution of the reconstructed J/ψ. Therefore, 〈pT〉uncor of the reconstructed v2 is also
shown in Fig. 2 (bottom right) as a function of centrality. For the two most central bins, 5%-20%
and 20%-40% the inclusive J/ψ v2 for pT ≥ 1.5 GeV/c are 0.101 ± 0.044(stat.) ± 0.003(syst.)
and 0.116 ± 0.045(stat.) ± 0.017(syst.), respectively. For the two most peripheral bins the v2 is
consistent with zero within uncertainties. Although there is a small variation with centrality, the
〈pT 〉uncor stays in the range (3.0, 3.3) GeV/c indicating that the bulk of the reconstructed J/ψ are
in the same intermediate pT range for all centralities. Thus, the observed centrality dependence
of the v2 for inclusive J/ψ with pT ≥ 1.5 GeV/c does not result from any bias in the sampled pT
distributions.
Fig. 3 shows the inclusive J/ψ v2(pT), using the invariant mass fit technique, for central, semi-
central and peripheral Pb-Pb collisions at 2.76 TeV. In the semi-central (20%-40%) case, taking
into account statistical and systematic uncertainties, the combined significance of a non-zero v2
in 2 ≤ pT < 6 GeV/c range is 3σ. At lower and higher transverse momentum the inclusive
J/ψ v2 is compatible with zero within uncertainties. In most central (5%-20%) and peripheral
(40%-60%) case, the large uncertainties do not allow any firm conclusion.
H. Yang / Nuclear Physics A 904–905 (2013) 673c–676c 675c
Figure 3: J/ψ v2 as a function of pT in various centrality bins: 5%-20%, 20%-40% and 40%-60%. The vertical bars
show the statistical uncertainties, and the boxes indicate the point-to-point uncorrelated systematic uncertainties from the
signal extraction.
3. Summary and conclusion
In summary, we reported the ALICE measurement of inclusive J/ψ v2 at forward rapidity in
Pb-Pb collisions at √sNN = 2.76 TeV. For non-central (20%-60%) collisions a hint of a non-zero
J/ψ elliptic flow is observed in the intermediate pT range in contrast to the zero v2 observed at
RHIC. Indication of a non-zero J/ψ v2 is also observed in semi-central (20%-40%) collisions at
intermediate pT. The integrated v2 of J/ψ with pT > 1.5 GeV/c in 5%-40% collisions also shows
a non-zero behavior. These measurements complement our earlier results on J/ψ suppression,
where a smaller suppression was seen at low transverse momentum at the LHC compared to
RHIC [2, 7, 14]. Both results taken together could indicate that a significant fraction of the
observed J/ψ are produced from a (re)combination of the initially produced charm quarks. Our
J/ψ elliptic flow results in Pb-Pb collisions at √sNN = 2.76 TeV are in qualitative agreement with
transport models that are able to reproduce our J/ψ RAA measurement.
References
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[2] B. Abelev et al. [ALICE Collaboration] Phys. Rev. Lett. 109, 072301, 2012.
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[5] Z. Tang [STAR collaboration], J. Phys. G38, 12417, 2011.
[6] K. Aamodt et al., [ALICE Collaboration], JINST 3, S08002, 2008.
[7] R. Arnardi, these proceedings.
[8] A. M. Poskanzer and S. A. Voloshin Phys. Rev. C 58, 1671, 1998.
[9] L. Massacrier, Hard Probes 2012 proceedings arXiv:1208.5401, and references therein.
[10] Y.-P. Liu, et al., Phys. Lett. B678, pp. 72–76, 2009 and priv. comm. in 2012.
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[14] E. Scomparin, these proceedings.
H. Yang / Nuclear Physics A 904–905 (2013) 673c–676c676c


Elliptic flow of J/ $\psi$ at forward rapidity in Pb-Pb collisions at 2.76 TeV with the ALICE experiment

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Elliptic flow of J/ψ\psiψ at forward rapidity in Pb-Pb collisions at 2.76 TeV with the ALICE experiment

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Elliptic flow of J/ $\psi$ at forward rapidity in Pb-Pb collisions at 2.76 TeV with the ALICE experiment