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Effects of Multiple Scattering in Cold Nuclear Matter on J/psi Suppression and <p_T^2> in Heavy Ion Collisions

Nuclear Theory · Submitted 24 Feb 2006 · 30 references

Pith's verdict: A careful MC study that credibly rules out 2D Gaussian cold-matter rescattering as the sole source of J/psi suppression, but the stronger 'any value of <k_T^2>' claim is tied to that specific kick model.

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arXiv IDnucl-th/0602068 (version 2)
Pith IDVGVSRSVW, Pith's permanent record of this paper and its review
CitationA.M. Glenn, Denes Molnar, J.L. Nagle. "Effects of Multiple Scattering in Cold Nuclear Matter on J/psi Suppression and <p_T^2> in Heavy Ion Collisions." arXiv:nucl-th/0602068 (2006). https://pith.science/paper/VGVSRSVW
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Referee report
The paper

The paper claims

A Monte-Carlo study of incoherent multiple scattering of charm quark pairs in cold nuclear matter concludes that no value of the transverse-momentum fluctuation strength can simultaneously reproduce the measured J/psi suppression and…

The reading

This paper sets out to test whether the J/psi suppression seen in heavy-ion collisions can be blamed on the charm quark pair being randomly knocked around in the surrounding cold nuclear matter. In the incoherent rescattering picture examined here, the same transverse kicks that suppress J/psi formation also broaden the produced J/psi's transverse momentum, so the two measurements are locked together on a single model curve. Scanning every value of the one free parameter, the average squared momentum transfer per scattering $\langle k_T^2\rangle$, the authors find that no point on that curve matches the SPS and RHIC data for suppression and $\langle p_T^2\rangle$ at the same time. If this holds, incoherent cold-matter rescattering cannot be the whole story of the anomalous J/psi suppression, and some other mechanism, such as a hot deconfined medium, must be at work.

What carries the argument

The load-bearing mechanism is a momentum-space random walk: each charm quark and antiquark receives a set of independent, small transverse momentum kicks whose total is Gaussian-distributed (Eq. 6), with the strength per unit pathlength set by $\langle k_T^2\rangle$. The accumulated change in the c-cbar relative momentum is driven by the nonrelativistic approximation $\Delta q^2 \approx \Delta k_T^2 + 2 \Delta k_T q \cos\theta$ (Eq. 7), which couples the suppression mechanism (growth of $q^2$ reduces the J/psi formation probability $F(q^2)$) to the observable broadening $\Delta\langle p_T^2\rangle$. The effective formation probabilities in Eq. (8) show how including fluctuations in the magnitude and direction of the kicks converts exponential suppression into a milder power-law behavior. A Monte-Carlo model of the nuclear collision geometry provides the pathlengths, and the event generator for proton-proton collisions provides the initial $q^2$ distribution of the pairs.

Extended reading notes

Core claim

The central claim is that in the incoherent multiple-scattering framework, with independent two-dimensional Gaussian transverse momentum kicks on the charm quark and the charm antiquark, the experimentally measured J/psi suppression and transverse momentum broadening from nucleus-nucleus collisions at the SPS and at RHIC cannot be described simultaneously for any value of the fluctuation strength parameter $\langle k_T^2\rangle$. The argument runs through the nonrelativistic relation between the change in the pair's relative momentum and the transverse momentum broadening (Eq. 7), which forces increasing suppression to come with increasing $\langle p_T^2\rangle$. In the $(R_{AA}, \Delta\langle p_T^2\rangle)$ plane, the model traces a one-parameter curve; the measured points from central SPS and RHIC collisions lie away from that curve. The same conclusion holds for both color-singlet and color-octet J/psi formation, and the paper stresses that fluctuations make suppression much weaker than the earlier constant-shift treatment, for a given rescattering strength.

Load-bearing premise

The conclusion rests on the assumption that the charm quark and antiquark are kicked independently with Gaussian-distributed transverse momenta, and that only the transverse relative momentum determines J/psi formation; if the kicks are correlated, or longitudinal momentum transfer matters, or the kick distribution is not Gaussian, the curve linking suppression and <$p_T^{2}$> could be different.

Editorial extensions

If this is right

  • Any incoherent rescattering model of this type predicts a one-parameter family of (suppression, <p_T^2>) pairs, so measuring both observables in the same system tightly constrains or excludes the model.
  • The earlier coherent-scattering conclusion that cold matter alone explains Pb+Pb suppression is shown to depend on ignoring fluctuations, since fluctuations dramatically weaken the suppression at a fixed rescattering strength.
  • With fluctuations included, color-singlet and color-octet formation probabilities become nearly indistinguishable, so J/psi suppression data alone cannot discriminate the production mechanism in this framework.
  • Since cold-matter rescattering cannot account for the data, additional suppression from a hot deconfined medium, or some other mechanism, is required to explain the observed J/psi yields in nucleus-nucleus collisions.
  • The same suppression-broadening correlation can be computed for other quarkonium states, such as the Upsilon, and compared with future data as a test of the incoherent multiple-scattering picture.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A testable extension is to model correlated kicks, where the quark and antiquark receive equal-and-opposite transverse momenta so the pair's total p_T is unchanged; this would break the tight relation between suppression and <p_T^2> and could in principle rescue this class of models.
  • The paper's no-fit statement is for the 2D Gaussian case; since the 3D random walk gives stronger suppression at moderate pathlengths, a full 3D analysis might shift the curve, although the mismatch for central events would likely survive.
  • The (R_AA, Delta<p_T^2>) curve could serve as a reference line for future p+Pb or Pb+Pb measurements at the LHC, offering a quick way to decide whether incoherent rescattering contributes significantly to quarkonium suppression.
Original abstract

Coherent multiple scatterings of c and cbar quark pairs in the environment of heavy ion collisions have been used in a previous work by Qiu et al. [Qiu:1998rz] to study J/psi suppression. That model suggests that heavy quark re-scatterings in a cold nuclear medium can completely explain the centrality dependence of the observed J/psi suppression in Pb+Pb collisions at the SPS [Abreu:2001kd]. Their calculations also revealed significant differences under the assumptions of a color singlet or color octet production mechanism. A more recent analytic calculation [Fujii:2003fq], which includes incoherent final-state re-scatterings with explicit momentum transfer fluctuations in three dimensions, indicates much less suppression and little sensitivity to the production mechanism. In this article, we study simultaneously both the J/psi suppression and p_T modifications, at SPS and RHIC energies. We mainly focus on incoherent momentum transfer fluctuations in two dimensions, which is more appropriate for the heavy-ion collision kinematics. Our analytic and Monte-Carlo calculations reinforce the analytic results in [Fujii:2003fq]. Additionally, we find that the experimental J/psi suppression and <p_T^2> from nucleus-nucleus collisions at the SPS or RHIC cannot simultaneously be described in this incoherent multiple scattering framework for any value of the fluctuation strength parameter <k_T^2>.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-23: 1 request, 6,456 input tokens.

What the abstract itself states, as probabilities: claims first 0.05 · states limitation 0.94 · human participants 0.01 · controlled comparison 0.09 · randomized assignment 0.01 · states quantitative result 0.09 · compares with prior results 0.97 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

Coherent multiple scatterings of c and cbar quark pairs in the environment of heavy ion collisions have been used in a previous work by Qiu et al. [Qiu:1998rz] to study J/psi suppression. That model suggests that heavy quark re-scatterings in a cold nuclear medium can completely explain the centrality dependence of the observed J/psi suppression in Pb+Pb collisions at the SPS [Abreu:2001kd]. Their calculations also revealed significant differences under the assumptions of a color singlet or color octet production mechanism. A more recent analytic calculation [Fujii:2003fq], which includes incoherent final-state re-scatterings with explicit momentum transfer fluctuations in three dimensions, indicates much less suppression and little sensitivity to the production mechanism. In this article, we study simultaneously both the J/psi suppression and p_T modifications, at SPS and RHIC energies. We mainly focus on incoherent momentum transfer fluctuations in two dimensions, which is more appropriate for the heavy-ion collision kinematics. Our analytic and Monte-Carlo calculations reinforce the analytic results in [Fujii:2003fq]. Additionally, we find that the experimental J/psi suppression and <p_T^2> from nucleus-nucleus collisions at the SPS or RHIC cannot simultaneously be described in this incoherent multiple scattering framework for any value of the fluctuation strength parameter <k_T^2>.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 Coherent multiple scatterings of c and cbar quark pairs in the environment of heavy ion collisions have been used in a previous work by Qiu et al. [Qiu:1998rz] to study J/psi suppression. background 1.00 0.03 0.01 asserted 1.00
s1 That model suggests that heavy quark re-scatterings in a cold nuclear medium can completely explain the centrality dependence of the observed J/psi suppression in Pb+Pb collisions at the SPS [Abreu:2001kd]. background 0.99 0.04 0.04 hedged possibility 0.89
s2 Their calculations also revealed significant differences under the assumptions of a color singlet or color octet production mechanism. background 0.96 0.04 0.02 asserted 1.00
s3 A more recent analytic calculation [Fujii:2003fq], which includes incoherent final-state re-scatterings with explicit momentum transfer fluctuations in three dimensions, indicates much less suppression and little sensitivity to the production mechanism. background 1.00 0.04 0.04 hedged possibility 0.88
s4 In this article, we study simultaneously both the J/psi suppression and p_T modifications, at SPS and RHIC energies. contribution 1.00 0.77 0.03 asserted 0.97
s5 We mainly focus on incoherent momentum transfer fluctuations in two dimensions, which is more appropriate for the heavy-ion collision kinematics. method 0.89 0.54 0.03 asserted 0.87
s6 Our analytic and Monte-Carlo calculations reinforce the analytic results in [Fujii:2003fq]. result 0.89 0.90 0.07 asserted 1.00
s7 Additionally, we find that the experimental J/psi suppression and <p_T^2> from nucleus-nucleus collisions at the SPS or RHIC cannot simultaneously be described in this incoherent multiple scattering framework for any value of the fluctuation strength parameter <k_T^2>. result 0.98 0.96 0.89 asserted 1.00

What kind of paper the classifier reports this is: theoretical result 0.82 · evidence from simulation or computation 0.87.

What was examined, and what was not

sources read
  • arXiv listing abstract v2
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. FIG. 1: Diagram of a nucleus-nucleus collision. Arrows at th
Figure 3. also shows a comparison of J/ψ suppression in the shifted q 2 model and the fluctuation model. Just like for the analytic study in Section II, we keep the average q 2 shift the same in both cases and therefore use hk 2 T i = 0.3
Figure 5. FIG. 5: The nuclear modification factor and ∆
Figure 6. FIG. 6: The nuclear modification factor and ∆
Figure 7. We show that for any parameter values of

Showing 5 of the paper's 7 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:nucl-th/0602068 by the authors.

References

Discussion

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