Absence of jet quenching in peripheral nucleus–nucleus collisions

Loizides, C.; Morsch, A.

doi:10.1016/j.physletb.2017.09.002

Cited by 68 publications

(51 citation statements)

References 32 publications

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“…The resulting change in N coll is qualitatively similar to earlier studies [70] on the influence of the nucleon-nucleon collision geometry on the determination of the R AA . However, a realistic modeling of the number of hard collisions per NN collision, and in general of the correlation between soft and hard particle production, is needed to be able to compare experimental data with calculations [71].…”

Section: Appendix B: Subnucleonic Degrees Of Freedommentioning

confidence: 99%

Improved Monte Carlo Glauber predictions at present and future nuclear colliders

2018

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We present the results of an improved Monte Carlo Glauber (MCG) model of relevance for collisions involving nuclei at center-of-mass energies of BNL RHIC ( √ s NN = 0.2 TeV), CERN LHC ( √ s NN = 2.76-8.8 TeV), and proposed future hadron colliders ( √ s NN ≈ 10-63 TeV). The inelastic pp cross sections as a function of √ s NN are obtained from a precise data-driven parametrization that exploits the many available measurements at LHC collision energies. We describe the nuclear density of a lead nucleus with two separated 2-parameter Fermi distributions for protons and neutrons to account for their different densities close to the nuclear periphery. Furthermore, we model the nucleon degrees of freedom inside the nucleus through a lattice with a minimum nodal separation, combined with a "recentering and reweighting" procedure, that overcomes some limitations of previous MCG approaches. The nuclear overlap function, number of participant nucleons and binary nucleonnucleon collisions, participant eccentricity and triangularity, overlap area and average path length are presented in intervals of percentile centrality for lead-lead (PbPb) and proton-lead (pPb) collisions at all collision energies. We demonstrate for collisions at √ s NN = 5.02 TeV that the central values of the Glauber quantities change by up to 7% in a few bins of reaction centrality, due to the improvements implemented, though typically remain within the previously assigned systematic uncertainties, while their new associated uncertainties are generally smaller (mostly below 5%) at all centralities than for earlier calculations. Tables for all quantities versus centrality at present and foreseen collision energies involving Pb nuclei, as well as for collisions of XeXe at √ s NN = 5.44 TeV, and AuAu and CuCu at √ s NN = 0.2 TeV, are provided. The source code for the improved Monte Carlo Glauber model is made publicly available.

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Section: Appendix B: Subnucleonic Degrees Of Freedommentioning

confidence: 99%

Improved Monte Carlo Glauber predictions at present and future nuclear colliders

2018

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“…Although there is a large normalization uncertainty, the R * AA is significantly below unity in this centrality range. Such a suppression in peripheral events is not expected to be caused by strong energy loss effects, but might be related to correlations between the charged-particle yields in the mid-rapidity region with event activity in the range 3 < |η| < 5.2 that is used to determine the event centrality [46]. Recent measurements of R AA in peripheral PbPb collisions by the ALICE Collaboration show a similar effect that has been interpreted as a bias caused by event selection and collision geometry [47].…”

Section: Resultsmentioning

confidence: 99%

Charged-particle nuclear modification factors in XeXe collisions at $$ \sqrt{s_{\mathrm{NN}}} = 5.44 $$ TeV

Sirunyan¹,

Tumasyan²,

Adam³

et al. 2018

J. High Energ. Phys.

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The differential yields of charged particles having pseudorapidity within |η| < 1 are measured using xenon-xenon (XeXe) collisions at √ s NN = 5.44 TeV. The data, corresponding to an integrated luminosity of 3.42 µb −1 , were collected in 2017 by the CMS experiment at the LHC. The yields are reported as functions of collision centrality and transverse momentum, p T , from 0.5 to 100 GeV. A previously reported p T spectrum from proton-proton collisions at √ s = 5.02 TeV is used for comparison after correcting for the difference in center-of-mass energy. The nuclear modification factors using this reference, R * AA , are constructed and compared to previous measurements and theoretical predictions. In head-on collisions, the R * AA has a value of 0.17 in the p T range of 6-8 GeV, but increases to approximately 0.7 at 100 GeV. Above ≈6 GeV, the XeXe data show a notably smaller suppression than previous results for lead-lead (PbPb) collisions at √ s NN = 5.02 TeV when compared at the same centrality (i.e., the same fraction of total cross section). However, the XeXe suppression is slightly greater than that for PbPb in events having a similar number of participating nucleons.The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter, and a brass and scintillator hadron calorimeter, each composed of a barrel and two endcap sections. Forward calorimeters extend the η coverage provided by the barrel and endcap detectors. Muons are detected in gas-ionization chambers embedded in the steel flux-return yoke outside the solenoid.The silicon tracker measures charged particles within the range |η| < 2.5. It consists of 1856 silicon pixel and 15 148 silicon strip detector modules. For nonisolated particles of 1 < p T < 10 GeV and |η| < 1.4, the track resolutions are typically 25-90 (45-150) µm in the transverse (longitudinal) impact parameter [25].The hadron forward (HF) calorimeter uses steel as an absorber and quartz fibers as the sensitive material. The two halves of the HF are located 11.2 m from the interaction region, one on each end, and together they provide coverage in the range 3.0 < |η| < 5.2.Events of interest are selected using a two-tiered trigger system [26]. During XeXe operation the first level trigger (L1), composed of custom hardware processors, uses information from the calorimeters to select events at a rate of around 4 kHz within a time interval of less than 4 µs. The second level, known as the high-level trigger (HLT), consists of a farm of processors running a version of the full event reconstruction software optimized for fast processing, and reduces the event rate to around 2 kHz before data storage.A more detailed description of the CMS detector, together with a definition of the coordinate system used and the relevant kinematic variables, can be found in Ref. [27].

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“…In Ref. [25], simulations with the HIJING generator and the Glauber+PYTHIA model can reproduce the suppression observed in an example peripheral bin. However, new measurements of EW boson R AA in this data show that the expected scaling holds, in fact showing a modest enhancement in peripheral events [26].…”

Section: Jet Quenching In Small Systemsmentioning

confidence: 99%

Hard processes in small systems

Perepelitsa¹

2019

Proceedings of 12th International Workshop on High-pT Physics in the RHIC/LHC Era — PoS(High-pT2017)

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Absence of jet quenching in peripheral nucleus–nucleus collisions

Cited by 68 publications

References 32 publications

Improved Monte Carlo Glauber predictions at present and future nuclear colliders

Improved Monte Carlo Glauber predictions at present and future nuclear colliders

Charged-particle nuclear modification factors in XeXe collisions at $$ \sqrt{s_{\mathrm{NN}}} = 5.44 $$ TeV

Hard processes in small systems

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