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Analysis of the apparent nuclear modification in peripheral Pb–Pb collisions at 5.02 TeV

Acharya, S ; Adolfsson, Jonatan LU ; Christiansen, Peter LU ; Ljunggren, Martin LU ; Nassirpour, Adrian LU orcid ; Oskarsson, Anders LU ; Silvermyr, David LU orcid ; Stenlund, Evert LU ; Vislavicius, Vytautas LU and Zou, S. (2019) In Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 793. p.420-432
Abstract
Charged-particle spectra at midrapidity are measured in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair s NN =5.02 TeV and presented in centrality classes ranging from most central (0–5%) to most peripheral (95–100%) collisions. Possible medium effects are quantified using the nuclear modification factor (R AA ) by comparing the measured spectra with those from proton–proton collisions, scaled by the number of independent nucleon–nucleon collisions obtained from a Glauber model. At large transverse momenta (8<p T <20GeV/c), the average R AA is found to increase from about 0.15 in 0–5% central to a maximum value of about 0.8 in 75–85% peripheral collisions, beyond which it falls off strongly to below 0.2 for the... (More)
Charged-particle spectra at midrapidity are measured in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair s NN =5.02 TeV and presented in centrality classes ranging from most central (0–5%) to most peripheral (95–100%) collisions. Possible medium effects are quantified using the nuclear modification factor (R AA ) by comparing the measured spectra with those from proton–proton collisions, scaled by the number of independent nucleon–nucleon collisions obtained from a Glauber model. At large transverse momenta (8<p T <20GeV/c), the average R AA is found to increase from about 0.15 in 0–5% central to a maximum value of about 0.8 in 75–85% peripheral collisions, beyond which it falls off strongly to below 0.2 for the most peripheral collisions. Furthermore, R AA initially exhibits a positive slope as a function of p T in the 8–20 GeV/c interval, while for collisions beyond the 80% class the slope is negative. To reduce uncertainties related to event selection and normalization, we also provide the ratio of R AA in adjacent centrality intervals. Our results in peripheral collisions are consistent with a PYTHIA-based model without nuclear modification, demonstrating that biases caused by the event selection and collision geometry can lead to the apparent suppression in peripheral collisions. This explains the unintuitive observation that R AA is below unity in peripheral Pb–Pb, but equal to unity in minimum-bias p–Pb collisions despite similar charged-particle multiplicities. © 2019 Conseil Européen pour la Recherche Nucléaire (Less)
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author
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author collaboration
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
volume
793
pages
13 pages
publisher
Elsevier
external identifiers
  • scopus:85065671184
ISSN
0370-2693
DOI
10.1016/j.physletb.2019.04.047
language
English
LU publication?
yes
additional info
Export Date: 28 May 2019
id
1b5008dd-ef23-42f3-9ae0-fcaf77bf8b01
date added to LUP
2019-05-28 09:25:21
date last changed
2023-04-09 13:20:53
@article{1b5008dd-ef23-42f3-9ae0-fcaf77bf8b01,
  abstract     = {{Charged-particle spectra at midrapidity are measured in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair s NN =5.02 TeV and presented in centrality classes ranging from most central (0–5%) to most peripheral (95–100%) collisions. Possible medium effects are quantified using the nuclear modification factor (R AA ) by comparing the measured spectra with those from proton–proton collisions, scaled by the number of independent nucleon–nucleon collisions obtained from a Glauber model. At large transverse momenta (8&lt;p T &lt;20GeV/c), the average R AA is found to increase from about 0.15 in 0–5% central to a maximum value of about 0.8 in 75–85% peripheral collisions, beyond which it falls off strongly to below 0.2 for the most peripheral collisions. Furthermore, R AA initially exhibits a positive slope as a function of p T in the 8–20 GeV/c interval, while for collisions beyond the 80% class the slope is negative. To reduce uncertainties related to event selection and normalization, we also provide the ratio of R AA in adjacent centrality intervals. Our results in peripheral collisions are consistent with a PYTHIA-based model without nuclear modification, demonstrating that biases caused by the event selection and collision geometry can lead to the apparent suppression in peripheral collisions. This explains the unintuitive observation that R AA is below unity in peripheral Pb–Pb, but equal to unity in minimum-bias p–Pb collisions despite similar charged-particle multiplicities. © 2019 Conseil Européen pour la Recherche Nucléaire}},
  author       = {{Acharya, S and Adolfsson, Jonatan and Christiansen, Peter and Ljunggren, Martin and Nassirpour, Adrian and Oskarsson, Anders and Silvermyr, David and Stenlund, Evert and Vislavicius, Vytautas and Zou, S.}},
  issn         = {{0370-2693}},
  language     = {{eng}},
  pages        = {{420--432}},
  publisher    = {{Elsevier}},
  series       = {{Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics}},
  title        = {{Analysis of the apparent nuclear modification in peripheral Pb–Pb collisions at 5.02 TeV}},
  url          = {{http://dx.doi.org/10.1016/j.physletb.2019.04.047}},
  doi          = {{10.1016/j.physletb.2019.04.047}},
  volume       = {{793}},
  year         = {{2019}},
}