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

The ALICE Collaboration, S. Acharya, E. J. Brücken, B. Chang, T. E. Hilden, D. J. Kim, V. Litichevskyi, M. M. Mieskolainen, R. Orava, J. E. Parkkila, J. Rak, S. S. Räsänen, S. Saarinen, M. Slupecki, T. W. Snellman, W. H. Trzaska, M. Vargyas, J. Viinikainen

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Charged-particle spectra at midrapidity are measured in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair root 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) < 20 GeV/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. (C) 2019 Conseil Europeen pour la Recherche Nucleaire. Published by Elsevier B.V.
Original languageEnglish
JournalPhysics Letters B
Volume793
Pages (from-to)420-432
Number of pages13
ISSN0370-2693
DOIs
Publication statusPublished - 10 Jun 2019
MoE publication typeA1 Journal article-refereed

Fields of Science

  • 114 Physical sciences
  • CHARGED-PARTICLE PRODUCTION
  • TRANSVERSE-MOMENTUM
  • CENTRALITY DEPENDENCE
  • JET
  • SUPPRESSION
  • PP

Cite this

The ALICE Collaboration, Acharya, S., Brücken, E. J., Chang, B., Hilden, T. E., Kim, D. J., ... Viinikainen, J. (2019). Analysis of the apparent nuclear modification in peripheral Pb-Pb collisions at 5.02 TeV. Physics Letters B, 793, 420-432. https://doi.org/10.1016/j.physletb.2019.04.047
The ALICE Collaboration ; Acharya, S. ; Brücken, E. J. ; Chang, B. ; Hilden, T. E. ; Kim, D. J. ; Litichevskyi, V. ; Mieskolainen, M. M. ; Orava, R. ; Parkkila, J. E. ; Rak, J. ; Räsänen, S. S. ; Saarinen, S. ; Slupecki, M. ; Snellman, T. W. ; Trzaska, W. H. ; Vargyas, M. ; Viinikainen, J. / Analysis of the apparent nuclear modification in peripheral Pb-Pb collisions at 5.02 TeV. In: Physics Letters B. 2019 ; Vol. 793. pp. 420-432.
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title = "Analysis of the apparent nuclear modification in peripheral Pb-Pb collisions at 5.02 TeV",
abstract = "Charged-particle spectra at midrapidity are measured in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair root 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) < 20 GeV/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. (C) 2019 Conseil Europeen pour la Recherche Nucleaire. Published by Elsevier B.V.",
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author = "{The ALICE Collaboration} and S. Acharya and Br{\"u}cken, {E. J.} and B. Chang and Hilden, {T. E.} and Kim, {D. J.} and V. Litichevskyi and Mieskolainen, {M. M.} and R. Orava and Parkkila, {J. E.} and J. Rak and R{\"a}s{\"a}nen, {S. S.} and S. Saarinen and M. Slupecki and Snellman, {T. W.} and Trzaska, {W. H.} and M. Vargyas and J. Viinikainen",
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The ALICE Collaboration, Acharya, S, Brücken, EJ, Chang, B, Hilden, TE, Kim, DJ, Litichevskyi, V, Mieskolainen, MM, Orava, R, Parkkila, JE, Rak, J, Räsänen, SS, Saarinen, S, Slupecki, M, Snellman, TW, Trzaska, WH, Vargyas, M & Viinikainen, J 2019, 'Analysis of the apparent nuclear modification in peripheral Pb-Pb collisions at 5.02 TeV', Physics Letters B, vol. 793, pp. 420-432. https://doi.org/10.1016/j.physletb.2019.04.047

Analysis of the apparent nuclear modification in peripheral Pb-Pb collisions at 5.02 TeV. / The ALICE Collaboration; Acharya, S.; Brücken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J.

In: Physics Letters B, Vol. 793, 10.06.2019, p. 420-432.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Analysis of the apparent nuclear modification in peripheral Pb-Pb collisions at 5.02 TeV

AU - The ALICE Collaboration

AU - Acharya, S.

AU - Brücken, E. J.

AU - Chang, B.

AU - Hilden, T. E.

AU - Kim, D. J.

AU - Litichevskyi, V.

AU - Mieskolainen, M. M.

AU - Orava, R.

AU - Parkkila, J. E.

AU - Rak, J.

AU - Räsänen, S. S.

AU - Saarinen, S.

AU - Slupecki, M.

AU - Snellman, T. W.

AU - Trzaska, W. H.

AU - Vargyas, M.

AU - Viinikainen, J.

PY - 2019/6/10

Y1 - 2019/6/10

N2 - Charged-particle spectra at midrapidity are measured in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair root 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) < 20 GeV/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. (C) 2019 Conseil Europeen pour la Recherche Nucleaire. Published by Elsevier B.V.

AB - Charged-particle spectra at midrapidity are measured in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair root 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) < 20 GeV/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. (C) 2019 Conseil Europeen pour la Recherche Nucleaire. Published by Elsevier B.V.

KW - 114 Physical sciences

KW - CHARGED-PARTICLE PRODUCTION

KW - TRANSVERSE-MOMENTUM

KW - CENTRALITY DEPENDENCE

KW - JET

KW - SUPPRESSION

KW - PP

U2 - 10.1016/j.physletb.2019.04.047

DO - 10.1016/j.physletb.2019.04.047

M3 - Article

VL - 793

SP - 420

EP - 432

JO - Physics Letters B

JF - Physics Letters B

SN - 0370-2693

ER -