Centrality dependence of electroweak boson production in PbPb collisions at the LHC

Abstract

Recent data on the nuclear modification of W and Z boson production measured by the ATLAS collaboration in PbPb collisions at $\sqrt{s_{\mathrm{nn}}}=5.02$ TeV show an enhancement in peripheral collisions, seemingly contradicting predictions of the Glauber model. The data were previously explained by arguing that the nucleon-nucleon cross section may be shadowed in nucleus-nucleus collisions, and hence suppressed compared to the proton-proton cross section at the same collision energy. This interpretation has quite significant consequences for the understanding of heavy-ion data, in particular in the context of the Glauber model. Instead, we provide an alternative explanation of the data by assuming that there is a mild bias present in the centrality determination of the measurement; on the size of the related systematic uncertainty. Using this assumption, we show that the data is in agreement with theoretical calculations using nuclear parton distribution functions. Finally, we speculate that the centrality dependence of the W${}^{-}$/W${}^{+}$ ratio may point to the relevance of a larger skin thickness of the Pb nucleus, which, if present, would result in a few percent larger PbPb cross section than currently accounted for in the Glauber model and may hence be the root of the centrality bias.

8 pages, 5 figures, 1 table, comments welcome

References in corpus (11)

• PYTHIA 6.4 Physics and Manual
• Glauber Modeling in High Energy Nuclear Collisions
• Accurate Determination of the Neutron Skin Thickness of ${}^{208}$Pb through Parity-Violation in Electron Scattering
• Measurement of the production and lepton charge asymmetry of $\text{W}$ bosons in Pb+Pb collisions at $\sqrt{s_{\mathbf{NN}}}=$ 2.76 TeV with the ATLAS detector
• Progress in the Glauber model at collider energies
• Measurement of visible cross sections in proton-lead collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV in van der Meer scans with the ALICE detector
• Measurement of distributions sensitive to the underlying event in inclusive Z-boson production in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detector
• Study of Z production in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV in the dimuon and dielectron decay channels
• $Z$ boson production in Pb+Pb collisions at $\sqrt{s_{\text{NN}}}$= 5.02 TeV measured by the ATLAS experiment
• Neutron skin and centrality classification in high-energy heavy-ion collisions at the LHC
• Constraints on the initial state of PbPb collisions via measurements of Z boson yields and azimuthal anisotropy at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV

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• Selection bias effects on high-$p_{\mathrm{T}}$ yield and correlation measurements in Oxygen+Oxygen collisions
• Measurement of the inclusive isolated-photon production cross section in pp and Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV