Measurement of electrons from beauty-hadron decays in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV and Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV
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2017-07Author
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The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval $1<p_{\rm T}<8$ GeV/$c$ in minimum-bias p–Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV and in $1.3<p_{\rm T}<8$ GeV/$c$ in the 20% most central Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. The pp reference spectra at $\sqrt{s}=5.02$ TeV and $\sqrt{s}=2.76$ TeV, needed for the calculation of the nuclear modification factors $R_{\rm pA}$ and $R_{\rm AA}$, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at $\sqrt{s}=7$ TeV. The $R_{\rm AA}$ is about 0.7 with an uncertainty of about 30% in the interval $3<p_{\rm T}<6$ GeV/$c$ and 0.47 with an uncertainty of 25% in $6<p_{\rm T}<8$ GeV/$c$. Below $p_{\rm T}=3$ GeV/$c$. the $R_{\rm AA}$ values increase with decreasing transverse momentum with systematic uncertainties of 30-45%. The $R_{\rm pA}$ is consistent with unity within systematic uncertainties of about 20% at high $p_{\rm T}$, increasing at low $p_{\rm T}$, and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured $R_{\rm pA}$ and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb–Pb collisions. Therefore, the observed reduction of $R_{\rm AA}$ below unity for high $p_{\rm T}$ can be ascribed to an effect of the hot and dense medium formed in Pb–Pb collisions.
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Adam J, Adamová D, Aggarwal MM, Aglieri Rinella G, Agnello M, Agrawal N, Ahammed Z, Ahmad SF, Ahn SU, Aiola S, Alme J, Helstrup H, Hetland KF, Kileng B, Altinpinar S, Djuvsland Ø, Lønne P, Nystrand J, Rehman Au, Røhrich D, Tambave GJ, Ullaland K, Velure A, Wagner B, Zhang H, Zhou Z, Zhu H, Arsene IC, Bätzing P, Dordic O, Eyyubova G, Lindal S, Mahmood SM, Milosevic J, Qvigstad H, Richter M, Røed K, Skaali TB, Tveter TS, Wikne JC, Zhao C, Langøy R, Lien JA, Akindinov A, Alam SN, De Albuquerque DS, Aleksandrov D, Alessandro B, Alexandre D, Alfaro Molina JR. Measurement of electrons from beauty-hadron decays in p-Pb collisions at √sNN=5.02 TeV and Pb-Pb collisions at √sNN=2.76 TeV. Journal of High Energy Physics (JHEP). 2017;2017:52Publisher
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