Measurement of beauty production via non-prompt ${\rm D}^{0}$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV

The production of non-prompt ${\rm D}^{0}$ mesons from beauty-hadron decays was measured at midrapidity ($\left| y \right| <~ 0.5$) in Pb-Pb collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{\rm NN}}=5.02~\mathrm{TeV}$ with the ALICE experiment at the LHC. Their nuclear modification factor ($R_{\rm AA}$), measured for the first time down to $p_{\rm T}=1~\mathrm{GeV}/c$ in the $0-10$% and $30-50$% centrality classes, indicates a significant suppression, up to a factor of about three, for $p_{\rm T} > 5~\mathrm{GeV}/c$ in the $0-10$% central Pb-Pb collisions. The data are described by models that include both collisional and radiative processes in the calculation of beauty-quark energy loss in the quark-gluon plasma, and quark recombination in addition to fragmentation as a hadronisation mechanism. The ratio of the non-prompt to prompt ${\rm D}^{0}$-meson $R_{\rm AA}$ is larger than unity for $p_{\rm T} > 4~\mathrm{GeV}/c$ in the $0-10$% central Pb-Pb collisions, as predicted by models in which beauty quarks lose less energy than charm quarks in the quark-gluon plasma because of their larger mass.


JHEP 12 (2022) 126
HEP Data
e-Print: arXiv:2202.00815 | PDF | inSPIRE

Figure 1

Invariant-mass distributions for $\rm D^0$ candidates in selected $p_{\rm T}$ intervals for the centrality class 0$-$10% and 30$-$50%. Fitted values for the $\rm D^0$ meson mass $\mu$, width $\sigma$, and raw yield $S$ are also given, the fraction of $\rm D^0$ candidates in the measured raw yield is reported with its statistical and systematic uncertainties. Top row: non-prompt $\rm D^0$ mesons with $1<\pt<2$ $\gev/c$ in the 0$-$10% centrality class, before (left) and after (right) subtraction of the background fit function. Bottom row: non-prompt $\rm D^0$ mesons with $1<\pt<2$ $\gev/c$ (left) and $7<\pt<8$ $\gev/c$ (right) in the 30$-$50% centrality class.

Figure 2

Top panel: non-prompt $\rm D^0$-meson $\pt$-differential production yields in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV in the 0$-$10% and 30$-$50% centrality classes. The pp reference spectra, $\left\langle T_{\rm AA} \right\rangle \times{\rm d}\sigma_{\rm pp}/{\rm d}{p_{\rm T}}$, are also shown. Middle and bottom panels: $\pT$-differential $\RAA$ in the 0$-$10% (middle) and 30$-$50% (bottom) centrality classes, compared with model predictions. Open markers indicate the points for which the pp reference is extrapolated (see text). Vertical bars, empty boxes, and the shaded box around $\RAA=1$ represent the statistical, systematic, and normalisation uncertainty, respectively.

Figure 3

Nuclear modification factor ($\RAA$) of non-prompt $\rm D^0$ mesons in the centrality classes 0$-$10% (left) and 30$-$50% (right), compared with the $\RAA$ of prompt $\rm D^0$ mesons . The statistical and total systematic uncertainties are shown as error bars and boxes, respectively. The normalisation uncertainties are shown as boxes around unity.

Figure 4

Non-prompt to prompt  $\Dzero$-meson $\RAA$ ratioas a function of $\pt$ in the 0$-$10% central Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV, compared to model predictions  (top), and to different modifications of LGR calculations (bottom).