Measurement of prompt $\rm{D_{s}^{+}}$-meson production and azimuthal anisotropy in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

The production yield and angular anisotropy of prompt ${D_s^+}$ mesons were measured as a function of transverse momentum ($p_{ T}$) in Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{ NN}} = 5.02$ TeV collected with the ALICE detector at the LHC. ${D_s^+}$ mesons and their charge conjugates were reconstructed at midrapidity ($|y|<~0.5$) from their hadronic decay channel ${D_s^+ \to \phi \pi^+}$, with ${\phi \to K^-K^+}$, in the $p_{ T}$ intervals $2<~p_{ T}<~50$ GeV/$c$ and $2<~p_{ T}<~36$ GeV/$c$ for the 0-10% and 30-50% centrality intervals. For $p_{ T}>10$ GeV/$c$, the measured ${D_s^+}$-meson nuclear modification factor $R_{ AA}$ is consistent with the one of non-strange D mesons within uncertainties, while at lower $p_{ T}$ a hint for a ${D_s^+}$-meson $R_{ AA}$ larger than that of non-strange D mesons is seen. The enhanced production of ${D_s^+}$ relative to non-strange D mesons is also studied by comparing the $p_{ T}$-dependent ${D_s^+/D^0}$ production yield ratios in Pb-Pb and in pp collisions. The ratio measured in Pb-Pb collisions is found to be on average higher than that in pp collisions in the interval $2<~p_{ T} <~8$ GeV/$c$ with a significance of 2.3$\sigma$ and 2.4$\sigma$ for the 0-10% and 30-50% centrality intervals. The azimuthal anisotropy coefficient $v_2$ of prompt ${D_s^+}$ mesons was measured in Pb-Pb collisions in the 30-50% centrality interval and is found to be compatible with that of non-strange D mesons. The main features of the measured $R_{ AA}$, ${D_s^+/D^0}$ ratio, and $v_2$ as a function of $p_{ T}$ are described by theoretical calculations of charm-quark transport in a hydrodynamically expanding quark-gluon plasma including hadronisation via charm-quark recombination with light quarks from the medium. The $p_{ T}$-integrated production yield of ${D_s^+}$ mesons is compatible with the prediction of the statistical hadronisation model.

 

Submitted to: PLB
e-Print: arXiv:2110.10006 | PDF | inSPIRE

Figure 1

Acceptance-times-efficiency factor for $\Ds$ mesons as a function of $\pt$. The $(\rm Acc \times \epsilon)$ factors for prompt (red) and non-prompt (blue) $\Ds{}$ mesons in Pb--Pb collisions for the 0--10\% centrality interval are shown, together with those for prompt (orange) and non-prompt (green) $\Ds{}$ mesons for the 30--50\% centrality interval.

Figure 2

Simultaneous fit to the invariant-mass spectrum and $v_2(M_{\mathrm{D}})$ of $\Ds{}$-meson candidates in the $4

Figure 3

$\pt$-differential production yields of prompt $\Ds$ mesons in the 0--10\% and 30--50\% centrality intervals in Pb--Pb collisions at $\sqrtsNN=5.02~\TeV$ compared to the pp reference~ scaled by the average nuclear overlap function $\av{\TAA}$ of the corresponding centrality interval. The open markers indicate where the pp reference is extrapolated using FONLL calculations. The $\pt$-differential yields in the 30--50\% centrality interval and the corresponding pp reference are scaled by a factor of $10^{-1}$ for better visibility. Statistical uncertainties (bars) and systematic uncertainties (boxes) are shown.

Figure 4

Nuclear modification factor $\RAA$ of prompt $\Ds$ mesons in the 0--10\% (left panel) and 30--50\% (right panel) centrality intervals in Pb--Pb collisions at $\sqrtsNN=5.02~\TeV$ compared with the one of prompt non-strange D mesons (average of $\Dzero$, $\Dplus$, and $\Dstar$)~. The empty (filled) boxes represent the species uncorrelated (correlated) systematic uncertainties. The normalisation uncertainty is represented by a filled box at $\RAA=1$.

Figure 5

Nuclear modification factor $\RAA$ of prompt $\Ds$ mesons (left panel) and non-strange D mesons~ (right panel) in the 0--10\% centrality interval in Pb--Pb collisions at $\sqrtsNN=5.02~\TeV$ compared with theoretical calculations based on charm-quark transport in a hydrodynamically expanding QGP implementing strangeness enhancement and hadronisation of charm quarks via coalescence in addition to fragmentation in the vacuum~. The boxes represent the total systematic uncertainties. The colour bands represent the theoretical uncertainty when available.

Figure 6

Top panels: $\Ds/\Dzero$ $\pt$-differential production ratios in the 0--10\% (left panel) and 30--50\% (middle panel) centrality intervals in Pb--Pb collisions at $\sqrtsNN=5.02~\TeV$ and in pp collisions (right panel) at the same centre-of-mass energy compared with theoretical calculations based on charm-quark transport in a hydrodynamically expanding QGP~ and on statistical hadronisation~. Bottom panels: $\Ds/\Dzero$ $\pt$-differential ratios in Pb--Pb collisions divided by those in pp collisions, in the 0--10\% (left panel) and 30--50\% (right panel) centrality intervals, compared with theoretical calculations.

Figure 7

Elliptic flow coefficient $v_2$ of prompt $\Ds$ mesons in the 30--50\% centrality interval in Pb--Pb collisions at $\sqrtsNN=5.02~\TeV$ compared with that of non-strange D mesons~ (left panel) and with theoretical calculations based on the charm-quark transport in a hydrodynamically expanding QGP~ (right panel).