CMS-HIN-21-003

CMS-HIN-21-003 ; CERN-EP-2022-219
Measurements of azimuthal anisotropy of nonprompt D$^{0} $ mesons in PbPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.02 TeV
CMS Collaboration
3 December 2022
Phys. Lett. B 850 (2024) 138389
Abstract: Measurements of the elliptic ($ v_{2} $) and triangular ($ v_{3} $) azimuthal anisotropy coefficients are presented for D$^{0} $ mesons produced in b hadron decays (nonprompt D$^{0} $ mesons) in lead-lead collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.02 TeV. The results are compared with previously published charm meson anisotropies measured using prompt D$^{0} $ mesons. The data were collected with the CMS detector in 2018 with an integrated luminosity of 0.58 nb$^{-1}$. Azimuthal anisotropy is sensitive to the interactions of quarks with the hot and dense medium created in heavy ion collisions. Comparing results for prompt and nonprompt D$^{0} $ mesons can assist in understanding the mass dependence of these interactions. The nonprompt results show lower magnitudes of $ v_{2} $ and $ v_{3} $ and weaker dependences on the meson transverse momentum and collision centrality than those found for prompt D$^{0} $ mesons. By comparing to theoretical predictions, the results imply that there is a mass hierarchy of quark interactions with the medium.
Links: e-print arXiv:2212.01636 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: An example of the fit to the invariant mass spectrum (left panel) and an example of the template fit of the inclusive D$^{0} $ meson yields, extracted as a function of DCA (right panel). The former fit is used for determining the total D$^{0} $ yields and the latter for determining the fraction of nonprompt D$^{0} $ mesons.
png pdf	Figure 1-a: An example of the fit to the invariant mass spectrum (left panel) and an example of the template fit of the inclusive D$^{0} $ meson yields, extracted as a function of DCA (right panel). The former fit is used for determining the total D$^{0} $ yields and the latter for determining the fraction of nonprompt D$^{0} $ mesons.
png pdf	Figure 1-b: An example of the fit to the invariant mass spectrum (left panel) and an example of the template fit of the inclusive D$^{0} $ meson yields, extracted as a function of DCA (right panel). The former fit is used for determining the total D$^{0} $ yields and the latter for determining the fraction of nonprompt D$^{0} $ mesons.
png pdf	Figure 2: The elliptic, $ v_{2} $ (upper panels), and the triangular, $ v_{3} $ (lower panels), flow coefficients of nonprompt and prompt (from Ref. [18]) D$^{0} $ mesons as functions of their $ p_{\mathrm{T}} $ and in three bins of centrality. The bars and the boxes represent statistical and systematic uncertainties, respectively.
png pdf	Figure 3: The elliptic, $ v_{2} $ (upper panel), and the triangular, $ v_{3} $ (lower panel), flow coefficients of nonprompt D$^{0} $ mesons as functions of their $ p_{\mathrm{T}} $ and in three bins of centrality. The bars and the boxes represent statistical and systematic uncertainties, respectively. The colored bands show theoretical predictions [49-56].

Summary

In summary, the elliptic ($ v_{2} $) and triangular ($ v_{3} $) flow harmonics of D$^{0} $ mesons that originate in b hadron decays (nonprompt D$^{0} $ mesons) are measured in lead-lead collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.02 TeV. The $ v_{2} $ results show a weak transverse momentum ($ p_{\mathrm{T}} $) dependence and suggest a slight increase for more peripheral collisions. An indication of a nonzero $ v_{3} $ coefficient is found for nonprompt D$^{0} $ mesons with 4 $ < p_{\mathrm{T}} < $ 6 GeV/$c$. The magnitudes of the flow coefficients are lower for nonprompt D$^{0} $ than for prompt D$^{0} $ mesons. This magnitude difference is more pronounced in the case of $ v_{2} $. Comparisons of the results to theoretical models suggest a mass hierarchy in quark interactions with the quark-gluon plasma, thereby extending our understanding of heavy quark interactions with the medium.

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