CMS-HIN-16-007

CMS-HIN-16-007 ; CERN-EP-2017-174
Measurement of prompt $\mathrm{D}^0$ meson azimuthal anisotropy in PbPb collisions at $ \sqrt{s_{_\mathrm{NN}}} = $ 5.02 TeV
CMS Collaboration
11 August 2017
Phys. Rev. Lett. 120 (2018) 202301
Abstract: The prompt $ \mathrm{D}^0 $ meson azimuthal anisotropy coefficients, $v_{2}$ and $v_{3}$, are measured at midrapidity ($\|y\| < $ 1.0) in PbPb collisions at a center-of-mass energy $ \sqrt{ s_{_\mathrm{NN}}} = $ 5.02 TeV per nucleon pair with data collected by the CMS experiment. The measurement is performed in the transverse momentum ($p_{\mathrm{T}}$) range of 1 to 40 GeV/$c$, for central and midcentral collisions. The $v_{2}$ coefficient is found to be positive throughout the $ p_{\mathrm{T}} $ range studied. The first measurement of the prompt $ \mathrm{D}^0 $ meson $v_{3}$ coefficient is performed, and values up to 0.07 are observed for $p_{\mathrm{T}}$ around 4 GeV/$c$. Compared to measurements of charged particles, a similar $ p_{\mathrm{T}} $ dependence, but smaller magnitude for $p_{\mathrm{T}} < $ 6 GeV/$c$, is found for prompt $ \mathrm{D}^0 $ meson $v_{2}$ and $v_{3}$ coefficients. The results are consistent with the presence of collective motion of charm quarks at low $ p_{\mathrm{T}} $ and a path length dependence of charm quark energy loss at high $ p_{\mathrm{T}} $, thereby providing new constraints on the theoretical description of the interactions between charm quarks and the quark-gluon plasma.
Links: e-print arXiv:1708.03497 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Example of simultaneous fit to the invariant mass spectrum and $v_{2}^{S+B}(m_{\rm inv})$ in the $ {p_{\mathrm {T}}} $ interval 4-5 GeV/$c$ for the centrality class 10-30%.
png pdf	Figure 2: Prompt $ \mathrm{D}^0 $ meson $v_{2}$ (upper) and $v_{3}$ (lower) coefficients at midrapidity ($\|y\| < $ 1.0) for the centrality classes 0-10% (left), 10-30% (middle), and 30-50% (right). The vertical bars represent statistical uncertainties, grey bands represent systematic uncertainties from nonprompt $ \mathrm{D}^0 $ mesons and open boxes represent other systematic uncertainties. The measured $v_{n}$ coefficient of charged particles at midpseudorapidity ($\|\eta \| < $ 1.0) [36] and theoretical calculations for prompt D meson $v_{n}$ coefficient [37,25,38,39,40] are also plotted for comparison.

Summary

In summary, measurements of prompt $ \mathrm{D}^0 $ meson azimuthal anisotropy coefficients, $v_{2}$ and $v_{3}$, using the scalar product method in PbPb collisions at $ \sqrt{ s_{_\mathrm{NN}}} = $ 5.02 TeV have been presented. The $v_{2}$ values are found to be positive in the $p_{\mathrm{T}}$ range of 1 to 40 GeV/$c$. The $v_{3}$ coefficient is measured for the first time, and values up to 0.07 are observed for $p_{\mathrm{T}}$ around 4 GeV/$c$. The $v_{2}$ coefficient is observed to be centrality dependent, while the $v_{3}$ coefficient shows little centrality dependence. Compared with those of charged particles, the measured $ \mathrm{D}^0 $ meson $v_{2}$ and $v_{3}$ coefficients are found to be smaller for $ p_{\mathrm{T}} < $ 6 GeV/$c$ but to have similar $p_{\mathrm{T}}$ dependence. Through the comparison with theoretical calculations, the $v_{2}$ and $v_{3}$ results at low $p_{\mathrm{T}}$ suggest that the charm quarks take part in the collective motion of the system. The $v_{2}$ values for $ p_{\mathrm{T}} > $ 6 GeV/$c$, which are consistent with those of charged particles, suggest that the path length dependence of charm quark energy loss is similar to that of light quarks. The results provide new constraints on models of the interactions between charm quarks and the quark-gluon plasma, and the charm quark energy loss mechanisms.

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