CMS-PAS-HIN-20-001

CMS-PAS-HIN-20-001
Probing charm quark dynamics via multiparticle azimuthal correlations in 5.02 TeV PbPb collisions
CMS Collaboration
January 2021

Abstract: Multiparticle azimuthal correlations of prompt $\mathrm{D}^{0}$ mesons are measured in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The data were collected using the CMS detector at the LHC in 2018, corresponding to an integrated luminosity of 0.58 nb $^{-1}$ . The second Fourier coefficient of the azimuthal distribution ( $v_2$ ) of $\mathrm{D}^{0}$ mesons is extracted for the first time using a four-particle cumulant method, as a function of $\mathrm{D}^{0}$ meson transverse momentum and event centrality. The prompt $\mathrm{D}^{0}$ meson $v_2$ ratios using four- and two-particle cumulant methods are below unity and comparable to those of charged particles. However, hints of deviation are seen in the most central and peripheral collisions. Comparison of these differences with two models sheds light on the origin of fluctuations.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PRL. The superseded preliminary plots can be found here.

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: An example of two-step fit of the mass spectrum and $v_2^{\text{sig+bkg}}(m_{\text{inv}})$ in the ${p_{\mathrm {T}}}$ interval 3-4 GeV for the centrality class 30-50%.
png pdf	Figure 2: Upper panel: prompt ${{\mathrm{D^0}}}$ meson ${v_{2}\{2\}}$ and ${v_{2}\{4\}}$ within the ${\| y \|} <$ 1 as a function of ${p_{\mathrm {T}}}$ , for the centrality classes 10-30% (left) and 30-50% (right) from PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The blue solid and dashed lines denote the DAB-MOD model calculations using Langevin dynamics transport for ${{v_{2}\{4\}}}$ and ${{v_{2}\{2\}}}$ , respectively. The green solid and dashed lines represent the DAB-MOD model calculation with energy loss process for ${{v_{2}\{4\}}}$ and ${{v_{2}\{2\}}}$ , respectively. Lower panel: the prompt ${{\mathrm{D^0}}}$ meson $v_2\{4\}/ {v_{2}\{2\}}$ are shown and compared to charged particles [37]. The vertical bars represent statistical uncertainties and open boxes denote the systematic uncertainties. The ${{v_{2}\{2\}}}$ values are taken from Ref. [38].
png pdf	Figure 3: Upper pannel: the prompt ${{\mathrm{D^0}}}$ meson ${v_{2}\{2\}}$ and ${v_{2}\{4\}}$ in the range ${\| y \|} <$ 1 as a function of centrality for 2.0 $< {p_{\mathrm {T}}} <$ 8.0 GeV in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The blue solid and dashed lines denote the DAB-MOD model calculations with Langevin dynamics transport for ${{v_{2}\{4\}}}$ and ${{v_{2}\{2\}}}$ , respectively. The green solid and dashed lines represent the DAB-MOD model calculation with energy loss process. Lower pannel: the prompt ${{\mathrm{D^0}}}$ meson $v_2\{4\}/ {v_{2}\{2\}}$ are compared to charged particles in the pseudorapidity range ${\| \eta \|} <$ 1 [37]. The vertical bars represent statistical uncertainties and open boxes denote the systematic uncertainties. The ${{v_{2}\{2\}}}$ values are taken from Ref. [38]. The blue and green solid lines show $v_2\{4\}/ {v_{2}\{2\}}$ under the DAB-MOD model with Langevin and energy loss transport process, respectively.

Summary

In summary, the first measurements of the elliptic flow for prompt

${{\mathrm{D^0}}}$ and

$\overline{\mathrm{D}}{}^0$ mesons using multiparticle correlations,

$v_2\{4\}$ , are presented. The

$v_2\{4\}$ values are systematically lower than the measured two-particle elliptical flow values of

$v_2\{2\}$ , as expected of event-by-event fluctuations in the flow signal. To further investigate the origin of

$v_2$ fluctuations,

$v_2\{4\}/v_2\{2\}$ ratios of prompt

${{\mathrm{D^0}}}$ mesons are compared to those of light flavor hadrons. Similar trends for both charm mesons and light flavor hadrons are observed, suggesting that the contributions from fluctuations of initial geometric conditions are dominant. Hints of splitting of

$v_2\{4\}/v_2\{2\}$ ratios between charm mesons and light flavor hadrons in the most central and most peripheral events suggests the influence of energy loss fluctuations.

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