CMS-HIN-16-001

CMS-HIN-16-001 ; CERN-EP-2017-186
Nuclear modification factor of $\mathrm{D}^0$ mesons in PbPb collisions at ${\sqrt{{s_{_{\mathrm{NN}}}}}} =$ 5.02 TeV
CMS Collaboration
16 August 2017
Phys. Lett. B 782 (2018) 474
Abstract: The transverse momentum ( $p_{\mathrm{T}}$ ) spectrum of prompt $\mathrm{D}^0$ mesons and their antiparticles has been measured via the hadronic decay channels $\mathrm{D}^0\to \mathrm{K}^{-} \pi^{+}$ and ${\overline{\mathrm{D}}}{}^0 \to \mathrm{K}^{+} \pi^{-}$ in pp and PbPb collisions at a centre-of-mass energy of 5.02 TeV per nucleon pair with the CMS detector at the LHC. The measurement is performed in the $\mathrm{D}^0$ meson $p_{\mathrm{T}}$ range of 2-100 GeV/ $c$ and in the rapidity range of $\| y \| <$ 1. The pp (PbPb) dataset used for this analysis corresponds to an integrated luminosity of 27.4 pb $^{-1}$ (530 $\mu$ b $^{-1}$ ). The measured $\mathrm{D}^0$ meson $p_{\mathrm{T}}$ spectrum in pp collisions is well described by perturbative QCD calculations. The nuclear modification factor, comparing $\mathrm{D}^0$ meson yields in PbPb and pp collisions, was extracted for both minimum-bias and the 10% most central PbPb interactions. For central events, the $\mathrm{D}^0$ meson yield in the PbPb collisions is suppressed by a factor of 5-6 compared to the pp reference in the $p_{\mathrm{T}}$ range of 6-10 GeV/ $c$ . For $\mathrm{D}^0$ mesons in the high- $p_{\mathrm{T}}$ range of 60-100 GeV/ $c$ , a significantly smaller suppression is observed. The results are also compared to theoretical calculations.
Links: e-print arXiv:1708.04962 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1: Examples of $\mathrm{D}^0$ candidate invariant mass distributions in pp (top) and PbPb (bottom) collisions at 5.02 TeV.
png pdf	Figure 1-a: Example of $\mathrm{D}^0$ candidate invariant mass distribution in pp collisions at 5.02 TeV.
png pdf	Figure 1-b: Example of $\mathrm{D}^0$ candidate invariant mass distribution in pp collisions at 5.02 TeV.
png pdf	Figure 1-c: Example of $\mathrm{D}^0$ candidate invariant mass distribution in PbPb collisions at 5.02 TeV.
png pdf	Figure 1-d: Example of $\mathrm{D}^0$ candidate invariant mass distribution in PbPb collisions at 5.02 TeV.
png pdf	Figure 2: (left) The ${p_{\mathrm {T}}}$ -differential production cross section of $\mathrm{D}^0$ mesons in pp collisions at ${\sqrt {s}} =$ 5.02 TeV. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty, listed in the legend and not included in the point-to-point uncertainties, comprises the uncertainties in the integrated luminosity measurement and the $\mathrm{D}^0$ meson $\mathcal {B}$ . Results are compared to FONLL [31] and GM-VFNS [33,34,35] calculations. (right) The ${p_{\mathrm {T}}}$ -differential production yields of $\mathrm{D}^0$ mesons divided by the nuclear overlap functions ${T_{\mathrm {AA}}}$ for PbPb collisions in the 0-100% (red) and 0-10% (blue) centrality ranges compared to the same pp cross sections shown in the left panel (black).
png pdf	Figure 2-a: The ${p_{\mathrm {T}}}$ -differential production cross section of $\mathrm{D}^0$ mesons in pp collisions at ${\sqrt {s}} =$ 5.02 TeV. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty, listed in the legend and not included in the point-to-point uncertainties, comprises the uncertainties in the integrated luminosity measurement and the $\mathrm{D}^0$ meson $\mathcal {B}$ . Results are compared to FONLL [31] and GM-VFNS [33,34,35] calculations.
png pdf	Figure 2-b: The ${p_{\mathrm {T}}}$ -differential production yields of $\mathrm{D}^0$ mesons divided by the nuclear overlap functions ${T_{\mathrm {AA}}}$ for PbPb collisions in the 0-100% (red) and 0-10% (blue) centrality ranges compared to the same pp cross sections shown in the left panel (black).
png pdf	Figure 3: ${R_{\mathrm {AA}}}$ as a function of ${p_{\mathrm {T}}}$ in the centrality range 0-100% (left) and 0-10% (right). The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty, represented as a grey box at ${R_{\mathrm {AA}}} =$ 1, comprises the uncertainties in the integrated luminosity measurement and ${T_{\mathrm {AA}}}$ value. The $\mathrm{D}^0$ ${R_{\mathrm {AA}}}$ values are also compared to calculations from various theoretical models [36,37,38,39,40,41,42,43,44,45,46].
png pdf	Figure 3-a: ${R_{\mathrm {AA}}}$ as a function of ${p_{\mathrm {T}}}$ in the centrality range 0-100%. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty, represented as a grey box at ${R_{\mathrm {AA}}} =$ 1, comprises the uncertainties in the integrated luminosity measurement and ${T_{\mathrm {AA}}}$ value. The $\mathrm{D}^0$ ${R_{\mathrm {AA}}}$ values are also compared to calculations from various theoretical models [36,37,38,39,40,41,42,43,44,45,46].
png pdf	Figure 3-b: ${R_{\mathrm {AA}}}$ as a function of ${p_{\mathrm {T}}}$ in the centrality range 0-10%. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty, represented as a grey box at ${R_{\mathrm {AA}}} =$ 1, comprises the uncertainties in the integrated luminosity measurement and ${T_{\mathrm {AA}}}$ value. The $\mathrm{D}^0$ ${R_{\mathrm {AA}}}$ values are also compared to calculations from various theoretical models [36,37,38,39,40,41,42,43,44,45,46].
png pdf	Figure 4: (left) Nuclear modification factor ${R_{\mathrm {AA}}}$ as a function of ${p_{\mathrm {T}}}$ in the centrality range 0-100% (green squares) compared to the ${R_{\mathrm {AA}}}$ of charged particles (red circles) [21], ${\mathrm {B}^{\pm }}$ mesons (blue triangles) [47] at 5.02 TeV and to the ${R_{\mathrm {AA}}}$ of nonprompt $\mathrm{J}/\psi$ meson (purple crosses and stars) at 2.76 TeV [14] in the same centrality range. (right) Nuclear modification factor ${R_{\mathrm {AA}}}$ as a function of ${p_{\mathrm {T}}}$ in the centrality range 0-10% (green squares) compared to the ${R_{\mathrm {AA}}}$ of charged particles (red circles) [21] in the same centrality range.
png pdf	Figure 4-a: Nuclear modification factor ${R_{\mathrm {AA}}}$ as a function of ${p_{\mathrm {T}}}$ in the centrality range 0-100% (green squares) compared to the ${R_{\mathrm {AA}}}$ of charged particles (red circles) [21], ${\mathrm {B}^{\pm }}$ mesons (blue triangles) [47] at 5.02 TeV and to the ${R_{\mathrm {AA}}}$ of nonprompt $\mathrm{J}/\psi$ meson (purple crosses and stars) at 2.76 TeV [14] in the same centrality range.
png pdf	Figure 4-b: Nuclear modification factor ${R_{\mathrm {AA}}}$ as a function of ${p_{\mathrm {T}}}$ in the centrality range 0-10% (green squares) compared to the ${R_{\mathrm {AA}}}$ of charged particles (red circles) [21] in the same centrality range.

Summary

In this Letter, the transverse momentum (

$p_{\mathrm{T}}$ ) spectra of prompt

$\mathrm{D}^0$ mesons in pp and PbPb collisions and the

$\mathrm{D}^0$ meson nuclear modification factor (

${R_{\mathrm{AA}}}$ ) in the central rapidity region (

$| y | <$ 1) at

${\sqrt{{s_{_{\text{NN}}}}}} =$ 5.02 TeV from CMS are presented. The

${R_{\mathrm{AA}}}$ of prompt

$\mathrm{D}^0$ mesons is measured as a function of their

$p_{\mathrm{T}}$ from 2 to 100 GeV/

$c$ in two centrality ranges, inclusive and 10% most central. The

$\mathrm{D}^0$ meson yield is found to be strongly suppressed in PbPb collisions when compared to the measured pp reference data scaled by the number of binary nucleon-nucleon collisions. These measurements are consistent with the

${R_{\mathrm{AA}}}$ of charged hadrons in both centrality intervals for

$p_{\mathrm{T}} >$ 4 GeV/

$c$ . A hint of a smaller suppression of

$\mathrm{D}^0$

${R_{\mathrm{AA}}}$ with respect to charged particle

${R_{\mathrm{AA}}}$ is observed for

$p_{\mathrm{T}} <$ 4 GeV/

$c$ . The

$\mathrm{D}^0$

${R_{\mathrm{AA}}}$ was found to be compatible with the

${\mathrm{B}^{\pm}}$

${R_{\mathrm{AA}}}$ in the intermediate

$p_{\mathrm{T}}$ region and significantly lower than the nonprompt

$\mathrm{J}/\psi$ meson

${R_{\mathrm{AA}}}$ at

${\sqrt{{s_{_{\text{NN}}}}}} =$ 2.76 TeV for

$p_{\mathrm{T}}<$ 10 GeV/

$c$ . Comparisons to different theoretical models show that the general trend of the

${R_{\mathrm{AA}}}$ is qualitatively reproduced at high

$p_{\mathrm{T}}$ . Comparisons to different theoretical models show that the general trend of the

${R_{\mathrm{AA}}}$ is qualitatively reproduced at high

$p_{\mathrm{T}}$ , while quantitative agreement for all centrality and

$p_{\mathrm{T}}$ selections is yet to be attained.

Additional Figures
png pdf	Additional Figure 1: Fraction of ${\mathrm {D}^{0}}$ mesons that come directly from c quark fragmentation as a function of $p_{\mathrm{T}}$ in pp collisions at 5.02 TeV.
png pdf	Additional Figure 2: Fraction of ${\mathrm {D}^{0}}$ mesons that come directly from c quark fragmentation as a function of $p_{\mathrm{T}}$ in the centrality range 0-100% in PbPb collisions at 5.02 TeV.
png pdf	Additional Figure 3: Fraction of ${\mathrm {D}^{0}}$ mesons that come directly from c quark fragmentation as a function of $p_{\mathrm{T}}$ in the centrality range 0-10% in PbPb collisions at 5.02 TeV.
png pdf	Additional Figure 4: Example of DCA distribution of ${\mathrm {D}^{0}}$ mesons (black marks) with templates of prompt (red histogram) and non-prompt (blue histogram) ${\mathrm {D}^{0}}$ mesons from simulations in pp collisions at 5.02 TeV.
png pdf	Additional Figure 5: Example of DCA distribution of ${\mathrm {D}^{0}}$ mesons (black marks) with templates of prompt (red histogram) and non-prompt (blue histogram) ${\mathrm {D}^{0}}$ mesons from simulations in the centrality range 0-100% in PbPb collisions at 5.02 TeV.
png pdf	Additional Figure 6: Example of DCA distribution of ${\mathrm {D}^{0}}$ mesons (black marks) with templates of prompt (red histogram) and non-prompt (blue histogram) ${\mathrm {D}^{0}}$ mesons from simulations in the centrality range 0-10% in PbPb collisions at 5.02 TeV.
png pdf	Additional Figure 7: Nuclear modification factor ${R_{\mathrm {AA}}}$ as a function of ${p_{\mathrm {T}}}$ in the centrality range 0-100%.
png pdf	Additional Figure 8: Nuclear modification factor ${R_{\mathrm {AA}}}$ as a function of ${p_{\mathrm {T}}}$ in the centrality range 0-10%.
png pdf	Additional Figure 9: Nuclear modification factor ${R_{\mathrm {AA}}}$ as a function of ${p_{\mathrm {T}}}$ in the centrality range 0-100 $%$ (green squares) compared to the ${R_{\mathrm {AA}}}$ of charged particles (red circles) [21] and ${\mathrm {B}^{\pm}}$ mesons (blue triangles) [48] at 5.02 TeV.

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