CMS-PAS-HIN-18-007

CMS-PAS-HIN-18-007
Measurement of the radial profile of $\mathrm{D^{0}}$ mesons in jets produced in pp and PbPb collisions at 5.02 TeV
CMS Collaboration
May 2018

Abstract: The first measurement of the radial distributions of $\mathrm{D^{0}}$ mesons in jets in PbPb and pp collisions is presented. Data samples of PbPb and pp collisions at a nucleon-nucleon center-of-mass energy of ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV, corresponding to integrated luminosities of 404 $\mu$ b $^{-1}$ and 27.4 pb $^{-1}$ , respectively, are recorded by the CMS detector at the LHC. The jets are reconstructed with an anti- $k_{\mathrm{T}}$ algorithm with a distance parameter of 0.3. The radial distribution of $\mathrm{D^{0}}$ mesons with transverse momentum $p_{\mathrm{T}} >$ 4 GeV/ $c$ are measured with respect to the jet axis. Modifications of $\mathrm{D^{0}}$ radial distribution in PbPb collisions are presented by comparing PbPb spectra to the pp reference data, indicating a redistribution of the $\mathrm{D^{0}}$ mesons close to the jet axis. This measurement provides new experimental constraints on the mechanisms of heavy-flavor production in proton-proton collisions as well as on the processes of parton energy loss and diffusion of heavy quarks inside the strongly interacting medium produced in heavy ion collisions.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Phy. Rev. Lett. 125 (2020) 102001. The superseded preliminary plots can be found here.

Figures	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1: Distributions of $\mathrm{D^{0}}$ mesons in jets as a function of the distance from the jet axis for jets of $p_{\mathrm {T}}^{\mathrm {jet}} >$ 60 GeV/ $c$ and $\|\eta ^{\mathrm {\mathrm {jet}}}\| <$ 1.6 measured in pp and PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV. The measurement is performed in the $\mathrm{D^{0}}$ $p_{\mathrm {T}}^{\mathrm {D}}$ range 4-20 GeV/ $c$ (left) and for $p_{\mathrm {T}}^{\mathrm {D}} >$ 20 GeV/ $c$ (right). Each spectrum is normalized to its integral in the region 0 $< r <$ 0.3. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The ratios of the $\mathrm{D^{0}}$ radial distributions of PbPb to pp are also presented in the middle panel of each figure. The predictions from the PYTHIA 8 event generator are also superimposed, and in the bottom panel the ratios of the $\mathrm{D^{0}}$ radial distributions of pp over PYTHIA 8 predictions are presented.
png pdf	Figure 1-a: Distribution of $\mathrm{D^{0}}$ mesons in jets as a function of the distance from the jet axis for jets of $p_{\mathrm {T}}^{\mathrm {jet}} >$ 60 GeV/ $c$ and $\|\eta ^{\mathrm {\mathrm {jet}}}\| <$ 1.6 measured in pp and PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV. The measurement is performed in the $\mathrm{D^{0}}$ $p_{\mathrm {T}}^{\mathrm {D}}$ range 4-20 GeV/ $c$ . Each spectrum is normalized to its integral in the region 0 $< r <$ 0.3. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The ratio of the $\mathrm{D^{0}}$ radial distributions of PbPb to pp are also presented in the middle panel of the figure. The predictions from the PYTHIA 8 event generator are also superimposed, and in the bottom panel the ratios of the $\mathrm{D^{0}}$ radial distributions of pp over PYTHIA 8 predictions are presented.
png pdf	Figure 1-b: Distribution of $\mathrm{D^{0}}$ mesons in jets as a function of the distance from the jet axis for jets of $p_{\mathrm {T}}^{\mathrm {jet}} >$ 60 GeV/ $c$ and $\|\eta ^{\mathrm {\mathrm {jet}}}\| <$ 1.6 measured in pp and PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV. The measurement is performed for $p_{\mathrm {T}}^{\mathrm {D}} >$ 20 GeV/ $c$ . Each spectrum is normalized to its integral in the region 0 $< r <$ 0.3. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The ratio of the $\mathrm{D^{0}}$ radial distributions of PbPb to pp are also presented in the middle panel of the figure. The predictions from the PYTHIA 8 event generator are also superimposed, and in the bottom panel the ratios of the $\mathrm{D^{0}}$ radial distributions of pp over PYTHIA 8 predictions are presented.

Summary

In summary, the first measurement of the radial distributions of

$\mathrm{D^{0}}$ mesons in jets in PbPb and pp collisions is performed with the CMS detector using jets with

$p_{\mathrm{T}}>$ 60 GeV/

$c$ and

$\mathrm{D^{0}}$ mesons with

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

$c$ . The modification of the

$\mathrm{D^{0}}$ radial distributions in PbPb collisions are studied by comparing the PbPb spectra to the pp reference data. The measurements indicate a modification of the

$\mathrm{D^{0}}$ radial profile in PbPb collisions at low

$\mathrm{D^{0}}$

$p_{\mathrm{T}}$ that vanishes at higher

$\mathrm{D^{0}}$

$p_{\mathrm{T}}$ . This measurement provides new experimental constraints on the mechanisms of heavy-flavor production in proton-proton collisions as well as on the processes of parton energy loss and diffusion of heavy quarks inside the quark-gluon plasma.

Additional Figures
png pdf	Additional Figure 1: Examples of $D^{0}$ candidate invariant mass distributions in 0.05 $< r <$ 0.1 pp collisions at 5.02 TeV, where $r$ is the angular distance between $D^{0}$ mesons and jets.
png pdf	Additional Figure 2: Examples of $D^{0}$ candidate invariant mass distributions in 0.05 $< r <$ 0.1 in PbPb collisions at 5.02 TeV, where $r$ is the angular distance between $D^{0}$ mesons and jets.
png pdf	Additional Figure 3: $r$ distribution of $D^{0}$ with 4 $< p_{T}^{D} <$ 20 GeV/c in PbPb collisions before background subtraction (black), the background contributions subtracted (Purple), and the result after background subtraction (orange).
png pdf	Additional Figure 4: Distributions of $D^{0}$ mesons in jets as a function of the distance from the jet axis for 4 $< p_{T}^{D} <$ 20 GeV/c measured in pp (blue) and PbPb (red) collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV.
png pdf	Additional Figure 5: Distributions of $D^{0}$ mesons in jets as a function of the distance from the jet axis for $p_{T}^{D} >$ 20 GeV/c measured in pp (blue) and PbPb (red) collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV.
png pdf	Additional Figure 6: Distributions of $D^{0}$ mesons in jets as a function of the distance from the jet axis for 4 $< p_{T}^{D} <$ 20 GeV/c measured in pp (blue) and PbPb (red) collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV. The ratio of the $D^{0}$ radial distributions of PbPb to pp are also presented in the lower panel.
png pdf	Additional Figure 7: Distributions of $D^{0}$ mesons in jets as a function of the distance from the jet axis for $p_{T}^{D} >$ 20 GeV/c measured in pp (blue) and PbPb (red) collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV. The ratio of the $D^{0}$ radial distributions of PbPb to pp are also presented in the lower panel.
png pdf	Additional Figure 8: The ratio of distributions of $D^{0}$ mesons in jets as a function of the distance from the jet axis for 4 $< p_{T}^{D} <$ 20 GeV/c measured in PbPb collisions to pp collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV.
png pdf	Additional Figure 9: The ratio of distributions of $D^{0}$ mesons in jets as a function of the distance from the jet axis for $p_{T}^{D} >$ 20 GeV/c measured in PbPb collisions to pp collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV.
png pdf	Additional Figure 10: Distributions of $D^{0}$ mesons in jets as a function of the distance from the jet axis for 4 $< p_{T}^{D} <$ 20 GeV/c measured in pp (blue) and PbPb (red) collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV. The predictions from the PYTHIA 8 event generator are also superimposed, and in the bottom panel the ratios of the $D^{0}$ radial profiles of pp over PYTHIA 8 predictions are presented.
png pdf	Additional Figure 11: Distributions of $D^{0}$ mesons in jets as a function of the distance from the jet axis for $p_{T}^{D} >$ 20 GeV/c measured in pp (blue) and PbPb (red) collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}=$ 5.02 TeV. The predictions from the PYTHIA 8 event generator are also superimposed, and in the bottom panel the ratios of the $D^{0}$ radial profiles of pp over PYTHIA 8 predictions are presented.

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