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| CMS-PAS-HIN-19-007 | ||
| Fragmentation of jets containing a ${\mathrm{J}/\psi}$ meson in PbPb and pp collisions at 5 TeV | ||
| CMS Collaboration | ||
| June 2020 | ||
| Abstract: Jets containing a ${\mathrm{J}/\psi}$ meson are studied in PbPb collisions at a center of mass energy of ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV, using the CMS detector at the LHC. Jets are selected to be in the transverse momentum range of 30 $ < {p_{\mathrm{T}}} < $ 40 GeV. The yield of ${\mathrm{J}/\psi}$ in these jets is evaluated as function of the jet fragmentation function variable $z$, the ratio of the ${\mathrm{J}/\psi}$ ${p_{\mathrm{T}}}$ to the jet ${p_{\mathrm{T}}}$. The nuclear modification factor is then derived by comparing the yield in PbPb to the corresponding expectation from pp data at the same collision energy. The suppression of the ${\mathrm{J}/\psi}$ yield shows a dependence on $z$, indicating that the interaction of the ${\mathrm{J}/\psi}$ with the quark-gluon plasma formed in heavy-ion collisions depends on the fragmentation pattern of the jet that gives rise to the ${\mathrm{J}/\psi}$ meson. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to PLB. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Projections of a two-dimensional fit used to extract the prompt ${\mathrm{J}/\psi}$ yield in PbPb collisions. Left: The invariant mass distribution. Right: The $l_{{\mathrm{J}/\psi}}$ distribution. |
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Figure 1-a:
Projections of a two-dimensional fit used to extract the prompt ${\mathrm{J}/\psi}$ yield in PbPb collisions. Left: The invariant mass distribution. Right: The $l_{{\mathrm{J}/\psi}}$ distribution. |
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Figure 1-b:
Projections of a two-dimensional fit used to extract the prompt ${\mathrm{J}/\psi}$ yield in PbPb collisions. Left: The invariant mass distribution. Right: The $l_{{\mathrm{J}/\psi}}$ distribution. |
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Figure 2:
Detector response matrices for jets containing a prompt ${\mathrm{J}/\psi}$ meson, showing the bin migration probability as a function of jet ${p_{\mathrm{T}}}$ and $z$. The response for pp collisions (left) is evaluated using PYTHIA 8. The response for PbPb collisions (right) is evaluated using PYTHIA 8 embedded into HYDJET. |
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Figure 2-a:
Detector response matrices for jets containing a prompt ${\mathrm{J}/\psi}$ meson, showing the bin migration probability as a function of jet ${p_{\mathrm{T}}}$ and $z$. The response for pp collisions (left) is evaluated using PYTHIA 8. The response for PbPb collisions (right) is evaluated using PYTHIA 8 embedded into HYDJET. |
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Figure 2-b:
Detector response matrices for jets containing a prompt ${\mathrm{J}/\psi}$ meson, showing the bin migration probability as a function of jet ${p_{\mathrm{T}}}$ and $z$. The response for pp collisions (left) is evaluated using PYTHIA 8. The response for PbPb collisions (right) is evaluated using PYTHIA 8 embedded into HYDJET. |
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Figure 3:
The main sources of systematic uncertainty, plotted as a function of $z$ in pp (left) and PbPb (right) collisions. |
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Figure 3-a:
The main sources of systematic uncertainty, plotted as a function of $z$ in pp (left) and PbPb (right) collisions. |
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Figure 3-b:
The main sources of systematic uncertainty, plotted as a function of $z$ in pp (left) and PbPb (right) collisions. |
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Figure 4:
Normalized $z$ distribution in pp collisions, compared to prompt and nonprompt PYTHIA 8 simulation, at generator level. The shaded boxes represent systematic uncertainties. |
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Figure 5:
Left: ${\mathrm{J}/\psi}$ yields as a function of $z$ in pp and PbPb collisions. Right: The nuclear modification factor $R_{\rm AA}$ as a function of $z$. Bars indicate statistical uncertainties, while systematic uncertainties are depicted as boxes. The box around unity shows the normalization uncertainties. |
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Figure 5-a:
Left: ${\mathrm{J}/\psi}$ yields as a function of $z$ in pp and PbPb collisions. Right: The nuclear modification factor $R_{\rm AA}$ as a function of $z$. Bars indicate statistical uncertainties, while systematic uncertainties are depicted as boxes. The box around unity shows the normalization uncertainties. |
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Figure 5-b:
Left: ${\mathrm{J}/\psi}$ yields as a function of $z$ in pp and PbPb collisions. Right: The nuclear modification factor $R_{\rm AA}$ as a function of $z$. Bars indicate statistical uncertainties, while systematic uncertainties are depicted as boxes. The box around unity shows the normalization uncertainties. |
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Figure 6:
The nuclear modification factor $R_{\rm AA}$ for two centrality selections of PbPb collisions as a function of $z$. Due to limited statistical precision, the lowest z bin is excluded. Bars indicate statistical uncertainties, while systematic uncertainties are depicted as boxes. The boxes around unity show the normalization uncertainties. |
| Summary |
| Jets containing a ${\mathrm{J}/\psi}$ meson were studied in pp and PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV, for jets of 30 $ < {p_{\mathrm{T}}} < $ 40 GeV and $|\eta| < $ 2. We compared the distribution of the fragmentation variable $z$, the ratio of the ${\mathrm{J}/\psi}$ ${p_{\mathrm{T}}}$ to that of the jet, between the two systems. The resulting nuclear modification factor shows a rising trend as a function of $z$. The suppression at low $z$ is found to be larger in the 20% most central events, compared to the rest. The results show explicitly that the ${\mathrm{J}/\psi}$ produced with a large degree of surrounding jet activity are more highly suppressed than those produced in isolation. |
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