CMS-PAS-HIN-18-012

CMS-PAS-HIN-18-012
Production of prompt and nonprompt $\mathrm{J}/\psi$ mesons in jets in pp collisions at $\sqrt{s} = $ 5.02 TeV
CMS Collaboration
May 2018

Abstract: The fragmentation of jets containing a $\mathrm{J}/\psi$ meson is studied in low pile-up pp data recorded in 2015, at a center-of-mass energy of $\sqrt{s} = $ 5.02 TeV. The fraction of the jet transverse momentum $p_{\rm T,jet}$ taken by the $\mathrm{J}/\psi$ is measured for both prompt and nonprompt $\mathrm{J}/\psi$ mesons. The value of $p_{\rm T,jet}$ is restricted to the range of 25-35 GeV. The $\mathrm{J}/\psi$ mesons are measured above 3 and 6.5 GeV, in the endcap and barrel regions of the CMS detector, respectively. Whereas the results for nonprompt $\mathrm{J}/\psi$ are well-modeled by simulations using a Monte Carlo generator, the prompt $\mathrm{J}/\psi$ are found to be accompanied by a larger level of jet activity. The fraction of $\mathrm{J}/\psi$ mesons that are found to be inside a jet within the $p_{\rm T,jet}$ selection is also reported, and found to be larger than simulation, for both prompt and nonprompt $\mathrm{J}/\psi$.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1: Invariant mass spectrum of $ {\mu ^+\mu ^-} $ pairs (left) and pseudo-proper decay length distribution (right) in pp collisions for 0 $ < \|y\| < $ 1.6, 6.5 $ < {p_{\mathrm {T}}} < $ 35.0 GeV. The result of the fit described in the text is also shown.
png pdf	Figure 1-a: Invariant mass spectrum of $ {\mu ^+\mu ^-} $ pairs in pp collisions for 0 $ < \|y\| < $ 1.6, 6.5 $ < {p_{\mathrm {T}}} < $ 35.0 GeV. The result of the fit described in the text is also shown.
png pdf	Figure 1-b: Pseudo-proper decay length distribution in pp collisions for 0 $ < \|y\| < $ 1.6, 6.5 $ < {p_{\mathrm {T}}} < $ 35.0 GeV. The result of the fit described in the text is also shown.
png pdf	Figure 2: The four-dimensional detector-response matrices for prompt (left) and nonprompt $ \mathrm{J}/\psi $ (right), as a function of jet ${p_{\mathrm {T}}}$ and $z$. The colors represent the bin-to-bin migration probabilities ranging from 0 (light yellow) to 1 (dark brown).
png pdf	Figure 2-a: The four-dimensional detector-response matrices for prompt $ \mathrm{J}/\psi $, as a function of jet ${p_{\mathrm {T}}}$ and $z$. The colors represent the bin-to-bin migration probabilities ranging from 0 (light yellow) to 1 (dark brown).
png pdf	Figure 2-b: The four-dimensional detector-response matrices for nonprompt $ \mathrm{J}/\psi $, as a function of jet ${p_{\mathrm {T}}}$ and $z$. The colors represent the bin-to-bin migration probabilities ranging from 0 (light yellow) to 1 (dark brown).
png pdf	Figure 3: Self-normalized prompt (left) and nonprompt $z$ distributions in the rapidity range $\|y\| < $ 1.6, for pp data and PYTHIA 8. For the nonprompt case, the $z$ distribution of the parent b hadron is also shown.
png pdf	Figure 3-a: Self-normalized prompt $z$ distributions in the rapidity range $\|y\| < $ 1.6, for pp data and PYTHIA 8.
png pdf	Figure 3-b: Self-normalized nonprompt $z$ distributions in the rapidity range $\|y\| < $ 1.6, for pp data and PYTHIA 8. The $z$ distribution of the parent b hadron is also shown.
png pdf	Figure 4: Self-normalized prompt (left) and nonprompt (right) $z$ distributions in the rapidity range 1.6 $ < \|y\| < 2.4$, for pp data and PYTHIA 8. For the nonprompt case, the $z$ distribution of the parent b hadron is also shown.
png pdf	Figure 4-a: Self-normalized prompt $z$ distributions in the rapidity range 1.6 $ < \|y\| < 2.4$, for pp data and PYTHIA 8.
png pdf	Figure 4-b: Self-normalized nonprompt $z$ distributions in the rapidity range 1.6 $ < \|y\| < 2.4$, for pp data and PYTHIA 8. The $z$ distribution of the parent b hadron is also shown.
png pdf	Figure 5: Left: The fraction of prompt and nonprompt $ \mathrm{J}/\psi $ in jets of 25 $ < {p_{\mathrm {T}}} < $ 35 GeV in pp data and in PYTHIA 8, compared to the total number of $ \mathrm{J}/\psi $ in the relevant the ${p_{\mathrm {T}}}$ interval, as indicated on the Figure. Right: The ratio of these $ \mathrm{J}/\psi $ -in-jet fractions in data compared to simulation for prompt and nonprompt $ \mathrm{J}/\psi $.
png pdf	Figure 5-a: The fraction of prompt and nonprompt $ \mathrm{J}/\psi $ in jets of 25 $ < {p_{\mathrm {T}}} < $ 35 GeV in pp data and in PYTHIA 8, compared to the total number of $ \mathrm{J}/\psi $ in the relevant the ${p_{\mathrm {T}}}$ interval, as indicated on the Figure.
png pdf	Figure 5-b: The ratio of these $ \mathrm{J}/\psi $ -in-jet fractions in data compared to simulation for prompt and nonprompt $ \mathrm{J}/\psi $.

Summary

In this analysis, the self-normalized $z$ distributions for $\mathrm{J}/\psi$ mesons in jets of 25 $ < {p_{\mathrm{T}}} < $ 35 GeV, for both prompt and nonprompt $\mathrm{J}/\psi$ production, were reported. The distributions are presented above a lower threshold of 3 and 6.5 GeV, in the endcap (1.6 $ < |y| < $ 2.4) and barrel ($|y| < $ 1.6) regions of the CMS detector, respectively. These results confirm the findings of LHCb [8], albeit in a different rapidity range and ${\sqrt{s}} $, namely that the nonprompt $ \mathrm{J}/\psi $ production is reasonably well modeled by simulation, in this case PYTHIA 8, but that the prompt $ \mathrm{J}/\psi $ production is qualiltatively different than predicted. Prompt $ \mathrm{J}/\psi $ in jets tend to carry a smaller fraction of the jet momentum, indicating that they are less isolated than suggested by production models. In addition, we also report the fraction of the $\mathrm{J}/\psi$ mesons in jets, for jets in the same window of ${p_{\mathrm{T}}}$ (25-35 GeV), and for $\mathrm{J}/\psi$ meson above aforementioned lower $ {p_{\mathrm{T}}} $ thresholds. This additional information should provide further constraints on models of $ \mathrm{J}/\psi $ production.

Additional Figures
png pdf	Additional Figure 1: The fraction of prompt $ \mathrm{J}/\psi $ in jets of 25 $ < {p_{\mathrm {T}}} < $ 35 GeV in pp data and in PYTHIA 8, compared to the total number of $ \mathrm{J}/\psi $ in the relevant the $ {p_{\mathrm {T}}} $ interval, as indicated on the Figure.
png pdf	Additional Figure 2: Data/MC ratio of the $ \mathrm{J}/\psi $ -in-jet fraction for prompt $ \mathrm{J}/\psi $.
png pdf	Additional Figure 3: The fraction of prompt $ \mathrm{J}/\psi $ in jets of 25 $ < {p_{\mathrm {T}}} < $ 35 GeV in pp data and in PYTHIA 8, compared to the total number of $ \mathrm{J}/\psi $ in the relevant the $ {p_{\mathrm {T}}} $ interval, as indicated on the Figure.
png pdf	Additional Figure 4: Data/MC ratio of the $ \mathrm{J}/\psi $ -in-jet fraction for nonprompt $ \mathrm{J}/\psi $.

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