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| CMS-HIN-22-001 ; CERN-EP-2024-138 | ||
| Search for nuclear modifications of $ {\mathrm{B}^{+}} $ meson production in pPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 8.16 TeV | ||
| CMS Collaboration | ||
| 7 July 2024 | ||
| Submitted to Phys. Rev. Lett. | ||
| Abstract: Nuclear medium effects on $ {\mathrm{B}^{+}} $ meson production are studied using the binary-collision scaled cross section ratio between events of different multiplicities from proton-lead collisions. Data, collected by the CMS experiment in 2016 at a nucleon-nucleon center-of-mass energy of $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 8.16 TeV, corresponding to an integrated luminosity of 175 nb$^{-1}$, were used. The scaling factors in the ratio are determined using a novel approach based on the $ \mathrm{Z}\to\mu^{-}\mu^{+} $ cross sections measured in the same events. The scaled ratio for $ {\mathrm{B}^{+}} $ is consistent with unity for all event multiplicities, putting stringent constraints on nuclear modification for heavy flavor. | ||
| Links: e-print arXiv:2407.05402 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
png pdf |
Figure 1:
Reconstructed $ \psi(\text{2S}) \mathrm{K^+} $ invariant mass distributions for $ {\mathrm{B}^{+}} $ meson candidates with 3 $ < p_{\mathrm{T}} < $ 50 GeV, in events with 2 $ < N_{\text{ch}} < $ 60 (left) or 110 $ < N_{\text{ch}} < $ 250 (right). The result of the fit described in the text is also shown. |
png pdf |
Figure 1-a:
Reconstructed $ \psi(\text{2S}) \mathrm{K^+} $ invariant mass distributions for $ {\mathrm{B}^{+}} $ meson candidates with 3 $ < p_{\mathrm{T}} < $ 50 GeV, in events with 2 $ < N_{\text{ch}} < $ 60 (left) or 110 $ < N_{\text{ch}} < $ 250 (right). The result of the fit described in the text is also shown. |
png pdf |
Figure 1-b:
Reconstructed $ \psi(\text{2S}) \mathrm{K^+} $ invariant mass distributions for $ {\mathrm{B}^{+}} $ meson candidates with 3 $ < p_{\mathrm{T}} < $ 50 GeV, in events with 2 $ < N_{\text{ch}} < $ 60 (left) or 110 $ < N_{\text{ch}} < $ 250 (right). The result of the fit described in the text is also shown. |
png pdf |
Figure 2:
(left) $ {\mathrm{B}^{+}} $ differential cross section in $ p_{\mathrm{T}} $ bins. Vertical bars (boxes) represent the statistical (systematic) uncertainties. The global systematic uncertainty, not included in the data points, comprises the uncertainties in the integrated luminosity measurement and the $ {\mathrm{B}^{+}} $ meson branching fraction. Results are compared to FONLL calculations, scaled by the number of binary nucleon-nucleon collisions. The yellow boxes represent the theoretical uncertainties from FONLL calculations [37,38,39]. (right) $ {\mathrm{B}^{+}} $ differential cross section shown in $ p_{\mathrm{T}} $ bins divided into classes of $ N_{\text{ch}} $. For better visibility, data points are scaled by a factor of 2 (blue), 4 (magenta), or 8 (red). Vertical bars represent total uncertainties. |
png pdf |
Figure 2-a:
(left) $ {\mathrm{B}^{+}} $ differential cross section in $ p_{\mathrm{T}} $ bins. Vertical bars (boxes) represent the statistical (systematic) uncertainties. The global systematic uncertainty, not included in the data points, comprises the uncertainties in the integrated luminosity measurement and the $ {\mathrm{B}^{+}} $ meson branching fraction. Results are compared to FONLL calculations, scaled by the number of binary nucleon-nucleon collisions. The yellow boxes represent the theoretical uncertainties from FONLL calculations [37,38,39]. (right) $ {\mathrm{B}^{+}} $ differential cross section shown in $ p_{\mathrm{T}} $ bins divided into classes of $ N_{\text{ch}} $. For better visibility, data points are scaled by a factor of 2 (blue), 4 (magenta), or 8 (red). Vertical bars represent total uncertainties. |
png pdf |
Figure 2-b:
(left) $ {\mathrm{B}^{+}} $ differential cross section in $ p_{\mathrm{T}} $ bins. Vertical bars (boxes) represent the statistical (systematic) uncertainties. The global systematic uncertainty, not included in the data points, comprises the uncertainties in the integrated luminosity measurement and the $ {\mathrm{B}^{+}} $ meson branching fraction. Results are compared to FONLL calculations, scaled by the number of binary nucleon-nucleon collisions. The yellow boxes represent the theoretical uncertainties from FONLL calculations [37,38,39]. (right) $ {\mathrm{B}^{+}} $ differential cross section shown in $ p_{\mathrm{T}} $ bins divided into classes of $ N_{\text{ch}} $. For better visibility, data points are scaled by a factor of 2 (blue), 4 (magenta), or 8 (red). Vertical bars represent total uncertainties. |
png pdf |
Figure 3:
The $ R_{\mathrm{HL}} $ for $ {\mathrm{B}^{+}} $ in $ p_{\mathrm{T}} $ bins for the highest and lowest multiplicity classes (left), and in the full $ p_{\mathrm{T}} $ range and as a function of the multiplicity density (right). The error bars correspond to the statistical uncertainty, and the boxes represent the sum in quadrature of systematic uncertainties. |
png pdf |
Figure 3-a:
The $ R_{\mathrm{HL}} $ for $ {\mathrm{B}^{+}} $ in $ p_{\mathrm{T}} $ bins for the highest and lowest multiplicity classes (left), and in the full $ p_{\mathrm{T}} $ range and as a function of the multiplicity density (right). The error bars correspond to the statistical uncertainty, and the boxes represent the sum in quadrature of systematic uncertainties. |
png pdf |
Figure 3-b:
The $ R_{\mathrm{HL}} $ for $ {\mathrm{B}^{+}} $ in $ p_{\mathrm{T}} $ bins for the highest and lowest multiplicity classes (left), and in the full $ p_{\mathrm{T}} $ range and as a function of the multiplicity density (right). The error bars correspond to the statistical uncertainty, and the boxes represent the sum in quadrature of systematic uncertainties. |
png pdf |
Figure 4:
Z boson differential cross section in $ p_{\mathrm{T}} $ bins for the different multiplicity classes. The vertical bars represent the total uncertainties. |
| Tables | |
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Table 1:
Fraction of the full event sample that contains a $ {\mathrm{B}^{+}} $ meson candidate in each multiplicity class, and corrected multiplicity for charged particles with $ |y| < $ 2.4 and $ p_{\mathrm{T}} > $ 0.4 GeV. Systematic uncertainties are given for the corrected multiplicities, while statistical uncertainties are negligible. |
png pdf |
Table 2:
Summary of differential cross sections ($ \mu$b GeV$^{-1}$) as a function of $ p_{\mathrm{T}} $($ {\mathrm{B}^{+}} $) in pPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 8.16 TeV. The uncertainties in the integrated luminosity measurement and the $ {\mathrm{B}^{+}} $ meson branching fraction are not included in the systematic uncertainties. |
| Summary |
| In summary, the $ {\mathrm{B}^{+}} $ meson differential production cross sections have been measured as a function of the meson transverse momentum in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of 8.16 TeV. The exclusive $ {\mathrm{B}^{+}}\!\to\! \mathrm{J}/\psi \mathrm{K^+} $ decay channel was used to reconstruct the $ {\mathrm{B}^{+}} $ mesons. The fixed-order next-to-leading logarithmic predictions are in agreement with the inclusive measurement. The $ {\mathrm{B}^{+}} $ cross section has been measured for the first time in different classes of charged-particle multiplicity in pPb collisions, revealing an expected rising trend in the $ {\mathrm{B}^{+}} $ production with increasing charged-particle multiplicity. The scaled ratio of $ {\mathrm{B}^{+}} $ meson cross sections in high- to low-multiplicity events were used to study nuclear medium effects on heavy flavor production. The scaling factors, characterizing the relative number of binary collisions between event classes of different multiplicities, were obtained, for the first time, in a data-driven way from ratios of the measured Z boson cross sections in the same events. The observed ratios are consistent with unity within uncertainties for all event selections studied, setting constraints on possible presence of medium effects in the $ {\mathrm{B}^{+}} $ meson production. The novel approach relying on the Z boson measurements to extract the scaling factors provides future opportunities for medium effect searches, particularly in small collision systems. |
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