CMS-PAS-HIN-19-011

CMS-PAS-HIN-19-011
Measurement of $\mathrm{B_s^0}$ and $\mathrm{B^+}$ meson yields in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV
CMS Collaboration
June 2020

Abstract: The $\mathrm{B_s^0}$ and $\mathrm{B^+}$ production cross sections are measured in PbPb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data sample, collected by the CMS detector at the LHC, corresponds to an integrated luminosity of 1.7 nb $^{-1}$ . The mesons are reconstructed in the exclusive decay channels $\mathrm{B_s^0}\rightarrow{J}/\psi\,\phi(1020)$ and $\mathrm{B^+}\rightarrow{J}/\psi\,K^{+}$ . The $\mathrm{B_s^0}$ meson is observed with a statistical significance in excess of 5 standard deviations for the first time in nucleus-nucleus collisions. The measurements are performed as a function of the transverse momentum of the B mesons, in the interval 7-50 GeV $/c$ , and of the PbPb collision centrality. The ratio of production yields of $\mathrm{B_s^0}$ and $\mathrm{B^+}$ is also presented.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PLB. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Invariant mass distributions of $\mathrm{B^{+}}$ (left) and $\mathrm{B_s^0}$ (right) candidates, for event centrality in the range 0-90%. The lower panels show the pulls, obtained as the difference between the data points and fit result, divided by the data uncertainty.
png pdf	Figure 1-a: Invariant mass distributions of $\mathrm{B^{+}}$ (left) and $\mathrm{B_s^0}$ (right) candidates, for event centrality in the range 0-90%. The lower panels show the pulls, obtained as the difference between the data points and fit result, divided by the data uncertainty.
png pdf	Figure 1-b: Invariant mass distributions of $\mathrm{B^{+}}$ (left) and $\mathrm{B_s^0}$ (right) candidates, for event centrality in the range 0-90%. The lower panels show the pulls, obtained as the difference between the data points and fit result, divided by the data uncertainty.
png pdf	Figure 2: The acceptance- and efficiency-corrected yields for the PbPb and $\mathrm{B_s^0}$ mesons, scaled by ${T_{\mathrm {AA}}}$ and ${N_{\text {MB}}}$ in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The results are shown as a function of the meson ${p_{\mathrm {T}}}$ (left), and of the event centrality (right), where the rightmost panel indicates the centrality-integrated result. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty comprises the uncertainties in ${T_{\mathrm {AA}}}$ , ${N_{\text {MB}}}$ and $\mathcal {B}$ (left) and the uncertainties in $\mathcal {B}$ (right).
png pdf	Figure 2-a: The acceptance- and efficiency-corrected yields for the PbPb and $\mathrm{B_s^0}$ mesons, scaled by ${T_{\mathrm {AA}}}$ and ${N_{\text {MB}}}$ in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The results are shown as a function of the meson ${p_{\mathrm {T}}}$ (left), and of the event centrality (right), where the rightmost panel indicates the centrality-integrated result. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty comprises the uncertainties in ${T_{\mathrm {AA}}}$ , ${N_{\text {MB}}}$ and $\mathcal {B}$ (left) and the uncertainties in $\mathcal {B}$ (right).
png pdf	Figure 2-b: The acceptance- and efficiency-corrected yields for the PbPb and $\mathrm{B_s^0}$ mesons, scaled by ${T_{\mathrm {AA}}}$ and ${N_{\text {MB}}}$ in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV. The results are shown as a function of the meson ${p_{\mathrm {T}}}$ (left), and of the event centrality (right), where the rightmost panel indicates the centrality-integrated result. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty comprises the uncertainties in ${T_{\mathrm {AA}}}$ , ${N_{\text {MB}}}$ and $\mathcal {B}$ (left) and the uncertainties in $\mathcal {B}$ (right).
png pdf	Figure 3: The ratio of production yields between $\mathrm{B_s^0}$ and PbPb mesons. (left) The ratio dependence on the meson ${p_{\mathrm {T}}}$ ; a prediction from the TAMU transport model [57], and fit to the $f_s/f_u$ ${p_{\mathrm {T}}}$ dependence by LHCb [58] in pp collisions at 13 TeV are also displayed. (right) The ratio dependence on the collision centrality; the average $f_s/f_u$ result obtained in pp 13 TeV collisions by LHCb [59] is also displayed as an horizontal bar; the rightmost panel shows the centrality-integrated measurement. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty on the yields ratio corresponds to the decay branching fractions $\mathcal {B}$ .
png pdf	Figure 3-a: The ratio of production yields between $\mathrm{B_s^0}$ and PbPb mesons. (left) The ratio dependence on the meson ${p_{\mathrm {T}}}$ ; a prediction from the TAMU transport model [57], and fit to the $f_s/f_u$ ${p_{\mathrm {T}}}$ dependence by LHCb [58] in pp collisions at 13 TeV are also displayed. (right) The ratio dependence on the collision centrality; the average $f_s/f_u$ result obtained in pp 13 TeV collisions by LHCb [59] is also displayed as an horizontal bar; the rightmost panel shows the centrality-integrated measurement. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty on the yields ratio corresponds to the decay branching fractions $\mathcal {B}$ .
png pdf	Figure 3-b: The ratio of production yields between $\mathrm{B_s^0}$ and PbPb mesons. (left) The ratio dependence on the meson ${p_{\mathrm {T}}}$ ; a prediction from the TAMU transport model [57], and fit to the $f_s/f_u$ ${p_{\mathrm {T}}}$ dependence by LHCb [58] in pp collisions at 13 TeV are also displayed. (right) The ratio dependence on the collision centrality; the average $f_s/f_u$ result obtained in pp 13 TeV collisions by LHCb [59] is also displayed as an horizontal bar; the rightmost panel shows the centrality-integrated measurement. The vertical bars (boxes) correspond to statistical (systematic) uncertainties. The global systematic uncertainty on the yields ratio corresponds to the decay branching fractions $\mathcal {B}$ .

Tables
png pdf	Table 1: Summary of systematic uncertainties on the production cross section measurements for PbPb and $\mathrm{B_s^0}$ for centrality ranges 0-30%, 30-90%, and 0-90%. The measurements are perfomed in the B kinematic region given by 10 $< {p_{\mathrm {T}}} <$ 50 GeV/ $c$ and $\|y\| <$ 2.4. The relative uncertainty values are shown, in percentage.

Summary

The production yields of

$\mathrm{B_s^0}$ and

$\mathrm{B^+}$ mesons, scaled by the nuclear overlap function

${T_{\mathrm{AA}}}$ and

${N_{\text{MB}}}$ , in PbPb collisions at a center-of-mass energy of 5.02 TeV per nucleon pair are presented as a function of the meson transverse momenta and event centrality. The B mesons are studied with the CMS detector at the LHC via the reconstruction of the exclusive hadronic decay channels

$\mathrm{B_s^0} \to \mathrm{J}/\psi\phi$ all and

$\mathrm{B^+} \to \mathrm{J}/\psi \mathrm{K^{+}}$ all. The measurements are performed within the B mesons fiducial region given by

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

$c$ for

$|y| <$ 2.4 and 7

$< {p_{\mathrm{T}}} <$ 50 GeV/

$c$ for 1.5

$< |y| <$ 2.4. The ratio of production yields for

$\mathrm{B_s^0}$ and

$\mathrm{B^+}$ in PbPb collisions is found to be statistically compatible with the corresponding fragmentation fraction ratio,

$f_s/f_u$ . These results extend and are compatible with those previously reported by the CMS Collaboration [24,36], and employ a three-fold larger PbPb data sample. The further investigation of possible hints of an enhancement of the ratio in PbPb relative to pp\ collisions will benefit from more precise PbPb and pp reference data taken at the same collision energy. The first observation of the

$\mathrm{B_s^0}$ meson in nucleus-nucleus collisions, with a statistical significance surpassing 5 standard deviations, is attained. The larger PbPb data sets that should be accumulated in upcoming high-luminosity LHC heavy ion runs will provide additional precision and shall help to further characterize the mechanisms of beauty hadronization in heavy ion collisions.

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