CMS-PAS-BPH-19-001

CMS-PAS-BPH-19-001
Relative cross sections of the ${\rm B_c^+(2S)}$ and ${\rm B_c^{*+}(2S)}$ states with respect to the ${\rm B_c^+}$ state in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
May 2020

Abstract: The ${\rm B_c^+(2S)}$ to ${\rm B_c^+}$ and ${\rm B_c^{+}(2S)}$ to ${\rm B_c^+}$ cross section ratios, as well as the ${\rm B_c^{+}(2S)}$ to ${\rm B_c^+(2S)}$ cross section ratio, are measured in proton-proton collisions at $\sqrt{s} =$ 13 TeV, using a data sample collected by the CMS experiment, corresponding to an integrated luminosity of 143 fb $^{-1}$ . The three measurements are made in the ${\rm B_c^+}$ phase space window defined by transverse momentum $p_{\rm T} >$ 15 GeV and absolute rapidity $\|y\| <$ 2.4, with the excited ${\rm B_c^{()+}(2S)}$ states reconstructed in their ${\rm B_c^+} \pi^+ \pi^-$ decay. The ${\rm B_c^+(2S)}$ to ${\rm B_c^+}$ , ${\rm B_c^{+}(2S)}$ to ${\rm B_c^+}$ , and ${\rm B_c^{+}(2S)}$ to ${\rm B_c^+(2S)}$ cross section ratios, including the (unknown) ${\rm B_c^{()+}(2S) \to B_c^+}\pi^+\pi^-$ branching fractions, are (3.57 $\pm$ 0.69 (stat) $\pm$ 0.32 (syst) )%, (4.91 $\pm$ 0.69 (stat) $\pm$ 0.57 (syst) )%, and 1.39 $\pm$ 0.35 (stat) $\pm$ 0.09 (syst), respectively, where the first uncertainty is statistical and the second is systematic. None of these ratios shows a significant dependence on the $p_{\rm T}$ or $\|y\|$ of the ${\rm B_c^+}$ . The shape of the invariant mass distribution of the dipions emitted in the ${\rm B_c^{(*)+}(2S) \to B_c^+}\pi^+\pi^-$ decays is also reported.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, PRD 102 (2020) 092007. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Invariant mass distribution of the ${\mathrm{B_c}^{+} \to \mathrm{J}/\psi \pi^{+}}$ candidates, after applying all event selection criteria. The fitted contributions are shown by the stacked distributions, the solid line representing their sum. Taken from Ref. [1].
png pdf	Figure 2: Invariant mass distribution of the ${{{\mathrm{B_c}^{()+}} (\text{2S})} \to {\mathrm{B_c}^{+}} \pi^{+}\pi^{-}}$ candidates, the ${{{\mathrm{B_c}^{()+}} (\text{2S})}}$ being the lower-mass peak. The fitted contributions are shown by the stacked distributions, the solid line representing their sum. Taken from Ref. [1].
png pdf	Figure 3: The $R^{+}$ , $R^{+}$ , and $R^{+} / R^{+}$ cross section ratios as a function of the ${\mathrm{B_c}^{+}}$ ${p_{\mathrm {T}}}$ (left) and the ${\mathrm{B_c}^{+}}$ ${\|y\|}$ (right). The markers are shown at the average ${\mathrm{B_c}^{+}}$ ${p_{\mathrm {T}}}$ or ${\|y\|}$ values of the events contributing to each bin.
png pdf	Figure 3-a: The $R^{+}$ , $R^{+}$ , and $R^{+} / R^{+}$ cross section ratios as a function of the ${\mathrm{B_c}^{+}}$ ${p_{\mathrm {T}}}$ (left) and the ${\mathrm{B_c}^{+}}$ ${\|y\|}$ (right). The markers are shown at the average ${\mathrm{B_c}^{+}}$ ${p_{\mathrm {T}}}$ or ${\|y\|}$ values of the events contributing to each bin.
png pdf	Figure 3-b: The $R^{+}$ , $R^{+}$ , and $R^{+} / R^{+}$ cross section ratios as a function of the ${\mathrm{B_c}^{+}}$ ${p_{\mathrm {T}}}$ (left) and the ${\mathrm{B_c}^{+}}$ ${\|y\|}$ (right). The markers are shown at the average ${\mathrm{B_c}^{+}}$ ${p_{\mathrm {T}}}$ or ${\|y\|}$ values of the events contributing to each bin.
png pdf	Figure 4: Normalized invariant mass distribution of the dipions emitted in the ${{{\mathrm{B_c}^{(*)+}} (\text{2S})} \to {\mathrm{B_c}^{+}} \pi^{+}\pi^{-}}$ decays, $M(\pi^{+}\pi^{-})$ . Both the statistical (inner tick marks) and the total (outer tick marks) uncertainties are represented. The histograms represent the two corresponding phase space distributions.

Tables
png pdf	Table 1: Ratios of the reconstruction efficiencies relevant for the determination of the $R^{+}$ , $R^{+}$ , and $R^{+} / R^{+}$ cross section ratios. The central values are followed by the several uncertainties mentioned in the text.
png pdf	Table 2: Systematic uncertainties (in %) on the cross section ratios, corresponding to the sources described in the text. The total uncertainty is the sum in quadrature of the individual terms.

Summary

The

${{\mathrm{B_c}^{+}} (\text{2S})}$ to

${\mathrm{B_c}^{+}}$ and

${{\mathrm{B_c}^{*+}} (\text{2S})}$ to

${\mathrm{B_c}^{+}}$ cross section ratios, as well as the

${{\mathrm{B_c}^{*+}} (\text{2S})}$ to

${{\mathrm{B_c}^{+}} (\text{2S})}$ cross section ratio, have been measured in proton-proton collisions at

$\sqrt{s} =$ 13 TeV. The measurement was made on the basis of a data sample collected by the CMS experiment in the Run 2 of the LHC (2015-2018), corresponding to an integrated luminosity of 143 fb

$^{-1}$ .

The

${{\mathrm{B_c}^{+}} (\text{2S})}$ to

${\mathrm{B_c}^{+}}$ ,

${{\mathrm{B_c}^{*+}} (\text{2S})}$ to

${\mathrm{B_c}^{+}}$ , and

${{\mathrm{B_c}^{*+}} (\text{2S})}$ to

${{\mathrm{B_c}^{+}} (\text{2S})}$ cross section ratios, including the (unknown)

${{{\mathrm{B_c}^{(*)+}} (\text{2S})} \to {\mathrm{B_c}^{+}} \pi^{+}\pi^{-}}$ branching fractions, are

$R^{+} =$ 3.57

$\pm$ 0.69 (stat)

$\pm$ 0.32 (syst) %

$R^{*+} =$ 4.91

$\pm$ 0.69 (stat)

$\pm$ 0.57 (syst) %

$R^{*+} / R^{+} =$ 1.39

$\pm$ 0.35 (stat)

$\pm$ 0.09 (syst)
where the first uncertainty is statistical and the second is systematic. No significant dependences on the

$p_{\mathrm{T}}$ or

$|y|$ of the

$\mathrm{B_c}^{+}$ mesons have been observed for any of these three ratios. The shapes of the invariant mass distributions of the dipions emitted in the

${{{\mathrm{B_c}^{(*)+}} (\text{2S})} \to {\mathrm{B_c}^{+}} \pi^{+}\pi^{-}}$ decays have also been reported. These results, obtained in the phase space region defined by

$\mathrm{B_c}^{+}$ transverse momentum

$p_{\mathrm{T}}>$ 15 GeV and

$\mathrm{B_c}^{+}$ absolute rapidity

$|y| <$ 2.4, are expected to provide important experimental information to improve the theoretical understanding of the nature of the

$\mathrm{\bar{b}c}$ heavy quarkonium states and of the processes behind their production.

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