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CMS-BPH-16-003 ; CERN-EP-2018-224

Studies of $\mathrm{B_{s2}^{*}(5840)^{0}}$ and $\mathrm{B_{s1}(5830)^{0}}$ mesons including the observation of the $\mathrm{B_{s2}^{*}(5840)^{0}} \to \mathrm{B^0} \mathrm{K_{S}^0}$ decay in proton-proton collisions at $\sqrt{s} =$ 8 TeV

CMS Collaboration

10 September 2018

Eur. Phys. J. C 78 (2018) 939

Abstract: Measurements of $\mathrm{B_{s2}^{*}(5840)^{0}}$ and $\mathrm{B_{s1}(5830)^{0}}$ mesons are performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of 19.6 fb$^{-1}$ , collected with the CMS detector at the LHC at a centre-of-mass energy of 8 TeV. The analysis studies $P$-wave $\mathrm{B_{s}^0}$ meson decays into $\mathrm{B^{(*)+}}\mathrm{K^{-}}$ and $\mathrm{B^{(*)0}}\mathrm{K_{S}^{0}}$, where the $\mathrm{B^{+}}$ and $\mathrm{B^{0}}$ mesons are identified using the decays $\mathrm{B^{+}}\to\mathrm{J/\psi}\mathrm{K^{+}}$ and ${\mathrm{B^{0}}\to\mathrm{J/\psi}\mathrm{K^{*}(892)^0}}$. The masses of the $P$-wave $\mathrm{B_{s}^0}$ meson states are measured and the natural width of the $\mathrm{B_{s2}^{*}(5840)^{0}}$ state is determined. The first measurement of the mass difference between the charged and neutral $\mathrm{B^{*}}$ mesons is also presented. The $\mathrm{B_{s2}^{*}(5840)^{0}}$ decay to $\mathrm{B^{0}}\mathrm{K_{S}^{0}}$ is observed, together with a measurement of its branching fraction relative to the $\mathrm{B_{s2}^{*}(5840)^{0}} \to \mathrm{B^{+}} \mathrm{K^{-}}$ decay.

Links: e-print arXiv:1809.03578 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures
png pdf	Figure 1: Invariant mass distributions of (a) ${\mathrm {J} / \psi} {{{\mathrm {K}}} ^+}$ and (b) ${\mathrm {J} / \psi} {{{\mathrm {K}}} ^{*0}}$ candidates in data with the fit results superimposed. The points represent the data, with the vertical bars giving the corresponding statistical uncertainties. The thick curves are results of the fits, the dash-dotted lines display the signal contributions, and the short-dashed lines show the combinatorial background contributions. The long-dashed line shows in (a) the contribution from the ${{\mathrm {B}} ^+} \to {\mathrm {J} / \psi} {\pi ^+}$ decay, and in (b) the contribution from partially reconstructed ${\mathrm {B}} \to {\mathrm {J} / \psi} {{{\mathrm {K}}} ^{*0}} \mathrm {X}$ decays. The dashed line in (b) displays the contribution from swapping ${{{\mathrm {K}}} ^\pm} \to {\pi ^\pm}$ in the reconstruction.
png pdf	Figure 1-a: Invariant mass distribution of ${\mathrm {J} / \psi} {{{\mathrm {K}}} ^+}$ candidates in data with the fit results superimposed. The points represent the data, with the vertical bars giving the corresponding statistical uncertainties. The thick curves are results of the fits, the dash-dotted lines display the signal contributions, and the short-dashed lines show the combinatorial background contributions. The long-dashed line shows the contribution from the ${{\mathrm {B}} ^+} \to {\mathrm {J} / \psi} {\pi ^+}$ decay.
png pdf	Figure 1-b: Invariant mass distribution of ${\mathrm {J} / \psi} {{{\mathrm {K}}} ^{*0}}$ candidates in data with the fit results superimposed. The points represent the data, with the vertical bars giving the corresponding statistical uncertainties. The thick curves are results of the fits, the dash-dotted lines display the signal contributions, and the short-dashed lines show the combinatorial background contributions. The long-dashed line shows the contribution from partially reconstructed ${\mathrm {B}} \to {\mathrm {J} / \psi} {{{\mathrm {K}}} ^{*0}} \mathrm {X}$ decays. The dashed line displays the contribution from swapping ${{{\mathrm {K}}} ^\pm} \to {\pi ^\pm}$ in the reconstruction.
png pdf	Figure 2: (a) Two-dimensional distribution of ${m_{{{\mathrm {B}} ^+} {{{\mathrm {K}}} ^-}}}$ versus ${m_{{{\mathrm {B}} ^+} {\pi ^-}}}$ in data. (b) The fitted ${{{\mathrm {B}} ^+} {\pi ^-}}$ invariant mass distribution. The points represent the data, the thick solid curve is the fit projection, the thin lines indicate the three excited ${{\mathrm {B}} ^0}$ signal contributions, the short-dashed curve is the combinatorial background, and the long-dashed lines show the contributions from the excited ${{\mathrm {B}} ^0_ {\mathrm {s}}}$ decays.
png pdf	Figure 2-a: Two-dimensional distribution of ${m_{{{\mathrm {B}} ^+} {{{\mathrm {K}}} ^-}}}$ versus ${m_{{{\mathrm {B}} ^+} {\pi ^-}}}$ in data.
png pdf	Figure 2-b: The fitted ${{{\mathrm {B}} ^+} {\pi ^-}}$ invariant mass distribution. The points represent the data, the thick solid curve is the fit projection, the thin lines indicate the three excited ${{\mathrm {B}} ^0}$ signal contributions, the short-dashed curve is the combinatorial background, and the long-dashed lines show the contributions from the excited ${{\mathrm {B}} ^0_ {\mathrm {s}}}$ decays.
png pdf	Figure 3: Invariant mass distributions of (a) ${{{\mathrm {B}} ^+} {{{\mathrm {K}}} ^-}}$ and (b) ${{{\mathrm {B}} ^0} {{{\mathrm {K}}} ^0_{\mathrm {S}}}}$ candidates with the results of the fit overlaid. The points represent the data, the thick solid curves are the results of the overall fits, and the thin solid lines display the signal contributions. The short-dashed lines show the combinatorial background contributions. The long-dashed lines show: in (a) the contributions from excited ${{\mathrm {B}} ^0}$ meson decays, and in (b) the contributions from swapping ${{{\mathrm {K}}} ^\pm} \to {\pi ^\pm}$ in the reconstruction of the ${{\mathrm {B}} ^0}$ mesons.
png pdf	Figure 3-a: Invariant mass distribution of ${{{\mathrm {B}} ^0} {{{\mathrm {K}}} ^0_{\mathrm {S}}}}$ candidates with the results of the fit overlaid. The points represent the data, the thick solid curves are the results of the overall fits, and the thin solid lines display the signal contributions. The short-dashed lines show the combinatorial background contributions. The long-dashed lines show the contributions from swapping ${{{\mathrm {K}}} ^\pm} \to {\pi ^\pm}$ in the reconstruction of the ${{\mathrm {B}} ^0}$ mesons.
png pdf	Figure 3-b: Invariant mass distributions of (a) ${{{\mathrm {B}} ^+} {{{\mathrm {K}}} ^-}}$ and (b) ${{{\mathrm {B}} ^0} {{{\mathrm {K}}} ^0_{\mathrm {S}}}}$ candidates with the results of the fit overlaid. The points represent the data, the thick solid curves are the results of the overall fits, and the thin solid lines display the signal contributions. The short-dashed lines show the combinatorial background contributions. The long-dashed lines show: in (a) the contributions from excited ${{\mathrm {B}} ^0}$ meson decays, and in (b) the contributions from swapping ${{{\mathrm {K}}} ^\pm} \to {\pi ^\pm}$ in the reconstruction of the ${{\mathrm {B}} ^0}$ mesons.

Tables
png pdf	Table 1: Results on the masses, mass differences, and natural widths of the ${{\mathrm {B}} ^{(*)}_{{\mathrm {s}}1,2}}$ mesons from previous measurements. The mass differences are defined as ${\Delta M_{{{\mathrm {B}} _{{\mathrm {s}}1}}}^{\pm}} \equiv {M({{\mathrm {B}} _{{\mathrm {s}}1}})-M_{{{\mathrm {B}} ^{*+}}}^{\mathrm {PDG}}-M_{{{{\mathrm {K}}} ^-}}^{\mathrm {PDG}}}$ and ${\Delta M_{{{\mathrm {B}} ^{*}_{{\mathrm {s}}2}}}^{\pm}} \equiv {M({{\mathrm {B}} ^{*}_{{\mathrm {s}}2}})-M_{{{\mathrm {B}} ^+}}^{\mathrm {PDG}}-M_{{{{\mathrm {K}}} ^-}}^{\mathrm {PDG}}}$, where the PDG superscript refers to the world-average mass values at the time of each publication.
png pdf	Table 2: The observed signal yields ($N$), natural widths ($\Gamma$), and mass differences from the fits to the ${m_{{{\mathrm {B}} {{\mathrm {K}}}}}}$ distributions in data. The uncertainties are statistical only.
png pdf	Table 3: Relative systematic uncertainties in percent in the ratios ${R^{0\pm}_{2}}$ and ${R^{0\pm}_{1}}$.
png pdf	Table 4: Relative systematic uncertainties in percent in the ratios ${R^{\pm}_{2*}}$, ${R^{0}_{2*}}$, ${R^{\pm}_{\sigma}}$, and ${R^{0}_{\sigma}}$.
png pdf	Table 5: Systematic uncertainties (in MeV) in the measured mass differences and natural width. The ${{\mathrm {B}} ^{*}_{{\mathrm {s}}2}}$ width is measured only in the ${{{\mathrm {B}} ^+} {{{\mathrm {K}}} ^-}}$ channel.

Summary

The $P$-wave $\mathrm{B_{s}^0}$ meson states are studied using a data sample corresponding to an integrated luminosity of 19.6 fb$^{-1}$ of proton-proton collisions collected by the CMS experiment at $\sqrt{s} =$ 8 TeV in 2012. Observation and evidence are reported for the decays $\mathrm{B_{s2}^{*}(5840)^{0}} \to \mathrm{B^0} \mathrm{K_{S}^0}$ and ${\mathrm{B_{s1}(5830)^{0}}\to\mathrm{B^{*0}}\mathrm{K_{S}^{0}}}$, respectively. Four ratios of branching fractions and two ratios of production cross sections multiplied by the branching fractions of the $P$-wave $\mathrm{B_{s}^0}$ mesons into a B meson and kaon are measured. In addition, the differences between the $\mathrm{B^{*}_{s1,2}}$ mass and the sum of the B meson and kaon mass are determined, as well as the $\mathrm{B_{s2}^{*}(5840)^{0}}$ natural width. Finally, using a new approach, the mass differences $M_{\mathrm{B^{0}}}-M_{\mathrm{B^{+}}}$ and $M_{\mathrm{B^{*0}}}-M_{\mathrm{B^{*+}}}$ are measured, where the latter is determined for the first time.

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