A pioneering machine-learning-based flavor-tagging algorithm combining same-side and opposite-side tagging is used to obtain the equivalent of 27$\,$000 tagged B$^0_\mathrm{s}$$\to$ J/$\psi\, \phi$(1020) decays from pp collisions at $\sqrt{s} =$ 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 96.5 fb$^{-1}$. A time- and flavor-dependent angular analysis of the $\mu^+\mu^-$K$^+$K$^-$ final state is used to measure parameters of the $\mathrm{B}^0_\mathrm{s}$-$\overline{\mathrm{B}}^0_\mathrm{s}$ system. The weak phase is measured to be $\phi_\mathrm{s}$ = $-$73 $\pm$ 23 (stat) $\pm$ 7 (syst) mrad, which, combined with a $\sqrt{s}$ = 8 TeV CMS result, gives $\phi_\mathrm{s}$ = $-$74 $\pm$ 23 mrad. This value differs from zero by 3.2 standard deviations, providing evidence for $CP$ violation in B$^0_\mathrm{s}$$\to$ J/$\psi\,\phi$(1020) decays. All measured physics parameters are found to agree with standard model predictions where available.
Measured values and uncertainties of the main parameters of interest, as obtained from the analysis to data at 13 TeV.
Values and uncertainties of the physics parameters obtained from the combination of the CMS 8 TeV and 13 TeV results using the BLUE method. The uncertainty includes both statistical and systematic sources.
Matrix of the correlations of the statistical uncertainties between pairs of physics parameters, as obtained from the analysis to data at 13 TeV.
The $CP$ violating weak phase $\phi_{\text{s}}$, and the decay width difference $\Delta\Gamma_{\text{s}}$ between the light and heavy $\mathrm{B_s}$ mass eigenstates are measured with the CMS detector at the LHC in a sample of reconstructed $\mathrm{B}_s \to \mathrm{J}/\psi\,\phi(1020) \to \mu^+\mu^-\,\mathrm{K}^+\mathrm{K}^-$ decays. The measurement is based on a data set corresponding to an integrated luminosity of $96.4\;\mathrm{fb}^{-1}$, collected in proton-proton collisions at a center-of-mass energy of $13\;\mathrm{TeV}$ in 2017-2018. To extract the values of $\phi_{\text{s}}$ and $\Delta\Gamma_{\text{s}}$, a time-dependent and flavor-tagged angular analysis of the $\mu^+\mu^-\,\mathrm{K}^+\mathrm{K}^-$ final state is performed. The analysis employs a novel opposite-side muon flavor tagger based on machine learning techniques, which, in conjunction with a dedicated tagging trigger, allowed to reach an unprecedented tagging power. The measurement yields $\phi_{\text{s}} = -0.011 \pm 0.050\,\mathrm{(stat)} \pm 0.010\,\mathrm{(syst)}\;\mathrm{rad}$, and $\Delta\Gamma_{\text{s}} = 0.114 \pm 0.014\,\mathrm{(stat)} \pm 0.007\,\mathrm{(syst)}\;\mathrm{ps}^{-1}$, in agreement with the standard model predictions. When combined with our previous measurement at a center-of-mass energy of 8 TeV, the following values are obtained: $\phi_{\text{s}} = -0.021 \pm 0.045\;\mathrm{rad}$, $\Delta\Gamma_{\text{s}} = 0.1074 \pm 0.0097\;\mathrm{ps}^{-1}$, a significant improvement over the 8 TeV result.
Results of the fit to the data at 13 TeV. Statistical uncertainties are obtained from the increase in $-\log{\mathcal{L}}$ by 0.5.
Values of parameter obtained combining the 13 TeV results with those obtained by CMS at 8 TeV.
Statistical correlation matrix of the physics parameters of interest, as obtained from the fit to data at 13 TeV.
The polarizations of promptly produced $\chi_\mathrm{c1}$ and $\chi_\mathrm{c2}$ mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at $\sqrt{s} = $ 8 TeV. The $\chi_\mathrm{c}$ states are reconstructed via their radiative decays $\chi_\mathrm{c}$ $\to$ $\mathrm{J}/\psi\, \gamma$, with the photons being measured through conversions to e$^+$e$^-$, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the $\chi_\mathrm{c2}$ to $\chi_\mathrm{c1}$ yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the $\mathrm{J}/\psi$ $\to$ $\mu^+\mu^-$ decay, in three ranges of $\mathrm{J}/\psi$ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum.
Yield ratios of chi_c2 over chi_c1 mesons as a function of phi (HX) in the J/psi pT range 8-12 GeV
Yield ratios of chi_c2 over chi_c1 mesons as a function of phi (HX) in the J/psi pT range 12-18 GeV
Yield ratios of chi_c2 over chi_c1 mesons as a function of phi (HX) in the J/psi pT range 18-30 GeV
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