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| CMS-BPH-20-001 ; CERN-EP-2020-110 | ||
| Measurement of the CP-violating phase ${\phi_{\mathrm{s}}}$ in the ${\mathrm{B^{0}_{s}}\to\mathrm{J}/\psi\,\phi(1020) \to \mu^{+}\mu^{-}\,{\mathrm{K^{+}}\mathrm{K^{-}}} } $ channel in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 5 July 2020 | ||
| Phys. Lett. B 816 (2021) 136188 | ||
| Abstract: The CP-violating weak phase ${\phi_{\mathrm{s}}}$ and the decay width difference $\Delta\Gamma_{\mathrm{s}}$ between the light and heavy $\mathrm{B^{0}_{s}}$ mass eigenstates are measured with the CMS detector at the LHC in a sample of 48 500 reconstructed ${\mathrm{B^{0}_{s}}\to\mathrm{J}/\psi\,\phi(1020) \to \mu^{+}\mu^{-}\,{\mathrm{K^{+}}\mathrm{K^{-}}} }$ events. The measurement is based on a data sample corresponding to an integrated luminosity of 96.4 fb$^{-1}$, collected in proton-proton collisions at $\sqrt{s} = $ 13 TeV in 2017-2018. To extract the values of ${\phi_{\mathrm{s}}}$ and $\Delta\Gamma_{\mathrm{s}}$, a time-dependent and flavor-tagged angular analysis of the $ {\mu^{+}\mu^{-}} {\mathrm{K^{+}}\mathrm{K^{-}}} $ final state is performed. The analysis employs a dedicated tagging trigger and a novel opposite-side muon flavor tagger based on machine learning techniques. The measurement yields ${\phi_{\mathrm{s}}} = -11 \pm 50 {\,\text{(stat)}} \pm 10 {\,\text{(syst)}} $ mrad and $\Delta\Gamma_{\mathrm{s}} = 0.114 \pm 0.014 {\,\text{(stat)}} \pm 0.007 {\,\text{(syst)}}$ ps$^{-1}$, in agreement with the standard model predictions. When combined with the previous CMS measurement at $\sqrt{s} = $ 8 TeV, the following values are obtained: ${\phi_{\mathrm{s}}} = -21 \pm 45 $ mrad, $\Delta\Gamma_{\mathrm{s}} = 0.1073 \pm 0.0097$ ps$^{-1}$, a significant improvement over the 8 TeV result. | ||
| Links: e-print arXiv:2007.02434 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Definition of the three angles ${\theta _\mathrm {T}}$, ${\psi _\mathrm {T}}$, and ${\varphi _\mathrm {T}} $ describing the topology of the ${\mathrm{B^{0}_{s}} \to \mathrm{J}/\psi \,\phi \to {\mu^{+} \mu^{-}} \, {\mathrm{K^{+}} \mathrm{K^{-}}}}$ decay. |
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Figure 2:
The invariant mass distribution of the ${\mathrm{B^{0}_{s}} \to \mathrm{J}/\psi \,\phi \to {\mu^{+} \mu^{-}} \, {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The vertical bars on the points represent the statistical uncertainties. The solid line represents a projection of the fit to data (as discussed in Section 5, solid markers), the dashed line corresponds to the signal, the dotted line to the combinatorial background, and the long-dashed line to the peaking background from $\mathrm{B}^{0} \to \mathrm{J}/\psi \, {\mathrm{K^{*(892)}}}^0 \to {\mu^{+} \mu^{-}} \,\mathrm{K^{+}} \pi^{-} $, as obtained from the fit. The distribution of the differences between the data and the fit, divided by the combined uncertainty in the data and the best fit function for each bin (pulls) is displayed in the lower panel. |
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Figure 3:
The ${ct}$ distribution (left) and its uncertainty (right) for the ${\mathrm{B^{0}_{s}} \to \mathrm{J}/\psi \,\phi \to {\mu^{+} \mu^{-}} \, {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The notations are as in Fig. 2. |
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Figure 3-a:
The ${ct}$ distribution for the ${\mathrm{B^{0}_{s}} \to \mathrm{J}/\psi \,\phi \to {\mu^{+} \mu^{-}} \, {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The notations are as in Fig. 2. |
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Figure 3-b:
The uncertainty in ${ct}$ for the ${\mathrm{B^{0}_{s}} \to \mathrm{J}/\psi \,\phi \to {\mu^{+} \mu^{-}} \, {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The notations are as in Fig. 2. |
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Figure 4:
Results of the calibration of the per-event mistag probability ${\omega _{\text {evt}}}$ based on ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}} \to {\mu^{+} \mu^{-}} \,\mathrm{K^{\pm}}}$ decays from the 2017 (left) and 2018 (right) data samples. The vertical bars represent the statistical uncertainties. The solid line shows a linear fit to data (solid markers). The pull distributions between the data and the fit function in each bin are shown in the lower panels. |
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Figure 4-a:
Results of the calibration of the per-event mistag probability ${\omega _{\text {evt}}}$ based on ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}} \to {\mu^{+} \mu^{-}} \,\mathrm{K^{\pm}}}$ decays from the 2017 data sample. The vertical bars represent the statistical uncertainties. The solid line shows a linear fit to data (solid markers). The pull distribution between the data and the fit function in each bin is shown in the lower panel. |
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Figure 4-b:
Results of the calibration of the per-event mistag probability ${\omega _{\text {evt}}}$ based on ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}} \to {\mu^{+} \mu^{-}} \,\mathrm{K^{\pm}}}$ decays from the 2018 data sample. The vertical bars represent the statistical uncertainties. The solid line shows a linear fit to data (solid markers). The pull distribution between the data and the fit function in each bin is shown in the lower panel. |
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Figure 5:
The angular distributions $\cos {\theta _\mathrm {T}} $ (left), $\cos {\psi _\mathrm {T}} $ (middle), and $ {\varphi _\mathrm {T}} $ (right) for the $\mathrm{B^{0}_{s}}$ candidates and the projections from the fit. The notations are as in Fig. 2. |
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Figure 5-a:
The $\cos {\theta _\mathrm {T}} $ angular distribution for the $\mathrm{B^{0}_{s}}$ candidates and the projections from the fit. The notations are as in Fig. 2. |
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Figure 5-b:
The $\cos {\psi _\mathrm {T}} $ angular distribution for the $\mathrm{B^{0}_{s}}$ candidates and the projections from the fit. The notations are as in Fig. 2. |
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Figure 5-c:
The $ {\varphi _\mathrm {T}} $ angular distribution for the $\mathrm{B^{0}_{s}}$ candidates and the projections from the fit. The notations are as in Fig. 2. |
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Figure 6:
The two-dimensional likelihood contours at 68% CL in the $ {\phi _{\mathrm {s}}} $-$ {\Delta \Gamma _{\mathrm {s}}} $ plane, for the CMS 8 TeV (dashed line), 13 TeV (dotted line), and combined (solid line) results. The SM prediction is shown with the diamond marker [1,3]. |
| Tables | |
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Table 1:
Angular and time-dependent terms of the signal model. |
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Table 2:
Calibrated opposite-side muon tagger performance evaluated using ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}}}$ events in the 2017 and 2018 data samples. The uncertainties shown are statistical only. |
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Table 3:
Results of the fit to data. Statistical uncertainties are obtained from the increase in $-\log{\mathcal {L}}$ by 0.5, whereas systematic uncertainties are described below and summarized in Table 4. |
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Table 4:
Summary of the systematic uncertainties. The dashes ({\text {--}}) mean that the corresponding uncertainty is not applicable. The total systematic uncertainty is obtained as the quadratic sum of the individual contributions. |
| Summary |
|
The CP-violating phase ${\phi_{\mathrm{s}}} $ and the decay width difference $\Delta\Gamma_{\mathrm{s}}$ between the light and heavy $\mathrm{B^{0}_{s}}$ meson mass eigenstates are measured using a total of 48 500 ${\mathrm{B^{0}_{s}}\to\mathrm{J}/\psi\,\phi(1020) \to \mu^{+}\mu^{-}\,{\mathrm{K^{+}}\mathrm{K^{-}}} }$ signal events, collected by the CMS experiment at the LHC in proton-proton collisions at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 96.4 fb$^{-1}$. Events are selected using a trigger that requires an additional muon, which can be exploited to infer the flavor of the $\mathrm{B^{0}_{s}}$ meson at the time of production. A novel opposite-side muon tagger based on deep neural networks has been developed to maximize the sensitivity of the present analysis. A high tagging power of ${\approx}$10% is achieved, aided by the requirement of an additional muon in the signal sample imposed at the trigger level. The CP-violating phase is measured to be ${\phi_{\mathrm{s}}} = -11 \pm 50 {\,\text{(stat)}} \pm 10 {\,\text{(syst)}}$ mrad, consistent both with the SM prediction ${\phi_{\mathrm{s}}} = {-36.96\,^{+0.72}_{-0.84}}$ mrad [1] and with the absence of CP violation in the mixing-decay interference. The decay width difference between the $\mathrm{B^{0}_{s}}$ mass eigenstates is measured to be $\Delta\Gamma_{\mathrm{s}}= 0.114 \pm 0.014 {\,\text{(stat)}} \pm 0.007 {\,\text{(syst)}}$ ps$^{-1}$, consistent with the theoretical prediction $\Delta\Gamma_{\mathrm{s}} = 0.091 \pm 0.013 $ ps$^{-1}$ [3]. In addition, the CP-violating parameter $|\lambda|$ and the average lifetime of the heavy and light $\mathrm{B^{0}_{s}}$ mass eigenstates, as well as their mass difference, have been measured. The uncertainties in all these measurements are dominated by the statistical components. The results presented in this Letter are further combined with those obtained by CMS at $\sqrt{s} = $ 8 TeV [13], yielding ${\phi_{\mathrm{s}}} = -21 \pm 45 $ mrad and $\Delta\Gamma_{\mathrm{s}}= 0.1073 \pm 0.0097$ ps$^{-1}$. These results are significantly more precise than those from the previous CMS measurement at 8 TeV, and can be used to further constrain possible new-physics effects in $\mathrm{B^{0}_{s}}$ meson decay and mixing. |
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