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| CMS-BPH-22-012 ; CERN-EP-2024-180 | ||
| Test of lepton flavor universality in semileptonic $ \mathrm{B}_{c}^{+} $ meson decays in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 1 August 2024 | ||
| Submitted to Phys. Rev. Lett. | ||
| Abstract: A measurement of the ratio of branching fractions $ R(\mathrm{J}/\psi) = \mathcal{B}(\mathrm{B}_{c}^{+}\to\mathrm{J}/\psi\tau^{+}\nu_{\!\tau}) / \mathcal{B}(\mathrm{B}_{c}^{+}\to\mathrm{J}/\psi\mu^{+}\nu_{\!\mu}) $ in the $ \mathrm{J}/\psi\to\mu^{+}\mu^{-} $, $ \tau^{+}\to\mu^{+}\nu_{\!\mu}\overline{\nu}_{\!\tau} $ decay channel is presented. This measurement uses a sample of proton-proton collision data collected at a center-of-mass energy of 13 TeV by the CMS experiment in 2018, corresponding to an integrated luminosity of 59.7 fb$ ^{-1} $. The measured ratio, $ R(\mathrm{J}/\psi) = $ 0.17 $ ^{+ 0.18}_{- 0.17} $ (stat) $^{+ 0.21}_{- 0.22}$ (syst) ${^+ 0.19}_{- 0.18}$ (theo) $=$ 0.17 $ \pm $ 0.33, agrees with the value of 0.2582 $ \pm $ 0.0038 predicted by the standard model, which assumes lepton flavor universality. | ||
| Links: e-print arXiv:2408.00678 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Normalized distributions of the $ \mathrm{IP3D}/\sigma_{\mathrm{IP3D}} $ observable for the $ \mathrm{B}_{c}^{+}\to\mathrm{J}/\psi\,\mu^{+}\nu_{\!\mu} $ and $ \mathrm{B}_{c}^{+}\to\mathrm{J}/\psi\,\tau^{+}\nu_{\!\tau} $ signal channels and the misID background. Events are selected in the region $ m(3\mu) < m_{\mathrm{B}_{c}^{+}} $. The first and last bins contain underflow and overflow events, respectively. |
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Figure 2:
Distributions of the $ q^2 $ observable in the signal-enriched category, defined by $ m(3\mu) < m_{\mathrm{B}_{c}^{+}} $ in the bin of $ q^2 > $ 5.5 GeV$^2 $ and $ \mathrm{IP3D}/\sigma_{\mathrm{IP3D}} > $ 2 (left) and of the $ L_{xy}/\sigma_{L_{xy}} $ observable in the category defined by $ m(3\mu) > m_{\mathrm{B}_{c}^{+}} $ (right). In each panel, data is compared to the best fit results. The ratio between the data and the expected sum of signal and background contributions is shown in the lower panel of each observable. The postfit total uncertainty in the expectation is represented by the hashed band. |
png pdf |
Figure 2-a:
Distributions of the $ q^2 $ observable in the signal-enriched category, defined by $ m(3\mu) < m_{\mathrm{B}_{c}^{+}} $ in the bin of $ q^2 > $ 5.5 GeV$^2 $ and $ \mathrm{IP3D}/\sigma_{\mathrm{IP3D}} > $ 2 (left) and of the $ L_{xy}/\sigma_{L_{xy}} $ observable in the category defined by $ m(3\mu) > m_{\mathrm{B}_{c}^{+}} $ (right). In each panel, data is compared to the best fit results. The ratio between the data and the expected sum of signal and background contributions is shown in the lower panel of each observable. The postfit total uncertainty in the expectation is represented by the hashed band. |
png pdf |
Figure 2-b:
Distributions of the $ q^2 $ observable in the signal-enriched category, defined by $ m(3\mu) < m_{\mathrm{B}_{c}^{+}} $ in the bin of $ q^2 > $ 5.5 GeV$^2 $ and $ \mathrm{IP3D}/\sigma_{\mathrm{IP3D}} > $ 2 (left) and of the $ L_{xy}/\sigma_{L_{xy}} $ observable in the category defined by $ m(3\mu) > m_{\mathrm{B}_{c}^{+}} $ (right). In each panel, data is compared to the best fit results. The ratio between the data and the expected sum of signal and background contributions is shown in the lower panel of each observable. The postfit total uncertainty in the expectation is represented by the hashed band. |
| Tables | |
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Table 1:
Summary of the category pair definitions and respective observables used in the fit. Each pair is also divided by passing or failing the isolation criterion. The first four category pairs are enriched in $ \mathrm{B}_{c}^{+}\to\mathrm{J}/\psi\,\tau^{+}\nu_{\!\tau} $, the following two enriched in $ \mathrm{B}_{c}^{+}\to\mathrm{J}/\psi\,\mu^{+}\nu_{\!\mu} $, and the last one enriched in misID and $ \mathrm{H}_{\mathrm{b}} $ background events. |
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Table 2:
Leading systematic uncertainties for the measurement of $ R(\mathrm{J}/\psi) $. The second column reports the uncertainty type: shape (S) or normalization (N). The last column shows the resulting uncertainty in the $ R(\mathrm{J}/\psi) $ measurement. |
| Summary |
|
In summary, using data collected by the CMS experiment in 2018 at a center-of-mass energy of 13 TeV, corresponding to 59.7 fb$ ^{-1} $ of integrated luminosity, we measured the ratio of two branching fractions, |
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