Study of $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ decays to charmonia and three light hadrons

Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1 collected with the LHCb detector, seven decay modes of the $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + meson into a J/ψ or ψ(2S) meson and three charged hadrons, kaons or pions, are studied. The decays $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → (ψ(2S) → J/ψπ+π−)π+, $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → ψ(2S)π+π−π+, $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → J/ψK+π−π+ and $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → J/ψK+K−K+ are observed for the first time, and evidence for the $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + → ψ(2S)K+K−π+, decay is found, where J/ψ and ψ(2S) mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different $$ {\mathrm{B}}_{\mathrm{c}}^{+} $$ B c + decays are reported as well as the fractions of the decays proceeding via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays.

Updated search for $$ {B}_c^{+} $$ decays to two charm mesons

A data set corresponding to an integrated luminosity of 9 fb−1 of proton-proton collisions collected by the LHCb experiment has been analysed to search for $$ {B}_c^{+}\to {D}_{(s)}^{\left(\ast \right)+}{\genfrac{}{}{0pt}{}{\left(\hbox{---} \right)}{D}}^{\left(\ast \right)0} $$ B c + → D s ∗ + — D ∗ 0 decays. The decays are fully or partially reconstructed, where one or two missing neutral pions or photons from the decay of an excited charm meson are allowed. Upper limits for the branching fractions, normalised to B+ decays to final states with similar topologies, are obtained for sixteen $$ {B}_c^{+} $$ B c + decay modes. For the decay $$ {B}_c^{+}\to {D}_s^{+}{\overline{D}}^0 $$ B c + → D s + D ¯ 0 , an excess with a significance of 3.4 standard deviations is found.

Next-to-leading-order QCD corrections to a vector bottomonium radiative decay into a charmonium

Within the framework of nonrelativistic QCD (NRQCD) factorization, we calculate the next-to-leading-order (NLO) perturbative corrections to the radiative decay Υ → ηc(χcJ) + γ. Both the helicity amplitudes and the helicity decay widths are obtained. It is the first computation for the processes involving both bottomonium and charmonium at two-loop accuracy. By employing the Cheng-Wu theorem, we are able to convert most of complex-valued master integrals (MIs) into real-valued MIs, which makes the numerical integration much efficient. Our results indicate the $$ \mathcal{O}\left({\alpha}_s\right) $$ O α s corrections are moderate for ηc and χc2 production, and are quite marginal for χc0 and χc1 production. It is impressive to note the NLO corrections considerably reduce the renormalization scale dependence in both the decay widths and the branching fractions for χcJ, and slightly improve that for ηc. With the NRQCD matrix elements evaluated via the Buchmüller-Tye potential model, we find the decay width for ηc production is one-order-of-magnitude larger than χcJ production, which may provide a good opportunity to search for Υ → ηc + γ in experiment. In addition, the decay width for χc1 production is several times larger than those for χc0,2. Finally, we find the NLO NRQCD prediction for the branching fraction of Υ → χc1 + γ is only half of the lower bound of the experimental data measured recently by Belle. Moreover, there exists serious contradiction between theory and experiment for Υ → ηc + γ. The discrepancies between theory and experiment deserve further research efforts.

Heavy + light pseudoscalar meson semileptonic transitions

A symmetry-preserving regularisation of a vector $$\times $$ × vector contact interaction (SCI) is used to deliver a unified treatment of semileptonic transitions involving $$\pi $$ π , K, $$D_{(s)}$$ D ( s ) , $$B_{(s,c)}$$ B ( s , c ) initial states. The framework is characterised by algebraic simplicity, few parameters, and the ability to simultaneously treat systems from Nambu–Goldstone modes to heavy+heavy mesons. Although the SCI form factors are typically somewhat stiff, the results are comparable with experiment and rigorous theory results. Hence, predictions for the five unmeasured $$B_{s,c}$$ B s , c branching fractions should be a reasonable guide. The analysis provides insights into the effects of Higgs boson couplings via current-quark masses on the transition form factors; and results on $$B_{(s)}\rightarrow D_{(s)}$$ B ( s ) → D ( s ) transitions yield a prediction for the Isgur–Wise function in fair agreement with contemporary data.

Searching for the Muon Decay to Three Electrons with the Mu3e Experiment

Mu3e is a dedicated experiment designed to find or exclude the charged lepton flavor violating μ→ eee decay at branching fractions above 10−16. The search is pursued in two operational phases: Phase I uses an existing beamline at the Paul Scherrer Institute (PSI), targeting a single event sensitivity of 2·10−15, while the ultimate sensitivity is reached in Phase II using a high intensity muon beamline under study at PSI. As the μ→ eee decay is heavily suppressed in the Standard Model of particle physics, the observation of such a signal would be an unambiguous indication of the existence of new physics. Achieving the desired sensitivity requires a high rate of muons (108 stopped muons per second) along with a detector with large kinematic acceptance and efficiency, able to reconstruct the low momentum of the decay electrons and positrons. To achieve this goal, the Mu3e experiment is mounted with an ultra thin tracking detector based on monolithic active pixel sensors for excellent momentum and vertex resolution, combined with scintillating fibers and tiles for precise timing measurements.

Search for a heavy Higgs boson decaying into two lighter Higgs bosons in the ττbb final state at 13 TeV

A search for a heavy Higgs boson H decaying into the observed Higgs boson h with a mass of 125 GeV and another Higgs boson hS is presented. The h and hS bosons are required to decay into a pair of tau leptons and a pair of b quarks, respectively. The search uses a sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb−1. Mass ranges of 240–3000 GeV for mH and 60–2800 GeV for $$ {m}_{{\mathrm{h}}_{\mathrm{S}}} $$ m h S are explored in the search. No signal has been observed. Model independent 95% confidence level upper limits on the product of the production cross section and the branching fractions of the signal process are set with a sensitivity ranging from 125 fb (for mH = 240 GeV) to 2.7 fb (for mH = 1000 GeV). These limits are compared to maximally allowed products of the production cross section and the branching fractions of the signal process in the next-to-minimal supersymmetric extension of the standard model.

Measurement of branching fractions of J/ψ and ψ(3686) decays to Σ+ and $$ \overline{\Sigma} $$−

Using 1310.6 × 106J/ψ and 448.1 × 106ψ(3686) events collected with the BESIII detector, the branching fractions of J/ψ decays to Σ+$$ \overline{\Sigma} $$ Σ ¯ − is measured to be (10.61 ± 0.04 ± 0.36) × 10−4, which is significantly more precise than the current world average. The branching fractions of ψ(3686) decays to Σ+$$ \overline{\Sigma} $$ Σ ¯ − is measured to be (2.52 ± 0.04 ± 0.09) × 10−4, which is consistent with the previous measurements. In addition, the ratio of $$ \mathcal{B} $$ B (ψ(3686) → Σ+$$ \overline{\Sigma} $$ Σ ¯ −)/$$ \mathcal{B} $$ B (J/ψ → Σ+$$ \overline{\Sigma} $$ Σ ¯ −) is determined to be (23.8 ± 1.1)% which violates the “12% rule”.