Narrow Results

We have updated theoretical studies of heavy vector quarkonium production, including $J/\mathrm{\Psi }$, ${\mathrm{\Psi }}^{\prime }$ and $\mathrm{\Upsilon }$, in the exclusive W-boson decays. Particularly, in the standard model the branching fraction of $W^{-}\to J/\mathrm{\Psi }{\ell }^{-}{\bar{\nu }}_{\ell }$ ($\ell =e$ or $\mu$) has been predicted to be about $8.5\times 10^{-7}$, which is substantially larger than those of two-body hadronic radiative W decays. Thus in the future high-luminosity experimental facilities, this rare channel could be very useful to search for the exclusive W-boson decays containing the hadronic final state. Furthermore, the surprisingly large decay rate can be explained by an electromagnetic fragmentation formalism. We have analyzed the lepton fragmentation and the photon fragmentation processes, and calculated their contributions to the differential decay rate of $W^{-}\to J/\mathrm{\Psi }{\ell }^{-}{\bar{\nu }}_{\ell }$ in the fragmentation limit. It is found that the fragmentation contribution agrees well with the result from the full calculation.

We review the recent measurements of rare and forbidden decays of charmed mesons at the B-factories. A preliminary result of the first measurement of orbitally excited meson radiative decay to D⁰γ final state, and the most sensitive determination of limits on the leptonic D⁰ → ℓ⁺ ℓ^- decays are briefly described.

An overview of selected recent results on mixing and CP-symmetry violation in the charm sector, and D meson rare decays, was presented at the Physics In Collision conference 2013 in Beijing.

Recent results on mixing, CP violation and rare decays in charm physics from the LHCb experiment are presented. Study of "wrong-sign" D⁰ → K⁺π^- decays provides the highest precision measurements to date of the mixing parameters x′² and y′, and of CP violation in this decay mode. Direct and indirect CP violation in the D⁰ system are probed to a sensitivity of around 10^-3 using D⁰ → K⁺K⁻ and D⁰ → π⁺π⁻ decays and found to be consistent with zero. Searches for the rare decays , and D⁰ → μ⁺μ⁻ find no evidence of signal, but set the best limits on branching fractions to date. Thus, despite many excellent results in charm physics from LHCb, no evidence for physics beyond the Standard Model is found.

The ratio of the leptonic charged kaon decays R_K = Γ(K^± → e^±ν)/Γ(K^± → μ^±ν) is sensitive to the structure of the weak interactions and can be precisely calculated within the Standard Model. Presence of New Physics can introduce a shift on its value of the order of a percent. The NA62 experiment at CERN SPS used data from a dedicated run in 2007 to perform a measurement of this ratio and probe the lepton universality. The data analysis technique and the final results are presented.

The NA48/2 and NA62 collaborations report on recent results, current status, and prospects of kaon physics at the CERN-SPS. The NA62 collaborations aims to measure the decay $K^{\pm }\to {\pi }^{\pm }\nu \bar{\nu }$ with an uncertainty of 10% or better. The NA62 detector and preliminary results from a pilot run in 2014 are presented. In addition, recent results of the NA48/2 collaboration are reported. A search for Dark Photons has been performed in ${\pi }^0$ decays via the kaon decays $K^{\pm }\to {\pi }^{\pm }{\pi }^0$ and $K^{\pm }{\pi }^0{\mu }^{\pm }\nu$. No dark photon signal was observed and new upper limits on the mixing parameter ${ϵ}^2$ and the dark photon mass were computed. We also report the first observation of the kaon decay $K^{\pm }\to {\pi }^{\pm }{\pi }^0{e}^{+}{e}^{-}$.

The covariant quark model with infrared confinement (CQM) is a well-suited theoretical framework to describe large variety of hadronic processes, including rare decays of heavy mesons. In this text we focus on the reactions $B\to K^{(\ast )}{\mu }^{+}{\mu }^{-}$, which have been recently measured by Refs. 1–4. The measurements include also information about the angular distributions and their significance is given by possible New Physics (NP) effects which are predicted in numerous beyond Standard Model (SM) scenarios. Even with clever choice of experimental observables, a model dependence cannot be fully removed from the theoretical predictions. In this text we present the computation of the $B\to K^{(\ast )}$ form factors within the CQM and give results for some of the most commonly used observables ($A_{FB}$, $F_L$).

In the Standard Model the electroweak coupling of the gauge bosons to leptons is independent of the lepton flavour. Semileptonic and rare decays of b quarks provide an ideal laboratory to test this property. Any violation of Lepton Flavour Universality would be a clear sign of physics beyond the Standard Model. In this work a review of the Lepton Flavour Universality tests performed using data collected by the LHCb experiment in 2011 and 2012 at a centre of mass energy of 7 and 8 TeV is presented.