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Register a new userAccumulating evidence for nonstandard leptonic decays of D_s mesons
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The measured rate for D_s -> l nu decays, where l is a muon or tau, is larger than the standard model prediction, which relies on lattice QCD, at the 3.8 sigma level. We discuss how robust the theoretical prediction is, and we show that the discrepancy with experiment may be explained by a charged Higgs boson or a leptoquark.
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We present a comparison of existing experimental data for the radiative leptonic decays $Ptoell u_ellgamma$, where $P=K$ or $pi$ and $ell=e$ or $mu$, from the KLOE, PIBETA, E787, ISTRA+ and OKA collaborations with theoretical predictions based on the recent non-perturbative determinations of the structure-dependent vector and axial-vector form factors, $F_V$ and $F_A$ respectively. These were obtained using lattice QCD+QED simulations at order $O(alpha_{mathrm{em}})$ in the electromagnetic coupling. We find good agreement with the KLOE data on $Kto e u_egamma$ decays from which the form factor $F^+=F_V+F_A$ can be determined. For $Ktomu u_mugamma$ decays we observe differences of up to 3,-,4 standard deviations at large photon energies between the theoretical predictions and the data from the E787, ISTRA+ and OKA experiments and similar discrepancies in some kinematical regions with the PIBETA experiment on radiative pion decays. A global study of all the kaon-decay data within the Standard Model results in a poor fit, largely because at large photon energies the KLOE and E787 data cannot be reproduced simultaneously in terms of the same form factor $F^+$. The discrepancy between the theoretical and experimental values of the form factor $F^-=F_V-F_A$ is even more pronounced. These observations motivate future improvements of both the theoretical and experimental determinations of the structure-dependent form factors $F^+$ and $F^-$, as well as further theoretical investigations of models of new physics which might for example, include possible flavor changing interactions beyond $V - A$ and/or non-universal corrections to the lepton couplings.
Inspired by the potential prospects of LHCb, Belle-II, STCF, CEPC and FCC-ee experiments, we discussed the probabilities of experimental investigation on the purely leptonic decays of the ground charged vector mesons including ${rho}^{pm}$, $K^{{ast}{pm}}$, $D_{d,s}^{{ast}{pm}}$ and $B_{u,c}^{{ast}{pm}}$.
It is well recognized that looking for new physics at lower energy colliders is a tendency which is complementary to high energy machines such as LHC. Based on large database of BESIII, we may have a unique opportunity to do a good job. In this paper we calculate the branching ratios of semi-leptonic processes $D^+_s to K^+ e^-e^+$, $D^+_s to K^+ e^-mu^+$ and leptonic processes $D^0 to e^-e^+$, $D^0 to e^-mu^+$ in the frames of $U(1)$ model, 2HDM and unparticle separately. It is found that both the $U(1)$ and 2HDM may influence the semi-leptonic decay rates, but only the $U(1)$ offers substantial contributions to the pure leptonic decays and the resultant branching ratio of $D^0 to e^-mu^+$ can be as large as $10^{-7}sim10^{-8}$ which might be observed at the future super $tau$-charm factory.
Using data collected near the Ds*+ Ds- peak production energy Ecm = 4170 MeV by the CLEO-c detector, we study the decays of Ds+ mesons to two pseudoscalar mesons. We report on searches for the singly-Cabibbo-suppressed Ds+ decay modes K+ eta, K+ eta, pi+ K0S, K+ pi0, and the isospin-forbidden decay mode Ds+ to pi+ pi0. We normalize with respect to the Cabibbo-favored Ds+ modes pi+ eta, pi+ eta, and K+ K0S, and obtain ratios of branching fractions: Ds+ to K+ eta / Ds+ to pi+ eta = (8.9 +- 1.5 +- 0.4)%, Ds+ to K+ eta / Ds+ to pi+ eta = (4.2 +- 1.3 +- 0.3)%, Ds+ to pi+ K0S / Ds+ to K+ K0S = (8.2 +- 0.9 +- 0.2)%, Ds+ to K+ pi0 / Ds+ to K+ K0S = (5.0 +- 1.2 +- 0.6)%, and Ds+ to pi+ pi0 / Ds+ to K+ K0S < 4.1% at 90% CL, where the uncertainties are statistical and systematic, respectively.
In recent years, hints for multi-lepton anomalies have been accumulated by the analysis of Large Hadron Collider (LHC) data, pointing towards the existence of beyond the Standard Model (SM) Higgs bosons: a new scalar particle $S$ with a mass $m_S$ in the range between $130,$GeV and $160,$GeV, produced from the decay of a heavier new scalar particle, $H$. Motivated by this observation, we perform a search for the signatures of $S$ within this mass region, which has been studied by CMS and ATLAS as a by-product of the SM Higgs searches in the side-bands of the kinematic regions. Combining the $gammagamma$ and $Zgamma$ channels, with associated leptons, di-jets, bottom quarks and missing energy, we obtain a local (global) significance of 5.1$sigma$ (4.8$sigma$) for a mass of $m_S= 151.5$,GeV and provide the preferred ranges for the corresponding (fiducial) cross sections. This is a strong indication for a scalar resonance $S$ decaying into photons, and, to a lesser extent to $Zgamma$, in association with missing energy, jets or leptons. Hints for the decays into, or production in association with, bottom quarks are statistically less significant. In order to test this hypothesis, we propose a search for $Hrightarrow gammagamma boverline{b},tau^+tau^- boverline{b}$ in asymmetric configurations that has not yet been performed by ATLAS and CMS.
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