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Register a new userSearches for 25 rare and forbidden decays of $D^+$ and $D_s^+$ mesons
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A search is performed for rare and forbidden charm decays of the form $D_{(s)}^+ to h^pm ell^+ ell^{(prime)mp}$, where $h^pm$ is a pion or kaon and $ell^{()pm}$ is an electron or muon. The measurements are performed using proton-proton collision data, corresponding to an integrated luminosity of $1.6text{fb}^{-1}$, collected by the LHCb experiment in 2016. No evidence is observed for the 25 decay modes that are investigated and $90%$ confidence level limits on the branching fractions are set between $1.4times10^{-8}$ and $6.4times10^{-6}$. In most cases, these results represent an improvement on existing limits by one to two orders of magnitude.
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In this document we present the latest result on rare/forbidden decays for D mesons at the BESIII experiment. Based on 2.92/fb data taken at the center-of-mass energy 3.773 GeV with the BESIII detector, the flavor-changing neutral current process of neutral D decays into two gammas is searched using a double tag technique, while the decays of charged D decays into a charged kaon/pion plus two electrons/positrons are studied based on a single tag method. The resulting upper limits are still above the Standard Model predictions.
We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type $D^0rightarrow h^{prime -} h^{-}ell^{prime +} ell^{+}$ and $D^0rightarrow h^{prime -} h^{+}ell^{primepm} ell^{mp}$, where $h$ and $h^{prime}$ represent a $K$ or $pi$ meson and $ell$ and $ell^{prime}$ an electron or muon. The analysis is based on $468$ fb$^{-1}$ of $e^+e^-$ annihilation data collected at or close to the $Y(4S)$ resonance with the BaBar detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes and we establish 90% confidence level upper limits on the branching fractions in the range $(1.0 - 30.6)times 10^{-7}$. The limits are between one and three orders of magnitude times more stringent than previous measurements.
We have searched for flavor-changing neutral current decays and lepton-number-violating decays of D^+ and D^+_s mesons to final states of the form h^+- e^-+ e^+, where h is either pi or K. We use the complete samples of CLEO-c open-charm data, corresponding to integrated luminosities of 818 pb^-1 at the center-of-mass energy E_CM = 3.774 GeV containing 2.4 x 10^6 D^+D^- pairs and 602 pb^-1 at E_CM = 4.170 GeV containing 0.6 x 10^6 D^*+-_s D^-+_s pairs. No signal is observed in any channel, and we obtain 90% confidence level upper limits on branching fractions B(D^+ --> pi^+ e^+ e^-) < 5.9 x 10^-6, B(D^+ --> pi^- e^+ e^+) < 1.1 x 10^-6, B(D^+ --> K^+ e^+ e^-) < 3.0 x 10^-6, B(D^+ --> K^- e^+ e^+) < 3.5 x 10^-6, B(D^+_s --> pi^+ e^+ e^-) < 2.2 x 10^-5, B(D^+_s --> pi^- e^+ e^+) < 1.8 x 10^-5, B(D^+_s --> K^+ e^+ e^-) < 5.2 x 10^-5, and B(D^+_s --> K^- e^+ e^+) < 1.7 x 10^-5.
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.
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.
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