Abstract
A search is performed for rare and forbidden charm decays of the form {D}_{(s)}^{+}to {h}^{pm }{mathrm{ell}}^{+}{mathrm{ell}}^{left(prime right)mp } , where h± is a pion or kaon and ℓ(′)± is an electron or muon. The measurements are performed using proton-proton collision data, corresponding to an integrated luminosity of 1.6 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 1.4 × 10−8 and 6.4 × 10−6. In most cases, these results represent an improvement on existing limits by one to two orders of magnitude.
Highlights
The potential of c → u + − processes to constrain new physics has been discussed in the literature [8,9,10,11]
The best limits in the other channels are measured by the BaBar collaboration [18], which has studied all channels, or by the CLEO collaboration, from searches in decay modes with dielectrons in the final state [19]
The minimum distance in the plane transverse to the beam of a track to a primary pp collision vertex (PV), the impact parameter (IP), is measured with a resolution of (15 + 29/pT) μm, where pT is the component of the momentum transverse to the beam, in GeV
Summary
The eight decay modes with two oppositely charged leptons of different flavour (D(+s) → π+e+μ−, D(+s) → π+μ+e−, D(+s) → K+e+μ−, D(+s) → K+μ+e−) are lepton-flavour violating (LFV) and lepton-number conserving decays. These decays have only negligible contributions from neutrino mixing in the SM. Non-resonant decays with a pion and two same-sign or opposite-sign muons in the final state have previously been searched for by LHCb with no evidence observed [17]. The best limits in the other channels are measured by the BaBar collaboration [18], which has studied all channels, or by the CLEO collaboration, from searches in decay modes with dielectrons in the final state [19]
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