ABSTRACT
The NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of 1.4×10^{17} protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton-antilepton final states is presented and a region of the parameter space is excluded at 90% confidence level, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV/c^{2} and coupling values in the range 10^{-6} to 4×10^{-5}. An interpretation of the e^{+}e^{-} search result in terms of the emission and decay of an axionlike particle is also presented.
ABSTRACT
Searches for the lepton number violating K^{+}âπ^{-}µ^{+}e^{+} decay and the lepton flavor violating K^{+}âπ^{+}µ^{-}e^{+} and π^{0}âµ^{-}e^{+} decays are reported using data collected by the NA62 experiment at CERN in 2017-2018. No evidence for these decays is found and upper limits of the branching ratios are obtained at 90% confidence level: B(K^{+}âπ^{-}µ^{+}e^{+})<4.2×10^{-11}, B(K^{+}âπ^{+}µ^{-}e^{+})<6.6×10^{-11} and B(π^{0}âµ^{-}e^{+})<3.2×10^{-10}. These results improve by 1 order of magnitude over previous results for these decay modes.
ABSTRACT
The relative abundance of the three decay modes B(0)âD(-)K(+), B(0)âD(-)π(+), and B(s)(0)âD(s)(-)π(+) produced in 7 TeV pp collisions at the LHC is determined from data corresponding to an integrated luminosity of 35 pb(-1). The branching fraction of B(0)âD(-)K(+) is found to be B(B(0)âD(-)K(+)) = (2.01 ± 0.18(stat) ± 0.14(syst)) × 10(-4). The ratio of fragmentation fractions f(s)/f(d) is determined through the relative abundance of B(s)(0)âD(s)(-)π(+) to B(0)âD(-)K(+) and B(0)âD(-)π(+), leading to f(s)/f(d) = 0.253 ± 0.017 ± 0.017 ± 0.020, where the uncertainties are statistical, systematic, and theoretical, respectively.