First observation and study of the K± → π0π0μ±ν decay

The NA48/2 experiment at CERN reports the first observation of the K± → π0π0μ±ν decay based on a sample of 2437 candidates with 15% background contamination collected in 2003–2004. The decay branching ratio in the kinematic region of the squared dilepton mass above 0.03 GeV2/c4 is measured to be (0.65 ± 0.03) × 10−6. The extrapolation to the full kinematic space, using a specific model, is found to be (3.45 ± 0.16) × 10−6, in agreement with chiral perturbation theory predictions

Search for baryon and lepton number violating decays D+→Λ ̄(Σ ̄0)e+ and D+→Λ(Σ0)e+

Using a 2.93 fb(-1) data sample of electron-positron collisions taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, which corresponds to (8296 +/- 31 +/- 64) x 10(3) D+ D- pairs, we search for the baryon and lepton number violating decays D+ -> (Lambda) over bar((Sigma) over bar (0))e(+) and D+ -> Lambda(Sigma(0))e(+). No obvious signals are found with the current statistics and upper limits on the branching fractions of these four decays are set at the level of 10(-6) at 90% confidence level

Search for the decay Ds+→γe+νe

A search for the rare radiative leptonic decay Dþs → γeþνe is performed for the first time using electron- positron collision data corresponding to an integrated luminosity of 3.19 fb−1, collected with the BESIII detector at a center-of-mass energy of 4.178 GeV. No evidence for the Dþs → γeþνe decay is seen, and an upper limit of BðDþs → γeþνeÞ < 1.3 × 10−4 is set on the partial branching fraction at a 90% confidence level for radiative photon energies E0γ > 0.01 GeV