arXiv subjects
Publications and source records attributed to Spasimir Balev.
The experiment NA62 at CERN collected a large sample of K+- leptonic decays in order to perform precise test of lepton universality, by measuring the helicity suppressed ratio R_K=Gamma(K+- --> e+- nu)/Gamma(K+- --> mu+- nu). The preliminary result of the analysis based on 51089 K+ --> e+nu candidates is R_K=(2.500+-0.016)x10^{-5}, consistent with the predictions of the Standard Model.
Recent results from the experiments NA48, NA48/1 and NA48/2 are presented, including: direct CP-violation and Dalitz plot slopes measurements for K+- --> 3 pi decays; pi pi scattering effects in K+- --> pi+- pi0 pi0 and Ke4 decays, as well as Ke4 form factors and branching fraction; measurements on radiative charged kaons and hyperon decays, semileptonic decays of neutral and charged kaons; KL --> pi+ pi- branching ratio and |eta+-| measurement; lepton universality check with Kl2 decays.
A high precision search for direct CP-violation in K+- --> 3 pi decays was performed by the NA48/2 experiment at CERN SPS. The asymmetry in the Dalitz plot linear slopes A_g = (g^+ - g^-)/(g^+ + g^-) is measured to be A^c_g = (-1.3 +- 2.3)x10^-4 by studying ~3.1x10^9 K+- --> pi+- pi+ pi- decays and A^n_g = (2.1 +- 1.9)x10^-4 by studying ~91x10^6 K+- --> pi+- pi0 pi0 decays. The unique double- beam system, the design of the detectors and the method of analysis provide good control of the instrumental charge asymmetries and allow to keep the precision of the result limited by statistics, reaching accuracy one order of magnitude better than in previous experiments.