New and recent results from NA48/2

Recent results from the NA48/2 experiment are presented. The most precise measurement of the charged kaon semileptonic form factors has been obtained from 4.28 million K ± e3 and 2.91 million K ± µ3 events collected in 2004. A sample of 1663 events of the very rare decay K ± → µ ± νe + e − has been collected in the region Mee > 140 MeV/c 2 with negligible background. The measured model independent decay rate is in agreement with ChPT predictions. The branching ratio of the K ± → π ± π 0 e + e − decay, never observed so far, has been obtained from a sample of 5000 candidates, in agreement with ChPT predictions. 1 The NA48/2 beam and detector The NA48/2 detector and beam have been described in details earlier 1,2. Two simultaneous K + and K − beams were produced by 400 GeV/c protons impinging on a beryllium target. Particles of opposite charge with a central momentum of 60 GeV/c and a momentum band of ±3.8% (rms) were selected by a system of magnets and collimators. Both beams of ≈ 1 cm width had similar paths within the decay volume contained in a 114 m long vacuum tank. Charged decay products were measured by a magnetic spectrometer consisting of four drift chambers (DCH) and a dipole magnet located between the second and third chamber. The spatial resolution of each chamber was ∼90 µm, and the momentum resolution was σ p /p = (1.02 ⊕ 0.044 · p)% (momentum p in Gev/c). The spectrometer was followed by a scintillator hodoscope (HOD) with a time resolution of ∼150 ps, whose signals were used to trigger the readout of events with at least one charged track A Liquid Krypton calorimeter (LKr), located behind the hodoscope, was used to measure the position and energy of electrons and photons. It is an approximately homogeneous ionization chamber with an active volume of 7 m 3 of liquid krypton, 27 X 0 deep, segmented transversally into projective cells, 2 × 2 cm 2 each. The transverse position of isolated showers was measured a for the NA48/2 Collaboration: