QCD studies with NA48 and NA62

Abstract

The NA48/2 and NA62 experiments at CERN have collected large samples of charged kaons decays in 2003-2004 and in 2007-2008, respectively. In this paper some recent results will be reported. A preliminary measurement by NA48/2 and by NA62 of the K ± → π ± γγ branching ratio is quoted, an analysis by NA62 of K + → e + νγ(SD + ) is shown, a first evidence of the K ± → π ± π 0 e + e − decay by NA48/2 is reported. New measurements of K l3 form factors are presented and finally the branching ratio of K e4 decays is shown. All the results are preliminary.Kaon decays are a privileged system to study low energy QCD interactions, especially in the chiral perturbation theory framework. The model can be tested at the O(p 4 ) and in some cases even at the O(p 6 ) order. The NA48/2 and NA62 experiments at CERN have collected the largest sample of charged kaon decays in the world. In this paper some recent preliminary results will be presented.The CERN kaon facility is located in the North Area extraction line of the SPS accelerator. The NA48/2 experiment took data in 2003/2004 with two simultaneous K ± beams produced by 400 GeV/c protons impinging on a beryllium target; the beamline selected kaons with a (60 ± 3) GeV/c momentum range. The NA62 experiment took data in 2007 and 2008 (R K phase) with a modified beam line which provided K + or K − with momenta of (74.0 ± 1.4) GeV/c. For both the experiments the main detectors, following the beam line, are a magnetic spectrometer (made by four drift chambers with a dipole magnet between the second and the third one) providing a momentum resolution σ p /p = 1.00% ⊕ 0.044% × p [NA48/2] and σ p /p = 0.48% ⊕ 0.009% × p [NA62], with p in GeV/c, a scintillator hodoscope with 150 ps time resolution and a Liquid Krypton Electromagnetic Calorimeter (127 cm thick and made by 13248 readout cells) with energy resolution σ E /E = 3.2%/ √ E ⊕ 9%/E ⊕ 0.42% with E in GeV. A detailed description of the detectors can be found in [1]. For a charged particle the ratio between the energy E in GeV measured by the electromagnetic calorimeter and the momentum p in GeV/c measured by the magnetic spectrometer is used for particle identification: electrons/positrons are selected requiring 0.95 < E/p < 1.05, muons are identified by E/p < 0.1 and the rest are charged pions; tighter cuts are used in some analysis. 1 on behalf of the NA48 and NA62 collaborations

Technological implications for RICH performance

“…The rejection factor to be achieved is 10 À 12 , of which 10 À 5 will come from kinematics and 10 À 5 from the muon veto. To the RICH therefore is requested to reach a rejection factor of 10 À 2 [10]. The experiment will run at the SPS (CERN) with a kaon beam working at 800 MHz.…”