Abstract
In 2003 and 2004, the NA48/2 experiment collected an unprecedented statistics of charged kaon decays to measure the CP violation in three pions. An additional extensive physics program has been carried out. In particular, it was possible to verify the predictions of low energy QCD in several processes, with high precision. In this paper we present the precise measurement of the charged kaon semileptonic form factors (FF) and the first observation of the K+ → π+π0e+e− decay. The semileptonic FF are measured on the sample collected in 2004 in a dedicated minimum bias run, to overcome the limitation imposed by the 3 pions triggers, while the first observation of the K+ → π+π0e+e− decay is based on the full sample of data collected in two years.
Highlights
In 2003 and 2004, the NA48/2 experiment collected an unprecedented statistics of charged kaon decays to measure the CP violation in three pions
In this paper we present the precise measurement of the charged kaon semileptonic form factors (FF) and the first observation of the K+ ! ⇡+⇡0e+e decay
The semileptonic FF are measured on the sample collected in 2004 in a dedicated minimum bias run, to overcome the limitation imposed by the 3 pions triggers, while the first observation of the K+ ! ⇡+⇡0e+e decay is based on the full sample of data collected in two years
Summary
The decay width of both Ke3 described in the Dalitz plot as (K± ! e±⇡0⌫) and Kμ3 a function of the lepton (K± ! μ±⇡0⌫), and pion energies. Where N is a normalization factor and dimensionless f±(t) are the so called vector form factors, described as a function of the squared four-momentum transferred to the lepton system, t = (P P )2 = (m2 + m2 2m E ). A cut for the track momentum p > 5 GeV is used in the electron selection while p > 10 GeV for the muons ensure a proper e ciency in the MUV detector. The PID is done by requiring and E/p > 0.9 (where E is the energy deposited in the LKr and p is the momentum measured by the spectrometer) for the electrons and no signal in time in the MUV. The muons are identified asking for an associated hit in time in the MUV and E/p < 0.9 For both channels, the background contribution has been evaluated by Monte Carlo. The 2/ndf for the fits are: 1004.6/1073 for quadratic, 1001.1/1074 for Pole and 998.3/1074 for dispersive fits
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