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The NA48/2 experiment at the CERN SPS has collected a large sample of K to pi pi0 gamma decays.Two amplitudes contribute to these decays. The dominant one comes from Inner Bremsstrahlung (IB) in the K to pi pi0 process. The second one is given by the Direct Emission (DE) of the photon at the weak vertex from an intermediate state of the decay. The simplest radiative transitions are electric dipole (E1) and magnetic dipole (M1). Electric amplitudes can interfere with IB, and CP violation and possible non-SM effects can show up in th e corresponding interference (INT) term.In this work a sub sample of the data has been analyzed. About 120000 K to pi pi0 gamma decays, with negligible background contamination have been reconstructed in the ranges 0.2
A search for the KS → pi 0mu+mu- decay was performed by the NA48/1 Collaboration at the CERN SPS accelerator. Six events were found with a background expectation of 0.22+0.18-0.11 in the data collected in 2002 from the high-intensity K S run. The measured branching ratio is: BR( KS → pi0mu+mu -) = [ 2.9+1.5-1.2 (stat) +/- 0.2(syst)] x 10-9, assuming that only vector currents contribute to the matrix element, and a unit form factor.
The authors study on the rare decay K{sub L} 2![pi]°[gamma][gamma], measure a{sub V}, and branching ratio by analyzing 96, 97 and 99 data. The measurements were taken by KTeV at Fermi National Accelerator Laboratory. After all cuts, they have 1982 K{sub L} 2![pi]°[gamma][gamma] candidate. The background level is estimated as 30%. K{sub L} 2![pi]°[gamma][gamma] branching ratio is measured as (1.29 ± 0.03(stat) ± 0.04(sys)) x 10−6. By using D'Ambrosio's theory to fit a{sub V}, a{sub V} = -( -0.31 ± 0.05(stat) ± 0.07(sys)).
The KTeV E799 experiment has conducted a search for the rare decay K{sub L} 2![pi]°°[gamma] via the topology K{sub L} 2![pi]°[pi]°{sub D}[gamma] (where [pi]°{sub D} 2![gamma]ee−). Due to Bose statistics of the [pi]° pair and the real nature of the photon, the K{sub L} 2![pi]°[pi]°[gamma] decay is restricted to proceed at lowest order by the CP conserving direct emission (DE) of an E2 electric quadrupole photon. The rate of this decay is interesting theoretically since chiral perturbation theory predicts that this process vanishes at level O(p4). Therefore, this mode probes chiral perturbation theory at O(p6). In this paper we report a determination of an upper limit of 2.43 x 10−7 (90% CL) for K{sub L} 2![pi]°[pi]°[gamma]. This is approximately a factor of 20 lower than previous results.
The authors report on a new measurement of the branching ratio B(K{sub L} → [pi]°[gamma][gamma]) using the KTeV detector. They reconstruct 1982 events with an estimated background of 608, that results in B(K{sub L} → [pi]°[Gamma][gamma]) = (1.29 ± 0.03{sub stat} ± 0.05{sub syst}) x 10−6. They also measure the parameter, a{sub V}, which characterizes the strength of vector meson exchange terms in this decay. They find a{sub V} = -0.31 ± 0.05{sub stat} ± 0.07{sub syst}. These results utilize the full KTeV data set collected from 1997 to 2000 and supersede earlier KTeV measurements of the branching ratio and a{sub V}.
The authors present a measurement of B([pi]0 2!e+e-[gamma])/B([pi]0 2![gamma][gamma]) using data taken in 1999 by the E832 KTeV experiment at Fermilab. The [pi]0s were produced by KL decays in flight that are fully reconstructed. They find 63,693 KL 2!3[pi]0 2![gamma][gamma] [gamma][gamma] e+e-[gamma] decays in KTeV data (an increase of a factor of ~ 20 in event statistics over previous experiments), and normalize to KL 2!3[pi]0 2!6[gamma], to extract B([pi]0 2!e+e-[gamma], me+e-> 15 MeV/c2