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Revision as of 15:07, 6 January 2009
Excited QCD
Tests of Chiral Perturbation Theory with Ke4 decays at NA48
The NA48/2 experiment at the CERN SPS has accumulated more than one million K+- --> Pi+ Pi- e+- nu (Ke4) rare decays. Such decays are a unique laboratory to study Pi Pi scattering close to threshold. The S-wave scattering lengths a0 and a2 in the isospin states I=0 and I=2 are measured with an unprecedented experimental precision of few percents, allowing accurate tests of Chiral Perturbation Theory predictions of similar precision. Using recent theoretical refinements related to isospin symmetry breaking mass effects, the extracted values confirm the most elaborated theoretical predictions:
a0 = 0.220 +- 0.005 and a2 = -0.0444 +- 0.0010.
The hadronic form factors of the decay and their energy variation are measured with an improved precision of 5-10 percents which will allow precise comparison with different model predictions.
Precision measurement of photon emission in K+- -> pi+- pi0 gamma decays
We report our final result on the measurement of direct photon emisson (DE) in the decay K+- -> pi+- pi0 gamma and its interference (INT) with the inner bremsstrahlung amplitude. For this measurement the full NA48/2 data set with about 600k reconstructed K+- -> pi+- pi0 gamma decays was analyzed, which is factor of 30 larger than for previous experiments and a factor of three w.r.t. our preliminary result.
From this, the sizes of both the DE and the INT amplitudes have been
measured with high precision, with the INT amplitude being observed for the first time. In addition, the CP violating asymmetry between K+ and K- has been obtained to be less than 10?3 in this channel.
