On 16 March, operation of the K Long Experiment (KLOE) detector ended after 23 months of continuous running at the DAFNE collider at Frascati. During this time the detector collected an integrated luminosity of 2.3 fb-1, corresponding to the observation of some 6.2 billion Φ decays. These data are in addition to the 450 pb-1 sample collected in shorter runs in 2000, 2001 and 2002.
DAFNE, the Frascati Φ-factory, has been performing increasingly well, delivering 200 pb-1 a month by the end of 2005. The efforts by the DAFNE and KLOE teams to ensure good data-taking conditions have resulted in their collecting a large homogeneous data sample in terms of machine background, beam energy and detector performance. Smooth trigger and data-acquisition operations, and continuous running of detector calibration ensured high-quality data.
KLOE has many unique aspects, in particular detector performance, the special environment at the Φ factory, the unique possibility of kaon species tagging, an open trigger and complete recording of all data. These allow the physics investigated to include such varied topics as precision measurements of kaon properties, the study of scalar mesons and the measurement of the hadronic cross-section at less than 1 GeV, which is necessary for calculating the muon anomaly. The Φ-meson decays are also a copious source of η and η’ mesons.
With the analysis of 450 pb-1 of data, KLOE has reached accuracies of a fraction of 1% in the measurements of the kaon absolute branching ratios and lifetimes. The results have already removed a problem with the unitarity of the quark-mixing matrix that dates back more than 30 years. The new data set will lead to improvements of all published results, especially in the Ks sector, and to new measurements of the poorly known hadronic cross-section near threshold.
DAFNE will resume operation by the FINUDA collaboration in a few months to investigate hypernuclei. Plans to upgrade the collider to DAFNE2 and the detector to KLOE2 are being studied.
