Speaker
Roberto Versaci
(INFN)
Description
The KLOE experiment has concluded its data taking in March 2006, having
acquired an integrated luminosity of 2.5 fb-1 of e+e- collisions at the
center of mass energy around the phi(1020) resonance. The complete data
set includes a sample of 100 million eta's produced through the radiative
decay phi --> eta gamma and tagged by means of the monochromatic recoil
photon.
This huge amount of data allows to perform the first test of CP violation
in eta decays through the study of the rare eta --> pi+ pi- e+ e- channel,
measuring the asymmetry between the pi+pi- and the e+e- decay planes in
the eta rest frame (Aphi). Being this process flavor conserving, such an
observation will point to unexpected mechanism of CP violation, thus
providing an hint of new physics beyond the Standard Model.
A study of the eta --> pi+ pi- e+ e- decay based on a data sample of
1.7 fb-1 will be presented. Electrons and pions are identified using
both the time of flight to the calorimeter and the momentum of each track.
Cuts on track momenta and on photon conversion on the beam pipe allow
to significantly reduce the background, with a final 20% contamination.
The analysis efficiency for the signal is ~8%, dominated by geometrical
acceptance.
The final sample of about 1600 signal events, 100 times larger than today
best measurement, is used to measure both the eta --> pi+ pi- e+ e-
branching fraction and the asymmetry Aphi.
Author
Roberto Versaci
(INFN)