Searching for eta to 3 gamma decay

Abstract

Data collected by the KLOE experiment in years 2001/2002 for a total integrated luminosity of 410 pb${}^{-1}$, corresponding to 17 million of produced $\eta$'s from the $\Phi \to \eta \gamma$ radiative decay, have been analyzed to look for the C-violating decay $\eta \to \gamma \gamma \gamma$. The signal is searched in events with 4 photons in the final state by using the spectrum of the most energetic photon. The background is evaluated from the data themself, doing a fifth degree polynomial fit outside the signal region, and extrapolating inside it. No signal has been observed and taking into account a selection efficiency $\epsilon =20.3$ we get from a likelihood fit Br$(\eta \to \gamma \gamma \gamma )\le 1.6\times 10^{-5}$ at 95% CL. The procedure has a systematic ambiguity at the 35 % level.

Contributed paper to EPS 2003 and LP 2003