Eur. Phys. J. C (2008) 55: 539-546
https://doi.org/10.1140/epjc/s10052-008-0634-2

Regular Article - Experimental Physics

A study of the radiative K_L→π^±e^∓νγ decay and search for direct photon emission with the KLOE detector

¹ Laboratori Nazionali di Frascati dell’INFN, Via E. Fermi, 40 – 00044, Frascati (Roma), Italy
² Institut für Experimentelle Kernphysik, Universität Karlsruhe, Karlsruhe, Germany
³ Dipartimento di Fisica, Università Lecce, Lecce, Italy
⁴ INFN Sezione di Lecce, Lecce, Italy
⁵ Dipartimento di Scienze Fisiche, Università “Federico II”, Napoli, Italy
⁶ INFN Sezione di Napoli, Napoli, Italy
⁷ Dipartimento di Energetica, Università “La Sapienza”, Roma, Italy
⁸ Dipartimento di Fisica, Università “La Sapienza”, Roma, Italy
⁹ INFN Sezione di Roma, Roma, Italy
¹⁰ Dipartimento di Fisica, Università “Tor Vergata”, Roma, Italy
¹¹ INFN Sezione di Roma Tor Vergata, Roma, Italy
¹² Dipartimento di Fisica, Università “Roma Tre”, Roma, Italy
¹³ INFN Sezione di Roma Tre, Roma, Italy
¹⁴ Physics Department, State University of New York, Stony Brook, USA
¹⁵ Institute of High Energy Physics, Academica Sinica, Beijing, China
¹⁶ Institute for Theoretical and Experimental Physics, Moscow, Russia

^* e-mail: Marco.Dreucci@lnf.infn.it

Received: 9 April 2008
Revised: 7 May 2008
Published online: 29 May 2008

Abstract

We present a measurement of the ratio R=Γ(K⁰ _e3γ;E^* _γ > 30 MeV, θ^* _γ>20^°)/Γ(K⁰ _e3) and a first measurement of the direct emission contribution in semileptonic K_L decays. The measurement was performed at the DA NE φ factory by selecting φ→K_LK_S decays with the KLOE detector. We use 328 pb^-1 of data, corresponding to about 3.5 million K⁰ _e3 events and about 9000 K⁰ _e3γ radiative events. Our result is R=(924±23_stat±16_syst)×10^-5 for the branching ratio and 〈X〉=-2.3±1.3_stat±1.4_syst for the effective strength parameter describing direct emission.