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Investigation of K_L, K_S --> pi+ pi- e+ e- decays

By LAI A, MARRAS D, BEVAN A, DOSANJH RS, GERSHON TJ, HAY B, KALMUS GE, LAZZERONI C, MUNDAY DJ, NEEDHAM MD, OLAIYA E, PARKER MA, WHITE TO, WOTTON SA, BARR G, BOCQUET G, CECCUCCI A, CUNDY D, DOBLE N, FALALEEV V, GATIGNON L, GONIDEC A, GORINI B, GOVI G, GRAFSTROM P, KUBISCHTA W, LENTI M, LUITZ S, MIKULEC I, NORTON A, PALESTINI S, PANZER-STEINDEL B, TAUREG H, VELASCO M, WAHL H, CHESHKOV C, GAPONENKO A, HRISTOV P, KEKELIDZE V, MADIGOJINE D, TATISHVILI G, POTREBENIKOV Y, ZINCHENKO A, KNOWLES I, MARTIN V, SACCO R, WALKER A, CONTALBRIGO M, DALPIAZ P., DUCLOS J, FRABETTI PL, GIANOLI A, MARTINI M, MASETTI L, PETRUCCI F, SAVRIE M, BIZZETI A, CALVETTI M, COLLAZUOL G, GRAZIANI G, IACOPINI E, VELTRI M, BECKER HG, EPPARD M, FOX H, HOLTZ K, KALTER A, KLEINKNECHT K, KOCH U, KOPKE L, DA SILVA PL, MAROUELLI P, PELLMANN I, PETERS A, SCHMIDT SA, SCHONHARTING V, SCHUE Y, WANKE R, WINHART A, WITTGEN M, CHOLLET JC, FAYARD L, ICONOMIDOU-FAYARD L, OCARIZ J, UNAL G, WINGERTER-SEEZ I, ANZIVINO G, CENCI P, IMBERGAMO E, LUBRANO P, MESTVIRISHVILI A, NAPPI A, PEPE M, PICCINI M, CASALI R, CERRI C, CIRILLI M, COSTANTINI F, FANTECHI R, GIUDICI S, MANNELLI I, PIERAZZINI G, SOZZI M, CHEZE JB, COGAN J, DE BEER M, DEBU P, FORMICA A, DE CASSAGNAC RG, MAZZUCATO E, PEYAUD B, TURLAY R, VALLAGE B, HOLDER M, MAIER A, ZIOLKOWSKI M, ARCIDIACONO R, BIINO C, CARTIGLIA N, CLEMENCIC M, MARCHETTO F, MENICHETTI E, NASSALSKI J, RONDIO E, SZLEPER M, WISLICKI W, WRONKA S, FISCHER G, JEITLER M, MARKYTAN M, NEUHOFER G, PERNICKA M, TAUROK A, WIDHALM L and CA NA48 COLLABORATION

Abstract

The K_L --> pi+ pi- e+ e− and K_S --> pi+ pi- e+ e- decay modes have been studied in detail using the NA48 detector at the CERN SPS. Based on the data collected during the 1998 and 1999 run periods, a sample of 1162 K_L --> pi+ pi- e+ e− candidates has been observed with an expected background level of 36.9 events, yielding the branching ratio measurement BR(K_L --> pi+ pi- e+ e−) = (3.08±0.20)×10−7. The distribution of events in the sin(phi) cos(phi) variable, where phi is the angle between the pi+pi- and the e+e−\ud decay planes in the kaon centre of mass, is found to exhibit a large CP-violating asymmetry with the value A_{phi} = (14.2 ± 3.6)%. For the K_S --> pi+ pi- e+ e- decay channel, 621 candidates have been identified in the 1999 data sample with an estimated background contribution of 0.7 event. The corresponding branching ratio has been determined to be BR(K_S --> pi+ pi- e+ e-) = (4.71 ± 0.32) × 10−5. The combined value of this measurement with the published 1998 result is BR(K_S --> pi+ pi- e+ e-) = (4.69 ± 0.30) × 10−5. No asymmetry is observed in this decay mode. Our results are in good agreement with theoretical predictions based on a phenomenological description of radiative kaon decays. The form factor parameters a1/a2 and gM1~ in the K_L --> pi+ pi- e+ e- direct emission process as well as the value of the K0 charge radius have\ud been extracted from the data

Year: 2003
DOI identifier: 10.1140/epjc
OAI identifier: oai:iris.unife.it:11392/1211639
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