Investigation of KL,S → π+π -e+e- decays

A. Lai*, D. Marras, A. Bevan, R. S. Dosanjh, T. J. Gershon, B. Hay, G. E. Kalmus, C. Lazzeroni, D. J. Munday, M. D. Needham, E. Olaiya, M. A. Parker, T. O. White, S. A. Wotton, G. Barr, G. Bocquet, A. Ceccucci, D. Cundy, N. Doble, V. FalaleevL. Gatignon, A. Gonidec, B. Gorini, G. Govi, P. Grafström, W. Kubischta, M. Lenti, S. Luitz, I. Mikulec, A. Norton, S. Palestini, B. Panzer-Steindel, H. Taureg, M. Velasco, H. Wahl, C. Cheshkov, A. Gaponenko, P. Hristov, V. Kekelidze, D. Madigojine, G. Tatishvili, Y. Potrebenikov, A. Zinchenko, I. Knowles, V. Martin, R. Sacco, A. Walker, M. Contalbrigo, P. Dalpiaz, J. Duclos, P. L. Frabetti, A. Gianoli, M. Martini, L. Masetti, F. Petrucci, M. Savrié, A. Bizzeti, M. Calvetti, G. Collazuol, G. Graziani, E. Iacopini, M. Veltri, H. G. Becker, M. Eppard, H. Fox, K. Holtz, A. Kalter, K. Kleinknecht, U. Koch, L. Köpke, P. Lopes da Silva, P. Marouelli, I. Pellmann, A. Peters, S. A. Schmidt, V. Schönharting, Y. Schué, R. Wanke, A. Winhart, M. Wittgen, J. C. Chollet, L. Fayard, L. Iconomidou-Fayard, J. Ocariz, G. Unal, I. Wingerter-Seez, G. Anzivino, P. Cenci, E. Imbergamo, P. Lubrano, A. Mestvirishvili, A. Nappi, M. Pepe, M. Piccini, R. Casali, C. Cerri, M. Cirilli, F. Costantini, R. Fantechi, S. Giudici, I. Mannelli, G. Pierazzini, M. Sozzi, J. B. Chéze, J. Cogan, M. de Beer, P. Debu, A. Formica, R. Granier de Cassagnac, E. Mazzucato, B. Peyaud, R. Turlay, B. Vallage, M. Holder, A. Maier, M. Ziolkowski, R. Arcidiacono, C. Biino, N. Cartiglia, M. Clemencic, F. Marchetto, E. Menichetti, J. Nassalski, E. Rondio, M. Szleper, W. Wislicki, S. Wronka, G. Fischer, M. Jeitler, M. Markytan, G. Neuhofer, M. Pernicka, A. Taurok, L. Widhalm

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

36 Scopus citations

Abstract

The KL → π+π-e +e- and KS → π+π -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 KL → π +π-e+e- candidates has been observed with an expected background level of 36.9 events, yielding the branching ratio measurement BR(KL → π+π -e+e-) = (3.08 ± 0.20) × 10 -7. The distribution of events in the sinφ cosφ variable, where φ is the angle between the π+π- and the e+e- decay planes in the kaon centre of mass, is found to exhibit a large CP-violating asymmetry with the value Aφ = (14.2 ± 3.6)%. For the KS → π+π -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 → π+π-e+e-) = (4.71 ± 0.32) × 10-5. The combined value of this measurement with the published 1998 result is BR(KS → π +π-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 g̃M1 in the K L → π+π-e+e- direct emission process as well as the value of the K0 charge radius have been extracted from the data.

Original languageEnglish (US)
Pages (from-to)33-49
Number of pages17
JournalEuropean Physical Journal C
Volume30
Issue number1
DOIs
StatePublished - Sep 2003

ASJC Scopus subject areas

  • Engineering (miscellaneous)
  • Physics and Astronomy (miscellaneous)

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