A Study of Time-dependent Cp -violating Asymmetries in B 0 ! J= K 0 S and B 0 ! (2s)k 0 the Babar Collaboration

We present a preliminary measurement of time-dependent CP -violating asymmetries in B ! J= K S and B ! (2S)K S decays recorded by the BABAR detector at the PEP-II asymmetricenergy B Factory at SLAC. The data sample consists of 9.0 fb 1 collected at the (4S) resonance and 0.8 fb 1 o -resonance. One of the neutral B mesons, produced in pairs at the (4S), is fully reconstructed. The avor of the other neutral B meson is tagged at the time of its decay, mainly with the charge of identi ed leptons and kaons. A neural network tagging algorithm is used to recover events without a clear lepton or kaon tag. The time di erence between the decays is determined by measuring the distance between the decay vertices. Wrong-tag probabilities and the time resolution function are measured with samples of fully-reconstructed semileptonic and hadronic neutral B nal states. The value of the asymmetry amplitude, sin2 , is determined from a maximum likelihood t to the time distribution of 120 tagged B ! J= K S and B ! (2S)K S candidates to be sin2 = 0:12 0:37 (stat) 0:09 (syst) (preliminary) . Submitted to the XXX International Conference on High Energy Physics, Osaka, Japan. The BABAR Collaboration B. Aubert, A. Boucham, D. Boutigny, I. De Bonis, J. Favier, J.-M. Gaillard, F. Galeazzi, A. Jeremie, Y. Karyotakis, J. P. Lees, P. Robbe, V. Tisserand, K. Zachariadou Lab de Phys. des Particules, F-74941 Annecy-le-Vieux, CEDEX, France A. Palano Universit a di Bari, Dipartimento di Fisica and INFN, I-70126 Bari, Italy G. P. Chen, J. C. Chen, N. D. Qi, G. Rong, P. Wang, Y. S. Zhu Institute of High Energy Physics, Beijing 100039, China G. Eigen, P. L. Reinertsen, B. Stugu University of Bergen, Inst. of Physics, N-5007 Bergen, Norway B. Abbott, G. S. Abrams, A. W. Borgland, A. B. Breon, D. N. Brown, J. Button-Shafer, R. N. Cahn, A. R. Clark, Q. Fan, M. S. Gill, S. J. Gowdy, Y. Groysman, R. G. Jacobsen, R. W. Kadel, J. Kadyk, L. T. Kerth, S. Kluth, J. F. Kral, C. Leclerc, M. E. Levi, T. Liu, G. Lynch, A. B. Meyer, M. Momayezi, P. J. Oddone, A. Perazzo, M. Pripstein, N. A. Roe, A. Romosan, M. T. Ronan, V. G. Shelkov, P. Strother, A. V. Telnov, W. A. Wenzel Lawrence Berkeley National Lab, Berkeley, CA 94720, USA P. G. Bright-Thomas, T. J. Champion, C. M. Hawkes, A. Kirk, S. W. O'Neale, A. T. Watson, N. K. Watson University of Birmingham, Birmingham, B15 2TT, UK T. Deppermann, H. Koch, J. Krug, M. Kunze, B. Lewandowski, K. Peters, H. Schmuecker, M. Steinke Ruhr Universitat Bochum, Inst. f. Experimentalphysik 1, D-44780 Bochum, Germany J. C. Andress, N. Chevalier, P. J. Clark, N. Cottingham, N. De Groot, N. Dyce, B. Foster, A. Mass, J. D. McFall, D. Wallom, F. F. Wilson University of Bristol, Bristol BS8 lTL, UK K. Abe, C. Hearty, T. S. Mattison, J. A. McKenna, D. Thiessen University of British Columbia, Vancouver, BC, Canada V6T 1Z1 B. Camanzi, A. K. McKemey, J. Tinslay Brunel University, Uxbridge, Middlesex UB8 3PH, UK V. E. Blinov, A. D. Bukin, D. A. Bukin, A. R. Buzykaev, M. S. Dubrovin, V. B. Golubev, V. N. Ivanchenko, A. A. Korol, E. A. Kravchenko, A. P. Onuchin, A. A. Salnikov, S. I. Serednyakov, Yu. I. Skovpen, A. N. Yushkov Budker Institute of Nuclear Physics, Siberian Branch of Russian Academy of Science, Novosibirsk 630090, Russia A. J. Lankford, M. Mandelkern, D. P. Stoker University of California at Irvine, Irvine, CA 92697, USA A. Ahsan, K. Arisaka, C. Buchanan, S. Chun University of California at Los Angeles, Los Angeles, CA 90024, USA