(Dated: We present a measurement of the decay amplitudes in B → J/ψ K ∗ (892) channels using 20 . 7 fb − 1 of data collected at the Υ (4 S ) resonance with the B A B AR detector at PEP-II. We measure a P -wave fraction R ⊥ = (16 . 0 ± 3 . 2 ± 1 . 4)% and a longitudinal polarization fraction (59 . 7 ± 2 . 8 ± 2 . 4)%. The measurement of a relative phase that is neither 0 nor π , φ k = 2 . 50 ± 0 . 20 ± 0 . 08 radians, favors a departure from the factorization hypothesis. Although the decay B → J/ψ Kπ proceeds mainly via K ∗ (892), there is also evidence for K ∗ 2 (1430) and Kπ S -wave contributions.

We present a new measurement of the KL-K~ mass difference (Am) using semileptonic decays of neutral kaons. The measurement yields Am = (0.5274 * 0.0029,Va1. f O.OOOS,,,,.) x lO”ti/s.

BABAR, the detector for the SLAC PEP-II asymmetric e+e- B Factory operating at the upsilon 4S resonance, was designed to allow comprehensive studies of CP-violation in B-meson decays. Charged particle tracks are measured in a multi-layer silicon vertex tracker surrounded by a cylindrical wire drift chamber. Electromagentic showers from electrons and photons are detected in an array of CsI crystals located just inside the solenoidal coil of a superconducting magnet. Muons and neutral hadrons are identified by arrays of resistive plate chambers inserted into gaps in the steel flux return of the magnet. Charged hadrons are identified by dE/dx measurements in the tracking detectors and in a ring-imaging Cherenkov detector surrounding the drift chamber. The trigger, data acquisition and data-monitoring systems, VME- and network-based, are controlled by custom-designed online software. Details of the layout and performance of the detector components and their associated electronics and software are presented.

R. Adler a, T. Alhalel b A. Angelopoulos c, A. Apostolakis c, E. Aslanides d,b G. Backenstoss a, C.P. Bee d,e, j. Bennet e, J.K. Bienlein f, P. Bloch d, Ch. Bula g, G. Burgun h, p. Carlson i, J. Carvalho J, E. Cawley e, S. Charalambous k, M. Chardalas k, G. Chardin h, H. Cobbaert J, S. Dedoussis k, M. Dejardin h, j. Derre h, M. Dodgson e, J.C. Dousse ~, J. Duclos h, A. Ealet b, B. Eckart a, L. Faravel ~, P. Fassnacht b, J.L. Faure h, C. Felder a, R. Ferreira-Marques J, W. Fetscher f, M. Fidecaro d, A. Filip6i6 m, D. Francis h, J.R. Fry ~, C. Fuglesang i, E. Gabathuler e, R. Garnet d.~, D. Garreta h, T. Geralis b, H.-J. Gerber f, A. Go °, P. Gumplinger f.l, C. Guyot h, P.F. Harrison e,2, p.j. Hayman ~, W.G. Heyes d.3, R.W. Hollander o, K. Jansson i, H.U. Johner ~, K. Jon-And i, A. Kerek i, j. Kern ~, P.-R. Kettle g, C. Kochowski h, p. Kokkas P, R. Kreuger o, T. Lawry n, R. Le Gac q, E. Machado j,d, p. Maley ¢, N. Manthos P, G. Marel d.h, M. Miku~ m, j.p. Miller n, F. Montanet b, T. Nakada g, A. Onofre J, B. Pagels ", P. Pavlopoulos d.4, F. Pelucchi b, j. Pinto da Cunha J, A. Policarpo J, G. Polivka a, H. Postma o, R. Rickenbach a, B.L. Roberts n, E. Rozaki c, T. Ruf f, L. Sacks e, L. Sakeliou c, P. Sanders e, C. Santoni a, K. Sarigiannis c~4, M. Sch~ifer f, L. Schaller ~, A. Schopper d, P. Schune h, U. Seljak m, S. Szilagyi i, L. Tauscher a, C. Thibault q, F. Touchard q, C. Touramanis k, F. Triantis P, D.A. Troester a.5, E. Van Beveren J, M. Van den Putte o, C.W.E. Van Eijk o, G. Varner ", S. Vlachos ~, P. Weber f, C. Witzig f.6, C. Yeche h, D. Zavrtanik m and D. Zimmerman "

The branching fractions of the exclusive decays ${B}^{0}\ensuremath{\rightarrow}{K}^{*0}\ensuremath{\gamma}$ and ${B}^{+}\ensuremath{\rightarrow}{K}^{*+}\ensuremath{\gamma}$ are measured from a sample of $(22.74\ifmmode\pm\else\textpm\fi{}0.36)\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ decays collected with the BABAR detector at the PEP-II asymmetric ${e}^{+}{e}^{\ensuremath{-}}$ collider. We find $B({B}^{0}\ensuremath{\rightarrow}{K}^{*0}\ensuremath{\gamma})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}[4.23\ifmmode\pm\else\textpm\fi{}0.40(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.22(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, $B({B}^{+}\ensuremath{\rightarrow}{K}^{*+}\ensuremath{\gamma})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}[3.83\ifmmode\pm\else\textpm\fi{}0.62(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.22(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and constrain the $\mathrm{CP}$-violating charge asymmetry to be $\ensuremath{-}0.170<{A}_{\mathrm{CP}}(B\ensuremath{\rightarrow}{K}^{*}\ensuremath{\gamma})<0.082$ at $90%$ C.L.

We report branching fraction measurements for exclusive decays of charged and neutral B mesons into two-body final states containing a charmonium meson. We use a sample of 22.72 +/- 0.36 million B anti-B events collected between October 1999 and October 2000 with the BABAR detector at the PEP-II storage rings at the Stanford Linear Accelerator Center. The charmonium mesons considered here are J/psi, psi(2S), and chi_c1, and the light meson in the decay is either a K, K^*, or pi^0.

The production of J/psi mesons in continuum e(+)e(-) annihilations has been studied with the BABAR detector at energies near the Y(4S) resonance. The mesons are distinguished from J/psi production in B decays through their center-of-mass momentum and energy. We measure the cross section e(+)e(-) --> J/psiX to be 2.52 +/- 0.21 +/- 0.21 pb. We set a 90% C.L. upper limit on the branching fraction for direct Y(4S) --> J/psiX decays at 4.7 x 10(-4).

We present a measurement of the decay amplitudes in B-->J/psiK*(892) channels using 20.7 fb(-1) of data collected at the Upsilon(4S) resonance with the BABAR detector at PEP-II. We measure a P-wave fraction R(perpendicular) = (16.0 +/- 3.2 +/- 1.4)% and a longitudinal polarization fraction (59.7 +/- 2.8 +/- 2.4)%. The measurement of a relative phase that is neither 0 nor pi, phi = 2.50 +/- 0.20 +/-0.08 radians, favors a departure from the factorization hypothesis. Although the decay B-->/psiK(pi) proceeds mainly via K*(892), there is also evidence for K2*(1430) and K(pi) S-wave contributions.

B^0-anti-B^0 flavor oscillations have been studied in 20.7 fb-1 of e^+e^- annihilation data collected in 1999 and 2000 with the BABAR detector at center-of-mass energies near the Upsilon(4S) resonance. The event sample consists of one B^0 meson fully reconstructed in a hadronic decay mode, while the flavor of the recoiling B^0 in the event is determined with a tagging algorithm that exploits the correlation between the flavor of the heavy quark and the charges of its decay products. By fitting the time development of the observed mixed and unmixed final states, the B^0-anti-B^0 oscillation frequency, Delta_md, is determined to be 0.519+/- 0.020+/- 0.016 ps^{-1}.

We have observed the decays B --> phiK and phiK* in a sample of over 45 million B mesons collected with the BABAR detector at the PEP-II collider. The measured branching fractions are B(B+--> phiK(+)) = (7.7(-1.4)(+1.6)+/-0.8) x 10(-6), B(B-0--> phiK(0)) = (8.1(-2.5)(+3.1)+/-0.8) x 10(-6), B(B+--> phiK*(+)) = (9.7(-3.4)(+4.2)+/-1.7) x 10(-6), and B(B-0--> phiK*(0)) = (8.7(-2.1)(+2.5)+/-1.1) x 10(-6). We also report the upper limit B(B+--> phi pi (+)) < 1.4 x 10(-6) (90% C.L.).

We present the results of searches for B decays to charmless two-body final states containing eta(') or omega mesons, based on 20.7 fb(-1) of data collected with the BABAR detector. We find the branching fractions Beta(B(+)-->eta(')K(+)) = (70+/-8+/-5) x 10(-6), Beta(B(0)-->eta(')K(0)) = (42(+13)(-11) +/- 4) x 10(-6), and Beta(B(+)-->omega pi(+)) = (6.6(+2.1)(-1.8) +/- 0.7) x 10(-6), where the first error quoted is statistical and the second is systematic. We give measurements of four additional modes for which the 90% confidence level upper limits are Beta(B(+)-->eta(')pi(+)) < 12 x 10(-6), Beta(B(+)-->omega K(+)) < 4 x 10(-6), Beta(B(0)-->omega K(0)) < 13 x 10(-6), and Beta(B(0)-->omega pi(0)) < 3 x 10(-6).

We present an updated measurement of time-dependent CP-violating asymmetries in neutral B decays with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. This result uses an additional sample of Upsilon(4S) decays collected in 2001, bringing the data available to 32 x 10(6) BB macro pairs. We select events in which one neutral B meson is fully reconstructed in a final state containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the standard model is proportional to sin2 beta, is derived from the decay time distributions in such events. The result sin2 beta = 0.59+/-0.14(stat)+/-0.05(syst) establishes CP violation in the B(0) meson system. We also determine absolute value of lambda = 0.93+/-0.09(stat)+/-0.03(syst), consistent with no direct CP violation.