421 research outputs found
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Polarized electron beams at SLAC
No full textSLAC has successfully accelerated high energy polarized electrons for the Stanford Linear Collider and fixed polarized nuclear target experiments. The polarized electron beams at SLAC use a gallium arsenide (GaAlAs for E-142) photon emission source to provide the beam of polarized electrons with polarization of approximately 28% (41% for E-142). While the beam emittance is reduced in the damping ring for SLC operation a system of bend magnets and superconducting solenoids preserve and orient the spin direction for maximum longitudinal polarization at the collision point. The electron polarization is monitored with a Compton scattering polarimeter, and was typically 22% at the e[plus]e[minus] collision point for the 1992 run. Improvements are discussed to increase the source polarization and to reduce the depolarization effects between the source and the collision point
Production of pi+, K+, K0, K*0, phi, p and Lambda0 in hadronic Z0 decays
No full textWe have measured the differential production cross sections as a function of scaled momentum xp=2p/Ec.m. of the identified hadron species π+, K+, K0, K*0, φ, p, Λ0, and of the corresponding antihadron species in inclusive hadronic Z0 decays, as well as separately for Z0 decays into light (u, d, s), c and b flavors. Clear flavor dependences are observed, consistent with expectations based upon previously measured production and decay properties of heavy hadrons. These results were used to test the QCD predictions of Gribov and Lipatov, the predictions of QCD in the modified leading logarithm approximation with the ansatz of local parton-hadron duality, and the predictions of three fragmentation models. The ratios of production of different hadron species were also measured as a function of xp and were used to study the suppression of strange meson, strange and non-strange baryon, and vector meson production in the jet fragmentation process. The light-flavor results provide improved tests of the above predictions, as they remove the contribution of heavy hadron production and decay from that of the rest of the fragmentation process. In addition we have compared hadron and antihadron production as a function of xp in light quark (as opposed to antiquark) jets. Differences are observed at high xp, providing direct evidence that higher-momentum hadrons are more likely to contain a primary quark or antiquark. The differences for pseudoscalar and vector kaons provide new measurements of strangeness suppression for high-xp fragmentation products. ©1999 The American Physical Society
Measurements of branching fractions and CP violating asymmetries in B0 ---> pi+ pi-, K+ pi-, K+ K- decays
No full textWe present measurements of branching fractions and CP-violating asymmetries for two-body neutral (B) over bar meson decays to charged pions and kaons based on a sample of about 88x10(6) Y(4S)-->B (B) over bar decays. From a time-independent fit we measure the charge-averaged branching fractions B(B-0-->pi(+)pi(-))=(4.7+/-0.6+/-0.2)x10(-6), B(B-0-->K(+)pi(-))=(17.9+/-0.9+/-0.7)x10(-6), and the direct CP-violating charge asymmetry A(Kpi)=-0.102+/-0.050+/-0.016 [-0.188,-0.016], where the ranges in square brackets indicate the 90% confidence intervals. From a time-dependent fit we measure the B-0-->pi(+)pi(-) CP-violating parameters S-pipi=0.02+/-0.34+/-0.05 [-0.54,+0.58] and C-pipi=-0.30+/-0.25+/-0.04 [-0.72,+0.12]
Study of B-0 -> J/psi K-(*)0 pi(+)pi(-) decays with the Collider detector at Fermilab
No full textWe report a study of the decays B-0 --> J/psiK((*)0) pi(+) pi(-), which involve the creation of a u(u) over bar or d(d) over bar quark pair in addition to a (b) over bar --> (c) over bar(c(s) over bar) decay. The data sample consists of 110 pb(-1) of p(p) over bar collisions at roots = 1.8 TeV collected by the CDF detector at the Fermilab Tevatron collider during 1992-1995. We measure the branching fractions to be B(B-0 --> J/psiK(*0) pi(+) pi(-)) = (6.6 +/- 1.9 +/- 1.1) X 10(-4) and B(B-0 --> J/psiK(0) pi(+) pi(-)) = (10.3 +/- 3.3 +/- 1.5) X 10(-4). Evidence is seen for contributions from psi(2S)K-(*)0, J/psiK(0) rho(0), J/psiK(*+) pi(-), and J/psiK(1)(1270)
Limits on D0 - anti-D0 mixing and CP violation from the ratio of lifetimes for decay to K- pi+, K- K+ and pi- pi+
No full textWe present a measurement of D-0-(D) over bar (0) mixing parameters using the ratios of lifetimes extracted from samples of D-0 mesons decaying to K(-)pi(+), K-K+, and pi(-)pi(+). Using 91 fb(-1) of data collected by the BABAR detector at the PEP-II asymmetric-energy B Factory, we obtain a value Y=[0.8+/-0.4(stat.)(-0.4)(+0.5)(syst.)]%, which, in the limit of CP conservation, corresponds to the mixing parameter y=DeltaGamma/2Gamma. Using the difference in lifetimes of D-0 and (D) over bar (0) mesons, we obtain the CP-violation parameter DeltaY=[-0.8+/-0.6(stat.)+/-0.2(syst.)]%
Measurement of B ---> K* gamma branching fractions and charge asymmetries
No full textThis is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2002 APSThe branching fractions of the exclusive decays B0→K*0γ and B+→K*+γ are measured from a sample of (22.74±0.36)×106 BB̅ decays collected with the BABAR detector at the PEP-II asymmetric e+e- collider. We find B(B0→K*0γ) = [4.23±0.40(stat)±0.22(syst)]×10-5, B(B+→K*+γ) = [3.83±0.62(stat)±0.22(syst)]×10-5 and constrain the CP-violating charge asymmetry to be -0.170<ACP(B→K*γ)<0.082 at 90% C.L.This work was supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the Swiss NSF, A. P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation
THE rho- INTERFERENCE PARAMETERS IN DIFFRACTIVE PHOTOPRODUCTION OF VECTOR MESONS ON HYDROGEN.
No full textMeasurement of the decays and
No full textWe have observed the decays B-->phi K and phi K^* in a sample of over 45 million B mesons collected with the BABAR detector at the PEP-II collider. The measured branching fractions are BF(B^+ --> phi K^+) = (7.7^{+1.6}_{-1.4}+/- 0.8) x 10^{-6}, BF(B^0 --> phi K^0) = (8.1^{+3.1}_{-2.5}+/- 0.8) x 10^{-6}, BF(B^+ --> phi K^{*+}) = (9.7^{+4.2}_{-3.4}+/- 1.7) x 10^{-6} and BF(B^0 --> phi K^{*0}) = (8.6^{+2.8}_{-2.4}+/- 1.1) x 10^{-6}. We also report the upper limit BF(B^+ --> phi pi^+) 1.4 x 10^{-6}$ (90% CL)
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