Search Results (14 total)

The network of resonant bar detectors of gravitational waves resumed coordinated observations within the International Gravitational Event Collaboration (IGEC-2). Four detectors are taking part in this Collaboration: ALLEGRO, AURIGA, EXPLORER and NAUTILUS. We present here the results of the search for gravitational wave bursts over 6 months during 2005, when IGEC-2 was the only gravitational wave observatory in operation. The implemented network data analysis is based on a time coincidence search among AURIGA, EXPLORER and NAUTILUS; ALLEGRO data was reserved for follow-up studies. The network amplitude sensitivity to bursts improved by a factor ≈3 over the 1997-2000 IGEC observations; the wider sensitive band also allowed the analysis to be tuned over a larger class of waveforms. Given the higher single-detector duty factors, the analysis was based on threefold coincidence, to ensure the identification of any single candidate of gravitational waves with high statistical confidence. The false detection rate was as low as 1 per century. No candidates were found.

We explore the rf characteristics of pipe cooled superconducting cavities versus bath cooled ones, using different pipe configurations and different liquid helium temperatures. Pipe cooled cavities can perform nearly as well as bath cooled ones, provided a suitable pipe configuration and cavity wall thickness is chosen. Pure thermal estimates and fits with experimental data show that pipe cooling is a viable solution for future cavities.

The 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<A_CP(B→K^*γ)<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 BB̅ 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/ψ, ψ(2S), and χ_c1, and the light meson in the decay is either a K, K^*, or π⁰.

We present a limit on the branching fraction for the decay B⁰→γγ using data collected at the ϒ(4S) resonance with the BABAR detector at the PEP-II asymmetric energy e⁺e^- collider. Based on the observation of one event in the signal region, out of a sample of 21.3×10⁶ e⁺e^-→ϒ(4S)→BB̅ decays, we establish an upper limit on the branching fraction of B(B⁰→γγ)<1.7×10^-6 at the 90% confidence level. This result substantially improves upon existing limits.

We present a measurement of the decay amplitudes in B→J/ψK^*(892) channels using 20.7 fb ^-1 of data collected at the ϒ(4S) resonance with the BABAR 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_∥  =  2.50±0.20±0.08 radians, favors a departure from the factorization hypothesis. Although the decay B→J/ψKπ proceeds mainly via K^*(892), there is also evidence for K₂^*(1430) and Kπ S-wave contributions.

We present the results of searches for B decays to charmless two-body final states containing η^′ or ω mesons, based on 20.7 fb^-1 of data collected with the BABAR detector. We find the branching fractions B(B⁺→η^′K⁺)  =  (70±8±5)×10^-6, B(B⁰→η^′K⁰)  =  (42_-11⁺¹³±4)×10^-6, and B(B⁺→ωπ⁺)  =  (6.6_-1.8^+2.1±0.7)×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 B(B⁺→η^′π⁺)<12×10^-6, B(B⁺→ωK⁺)<4×10^-6, B(B⁰→ωK⁰)<13×10^-6, and B(B⁰→ωπ⁰)<3×10^-6.

The B⁰ and B⁺ meson lifetimes have been measured in e⁺e^- annihilation data collected in 1999 and 2000 with the BABAR detector at center-of-mass energies near the ϒ(4S) resonance. Events are selected in which one B meson is fully reconstructed in a hadronic final state while the second B meson is reconstructed inclusively. A combined fit to the B⁰ and the B⁺ decay time difference distributions yields τ_B⁰  =  1.546±0.032(stat)±0.022(syst)  ps, τ_B⁺  =  1.673±0.032(stat)±0.023(syst)  ps, and τ_B⁺/τ_B⁰  =  1.082±0.026(stat)±0.012(syst).

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

We present measurements, based on a sample of approximately 23×10⁶ BB̅ pairs, of the branching fractions and a search for CP-violating charge asymmetries in charmless hadronic decays of B mesons into two-body final states of kaons and pions. We find the branching fractions B(B⁰→π⁺π^-)  =  (4.1±1.0±0.7)×10^-6, B(B⁰→K⁺π^-)  =  (16.7±1.6±1.3)×10^-6, B(B⁺→K⁺π⁰)  =  (10.8_-1.9^+2.1±1.0)×10^-6, B(B⁺→K⁰π⁺)  =  (18.2_-3.0^+3.3±2.0)×10^-6, B(B⁰→K⁰π⁰)  =  (8.2_-2.7^+3.1±1.2)×10^-6. We also report 90% confidence level upper limits for B meson decays to the π⁺π⁰, K⁺K^-, and K̅ ⁰K⁺ final states. In addition, charge asymmetries have been found to be consistent with zero, where the statistical precision is in the range of ±0.10 to ±0.18, depending on the decay mode.

We have observed the decays B→φK and φK^* 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⁺→φK⁺)  =  (7.7_-1.4^+1.6±0.8)×10^-6, B(B⁰→φK⁰)  =  (8.1_-2.5^+3.1±0.8)×10^-6, B(B⁺→φK^*+)  =  (9.7_-3.4^+4.2±1.7)×10^-6, and B(B⁰→φK^*0)  =  (8.7_-2.1^+2.5±1.1)×10^-6. We also report the upper limit B(B⁺→φπ⁺)<1.4×10^-6 ( 90% C.L.).

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 ϒ(4S) decays collected in 2001, bringing the data available to 32×10⁶ BB̅ 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 sin2β, is derived from the decay time distributions in such events. The result sin2β  =  0.59±0.14(stat)±0.05(syst) establishes CP violation in the B⁰ meson system. We also determine |λ|  =  0.93±0.09(stat)±0.03(syst), consistent with no direct CP violation.

This paper describes a study of pinning forces in Ag/Bi-based wires and small coils. The goal of this analysis is to characterize and to compare the main pinning mechanisms in wires (short samples) and prototype practical devices, e.g., coils (long samples). The effects of thermal activation were found to hinder the straightforward determination of the pinning parameters from the critical current data. However, we succeeded in extracting these parameters from the irreversibility line. The scaling law for the pinning force employing the irreversibility field in virtue of the scale for magnetic fields was derived theoretically. The best fit to the experimentally determined pinning forces gave the flux-creep model corresponding to the power-law current—voltage dependence J∝Eⁿ. © 1996 The American Physical Society.

Measurements of fundamental and higher harmonics of ac susceptibility of polycrystalline low-T_c and high-T_c superconductors show a failure of the critical-state model in describing the higher harmonics dependence on temperature at fixed dc and ac magnetic fields. The results of measurements at different frequencies suggest that an effect of the fluxon dynamics could take place. Indeed simple considerations lead to the conclusion that thermally activated flux flow, flux creep, and flux flow (FF) should have an important role in determining the higher harmonics of ac susceptibility. A simplified critical-state model, only including pinning and FF, seems to explain part of the experimental results.