10071375
Measurement of the direct photon spectrum in upsilon (1s) decays
Using data taken with the CLEO II detector at the Cornell Electron Storage Ring, the authors have determined the ratio of branching fractions: R{sub {gamma}} {triple_bond} {Gamma}({Upsilon}(1S) {yields} {gamma}gg)/{Gamma}({Upsilon}(1S) {yields} ggg) = (2.75 {+-} 0.04(stat.) {+-} 0.15(syst.))%. From this ratio, the authors have determined the QCD scale parameter {Lambda}{sub {ovr MS}} (defined in the modified minimal subtraction scheme) to be {Lambda}{sub {ovr MS}} = 233 {+-} 11 {+-} 59 MeV, from which they determine a value for the strong coupling constant {alpha}{sub s}(M{sub {Upsilon}(1S)}) = 0.163 {+-} 0.002 {+-} 0.014, or {alpha}{sub s}(M{sub Z}) = 0.110 {+-} 0.001 {+-} 0.007.
34604877
Measurement of Cabibbo-suppressed decays of the tau lepton.
Branching ratios for the dominant Cabibbo-suppressed decays of the [tau] lepton have been measured by CLEO II in [ital e][sup +][ital e][sup [minus]] annihilation at the Cornell Electron Storage Ring ([radical][ital s] [similar to]10.6 GeV) using kaons with momenta below 0.7 GeV/[ital c]. The inclusive branching ratio into one charged kaon is (1.60[plus minus]0.12[plus minus]0.19)%. For the exclusive decays, [ital B]([tau][sup [minus]][r arrow][ital K][sup [minus]][nu][sub [tau]])=(0.66[plus minus]0.07[plus minus]0.09)%, [ital B]([tau][sup [minus]][r arrow][ital K][sup [minus]][pi][sup 0][nu][sub [tau]])=(0.51 [plus minus]0.10[plus minus]0.07)%, and, based on three events, [ital B]([tau][sup [minus]][r arrow][ital K][sup [minus]]2[pi][sup 0][nu][sub [tau]])[lt]0.3% at the 90% confidence level. These represent significant improvements over previous results. [ital B]([tau][sup [minus]][r arrow][ital K][sup [minus]][pi][sup 0][nu][sub [tau]]) is measured for the first time with exclusive [pi][sup 0] reconstruction.
117035924
Measurement of B (tau- ---> tau-neutrino K- K0) and b (tau- ---> tau-neutrino K- K0 pi0)
12584275
Study of charmless hadronic B meson decays to pseudoscalar-vector final states.
We report results of searches for charmless hadronic B meson decays to pseudoscalar( pi(+/-), K+/-, pi(0), or K(0)(S))-vector( rho, K(*), or omega) final states. By using 9.7x10(6) BB pairs collected with the CLEO detector, we report the first observation of B(-)--->pi(-)rho(0), B(0)-->pi(+/-)rho(-/+), and B(-)-->pi(-)omega, which are expected to be dominated by hadronic b-->u transitions. The measured branching fractions are (10.4(+3.3)(-3.4)+/-2.1)x10(-6), (27.6(+8.4)(-7.4)+/-4.2)x10(-6), and (11.3(+3.3)(-2.9)+/-1. 4)x10(-6), respectively. Branching fraction upper limits are set for all of the other decay modes investigated.
181671081
Search for B ---> K lepton+ lepton- and B ---> K* lepton+ lepton- decays
16089528
Observation of radiative leptonic decay of the tau lepton
Using 4.68 fb(-1) of e(+)e(-) annihilation data collected with the CLEO II detector at the Cornell Electron Storage Ring, we have studied tau radiative decays tau(-)-->nu(tau)&mgr;(-)nu;(&mgr;)gamma and tau(-)-->nu(tau)e(-)nu;(e)gamma. For a 10 MeV minimum photon energy in the tau rest frame, the branching fraction for radiative tau decay to a muon or electron is measured to be (3.61+/-0.16+/-0. 35)x10(-3) or (1.75+/-0.06+/-0.17)x10(-2), respectively. The branching fractions are in agreement with standard model theoretical predictions.
207872897
Radio imaging of the very-high-energy gamma-ray emission region in the central engine of a radio galaxy.
The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 10(12) electron volts and are bright sources of very-high-energy (VHE) gamma-ray emission, it is not yet known where the VHE emission originates. Here we report on radio and VHE observations of the radio galaxy Messier 87, revealing a period of extremely strong VHE gamma-ray flares accompanied by a strong increase of the radio flux from its nucleus. These results imply that charged particles are accelerated to very high energies in the immediate vicinity of the black hole.
119201394
THE DISCOVERY OF gamma-RAY EMISSION FROM THE BLAZAR RGB J0710+591
The high-frequency-peaked BL Lacertae object RGB J0710+591 was observed in the very high-energy (VHE; E > 100 GeV) wave band by the VERITAS array of atmospheric Cherenkov telescopes. The observations, taken between 2008 December and 2009 March and totaling 22.1 hr, yield the discovery of VHE gamma rays from the source. RGB J0710+591 is detected at a statistical significance of 5.5 standard deviations (5.5{sigma}) above the background, corresponding to an integral flux of (3.9 {+-} 0.8) x 10{sup -12} cm{sup -2} s{sup -1} (3% of the Crab Nebula's flux) above 300 GeV. The observed spectrum can be fit by a power law from 0.31 to 4.6 TeV with a photon spectral index of 2.69 {+-} 0.26{sub stat} {+-} 0.20{sub sys}. These data are complemented by contemporaneous multiwavelength data from the Fermi Large Area Telescope, the Swift X-ray Telescope, the Swift Ultra-Violet and Optical Telescope, and the Michigan-Dartmouth-MIT observatory. Modeling the broadband spectral energy distribution (SED) with an equilibrium synchrotron self-Compton model yields a good statistical fit to the data. The addition of an external-Compton component to the model does not improve the fit nor brings the system closer to equipartition. The combined Fermi and VERITAS data constrain the properties ofmore » the high-energy emission component of the source over 4 orders of magnitude and give measurements of the rising and falling sections of the SED.« less
18988438
VERITAS Discovery of >200 GeV Gamma-Ray Emission from the Intermediate-Frequency-Peaked BL Lacertae Object W Comae
We report the detection of very high-energy -ray emission from the intermediate-frequencypeaked BLLacertae object WComae (z = 0.102) by VERITAS, an array of four imaging atmospheric-Cherenkov telescopes. The source was observed between January and April 2008. A strong outburst of -ray emission was measured in the middle of March, lasting for only four days. The energy spectrum measured during the two highest flare nights is fit by a power-law and is found to be very steep, with a differential photon spectral index of = 3 .81±0.35stat±0.34syst. The integral photon flux above 200GeV during those two nights corresponds to roughly 9% of the flux from the Crab Nebula. Quasi-simultaneous Swift observations at X-ray energies were triggered by the VERITAS observations. The spectral energy distribution of the flare data can be described by synchrotron-self-Compton (SSC) or external-Compton (EC) leptonic jet models, with the latter offering a more natural set of parameters to fit the data.
120622268
Status report from VERITAS
VERITAS is a ground-based gamma-ray observatory covering energies between 100 GeV and 50 TeV and will start operating by January 2007. We give a brief report of the construction status and performance characteristics of the telescopes.
118396807
Study of exclusive charmless semileptonic decays of the B meson