54921026
Measurement of the light antiquark flavor asymmetry in the nucleon sea
A precise measurement of the ratio of Drell-Yan yields from an 800 GeV/c proton beam incident on hydrogen and deuterium targets is reported. Over 140000 Drell-Yan muon pairs with dimuon mass M{sub {mu}{sup +}{mu}{sup {minus}}}{ge}4.5 GeV/c{sup 2} were recorded. From these data, the ratio of antidown ({bar d} ) to antiup ({bar u} ) quark distributions in the proton sea is determined over a wide range in Bjorken x . A strong x dependence is observed in the ratio {bar d}/{bar u} , showing substantial enhancement of {bar d} with respect to {bar u} for x{lt}0.2 . This result is in fair agreement with recent parton distribution parametrizations of the sea. For x{gt}0.2 , the observed {bar d}/{bar u} ratio is much nearer unity than given by the parametrizations. {copyright} {ital 1998} {ital The American Physical Society}
123472634
Unnatural parity resonances in the positron-excited hydrogen system
We present an investigation of resonances with unnatural parities in positron scattering by excited hydrogen. The momentum space coupled channels optical potential method has been used. Positronium formation channels have been included via a complex equivalent local potential. States with angular momenta L = 1 to L = 2 and parity (−1)L+1 are calculated.
121866403
GENERATION OF ULTRA-SHORT ELECTRON BUNCHES FOR LIGHT SOURCE RESEARCH
An S-band thermionic 1.5-cell rf gun injector system is being built at NSRRC for Taiwan Photon Source (TPS) booster. At optimized field ratio, an electron beam with linear energy chirp can be generated by the rf gun. The beam is then compressed by an alpha magnet such that ultra-short electron bunches at femto-second bunch length can be obtained. Particle dynamics has been studied for an rf gun with nose cone at the cathode, simulation results show that 74 pC bunches at about 97 fs is achievable. Some of the critical components such as the rf gun and alpha magnet have been fabricated and being tested in house. Experiments for intense coherent THz radiations and tunable femto-second X-ray from ultra-short bunches are being proposed as future applications.
119258527
Scale-invariant fluctuations from Galilean genesis
We study the spectrum of cosmological fluctuations in scenarios such as Galilean Genesis \cite{Nicolis} in which a spectator scalar field acquires a scale-invariant spectrum of perturbations during an early phase which asymptotes in the far past to Minkowski space-time. In the case of minimal coupling to gravity and standard scalar field Lagrangian, the induced curvature fluctuations depend quadratically on the spectator field and are hence non-scale-invariant and highly non-Gaussian. We show that if higher dimensional operators (the same operators that lead to the η-problem for inflation) are considered, a linear coupling between background and spectator field fluctuations is induced which leads to scale-invariant and Gaussian curvature fluctuations.
219162055
Wavelet Band Powers of the Primordial Power Spectrum from CMB Data
Measuring the primordial matter power spectrum is our primary means of probing unknown physics in the very early universe. We allow the primordial power spectrum to be an arbitrary function, and parametrize it in terms of wavelet band powers. Current cosmological data correspond to 11 such wavelet bands. We derive constraints on these band powers as well as H0, Ωbh and Ωmh from current Cosmic Microwave Background Anisotropy (CMB) data using the Markov Chain Monte Carlo (MCMC) technique. Our results indicate a feature in the primordial power spectrum at 0.008 <∼ k/(hMpc−1) <∼ 0.1. MAP and Planck data should allow us to put tighter constraints on the primordial power spectrum.
41231566
Quantitative Analysis of CME Deflections in the Corona
In this paper, ten CME events viewed by the STEREO twin spacecraft are analyzed to study the deflections of CMEs during their propagation in the corona. Based on the three-dimensional information of the CMEs derived by the graduated cylindrical shell (GCS) model (Thernisien, Howard, and Vourlidas in Astrophys. J.652, 1305, 2006), it is found that the propagation directions of eight CMEs had changed. By applying the theoretical method proposed by Shen et al. (Solar Phys.269, 389, 2011) to all the CMEs, we found that the deflections are consistent, in strength and direction, with the gradient of the magnetic energy density. There is a positive correlation between the deflection rate and the strength of the magnetic energy density gradient and a weak anti-correlation between the deflection rate and the CME speed. Our results suggest that the deflections of CMEs are mainly controlled by the background magnetic field and can be quantitatively described by the magnetic energy density gradient (MEDG) model.
2164692
Precise measurement of the pi+-->pi0 e+nu branching ratio.
Using a large acceptance calorimeter and a stopped pion beam we have made a precise measurement of the rare pi(+)-->pi(0)e(+)nu (pi(beta)) decay branching ratio. We have evaluated the branching ratio by normalizing the number of observed pi(beta) decays to the number of observed pi(+)-->e(+)nu (pi(e2)) decays. We find the value of Gamma(pi(+)-->pi(0)e(+)nu)/Gamma(total)=[1.036+/-0.004(stat)+/-0.004(syst)+/-0.003(pi(e2))]x10(-8), where the first uncertainty is statistical, the second systematic, and the third is the pi(e2) branching ratio uncertainty. Our result agrees well with the standard model prediction.
298393
Cosmological constant and advanced gravitational wave detectors
Interferometric gravitational wave detectors could measure the frequency sweep of a binary inspiral (characterized by its chirp mass) to high accuracy. The observed chirp mass is the intrinsic chirp mass of the binary source multiplied by (1+z), where z is the redshift of the source. Assuming a nonzero cosmological constant, we compute the expected redshift distribution of observed events for an advanced LIGO detector. We find that the redshift distribution has a robust and sizable dependence on the cosmological constant; the data from advanced LIGO detectors could provide an independent measurement of the cosmological constant. {copyright} {ital 1997} {ital The American Physical Society}