118550171
Zero‐crossing angle of the np analyzing power below 300 MeV
The zero point of the analyzing power for neutron‐proton scattering has been measured as a function of scattering angle for 4 incident neutron energies, 174.3, 202.4, 216.5, and 260.3 MeV. The accuracy is ±0.25°. (AIP)
8943074
Precision Measurement of Charge Symmetry Breaking in np Elastic Scattering at 347 MeV.
Charge symmetry breaking in np elastic scattering at 347 MeV has been measured with high precision. From fits of the measured asymmetry curves over the angular range 53.4{degree} {le} {theta}{sub cm} {le} 86.9{degree}, the difference in the center-of-mass zero-crossing angles of the analyzing powers was determined to be 0.438{degree} {+-} 0.054{degree} (stat.) {+-} 0.051{degree} (syst.). Using the experimentally determined slope of the analyzing power, dA/d{theta} = ({minus}1.35 {+-} 0.05) {times} 10{sup {minus}2} deg{sup {minus}1}, this is equivalent to {Delta}A = [59 {+-} 7(stat.) {+-} 7(syst.) {+-} 2(syst.)] {times} 10{sup {minus}4}. Predictions of nucleon-nucleon interaction models based on meson exchange agree well with this result.
2001409
Molecular organization of Gram-negative peptidoglycan
The stress-bearing component of the bacterial cell wall—a multi-gigadalton bag-like molecule called the sacculus—is synthesized from peptidoglycan. Whereas the chemical composition and the 3-dimensional structure of the peptidoglycan subunit (in at least one conformation) are known, the architecture of the assembled sacculus is not. Four decades' worth of biochemical and electron microscopy experiments have resulted in two leading 3-D peptidoglycan models: “Layered” and “Scaffold”, in which the glycan strands are parallel and perpendicular to the cell surface, respectively. Here we resolved the basic architecture of purified, frozen-hydrated sacculi through electron cryotomography. In the Gram-negative sacculus, a single layer of glycans lie parallel to the cell surface, roughly perpendicular to the long axis of the cell, encircling the cell in a disorganized hoop-like fashion.
89312476
Beam tests with microstrip gas counters
We have measured the efficiency, timing and pulse heights in several types of microstrip Gas Chambers with plastic substrates passivated with a thin Nickel layer. We used as active gas mixtures Argon/Isobutane and CF/sub 4//Isobutane. We placed the detectors in a secondary beam at TRIUMF tuned to a momentum of 100 MeV/c of pions, muons and electrons. Preliminary results indicate good efficiency for minimum ionizing particles in Argon/Isobutane mixtures but lesser efficiency in CF/sub 4/ based gases indicating the importance of high quality preamplifiers to increase the signal to noise ratio.<<ETX>>
118122140
A preliminary result of the second np charge symmetry breaking experiment at TRIUMF
TRIUMF experiment 369, a measurement of charge symmetry breaking in np elastic scattering at 350 MeV, has completed data taking. Scattering asymmetries were measured with a polarized (unpolarized) neutron beam incident on an unpolarized (polarized) frozen spin target. Coincident scattered neutrons and recoil protons were detected by a mirror symmetric detection system in the center of mass angle range from 50°–90°. A preliminary result for the difference of the zero‐crossing angles, where analyzing powers cross zero, is Δθcm=0.48°±0.08°(stat.)±0.08°(syst.) based on fits over the angle range 55.8°≤θcm≤85.4°. The difference of the analyzing powers ΔA≡An−Ap, where the subscripts denote polarized nucleons, was deduced with dA/dθcm=−1.47×10−2 deg−1 from phase shift analyses to be [71±12(stat.)±12(syst.)]×10−4. It is expected that when all data are analyzed a statistical accuracy of about 7×10−4 in ΔA will be achieved.
56044971
The HKS experiment on Λ-hypernuclear spectroscopy via electroproduction at JLab
The HKS (Jlab E01-011) experiment on spectroscopy of Λ-hypernuclei using (e,e'K + ) reaction was successfully carried out in 2005. This paper gives a brief description of the experiment and its technique and shows some of the preliminary spectra that are still under analysis.
55784411
Test of fundamental symmetries via the Primakoff effect
The three neutral pseudoscalar mesons, pi^0, eta and eta', represent one of the most interesting systems in strong interaction physics. A study of the electromagnetic properties of these mesons provides a sensitive probe of the symmetry structure of QCD at low energy. A comprehensive experimental program at Jefferson Laboratory (Jlab) is aimed at gathering high precision measurements on the two-photon decay widths and transition form factors at low Q^2 of pi^0, eta and eta' via the Primakoff effect. The completed experiments on the pi^0 radiative decay width at Jlab 6 GeV, and other planned measurements at Jlab 12 GeV will provide a rich laboratory to test the chiral anomaly and to study the origin and dynamics of chiral symmetry breaking at the confinement scale of QCD.
119224046
The signature of an anisotropic distribution of gamma-ray bursts
Anomalies of the cosmic microwave background (CMB) maps have been widely acquainted nowadays from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite to the Planck satellite. One of the anomalies is a multipole alignment from $l=2$ to $l=5$. In our work, we investigate the angular distribution of gamma-ray bursts (GRBs) to find whether there is the same anomaly of GRB as CMB. We perform spherical harmonics expansion on GRB samples to derive coefficients of a few first terms of the expansion terms and find that there is rough multipole alignment from $l=2$ to $l=4$ while the dipole and $l=5$ multipole is in a distant direction, and that the quadrupole is obviously planar and the other ones are normal.