119228127
Incoherent photoproduction of pseudoscalar mesons off nuclei at forward angles
Recent advances in the photon tagging facilities together with the novel, high-resolution fast calorimetry make it possible to perform photoproduction cross section measurements of pseudoscalar mesons on nuclei with a percent level accuracy. The extraction of the radiative decay widths, needed for testing the symmetry breaking effects in QCD, from these measurements at small angles is done by the Primakoff method. This method requires theoretical treatment of all processes participating in these reactions at the same percent level. The most updated description of general processes, including the nuclear coherent amplitude, is done in our previous paper. In this work, in the framework of the Glauber multiple scattering theory, we obtain analytical expressions for the incoherent cross section of the photoproduction of pseudoscalar mesons off nuclei accounting for the mesons absorption in nuclei and the Pauli suppression at forward production angles. As illustrations of the obtained formulas, we calculate the incoherent cross section for photoproduction from a closed shell nucleus, 16O, and from an unclosed shell nucleus, 12C. These calculations allow one to compare different approaches and estimate their impact on the incoherent cross section of the processes under consideration.
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>>
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.
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.
121399962
Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers
Abstract A time-zero fission fragment (FF) detector, based on the technique of low-pressure multiwire proportional chambers (LPMWPC), has been designed and constructed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the method of time-zero reconstruction were investigated using fission fragments from a 252 Cf spontaneous fission source. The influence of the ionization energy loss was also studied. It is shown that Heptane, Hexane, and Isobutane gases at a pressure of 1–2 Torr are all suitable for such a FF detector. As desired by experiment, a timing resolution of about 200 ps (FWHM) for a chamber size of 21×21 cm 2 was achieved.
117101551
Comments on "eta -> gamma gamma Decay Width via the Primakoff Cross Section"
In a recent article by Rodrigues et al. [1] eta photo-nuclear data taken by Browman et al. [2] in 1974 were refit as a means to extract the eta->gamma gamma decay width. The key assertion in the author's analysis is attributing backgrounds in the eta angular distribution to nuclear incoherent production only. We disagree with this assertion and question the validity of the fitting procedure utilized in [1]. A reanalysis of the Cornell Primakoff data requires a detailed understanding of the hadronic and accidental backgrounds in the data, and the authors of [1] have not accomplished this task. [1] T. E. Rodrigues et al., Phys. Rev. Lett., 101, 012301 (2008). [2] A. Browman et al., Phys. Rev. Lett. 32, 1067 (1974).
117854820
A study of the sensitivity of the H dibaryon search experiment E813 at BNL through (Sigma(-),p)(atom) to Lambda + n
36505928
Precision Measurement of η → γγ Decay Width via the Primakoff Effect
A precision measurement of the η → γγ decay width via the Primakoff effect is underway in Hall D at Jefferson Lab. The decay width will be extracted from measured differential cross sections at forward angles on two light targets, liquid hydrogen and 4He, using a 11.5 GeV tagged photon beam. Results of this experiment will not only potentially resolve a long standing discrepancy between the Primakoff and the collider measurements, but will also reduce the experimental uncertainty by a factor of two on the average value of previous experimental results listed by the Particle Data Group(PDG) [1]. It will directly improve all other η partial decay widths which rely on the accuracy of the η radiative decay width. The projected 3% precision on the Γ(η → γγ) measurement will have a significant impact on the experimental determination of the fundamental parameters in QCD, such as the ratio of light quark masses (mu,md ,ms) and the η −η ′ mixing angle. It will be a sensitive probe for understanding QCD symmetries and the origin and the dynamics of QCD symmetry breaking.
115608139
Search of new physics via eta rare decays
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.