Upgraded photon calorimeter with integrating readout for Hall A Compton Polarimeter at Jefferson Lab

The photon arm of the Compton polarimeter in Hall A of Jefferson Lab has been upgraded to allow for electron beam polarization measurements with better than 1% accuracy. The data acquisition system (DAQ) now includes an integrating mode, which eliminates several systematic uncertainties inherent in the original counting-DAQ setup. The photon calorimeter has been replaced with a Ce-doped GSO crystal, which has a bright output and fast response, and works well for measurements using the new integrating method at electron beam energies from 1 to 6 GeV.Comment: 16 pages, 15 figure

Quantitative Treatment of Decoherence

We outline different approaches to define and quantify decoherence. We argue that a measure based on a properly defined norm of deviation of the density matrix is appropriate for quantifying decoherence in quantum registers. For a semiconductor double quantum dot qubit, evaluation of this measure is reviewed. For a general class of decoherence processes, including those occurring in semiconductor qubits, we argue that this measure is additive: It scales linearly with the number of qubits.Comment: Revised version, 26 pages, in LaTeX, 3 EPS figure

Cut-points for waist circumference in Europids and South Asians

There is little strong evidence that currently recommended higher waist circumference cut-points for Europids compared with South Asians are associated with similar risk for type 2 diabetes. This study was designed to provide such evidence. Longitudinal studies over 5 years were conducted among 5,515 Europid and 2,214 ethnically South Asian participants. Age-standardized diabetes incidence at different levels of waist circumference and incidence difference relative to a reference value were calculated. The Youden Index was used to determine waist circumference cut-points. At currently recommended cut-points, estimated annual diabetes incidence for a 50-year-old Europid was &lt;0.6% for both sexes, and for a 50-year-old South Asian, 5.8% for men and 2.1% for women. Annual diabetes incidence of 1% was observed for a 50 year old at a waist circumference 35&ndash;40 cm greater in Europid compared to South Asian men and women. Incidence difference between recommended cut-points and a reference value (80 cm in men, 70 cm in women) was 0.3 and 4.4% per year for Europid and South Asian men, and 0.2 and 0.8% per year for Europid and South Asian women, respectively. Waist circumference cut-points chosen using the Youden Index were shown to be dependent on obesity levels in the population. The much higher observed risk of diabetes in South Asians compared to Europids at the respective recommended waist circumference cut-points suggests that differences between them should be greater. Approaches that use the Youden Index to select waist circumference cut-points are inappropriate and should not be used for this purpose.<br /

On the macroscopic formation length for GeV photons

Experimental results for the radiative energy loss of 206 and 234 GeV electrons in 5–10 μm thin Ta targets are presented. An increase in radiation emission probability at low photon energies compared to a 100 μm thick target is observed. This increase is due to the formation length of the GeV photons exceeding the thickness of the thin foils, the so-called Ternovskii–Shul'ga–Fomin (TSF) effect. The formation length of GeV photons from a multi-hundred GeV projectile is through the TSF effect shown directly to be a factor 1010 longer than their wavelength

Search for three-nucleon short-range correlations in light nuclei

We present new data probing short-range correlations (SRCs) in nuclei through the measurement of electron scattering off high-momentum nucleons in nuclei. The inclusive ^{4}He/^{3}He cross section ratio is observed to be both x and Q^{2} independent for 1.52, our data support the hypothesis that a previous claim of three-nucleon correlation dominance was an artifact caused by the limited resolution of the measurement. While 3N-SRCs appear to have an important contribution, our data show that isolating 3N-SRCs is significantly more complicated than for 2N-SRCs.United States. Department of Energy (Contract DE-AC05-06OR23177)United States. Department of Energy (Contract DE-AC02-06CH11357)United States. Department of Energy (Contract DE-FG02-96ER40950

Precision Measurement of the p(e,e ' p)pi(0) Reaction at Threshold

New results are reported from a measurement of $\pi^0$ electroproduction near threshold using the $p(e,e^{\prime} p)\pi^0$ reaction. The experiment was designed to determine precisely the energy dependence of $s-$ and $p-$wave electromagnetic multipoles as a stringent test of the predictions of Chiral Perturbation Theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a two-spectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the $\phi^*_{\pi}$ and $\theta^*_{\pi}$ angles in the $p \pi^0$ center-of-mass was obtained for invariant energies above threshold from 0.5 MeV up to 15 MeV. The 4-momentum transfer $Q^2$ coverage ranges from 0.05 to 0.155 (GeV/c)$^2$ in fine steps. A simple phenomenological analysis of our data shows strong disagreement with $p-$wave predictions from ChPT for $Q^2>0.07$ (GeV/c)$^2$, while the $s-$wave predictions are in reasonable agreement.Comment: 5 pages, 6 figure

Q

The Qweak experiment, which took data at Jefferson Lab in the period 2010 - 2012, will precisely determine the weak charge of the proton by measuring the parity-violating asymmetry in elastic e-p scattering at 1.1 GeV using a longitudinally polarized electron beam and a liquid hydrogen target at a low momentum transfer of Q2 = 0.025 (GeV/c)2. The weak charge of the proton is predicted by the Standard Model and any significant deviation would indicate physics beyond the Standard Model. The technical challenges and experimental apparatus for measuring the weak charge of the proton will be discussed, as well as the method of extracting the weak charge of the proton. The results from a small subset of the data, that has been published, will also be presented. Furthermore an update will be given of the current status of the data analysis