R.G. Arnold

Measurements of the Proton and Deuteron Spin Structure Function g2 and Asymmetry A2

We have measured proton and deuteron virtual photon-nucleon asymmetries A2p and A2d and structure functions g2p and g2d over the range 0.03<x<0.8 and 1.3<Q2<10 (GeV/c)2 by inelastically scattering polarized electrons off polarized ammonia targets. Results for A2 are significantly smaller than the positivity limit sqrt(R) for both targets. Within experimental precision, the g2 data are well-described by the twist-2 contribution g2WW. Twist-3 matrix elements have been extracted and are compared to theorectical predictions.

Measurements of R = σL/σT for 0.03 < x < 0.1 and Fit to World Data

Abstract Measurements were made at SLAC of the cross section for scattering 29 GeV electrons from carbon at a laboratory angle of 4.5°, corresponding to 0.03Measurements were made at SLAC of the cross section for scattering 29 GeV electrons from carbon at a laboratory angle of 4.5 degrees, corresponding to 0.03<x<0.1 and 1.3<Q^2<2.7 GeV^2. Values of R=sigma_L/sigma_T were extracted in this kinematic range by comparing these data to cross sections measured at a higher beam energy by the NMC collaboration. The results are in reasonable agreement with pQCD calculations and with extrapolations of the R1990 parameterization of previous data. A new fit is made including these data and other recent results.

Precision measurement of the proton and deuteron spin structure functions g2 and asymmetries A2

We have measured the spin structure functions g{sub 2}{sup p} and g{sub 2}{sup d} and the virtual photon asymmetries A{sub 2}{sup p} and A{sub 2}{sup d} over the kinematic range 0.02 {le} x {le} 0.8 and 0.7 {le} Q{sup 2} {le} 20 GeV{sup 2} by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH{sub 3} and {sup 6}LiD targets. Our measured g{sub 2} approximately follows the twist-2 Wandzura-Wilczek calculation. The twist-3 reduced matrix elements d{sub 2}{sup p} and d{sub 2}{sup n} are less than two standard deviations from zero. The data are inconsistent with the Burkhardt-Cottingham sum rule if there is no pathological behavior as x {yields} 0. The Efremov-Leader-Teryaev integral is consistent with zero within our measured kinematic range. The absolute value of A{sub 2} is significantly smaller than the A{sub 2} < {radical}(R(1+A{sub 1})/2) limit.

Developing ‘integrative’ zebrafish models of behavioral and metabolic disorders

Recently, the pathophysiological overlap between metabolic and mental disorders has received increased recognition. Zebrafish (Danio rerio) are rapidly becoming a popular model organism for translational biomedical research due to their genetic tractability, low cost, quick reproductive cycle, and ease of behavioral, pharmacological or genetic manipulation. High homology to mammalian physiology and the availability of well-developed assays also make the zebrafish an attractive organism for studying human disorders. Zebrafish neurobehavioral and endocrine phenotypes show promise for the use of zebrafish in studies of stress, obesity and related behavioral and metabolic disorders. Here, we discuss the parallels between zebrafish and other model species in stress and obesity physiology, as well as outline the available zebrafish models of weight gain, metabolic deficits, feeding, stress, anxiety and related behavioral disorders. Overall, zebrafish demonstrate a strong potential for modeling human behavioral and metabolic disorders, and their comorbidity.

Measurements of the Delta(1232) transition form factor and the ratio sigma(n)/sigma(p) from inelastic electron-proton and electron-deuteron scattering

Measurements of inclusive electron-scattering cross sections using hydrogen and deuterium targets in the region of the Delta(1232) resonance are reported. A global fit to these new data and previous data in the resonance region is also reported for the proton. Transition form factors have been extracted from the proton cross sections for this experiment over the four-momentum transfer squared range 1.64 < Q~2 < 6.75 (GeV/c)~2 and from previous data over the range 2.41 < Q~2 < 9.82 (GeV/c)~2. The results confirm previous reports that the Delta(1232) transition form factor decreases more rapidly with Q~2 than expected from perturbative QCD. The ratio of sigma _n \sigma_p in the \Delta(1232) resonance region has been extracted from the deuteron data for this experiment in the range 1.64 < Q~2 < 3.75 (GeV/c)~2 and for a previous experiment in the range 2.4 < Q~2 < 7.9 (GeV/c)~2. A study has been made of the model dependence of these results. This ratio sigma_n\sigma_p for \Delta(1232) production is slightly less than unity, while sigma_n\sigma_p for the nonresonant cross sections is approximately 0.5, which is consistent with deep inelastic scattering results.

Precision measurement of R=σL/σT and F2 in deep inelastic electron scattering

Abstract We report new results on a precision measurement of the ratio R= σ L / σ T , and the structure function F 2 , for deep inelastic electron-nucleon scattering in the range 0.2≤×≤0.5 and 1≤Q 2 ≤10 (GeV/c) 2 . Our results show, for the first time, a clear falloff of R with increasing Q 2 . Our R and F 2 results are in good agreement with QCD predictions only when corrections for target mass effects are included.

Two body photodisintegration of the deuteron up to 2.8 GeV

Measurements were performed for the photodisintegration cross section of the deuteron for photon energies from 1.6 GeV to 2.8 GeV and center‐of‐mass angles from 37° to 90°. The measured cross section at θcm=90° are in agreement with the constituent counting rules.

Measurements of the Q{sup 2}-Dependence of the Proton and Neutron Spin Structure Functions g{sub 1}{sup p} and g{sub 1}{sup n}

The structure functions g{sub 1}{sup p} and g{sub 1}{sup n} have been measured over the range 0.014 < x < 0.9 and 1 < Q{sup 2} < 40 GeV{sup 2} using deep-inelastic scattering of 48 GeV longitudinally polarized electrons from polarized protons and deuterons. The authors find that the Q{sup 2} dependence of g{sub 1}{sup p}(g{sub 1}{sup n}) at fixed x is very similar to that of the spin-averaged structure function F{sub 1}{sup p} (F{sub 1}{sup n}). From an NLO QCD fit to all available data they find Gamma{sub 1}{sup p}-Gamma{sub 1}{sup p} = 0.176 {+-} 0.003 {+-} 0.007 at Q{sup 2} = 5 GeV{sub 2}, in agreement with the Bjorken sum rule prediction of 0.182 {+-} 0.005.

Measurements of the proton and deuteron spin structure functionsg1andg2

Measurements are reported of the proton and deuteron spin structure functions g1 at beam energies of 29.1, 16.2, and 9.7 GeV and g2 at a beam energy of 29.1 GeV. The integrals of g1 over x have been evaluated at fixed Q**2 = 3 (GeV/c)**2 using the full data set. The Q**2 dependence of the ratio g1/F1 was studied and found to be small for Q**2>1 (GeV/c)**2. Within experimental precision the g2 data are well-described by the Wandzura-Wilczek twist-2 contribution. Twist-3 matrix elements were extracted and compared to theoretical predictions. The asymmetry A2 was measured and found to be significantly smaller than the positivity limit for both proton and deuteron targets. A2 for the proton is found to be positive and inconsistent with zero. Measurements of g1 in the resonance region show strong variations with x and Q**2, consistent with resonant amplitudes extracted from unpolarized data. These data allow us to study the Q**2 dependence of the first moments of g1 below the scaling region.

Inclusive electron scattering from nuclei at {ital x}{approx_equal}1

The inclusive A(e, e{prime}) cross section for x {approx_equal} 1 was measured on {sup 2}H, C, Fe, and Au for momentum transfers Q{sup 2} from 1-7 (GeV/c){sup 2}. The scaling behavior of the data was examined in the region of transition from y-scaling to x-scaling. Throughout this transitional region, the data exhibit {zeta}-scaling, reminiscent of the Bloom-Gilman duality seen in free nucleon scattering.