Quark-Hadron Duality and γ∗p→Δ\gamma^* p \to \Delta Form Factors

We use local quark-hadron duality to estimate the purely nonperturbative soft contribution to the $\gamma^*p\to \Delta$ form factors. Our results are in agreement with existing experimental data. We predict that the ratio $G_E^*(Q^2)/G_M^*(Q^2)$ is small for all accessible $Q^2$, in contrast to the pQCD expectations that $G_E^*(Q^2)\to -G_M^*(Q^2)$.Comment: 15 pages, LaTeX + 4 PS-figures enclosed in one uuencoded, compressed fil

Kinematics of diffuse ionized gas in the disk halo interface of NGC 891 from Fabry-P\'erot observations

The properties of the gas in halos of galaxies constrain global models of the interstellar medium. Kinematical information is of particular interest since it is a clue to the origin of the gas. Here we report observations of the kinematics of the thick layer of the diffuse ionized gas in NGC 891 in order to determine the rotation curve of the halo gas. We have obtained a Fabry-P\'erot data cube in Halpha to measure the kinematics of the halo gas with angular resolution much higher than obtained from HI 21 cm observations. The data cube was obtained with the TAURUS II spectrograph at the WHT on La Palma. The velocity information of the diffuse ionized gas extracted from the data cube is compared to model distributions to constrain the distribution of the gas and in particular the halo rotation curve. The best fit model has a central attenuation tau_H-alpha=6, a dust scale length of 8.1 kpc, an ionized gas scale length of 5.0 kpc. Above the plane the rotation curve lags with a vertical gradient of -18.8 km/s/kpc. We find that the scale length of the H-alpha must be between 2.5 and 6.5 kpc. Furthermore we find evidence that the rotation curve above the plane rises less steeply than in the plane. This is all in agreement with the velocities measured in the HI.Comment: A&A, in press. 13 pages, 19 figure

Cerebral blood flow and behavioural effects of caffeine in habitual and non-habitual consumers of caffeine: A near infrared spectroscopy study

Caffeine has been shown to modulate cerebral blood flow, with little evidence of tolerance to these effects following habitual use. However, previous studies have focused on caffeine levels much higher than those found in dietary servings and have compared high caffeine consumers with low consumers rather than 'non-consumers'. The current placebo-controlled double-blind, balanced-crossover study employed near infrared spectroscopy to monitor pre-frontal cerebral-haemodynamics at rest and during completion of tasks that activate the pre-frontal cortex. Twenty healthy young habitual and non-habitual consumers of caffeine received 75mg caffeine or placebo. Caffeine significantly decreased cerebral blood flow but this was subject to a significant interaction with consumption status, with no significant effect being shown in habitual consumers and an exaggerated effect in non-habitual consumers. These findings suggest that caffeine, at levels typically found in a single dietary serving, is able to modulate cerebral blood flow but these effects are subject to tolerance

A-dependence of nuclear transparency in quasielastic A(e,e'p) at high Q^2

The A-dependence of the quasielastic A(e,e'p) reaction has been studied at SLAC with H-2, C, Fe, and Au nuclei at momentum transfers Q^2 = 1, 3, 5, and 6.8 (GeV/c)^2. We extract the nuclear transparency T(A,Q^2), a measure of the average probability that the struck proton escapes from the nucleus A without interaction. Several calculations predict a significant increase in T with momentum transfer, a phenomenon known as Color Transparency. No significant rise within errors is seen for any of the nuclei studied.Comment: 5 pages incl. 2 figures, Caltech preprint OAP-73

Electromagnetic N−ΔN - \Delta transition form factors in a light-front constituent quark model

A parameter-free evaluation of the $N - \Delta$ electromagnetic transition form factors is carried out in a light-front constituent quark model, based on $N$ and $\Delta$ eigenstates of a mass operator which reproduces a large set of hadron energy levels. A one-body electromagnetic current, including the constituent quark form factors previously determined within the same approach from nucleon and pion experimental data, is used. Our prediction for the magnetic transition form factor is compared with the results both of phenomenological analyses of experimental data for the $\Delta$ electroproduction, and of an analysis which includes the effects of off-energy-shell $\pi - N$ final state interaction.Comment: 13 pages as .uu encoded postscript file; to appear in Phys. Lett.

Polarization transfer in the d(epol,e' ppol)n reaction up to Q^2=1.61 (GeV/c)^2

The recoil proton polarization was measured in the d(epol,e' ppol)n reaction in Hall A of the Thomas Jefferson National Accelerator Facility (JLab). The electron kinematics were centered on the quasielastic peak (x_{Bj}~1) and included three values of the squared four-momentum transfer, Q^2=0.43, 1.00 and 1.61 (GeV/c)^2. For Q^2=0.43 and 1.61 (GeV/c)^2, the missing momentum, p_m, was centered at zero while for Q^2=1.00 (GeV/c)^2 two values of p_m were chosen: 0 and 174 MeV/c. At low p_m, the Q^2 dependence of the longitudinal polarization, P_z', is not well described by a state-of-the-art calculation. Further, at higher p_m, a 3.5 sigma discrepancy was observed in the transverse polarization, P_x'. Understanding the origin of these discrepancies is important in order to confidently extract the neutron electric form factor from the analogous d(epol,e' npol)p experiment.Comment: 6 pages, 4 figures; updated text, figures and table

Quark-Hadron Duality in Neutron (3He) Spin Structure

We present experimental results of the first high-precision test of quark-hadron duality in the spin-structure function g_1 of the neutron and $^3$He using a polarized 3He target in the four-momentum-transfer-squared range from 0.7 to 4.0 (GeV/c)^2. Global duality is observed for the spin-structure function g_1 down to at least Q^2 = 1.8 (GeV/c)^2 in both targets. We have also formed the photon-nucleon asymmetry A_1 in the resonance region for 3He and found no strong Q^2-dependence above 2.2 (GeV/c)^2.Comment: 13 pages, 3 figure