1,046 research outputs found
Proton and neutron polarized structure functions from low to high Q**2
Phenomenological parameterizations of proton and neutron polarized structure
functions, g1p and g1n, are developed for x > 0.02 using deep inelastic data up
to ~ 50 (GeV/c)**2 as well as available experimental results on photo- and
electro-production of nucleon resonances. The generalized Drell-Hearn-Gerasimov
sum rules are predicted from low to high values of Q**2 and compared with
proton and neutron data. Furthermore, the main results of the power correction
analysis carried out on the Q**2-behavior of the polarized proton Nachtmann
moments, evaluated using our parameterization of g1p, are briefly summarized.Comment: Proceedings of the II International Symposium on the
Gerasimov-Drell-Hearn sum rule and the spin structure of the nucleon, Genova
(Italy), July 3-6, 200
The proton structure function F2 in the resonance region
Unique measurement of the proton structure function F2 in a wide
two-dimensional region of x and Q**2 has been reported. The accessible
kinematics covers entire resonance region up to W=2.5 GeV in the Q**2 interval
from 0.1 to 4.5 GeV**2. Obtained data allowed for the first time an evaluation
of moments of the structure function F2 directly from experimental data as well
as an intensive study of the Bloom-Gilman duality phenomenon.Comment: 6 pages, 4 figures, Proceedings of GDH2002 Conference, 3-6 July 2002,
Genova, Italy, to be published in World Scientifi
A solvable model for small-x physics in D > 4 dimensions
I present a simplified model for the gluon Green's function governing
high-energy QCD dynamics, in arbitrary space-time dimensions. The BFKL integral
equation (either with or without running coupling) reduces to a second order
differential equation that can be solved in terms of Bessel and hypergeometric
functions. Explicit expressions for the gluon density and its anomalous
dimension are derived in MS and Q_0 factorization schemes. This analysis
illustrates the qualitative features of the QCD gluon density in both
factorization schemes. In addition, it clarifies the mathematical properties
and validates the results of the ``gamma-representation'' method proposed by
M.Ciafaloni and myself for extracting resummed next-to-leading-log x anomalous
dimensions of phenomenological relevance in the two schemes.Comment: 30 pages, 9 figure
Helicity components of the cross section for double charged-pion production by real photons on protons
The helicity components σ1/2 and σ3/2 of the cross section for double charged-pion production by real photons on a nucleon are calculated within a phenomenological approach developed previously. A high sensitivity of the σ1/2–σ3/2 asymmetry to the contribution of nucleon resonances having strongly different electromagnetic helicity amplitudes A1/2 and A3/2 is demonstrated. This feature is of importance for seeking "missing" baryon states
Quasi-elastic and inelastic inclusive electron scattering from an oxygen jet target
The results of an experiment on inclusive electron scattering from an oxygen
jet target, performed in a wide range of energy and momentum transfer covering
both quasi-elastic and (1232) resonance regions, are reported. In the
former region the theoretical predictions, obtained including effects of
nucleon-nucleon correlations in both initial and final states, give a good
description of the experimental data. In the inelastic region a broadening as
well as a damping of the resonant part of the cross section with respect to the
free nucleon case is observed. The need of more detailed calculations including
nuclear structure effects on the electroproduction cross section of nucleon
resonances is highlighted.Comment: to appear in Nucl. Phys.
Analysis of the Response of CVD Diamond Detectors for UV and sX-Ray Plasma Diagnostics Installed at JET
Abstract Diamond detectors are very promising candidates for plasma diagnostics in a harsh environment. In fact, they have several proprieties which make them suitable for magnetic fusion devices: radiation hardness, high thermal conductivity, high resistivity, high carrier mobility and a large bandgap (5.5 eV). The latter makes them insensitive to visible radiation and allows low noise measurements without any cooling. In 2008 two CVD (Chemical Vapour Deposition) single crystal diamond (SCD) detectors were installed at the JET tokamak as extreme UV and soft X-Ray diagnostics [1]. In this work the neutron background in these detectors was measured shielding the UV and soft X-Ray radiation by closing a local vacuum valve. The UV detector was found to be insensitive to the neutron flux, while the soft X Ray detector signal exhibited spikes during the highest neutron rate pulse (neutron rate 10 16 n / s , which corresponds to a flux of φ n ∼10 5 n / cm 2 s in the detector location). These spikes were found to be due to the (n,p) reaction within the plastic filter in front of the soft X-Ray detector. The UV SCD was also used to perform time of flight (ToF) measurements in laser ablation experiments. ToFs were found to be an order of magnitude higher than expected if only the drift velocity is considered. This discrepancy could be due to a delay between the arrival time of the impurities in the plasma and their emission in an energy range which SCD is sensitive to ( Eph >5.5 eV). The delay is found to be comparable with the expected ionization times for edge plasma conditions
A Phenomenological Description of (\pi^{-}\Delta^{++}) Photo- and Electroproduction in Nucleon Resonance Region
The (\pi^{-}\Delta^{++}) production on the nucleon by real and virtual
photons is discussed as initial step in a simple model approach for the two
pion photo- and electroproduction on the nucleon, with emphasis on nucleon
resonance excitation which is of interest for new facilities like TJNAF. A
calculation for (\pi^{-}\Delta^{++}) channel in resonance excitation region is
presented and compared to existing experimental data along with a discussion of
physical effects that we find to be of relevance. The calculation is proposed
as a starting basis for the investigation of (N^{*}) electromagnetic form
factors using experimental data about two pion production by real and virtual
photons.Comment: 36 pages, 14 figures, to be published in Nucl. Phys.
Thin Ice Target for O(p,p') experiment
A windowless and self-supporting ice target is described. An ice sheet with a
thickness of 29.7 mg/cm cooled by liquid nitrogen was placed at the target
position of a magnetic spectrometer and worked stably in the O
experiment at MeV. Background-free spectra were obtained.Comment: 14 pages, 4 figures, Nucl. Instr. & Meth. A (in press
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