334 research outputs found
Spin Structure Functions of the Deuteron Measured with CLAS in and Above the Resonance Region
Spin structure functions of the nucleon in the region of large x and small to moderate Q2 continue to be of high current interest. The first moment of the spin structure function g1, Γ1, goes through a rapid transition from the photon point (Q2 = 0), where it is constrained by the Gerasimov-Drell-Hearn sum rule, to the deep inelastic limit where it is sensitive to the nucleon spin fraction carried by quarks. The interesting behavior in the transition region is dominated by baryon resonance excitations. We concluded an experiment to measure these observables for deuterium as part of the “EG1” run group in Jefferson Lab\u27s Hall B. We used a highly polarized electron beam with energies from 1.6 GeV to 5.7 GeV and a cryogenic polarized ND3 target together with the CEBAF Large Acceptance Spectrometer (CLAS) to accumulate over 11 billion events. In this thesis, we present results for the spin structure function [special characters omitted](x, Q2), as well as its first moment, [special characters omitted](Q2) in and above the resonance region over a Q2 range from 0.05 to 5 GeV2, based on the data taken with beam energies of 1.6 and 5.7 GeV. We also extract the behavior of [special characters omitted](x) at large x. Our data are consistent with the Hyperfine-perturbed quark model calculation which predicts that [special characters omitted](x → 1) → 1. We also see evidence for duality in [special characters omitted](x, Q2) at Q2\u3e 1.5 GeV2
Determination of gluon polarization from deep inelastic scattering and collider data
We investigate impact of -production data at Relativistic Heavy Ion
Collider (RHIC) and future E07-011 experiment for the structure function
of the deuteron at the Thomas Jefferson National Accelerator Facility (JLab) on
studies of nucleonic spin structure, especially on the polarized gluon
distribution function. By global analyses of polarized lepton-nucleon
scattering and the -production data, polarized parton distribution
functions are determined and their uncertainties are estimated by the Hessian
method. Two types of the gluon distribution function are investigated. One is a
positive distribution and the other is a node-type distribution which changes
sign at . Although the RHIC data seem to favor the node
type for , it is difficult to determine a precise functional form
from the current data. However, it is interesting to find that the gluon
distribution is positive at large () due to constraints
from the scaling violation in and RHIC data. The JLab-E07-011
measurements for should be also able to reduce the gluon uncertainty,
and the reduction is comparable to the one by RUN-5 -production data at
RHIC. The reduction is caused by the error correlation between polarized
antiquark and gluon distributions and by a next-to-leading-order (NLO) gluonic
effect in the structure function . We find that the JLab-E07-011 data
are accurate enough to probe the NLO gluonic term in . Both RHIC and JLab
data contribute to better determination of the polarized gluon distribution in
addition to improvement on polarized quark and antiquark distributions.Comment: 11 pages, 9 eps figures, To be published in Nuclear Physics B. AAC08
FORTRAN package is available at the web site http://spin.riken.bnl.gov/aac
Unique Electron Polarimeter Analyzing Power Comparison and Precision Spin-Based Energy Measurement
Precision measurements of the relative analyzing powers of five electron beam polarimeters, based on Compton, Moller, and Mott scattering, have been performed using the CEBAF accelerator at the Thomas Jefferson National Accelerator Facility ( Jefferson Laboratory). A Wien filter in the 100 keV beam line of the injector was used to vary the electron spin orientation exiting the injector. High statistical precision measurements of the scattering asymmetry as a function of the spin orientation were made with each polarimeter. Since each polarimeter receives beam with the same magnitude of polarization, these asymmetry measurements permit a high statistical precision comparison of the relative analyzing powers of the five polarimeters. This is the first time a precise comparison of the analyzing powers of Compton, Moller, and Mott scattering polarimeters has been made. Statistically significant disagreements among the values of the beam polarization calculated from the asymmetry measurements made with each polarimeter reveal either errors in the values of the analyzing power or failure to correctly include all systematic effects. The measurements reported here represent a first step toward understanding the systematic effects of these electron polarimeters. Such studies are necessary to realize high absolute accuracy (ca. 1%) electron polarization measurements, as required for some parity violation measurements planned at Jefferson Laboratory. Finally, a comparison of the value of the spin orientation exiting the injector that provides maximum longitudinal polarization in each experimental hall leads to an independent and very precise ( better than 10-4) absolute measurement of the final electron beam energy
Hyperon Photoproduction in the Nucleon Resonance Region
High-statistics cross sections and recoil polarizations for the reactions γ+p → K++ Λ and γ+p→K++ Σ0 have been measured at CLAS for center-of-mass energies between 1.6 and 2.3 GeV. In the K+Λ channel we confirm a resonance-like structure near W = 1.9 GeV at backward kaon angles. Our data show more complex s- and u- channel behavior than previously seen, since structure is also present at forward angles, but not at central angles. The position and width change with angle, indicating that more than one resonance is playing a role. Large positive Λ polarization at backward angles, which is also energy dependent, is consistent with sizable s- or u-channel contributions. Presently available model calculations cannot explain these aspects of the data
η Photoproduction on the Proton for Photon Energies From 0.75 to 1.95 GeV
Differential cross sections for γp→ηp have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W = 1.75 GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S11 resonance with mass ∼1.8 GeV couples to the ηN channel
The Jlab Upgrade - Studies of the Nucleon with CLAS12
An overview is presented on the program to study the nucleon structure at the
12 GeV JLab upgrade using the CLAS12 detector. The focus is on deeply virtual
exclusive processes to access the generalized parton distributions,
semni-inclusive processes to study transverse momentum dependent distribution
functions, and inclusive spin structure functions and resonance transition form
factors at high Q^2 and with high precision.Comment: 7 pages, 12 figures, NSTAR 2007 conference, Bonn, September 5-8, 200
Experimental Study of Isovector Spin Sum Rules
We present the Bjorken integral extracted from Jefferson Lab experiment EG1b for 0.05\u3c Q2 2. The integral is fit to extract the twist-4 element f p−n2 which appears to be relatively large and negative. Systematic studies of this higher twist analysis establish its legitimacy at Q2 around 1 GeV2. We also performed an isospin decomposition of the generalized forward spin polarizability γ0. Although its isovector part provides a reliable test of the calculation techniques of chiral perturbation theory, our data disagree with the calculations
Moments of the spin structure functions g(1)(p) and g(1)(d) for 0.05 \u3c Q(2) \u3c 3.0 GeV2
The spin structure functions g, for the proton and the deuteron have been measured over a wide kinematic range in x and Q(2) using 1.6 and 5.7 GeV longitudinally polarized electrons incident upon polarized NH3 and ND3 targets at Jefferson Lab. Scattered electrons were detected in the CEBAF Large Acceptance Spectrometer, for 0.05 \u3c Q(2) \u3c 5 GeV2 and W \u3c 3 GeV. The first moments of g(1) for the proton and deuteron are presented - both have a negative slope at low Q(2), as predicted by the extended Gerasimov-Drell-Hearn sum rule. The first extraction of the generalized forward spin polarizability of the proton gamma(p)(0) is also reported. This quantity shows strong Q(2) dependence at low Q(2). Our analysis of the Q(2) evolution of the first moment of g, shows agreement in leading order with Heavy Baryon Chiral Perturbation Theory. However, a significant discrepancy is observed between the gamma(p)(0) data and Chiral Perturbation calculations for gamma(p)(0), even at the lowest Q(2). (C) 2009 Elsevier B.V. All rights reserved
Measurement of Beam-Spin Asymmetries for π⁺ Electroproduction Above the Baryon Resonance Region
We report the first evidence for a nonzero beam-spin azimuthal asymmetry in the electroproduction of positive pions in the deep-inelastic kinematic region. Data for the reaction e→pe\u27π+X have been obtained using a polarized electron beam of 4.3 GeV with the CEBAF Large Acceptance Spectrometer at the Thomas Jefferson National Accelerator Facility. The amplitude of the sin ᵠ modulation increases with the momentum of the pion relative to the virtual photon, z. In the range z = 0.5-0.8 the average amplitude is 0.038 ± 0.005 ± 0.003 for a missing mass Mx \u3e 1.1 GeV and 0.037 ± 0.007 ± 0.004 for Mx \u3e1.4 GeV
Polarized parton distributions from NLO QCD analysis of world DIS and SIDIS data
The combined analysis of polarized DIS and SIDIS data is performed in NLO
QCD. The new parametrization on polarized PDFs is constructed. The
uncertainties on PDFs and their first moments are estimated applying the
modified Hessian method.
The especial attention is paid to the impact of novel SIDIS data on the
polarized distributions of light sea and strange quarks. In particular, the
important question of polarized sea symmetry is studied in comparison with the
latest results on this subject
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