58 research outputs found
Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction
We present results on the electroexcitation of the low mass resonances Delta(1232)P-33, N(1440)P-11, N(1520)D-13, and N(1535)S-11 in a wide range of Q(2). The results were obtained in the comprehensive analysis of data from the Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility (JLab) on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for pi electroproduction off the proton. The data were analyzed using two conceptually different approaches-fixed-t dispersion relations and a unitary isobar model-allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the Delta(1232)P-33 show the importance of a meson-cloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for Q(2) N(1520)D-13 and N(1535)S-11 longitudinal helicity amplitudes with good precision. For the N(1535)S-11, these results became a challenge for quark models and may be indicative of large meson-cloud contributions or of representations of this state that differ from a 3q excitation. The transverse amplitudes for the N(1520)D-13 clearly show the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q(2)\u3e1 GeV2, confirming a long-standing prediction of the constituent quark model
Evidence for the onset of color transparency in rho(0) electroproduction off nuclei
We have measured the nuclear transparency of the incoherent diffractive A(e,e\u27 rho(0)) process in C-12 and Fe-56 targets relative to H-2 using a 5 GeV electron beam. The nuclear transparency, the ratio of the produced rho(0,)s on a nucleus relative to deuterium, which is sensitive to rho A interaction, was studied as function of the coherence length (l(c)), a lifetime of the hadronic fluctuation of the virtual photon, and the four-momentum transfer squared (Q(2)). While the transparency for both C-12 and Fe-56 showed no lc dependence, a significant Q(2) dependence was measured, which is consistent with calculations that included the color transparency effects. (C) 2012 Elsevier B.V. All rights reserved
Measurement of the Neutron F-2 Structure Function via Spectator Tagging with CLAS
We report on the first measurement of the F-2 structure function of the neutron from the semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to less than or similar to 100 MeV/c and their angles to greater than or similar to 100 degrees relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The F-2(n) data collected cover the nucleon-resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65 \u3c Q(2) \u3c 4.52 GeV2, with uncertainties from nuclear corrections estimated to be less than a few percent. These measurements provide the first determination of the neutron to proton structure function ratio F-2(n)/F-2(p) at 0.2 less than or similar to x less than or similar to 0.8 with little uncertainty due to nuclear effects
Precision measurements of g(1) of the proton and of the deuteron with 6 GeV electrons
The inclusive polarized structure functions of the proton and deuteron, g(1)(p) and g(1)(d) , were measured with high statistical precision using polarized 6 GeV electrons incident on a polarized ammonia target in Hall B at Jefferson Laboratory. Electrons scattered at laboratory angles between 18 and 45 degrees were detected using the CEBAF Large Acceptance Spectrometer (CLAS). For the usual deep inelastic region kinematics, Q(2) \u3e 1 GeV2 and the final-state invariant mass W \u3e 2 GeV, the ratio of polarized to unpolarized structure functions g(1)/F-1 is found to be nearly independent of Q(2) at fixed x. Significant resonant structure is apparent at values of W up to 2.3 GeV. In the framework of perturbative quantum chromodynamics, the high-W results can be used to better constrain the polarization of quarks and gluons in the nucleon, as well as high-twist contributions
Semi-Inclusive Pi(0) Target and Beam-Target Asymmetries from 6 GeV Electron Scattering with CLAS
We present precision measurements of the target and beam-target spin asymmetries from neutral pion electroproduction in deep-inelastic scattering (DIS) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. We scattered 6-GeV, longitudinally polarized electrons off longitudinally polarized protons in a cryogenic 14NH3 target, and extracted double and single target spin asymmetries for ep→e′ π0 X in multidimensional bins in four-momentum transfer (1.0 2 \u3c 3.2 GeV2), Bjorken -x (0.12 \u3c x \u3c 0.48), hadron energy fraction (0.4 \u3c z 0.7), tranverse pion meomentum (0 \u3c PT \u3c 1.0 GeV), and azimuthal angle ϕh between the lepton scattering and hadron production planes. We extracted asymmetries as a function of both x and PT, which provides access to transverse-momentum distributions of longitudinally polarized quarks. The double spin asymmetries depend weakly on PT. The sin 2ϕh moments are zero within uncertainties, which is consistent with the expected suppression of the Collins fragmentation function. The observed sin ϕh moments suggest that quark gluon correlations are significant at large x
A study on wire breakage and parametric efficiency of the wire electro chemical discharge machining process 1
Abstract: -The Wire Electrochemical Discharge Machining (WECDM) is a nonconventional process, typically used in cutting brittle and hard non-conductive materials. The WECDM is relatively new research area compared to its principle process-'Electro Chemical Discharge Machining (ECDM). In the current investigation, the wire breakage problem, commonly encountered while machining fine slots has been addressed. The aim was to reduce the wire breakage through optimum parametric settings, to understand the wire breaking voltages at different electrolytic concentrations along with its effect on the MRR, length of cut and width of cut. In this study, zinc diffused brass wire of fine diameter (0.20 mm) was used in experiments and the results of the same are being reported in the paper. The response parameters used in the investigation were MRR and width of cut; while the process parameters were workpiece feed rate, electrolyte concentrations and applied voltage
Near-threshold Photoproduction of Phi Mesons from Deuterium
We report the first measurement of the differential cross section on
-meson photoproduction from deuterium near the production threshold for a
proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson
Lab. The measurement was carried out by a triple coincidence detection of a
proton, and near the theoretical production threshold of 1.57 GeV.
The extracted differential cross sections for the initial
photon energy from 1.65-1.75 GeV are consistent with predictions based on a
quasifree mechanism. This experiment establishes a baseline for a future
experimental search for an exotic -N bound state from heavier nuclear
targets utilizing subthreshold/near-threshold production of mesons
Absorption of the and Mesons in Nuclei
Due to their long lifetimes, the and mesons are the ideal
candidates for the study of possible modifications of the in-medium
meson-nucleon interaction through their absorption inside the nucleus. During
the E01-112 experiment at the Thomas Jefferson National Accelerator Facility,
the mesons were photoproduced from H, C, Ti, Fe, and Pb targets. This
paper reports the first measurement of the ratio of nuclear transparencies for
the channel. The ratios indicate larger in-medium widths compared
with what have been reported in other reaction channels.Comment: 6 pages, 4 figure
Differential cross sections and recoil polarizations for the reaction gamma p -> K+ Sigma0
High-statistics measurements of differential cross sections and recoil
polarizations for the reaction have been
obtained using the CLAS detector at Jefferson Lab. We cover center-of-mass
energies () from 1.69 to 2.84 GeV, with an extensive coverage in the
production angle. Independent measurements were made using the
() and () final-state topologies,
and were found to exhibit good agreement. Our differential cross sections show
good agreement with earlier CLAS, SAPHIR and LEPS results, while offering
better statistical precision and a 300-MeV increase in coverage.
Above GeV, - and -channel Regge scaling behavior
can be seen at forward- and backward-angles, respectively. Our recoil
polarization () measurements represent a substantial increase in
kinematic coverage and enhanced precision over previous world data. At forward
angles we find that is of the same magnitude but opposite sign as
, in agreement with the static SU(6) quark model prediction of
. This expectation is violated in some mid- and
backward-angle kinematic regimes, where and are of
similar magnitudes but also have the same signs. In conjunction with several
other meson photoproduction results recently published by CLAS, the present
data will help constrain the partial wave analyses being performed to search
for missing baryon resonances.Comment: 23 pages, 17 figure
Precision measurements of of the proton and the deuteron with 6 GeV electrons
The inclusive polarized structure functions of the proton and deuteron, g1p
and g1d, were measured with high statistical precision using polarized 6 GeV
electrons incident on a polarized ammonia target in Hall B at Jefferson
Laboratory. Electrons scattered at lab angles between 18 and 45 degrees were
detected using the CEBAF Large Acceptance Spectrometer (CLAS). For the usual
DIS kinematics, Q^2>1 GeV^2 and the final-state invariant mass W>2 GeV, the
ratio of polarized to unpolarized structure functions g1/F1 is found to be
nearly independent of Q^2 at fixed x. Significant resonant structure is
apparent at values of W up to 2.3 GeV. In the framework of perturbative QCD,
the high-W results can be used to better constrain the polarization of quarks
and gluons in the nucleon, as well as high-twist contributions
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