We present a study of high energy photodisintegration of proton-pairs through the γ+He3→p+p+n channel. Photon energies, Eγ, from 0.8 to 4.7 GeV were used in kinematics corresponding to a proton pair ...with high relative momentum and a neutron nearly at rest. The s−11 scaling of the cross section, as predicted by the constituent counting rule for two nucleon photodisintegration, was observed for the first time. The onset of the scaling is at a higher energy and the cross section is significantly lower than for deuteron (pn pair) photodisintegration. For Eγ below the scaling region, the scaled cross section was found to present a strong energy-dependent structure not observed in deuteron photodisintegration.
The bremsstrahlung tagged photon beam in Hall B at JLab Sober, D.I.; Crannell, Hall; Longhi, Alberto ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2000, Letnik:
440, Številka:
2
Journal Article
Recenzirano
We describe the design and commissioning of the photon tagging beamline installed in experimental Hall B at the Thomas Jefferson National Accelerator Facility (JLab). This system can tag photon ...energies over a range from 20% to 95% of the incident electron energy, and is capable of operation with beam energies up to 6.1
GeV. A single dipole magnet is combined with a hodoscope containing two planar arrays of plastic scintillators to detect energy-degraded electrons from a thin bremsstrahlung radiator. The first layer of 384 partially overlapping small scintillators provides photon energy resolution, while the second layer of 61 larger scintillators provides the timing resolution necessary to form a coincidence with the corresponding nuclear interaction triggered by the tagged photon. The definitions of overlap channels in the first counter plane and of geometric correlation between the two planes are determined using digitized time information from the individual counters. Auxiliary beamline devices are briefly described, and performance results to date under real operating conditions are presented. The entire photon-tagging system has met or exceeded its design goals.
We report a new, high-precision measurement of the proton elastic form factor ratio μpGE/GM for the four-momentum transfer squared Q2=0.3–0.7(GeV/c)2. The measurement was performed at Jefferson Lab ...(JLab) in Hall A using recoil polarimetry. With a total uncertainty of approximately 1%, the new data clearly show that the deviation of the ratio μpGE/GM from unity observed in previous polarization measurements at high Q2 continues down to the lowest Q2 value of this measurement. The updated global fit that includes the new results yields an electric (magnetic) form factor roughly 2% smaller (1% larger) than the previous global fit in this Q2 range. We obtain new extractions of the proton electric and magnetic radii, which are 〈rE2〉1/2=0.875±0.010 fm and 〈rM2〉1/2=0.867±0.020 fm. The charge radius is consistent with other recent extractions based on the electron–proton interaction, including the atomic hydrogen Lamb shift measurements, which suggests a missing correction in the comparison of measurements of the proton charge radius using electron probes and the recent extraction from the muonic hydrogen Lamb shift.
Solid ammonia is commonly used as a dynamically polarized proton target for electron and muon scattering cross-section asymmetry measurements. As spin 1$^{+}$ particles, the $^{14}$N nuclei in the ...target are also polarized and contribute a non-trivial asymmetry background that should be addressed. HereWe describe here a method to extract the nitrogen contribution to the asymmetry, and report the cross-section asymmetries of electron-nitrogen scattering at beam energies of $E=1.7$ GeV and $E=2.2$ GeV, and momentum transfer of $Q^{2}=0.023-0.080$ GeV$^{2}$.
Proton Polarimeter Calibration between 82 and 217 MeV Glister, J; Lee, B; Beck, A ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2009, Letnik:
606, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The proton analyzing power in carbon has been measured for energies of 82 to 217 MeV and proton scattering angles of 5 to 41 degrees. The measurements were carried out using polarized protons from ...the elastic scattering H(pol. e, pol. p) reaction and the Focal Plane Polarimeter (FPP) in Hall A of Jefferson Lab. A new parameterization of the FPP p-C analyzing power was fit to the data, which is in good agreement with previous parameterizations and provides an extension to lower energies and larger angles. The main conclusions are that all polarimeters to date give consistent measurements of the carbon analyzing power, independently of the details of their construction and that measuring on a larger angular range significantly improves the polarimeter figure of merit at low energies.
We report a measurement of the spin polarization of the recoiling neutron in deuterium photodisintegration, utilizing a new large acceptance polarimeter within the Crystal Ball at MAMI. The measured ...photon energy range of 300-700 MeV provides the first measurement of recoil neutron polarization at photon energies where the quark substructure of the deuteron plays a role, thereby providing important new constraints on photodisintegration mechanisms. A very high neutron polarization in a narrow structure centered around E_{γ}∼570 MeV is observed, which is inconsistent with current theoretical predictions employing nucleon resonance degrees of freedom. A Legendre polynomial decomposition suggests this behavior could be related to the excitation of the d^{*}(2380) hexaquark.
Backward-angle meson electroproduction above the resonance region, which was previously ignored, is anticipated to offer unique access to the three quark plus sea component of the nucleon wave ...function. In this Letter, we present the first complete separation of the four electromagnetic structure functions above the resonance region in exclusive ω electroproduction off the proton, ep→e′pω, at central Q2 values of 1.60, 2.45 GeV2, at W=2.21 GeV. The results of our pioneering −u≈−umin study demonstrate the existence of a unanticipated backward-angle cross section peak and the feasibility of full L/T/LT/TT separations in this never explored kinematic territory. At Q2=2.45 GeV2, the observed dominance of σT over σL, is qualitatively consistent with the collinear QCD description in the near-backward regime, in which the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes: universal nonperturbative objects only accessible through backward-angle kinematics.
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