Search

Abstract: Color polarizabilities of the neutron are extracted from data on the lowest moment of the spin-dependent structure function. New data in the resonance region from Jefferson Lab at , in combination with world data at higher , allow a systematic determination of the corrections, and provide the first constraints on corrections. The results suggest that higher-twist effects in the neutron are small, and that quark–hadron duality may be approximately valid, even down to . [Copyright &y& Elsevier]

Sum rules offer the opportunity to test our understanding of the structure of a system on general grounds. In this paper we investigate the3He nucleus using the Gerasimov-Drell-Hearn and Burkhardt-Cottingham sum rules. We have previously used the polarized3He target measurements to extract the neutron spin structure, our goal here is to investigate rather the3He nucleus. We have determined for the first time theQ2 evolution ofandfor3He in the range 0.1 GeV2 =Q2 = 0.9 GeV2 with good precision.G1(Q2) displays a smooth variation from high to lowQ2. However, we do not see yet its expected turnover toward the real photon limit value. On the other hand the Burkhardt-Cottingham sum rule holds at all measuredQ2s within uncertainties due mainly to cancellations between the elastic, quasielastic and the?(1232) resonance contributions. [ABSTRACT FROM AUTHOR]

Guided by the recent experimental confirmation of the validity of the Effective Momentum Approximation (EMA) in quasi-elastic scattering off nuclei, we have re-examined the extraction of the Longitudinal and Transverse Response Functions in medium-weight and heavy nuclei. In the EMA we have performed a Rosenbluth separation of the available world data on 40Ca, 48Ca, 56Fe and 208Pb. We find that the Longitudinal Response Function for these nuclei is ”quenched” and that the Coulomb sum is not saturated, at odds with recent claims in the literature. [ABSTRACT FROM AUTHOR]

We have determined the proton and the neutron charge radii from a global analysis of the proton and the neutron elastic form factors, after first performing a flavor decomposition of these form factors under charge symmetry in the light cone frame formulation. We then extracted the transverse mean-square radii of the flavor dependent quark distributions. In turn, these are related in a model-independent way to the proton and neutron charge radii but allow us to take into account motion effects of the recoiling nucleon for data at finite but high momentum transfer. In the proton case we find ⟨ r p ⟩ = 0.852 ± 0. 002 (stat.) ± 0. 009 (syst.) (fm) , consistent with the proton charge radius obtained from muonic hydrogen spectroscopy [1-2]. The current method improves on the precision of the ⟨ r p ⟩ extraction based on the form factor measurements. Furthermore, we find no discrepancy in the ⟨ r p ⟩ determination among the different electron scattering measurements, all of which, utilizing the current method of extraction, result in a value that is consistent with the smallest ⟨ r p ⟩ extraction from the electron scattering measurements [3]. Concerning the neutron case, past results relied solely on the neutron-electron scattering length measurements, which suffer from an underestimation of underlying systematic uncertainties inherent to the extraction technique. Utilizing the present method we have performed the first extraction of the neutron charge radius based on nucleon form factor data, and we find ⟨ r n 2 ⟩ = - 0.122 ± 0. 004 (stat.) ± 0. 010 (syst.) (fm 2) . [ABSTRACT FROM AUTHOR]

The solenoidal large intensity device (SoLID) is a new experimental apparatus planned for Hall A at the Thomas Jefferson National Accelerator Facility (JLab). SoLID will combine large angular and momentum acceptance with the capability to handle very high data rates at high luminosity. With a slate of approved high-impact physics experiments, SoLID will push JLab to a new limit at the QCD intensity frontier that will exploit the full potential of its 12 GeV electron beam. In this paper, we present an overview of the rich physics program that can be realized with SoLID, which encompasses the tomography of the nucleon in 3D momentum space from semi-inclusive deep inelastic scattering, expanding the phase space in the search for new physics and novel hadronic effects in parity-violating DIS, a precision measurement of J / ψ production at threshold that probes the gluon field and its contribution to the proton mass, tomography of the nucleon in combined coordinate and momentum space with deep exclusive reactions, and more. To meet the challenging requirements, the design of SoLID described here takes full advantage of recent progress in detector, data acquisition and computing technologies. In addition, we outline potential experiments beyond the currently approved program and discuss the physics that could be explored should upgrades of CEBAF become a reality in the future. [ABSTRACT FROM AUTHOR]

The nucleon has been used as a laboratory to investigate its own spin structure and quantum chromodynamics. New experimental data on nucleon spin structure at low to intermediate momentum transfers combined with existing high momentum transfer data offer a comprehensive picture of the transition region from the confinement regime of the theory to its asymptotic freedom regime. Insight for some aspects of the theory is gained by exploring lower moments of spin structure functions and their corresponding sum rules (i.e. the Gerasimov–Drell–Hearn, Bjorken and Burkhardt–Cottingham). These moments are expressed in terms of an operator-product expansion using quark and gluon degrees of freedom at moderately large momentum transfers. The sum rules are verified to good accuracy assuming that no singular behavior of the structure functions is present at very high excitation energies. The higher-twist contributions have been examined through the moments evolution as the momentum transfer varies from higher to lower values. Furthermore, QCD-inspired low-energy effective theories, which explicitly include chiral symmetry breaking, are tested at low momentum transfers. The validity of these theories is further examined as the momentum transfer increases to moderate values. It is found that chiral perturbation calculations agree reasonably well with the first moment of the spin structure function g1 at momentum transfer of 0.1 GeV2 but fail to reproduce the neutron data in the case of the generalized polarizability δLT. [ABSTRACT FROM AUTHOR]

The Spin Asymmetries of the Nucleon Experiment (SANE) performed inclusive, double-polarized electron scattering measurements of the proton at the Continuous Electron Beam Accelerator Facility at Jefferson Lab. A novel detector array observed scattered electrons of four-momentum transfer 2 . 5 < Q 2 < 6 . 5 GeV 2 and Bjorken scaling 0 . 3 < x < 0 . 8 from initial beam energies of 4.7 and 5.9 GeV. Employing a polarized proton target whose magnetic field direction could be rotated with respect to the incident electron beam, both parallel and near perpendicular spin asymmetries were measured, allowing model-independent access to transverse polarization observables A 1 , A 2 , g 1 , g 2 and moment d 2 of the proton. This document summarizes the operation and performance of the polarized target, polarized electron beam, and novel detector systems used during the course of the experiment, and describes analysis techniques utilized to access the physics observables of interest. [ABSTRACT FROM AUTHOR]

UV-glass photomultiplier tubes (PMTs) have poor photon detection efficiency for wavelengths below 300 nm due to the opaqueness of the window material. Costly quartz PMTs could be used to enhance the efficiency below 300 nm. A less expensive solution that dramatically improves this efficiency is the application of a thin film of a p-terphenyl (PT) wavelength shifter on UV-glass PMTs. This improvement was quantified for Photonis XP4500B PMTs for wavelengths between 200 nm and 400 nm. The gain factor ranges up to 5 . 4 ± 0 . 5 at a wavelength of 215 nm, with a material load of 110 ± 10 μ g ∕ cm 2 (894 nm). The wavelength shifter was found to be fully transparent for wavelengths greater than 300 nm. The resulting gain in detection efficiency, when used in a typical C̆erenkov counter, was estimated to be of the order of 40%. Consistent coating quality was assured by a rapid gain testing procedure using narrow-band UV LEDs. Based on these results, 200 Photonis XP4500B PMTs were treated with PT for the upgraded low-threshold C̆erenkov counter (LTCC) to be used in the CEBAF Large Acceptance Spectrometer upgraded detector (CLAS12) at the Thomas Jefferson National Accelerator Facility. [ABSTRACT FROM AUTHOR]

Superconducting nanowire single photon detectors are capable of single-photon detection across a large spectral range with near unity detection efficiency, picosecond timing jitter, and sub-10 μ m position resolution, at rates as high as 109 counts/s. In an effort to bring this technology into nuclear physics experiments, we fabricate niobium nitride (NbN) nanowire detectors using ion beam assisted sputtering and test their performance in strong magnetic fields. We demonstrate that these devices are capable of detection of 400 nm wavelength photons with saturated internal quantum efficiency at temperatures of 3 K and in magnetic fields of up to 5 T at high count rates and with nearly zero dark counts. [ABSTRACT FROM AUTHOR]

We report on new measurements of the electric Generalized Polarizability (GP) of the proton α E in a kinematic region where a puzzling dependence on momentum transfer has been observed, and we have found that α E = (5. 3 ± 0. 6 s t a t ± 1. 3 s y s) 10 - 4 fm3 at Q 2 = 0. 20 (GeV/c)2. The new measurements, when considered along with the rest of the world data, suggest that α E can be described by either a local plateau or by an enhancement in the region Q 2 = 0. 20 (GeV/c)2 to 0.33 (GeV/c)2. The experiment also provides the first measurement of the Coulomb quadrupole amplitude in the N → Δ transition through the exploration of the p (e , e p) γ reaction. The new measurement gives C M R = (- 4. 4 ± 0. 8 s t a t ± 0. 6 s y s) % at Q 2 = 0. 20 (GeV/c)2 and is consistent with the results from the pion electroproduction world data. It has been obtained using a completely different extraction method, and therefore represents a strong validation test of the world data model uncertainties. [ABSTRACT FROM AUTHOR]