nan Nuruzzaman

Measurements of parity-violating asymmetries in electron-deuteron scattering in the nucleon resonance region.

We report on parity-violating asymmetries in the nucleon resonance region measured using inclusive inelastic scattering of 5-6 GeV longitudinally polarized electrons off an unpolarized deuterium target. These results are the first parity-violating asymmetry data in the resonance region beyond the Δ(1232). They provide a verification of quark-hadron duality-the equivalence of the quark- and hadron-based pictures of the nucleon-at the (10-15)% level in this electroweak observable, which is dominated by contributions from the nucleon electroweak γZ interference structure functions. In addition, the results provide constraints on nucleon resonance models relevant for calculating background corrections to elastic parity-violating electron scattering measurements.

Precision Measurement of the Neutron Twist-3 Matrix Element d^n_2: Probing Color Forces

Double-spin asymmetries and absolute cross sections were measured at large Bjorken x  (0.25≤x≤0.90), in both the deep-inelastic and resonance regions, by scattering longitudinally polarized electrons at beam energies of 4.7 and 5.9 GeV from a transversely and longitudinally polarized (3)He target. In this dedicated experiment, the spin structure function g(2)((3)He) was determined with precision at large x, and the neutron twist-3 matrix element d(2)(n) was measured at ⟨Q(2)⟩ of 3.21 and 4.32  GeV(2)/c(2), with an absolute precision of about 10(-5). Our results are found to be in agreement with lattice QCD calculations and resolve the disagreement found with previous data at ⟨Q(2)⟩=5  GeV(2)/c(2). Combining d(2)(n) and a newly extracted twist-4 matrix element f(2)(n), the average neutron color electric and magnetic forces were extracted and found to be of opposite sign and about 30  MeV/fm in magnitude.

Precision Measurements of

We have performed precision measurements of the double-spin virtual-photon asymmetry A_1 on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized ^3He target. Our data cover a wide kinematic range 0.277 ≤ x ≤0.548 at an average Q^2 value of 3.078 (GeV/c)^2, doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with a previous observation of an A_1^n zero crossing near x=0.5. We find no evidence of a transition to a positive slope in (Δd+Δd)/(d+d) up to x=0.548x=0.548.

A_1^n

We report on new p(e,e′p)π∘p(e,e′p)π∘ measurements at the Δ+(1232)Δ+(1232) resonance at the low momentum transfer region, where the mesonic cloud dynamics is predicted to be dominant and rapidly changing, offering a test bed for chiral effective field theory calculations. The new data explore the Q2Q2 dependence of the resonant quadrupole amplitudes and for the first time indicate that the Electric and the Coulomb quadrupole amplitudes converge as Q2→0Q2→0. The measurements of the Coulomb quadrupole amplitude have been extended to the lowest momentum transfer ever reached, and suggest that more than half of its magnitude is attributed to the mesonic cloud in this region. The new data disagree with predictions of constituent quark models and are in reasonable agreement with dynamical calculations that include pion cloud effects, chiral effective field theory and lattice calculations. The measurements indicate that improvement is required to the theoretical calculations and provide valuable input that will allow their refinements.

in the Deep Inelastic Regime

We report on the results of the E06-014 experiment performed at Jefferson Lab in Hall A, where a precision measurement of the twist-3 matrix element d_2 of the neutron (d^n_2) was conducted. The quantity dn_2 represents the average color Lorentz force a struck quark experiences in a deep inelastic electron scattering event off a neutron due to its interaction with the hadronizing remnants. This color force was determined from a linear combination of the third moments of the ^3He spin structure functions, g_1 and g_2, after nuclear corrections had been applied to these moments. The structure functions were obtained from a measurement of the unpolarized cross section and of double-spin asymmetries in the scattering of a longitudinally polarized electron beam from a transversely and a longitudinally polarized ^3He target. The measurement kinematics included two average Q^2 bins of 3.2  GeV^2 and 4.3  GeV^2, and Bjorken-x 0.25≤ x ≤0.90 covering the deep inelastic and resonance regions. We have found that d^n_2 is small and negative for ⟨Q^2⟩=3.2  GeV^2, and even smaller for ⟨Q^2⟩=4.3  GeV^2, consistent with the results of a lattice QCD calculation. The twist-4 matrix element f^n_2 was extracted by combining our measured d^n_2 with the world data on the first moment in x of g^n_1, Γ^n_1. We found f^n_2 to be roughly an order of magnitude larger than dn2. Utilizing the extracted d^n_2 and f^n_2 data, we separated the Lorentz color force into its electric and magnetic components, F^(y,n)_E and F^(y,n)_B, and found them to be equal and opposite in magnitude, in agreement with the predictions from an instanton model but not with those from QCD sum rules. Furthermore, using the measured double-spin asymmetries, we have extracted the virtual photon-nucleon asymmetry on the neutron A^n_1, the structure function ratio g^n_1/F^n_1, and the quark ratios (Δu+Δu)/(u+u) and (Δd+Δd)/(d+d). These results were found to be consistent with deep-inelastic scattering world data and with the prediction of the constituent quark model but at odds with the perturbative quantum chromodynamics predictions at large x.

Electroexcitation of the Δ+(1232) at low momentum transfer

Large experimental programmes in the fields of nuclear and particle physics search for evidence of physics beyond that explained by current theories. The observation of the Higgs boson completed the set of particles predicted by the standard model, which currently provides the best description of fundamental particles and forces. However, this theory’s limitations include a failure to predict fundamental parameters, such as the mass of the Higgs boson, and the inability to account for dark matter and energy, gravity, and the matter–antimatter asymmetry in the Universe, among other phenomena. These limitations have inspired searches for physics beyond the standard model in the post-Higgs era through the direct production of additional particles at high-energy accelerators, which have so far been unsuccessful. Examples include searches for supersymmetric particles, which connect bosons (integer-spin particles) with fermions (half-integer-spin particles), and for leptoquarks, which mix the fundamental quarks with leptons. Alternatively, indirect searches using precise measurements of well predicted standard-model observables allow highly targeted alternative tests for physics beyond the standard model because they can reach mass and energy scales beyond those directly accessible by today’s high-energy accelerators. Such an indirect search aims to determine the weak charge of the proton, which defines the strength of the proton’s interaction with other particles via the well known neutral electroweak force. Because parity symmetry (invariance under the spatial inversion (x, y, z) → (−x, −y, −z)) is violated only in the weak interaction, it provides a tool with which to isolate the weak interaction and thus to measure the proton’s weak charge1. Here we report the value 0.0719 ± 0.0045, where the uncertainty is one standard deviation, derived from our measured parity-violating asymmetry in the scattering of polarized electrons on protons, which is −226.5 ± 9.3 parts per billion (the uncertainty is one standard deviation). Our value for the proton’s weak charge is in excellent agreement with the standard model2 and sets multi-teraelectronvolt-scale constraints on any semi-leptonic parity-violating physics not described within the standard model. Our results show that precision parity-violating measurements enable searches for physics beyond the standard model that can compete with direct searches at high-energy accelerators and, together with astronomical observations, can provide fertile approaches to probing higher mass scales. Measurement of the asymmetry in the parity-violating scattering of polarized electrons on protons gives the weak charge of the proton as 0.0719 ± 0.0045, in agreement with the standard model.Large experimental programmes in the fields of nuclear and particle physics search for evidence of physics beyond that explained by current theories. The observation of the Higgs boson completed the set of particles predicted by the standard model, which currently provides the best description of fundamental particles and forces. However, this theory’s limitations include a failure to predict fundamental parameters, such as the mass of the Higgs boson, and the inability to account for dark matter and energy, gravity, and the matter–antimatter asymmetry in the Universe, among other phenomena. These limitations have inspired searches for physics beyond the standard model in the post-Higgs era through the direct production of additional particles at high-energy accelerators, which have so far been unsuccessful. Examples include searches for supersymmetric particles, which connect bosons (integer-spin particles) with fermions (half-integer-spin particles), and for leptoquarks, which mix the fundamental quarks with leptons. Alternatively, indirect searches using precise measurements of well predicted standard-model observables allow highly targeted alternative tests for physics beyond the standard model because they can reach mass and energy scales beyond those directly accessible by today’s high-energy accelerators. Such an indirect search aims to determine the weak charge of the proton, which defines the strength of the proton’s interaction with other particles via the well known neutral electroweak force. Because parity symmetry (invariance under the spatial inversion (x, y, z) → (−x, −y, −z)) is violated only in the weak interaction, it provides a tool with which to isolate the weak interaction and thus to measure the proton’s weak charge1. Here we report the value 0.0719 ± 0.0045, where the uncertainty is one standard deviation, derived from our measured parity-violating asymmetry in the scattering of polarized electrons on protons, which is −226.5 ± 9.3 parts per billion (the uncertainty is one standard deviation). Our value for the proton’s weak charge is in excellent agreement with the standard model2 and sets multi-teraelectronvolt-scale constraints on any semi-leptonic parity-violating physics not described within the standard model. Our results show that precision parity-violating measurements enable searches for physics beyond the standard model that can compete with direct searches at high-energy accelerators and, together with astronomical observations, can provide fertile approaches to probing higher mass scales.Measurement of the asymmetry in the parity-violating scattering of polarized electrons on protons gives the weak charge of the proton as 0.0719 ± 0.0045, in agreement with the standard model.

Measurements of

Spectroscopy of a

d_{2}^{n}

^{10}_{\Lambda}

and

Be hypernucleus was carried out at JLab Hall C using the

A_{1}^{n}

(e,e^{\prime}K^{+})