arXiv subjects

D. Flay

Publications and source records attributed to D. Flay.

At least 37 records · Page 2Linked to original sources

arXiv2019

Measurement of the single-spin asymmetry $A_y^0$ in quasi-elastic $^3$He$^\uparrow$($e,e'n$) scattering at $0.4 < Q^2 < 1.0$ GeV$/c^2$

Due to the lack of free neutron targets, studies of the structure of the neutron are typically made by scattering electrons from either $^2$H or $^3$He targets. In order to extract useful neutron information from a $^3$He target, one must understand how the neutron in a $^3$He system differs from a free neutron by taking into account nuclear effects such as final state interactions and meson exchange currents. The target single spin asymmetry $A_y^0$ is an ideal probe of such effects, as any deviation from zero indicates effects beyond plane wave impulse approximation. New measurements of the target single spin asymmetry $A_y^0$ at $Q^2$ of 0.46 and 0.96 (GeV/$c)^2$ were made at Jefferson Lab using the quasi-elastic $^3\mathrm{He}^{\uparrow}(e,e'n)$ reaction. Our measured asymmetry decreases rapidly, from $>20\%$ at $Q^2=0.46$ (GeV/$c)^2$ to nearly zero at $Q^2=0.96$ (GeV$/c)^2$, demonstrating the fall-off of the reaction mechanism effects as $Q^2$ increases. We also observed a small $ε$-dependent increase in $A_y^0$ compared to previous measurements, particularly at moderate $Q^2$. This indicates that upcoming high $Q^2$ measurements from the Jefferson Lab 12 GeV program can cleanly probe neutron structure from polarized $^3$He using plane wave impulse approximation.

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arXiv2019

Virtual Compton Scattering measurements in the nucleon resonance region

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 $α_E = (5.3 \pm 0.6_{stat} \pm 1.3_{sys})~10^{-4} fm^3$ 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 $N \rightarrow Δ$ transition through the exploration of the $p(e,e'p)γ$ reaction. The new measurement gives $CMR = (-4.4 \pm 0.8_{stat} \pm 0.6_{sys})~\%$ 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.

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arXiv2018

Revealing Color Forces with Transverse Polarized Electron Scattering

The Spin Asymmetries of the Nucleon Experiment (SANE) measured two double spin asymmetries using a polarized proton target and polarized electron beam at two beam energies, 4.7 GeV and 5.9 GeV. A large-acceptance open-configuration detector package identified scattered electrons at 40$^{\circ}$ and covered a wide range in Bjorken $x$ ($0.3 < x < 0.8$). Proportional to an average color Lorentz force, the twist-3 matrix element, $\tilde{d}_2^p$, was extracted from the measured asymmetries at $Q^2$ values ranging from 2.0 to 6.0 GeV$^2$. The data display the opposite sign compared to most quark models, including the lattice QCD result, and an apparently unexpected scale dependence. Furthermore when combined with the neutron data in the same $Q^2$ range the results suggest a flavor independent average color Lorentz force.

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arXiv2018

Proton Form Factor Ratio, $μ_p G_E^p/G_M^p$ from Double Spin Asymmetry

The ratio of the electric and magnetic form factor of the proton, $μ_p G_E^p/G_M^p$, has been measured for elastic electron-proton scattering with polarized beam and target up to four-momentum transfer squared, $Q^2=5.66$ (GeV/c)$^2$ using the double spin asymmetry for target spin orientation aligned nearly perpendicular to the beam momentum direction. This measurement of $μ_p G_E^p/G_M^p$ agrees with the $Q^2$ dependence of previous recoil polarization data and reconfirms the discrepancy at high $Q^2$ between the Rosenbluth and the polarization-transfer method with a different measurement technique and systematic uncertainties uncorrelated to those of the recoil-polarization measurements. The form factor ratio at $Q^2$=2.06 (GeV/c)$^2$ has been measured as $μ_p G_E^p/G_M^p = 0.720 \pm 0.176_{stat} \pm 0.039_{sys}$, which is in agreement with an earlier measurement with the polarized target technique at similar kinematics. The form factor ratio at $Q^2$=5.66 (GeV/c)$^2$ has been determined as $μ_p G_E^p/G_M^p=0.244\pm0.353_{stat}\pm0.013_{sys}$, which represents the highest $Q^2$ reach with the double spin asymmetry with polarized target to date.

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arXiv2018

Search for three-nucleon short-range correlations in light nuclei

We present new data probing short-range correlations (SRCs) in nuclei through the measurement of electron scattering off high-momentum nucleons in nuclei. The inclusive 4He/3He cross section ratio is observed to be both x and Q2 independent for 1.5 < x < 2, confirming the dominance of two- nucleon (2N) short-range correlations (SRCs). For x > 2, our data do not support a previous claim of three-nucleon (3N) correlation dominance. While contributions beyond those from stationary 2N- SRCs are observed, our data show that isolating 3N-SRCs is more complicated than for 2N-SRCs.

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arXiv2018

Measurement of double-polarization asymmetries in the quasi-elastic $^3\vec{\mathrm{He}}(\vec{\mathrm{e}},\mathrm{e}'\mathrm{p})$ process

We report on a precise measurement of double-polarization asymmetries in electron-induced breakup of $^3\mathrm{He}$ proceeding to $\mathrm{pd}$ and $\mathrm{ppn}$ final states, performed in quasi-elastic kinematics at $Q^2 = 0.25\,(\mathrm{GeV}/c)^2$ for missing momenta up to $250\,\mathrm{MeV}/c$. These observables represent highly sensitive tools to investigate the electromagnetic and spin structure of $^3\mathrm{He}$ and the relative importance of two- and three-body effects involved in the breakup reaction dynamics. The measured asymmetries cannot be satisfactorily reproduced by state-of-the-art calculations of $^3\mathrm{He}$ unless their three-body segment is adjusted, indicating that the spin-dependent part of the nuclear interaction governing the three-body breakup process is much smaller than previously thought.

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arXiv2017

Design and Performance of the Spin Asymmetries of the Nucleon Experiment

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.

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arXiv2017

Extraction of the Neutron Electric Form Factor from Measurements of Inclusive Double Spin Asymmetries

$[Background]$ Measurements of the neutron charge form factor, $G^n_E$, are challenging due to the fact that the neutron has no net charge. In addition, measurements of the neutron form factors must use nuclear targets which require accurately accounting for nuclear effects. Extracting $G^n_E$ with different targets and techniques provides an important test of our handling of these effects. $[Purpose]$ The goal of the measurement was to use an inclusive asymmetry measurement technique to extract the neutron charge form factor at a four-momentum transfer of $1~(\rm{GeV/c})^2$. This technique has very different systematic uncertainties than traditional exclusive measurements and thus serves as an independent check of whether nuclear effects have been taken into account correctly. $[Method]$ The inclusive quasi-elastic reaction $^3\overrightarrow{\rm{He}}(\overrightarrow{e},e')$ was measured at Jefferson Lab. The neutron electric form factor, $G_E^n$, was extracted at $Q^2 = 0.98~(\rm{GeV/c})^2$ from ratios of electron-polarization asymmetries measured for two orthogonal target spin orientations. This $Q^2$ is high enough that the sensitivity to $G_E^n$ is not overwhelmed by the neutron magnetic contribution, and yet low enough that explicit neutron detection is not required to suppress pion production. $[Results]$ The neutron electric form factor, $G_E^n$, was determined to be $0.0414\pm0.0077\;{(stat)}\pm0.0022\;{(syst)}$; providing the first high precision inclusive extraction of the neutron's charge form factor. $[Conclusions]$ The use of the inclusive quasi-elastic $^3\overrightarrow{\rm{He}}(\overrightarrow{e},e')$ with a four-momentum transfer near $1~(\rm{GeV/c})^2$ has been used to provide a unique measurement of $G^n_E$. This new result provides a systematically independent validation of the exclusive extraction technique results.

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arXiv2017

A Glimpse of Gluons through Deeply Virtual Compton Scattering on the Proton

The proton is composed of quarks and gluons, bound by the most elusive mechanism of strong interaction called confinement. In this work, the dynamics of quarks and gluons are investigated using deeply virtual Compton scattering (DVCS): produced by a multi-GeV electron, a highly virtual photon scatters off the proton which subsequently radiates a high energy photon. Similarly to holography, measuring not only the magnitude but also the phase of the DVCS amplitude allows to perform 3D images of the internal structure of the proton. The phase is made accessible through the quantum-mechanical interference of DVCS with the Bethe-Heitler (BH) process, in which the final photon is emitted by the electron rather than the proton. We report herein the first full determination of the BH-DVCS interference by exploiting the distinct energy dependences of the DVCS and BH amplitudes. In the high energy regime where the scattering process is expected to occur off a single quark in the proton, these accurate measurements show an intriguing sensitivity to gluons, the carriers of the strong interaction.

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arXiv2017

Rosenbluth separation of the $π^0$ Electroproduction Cross Section off the Neutron

We report the first longitudinal/transverse separation of the deeply virtual exclusive $π^0$ electroproduction cross section off the neutron and coherent deuteron. The corresponding four structure functions $dσ_L/dt$, $dσ_T/dt$, $dσ_{LT}/dt$ and $dσ_{TT}/dt$ are extracted as a function of the momentum transfer to the recoil system at $Q^2$=1.75 GeV$^2$ and $x_B$=0.36. The $ed \to edπ^0$ cross sections are found compatible with the small values expected from theoretical models. The $en \to enπ^0$ cross sections show a dominance from the response to transversely polarized photons, and are in good agreement with calculations based on the transversity GPDs of the nucleon. By combining these results with previous measurements of $π^0$ electroproduction off the proton, we present a flavor decomposition of the $u$ and $d$ quark contributions to the cross section.

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arXiv2016

Rosenbluth separation of the $π^0$ electroproduction cross section

We present deeply virtual $π^0$ electroproduction cross-section measurements at $x_B$=0.36 and three different $Q^2$--values ranging from 1.5 to 2 GeV$^2$, obtained from experiment E07-007 that ran in the Hall A at Jefferson Lab. The Rosenbluth technique was used to separate the longitudinal and transverse responses. Results demonstrate that the cross section is dominated by its transverse component, and thus is far from the asymptotic limit predicted by perturbative Quantum Chromodynamics. An indication of a non-zero longitudinal contribution is provided by the interference term $σ_{LT}$ also measured. Results are compared with several models based on the leading twist approach of Generalized Parton Distributions (GPDs). In particular, a fair agreement is obtained with models where the scattering amplitude is described by a convolution of chiral-odd (transversity) GPDs of the nucleon with the twist-3 pion distribution amplitude. Therefore, neutral pion electroproduction may offer the exciting possibility of accessing transversity GPDs through experiment.

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arXiv2016

Measurements of $d_{2}^{n}$ and $A_{1}^{n}$: Probing the neutron spin structure

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 ($d_{2}^{n}$) was conducted. This quantity 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 spin structure functions $g_1$ and $g_2$ on $^{3}$He after nuclear corrections had been applied to these moments. The kinematics included two average $Q^{2}$ bins of $3.2$ GeV$^{2}$ and $4.3$ GeV$^{2}$, and Bjorken-$x$ $0.25 \leq x \leq 0.90$ covering the DIS and resonance regions. We found $d_2^n$ to be small and negative for $ = 3.2$ GeV$^{2}$, and smaller for $ = 4.3$ GeV$^{2}$, consistent with a lattice QCD calculation. The twist-4 matrix element $f_{2}^{n}$ was extracted by combining our $d_{2}^{n}$ with the world data on $Γ_{1}^{n} = \int_{0}^{1} g_{1}^{n} dx$. We found $f_{2}^{n}$ to be roughly an order of magnitude larger than $d_{2}^{n}$. Utilizing the extracted $d_{2}^{n}$ and $f_{2}^{n}$ data, we separated the color force into its electric and magnetic components, $F_{E}^{y,n}$ and $F_{B}^{y,n}$, and found them to be equal and opposite in magnitude, in agreement with instanton model predictions but not with those from QCD sum rules. Additionally, we have extracted the neutron virtual photon-nucleon asymmetry $A_{1}^{n}$, the structure function ratio $g_{1}^{n}/F_{1}^{n}$, and the quark ratios $(Δu + Δ\bar{u})/(u + \bar{u})$ and $(Δd + Δ\bar{d})/(d + \bar{d})$. These results were found to be consistent with DIS world data and with the prediction of the constituent quark model but at odds with those of perturbative QCD at large $x$.

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arXiv2016

Electroexcitation of the $Δ^{+}(1232)$ at low momentum transfer

We report on new p$(e,e^\prime p)π^\circ$ measurements at the $Δ^{+}(1232)$ resonance at the low momentum transfer region. The mesonic cloud dynamics is predicted to be dominant and rapidly changing in this kinematic region offering a test bed for chiral effective field theory calculations. The new data explore the low $Q^2$ dependence of the resonant quadrupole amplitudes while extending the measurements of the Coulomb quadrupole amplitude to the lowest momentum transfer ever reached. The results 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 reported measurements suggest that improvement is required to the theoretical calculations and provide valuable input that will allow their refinements.

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arXiv2015

Measurement of the Target-Normal Single-Spin Asymmetry in Quasi-Elastic Scattering from the Reaction $^3$He$^\uparrow(e,e^\prime)$

We report the first measurement of the target single-spin asymmetry, $A_y$, in quasi-elastic scattering from the inclusive reaction $^3$He$^{\uparrow}(e,e^\prime)$ on a $^3$He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A non-zero $A_y$ can arise from the interference between the one- and two-photon exchange processes which is sensitive to the details of the sub-structure of the nucleon. An experiment recently completed at Jefferson Lab yielded asymmetries with high statistical precision at $Q^{2}=$ 0.13, 0.46 and 0.97 GeV$^{2}$. These measurements demonstrate, for the first time, that the $^3$He asymmetry is clearly non-zero and negative with a statistical significance of (8-10)$σ$. Using measured proton-to-$^{3}$He cross-section ratios and the effective polarization approximation, neutron asymmetries of $-$(1-3)% were obtained. The neutron asymmetry at high $Q^2$ is related to moments of the Generalized Parton Distributions (GPDs). Our measured neutron asymmetry at $Q^2=0.97$ GeV$^2$ agrees well with a prediction based on two-photon exchange using a GPD model and thus provides a new, independent constraint on these distributions.

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arXiv2014

Measurement of Parity-Violating Asymmetry in Electron-Deuteron Inelastic Scattering

The parity-violating asymmetries between a longitudinally-polarized electron beam and an unpolarized deuterium target have been measured recently. The measurement covered two kinematic points in the deep inelastic scattering region and five in the nucleon resonance region. We provide here details of the experimental setup, data analysis, and results on all asymmetry measurements including parity-violating electron asymmetries and those of inclusive pion production and beam-normal asymmetries. The parity-violating deep-inelastic asymmetries were used to extract the electron-quark weak effective couplings, and the resonance asymmetries provided the first evidence for quark-hadron duality in electroweak observables. These electron asymmetries and their interpretation were published earlier, but are presented here in more detail.

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arXiv2014

Measurement of double-polarization asymmetries in the quasi-elastic $^3\vec{\mathrm{He}}(\vec{\mathrm{e}},\mathrm{e}'\mathrm{d})$ process

We present a precise measurement of double-polarization asymmetries in the $^3\vec{\mathrm{He}}(\vec{\mathrm{e}},\mathrm{e}'\mathrm{d})$ reaction. This particular process is a uniquely sensitive probe of hadron dynamics in $^3\mathrm{He}$ and the structure of the underlying electromagnetic currents. The measurements have been performed in and around quasi-elastic kinematics at $Q^2 = 0.25\,(\mathrm{GeV}/c)^2$ for missing momenta up to $270\,\mathrm{MeV}/c$. The asymmetries are in fair agreement with the state-of-the-art calculations in terms of their functional dependencies on $p_\mathrm{m}$ and $ω$, but are systematically offset. Beyond the region of the quasi-elastic peak, the discrepancies become even more pronounced. Thus, our measurements have been able to reveal deficiencies in the most sophisticated calculations of the three-body nuclear system, and indicate that further refinement in the treatment of their two- and/or three-body dynamics is required.

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arXiv2014

Probing the Repulsive Core of the Nucleon-Nucleon Interaction via the 4He(e,e'pN) Triple-Coincidence Reaction

We studied simultaneously the 4He(e,e'p), 4He(e,e'pp), and 4He(e,e'pn) reactions at Q^2=2 [GeV/c]2 and x_B>1, for a (e,e'p) missing-momentum range of 400 to 830 MeV/c. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A=2 system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum in a region where the nucleon-nucleon force is expected to change from predominantly tensor to repulsive. Neutron-proton pairs dominate the high-momentum tail of the nucleon momentum distributions, but their abundance is reduced as the nucleon momentum increases beyond ~500 MeV/c. The extracted fraction of proton-proton pairs is small and almost independent of the missing momentum in the range we studied. Our data are compared with ab-initio calculations of two-nucleon momentum distributions in 4He.

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arXiv2014

A Precision Measurement of the Neutron Twist-3 Matrix Element $d_2^n$: Probing Color Forces

Double-spin asymmetries and absolute cross sections were measured at large Bjorken $x$ (0.25 $ \le x \le $ 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 $g_2$ on $^3$He was determined with precision at large $x$, and the neutron twist-three matrix element $d_2^n$ was measured at $\left< Q^2\right>$ 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 $\left< Q^2\right> =$ 5 GeV$^2$/$c^2$. Combining $d_2^n$ and a newly extracted twist-four 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.

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