arXiv subjects

E. Piasetzky

Publications and source records attributed to E. Piasetzky.

At least 55 records · Page 3Linked to original sources

arXiv2020

Laser Calibration System for Time of Flight Scintillator Arrays

A laser calibration system was developed for monitoring and calibrating time of flight (TOF) scintillating detector arrays. The system includes setups for both small- and large-scale scintillator arrays. Following test-bench characterization, the laser system was recently commissioned in experimental Hall B at the Thomas Jefferson National Accelerator Facility for use on the new Backward Angle Neutron Detector (BAND) scintillator array. The system successfully provided time walk corrections, absolute time calibration, and TOF drift correction for the scintillators in BAND. This showcases the general applicability of the system for use on high-precision TOF detectors.

physics.ins-det↗

arXiv2020

Modified Structure of Protons and Neutrons in Correlated Pairs

The atomic nucleus is made of protons and neutrons (nucleons), that are themselves composed of quarks and gluons. Understanding how the quark-gluon structure of a nucleon bound in an atomic nucleus is modified by the surrounding nucleons is an outstanding challenge. Although evidence for such modification, known as the EMC effect, was first observed over 35 years ago, there is still no generally accepted explanation of its cause. Recent observations suggest that the EMC effect is related to close-proximity Short Range Correlated (SRC) nucleon pairs in nuclei. Here we report the first simultaneous, high-precision, measurements of the EMC effect and SRC abundances. We show that the EMC data can be explained by a universal modification of the structure of nucleons in neutron-proton (np) SRC pairs and present the first data-driven extraction of this universal modification function. This implies that, in heavier nuclei with many more neutrons than protons, each proton is more likely than each neutron to belong to an SRC pair and hence to have its quark structure distorted.

nucl-ex↗

arXiv2020

Neutron valence structure from nuclear deep inelastic scattering

Mechanisms of spin-flavor SU(6) symmetry breaking in Quantum Chromodynamics (QCD) are studied via an extraction of the free neutron structure function from a global analysis of deep inelastic scattering (DIS) data on the proton and on nuclei from $A = 2$ (deuterium) to 208 (lead). Modification of the structure function of nucleons bound in atomic nuclei (known as the EMC effect) are consistently accounted for within the framework of a universal modification of nucleons in short-range correlated (SRC) pairs. Our extracted neutron-to-proton structure function ratio $F_2^n/F_2^p$ becomes constant for $x_B \ge 0.6$, equalling $0.47 \pm 0.04$ as $x_B \rightarrow 1$, in agreement with theoretical predictions of perturbative QCD and the Dyson Schwinger equation, and in disagreement with predictions of the Scalar Diquark dominance model. We also predict $F_2^{^3\mathrm{He}}/F_2^{^3\mathrm{H}}$, recently measured, yet unpublished, by the MARATHON collaboration, the nuclear correction function that is needed to extract $F_2^n/F_2^p$ from $F_2^{^3\mathrm{He}}/F_2^{^3\mathrm{H}}$, and the theoretical uncertainty associated with this extraction.

nucl-th↗

arXiv2020

Generalized Contact Formalism Analysis of the $^4$He$(e,e'pN)$ Reaction

Measurements of short-range correlations in exclusive $^4$He$(e,e'pN)$ reactions are analyzed using the Generalized Contact Formalism (GCF). We consider both instant-form and light-cone formulations with both the AV18 and local N2LO(1.0) nucleon-nucleon ($NN$) potentials. We find that kinematic distributions, such as the reconstructed pair opening angle, recoil neutron momentum distribution, and pair center of mass motion, as well as the measured missing energy, missing mass distributions, are all well reproduced by GCF calculations. The missing momentum dependence of the measured $^4$He$(e,e'pN)$ / $^4$He$(e,e'p)$ cross-section ratios, sensitive to nature of the $NN$ interaction at short-distacnes, are also well reproduced by GCF calculations using either interaction and formulation. This gives credence to the GCF scale-separated factorized description of the short-distance many-body nuclear wave-function.

nucl-th↗

arXiv2020

Dispersive Corrections to the Born Approximation in Elastic Electron-Nucleus Scattering in the Intermediate Energy Regime

Measurements of elastic electron scattering data within the past decade have highlighted two-photon exchange contributions as a necessary ingredient in theoretical calculations to precisely evaluate hydrogen elastic scattering cross sections. This correction can modify the cross section at the few percent level. In contrast, dispersive effects can cause significantly larger changes from the Born approximation. The purpose of this experiment is to extract the carbon-12 elastic cross section around the first diffraction minimum, where the Born term contributions to the cross section are small to maximize the sensitivity to dispersive effects. The analysis uses the LEDEX data from the high resolution Jefferson Lab Hall A spectrometers to extract the cross sections near the first diffraction minimum of 12C at beam energies of 362 MeV and 685 MeV. The results are in very good agreement with previous world data, although with less precision. The average deviation from a static nuclear charge distribution expected from linear and quadratic fits indicate a 30.6% contribution of dispersive effects to the cross section at 1 GeV. The magnitude of the dispersive effects near the first diffraction minimum of 12C has been confirmed to be large with a strong energy dependence and could account for a large fraction of the magnitude for the observed quenching of the longitudinal nuclear response. These effects could also be important for nuclei radii extracted from parity-violating asymmetries measured near a diffraction minimum.

nucl-ex↗

arXiv2019

Comparing proton momentum distributions in $A=2$ and 3 nuclei via $^2$H $^3$H and $^3$He $(e, e'p)$ measurements

We report the first measurement of the $(e,e'p)$ reaction cross-section ratios for Helium-3 ($^3$He), Tritium ($^3$H), and Deuterium ($d$). The measurement covered a missing momentum range of $40 \le p_{miss} \le 550$ MeV$/c$, at large momentum transfer ($\langle Q^2 \rangle \approx 1.9$ (GeV$/c$)$^2$) and $x_B>1$, which minimized contributions from non quasi-elastic (QE) reaction mechanisms. The data is compared with plane-wave impulse approximation (PWIA) calculations using realistic spectral functions and momentum distributions. The measured and PWIA-calculated cross-section ratios for $^3$He$/d$ and $^3$H$/d$ extend to just above the typical nucleon Fermi-momentum ($k_F \approx 250$ MeV$/c$) and differ from each other by $\sim 20\%$, while for $^3$He/$^3$H they agree within the measurement accuracy of about 3\%. At momenta above $k_F$, the measured $^3$He/$^3$H ratios differ from the calculation by $20\% - 50\%$. Final state interaction (FSI) calculations using the generalized Eikonal Approximation indicate that FSI should change the $^3$He/$^3$H cross-section ratio for this measurement by less than 5\%. If these calculations are correct, then the differences at large missing momenta between the $^3$He/$^3$H experimental and calculated ratios could be due to the underlying $NN$ interaction, and thus could provide new constraints on the previously loosely-constrained short-distance parts of the $NN$ interaction.

nucl-ex↗

arXiv2019

Measurement of Nuclear Transparency Ratios for Protons and Neutrons

This paper presents, for the first time, measurements of neutron transparency ratios for nuclei relative to C measured using the (e,e'n) reaction, spanning measured neutron momenta of 1.4 to 2.4 GeV/c. The transparency ratios were extracted in two kinematical regions, corresponding to knockout of mean-field nucleons and to the breakup of Short-Range Correlated nucleon pairs. The extracted neutron transparency ratios are consistent with each other for the two measured kinematical regions and agree with the proton transparencies extracted from new and previous (e,e'p) measurements, including those from neutron-rich nuclei such as lead. The data also agree with and confirm the Glauber approximation that is commonly used to interpret experimental data. The nuclear-mass-dependence of the extracted transparencies scales as A^α with α = -0.289 {\pm} 0.007, which is consistent with nuclear-surface dominance of the reactions.

nucl-ex↗

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.

nucl-ex↗

arXiv2019

Comment on "Searching for flavor dependence in nuclear quark behavior"

Weinstein, et. al [1] [PRL 106, 052301 (2011)] and Hen, et. al [2] [PRC 85, 047301 (2012)] observed a correlation between the EMC effect and the amount of short range correlated (SRC) pairs in nuclei which implies that quark distributions are different in SRC pairs as compared with free nucleons. Schmookler, et. al [3] [Nature 566, 354 (2019)] bolstered this by showing that the EMC data can be explained by a universal modification of the structure of nucleons in neutron-proton SRC pairs and presented the first data-driven extraction of this universal modification function (UMF). Arrington and Fomin [4] [arxiv 1903.12535] attempt to gain insight into the correlation between the EMC effect and SRCs by distinguishing between correlated nucleon pairs at high-virtuality (HV) vs. high local-density (LD). However, there is an inconsistency in their derivations of the UMFs, FLD univ and FHV , causing a non-physical difference between them for asymmetric nuclei. In addition, the univ combinatorial scaling they used to extract high-LD np, pp and nn pairs from measured HV np pairs is contradicted by realistic ab-initio Quantum Monte-Carlo (QMC) calculations.

nucl-ex↗

arXiv2019

The influence of Fermi motion on the comparison of the polarization transfer to a proton in elastic $\vec ep$ and quasi-elastic $\vec eA$ scattering

A comparison between polarization-transfer to a bound proton in quasi-free kinematics by the A$(\vec{e},e'\vec p)$ knockout reaction and that in elastic scattering off a free proton can provide information on the characteristics of the bound proton. In the past the reported measurements have been compared to those of a free proton with zero initial momentum. We introduce, for the first time, expressions for the polarization-transfer components when the proton is initially in motion and compare them to the $^2$H data measured at the Mainz Microtron (MAMI). We show the ratios of the transverse ($P_x$) and longitudinal ($P_z$) components of the polarization transfer in $^2\textrm{H}(\vec{e},e'\vec p)\textrm{n}$, to those of elastic scattering off a "moving proton", assuming the proton's initial (Fermi) momentum equals the negative missing momentum in the measured reaction. We found that the correction due to the proton motion is up to 20\% at high missing momentum. However the effect on the double ratio $\frac{(P_x/P_z)^A}{(P_x/P_z)^{^1\!\textrm{H}}}$ is largely canceled out, as shown for both $^2$H and $^{12}$C data. This implies that the kinematics is not the primary cause for the deviations between quasi-elastic and elastic scattering reported previously.

nucl-ex↗

arXiv2019

Direct Observation of Proton-Neutron Short-Range Correlation Dominance in Heavy Nuclei

We measured the triple coincidence A(e,e'np) and A(e,e'pp) reactions on carbon, aluminum, iron, and lead targets at Q2 > 1.5 (GeV/c)2, xB > 1.1 and missing momentum > 400 MeV/c. This was the first direct measurement of both proton-proton (pp) and neutron-proton (np) short-range correlated (SRC) pair knockout from heavy asymmetric nuclei. For all measured nuclei, the average proton-proton (pp) to neutron-proton (np) reduced cross-section ratio is about 6%, in agreement with previous indirect measurements. Correcting for Single-Charge Exchange effects decreased the SRC pairs ratio to ~ 3%, which is lower than previous results. Comparisons to theoretical Generalized Contact Formalism (GCF) cross-section calculations show good agreement using both phenomenological and chiral nucleon-nucleon potentials, favoring a lower pp to np pair ratio. The ability of the GCF calculation to describe the experimental data using either phenomenological or chiral potentials suggests possible reduction of scale- and scheme-dependence in cross section ratios. Our results also support the high-resolution description of high-momentum states being predominantly due to nucleons in SRC pairs.

nucl-ex↗

arXiv2019

Can Long-Range Nuclear Properties Be Influenced By Short Range Interactions? A chiral dynamics estimate

Recent experiments and many-body calculations indicate that approximately 20\% of the nucleons in medium and heavy nuclei ($A\geq12$) are part of short-range correlated (SRC) primarily neutron-proton ($np$) pairs. We find that using chiral dynamics to account for the formation of $np$ pairs due to the effects of iterated and irreducible two-pion exchange leads to values consistent with the 20\% level. We further apply chiral dynamics to study how these correlations influence the calculations of nuclear charge radii, that traditionally truncate their effect, to find that they are capable of introducing non-negligible effects.

nucl-th↗

arXiv2018

Technical Supplement to "Polarization Transfer Observables in Elastic Electron-Proton Scattering at Q$^2$ = 2.5, 5.2, 6.8, and 8.5 GeV$^2$"

The GEp-III and GEp-2$γ$ experiments, carried out in Jefferson Lab's Hall C from 2007-2008, consisted of measurements of polarization transfer in elastic electron-proton scattering at momentum transfers of $Q^2 = 2.5, 5.2, 6.8,$ and $8.54$ GeV$^2$. These measurements were carried out to improve knowledge of the proton electromagnetic form factor ratio $R = μ_p G_E^p/G_M^p$ at large values of $Q^2$ and to search for effects beyond the Born approximation in polarization transfer observables at $Q^2 = 2.5$ GeV$^2$. The final results of both experiments were reported in a recent archival publication. A full reanalysis of the data from both experiments was carried out in order to reduce the systematic and, for the GEp-2$γ$ experiment, statistical uncertainties. This technical note provides additional details of the final analysis omitted from the main publication, including the final evaluation of the systematic uncertainties.

nucl-ex↗

arXiv2018

Polarization Transfer Observables in Elastic Electron Proton Scattering at $Q^2 = $2.5, 5.2, 6.8, and 8.5 GeV$^2$

The GEp-III and GEp-2$γ$ experiments were carried out in Jefferson Lab's (JLab's) Hall C from 2007-2008, to extend the knowledge of $G_E^p/G_M^p$ to the highest practically achievable $Q^2$ and to search for effects beyond the Born approximation in polarization transfer observables of elastic $\vec{e}p$ scattering. This article reports an expanded description of the common experimental apparatus and data analysis procedure, and the results of a final reanalysis of the data from both experiments, including the previously unpublished results of the full-acceptance data of the GEp-2$γ$ experiment. The Hall C High Momentum Spectrometer detected and measured the polarization of protons recoiling elastically from collisions of JLab's polarized electron beam with a liquid hydrogen target. A large-acceptance electromagnetic calorimeter detected the elastically scattered electrons in coincidence to suppress inelastic backgrounds. The final GEp-III data are largely unchanged relative to the originally published results. The statistical uncertainties of the final GEp-2$γ$ data are significantly reduced at $ε= 0.632$ and $0.783$ relative to the original publication. The decrease with $Q^2$ of $G_E^p/G_M^p$ continues to $Q^2 = 8.5$ GeV$^2$, but at a slowing rate relative to the approximately linear decrease observed in earlier Hall A measurements. At $Q^2 = 2.5$ GeV$^2$, the proton form factor ratio $G_E^p/G_M^p$ shows no statistically significant $ε$-dependence, as expected in the Born approximation. The ratio $P_\ell/P_\ell^{Born}$ of the longitudinal polarization transfer component to its Born value shows an enhancement of roughly 1.4\% at $ε= 0.783$ relative to $ε= 0.149$, with $\approx 1.9σ$ significance based on the total uncertainty, implying a similar effect in the transverse component $P_t$ that cancels in the ratio $R$.

nucl-ex↗

arXiv2018

High-resolution hypernuclear spectroscopy at Jefferson Lab, Hall A

The experiment E94-107 in Hall A at Jefferson Lab started a systematic study of high resolution hypernuclear spectroscopy in the 0p-shell region of nuclei such as the hypernuclei produced in electroproduction on 9Be, 12C and 16O targets. In order to increase counting rates and provide unambiguous kaon identification two superconducting septum magnets and a ring-imaging Cherenkov detector were added to the Hall A standard equipment. The high-quality beam, the good spectrometers and the new experimental devices allowed us to obtain very good results. For the first time, measurable strength with sub-MeV energy resolution was observed for the core-excited states of Lambda 12B. A high-quality Lambda 16N hypernuclear spectrum was likewise obtained. A first measurement of the Lambda binding energy for Lambda 16N, calibrated against the elementary reaction on hydrogen, was obtained with high precision, 13.76 +/- 0.16 MeV. Similarly, the first Lambda 9Li hypernuclear spectrum shows general agreement with theory (distorted-wave impulse approximation with the SLA and BS3 electroproduction models and shell-model wave functions). Some disagreement exists with respect to the relative strength of the states making up the first multiplet. A Lambda separation energy of 8.36 MeV was obtained, in agreement with previous results. It has been shown that the electroproduction of hypernuclei can provide information complementary to that obtained with hadronic probes and the gamma-ray spectroscopy technique.

nucl-ex↗

arXiv2018

The center of mass motion of short-range correlated nucleon pairs studied via the A(e,e'pp) reaction

Short-Range Correlated (SRC) nucleon pairs are a vital part of the nucleus, accounting for almost all nucleons with momentum greater than the Fermi momentum (kF). A fundamental characteristic of SRC pairs is having large relative momenta as compared to kF, and smaller center-of-mass (c.m.) which indicates a small separation distance between the nucleons in the pair. Determining the c.m. momentum distribution of SRC pairs is essential for understanding their formation process. We report here on the extraction of the c.m. motion of proton-proton (pp) SRC pairs in Carbon and, for the first time in heavier and ansymetric nuclei: aluminum, iron, and lead, from measurements of the A(e,e'pp) reaction. We find that the pair c.m. motion for these nuclei can be described by a three-dimensional Gaussian with a narrow width ranging from 140 to 170 MeV/c, approximately consistent with the sum of two mean-field nucleon momenta. Comparison with calculations appears to show that the SRC pairs are formed from mean-field nucleons in specific quantum states.

nucl-ex↗

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.

nucl-ex↗

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.

nucl-ex↗