arXiv subjects

E. Piasetzky

Publications and source records attributed to E. Piasetzky.

At least 37 records · Page 2Linked to original sources

arXiv2021

Search for a bound di-neutron by comparing $^3$He(e,e'p)d and $^3$H(e,e'p)X measurements

We report on a search for a bound di-neutron by comparing electron-induced proton-knockout $(e,e'p)$ measurements from Helium-3 ($^3$He) and Tritium ($^3$H). The measurements were performed at Jefferson Lab Hall A with a 4.326 GeV electron beam, and kinematics of large momentum transfer $Q^2 \approx 1.9$ (GeV/$c$)$^2$ and $x_B>1$, to minimize contributions from non quasi-elastic (QE) reaction mechanisms. Analyzing the measured $^3$He missing mass ($M_{miss}$) and missing energy ($E_{miss}$) distributions, we can distinguish the two-body break-up reaction, in which the residual proton-neutron system remains bound as a deuteron. In the $^3$H mirror case, under the exact same kinematic conditions, we do not identify a signature for a bound di-neutron with similar binding energy to that of the deuteron. We calculate exclusion limits as a function of the di-neutron binding energy and find that, for binding equivalent to the deuteron, the two-body break-up cross section on $^3$H is less than 0.9% of that on $^3$He in the measured kinematics at the 95% confidence level.

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arXiv2021

Characterization of Muon and Electron Beams in the Paul Scherrer Institute PiM1 Channel for the MUSE Experiment

The MUon Scattering Experiment, MUSE, at the Paul Scherrer Institute, Switzerland, investigates the proton charge radius puzzle, lepton universality, and two-photon exchange, via simultaneous measurements of elastic muon-proton and electron-proton scattering. The experiment uses the PiM1 secondary beam channel, which was designed for high precision pion scattering measurements. We review the properties of the beam line established for pions. We discuss the production processes that generate the electron and muon beams, and the simulations of these processes. Simulations of the $π$/$μ$/$e$ beams through the channel using TURTLE and G4beamline are compared. The G4beamline simulation is then compared to several experimental measurements of the channel, including the momentum dispersion at the IFP and target, the shape of the beam spot at the target, and timing measurements that allow the beam momenta to be determined. We conclude that the PiM1 channel can be used for high precision $π$, $μ$, and $e$ scattering.

physics.ins-det↗

arXiv2021

$^{12}$C(e,e'pN) Measurements of Short Range Correlations in the Tensor-to-Scalar Interaction Transition Region

High-momentum configurations of nucleon pairs at short-distance are probed using measurements of the $^{12}$C$(e,e'p)$ and $^{12}$C$(e,e'pN)$ reactions (where $N$ is either $n$ or $p$), at high-$Q^2$ and $x_B>1.1$. The data span a missing-momentum range of 300--1000 MeV/c and are predominantly sensitive to the transition region of the strong nuclear interaction from a Tensor to Scalar interaction. The data are well reproduced by theoretical calculations using the Generalized Contact Formalism with both chiral and phenomenological nucleon-nucleon ($NN$) interaction models. This agreement suggests that the measured high missing-momentum protons up to $1000$ MeV/c predominantly belong to short-ranged correlated (SRC) pairs. The measured $^{12}$C$(e,e'pN)$ / $^{12}$C$(e,e'p)$ and $^{12}$C$(e,e'pp)$ / $^{12}$C$(e,e'pn)$ cross-section ratios are consistent with a decrease in the fraction of proton-neutron SRC pairs and increase in the fraction of proton-proton SRC pairs with increasing missing momentum. This confirms the transition from an isospin-dependent tensor $NN$ interaction at $\sim 400$ MeV/c to an isospin-independent scalar interaction at high-momentum around $\sim 800$ MeV/c as predicted by theoretical calculation.

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arXiv2021

Measurement of the Nucleon $F^n_2/F^p_2$ Structure Function Ratio by the Jefferson Lab MARATHON Tritium/Helium-3 Deep Inelastic Scattering Experiment

The ratio of the nucleon $F_2$ structure functions, $F_2^n/F_2^p$, is determined by the MARATHON experiment from measurements of deep inelastic scattering of electrons from $^3$H and $^3$He nuclei. The experiment was performed in the Hall A Facility of Jefferson Lab and used two high resolution spectrometers for electron detection, and a cryogenic target system which included a low-activity tritium cell. The data analysis used a novel technique exploiting the mirror symmetry of the two nuclei, which essentially eliminates many theoretical uncertainties in the extraction of the ratio. The results, which cover the Bjorken scaling variable range $0.19 < x < 0.83$, represent a significant improvement compared to previous SLAC and Jefferson Lab measurements for the ratio. They are compared to recent theoretical calculations and empirical determinations of the $F_2^n/F_2^p$ ratio.

hep-ex↗

arXiv2021

Unperturbed inverse kinematics nucleon knockout measurements with a 48 GeV/c carbon beam

From superconductors to atomic nuclei, strongly-interacting many-body systems are ubiquitous in nature. Measuring the microscopic structure of such systems is a formidable challenge, often met by particle knockout scattering experiments. While such measurements are fundamental for mapping the structure of atomic nuclei, their interpretation is often challenged by quantum mechanical initial- and final-state interactions (ISI/FSI) of the incoming and scattered particles. Here we overcome this fundamental limitation by measuring the quasi-free scattering of 48 GeV/c 12C ions from hydrogen. The distribution of single protons is studied by detecting two protons at large angles in coincidence with an intact 11B nucleus. The 11B detection is shown to select the transparent part of the reaction and exclude the otherwise large ISI/FSI that would break the 11B apart. By further detecting residual 10B and 10Be nuclei, we also identified short-range correlated (SRC) nucleon-nucleon pairs, and provide direct experimental evidence for the separation of the pair wave-function from that of the residual many-body nuclear system. All measured reactions are well described by theoretical calculations that do not contain ISI/FSI distortions. Our results thus showcase a new ability to study the short-distance structure of short-lived radioactive atomic nuclei at the forthcoming FAIR and FRIB facilities. These studies will be pivotal for developing a ground-breaking microscopic understanding of the structure and properties of nuclei far from stability and the formation of visible matter in the universe.

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arXiv2021

Nucleon off-shell structure and the free neutron valence structure from A=3 inclusive electron scattering measurements

Understanding the differences between the distribution of quarks bound in protons and neutrons is key for constraining the mechanisms of SU(6) spin-flavor symmetry breaking in Quantum Chromodynamics (QCD). While vast amounts of proton structure measurements were done, data on the structure of the neutron is much more spars as experiments typically extract the structure of neutrons from measurements of light atomic nuclei using model-dependent corrections for nuclear effects. Recently the MARATHON collaboration performed such an extraction by measuring inclusive deep-inelastic electron-scattering on helium-3 and tritium mirror nuclei where nuclear effects are expected to be similar and thus be suppressed in the helium-3 to tritium ratio. Here we evaluate the model dependence of this extraction by examining a wide range of models including the effect of using instant-form and light-cone nuclear wave functions and several different parameterizations of nucleon modification effects, including those with and without isospin dependence. We find that, while the data cannot differentiate among the different models of nuclear structure and nucleon modification, they consistently prefer a neutron-to-proton structure function ratio of at $x_B \rightarrow 1$ of $\sim 0.4$ with a typical uncertainty ($1σ$) of $\sim0.05$ and $\sim0.10$ for isospin-independent and isospin-dependent modification models, respectively. While strongly favoring SU(6) symmetry breaking models based on perturbative QCD and the Schwinger-Dyson equation calculation, the MARATHON data do not completely rule out the scalar di-quark models if an isospin-dependent modification exist.

hep-ph↗

arXiv2021

Inclusive Electron Scattering And The GENIE Neutrino Event Generator

The extraction of neutrino mixing parameters from accelerator-based neutrino oscillation experiments relies on proper modeling of neutrino-nucleus scattering processes using neutrino-interaction event generators. Experimental tests of these generators are difficult due to the broad range of neutrino energies produced in accelerator-based beams and the low statistics of current experiments. Here we overcome these difficulties by exploiting the similarity of neutrino and electron interactions with nuclei to test neutrino event generators using high-precision inclusive electron scattering data. To this end, we revised the electron-scattering mode of the GENIE event generator ($e$-GENIE) to include electron-nucleus bremsstrahlung radiation effects and to use, when relevant, the exact same physics models and model parameters, as the standard neutrino-scattering version. We also implemented new models for quasielastic (QE) scattering and meson exchange currents (MEC) based on the theory-inspired SuSAv2 approach. Comparing the new $e$-GENIE predictions with inclusive electron scattering data, we find an overall adequate description of the data in the QE- and MEC-dominated lower energy transfer regime, especially when using the SuSAv2 models. Higher energy transfer-interactions, which are dominated by resonance production, are still not well modeled by $e$-GENIE.

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arXiv2021

Extracing the number of short-range corerlated nucleon pairs from inclusive electron scattering data

The extraction of the relative abundances of short-range correlated (SRC) nucleon pairs from inclusive electron scattering is studied using the generalized contact formalism (GCF) with several nuclear interaction models. GCF calculations can reproduce the observed scaling of the cross-section ratios for nuclei relative to deuterium at high-$x_B$ and large-$Q^2$, $a_2=(σ_A/A)/(σ_d/2)$. In the non-relativistic instant-form formulation, the calculation is very sensitive to the model parameters and only reproduces the data using parameters that are inconsistent with ab-initio many-body calculations. Using a light-cone GCF formulation significantly decreases this sensitivity and improves the agreement with ab-initio calculations. The ratio of similar mass isotopes, such as $^{40}$Ca and $^{48}$Ca, should be sensitive to the nuclear asymmetry dependence of SRCs, but is found to also be sensitive to low-energy nuclear structure. Thus the empirical association of SRC pair abundances with the measured $a_2$ values is only accurate to about $20\%$. Improving this will require cross-section calculations that reproduce the data while properly accounting for both nuclear structure and relativistic effects.

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arXiv2021

Scale and Scheme Independence and Position-Momentum Equivalence of Nuclear Short-Range Correlations

Ab-initio Quantum Monte Carlo (QMC) calculations of nuclei from deuterium to 40Ca, obtained using four different phenomenological and local chiral nuclear potentials, are analyzed using the Generalized Contact Formalism (GCF). We extract spin- and isospin-dependent "nuclear contact terms" for each interaction in both coordinate and momentum space. The extracted contact terms, that count the number of short-range correlated (SRC) pairs with different quantum numbers, are dependent on the nuclear interaction model used in the QMC calculation. However, the ratios of contact terms for a nucleus A to deuterium (for spin-1 pn pairs) or to 4He (for all NN pairs) are independent of the nuclear interaction model and are the same for both short-distance and high-momentum pairs. This implies that the relative abundance of short-range pairs in the nucleus is a long-range (mean-field) quantity that is insensitive to the short-distance nature of the nuclear force. Measurements of exclusive (e,e'NN) pair breakup processes are instead more sensitive to short-range dynamics

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arXiv2020

Novel observation of isospin structure of short-range correlations in calcium isotopes

Short Range Correlations (SRCs) have been identified as being responsible for the high momentum tail of the nucleon momentum distribution, n(k). Hard, short-range interactions of nucleon pairs generate the high momentum tail and imprint a universal character on n(k) for all nuclei at large momentum. Triple coincidence experiments have shown a strong dominance of np pairs, but these measurements involve large final state interactions. This paper presents the results from Jefferson Lab experiment E08014 which measured inclusive electron scattering cross-section from Ca isotopes. By comparing the inclusive cross section from 48Ca to 40Ca in a kinematic region dominated by SRCs we provide a new way to study the isospin structure of SRCs.

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arXiv2020

Comparison of recoil polarization in the $^{12}{\rm C}(\vec{e},{e}'\vec{p})$ process for protons extracted from $s$ and $p$ shell

We present first measurements of the double ratio of the polarization transfer components $(P^{\prime}_{\!x} \!/ P^{\prime}_{\!z} )_p/ (P^{\prime}_{\!x} \!/ P^{\prime}_{\!z} )_s$ for knock-out protons from $s$ and $p$ shells in $^{12}{\rm C}$ measured by the $^{12}{\rm C}(\vec{e},{e}'\vec{p}\,)$ reaction in quasi-elastic kinematics. The data are compared to theoretical predictions in relativistic distorted-wave impulse approximation. Our results show that differences between $s$- and $p$-shell protons, observed when compared at the same initial momentum (missing momentum) largely disappear when the comparison is done at the same proton virtuality. We observe no density-dependent medium modifications for protons from $s$ and $p$ shells with the same virtuality in spite of the large differences in the respective nuclear densities.

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arXiv2020

Probing the core of the strong nuclear interaction

The strong nuclear interaction between nucleons (protons and neutrons) is the effective force that holds the atomic nucleus together. This force stems from fundamental interactions between quarks and gluons (the constituents of nucleons) that are described by the equations of Quantum Chromodynamics (QCD). However, as these equations cannot be solved directly, physicists resort to describing nuclear interactions using effective models that are well constrained at typical inter-nucleon distances in nuclei but not at shorter distances. This limits our ability to describe high-density nuclear matter such as in the cores of neutron stars. Here we use high-energy electron scattering measurements that isolate nucleon pairs in short-distance, high-momentum configurations thereby accessing a kinematical regime that has not been previously explored by experiments, corresponding to relative momenta above 400 MeV/c. As the relative momentum between two nucleons increases and their separation thereby decreases, we observe a transition from a spin-dependent tensor-force to a predominantly spin-independent scalar-force. These results demonstrate the power of using such measurements to study the nuclear interaction at short-distances and also support the use of point-like nucleons with two- and three-body effective interactions to describe nuclear systems up to densities several times higher than the central density of atomic nuclei.

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arXiv2020

Studying Short-Range Correlations with Real Photon Beams at GlueX

The past few years has seen tremendous progress in our understanding of short-range correlated (SRC) pairing of nucleons within nuclei, much of it coming from electron scattering experiments leading to the break-up of an SRC pair. The interpretation of these experiments rests on assumptions about the mechanism of the reaction. These assumptions can be directly tested by studying SRC pairs using alternate probes, such as real photons. We propose a 30-day experiment using the Hall D photon beam, nuclear targets, and the GlueX detector in its standard configuration to study short-range correlations with photon-induced reactions. Several different reaction channels are possible, and we project sensitivity in most channels to equal or exceed the 6 GeV-era SRC experiments from Halls A and B. The proposed experiment will therefore decisively test the phenomena of np dominance, the short-distance NN interaction, and reaction theory, while also providing new insight into bound nucleon structure and the onset of color transparency.

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arXiv2020

Nucleon-nucleon correlations and the single-particle strength in atomic nuclei

We propose a phenomenological approach to examine the role of short- and long-range nucleon-nucleon correlations in the quenching of single-particle strength in atomic nuclei and their evolution in asymmetric nuclei and neutron matter. These correlations are thought to be the reason for the quenching of spectroscopic factors observed in $\rm (e,e'p)$, $\rm (p,2p)$ and transfer reactions. We show that the recently observed increase of the high-momentum component of the protons in neutron-rich nuclei is consistent with the reduced proton spectroscopic factors. Our approach connects recent results on short-range correlations from high-energy electron scattering experiments with the quenching of spectroscopic factors and addresses for the first time quantitatively this intriguing question in nuclear physics, in particular regarding its isospin dependence. We also speculate about the nature of a {\sl quasi-proton} (nuclear polaron) in neutron matter and its kinetic energy, an important quantity for the properties of neutron stars.

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arXiv2020

Short-Range Correlations and the Nuclear EMC Effect in Deuterium and Helium-3

The EMC effect in deuterium and helium-3 is studied using a convolution formalism that allows isolating the impact of high-momentum nucleons in short-ranged correlated (SRC) pairs. We assume that the modification of the structure function of bound nucleons is given by a universal (i.e. nucleus independent) function of their virtuality, and find that the effect of such modifications is dominated by nucleons in SRC pairs. This SRC-dominance of nucleon modifications is observed despite the fact that the bulk of the nuclear inelastic scattering cross-section comes from interacting with low-momentum nucleons. These findings are found to be robust to model details including nucleon modification function parametrization, free nucleon structure function and treatment of nucleon motion effects. While existing data cannot discriminate between such model details, we present predictions for measured, but not yet published, tritium EMC effect and tagged nucleon structure functions in deuterium that are sensitive to the neutron structure functions and bound nucleon modification functions.

hep-ph↗

arXiv2020

The SPOT-IL Positron Beam Construction and Its Use for Doppler Broadening Measurement of Titanium Thin Films

The construction and first operation of the slow positron beam built at the Hebrew University is reported here. The beam follows a traditional design, using a 22Na source, a Tungsten moderator, and a target cell equipped with a load-lock system for easy sample insertion. The beam energy varies between 0.03 keV and 30 keV. The detection system consists of two high purity Germanium detectors, facing each other, allowing low-background Doppler-Broadening (DB) measurements. Event readout is done using a state-of-the-art compact desktop system. The target cell is designed to allow a combined measurement of DB and sample conductivity, with the flexibility to add more detection options in the future. The beam has been successfully tested by using it to charecterize Titanium (Ti) films. Two 1.2 μm Ti films -- as produced, and after annealing, were measured at various energies (2 keV - 25 keV), and the results show consistent behavior with previous measurements.

physics.ins-det↗

arXiv2020

The CLAS12 Backward Angle Neutron Detector (BAND)

The Backward Angle Neutron Detector (BAND) of CLAS12 detects neutrons emitted at backward angles of $155^\circ$ to $175^\circ$, with momenta between $200$ and $600$ MeV/c. It is positioned 3 meters upstream of the target, consists of $18$ rows and $5$ layers of $7.2$ cm by $7.2$ cm scintillator bars, and read out on both ends by PMTs to measure time and energy deposition in the scintillator layers. Between the target and BAND there is a 2 cm thick lead wall followed by a 2 cm veto layer to suppress gammas and reject charged particles. This paper discusses the component-selection tests and the detector assembly. Timing calibrations (including offsets and time-walk) were performed using a novel pulsed-laser calibration system, resulting in time resolutions better than $250$ ps (150 ps) for energy depositions above 2 MeVee (5 MeVee). Cosmic rays and a variety of radioactive sources were used to calibration the energy response of the detector. Scintillator bar attenuation lengths were measured. The time resolution results in a neutron momentum reconstruction resolution, $δp/p < 1.5$\% for neutron momentum $200\le p\le 600$ MeV/c. Final performance of the BAND with CLAS12 is shown, including electron-neutral particle timing spectra and a discussion of the off-time neutral contamination as a function of energy deposition threshold.

physics.ins-det↗

arXiv2020

Probing few-body nuclear dynamics via 3H and 3He (e,e'p)pn cross-section measurements

We report the first measurement of the \eep three-body breakup reaction cross sections in helium-3 ($^3$He) and tritium ($^3$H) at large momentum transfer ($\langle Q^2 \rangle \approx 1.9$ (GeV/c)$^2$) and $x_B>1$ kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta $40 \le p_{miss} \le 500$ MeV/c that, in the QE limit with no rescattering, equals the initial momentum of the probed nucleon. The measured cross sections are compared with state-of-the-art ab-initio calculations. Overall good agreement, within $\pm20\%$, is observed between data and calculations for the full $p_{miss}$ range for $^3$H and for $100 \le p_{miss} \le 350$ MeV/c for $^3$He. Including the effects of rescattering of the outgoing nucleon improves agreement with the data at $p_{miss} > 250$ MeV/c and suggests contributions from charge-exchange (SCX) rescattering. The isoscalar sum of $^3$He plus $^3$H, which is largely insensitive to SCX, is described by calculations to within the accuracy of the data over the entire $p_{miss}$ range. This validates current models of the ground state of the three-nucleon system up to very high initial nucleon momenta of $500$ MeV/c.

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