83 research outputs found
The nuclear contacts and short range correlations in nuclei
Atomic nuclei are complex strongly interacting systems and their exact
theoretical description is a long-standing challenge. An approximate
description of nuclei can be achieved by separating its short and long range
structure. This separation of scales stands at the heart of the nuclear shell
model and effective field theories that describe the long-range structure of
the nucleus using a mean- field approximation. We present here an effective
description of the complementary short-range structure using contact terms and
stylized two-body asymptotic wave functions. The possibility to extract the
nuclear contacts from experimental data is presented. Regions in the two-body
momentum distribution dominated by high-momentum, close-proximity, nucleon
pairs are identified and compared to experimental data. The amount of
short-range correlated (SRC) nucleon pairs is determined and compared to
measurements. Non-combinatorial isospin symmetry for SRC pairs is identified.
The obtained one-body momentum distributions indicate dominance of SRC pairs
above the nuclear Fermi-momentum.Comment: Accepted for publication in Physics Letters. 6 pages, 2 figure
Nucleon-Nucleon Correlations, Short-Lived Excitations, and the Quarks Within
This article reviews our current understanding of how the internal quark structure of a nucleon bound in nuclei differs from that of a free nucleon. The interpretation of measurements of the European Muon Collaboration (EMC) effect for valence quarks, a reduction in the deep inelastic scattering cross-section ratios for nuclei relative to deuterium, and its possible connection to nucleon-nucleon short-range correlations (SRCs) in nuclei are focused on. This review and new analysis (involving the amplitudes of non-nucleonic configurations in the nucleus) of the available experimental and theoretical evidence shows that there is a phenomenological relation between the EMC effect and the effects of SRCs that is not an accident. The influence of strongly correlated neutron-proton pairs involving highly virtual nucleons is responsible for both effects. These correlated pairs are temporary high-density fluctuations in the nucleus in which the internal structure of the nucleons is briefly modified. This conclusion needs to be solidified by the future experiments and improved theoretical analyses that are discussed herein
Energy and momentum dependence of nuclear short-range correlations - Spectral function, exclusive scattering experiments and the contact formalism
Results of electron-induced one- and two-nucleon hard knockout reactions,
and , in kinematics sensitive to nuclear short-range
correlations, are studied using the nuclear contact formalism. A relation
between the spectral function and the nuclear contacts is derived and used to
analyze the dependence of the data on the initial energy and momentum of the
knocked-out proton. The ratio between the number of emitted proton-proton pairs
and proton-neutron pairs is shown to depend predominantly on a single ratio of
contacts. This ratio is expected to present a deep minima in the initial energy
and momentum plane, associated with the node in the proton-proton wave
function. The formalism is applied to analyze data from recent He and
C electron-scattering experiments performed at Jefferson laboratory.
Different nucleon-nucleon potentials were used to asses the model-dependence of
the results. For the ratio of proton-proton to proton-neutron pairs in He,
a fair agreement with the experimental data is obtained using the two
potentials, whereas for the ratio of proton-proton pairs to the total
knocked-out protons in C, some of the features of the theory are not
seen in the experimental data. Several possible explanations for this
disagreement are discussed. It is also observed that the spectral function at
specific domains of the momentum-energy plane is sensitive to the
nucleon-nucleon interaction. Based on this sensitivity, it might be possible to
constrain the short range part of the nuclear potential using such experimental
data
Nucleon-Nucleon Correlations, Short-Lived Excitations, and the Quarks Within
This article reviews our current understanding of how the internal quark structure of a nucleon bound in nuclei differs from that of a free nucleon. The interpretation of measurements of the European Muon Collaboration (EMC) effect for valence quarks, a reduction in the deep inelastic scattering cross-section ratios for nuclei relative to deuterium, and its possible connection to nucleon-nucleon short-range correlations (SRCs) in nuclei are focused on. This review and new analysis (involving the amplitudes of non-nucleonic configurations in the nucleus) of the available experimental and theoretical evidence shows that there is a phenomenological relation between the EMC effect and the effects of SRCs that is not an accident. The influence of strongly correlated neutron-proton pairs involving highly virtual nucleons is responsible for both effects. These correlated pairs are temporary high-density fluctuations in the nucleus in which the internal structure of the nucleons is briefly modified. This conclusion needs to be solidified by the future experiments and improved theoretical analyses that are discussed herein
Short range correlations and the isospin dependence of nuclear correlation functions
Pair densities and associated correlation functions provide a critical tool
for introducing many-body correlations into a wide-range of effective theories.
Ab initio calculations show that two-nucleon pair-densities exhibit strong spin
and isospin dependence. However, such calculations are not available for all
nuclei of current interest. We therefore provide a simple model, which involves
combining the short and long separation distance behavior using a single
blending function, to accurately describe the two-nucleon correlations inherent
in existing ab initio calculations. We show that the salient features of the
correlation function arise from the features of the two-body short-range
nuclear interaction, and that the suppression of the pp and nn pair-densities
caused by the Pauli principle is important. Our procedure for obtaining
pair-density functions and correlation functions can be applied to heavy nuclei
which lack ab initio calculations.Comment: 5 pages, 4 figure
Michel electron reconstruction using cosmic-ray data from the MicroBooNE LArTPC
The MicroBooNE liquid argon time projection chamber (LArTPC) has been taking data at Fermilab since 2015 collecting, in addition to neutrino beam, cosmic-ray muons. Results are presented on the reconstruction of Michel electrons produced by the decay at rest of cosmic-ray muons. Michel electrons are abundantly produced in the TPC, and given their well known energy spectrum can be used to study MicroBooNE's detector response to low-energy electrons (electrons with energies up to ∼ 50 MeV). We describe the fully-automated algorithm developed to reconstruct Michel electrons, with which a sample of ∼ 14,000 Michel electron candidates is obtained. Most of this article is dedicated to studying the impact of radiative photons produced by Michel electrons on the accuracy and resolution of their energy measurement. In this energy range, ionization and bremsstrahlung photon production contribute similarly to electron energy loss in argon, leading to a complex electron topology in the TPC. By profiling the performance of the reconstruction algorithm on simulation we show that the ability to identify and include energy deposited by radiative photons leads to a significant improvement in the energy measurement of low-energy electrons. The fractional energy resolution we measure improves from over 30% to ∼ 20% when we attempt to include radiative photons in the reconstruction. These studies are relevant to a large number of analyses which aim to study neutrinos by measuring electrons produced by ν e interactions over a broad energy range. Keywords: Michel electrons, LArTPC, MicroBooN
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