New data strengthen the connection between Short Range Correlations and the EMC effect

Recently published measurements of the two nucleon short range correlation ($NN$-SRC) scaling factors, $a_2(A/d)$, strengthen the previously observed correlation between the magnitude of the EMC effect measured in electron deep inelastic scattering at $0.35\le x_B\le 0.7$ and the SRC scaling factor measured at $x_B \ge 1$. The new results have improved precision and include previously unmeasured nuclei. The measurements of $a_2(A/d)$ for $^9$Be and $^{197}$Au agree with published predictions based on the EMC-SRC correlation. This paper examines the effects of the new data and of different corrections to the data on the slope and quality of the EMC-SRC correlation, the size of the extracted deuteron IMC effect, and the free neutron structure function. The results show that the linear EMC-SRC correlation is robust and that the slope of the correlation is insensitive to most combinations of corrections examined in this work. This strengthens the interpretation that both $NN$-SRC and the EMC effect are related to high momentum nucleons in the nucleus.Comment: 4 pages, 1 figure. v3: minor changes to respond to PRC referee comments. v2: Minor errors in tabulated data corrected. No change to text or conclusion

Hammer events, neutrino energies, and nucleon-nucleon correlations

Neutrino oscillation measurements depend on a difference between the rate of neutrino-nucleus interactions at different neutrino energies or different distances from the source. Knowledge of the neutrino energy spectrum and neutrino-detector interactions are crucial for these experiments. Short range nucleon-nucleon correlations in nuclei (SRC) affect properties of nuclei. The ArgoNeut liquid Argon Time Projection Chamber (lArTPC) observed neutrino-argon scattering events with two protons back-to-back in the final state ("hammer" events) which they associated with SRC pairs. The MicroBoone lArTPC will measure far more of these events. We simulate hammer events using two simple models. We use the well-known electron-nucleon cross section to calculate e-argon interactions where the e- scatters from a proton, ejecting a pi+, and the pi+ is then absorbed on a moving deuteron-like $np$ pair. We also use a model where the electron excites a nucleon to a Delta, which then deexcites by interacting with a second nucleon. The pion production model results in two protons very similar to those of the hammer events. These distributions are insensitive to the momentum of the $np$ pair that absorbed the $\pi$. The incident neutrino energy can be reconstructed from just the outgoing lepton. The Delta process results in two protons that are less similar to the observed events. ArgoNeut hammer events can be described by a simple pion production and reabsorption model. These hammer events in MicroBooNE can be used to determine the incident neutrino energy but not to learn about SRC. We suggest that this reaction channel could be used for neutrino oscillation experiments to complement other channels with higher statistics but different systematic uncertainties.Comment: Text improved in response to PRC referee comment

Disentangling the EMC Effect

The deep inelastic scattering cross section for scattering from bound nucleons differs from that of free nucleons.This phenomena, first discovered 30 years ago, is known as the EMC effect and is still not fully understood. Recent analysis of world data showed that the strength of the EMC effect is linearly correlated with the relative amount of Two-Nucleon Short Range Correlated pairs (2N-SRC) in nuclei. The latter are pairs of nucleons whose wave functions overlap, giving them large relative momentum and low center of mass momentum, where high and low is relative to the Fermi momentum of the nucleus. The observed correlation indicates that the EMC effect, like 2N-SRC pairs, is related to high momentum nucleons in the nucleus. This paper reviews previous studies of the EMC-SRC correlation and studies its robustness. It also presents a planned experiment aimed at studying the origin of this EMC-SRC correlation.Comment: 8 pages, 3 figures. Proceedings of plenary talk at CIPANP 201

The EMC Effect and High Momentum Nucleons in Nuclei

Recent developments in understanding the influence of the nucleus on deep-inelastic structure functions, the EMC effect, are reviewed. A new data base which expresses ratios of structure functions in terms of the Bjorken variable $x_A=AQ^2/(2M_A q_0)$ is presented. Information about two-nucleon short-range correlations from experiments is also discussed and the remarkable linear relation between short-range correlations and teh EMC effect is reviewed. A convolution model that relates the underlying source of the EMC effect to modification of either the mean-field nucleons or the short-range correlated nucleons is presented. It is shown that both approaches are equally successful in describing the current EMC data.Comment: 31 pages, 11 figure

Extracting the Mass Dependence and Quantum Numbers of Short-Range Correlated Pairs from A(e,e'p) and A(e,e'pp) Scattering

The nuclear mass dependence of the number of short-range correlated (SRC) proton-proton (pp) and proton-neutron (pn) pairs in nuclei is a sensitive probe of the dynamics of short-range pairs in the ground state of atomic nuclei. This work presents an analysis of electroinduced single-proton and two-proton knockout measurements off 12C, 27Al, 56Fe, and 208Pb in kinematics dominated by scattering off SRC pairs. The nuclear mass dependence of the observed A(e,e'pp)/12C(e,e'pp) cross-section ratios and the extracted number of pp- and pn-SRC pairs are much softer than the mass dependence of the total number of possible pairs. This is in agreement with a physical picture of SRC affecting predominantly nucleon-nucleon pairs in a nodeless relative-S state of the mean-field basis.Comment: 6 pages, 3 figure

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.Comment: 6 pages, 0 figures. This version includes many improvement

Measurement of transparency ratios for protons from short-range correlated pairs

Nuclear transparency, Tp(A), is a measure of the average probability for a struck proton to escape the nucleus without significant re-interaction. Previously, nuclear transparencies were extructed for quasi-elastic A(e,e'p) knockout of protons with momentum below the Fermi momentum, where the spectral functions are well known. In this paper we extract a novel observable, the transparency ratio, Tp(A)/T_p(12C), for knockout of high-missing-momentum protons from the breakup of short range correlated pairs (2N-SRC) in Al, Fe and Pb nuclei relative to C. The ratios were measured at momentum transfer Q^2 > 1.5 (GeV/c)^2 and x_B > 1.2 where the reaction is expected to be dominated by electron scattering from 2N-SRC. The transparency ratios of the knocked-out protons coming from 2N-SRC breakup are 20 - 30% lower than those of previous results for low missing momentum. They agree with Glauber calculations and agree with renormalization of the previously published transparencies as proposed by recent theoretical investigations. The new transparencies scale as A^-1/3, which is consistent with dominance of scattering from nucleons at the nuclear surface.Comment: 6 pages, 4 figure

Short Range Correlations and the EMC Effect

This paper shows quantitatively that the magnitude of the EMC effect measured in electron deep inelastic scattering (DIS) at intermediate $x_B$, $0.35\le x_B\le 0.7$, is linearly related to the Short Range Correlation (SRC) scaling factor obtained from electron inclusive scattering at $x_B\ge 1.$. The observed phenomenological relationship is used to extract the ratio of the deuteron to the free $pn$ pair cross sections, the DIS cross section for a free neutron, and $F_2^n/F_2^p$, the ratio of the free neutron to free proton structure functions. We speculate that the observed correlation is because both the EMC effect and SRC are dominated by the high virtuality (high momentum) nucleons in the nucleus.Comment: 5 pages, 2 figures, minor changes for PRL acceptance, reference 12 correcte