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New Properties of High Momentum Distribution of Nucleons in Asymmetric Nuclei  [PDF]
Misak M. Sargsian
Physics , 2012, DOI: 10.1103/PhysRevC.89.034305
Abstract: Based on the recent experimental observations of the dominance of tensor interaction in the ~250-600~MeV/c momentum range of nucleons in nuclei, the existence of two new properties for high-momentum distribution of nucleons in asymmetric nuclei is suggested. The first property is the approximate scaling relation between proton and neutron high-momentum distributions weighted by their relative fractions in the nucleus. The second property is the inverse proportionality of the strength of the high-momentum distribution of protons and neutrons to the same relative fractions. Based on these two properties the high-momentum distribution function for asymmetric nuclei has been modeled and demonstrated that it describes reasonably well the high-momentum characteristics of light nuclei. However, the most surprising result is obtained for neutron rich nuclei with large A, for which a substantial relative abundance of high-momentum protons as compared to neutrons is predicted. For example, the model predicts that in Au the relative fraction of protons with momenta above $k_{F} \sim 260$~MeV/c is 50% more than that of neutrons. Such a situation may have many implications for different observations in nuclear physics related to the properties of a proton in neutron rich nuclei.
Disentangling the EMC Effect  [PDF]
E. Piasetzky,O. Hen,L. B. Weinstein
Physics , 2012, DOI: 10.1063/1.4826792
Abstract: 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.
The EMC Effect and Short-Range Correlations  [PDF]
Misak M Sargsian
Physics , 2012, DOI: 10.1063/1.4826823
Abstract: We overview the progress made in studies of EMC and short range correlation (SRC) effects with the special emphasis given to the recent observation of the correlation between the slope of the EMC ratio at Bjorken x<1 and the scale factor of the same ratio at x>1 that measures the strength of the SRCs in nuclei. This correlation may indicate the larger modification of nucleons with higher momentum thus making the nucleon virtuality as the most relevant parameter of medium modifications. To check this conjecture we study the implication of several properties of high momentum component of the nuclear wave function on the characteristics of EMC effect. We observe two main reasons for the EMC-SRC correlation: first, the decrease of the contribution from the nuclear mean field due to the increase, with A, the fraction of the high momentum component of nuclear wave function. Second, the increase of the medium modification of nucleons in SRC. Our main prediction however is the increase of the proton contribution to the EMC effect for large A asymmetric nuclei. This prediction is based on the recent observation of the strong dominance of pn SRCs in the high momentum component of nuclear wave function. Our preliminary calculation based on this prediction of the excess of energetic and modified protons in large A nuclei describes reasonably well the main features of the observed EMC-SRC correlation.
New measurements of high-momentum nucleons and short-range structures in nuclei  [PDF]
N. Fomin,J. Arrington,R. Asaturyan,F. Benmokhtar,W. Boeglin,P. Bosted,A. Bruell,M. H. S. Bukhari,E. Chudakov,B. Clasie,S. H. Connell,M. M. Dalton,A. Daniel,D. B. Day,D. Dutta,R. Ent,L. El Fassi,H. Fenker,B. W. Filippone,K. Garrow,D. Gaskell,C. Hill,R. J. Holt,T. Horn,M. K. Jones,J. Jourdan,N. Kalantarians,C. E. Keppel,D. Kiselev,M. Kotulla,R. Lindgren,A. F. Lung,S. Malace,P. Markowitz,P. McKee,D. G. Meekins,H. Mkrtchyan,T. Navasardyan,G. Niculescu,A. K. Opper,C. Perdrisat,D. H. Potterveld,V. Punjabi,X. Qian,P. E. Reimer,J. Roche,V. M. Rodriguez,O. Rondon,E. Schulte,J. Seely,E. Segbefia,K. Slifer,G. R. Smith,P. Solvignon,V. Tadevosyan,S. Tajima,L. Tang,G. Testa,R. Trojer,V. Tvaskis,W. F. Vulcan,C. Wasko,F. R. Wesselmann,S. A. Wood,J. Wright,X. Zheng
Physics , 2011, DOI: 10.1103/PhysRevLett.108.092502
Abstract: We present new measurements of electron scattering from high-momentum nucleons in nuclei. These data allow an improved determination of the strength of two-nucleon correlations for several nuclei, including light nuclei where clustering effects can, for the first time, be examined. The data also include the kinematic region where three-nucleon correlations are expected to dominate.
New analysis of the common nuclear dependence of the EMC effect and short-range correlations  [PDF]
Nadia Fomin
Physics , 2012, DOI: 10.1063/1.4826831
Abstract: The strong repulsive core of the nucleon-nucleon (NN) interaction at short distances prevents nucleons from becoming close to each other. This gives rise to high-momentum nucleons in the nucleus that cannot be explained in the context of the mean field and are commonly called short-range correlations (SRCs). They are responsible for the strength seen in momentum distribution tails seen in all nuclei, and we can obtain a relative measure of SRCs via cross section ratios to light nuclei. Recent inclusive scattering data from Jefferson Lab have allowed a precise determination of the A-dependence of SRCs in nuclei and suggests that, like the EMC effect, it is especially sensitive to the nuclear local density. These new results, as well as a new analysis of the relationship between SRCs and the EMC effect, will be presented and discussed.
New data strengthen the connection between Short Range Correlations and the EMC effect  [PDF]
O. Hen,E. Piasetzky,L. B. Weinstein
Physics , 2012, DOI: 10.1103/PhysRevC.85.047301
Abstract: 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.
QCD and QED dynamics of the EMC effect  [PDF]
Leonid Frankfurt,Mark Strikman
Physics , 2012, DOI: 10.1142/S0218301312300020
Abstract: Applying exact QCD sum rules for the baryon charge and energy-momentum we demonstrate that if nucleons are the only degrees of freedom of nuclear wave function, the structure function of a nucleus would be the additive sum of the nucleon distributions at the same Bjorken x = AQ^2/2(p_Aq)< 0.5 up to very small Fermi motion corrections if x>0.05. Thus the difference of the EMC ratio from one reveals the presence of non-nucleonic degrees of freedom in nuclei. Using exact QCD sum rules we show that the ratio R_A(x_p,Q^2) used in experimental studies, where x_p = Q^2/2q_0 m_p deviates from one even if a nucleus consists of nucleons with small momenta only. Use of the Bjorken x leads to additional decrease of R_A(x,Q^2) as compared to the x_p plots. Coherent contribution of equivalent photons into photon component of parton wave function of a nucleus unambiguously follows from Lorentz transformation of the rest frame nucleus Coulomb field. For A~200 photons carry ~0.0065 fraction of the light momentum of nucleus almost compensates the difference between data analysis in terms of Bjorken x and x_p. Different role of higher twist effects for Q^2 probed at electron and muon beams is emphasized. Direct observations of large and predominantly nucleonic short-range correlations in nuclei pose a serious challenge for most of the models of the EMC effect for x>0.6. The data are consistent with a scenario in which the hadronic EMC effect reflects fluctuations of inter nucleon interaction due to fluctuations of color distribution in the interacting nucleons. The dynamic realization of this scenario is the model in which the 3q (3qg) configurations with x > 0.5 parton have a weaker interaction with nearby nucleons, leading to suppression of such configurations giving a right magnitude of the EMC effect. The directions for the future studies and challenging questions are outlined.
Polarized structure functions of nucleons and nuclei  [PDF]
W. Bentz,I. C. Clo?t,T. Ito,A. W. Thomas,K. Yazaki
Physics , 2007, DOI: 10.1016/j.ppnp.2007.12.021
Abstract: We determine the quark distributions and structure functions for both unpolarized and polarized DIS of leptons on nucleons and nuclei. The scalar and vector mean fields in the nucleus modify the motion of the quarks inside the nucleons. By taking into account this medium modification, we are able to reproduce the experimental data on the unpolarized EMC effect, and to make predictions for the polarized EMC effect. We discuss examples of nuclei where the polarized EMC effect could be measured. We finally present an extension of our model to describe fragmentation functions.
EMC effect, short-range nuclear correlations, neutron stars  [PDF]
Mark Strikman
Physics , 2011, DOI: 10.1063/1.3700568
Abstract: The recent x>1 (e,e') and correlation experiments at momentum transfer Q^2 \ge 2 GeV^2 confirm presence of short-range correlations (SRC) in nuclei mostly build of nucleons. Recently we evaluated in a model independent way the dominant photon contribution to the nuclear structure. Taking into account this effect and using definition of x consistent with the exact kinematics of eA scattering (with exact sum rules) results in the significant reduction of R_A(x,Q^2)=F_{2A}(x,Q^2)/F_{2N}(x,Q^2) ratio which explains \sim 50% of the EMC effect for x\le 0.55 where Fermi motion effects are small. The remaining part of the EMC effect at $x\ge 0.5$ is consistent with dominance of the contribution of SRCs. Implications for extraction of the F_{2n}/F_{2p} ratio are discussed. Smallness of the non-nucleonic degrees of freedom in nuclei matches well the recent observation of a two-solar mass neutron star, and while large pn SRCs lead to enhancement of the neutron star cooling rate for kT\le 0.01 MeV.
New Measurements of the EMC Effect in Few-Body Nuclei  [PDF]
J. Arrington,for the JLab E03-103 collaboration
Physics , 2007, DOI: 10.1088/1742-6596/69/1/012024
Abstract: Measurements of the EMC effect show that the quark distributions in nuclei are not simply the sum of the quark distributions of the constituent nucleons. However, interpretation of the EMC effect is limited by the lack of a reliable baseline calculation of the effects of Fermi motion and nucleon binding. We present preliminary results from JLab experiment E03-103, a precise measurement of the EMC effect in few-body and heavy nuclei. These data emphasize the large-x region, where binding and Fermi motion effects dominate, and thus will provide much better constraints on the effects of binding. These data will also allow for comparisons to calculations for few-body nuclei, where the uncertainty in the nuclear structure is minimized.
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