Erratum: Chiral Solitons in Nuclei: Saturation, EMC Effect, and Drell-Yan Experiments [Phys. Rev. Lett.91, 212301 (2003)]

Abstract

The Chiral Quark-Soliton model of the nucleon contains a mechanism for an attractive interaction between nucleons. This, along with the exchange of vector mesons between nucleons, is used to compute the saturation properties of infinite nuclear matter. This provides a new way to asses the effects of the nuclear medium on a nucleon that includes valence and sea quarks. We show that the model simultaneously describes the nuclear EMC effect and the related Drell-Yan experiments.One frontier of strong interaction physics lies in the intermediate range of length scales available to present experiments where neither the fundamental theory, Quantum Chromodynamics (QCD), nor its low energy effective theory, Chiral Perturbation Theory, have useful perturbative expansions. Neither fundamental quarks nor point-like hadrons provide a complete description, so including the non-perturbative information that hadrons are bound states of valence quarks in a polarized vacuum is necessary. One way to probe these intermediate length scales and this non-perturbative physics is to examine the short distance structure of a large object. The prime example is the European Muon Collaboration (EMC) effect [1] where the short distance (∼ 5 GeV, or ∼ 10 −2 fm) structure of nuclei differs from that of a collection of free nucleons. This measurement showed that bound nucleons are different than free ones, and implied that the medium modifications could be significant for any nuclear observable [2]. Indeed, a recent paper [3] obtains evidence for a medium modification of the elastic proton form factor.Our central concern is the depletion of the nuclear structure function F A 2 (x) in the valence quark regime 0.3 < ∼ x < ∼ 0.8. While the general interpretation is that a valence quark in a bound nucleon has less momentum than in a free one, corresponding to some increased length scale, the specific mechanism for this has eluded a universally accepted explanation for 20 years [2,4,5,6]. A popular explanation is the so-called 'binding' effect which originates from a possible mechanism in which mesons binding the nucleus carry momentum. An important consequence is that the mesonic presence would enhance the anti-quark content of the nucleus [7,8]. Such an effect has not been seen in Drell-Yan experiments [9] in which a quark in a proton beam annihilates with an antiquark in a nuclear target producing a muon pair. Furthermore, relativistic treatments, including the lightcone approach needed to obtain the nucleon structure function, of the binding effect with structureless hadrons fail [10,11,12,13], suggesting that modifications of the internal quark structure of the nucleon are required to explain the deep inelastic scattering data.Any description of the EMC effect must be consistent with the constraints set by both deep inelastic scattering and Drell-Yan data. Thus a successful model must include antiquarks as well as quarks, and show how the medium modifies both the valence and sea quark distributions. Our purpose is to provide a mechanis...

Role of the nuclear vector potential in deep inelastic scattering

“…It has been argued that the quark struck by the hard photon should not feel the nucleon vector potential 3V 0 , and accounting for this causes a shift in the argument of the distribution function, and a change in its normalization. This shift seems to have a significant effect on computed numerical results [8,16], but its presence is not immediately apparent in other work [17].…”

“…The mean-field should provide important effects for quarks in the target ground state and should vanish for high-energy quarks. Thus both sets of authors [8,16] and [17] use a physically reasonable procedure. The rigorous task of deriving a vector potential with the ability to account for both the high and low energy limits of the quark self-energy in nuclear matter remains a task for the future.…”

“…Smith & Miller [17] and Thomas et al [8,16] each use an expression for the in-medium quark distribution function [22]:…”

“…More recently, a quark-diquark description of the single nucleon [13,14], based on the NJL model [10], was combined with the mean field description of nuclear matter [11,12]. Another set of work is based on a nuclear matter version [17] of the chiral quark soliton model of Diakonov et al [18]. Here, the nuclear attraction is generated by the exchange of pairs of pions (yielding an effective scalar potential) with the environment, and the repulsion arises from vector meson exchange.…”

“…This is a daunting task. One way to proceed [8]- [17] is to use a mean field models in which quarks in a given nucleon feel the influence of mesons produced by the average field of the nucleus. Such models should account for the saturation properties of nuclear matter, as well as the structure functions of the free nucleon.…”