Abstract
Recent high-precision measurements of nuclear deep inelastic scattering at high x and moderate 6 < Q$^2$ < 9GeV$^2$ give a rare opportunity to reach the quark distributions in the {\it superfast} region, in which the momentum fraction of the nucleon carried by its constituent quark is larger than the total fraction of the nucleon at rest, x>1. We derive the leading-order QCD evolution equation for such quarks with the goal of relating the moderate-Q$^2$ data to the two earlier measurements of superfast quark distributions at large 60 < Q$^2$ < 200~GeV$^2$. Since the high-Q$^2$ measurements gave strongly contradictory estimates of the nuclear effects that generate superfast quarks, relating them to the high-precision, moderate-Q$^2$ data through QCD evolution allows us to clarify this longstanding issue. Our calculations indicate that the moderate-Q$^2$ data at $x\lesssim 1.05$ are in better agreement with the high-Q$^2$ data measured in (anti)neutrino-nuclear reactions which require substantial high-momentum nuclear effects in the generation of superfast quarks. Our prediction for the high-Q$^2$ and x>1.1 region is somewhat in the middle of the neutrino-nuclear and muon-nuclear scattering data.
Highlights
With the operation of the Large Hadron Collider (LHC), the high-energy upgrade of Jefferson Lab (JLab), and the anticipation of the future electron-ion collider (EIC), the issue of understanding the partonic structure of nuclei is currently a very important topic
VI we present a simple parametrization of the F2A parameters that allows estimation of the structure function over a wide range of Q2 relevant to LHC and EIC kinematics
The functional form of the fit was chosen to have a log Q2 term to be consistent with QCD evolution. Using this fit, the extracted Fð20AÞðξ; Q20Þ at Q20 1⁄4 7 GeV2 was extrapolated to the BCDMS and CCFR kinematics at large ξ. This extrapolation [23] resulted in the slope factor of s 1⁄4 15 Æ 0.5 for the 12C target indicating that the JLab data are consistent with the BCDMS results, with the latter showing only marginal strength of high-momentum component in the nuclear wave function [21]
Summary
With the operation of the Large Hadron Collider (LHC), the high-energy upgrade of Jefferson Lab (JLab), and the anticipation of the future electron-ion collider (EIC), the issue of understanding the partonic structure of nuclei is currently a very important topic. MA is the mass of the nucleus A, and −Q2 and q0 are the square of invariant momentum transfer and the energy transferred to the nucleus in its rest frame Since no such quark can be produced by QCD dynamics confined to a single nucleon without internucleon interactions, probing superfast quarks requires direct interplay between QCD and nuclear dynamics. Superfast quarks can be probed in more unconventional processes such as semi-inclusive nuclear DIS processes with tagged spectator nucleons [18,19,20], DIS production in the forward direction with xF > 1, or large transverse momentum dijet production in p þ A → dijet þ X reactions at LHC kinematics [12]. To carry out this study, we derive the QCD evolution equation for the nuclear structure function F2A and calculate the evolution of the Jefferson Lab data up to the Q2 range of the BCDMS and CCFR experiments.
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