Applications of quark-hadron duality in F2 structure function

TL;DR

This study tests quark-hadron duality in the large-$x$ regime by analyzing high-precision $F_2$ data from electron scattering in the nucleon resonance region ($W^{2}$ up to 4 GeV$^{2}$) at $Q^{2}$ as high as several GeV$^{2}$. By comparing resonance-region measurements with state-of-the-art PDF parameterizations (and incorporating target-mass and higher-twist effects), the work reveals that the apparent breakdown of duality at moderate $Q^{2}$ saturates around $Q^{2}\approx4\ \mathrm{GeV}^2$, indicating only small violations of perturbative evolution in the resonance region. The discrepancies with CTEQ6M and MRST2004 at large $x$ are traced mainly to unconstrained large-$x$ PDFs, while ALEKHIN and ALLM97 show that higher-twist contributions are comparable between resonance and DIS data. The results suggest that properly averaged resonance data can be used to constrain PDFs at large $x$ in global fits, improving our understanding of valence-quark dynamics and reducing uncertainties in high-energy predictions.

Abstract

Inclusive electron-proton and electron-deuteron inelastic cross sections have been measured at Jefferson Lab (JLab) in the resonance region, at large Bjorken x, up to 0.92, and four-momentum transfer squared Q2 up to 7.5 GeV2 in the experiment E00-116. These measurements are used to extend to larger x and Q2 precision, quantitative, studies of the phenomenon of quark-hadron duality. Our analysis confirms, both globally and locally, the apparent violation of quark-hadron duality previously observed at a Q2 of 3.5 GeV2 when resonance data are compared to structure function data created from CTEQ6M and MRST2004 parton distribution functions (PDFs). More importantly, our new data show that this discrepancy saturates by Q2 ~ 4 Gev2, becoming Q2 independent. This suggests only small violations of Q2 evolution by contributions from the higher-twist terms in the resonance region which is confirmed by our comparisons to ALEKHIN and ALLM97.We conclude that the unconstrained strength of the CTEQ6M and MRST2004 PDFs at large x is the major source of the disagreement between data and these parameterizations in the kinematic regime we study and that, in view of quark-hadron duality, properly averaged resonance region data could be used in global QCD fits to reduce PDF uncertainties at large x.

Figures (32)

• Figure 1: (Color online) Existing $F_{2}^{p}$ parameterizations at a $Q^2$ value of 4 GeV$^2$. CTEQ6M cteq, MRST2004 mrst, ALLM97 allm97 and ALEKHIN alekhin_05alekhin_03 were used for the quark-hadron duality studies presented in Sect. 4. Target mass corrections were added to CTEQ6M and MRST2004 (see text). The M.E. Christy eric_param parameterization is shown for comparison.
• Figure 2: (Color online) Existing $F_{2}^{p}$ parameterizations at a $Q^2$ value of 8 GeV$^2$. CTEQ6M cteq, MRST2004 mrst, ALLM97 allm97 and ALEKHIN alekhin_05alekhin_03 were used for the quark-hadron duality studies presented in Sect. 4. Target mass corrections were added to CTEQ6M and MRST2004 (see text). The M.E. Christy eric_param parameterization is shown for comparison.
• Figure 3: (Color online) The difference between the current as given by the BCM2 after calibration and the current as given by the Unser. The two calibration runs, 46203 and 46667 were taken one month apart and yielded very similar results for the BCM2 gain and offset (see text).
• Figure 4: (Color online) Relative hydrogen and deuterium target yield versus beam current. The correction for the boiling effect is obtained from a linear fit to the data shown as the dotted line.
• Figure 5: An example of the distribution of number of photoelectrons collected in the HMS Cerenkov detector. The pion peak appears at zero while electrons produce on average about 13 photoelectrons. As it will be discussed later in the text, a cut of number of photoelectrons = 2 was used to separate electrons from pions.