Parton Distributions, d/u, and Higher Twist Effects at High X

Abstract

A re-analysis of the NMC and SLAC data leads to a great improvement in our knowledge of the valence d and u parton distribution functions at high x. Standard parton distributions with our modifications are in good agreement with QCD predictions for d/u at x=1, and with the CDHSW nu p and nubar p data, the HERA charged current cross section data, the collider high-P_t jet data, and the CDF W asymmetry data. With the inclusion of target mass and higher twist corrections, the modified PDF's also describe all DIS data up to x = 0.98 and down to Q^2 = 1 GeV^2.

Figures (5)

• Figure 1: (a) The total correction for nuclear effects (binding and Fermi motion) in the deuteron, $F_2^d/F_2^{n+p}$, as a function of $x$, extracted from fits to the nuclear dependence of SLAC $F_2$ electron scattering data (compared to theoretical model [6]). (b) Comparison of NMC $F_2^{n+p}/F_2^p$ (corrected for nuclear effects) and the prediction in NLO using the MRS(R2) PDF with and without our proposed modification to the $d/u$ ratio.
• Figure 2: (a) The $d/u$ distributions at $Q^2$=$16$ GeV$^2$ as a function of $x$ for the standard and modified MRS(R2) PDF compared to the CDHSW data. (b) Comparison of the CDF $W$ asymmetry data with NLO standard CTEQ3M, MRS(R2), and modified MRS(R2) as a function of the lepton rapidity. The standard CTEQ3M with a resummation calculation is also shown for comparison.
• Figure 3: (a) The HERA charged current cross section data and (b) the CDF and D0 inclusive jet cross section data are compared with both standard and modified PDF's.
• Figure 4: The description of higher twist fit using the renormalon model with the modified NLO MRS(R2) PDF. The CCFR neutrino data is also shown for comparison. (a) Comparison of $F_2$ and NLO prediction with and without higher twist contributions. (b) Comparison of $R$ and NLO prediction with and without the renormalon higher twist contributions.
• Figure 5: Comparison of SLAC $F_2^p$ data with the predictions of the modified MRS(R2), CTEQ4M and the CTEQ toy model at high $x$ and higher $Q^2$ ($20<Q^2<31$ GeV$^2$). (a) Ratio to pQCD, (b) ratio to pQCD with TM effects, and (c) ratio to pQCD with TM and higher twist effects