Determination of nuclear parton distribution functions and their uncertainties at next-to-leading order (0709.3038v2)

Abstract: Nuclear parton distribution functions (NPDFs) are determined by global analyses of experimental data on structure-function ratios F_2^A/F_2^{A'} and Drell-Yan cross-section ratios \sigma_{DY}^A/\sigma_{DY}^{A'}. The analyses are done in the leading order (LO) and next-to-leading order (NLO) of running coupling constant \alpha_s. Uncertainties of the NPDFs are estimated in both LO and NLO for finding possible NLO improvement. Valence-quark distributions are well determined, and antiquark distributions are also determined at x<0.1. However, the antiquark distributions have large uncertainties at x>0.2. Gluon modifications cannot be fixed at this stage. Although the advantage of the NLO analysis, in comparison with the LO one, is generally the sensitivity to the gluon distributions, gluon uncertainties are almost the same in the LO and NLO. It is because current scaling-violation data are not accurate enough to determine precise nuclear gluon distributions. Modifications of the PDFs in the deuteron are also discussed by including data on the proton-deuteron ratio F_2^D/F_2^p in the analysis. A code is provided for calculating the NPDFs and their uncertainties at given x and Q^2 in the LO and NLO.

• The paper determines nuclear PDFs through comprehensive global analyses of structure-function and Drell–Yan ratios, underlining their role in high-energy nuclear physics.
• It employs both LO and NLO calculations to improve constraints on valence quark distributions at x < 0.1 while highlighting limitations for antiquark and gluon estimates.
• The research provides a computational tool for NPDF applications in heavy-ion and neutrino experiments and stresses the need for more precise scaling-violation data.

Determination of Nuclear Parton Distribution Functions and Their Uncertainties at Next-to-Leading Order

The paper investigates the determination of Nuclear Parton Distribution Functions (NPDFs) through comprehensive global analyses of experimental data focused on structure-function ratios and Drell-Yan cross-section ratios. The analyses highlight the importance of accounting for NPDFs in precision measurements and their implications for understanding high-energy nuclear reactions. This work extends prior research by implementing both Leading Order (LO) and Next-to-Leading Order (NLO) calculations to assess NPDF uncertainties and their potential improvements.

One of the primary findings is the determination of valence-quark distributions with high confidence, particularly at smaller values of the Bjorken scaling variable $x < 0.1$, where they are better constrained by experimental data. However, the estimation of antiquark distributions, although reliable at $x < 0.1$, becomes less precise at $x > 0.2$, indicating the need for further exploration in this domain. The paper shows that gluon distribution modifications remain elusive due to current limitations in scaling-violation data, which preclude precise definition of nuclear gluon distributions.

Despite the inclusion of NLO terms, which theoretically enhance the sensitivity to gluon distributions, the research finds that uncertainties in these distributions are comparably large at both LO and NLO. This is attributed to insufficiently accurate scaling-violation data available at present.

Numerical results demonstrate reasonable consistency with experimental structure function data across a variety of nuclear targets. Still, the analysis illustrates a pronounced need for more accurate and extensive data to discern nuanced gluon modifications. The paper's analysis method incorporated flavor asymmetry in the antiquark distributions, recognizing recent observational evidence for flavor differentiation such as the violation of the Gottfried sum rule.

The implications of this research extend to multiple domains, including heavy-ion collision studies, wherein NPDFs hold significant promise for exploring quark-gluon plasma and other nuclear phenomena. Additionally, the data have potential applications in neutrino physics, where precise determinations of nuclear corrections are critical for neutrino oscillation experiments.

Practically, the paper provides a code for computing NPDFs and their uncertainties at specific values of $x$ and $Q^2$, enabling other researchers to apply these functions in their calculations. The potential for refining NPDFs will rely heavily on future experiments that can provide more precise measurements, especially concerning the gluon distributions.

In conclusion, the work suggests that further improvements in high precision experimental data, combined with robust theoretical analysis models, could yield substantial progress in comprehending the underlying complexities of nuclear parton distributions, most notably in the realms where gluonic contributions are pivotal. As nuclear parton distribution estimates evolve, they will facilitate both theoretical advancements and experimental explorations of nuclear matter under extreme conditions, paving the way for more comprehensive and accurate high-energy nuclear physics predictions.