Distribution functions for partons in nuclei

Abstract

We suggest that a previously conjectured relation between Structure Functions (SF) for nuclei and nucleons also links distribution functions (df) for partons in a nucleus and in nucleons. The above suggestion ensures in principle identical results for SF F A 2 , whether computed with hadronic or partonic degrees of freedom. In practice there are differences, due to different F n 2 input. We show that the thus defined nuclear parton distribution functions (pdf) respect standard sumrules. In addition we numerically compare some moments of nuclear SF, and find agreement between results, using hadronic and partonic descriptions. We present computations of EMC ratios for both and compare those with hadronic predictions and data. In spite of substantial differences in the participating SF, the two representations produce approximately the same EMC ratios. The apparent correlation between the above deviations is ascribed to a sumrule for F A 2 . We conclude with a discussion of alternative approaches to nuclear pdf. On Distribution Functions for Partons in Nuclei AbstractWe suggest that a previously conjectured relation between Structure Functions (SF) for nuclei and nucleons also links distribution functions (df) for partons in a nucleus and in nucleons. The above suggestion ensures in principle identical results for SF F A 2 , whether computed with hadronic or partonic degrees of freedom. In practice there are differences, due to different F n 2 input. We show that the thus defined nuclear parton distribution functions (pdf) respect standard sumrules.In addition we numerically compare some moments of nuclear SF, and find agreement between results, using hadronic and partonic descriptions. We present computations of EMC ratios for both and compare those with hadronic predictions and data. In spite of substantial differences in the participating SF, the two representations produce approximately the same EMC ratios. The apparent correlation between the above deviations is ascribed to a sumrule for F A 2 . We conclude with a discussion of alternative approaches to nuclear pdf.

Relation between nuclear and nucleon structure functions and their moments

“…In particular [10,12] M A,th (n = 2, Q 2 → ∞) → In spite of the above remarks, S D for low n accurately follows the theoretical curves, but for increasing n data overshoots predictions up to ≈15% (Fig. 5).…”

“…The latter can be evaluated by use of purely hadronic notions, such as single-nucleon spectral functions, nuclear density matrices of various orders, NN forwardscattering amplitudes (fsa's), etc. Support for the validity of convolution (1.3) came mainly from the reasonable description of a large body of inclusive scattering cross-section data for Q 2 > ∼ Q 2 0 ≈ 2.5 GeV 2 [7][8][9]. For later reference, we mention that convolution (1.3) has its deficiencies.…”

“…[8]). In a straightforward way one can generalize the above for any target A, including the averaged N. The latter requires in addition to F p 2 knowledge of F n 2 , for which there is no direct experimental information.…”

“…The above requirement is not anywhere sufficient to determine those pdf's, and the apparent freedom is exploited by two deliberate choices [10]. An inessential choice is one for which we assume F A 2 to be the same combination of nuclear pdf's, as F N 2 is of nucleon ones; thus (for clarity we drop the x, Q 2 dependence in arguments)…”

“…In practice the input F n 2 for the two differs (see Ref. [10] for a discussion). Between parentheses we add that, being the same SF as in that of convolution (1.3), f carries along the above-mentioned deficiencies.…”