Parton distributions: a new global analysis

Abstract

We present a new analysis of parton distributions of the proton. This incorporates a wide range of new data, an improved treatment of heavy flavours and a reexamination of prompt photon production. The new set (MRST) shows systematic differences from previous sets of partons which can be identified with particular features of the new data and with improvements in the analysis. An 'explanation' of the behaviour seen on the Caldwell plot is offered.

Measurement of the anti-quark flavor asymmetry in the nucleon sea

“…σ pd /2σ pp for the iterative process, it was assumed that an existing PDF parameterization accurately described the quark distributions and the quantitȳ d(x) +ū(x) since these quantities have been constrained by previous measurements. The parameterizations used were CTEQ4M [15], MRS(R2) [16] and MRST [28]. While the ratio ofd(x) toū(x) was very poorly constrained in these parameterizations and therefore was adjusted with each iteration, the sum ofd(x) andū(x) was reasonably well known and it was held constant.…”

“…These parton distribution functions are shown for Q 2 = 54 The results from all three mass settings have been combined. The curves are the calculated cross section ratio using CTEQ4M [15], MRS(R2) [16], and MRST [28]. The bottom curve is calculated using CTEQ4M whered −ū has been set to zero.…”

Theoretical aspects of high-Q2deep inelastic scattering

“…propagates directly through to high Q 2 . For fixed-target DIS data at medium-large x, this uncertainty is of order ±3% (see for example [4]). Second, any uncertainty on α s (Q 2 ) affects the evolution of F 2 via the large-x DGLAP equation…”

“…4, taken from Ref. [4]. Evidently the error on α s induces an uncertainty of order ±5% in F 2 at high Q 2 ∼ 10 5 GeV 2 .…”

“…In Fig. 5 [4]. In the MRST fit, NMC n/p data are used to constrain the large-x d-quark pdf in this way.…”