Improved parton distributions from global analysis of recent deep inelastic scattering and inclusive jet data

Abstract

The impact of recent precision measurements of DIS structure functions and inclusive jet production at the Fermilab Tevatron on the global QCD analysis of parton distribution functions is studied in detail. Particular emphasis is placed on exploring the range of variation of the gluon distribution G(x,Q) allowed by these new data. The strong coupling of G(x,Q) with ␣ s is fully taken into account. A new generation of CTEQ parton distributions, CTEQ4, is presented. It consists of the three standard sets ͓modified minimal subtraction (MS), deep inelastic scattering ͑DIS͒, and leading order ͑LO͔͒, a series that gives a range of parton distributions with corresponding ␣ s 's, and a set with a low starting value of Q. Previously obtained gluon distributions that are consistent with the high E t jet cross section are also discussed in the context of this new global analysis.

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.…”

“…This method of fitting all the relevant data is called a global fit. Two groups that have generated global fits parameterizing the nucleon sea are CTEQ [15] and MRS [16]. Prior to the measurements by NMC and NA51, the usual assumption was thatd(x) =ū(x).…”

“…This poorly constrained parameterization, shown 11 These 'other methods', which will not be discussed in this dissertation, include neutrino induced DIS, W production asymmetry, and Semi-inclusive DIS. [15] prior to FNAL E866/NuSea. These parton distribution functions are shown for Q 2 = 54 GeV 2 .…”

“…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.…”

“…I know you have more to teach me, I hope you don't stop. 6 An old parameterization of the proton published by CTEQ [15] prior to FNAL E866/NuSea. These parton distribution functions are shown for Q 2 = 54 The results from all three mass settings have been combined.…”