Abstract
Experimental measurements in deep-inelastic scattering and lepton-pair production on deuterium targets play an important role in the flavor separation of u and d (anti)quarks in global QCD analyses of the parton distribution functions (PDFs) of the nucleon. We investigate the impact of theoretical corrections accounting for the light-nuclear structure of the deuteron upon the fitted u, d-quark, gluon, and other PDFs in the CJ15 and CT18 families of next-to-leading order CTEQ global analyses. The investigation is done using the L_2 sensitivity statistical method, which provides a common metric to quantify the strength of experimental constraints on various PDFs and ratios of PDFs in the two distinct fitting frameworks. Using the L_2 sensitivity and other approaches, we examine the compatibility of deuteron data sets with other fitted experiments under varied implementations of the deuteron corrections. We find that freely-fitted deuteron corrections modify the PDF uncertainty at large momentum fractions and will be relevant for future PDFs affecting electroweak precision measurements.
Highlights
We illustrate the importance of fixed-target data in the determination of the weak mixing angle with the help of Lagrange Multiple (LM) scans [21] in Fig. 2, in which we examine the dependence of the figure-of-merit function χ 2 in the CT18Z nextto-next-to-leading order (NNLO) analysis [11] on the values of the valence uval and dval quarks at x = 0.03 and Q = 85 GeV
JLab (CJ) and CTEQ-TEA (CT), using the L2 sensitivity statistical metric developed in Refs. [15,16]
We made a number of technical adjustments to each framework in order to reconcile the CT and CJ treatment of parton distribution functions (PDFs) uncertainties and thereby render them sufficiently similar to be meaningfully juxtaposed
Summary
Extracting parton-level information from nuclear data sets involving the deuteron or heavier targets requires an understanding of the effects of the nuclear environment [8,14]. It has been known empirically for some time that the structure functions of these heavier nuclear targets exhibit x- and Adependent deviations from the structure function of the physical deuteron, owing to a variety of physical processes characterizing the nuclear medium [50,51,52,53], including the heavy-nucleus analogue of the EMC and Fermi-motion effects discussed for the deuteron at high x, and nuclear (anti)shadowing phenomena at lower x To address these effects, the CT group corrects DIS cross sections on iron (CCFR [47], CDHSW [54], and NuTeV [48]) and proton-copper Drell–Yan (E605 [55]) to the corresponding cross sections on deuterium using a phenomenological parametrization of the nuclear-todeuteron cross section ratios based on results in [51] (see [56], Fig. 2a), which depends on x but not on Q2 in the fitted region. We will accomplish this by analyzing the L2 sensitivity to various PDFs [16], a simple informative figure of merit that allows us to look inside the CJ and CT fits and understand the constraints from the fitted experiments on various parton flavors in an expansive region of x and Q
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