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.
We revise the b∗ model for the Collins–Soper–Sterman resummed form factor to improve description of the leading-power contribution at nearly nonperturbative impact parameters. This revision leads to ...excellent agreement of the transverse momentum resummation with the data in a global analysis of Drell–Yan lepton pair and Z boson production. The nonperturbative contributions are found to follow universal quasi-linear dependence on the logarithm of the heavy boson invariant mass, which closely agrees with an estimate from the infrared renormalon analysis.
In order to measure spin-dependent parton distributions in production of
W
± bosons using the non-hermetic detectors of the Relativistic Heavy Ion Collider, an accurate model for distributions of ...charged leptons from the
W-boson decay is needed. We discuss the predictions for production and decay of the
W bosons based on a calculation for resummation of large logarithmic contributions originating from multiple soft gluon radiation. We compare the predictions for the spin-dependent resummed cross sections with the corresponding next-to-leading order results. We show that the lepton-level asymmetries can be reliably predicted by the resummation calculation and directly compared to the experimental data. A program for the numerical analysis of such cross sections in
γ
∗
-,
W
±-, and
Z
0-boson production is also presented.
Accurate measurement of spin-dependent parton distributions in production of electroweak bosons with polarized proton beams at the Relativistic Heavy Ion Collider depends on good understanding of QCD ...radiation at small transverse momenta
q
T
of vector bosons. We present a theoretical formalism for small-
q
T
resummation of the cross sections for production of
γ
∗
,
W
±, and
Z
0 bosons, with the subsequent decay of these bosons into lepton pairs, for arbitrary longitudinal polarizations of the proton beams.
The impact of recent measurements of heavy-flavour production in deep inelastic
ep
scattering and in
pp
collisions on parton distribution functions is studied in a QCD analysis in the fixed-flavour ...number scheme at next-to-leading order. Differential cross sections of charm- and beauty-hadron production measured by LHCb are used together with inclusive and heavy-flavour production cross sections in deep inelastic scattering at HERA. The heavy-flavour data of the LHCb experiment impose additional constraints on the gluon and the sea-quark distributions at low partonic fractions
x
of the proton momentum, down to
x
∼
5
×
10
-
6
. This kinematic range is currently not covered by other experimental data in perturbative QCD fits.
An overwhelming number of theoretical predictions for hadron colliders require parton distribution functions (PDFs), which are an important ingredient of theory infrastructure for the next generation ...of high-energy experiments. Here this whitepaper summarizes the status and future prospects for determination of high-precision PDFs applicable in a wide range of energies and experiments, in particular in precision tests of the Standard Model and in new physics searches at the high-luminosity Large Hadron Collider and Electron–Ion Collider. We discuss the envisioned advancements in experimental measurements, QCD theory, global analysis methodology, and computing that are necessary to bring unpolarized PDFs in the nucleon to the N2LO and N3LO accuracy in the QCD coupling strength. Special attention is given to the new tasks that emerge in the era of the precision PDF analysis, such as those focusing on the robust control of systematic factors both in experimental measurements and theoretical computations. Various synergies between experimental and theoretical studies of the hadron structure are explored, including opportunities for studying PDFs for nuclear and meson targets, PDFs with electroweak contributions or dependence on the transverse momentum, for incisive comparisons between phenomenological models for the PDFs and computations on discrete lattice, and for cross-fertilization with machine learning/AI approaches.
The Large Hadron–Electron Collider at the HL-LHC Aksakal, H; Alekhin, S; Allport, P P ...
Journal of physics. G, Nuclear and particle physics,
11/2021, Letnik:
48, Številka:
11
Journal Article
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