We describe the implementation of quantum electrodynamic (QED) evolution at leading order (LO) along with quantum chromodynamic (QCD) evolution at next-to-leading order (NLO) in the CTEQ-TEA global ...analysis package. The inelastic contribution to the photon parton distribution function (PDF) is described by a two-parameter ansatz, coming from radiation off the valence quarks, and based on the CT14 NLO PDFs. Setting the two parameters to be equal allows us to completely specify the inelastic photon PDF in terms of the inelastic momentum fraction carried by the photon, (ProQuest: Formulae and/or non-USASCII text omitted), at the initial scale Q sub(0)=1.295GeV. We obtain constraints on the photon PDF by comparing with ZEUS data S. Chekanov et al.(ZEUS Collaboration), Phys. Lett. B 687, 16 (2010) on the production of isolated photons in deep inelastic scattering, eparrowrightegamma+X. For this comparison we present a new perturbative calculation of the process that consistently combines the photon-initiated contribution with the quark-initiated contribution. Comparison with the data allows us to put a constraint at the 90% confidence level of (ProQuest: Formulae and/or non-USASCII text omitted) for the inelastic photon PDF at the initial scale of Q sub(0)=1.295GeV in the one-parameter radiative ansatz. The resulting inelastic CT14QED PDFs will be made available to the public. In addition, we also provide CT14QEDinc PDFs, in which the inclusive photon PDF at the scale Q sub(0) is defined by the sum of the inelastic photon PDF and the elastic photon distribution obtained from the equivalent photon approximation.
We present new parton distribution functions (PDFs) at next-to-next-to-leading order (NNLO) from the CTEQ-TEA global analysis of quantum chromodynamics. These differ from previous CT PDFs in several ...respects, including the use of data from LHC experiments and the new D0 charged-lepton rapidity asymmetry data, as well as the use of a more flexible parametrization of PDFs that, in particular, allows a better fit to different combinations of quark flavors. Predictions for important LHC processes, especially Higgs boson production at 13 TeV, are presented. These CT14 PDFs include a central set and error sets in the Hessian representation. For completeness, we also present the CT14 PDFs determined at the LO and the NLO in QCD. Besides these general-purpose PDF sets, we provide a series of (N)NLO sets with various alpha sub()svalues and additional sets in general-mass variable flavor number schemes, to deal with heavy partons, with up to three, four, and six active flavors
We derive all order soft gluon resummation in dijet azimuthal angular correlation in hadronic collisions at the next-to-leading logarithmic level. The relevant coefficients for the Sudakov ...resummation factor, the soft and hard factors, are calculated. The theory predictions agree well with the experimental data from D0 Collaboration at the Tevatron. This provides a benchmark calculation for the transverse momentum dependent QCD resummation for jet productions in hadron collisions.
We present the new parton distribution functions (PDFs) from the CTEQ-TEA collaboration, obtained using a wide variety of high-precision Large Hadron Collider (LHC) data, in addition to the combined ...HERA I + II deep-inelastic scattering dataset, along with the datasets present in the CT14 global QCD analysis. New LHC measurements in single-inclusive jet production with the full rapidity coverage, as well as production of Drell-Yan pairs, top-quark pairs, and high-pT Z bosons, are included to achieve the greatest sensitivity to the PDFs. The parton distributions are determined at next-to-leading order and next-to-next-to-leading order, with each of these PDFs accompanied by error sets determined using the Hessian method. Fast PDF survey techniques, based on the Hessian representation and the Lagrange multiplier method, are used to quantify the preference of each data set to quantities such as αs(mZ), and the gluon and strange quark distributions. We designate the main resulting PDF set as CT18. The ATLAS 7 TeV precision W / Z data are not included in CT18, due to their tension with other datasets in the global fit. Alternate PDF sets are generated including the ATLAS precision 7 TeV W / Z data (CT18A), a new scale choice for low- x DIS data (CT18X), or all of the above with a slightly higher choice for the charm mass (CT18Z). Theoretical calculations of standard candle cross sections at the LHC (such as the g g fusion Higgs boson cross section) are presented.
xWe discuss how to apply the Hessian method (i) to predict the impact of a new data set (or sets) on the parton distribution functions (PDFs) and their errors, by producing an updated best-fit PDF ...and error PDF sets, such as the CTEQ-TEA PDFs; (ii) to predict directly the effect of a new data set on the PDF errors of any other set of observables, without the need to recalculate using the new error PDFs; and (iii) to transform the original set into a reduced set of error PDFs which is optimized for a specific set of observables to reproduce the PDF-induced uncertainties to any specified precision. We present a software package, ePump (Error PDF Updating Method Package), that can be used to update or optimize a set of PDFs, including the best-fit PDF set and Hessian eigenvector pairs of PDF sets (i.e., error PDFs), and to update any other set of observables. We demonstrate the potential of the program by presenting selected phenomenological applications relevant to the Large Hadron Collider. Special care is given to discuss the assumptions made and the limitations of this theoretical framework compared to a treatment by the full global-analysis program.
We present a fully differential next-to-next-to-leading-order calculation of t-channel single top quark production and decay at the LHC under a narrow-width approximation and neglecting cross talk ...between incoming protons. We focus on the fiducial cross sections at 13 TeV, finding that the next-to-next-to-leading-order QCD corrections can reach the level of −6%. The scale variations are reduced to the level of a percent. Our results can be used to improve experimental acceptance estimates and the measurements of the single top quark production cross section and the top quark electroweak couplings.
The strong force which binds hadrons is described by the theory of quantum chromodynamics (QCD). Determining the character and manifestations of QCD is one of the most important and challenging ...outstanding issues necessary for a comprehensive understanding of the structure of hadrons. Within the context of the QCD parton picture, the parton distribution functions (PDFs) have been remarkably successful in describing a wide variety of processes. However, these PDFs have generally been confined to the description of collinear partons within the hadron. New experiments and facilities provide the opportunity to additionally explore the transverse structure of hadrons which is described by generalized parton distributions (GPDs) and transverse-momentum-dependent parton distribution functions (TMD PDFs). In our previous report Lin et al. (2018), we compared and contrasted the two main approaches used to determine the collinear PDFs: the first based on perturbative QCD factorization theorems, and the second based on lattice-QCD calculations. In the present report, we provide an update of recent progress on the collinear PDFs, and also expand the scope to encompass the generalized PDFs (GPDs and TMD PDFs). We review the current state of the various calculations, and consider what new data might be available in the near future. We also examine how a shared effort can foster dialog between the PDF and lattice-QCD communities, and yield improvements for these generalized PDFs.
We study the multiple soft gluon radiation effects in Z-boson plus jet production at the LHC. By applying the transverse-momentum-dependent factorization formalism, the large logarithms introduced by ...the small total transverse momentum of the Z-boson plus leading-jet final-state system are resummed to all orders in the expansion of the strong interaction coupling at the accuracy of the next-to-leading logarithm (NLL). We also compare the prediction of our resummation calculation to the CMS data by employing a reweighting procedure to estimate the effect from imposing kinematic cuts on the leptons from Z-boson decay, and we find good agreement for both the imbalance transverse momentum and the azimuthal angle correlation of the final-state Z-boson and leading-jet system, for pp→Z+jet production at the LHC.
PDF
