We present the new nCTEQ15 set of nuclear parton distribution functions (nPDFs) with uncertainties. This fit extends the CTEQ proton PDFs to include the nuclear dependence using data on nuclei all the way up to 208 Pb. The uncertainties are determined using the Hessian method with an optimal rescaling of the eigenvectors to accurately represent the uncertainties for the chosen tolerance criteria. In addition to the Deep Inelastic Scattering (DIS) and Drell-Yan (DY) processes, we also include inclusive pion production data from RHIC to help constrain the nuclear gluon PDF. Furthermore, we investigate the correlation of the data sets with specific nPDF flavor components, and asses the impact of individual experiments. We also provide comparisons of the nCTEQ15 set with recent fits from other groups.

We present a Monte Carlo generator that implements significant theoretical improvements in the simulation of top-quark pair production and decay at the LHC. Spin correlations and off-shell effects in top-decay chains are described in terms of exact matrix elements for pp → + ν l −ν l bb at order α 4 α 2 S plus full NLO QCD corrections, where the leptons and l belong to different families, and b quarks are massive. Thus, the contributions from tt and W t single-top production, plus contributions without top resonances and all relevant quantum interferences between different channels are fully included. Matrix elements are matched to the Pythia8 parton shower using a recently proposed method that allows for a consistent treatment of resonances in the POWHEG framework. These theoretical improvements are especially important for the interpretation of precision measurements of the top-quark mass, for single-top analyses in the W t channel, and for tt and W t backgrounds in the presence of jet vetoes or cuts that enhance off-shell effects. The new generator is based on a process-independent interface of the OpenLoops amplitude generator with the POWHEG-BOX framework.

In this work we present a new subtraction method for next-to-leading order calculations that is particularly convenient even when narrow resonances are present. The method is particularly suitable for the implementation of next-to-leading order calculations matched to parton shower generators. It allows at the same time for the inclusion of all finite width effects, including interferences, and for a consistent treatment of resonances in the shower approach, preserving the mass of resonances near their peak. We implement our method, in a fully general and automatic way, within the POWHEG BOX framework, and illustrate it using as a test case the process of pp → µ + ν µ j b j, that is dominated by t-channel single top production.

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We provide a comprehensive comparison of W ± /Z vector boson production data in pPb and PbPb collisions at the LHC with predictions obtained using the nCTEQ15 PDFs. We identify the measurements which have the largest potential impact on the PDFs, and estimate the effect of including these data using a Bayesian reweighting method. We find this data set can provide information as regards both the nuclear corrections and the heavy flavor (strange quark) PDF components. As for the proton, the parton flavor determination/separation is dependent on nuclear corrections (from heavy target DIS, for example), this information can also help improve the proton PDFs.