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Based on a general form of the effective vertex functions for the decays of P-wave charmonia χcJ, angular distribution formulas for the subsequent decays χcJ → J/ψγ and J/ψ → μ+μ− are derived. The formulas are the same as those obtained in a different approach in the literature. Our formulas are expressed in a more general form, including parity violation effects and the full angular dependence of J/ψ and muon in the cascade decay χcJ → J/ψγ → μ+μ−γ. The χcJ polarization observables are expressed in terms of rational functions of the spin density matrix elements of χcJ production. Generalized rotation-invariant relations for arbitrary integer-spin particles are also derived and their expressions in terms of observable angular distribution parameters are given in the χc1 and χc2. To complement our previous direct -J/μ polarization result, we also discuss the impact on the observable prompt-J/ψ polarization. As an illustrative application of our angular distribution formulas, we present the angular distributions in terms of the tree-level spin density matrix elements of χc1 and χc2 production in several different frames at the Large Hadron Collider. Moreover, a reweighting method is also proposed to determine the entire set of the production spin density matrix elements of the χc2, some of which disappear or are suppressed for vanishing higher-order multipole effects making the complete extraction difficult experimentally. [ABSTRACT FROM AUTHOR]

The dijet invariant mass distributions from the hadronic decay of unpolarized top quark (t → bW+ followed by W+ → ud̄) are calculated, including the next-to-leading order QCD radiative corrections. We treat the top decay in the complex mass scheme due to the existence of the intermediate state W boson. Our analytical expressions are also available in different dimensional regularization schemes and γ5 strategies. Finally, in order to construct the jets, we use different jet algorithms to compare their influences on our results. The obtained dijet mass distributions from the top quark decay are useful to distinguish these dijets from those produced via other sources and to clarify the issue about the recent CDF Collaboration's Wjj anomaly. [ABSTRACT FROM AUTHOR]

We critically (re)examine the associated production process of a J/ψ meson plus an open charm hadron at the LHC in the proton-proton (pp) and proton-lead (pPb) collisions. Such a process is very intriguing in the sense of tailoring to explore the double parton structure of nucleons and to determine the geometry of partons in nuclei. In order to interpret the existing pp data with the LHCb detector at the center-of-mass energy √s=7 TeV, we introduce two overlooked mechanisms for the double parton scattering (DPS) and single parton scattering (SPS) processes. Besides the conventional DPS mode, where the two mesons are produced almost independently in the two separate scattering subprocesses, we propose a novel DPS mechanism that the two constituent (heavy) quarks stemming from two hard scatterings can form into a composite particle, like the J/ψ meson, during the hadronization phase. It yields a strong correlation in the final state from the two distinct scattering subprocesses per hadron-hadron collision. Such a mechanism should be ubiquitous for quarkonium associated production processes involving more-than-one pair of same-flavor heavy quarks. However, it turns out the corresponding contribution is small in J/ψ+c¯c hadroproduction. On the contrary, we point out that the resummation of the initial state logarithms due to gluon splitting into a charm quark pair is crucial to understand the LHCb measurement, which was overlooked in the literature. We perform a proper matching between the perturbative calculations in different initial-quark flavor number schemes, generically referring to the variable flavor number scheme. The new variable flavor number scheme calculation for the process strongly enhances the SPS cross sections, almost closing the discrepancies between theory and experiment. Finally, we present our predictions for the forthcoming LHCb measurement in pPb collisions at √sNN=8.16 TeV. Some interesting observables are exploited to set up the control regions of the DPS signal and to probe the impact-parameter-dependent parton densities in lead. [ABSTRACT FROM AUTHOR]

We propose a new method to determine the spatially or impact-parameter dependent nuclear parton distribution functions (nPDFs) using the double parton scattering (DPS) processes in high-energy heavy-ion (proton-nucleus and nucleus-nucleus) collisions. We derive a simple generic DPS formula in nuclear collisions by accommodating both the nuclear collision geometry and the spatially dependent nuclear modification effect, under the assumption that the impact-parameter dependence of nPDFs is only related to the nuclear thickness function. While the geometric effect is widely adopted, the impact of the spatially dependent nuclear modification on DPS cross sections has been overlooked so far, which can, however, be significant when the initial nuclear modification is large. In turn, the DPS cross sections in heavy-ion collisions can provide useful information on the spatial dependence of nPDFs. They can be, in general, obtained in minimum-bias nuclear collisions, featuring the virtue of independence of Glauber modeling. [ABSTRACT FROM AUTHOR]

We present for the first time the full automation of collider predictions matched with parton showers at the next-to-leading accuracy in QCD within nontrivial extensions of the standard model. The sole inputs required from the user are the model Lagrangian and the process of interest. As an application of the above, we explore scenarios beyond the standard model where new colored scalar particles can be pair produced in hadron collisions. Using simplified models to describe the new field interactions with the standard model, we present precision predictions for the LHC within the MADGRAPH5_aMC@NLO framework. [ABSTRACT FROM AUTHOR]

We present the reweighting of two sets of nuclear parton distribution functions (PDFs), nCTEQ15 and EPPS16, using a selection of experimental data on heavy-flavor meson [D0, J/ψ, B→J/ψ and Υ(1S)] production in proton-lead collisions at the LHC which were not used in the original determination of these nuclear PDFs. The reweighted PDFs exhibit significantly smaller uncertainties thanks to these new heavy-flavor constraints. We present a comparison with another selection of data from the LHC and relativistic heavy ion collider (RHIC) which were not included in our reweighting procedure. The comparison is overall very good and serves as a validation of these reweighted nuclear PDF sets, which we dub nCTEQ15rwHF and EPPS16rwHF. This indicates that the LHC and forward RHIC heavy-flavor data can be described within the standard collinear factorization framework with the same (universal) small-x gluon distribution. We discuss how we believe such reweighted PDFs should be used as well as the limitations of our procedure. [ABSTRACT FROM AUTHOR]