We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.

We calculate the cross sections of inclusive J/ψ production in photoproduction and two-photon scattering, involving both direct and resolved photons, and in e + e − annihilation at next-to-leading order (NLO) within the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD), including the full relativistic corrections due to the intermediate 1 S J color-octet (CO) states. Exploiting also our previous results on hadroproduction, we perform a combined fit of the respective CO long-distance matrix elements (LDMEs) to all available highquality data of inclusive J/ψ production, from KEKB, LEP II, RHIC, HERA, the Tevatron, and the LHC, comprising a total of 194 data points from 26 data sets.

We study the polarization observables of J/ψ hadroproduction at next-to-leading order within the factorization formalism of nonrelativistic quantum chromodynamics. We complete the present knowledge of the relativistic corrections by also providing the contribution due to the intermediate 3 P [8] J color-octet states at this order, which turns out to be quite significant. Exploiting the color-octet long-distance matrix elements previously extracted through a global fit to experimental data of unpolarized J/ψ production, we provide theoretical predictions in the helicity and Collins-Soper frames and compare them with data taken by CDF at Fermilab Tevatron I and II and by ALICE at CERN LHC. The notorious CDF J/ψ polarization anomaly familiar from leading-order analyses persists at the quantum level, while the situation looks promising for the LHC, which is bound to bring final clarification.

The most precise top quark mass measurements use kinematic reconstruction methods, determining the top mass parameter of a Monte Carlo event generator m MC t . Because of hadronization and parton-shower dynamics, relating m MC t to a field theory mass is difficult. We present a calibration procedure to determine this relation using hadron level QCD predictions for observables with kinematic mass sensitivity. The highest precision measurements are based on direct reconstruction methods exploiting kinematic properties related to the top quark mass, and are based on multivariate fits that depend on a maximum amount of information on the top decay final states. This includes template and matrix element fits for distributions such as the measured invariant mass. These observables are highly differential, depending on experimental cuts and jet dynamics. Multipurpose Monte Carlo (MC) event generators are employed to do the analysis, and the results are influenced by both perturbative and nonperturbative QCD effects. Thus, the measured mass is the top mass parameter m MC t contained in the particular MC event generator. Its interpretation may also depend in part on the MC tuning and the observables used in the analysis.The systematic uncertainties from MC modeling are a dominant uncertainty in the above measurements, but do not address how m MC t is related to a mass parameter defined precisely in quantum field theory that can be globally used for higher-order predictions. The relation is nontrivial because it requires an understanding of the interplay between the partonic components of the MC generator (hard matrix elements and parton shower) and the hadronization model. In the context of top quark mass determinations, it is often assumed that MC generators should be considered as models whose partonic components and hadronization models are, through the tuning procedure, capable of describing experimental data to a precision that is higher than that of their partonic input.In the past m MC t has been frequently identified with the pole mass. This is compatible with parton-shower implementations for massive quarks, but a direct identification is disfavored because of sensitivity to nonperturbative effects from below the MC shower cutoff, Λ c ∼ 1 GeV. Also, the pole mass has an OðΛ QCD Þ renormalon ambiguity, while m MC t does not (since partonic information is not employed below Λ c ). It has been argued [4,5] can be calibrated into a field theory mass scheme through a fit of MC predictions to hadron level QCD computations for observables closely related to the distributions that enter the experimental analyses. In this Letter we provide a precise quantitative study on the interpretation of m MC t in terms of the MSR and pole mass schemes based on a hadron level prediction for the variable τ 2 for the production of a boosted top-antitop quark pair in e þ e − annihilation. It is defined aswhere the sum is over the 3-momenta of all final state particles, the maximum defines the thrust axisñ t , and Q is the center-of-ma...

We analyze the first measurement of ηc production, performed by the LHCb Collaboration, in the nonrelativistic-QCD (NRQCD) factorization framework at next-to-leading order (NLO) in the strong-coupling constant αs and the relative velocity v of the bound quarks including the feeddown from hc mesons. Converting the long-distance matrix elements (LDMEs) extracted by various groups from J/ψ yield and polarization data to the ηc case using heavy-quark spin symmetry, we find that the resulting NLO NRQCD predictions greatly overshoot the LHCb data, while the color-singlet model provides an excellent description.PACS numbers: 12.38. Bx, 12.39.St, 13.85.Ni, 14.40.Pq Despite concerted experimental and theoretical efforts ever since the discovery of the J/ψ meson in the November revolution of 1974 (The Nobel Prize in Physics 1976), the genuine mechanism underlying the production and decay of heavy quarkonia, which are QCD bound states of a heavy quark Q = c, b and its antiparticle Q, has remained mysterious. The effective quantum field theory of nonrelativistic QCD (NRQCD) [1] endowed with an appropriate factorization theorem [2] arguably constitutes the most probable candidate theory at the present time. This implies a separation of process-dependent shortdistance coefficients (SDCs), to be calculated perturbatively as expansions in the strong-coupling constant α s , from supposedly universal long-distance matrix elements (LDMEs), to be extracted from experiment. The relative importance of the latter is subject to velocity scaling rules [3], which predict each of the LDMEs to scale with a definite power of the heavy-quark velocity v. In this way, the theoretical predictions are organized as double expansions in α s and v. A crucial feature of this formalism is that the QQ pair can at short distances be produced in any Fock state n = 2S+1 L [a] J with definite spin S, orbital angular momentum L, total angular momentum J, and color multiplicity a = 1, 8. In this way, it complements the color-singlet (CS) model (CSM), which only includes the very 2S+1 L [1] J state of the physical quarkonium, and thus cures a severe conceptual shortcoming of the latter, namely the existence of uncanceled infrared (IR) singularities beyond L = 0. However, the CSM does provide IR-finite NLO predictions for S-wave charmonia, such as the η c and J/ψ mesons considered here.Despite its theoretical rigor, NRQCD factorization has reached the crossroads in the J/ψ case. While a global fit [4] to the J/ψ yields measured in hadroproduction, photoproduction, γγ scattering, and e + e − annihilation successfully pins down the leading color-octet (CO) LDMEs,, in compliance with the velocity scaling rules, the resulting predictions for J/ψ polarization in hadroproduction are in striking disagreement with measurements at the Fermilab Tevatron and the CERN LHC [5]. Vice versa, fits to data on J/ψ yield and polarization in hadroproduction work reasonably well [6][7][8], but hopelessly fail in comparisons to the world's data from other than hadronic collis...