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We study transverse momentum resummation for the azimuthal angular correlation in dijet production in hadron collisions based on the Collins-Soper-Sterman formalism. The complete one-loop calculations are carried out in the collinear framework for the differential cross sections at low imbalance transverse momentum between the two jets. Important cross-checks are performed to demonstrate that the soft divergences are canceled out between different diagrams and, in particular, for those associated with the final state jets. The leading and subleading logarithms are identified. All order resummation is derived following the transverse momentum dependent factorization at this order. Its phenomenological applications are also presented. [ABSTRACT FROM AUTHOR]

We study the transverse momentum dependent (TMD) parton distributions in the newly proposed quasiparton distribution function framework in Euclidean space. In this framework, the parton distributions can be extracted from lattice observables in a systematic expansion of 1/Pz, where Pz is the hadron momentum. A soft factor subtraction is found to be essential to make the TMDs calculable on the lattice. We show that the quasi-TMDs with the associated soft factor subtraction can be applied in hard QCD scattering processes such as Drell-Yan lepton pair production in hadronic collisions. This allows future lattice calculations to provide information on the nonperturbative inputs and energy evolutions for the TMDs. Extension to the generalized parton distributions and quantum phase space Wigner distributions will lead to a complete nucleón tomography on the lattice. [ABSTRACT FROM AUTHOR]

The nuclear suppression of heavy quarkonium production at low transverse momentum in pA collisions in high energy scatterings is investigated in the small-x factorization formalism. A universal suppression is found in the large Nc limit between the two formalisms to describe the heavy quarkonium production: the nonrelativistic QCD and the color-evaporation model. This provides an important probe to the saturation momentum at small x in the big nucleus. We also comment on the phenomenological applications of our results. [ABSTRACT FROM AUTHOR]

In this paper, we study the Bc-meson exclusive decays to S-wave charmonia and light pseudoscalar or vector mesons, i.e., π, K, ρ, and K* at the next-to-leading order (NLO) in the QCD coupling. The nonfactorizable contribution is included, which is absent in traditional naive factorization. Numerical results show that NLO QCD corrections markedly enhance the branching ratio with a K factor of 1.75 for Bc± → ηcπ± and 1.31 for Bc± → J/Ψπ± using certain input parameters. And the theoretical uncertainties for their branching ratios are reduced compared with that of direct tree-level calculation. In order to investigate the asymptotic behavior, the analytic form is obtained in the heavy quark limit, i.e., mb → ∞. We note that annihilation topologies contribute trivia in this limit, and the corrections at leading order in z=mc/mb expansion come from form factors and hard spectator interactions. At last, some related phenomenologies are also discussed. [ABSTRACT FROM AUTHOR]

We examine the QCD evolution for the transverse momentum dependent observables in hard processes of semi-inclusive hadron production in deep inelastic scattering and Drell-Yan lepton pair production in pp collisions, including the spin-average cross sections and Sivers single transverse spin asymmetries. We show that the evolution equations derived by a direct integral of the Collins-Soper-Sterman evolution kernel from low to high Q can describe well the transverse momentum distributions of the unpolarized cross sections in the Q² range from 2 to 100 GeV². In addition, the matching is established between our evolution and the Collins-Soper-Sterman resummation with b* prescription and Konychev-Nodalsky parametrization of the nonperturbative form factors, which are formulated to describe the Drell-Yan lepton pair and W/Z boson production in hadronic collisions. With these results, we present the predictions for the Sivers single transverse spin asymmetries in Drell-Yan lepton pair production and W± boson production in polarized pp and π- p collisions for several proposed experiments. We emphasize that these experiments will not only provide crucial test of the sign change of the Sivers asymmetry but also provide important opportunities to study the QCD evolution effects. [ABSTRACT FROM AUTHOR]

We extend the nonrelativistic QCD (NRQCD) prediction for the production of heavy quarkonium with low transverse momentum in hadronic collisions by taking into account effects from all-order soft gluon resummation. Following the Collins-Soper-Sterman formalism, we resum the most singular terms in the partonic subprocesses. The theoretical predictions of J/? and ? productions are compared to the experimental data from the fixed target experiments (E866) and the collider experiments (RHIC, Tevatron, LHC). The associated nonperturbative Sudakov form factor for the gluon distributions is found to be different from the previous assumption of rescaling the quark form factor by the ratio of color factors. This conclusion should be further checked by future experiments on Higgs boson and/or diphoton production in pp collisions. We also comment on the implication of our results on determining the color-octet matrix elements associated with the J/? and ? productions in the NRQCD factorization formalism. [ABSTRACT FROM AUTHOR]

We investigate the energy evolution of the azimuthal spin asymmetries in semi-inclusive hadron production in deep inelastic scattering (SIDIS) and Drell-Yan lepton pair production in pp collisions. The scale dependence is evaluated by applying an approximate solution to the Collins-Soper-Sterman evolution equation at one-loop order, which is adequate for moderate Q² variations. This describes well the unpolarized cross sections for the SIDIS and Drell-Yan process in the Q² range of 2.4-100 GeV². A combined analysis of the Sivers asymmetries in SIDIS from HERMES and COMPASS experiments and the predictions for the Drell-Yan process at RHIC at √S = 200 GeV are presented. We further extend to the Collins asymmetries and find, for the first time, a consistent description for HERMES/COMPASS and BELLE experiments with the evolution effects. We emphasize an important test of the evolution effects by studying di-hadron azimuthal asymmetry in e+e- annihilation at moderate energy range, such as at BEPC at √S = 4.6 GeV. [ABSTRACT FROM AUTHOR]

We investigate the gluon distribution functions and their contributions to the Higgs boson production in pp collisions in the transverse momentum-dependent factorization formalism. In addition to the usual azimuthal symmetric transverse momentum-dependent gluon distribution, we find that the azimuthal correlated gluon distribution also contributes to the Higgs boson production. This explains recent findings on the additional contribution in the transverse momentum resummation for the Higgs boson production as compared to that for electroweak boson production processes. We further examine the small-x naive kt-factorization in the dilute region and find that the azimuthal correlated gluon distribution contribution is consistently taken into account. The result agrees with the transverse momentum-dependent factorization formalism. We comment on the possible breakdown of the naive kt-factorization in the dense medium region, due to the unique behaviors for the gluon distributions. [ABSTRACT FROM AUTHOR]

Quantum chromodynamics (QCD) claims that the major source of the nucleon invariant mass is not the Higgs mechanism but the trace anomaly in the QCD energy-momentum tensor. Although experimental and theoretical results support such a conclusion, a direct demonstration is still absent. We present the first lattice QCD calculation of the quark and gluon trace anomaly contributions to the hadron masses, using the overlap fermion on the 2 + 1 -flavor dynamical domain wall quark ensemble at m π = 340 MeV and lattice spacing a = 0.1105 fm. The result shows that the gluon trace anomaly contributes to most of the nucleon mass, the contribution in the pion state is smaller than that in others nearly by a factor of ~10, and the gluon trace anomaly density in the center of the pion is negative. The gluon trace anomaly coefficient g3 = − 0.056 (6) we obtained is consistent with its regularization-independent leading-order value (-1+2Nf/3)/(4π)2 perfectly. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We study the soft gluon radiation effects for the s-channel single top quark production at the LHC. By applying the transverse momentum dependent factorization formalism, the large logarithms about the small total transverse momentum (q⊥) of the single-top plus one-jet final state system are resummed to all orders in the expansion of the strong interaction coupling at the accuracy of next-to-leading Logarithm (NLL). We compare our numerical results with pythia and find that both the q⊥ and ϕ* observables from pythia are consistent with our prediction. Furthermore, we point out that the soft gluon radiation effects from the final state become significant in this process, especially for the boosted kinematical region. [ABSTRACT FROM AUTHOR]

We study the effect of multiple soft gluon radiation on the kinematical distributions of the t-channel single top quark production at the LHC. By applying the transverse momentum-dependent factorization formalism, large logarithms (of the ratio of large invariant mass Q and small total transverse momentum q⊥ of the single-top plus one-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, including the complete next-to-leading-order corrections. We show that the main difference from PYTHIA prediction lies in the inclusion of the exact color coherence effect between the initial and final states in our resummation calculation, which becomes more important when the final state jet is required to be in the forward region. We further propose to apply the experimental observable ϕ*, similar to the one used in analyzing precision Drell-Yan data, to test the effect of multiple gluon radiation in the single-top events. The effect of the bottom quark mass is also discussed. [ABSTRACT FROM AUTHOR]

We investigate the nucleon tensor charge from current experiments by a combined analysis of the Collins asymmetries in two hadron production in e+e− annihilations and semi-inclusive hadron production in deep inelastic scattering processes. The transverse momentum dependent evolution is taken into account, for the first time, in the global fit of the Collins fragmentation functions and the quark transversity distributions at the approximate next-to-leading logarithmic order. We obtain the nucleon tensor charge contribution from up and down quarks as δu = +0.30+0.12−0.08 and δd = −0.20+0.28−0.11 at 90% confidence level for momentum fraction 0.0065 ≤ xB ≤ 0.35 and Q² = 10 GeV² [ABSTRACT FROM AUTHOR]

The mass components of charmoniumlike states are investigated through the decomposition of QCD energy-momentum tensor (EMT) on lattice. The quark mass contribution ⟨Hm⟩ and the momentum fraction ⟨x⟩ of valence charm quark and antiquark are calculated for conventional 1S, 1P, 1D charmonia and the exotic 1-+ charmoniumlike state, based on the Nf=2+1 gauge configurations generated by the RBC/UKQCD collaboration. It is found that ⟨Hm⟩ is close to each other and around 2.0 to 2.2 GeV for these states, which implies that the mass splittings among these states come almost from the gluon contribution of QCD trace anomaly. The ⟨x⟩ of the 1-+ state is only around 0.55, while that in conventional charmonia is around 0.7 to 0.8. This difference manifests that the proportion of light quarks and gluons in the 1-+ charmoniumlike state is significantly larger than conventional states. [ABSTRACT FROM AUTHOR]

We analyze the lattice spacing dependence for the pion unpolarized matrix element of a quark bilinear operator with a Wilson link (parton quasidistribution functions operator, quasi-PDFs) in the rest frame, using 13 lattice spacings ranging from 0.032 to 0.121 fm. We compare results for three different fermion actions with or without good chiral symmetry on dynamical gauge ensembles from three collaborations. This investigation is motivated by the fact that the gauge link generates a 1 / a divergence, the cancellation of which in many ratios can be numerically tricky. Indeed, our results show that this cancellation deteriorates with decreasing lattice spacing, and that the RI/MOM method leaves a linearly divergent residue for quasi-PDFs. We also show that in the Landau gauge the interaction between the Wilson link and the external state results in a linear divergence which depends on the discretized fermion action. [ABSTRACT FROM AUTHOR]

We present a detailed lattice QCD study of the unpolarized isovector quark parton distribution function (PDF) using a large-momentum effective theory framework. We choose a quasi-PDF defined by a spatial correlator which is free from mixing with other operators of the same dimension. In the lattice simulation, we use a Gaussian-momentum-smeared source at Mπ=356  MeV and Pz∈{1.8,2.3}  GeV. To control the systematics associated with the excited states, we explore five different source-sink separations. The nonperturbative renormalization is conducted in a regularization-independent momentum subtraction scheme, and the matching between the renormalized quasi-PDF and ̅MS PDF is calculated based on perturbative QCD up to one-loop order. Systematic errors due to renormalization and perturbative matching are also analyzed in detail. Our results for light-cone PDF are in reasonable agreement with the latest phenomenological analysis. [ABSTRACT FROM AUTHOR]