Search

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]

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 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]