nucl-th digest · Sep 21, 2016

Glue spin and helicity in proton from lattice QCD

We report the first lattice QCD calculation of the glue spin in the nucleon. The lattice calculation is carried out with valence overlap fermions on 2+1 flavor DWF gauge configurations on four lattice spacings and four volumes including an ensemble with physical values for the quark masses. The glue spin

S_{G}

in the Coulomb gauge in the

MS

scheme is obtained with the 1-loop perturbative matching. We find the results fairly insensitive to lattice spacing and quark masses. We also find that the proton momentum dependence of

S_{G}

in the range

0 \leq ∣ p ∣ < 1.5

GeV is very mild, and we determine it in the large momentum limit to be

S_{G} = 0.251 (47) (16)

at the physical pion mass in the

MS

scheme at

μ^{2} = 10

GeV

^{2}

. If the matching procedure in large momentum effective theory is neglected,

S_{G}

is equal to the glue helicity measured in high-energy scattering experiments.

Comments:: Version accepted for publication in Physical Review Letters, 4 pages, 4 figures, supplemental materials are attached after the content
Subjects:: High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:: 1609.05937 [pdf]

PRL(2017)·97 citations

[Submitted on 20 Sept 2016] (cross-list from hep-ph)

Multi-particle correlations and KNO scaling in the medium-induced jet evolution

Miguel A. Escobedo🇫🇷 · Edmond Iancu🇫🇷

We study the gluon distribution produced via successive medium-induced branchings by an energetic jet propagating through a weakly-coupled quark-gluon plasma. We show that under suitable approximations the evolution of the jet can be described as a classical stochastic process, which is exactly solvable. For this process, we construct exact analytic solutions for all the n-point correlation functions (the n-body densities in the space of energy). The corresponding results for the one-point and the two-point functions were already known, but those for the higher-point functions are new. These results demonstrate strong correlations associated with the existence of common ancestors in the branching process. By integrating these n-point functions over the gluon energies, we deduce the mean gluon multiplicity $⟨ N ⟩$ as well as the higher moments $⟨ N^{p} ⟩$ with $p \geq 2$ . We find that the multiplicities of the soft gluons are parametrically large and show a remarkable regularity, known as Koba-Nielsen-Olesen (KNO) scaling: the reduced moments $⟨ N^{p} ⟩ / ⟨ N ⟩^{p}$ are pure numbers, independent of any of the physical parameters of the problem. We recognize a special negative binomial distribution which is characterized by large statistical fluctuations. These predictions can be tested in Pb+Pb collisions at the LHC, via event-by-event measurements of the di-jet asymmetry.

Comments:: 31 pages, 7 figures
Subjects:: High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:: 1609.06104 [pdf]

JHEP(2016)·11 citations

Wednesday·September 21, 2016

Glue spin and helicity in proton from lattice QCD

Multi-particle correlations and KNO scaling in the medium-induced jet evolution

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