A new slant on hadron structure Detmold, W; Leinweber, D B; Melnitchouk, W ...
Pramāṇa,
08/2001, Letnik:
57, Številka:
2-3
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
Rather than regarding the restriction of current lattice QCD simulations to quark masses that are 5–10 times larger than those observed as a problem, we note that this presents a wonderful ...opportunity to deepen our understanding of QCD. Just as it has been possible to learn a great deal about QCD by treating Nc as a variable, so the study of hadron properties as a function of quark mass is leading us to a deeper appreciation of hadron structure. As examples we cite progress in using the chiral properties of QCD to connect hadron masses, magnetic moments, charge radii and structure functions calculated at large quark masses within lattice QCD with the values observed physically.
Asymmetries in the quark momentum distributions in the proton reveal fundamental aspects of strong interaction physics. Differences between {anti u} and {anti d} quarks in the proton sea provide ...insight into the dynamics of the pion cloud around the nucleon and the nature of chiral symmetry breaking. Polarized flavor asymmetries allow the effects of pion clouds to be disentangled from those of antisymmetrization. Asymmetries between s and {anti s} quark distributions in the nucleon are also predicted from the chiral properties of QCD.
We perform a global QCD analysis of high energy scattering data within the JAM Monte Carlo framework, including a coupling to a dark photon that augments the standard model electroweak coupling via ...kinetic mixing with the hypercharge \(B\) boson. Including the most recent measurement of the anomalous magnetic moment of the muon as a constraint, we find a significant reduction in the combined \(\chi^2\), favoring the inclusion of a dark photon, with a statistical significance in excess of 8\(\sigma\). With respect to the experimental data, the improvements in the theoretical predictions are spread across a wide range of \(x\) and \(Q^2\), with the largest improvement corresponding to neutral current data from HERA, while the best fit yields a value of \(g-2\) which significantly reduces the disagreement with the latest experimental determination. The best fit yields a dark photon mass in the range 4.2--6.2 GeV and a mixing parameter of order 0.1.
The self-energies of the full set of flavor SU(3) octet and decuplet baryons are computed within a relativistic chiral effective theory framework. The leading nonanalytic chiral behavior is derived ...for the octet and decuplet masses, and a finite-range regularization consistent with Lorentz and gauge invariance is applied to account for the finite size of the baryons. Using a four-dimensional dipole form factor, the relative importance of various meson-baryon loop contributions to the self-energies is studied numerically as a function of the dipole range parameter and meson mass, and comparison is made between the relativistic results and earlier approximations within the heavy baryon limit.
Asymmetries in the quark momentum distributions in the proton reveal fundamental aspects of strong interaction physics. Differences between {anti u} and {anti d} quarks in the proton sea provide ...insight into the dynamics of the pion cloud around the nucleon and the nature of chiral symmetry breaking. Polarized flavor asymmetries allow the effects of pion clouds to be disentangled from those of antisymmetrization. Asymmetries between s and {anti s} quark distributions in the nucleon are also predicted from the chiral properties of QCD.
AI-supported algorithms, particularly generative models, have been
successfully used in a variety of different contexts. In this work, we
demonstrate for the first time that generative adversarial ...networks (GANs) can
be used in high-energy experimental physics to unfold detector effects from
multi-particle final states, while preserving correlations between kinematic
variables in multidimensional phase space. We perform a full closure test on
two-pion photoproduction pseudodata generated with a realistic model in the
kinematics of the Jefferson Lab CLAS g11 experiment. The overlap of different
reaction mechanisms leading to the same final state associated with the CLAS
detector's nontrivial effects represents an ideal test case for AI-supported
analysis. Uncertainty quantification performed via bootstrap provides an
estimate of the systematic uncertainty associated with the procedure. The test
demonstrates that GANs can reproduce highly correlated multidifferential cross
sections even in the presence of detector-induced distortions in the training
datasets, and provides a solid basis for applying the framework to real
experimental data.
I review quark momentum distributions in the nucleon at large momentum fractions x. Particular attention is paid to the impact of nuclear effects in deuterium on the d/u quark distribution ratio as x ...-> 1. A new global study of parton distributions, using less restrictive kinematic cuts in Q^2 and W^2, finds strong suppression of the d quark distribution once nuclear corrections are accounted for.
The authors examine the consequences of local duality for elastic scattering, and derive model-independent relations between structure functions at x{approximately}1 and elastic electromagnetic form ...factors.
PDF
