290 research outputs found
Amplitude analysis and the nature of the Zc(3900)
The microscopic nature of the XYZ states remains an unsettled topic. We show
how a thorough amplitude analysis of the data can help constraining models of
these states. Specifically, we consider the case of the Zc(3900) peak and
discuss possible scenarios of a QCD state, virtual state, or a kinematical
enhancement. We conclude that current data are not precise enough to
distinguish between these hypotheses, however, the method we propose, when
applied to the forthcoming high-statistics measurements should shed light on
the nature of these exotic enhancements.Comment: 14 pages, 10 figures, 3 tables. Version accepted for publication on
Phys.Lett.
On the and Photoproduction Beam Asymmetry at High Energies
We show that, in the Regge limit, beam asymmetries in and
photoproduction are sensitive to hidden strangeness components. Under
reasonable assumptions about the couplings we estimate the contribution of the
Regge pole, which is expected to be the dominant hidden strangeness
contribution. The ratio of the asymmetries in and production is
estimated to be close to unity in the forward region at the photon energy ~GeV, relevant for the upcoming
measurements at Jefferson Lab.Comment: 9 pages, 4 figure
Structure of Pion Photoproduction Amplitudes
We derive and apply the finite energy sum rules to pion photoproduction. We
evaluate the low energy part of the sum rules using several state-of-the-art
models. We show how the differences in the low energy side of the sum rules
might originate from different quantum number assignments of baryon resonances.
We interpret the observed features in the low energy side of the sum rules with
the expectation from Regge theory. Finally, we present a model, in terms of a
Regge-pole expansion, that matches the sum rules and the high-energy
observables.Comment: 19 pages, 15 figures and 4 table
Determination of the pole position of the lightest hybrid meson candidate
Mapping states with explicit gluonic degrees of freedom in the light sector
is a challenge, and has led to controversies in the past. In particular, the
experiments have reported two different hybrid candidates with spin-exotic
signature, pi1(1400) and pi1(1600), which couple separately to eta pi and eta'
pi. This picture is not compatible with recent Lattice QCD estimates for hybrid
states, nor with most phenomenological models. We consider the recent partial
wave analysis of the eta(') pi system by the COMPASS collaboration. We fit the
extracted intensities and phases with a coupled-channel amplitude that enforces
the unitarity and analyticity of the S-matrix. We provide a robust extraction
of a single exotic pi1 resonant pole, with mass and width 1564 +- 24 +- 86 MeV
and 492 +- 54 +- 102 MeV, which couples to both eta(') pi channels. We find no
evidence for a second exotic state. We also provide the resonance parameters of
the a2(1320) and a2'(1700).Comment: 6 pages + 3 pages of supplemental material. Version to appear on
Phys.Rev.Let
Finite-Energy Sum Rules in Eta Photoproduction off the Nucleon
The reaction is studied in the high-energy regime
(with photon lab energies GeV) using
information from the resonance region through the use of finite-energy sum
rules (FESR). We illustrate how analyticity allows one to map the t-dependence
of the unknown Regge residue functions. We provide predictions for the energy
dependence of the beam asymmetry at high energies.Comment: Joint Physics Analysis Cente
Global analysis of charge exchange meson production at high energies
Many experiments that are conducted to study the hadron spectrum rely on peripheral resonance production. Hereby, the rapidity gap allows the process to be viewed as an independent fragmentation of the beam and the target, with the beam fragmentation dominated by production and decays of meson resonances. We test this separation by determining the kinematic regimes that are dominated by factorizable contributions, indicating the most favorable regions to perform this kind of experiments. In doing so, we use a Regge model to analyze the available world data of charge exchange meson production with beam momentum above 5 GeV in the laboratory frame that are not dominated by either pion or Pomeron exchanges. We determine the Regge residues and point out the kinematic regimes which are dominated by factorizable contributions
NetKet 3: Machine Learning Toolbox for Many-Body Quantum Systems
We introduce version 3 of NetKet, the machine learning toolbox for many-body quantum physics. NetKet is built around neural-network quantum states and provides efficient algorithms for their evaluation and optimization. This new version is built on top of JAX, a differentiable programming and accelerated linear algebra framework for the Python programming language. The most significant new feature is the possibility to define arbitrary neural network ansätze in pure Python code using the concise notation of machine-learning frameworks, which allows for just-in-time compilation as well as the implicit generation of gradients thanks to automatic differentiation. NetKet 3 also comes with support for GPU and TPU accelerators, advanced support for discrete symmetry groups, chunking to scale up to thousands of degrees of freedom, drivers for quantum dynamics applications, and improved modularity, allowing users to use only parts of the toolbox as a foundation for their own code
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