The Hadron Spectrum Collaboration
The Hadron Spectrum Collaboration (hadspec) makes use of the
numerical approach to Quantum Chromodynamics known as lattice QCD to
study the spectrum of hadrons. An international collaboration of
scientists in Europe and the US, we aim to understand how
quarks and gluons confine themselves within the strongly interacting
mesons and baryons observed in nature.
News
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hadspec Collaboration Meeting at UC Berkeley
The hadspec collaboration met at UC Berkeley in July to discuss
their ongoing research efforts in hadron spectroscopy and their plans
for the future. Collaboration members took the opportunity to lecture
at a Summer School happening at the same time and location, and to
present at a workshop the following week.
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Scalar and tensor charmonium resonances computed from QCD
Using lattice QCD, scalar and tensor charmonium resonances have been determined from coupled-channel scattering amplitudes. Unstable charmonium resonances are readily observed at modern hadron physics experiments but often produce puzzling features. This new work demonstrates that by using QCD, and constraints between scattering amplitudes such as unitarity, features observed in different decay modes can be unified into a single description of a complex resonance pole coupled to multiple channels. This work has been published in Physical Review Letters and Physical Review D as Editors’ Suggestions.
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Hadspec calculates three-pion scattering amplitude
For the first time in lattice QCD, a three-hadron scattering amplitude has been determined using a general workflow that does not make use of model assumptions or a perturbative expansion. Focusing on the maximum isospin three-pion channel ($\pi^+ \pi^+ \pi^+ \to \pi^+ \pi^+ \pi^+$) the calculation uses a relativistic finite-volume formalism to relate lattice energies to the physical scattering amplitude. The work has been published in Physical Review Letters as an Editors’ Suggestion.
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Hadspec studies decays of a $1^{-+}$ hybrid meson
For the first time in lattice QCD, a calculation has shown the
presence of an exotic $1^{-+}$ state appearing as an unstable
resonance. The result shows that the longstanding model-based
proposal that such a state would couple more strongly to the $\pi
b_1$ final-state than the lower-lying $\pi \eta, \pi \eta'$ and $\pi
\rho$ final-states is confirmed. Possible implications for the
recently observed $\pi_1$ experimental candidate state are discussed. The calculation appears in a preprint posted to the arXiv,
and has been accepted for publication in Physical Review D.
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