Colin Morningstar
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Lattice QCD studies of excited resonances July 30 - August 31, 2012 SUMMARY
Quantum Chromodynamics, when combined with the electroweak interactions, underlies all of nuclear physics, from the spectrum and structure of hadrons to the most complex nuclear reactions. Lattice gauge theory calculations enable the first-principles study of the low-energy properties of QCD, and have, to date, provided predictions of hadron masses and coupling constants, recently reaching the one-percent level of accuracy for some quantities. Only very recently have computer resources and novel methodologies and algorithmic developments allowed preliminary studies of excited- and multi-hadron states using lattice QCD. However, progress has been rapid and within the next few years, benchmark calculations of basic nuclear observables at the physical point are expected, including predictions of the low-lying excited-baryon levels and a compelling observation of the deuteron. In view of these rapid developments, this program will bring together lattice QCD practitioners and other interested physicists to report on progress and discuss the scientific challenges. Below we list a selection of scientic goals that will be addressed in the program.
- What is the low-lying excited spectrum of mesons and baryons? (Figure 1 shows
recent results for the excited-meson spectrum.)
- Which two- and three-baryon systems involving hyperons are bound in nature and
what are their binding energies? (Figure 2 shows existing evidence of a bound H-
dibaryon with various extrapolation estimates.)
- What are the low-energy hyperon-hyperon and hyperon-nucleon phase shifts, and how
will knowledge of these quantities help unravel the role of hyperons and hypernuclei
in dense matter such as might occur in the cores of neutron stars?
- How do nuclei and nuclear interactions depend on the fundamental parameters of nature? Do the fine-tunings that permeate nuclear physics, and already show up in s-wave nucleon-nucleon scattering, disappear as the quark masses are varied?
- What is the most effective way of extracting information about unstable resonances
from finite-box stationary-state energies?
- What is the mapping between nuclear reaction observables (e.g. fusion cross sections)
and the eigenstates of the QCD Hamiltonian in a finite volume that one measures on
the lattice?
- How will electromagnetism be included in lattice QCD calculations of nuclear properties and interactions? In particular, how should electromagnetic effects be included in lattice calculations of charged-particle scattering and nuclear binding energies?
- What is the most cost-effective method for extracting excited levels from a lattice
QCD calculation?
- Can better variance reduction methods be found?
- How will the bottleneck in the number of spin-color contractions be overcome in the study of many-baryon systems?
A. Nuclear Physics from Lattice QCDB. Essential Theoretical DevelopmentsC. Essential Algorithmic DevelopmentsFIG. 1: Masses of the low-lying meson spectrum in units of the nucleon mass classified by irreducible representation of the hypercubic group. FIG. 2: Extrapolations of the LQCD results for the binding of the H-dibaryon. The left(right) panel shows an extrapolation quadratic(linear) in the pion mass. The green dashed vertical line corresponds to the physical pion mass. |