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Search Results: 1 - 10 of 402757 matches for " Pamela M. Pennington "
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Structure of the Scalars
Pennington, M. R.
High Energy Physics - Phenomenology , 2007,
Abstract: The PDG Tables list more scalar mesons than can fit into one quark model nonet: indeed, even more than can belong to two multiplets. Consequently, some of these must be states beyond the quark model. So which of these is ${\bar q}q$ or ${\bar{qq}}qq$ or multi-meson molecule or largely glue? How experiment can help us distinguish between these possibilities is discussed.
Location, correlation, radiation: where is the $\sigma$, what is its structure and what is its coupling to photons?
Pennington, M. R.
High Energy Physics - Phenomenology , 2007, DOI: 10.1142/S0217732307024188
Abstract: Scalar mesons are a key expression of the infrared regime of QCD. The lightest of these is the $\sigma$. Now that its pole in the complex energy plane has been precisely located, we can ask whether this state is transiently ${\bar q}q$ or ${\bar {qq}} qq$ or a multi-meson molecule or largely glue? The two photon decay of the $\sigma$ can, in principle, discriminate between these possibilities. We review here how the $\gamma\gamma\to\pi^+\pi^-$, $\pi^0\pi^0$ cross-sections can be accurately computed. The result not only agrees with experiment, but definitively fixes the radiative coupling of the $\sigma$. This equates to a two photon width of $(4.1 \pm 0.3)$ keV, which accords with the simple non-relativistic quark model expectation for a ${\bar u}u, {\bar d}d$ scalar. Nevertheless, robust predictions from relativistic strong coupling QCD are required for each of the possible compositions before we can be sure which one really delivers the determined $\gamma\gamma$ coupling.
Can experiment distinguish tetraquark scalars, molecules and $\qq$ mesons?
Pennington, M. R.
High Energy Physics - Phenomenology , 2007, DOI: 10.1143/PTPS.168.143
Abstract: Scalar mesons are a key expression of the strong coupling regime of QCD. How those with $I_3=0$ couple to two photons supplies important information about which is transiently ${\bar q}q$ or ${\bar {qq}} qq$ or multi-meson molecule or largely glue, provided (i) we know the location of the corresponding poles in the complex energy plane, and (ii) we have reliable predictions from strong coupling QCD of the radiative widths for these compositions. Number (i) is being supplied by careful analyses of high statistics data particularly that coming from $B$, $D$, $J/\psi$ and $\phi$ decays. Number (ii) is still required, before we can answer the question in the title.
Testing Chiral Symmetry Breaking at DAPHNE
M. R. Pennington
Physics , 1996, DOI: 10.1016/S0375-9474(97)00438-7
Abstract: The spontaneous breakdown of the chiral symmetry of the QCD Lagrangian ensures that $\pi\pi$ interactions are weak at low energies. How weak depends on the nature of explicit symmetry breaking. Measurements of $K_{e4}$ decays at DA$\Phi$NE will provide a unique insight into this mechanism and test whether the $q{\overline q}$--condensate is large or small.
Calculating hadronic properties in strong QCD
M. R. Pennington
Physics , 1996,
Abstract: This talk, given at the Second Workshop on ELFE Physics, St Malo, France, September 1996, presents a brief review of the progress that has been made in calculating the properties of hadrons in strong QCD.
Hadron '95 --- Summary: Part I
M. R. Pennington
Physics , 1995,
Abstract: Part I of this summary is concerned with selected results on natural parity states presented at this conference, in particular the glueball candidates the $f_0(1510)$ and $\xi(2230)$. Unnatural parity and exotic states are discussed by Suh-Urk Chung
Exciting Baryons: now and in the future
M. R. Pennington
Physics , 2011, DOI: 10.1063/1.3701208
Abstract: This is the final talk of NSTAR2011 conference. It is not a summary talk, but rather a looking forward to what still needs to be done in excited baryon physics. In particular, we need to hone our tools connecting experimental inputs with QCD. At present we rely on models that often have doubtful connections with the underlying theory, and this needs to be dramatically improved, if we are to reach definitive conclusions about the relevant degrees of freedom of excited baryons. Conclusions that we want to have by NSTAR2021.
The production model of Ishida et al. and unitarity
M. R. Pennington
Physics , 1997,
Abstract: The relation between scattering and production amplitudes imposed by unitarity and analyticity, recently criticised by Ishida et al., is explained.
Low Energy Hadron Physics
M. R. Pennington
Physics , 2000,
Abstract: Ask a group of particle theorists about low energy hadron physics and they will say that this is a subject that belongs to the age of the dinosaurs. However, it is GeV physics that controls the outcome of every hadronic interaction at almost every energy. Confinement of quarks and gluons (and any other super-constituents) means that it is the femto-universe that determines what experiments detect. What we have to learn at the start of the 21st century is discussed.
Why is GeV physics relevant in the age of the LHC?
M. R. Pennington
Physics , 2014, DOI: 10.1007/s10751-014-1033-8
Abstract: The contribution that Jefferson Lab has made, with its 6 GeV electron beam, and will make, with its 12 GeV upgrade, to our understanding of the way the fundamental interactions work, particularly strong coupling QCD, is outlined. The physics at the GeV scale is essential even in TeV collisions.
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