The Exo(tic) Had(ron) Collaboration started in 2023 to explore all aspects of exotic hadron physics, from predictions within lattice QCD, through reliable extraction of their existence and properties from experimental data, to descriptions of their structure within phenomenological models.
News
Read allA Constituent Model of Light Hybrid Meson Decays
The discovery of hybrid mesons will be greatly simplified if their couplings to decay channels are understood. To this end, Christian Farina (Pitt graduate student) and Eric Swanson (Pitt, co-PI), have modeled hybrid decay in terms of gluon dissociation as specified by the Hamiltonian of QCD in Coulomb gauge. The results indicate that direct observation of the light vector hybrid will be difficult, that the hybrid $\pi(1800)$ has distinct decay characteristics, and that a hybrid $\eta_1(1750)$ Read more
Three particles with coupled channels
The extension of the three-particles formalism to multiple three-particle channels has been carried out by ExoHad members Zack Draper (UW graduate student) and Steve Sharpe (UW, co-PI), in a paper submitted to the arXiv. This is done in the context of the $\pi\pi\eta$ and $K \bar K \pi$ system in isosymmetric QCD, where, if one enforces positive G parity, as well as conservation of $J^P$, there is no mixing with the $2\pi$ or $3\pi$ systems. This two-channel system is suitable for studying the Read more
Revisiting $J/\psi$ photoproduction at threshold
The study of $J/\psi$ photoproduction at low energies has consequences for the understanding of multiple aspects of nonperturbative QCD, ranging from mechanical properties of the proton, to the binding inside nuclei, and the existence of hidden-charm pentaquarks. A work by the JPAC collaboration, led by Daniel Winney (SCNU), Cesar Fernandez-Ramirez (UNED & UNAM), and Alessandro Pilloni (Messina), Adam Szczepaniak (Indiana U., PI), and Jinfeng Liao (Indiana U., co-PI), together with Astrid Read more
No ambiguities in the partial wave analysis for hybrids
The extraction of partial waves from experimental cross sections can be plagued by mathematical ambiguities, that is by the fact that different sets of partial waves can lead to the very same physical observables. This fact was originally studied in the spinless case, and it is known as Barrelet zeroes. When particles carry spin, the presence of additional polarization observables can help resolving those ambiguities. While there is no general solution to this problem, it is important to focus Read more
Dispersion relations and Lattice QCD pinpoint the $\sigma$ meson
Lattice QCD is the model-independent, theoretical approach to study low-energy strong interactions. We can study unstable particles, known as resonances, using modeled reaction amplitudes describing lattice QCD spectra. These amplitudes satisfy only a subset of the mathematical requirements, unitarity, but fail to implement crossing symmetry and analyticity. This is a problem when extrapolating amplitudes far from the data region, e.g. in the case of resonances like the $\sigma$, leading to Read more
Extension of finite-volume three-body formalism to scattering of particles with spin
The extension to include spin in the three-particle formalism was carried out in the context of the three-neutron system in a paper by ExoHad members Zack Draper (UW graduate student) and Steve Sharpe (UW, co-PI) in collaboration with Max Hansen (Edinburgh) and Fernando Romero-Lopez (MIT). The inclusion of spin is more complicated for three-particle systems than for two-particles, because of the need to consider several reference frames: the overall center-of-mass frame (CMF), and the three Read more
New hires working on ExoHad
The Collaboration is happy to announce that two members, Andrew Jackura and Arkaitz Rodas, were hired on tenure-track positions to continue developing the ExoHad program. Moreover, Vanamali Shastry has joined a postdoctoral researcher position.
Andrew Jackura is an Assistant Professor of Physics in the Nuclear Theory group at William & Mary. Andrew joined William & Mary in August 2023 as part of the ExoHad initiative.
Andrew’s research focuses on few-body nuclear and particle reactions, using Read more
ExoHad received funding
The ExoHad project has just been funded with 1.8 million dollars from the U.S. Department of Energy, within the program "Topical Theory Collaborations in Nuclear Physics", which aims at solving challenging and complex issues central to advancing knowledge in nuclear physics. The effort brings together the world’s top nuclear theorists to advance theoretical frameworks for the accurate prediction of nuclear interactions and properties of nuclear matter.
The PI of ExoHad is Adam Szczepaniak Read more