Dene Hoffman

Welcome to my website! I’m a PhD candidate in the physics department at Carnegie Mellon University studying the strong force through the GlueX collaboration. GlueX is a multinational collaboration located in Hall D at Jefferson Lab which collides high-energy photons (produced from JLab’s electron beam) with a proton target.

We then search for particles with exotic quark content. Standard composite particles are identified by the number of quarks they contain: Mesons contain a quark and antiquark, baryons contain three quarks. Recently, several collaborations have generated some experimental evidence for tetraquarks–bound states with two quarks and two antiquarks, and pentaquarks (five quark states). Lattice simulations predict some additional states such as glueballs (particles with no quarks, just the “gluons” which typically hold them together), and hybrid mesons, mesons with a valence gluon which contributes to the total angular momentum.

My thesis work consists of a study of \(K_S K_S\) (two K-short) decays in photoproduction. This gives us access to even-spin \(f\) and \(a\) mesons (light, flavorless particles with isospin \(I_3=0\) and \(I_3=1\) respectively), the former of which is interesting for several reasons. First, they share the same quantum numbers (numbers we use to classify particles) as glueballs, hypothetical particles which contain only gluons, the force-carrier of the strong force. Glueballs are predicted by simulations of the strong force and the action of quantum chromodynamics (QCD) on a lattice. Unfortunately, the second reason the \(f\) mesons are interesting is that there seem to be too many of them to sort into a typical meson nonet.

While one might hope that we could identify one of these extra particles as the glueball, this possibility has been experimentally ruled out through predicted branching fractions. The likely theory is that the light scalar glueball mixes with three of the \(f_0\) states, so we can investigate the mixing angle by measuring the properties of these particles.