Dene Hoffman

Physics PhD Candidate studying glueballs at GlueX

I'm currently a graduate student 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 with a proton target.

The main goal of GlueX is a search for particles with exotic quark content. Standard composite particles are identified in two main categories, mesons (made of a quark-antiquark pair) and baryons (three quarks). However, there has been recent experimental evidence of states with more than three quarks, dubbed tetraquarks, pentaquarks, etc. Computer simulations (Lattice QCD) predict additional states such as glueballs, which contain no quarks at all and are just bound states of the "gluons" that hold matter together, and hybrid mesons, where a valence gluon contributes to the total angular momentum to produce "forbidden" quantum numbers.

My thesis work consists of a study of $K_SK_S$ (pairs of K-short mesons) photoproduction. This gives us access to even-spin $f$ and $a$ mesons (light, flavorless particles with isospin $I_3 = 0$ and $1$ respectively), the former of which are interesting for several reasons. First, they share many of the same quantum numbers, the values we use to classify particles, with glueballs, hypothetical particles that contain only gluons, the force-carrier of the strong interaction. The lightest of these glueballs is predicted to look nearly identical to some of the $f_0$ mesons (spin-$0$ $f$ mesons), and it turns out that there are too many of these $f_0$ mesons seen in experiments for them to all be compatible with the quark model.

However, the downside of this particular study is that there are lots of other particles present in the $K_SK_S$ channel, and many of them overlap each other. Hopefully my work at GlueX can provide a small step in disentangling this complex set of states and move us closer to understanding the complex physics of quantum chromodynamics.

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