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Hadron Physics and the Search for Hexaquarks at MAMI

Fri., Mar. 1, 2019 3:30 p.m. - Fri., Mar. 1, 2019 4:30 p.m.

Location: CL 410

Abstract: Protons and neutrons are not fundamental particles, they are themselves formed of other particles. We refer to the particles that make up protons and neutrons as quarks. Quarks are fundamental particles. Quarks interact with each other via the strong nuclear force, one of the four fundamental forces of nature. The strong nuclear force is challenging to understand and model theoretically. Our understanding of this force primarily comes from experimentally measuring particle interactions and examining the particles that are formed in these interactions.

Particles formed of quarks are referred to as hadrons.  All of the well known and measured hadrons discovered so far are formed of two quarks (referred to as mesons) or three quarks (referred to as baryons).   However, hadrons formed of differing numbers of quarks are not forbidden by our theoretical models.  In recent years, there have been a number of experiments that have claimed observation of states formed of four (tetraquarks), five (pentaquarks), or six (hexaquarks).  In this talk of two halves, I will introduce the field of hadron physics with a brief discussion of the why, what, where and how of the field.  I will cover some of the hot topics in the field and the current and upcoming facilities involved.

In the second half of this talk, I will discuss one particular facility, the A2 Hall at hte Mainzer Microtron (MAMI), in more detail.  At this facility a high energy electron beam is utilised to produce a beam of photons.  These photons are incident upon a target of liquid deuterium (a hydrogen atom with a proton and a neutron in the nucleus).  The particles produced when the photon beam interacts with the target are measured by a detector array that surrounds the target.  I will discuss the equipment and analysis procedure involved in such a measurement, particularly the newly constructed and installed polarimeter setup.  This setup was utilised in a recent experimental measurement.  The latest results from the ongoing analysis of the data and the potential implications of these results for an exciting new hexaquark state, the d*(2380), will be presented.