Search of hybrids in multi-meson final states with the GlueX experiment at the Thomas Jefferson National Accelerator Facility (JLab)

• Applicant: Professorin Dr. Annika Thiel
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2018 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 410404013

The surrounding matter is build-up of protons and neutrons, the so-called nucleons. These particles are composed of three quarks, which are bound inside the nucleon by the strong interaction. The strong interaction is transmitted by gluons, which have the special feature that they are self-interacting particles. This leads to the fact that the quarks and gluons are bound inside the so-called hadrons and cannot be observed as free particles. This observation is called Confinement. There are two different types of hadrons known: the baryons, which consistent of three quarks, and the mesons, which are build-up of a quark-antiquark pair. Even the first publications hinted to the fact that there might be additional particles, for example penta-quarks containing four quarks and tetra-quarks which include five quarks. Particles containing gluonic contributions could also be possible, for example hybrid mesons with a quark-antiquark and a gluon, or even pure states of glue, the so-called glueballs.During the last years evidence was found by several experiment for penta- and tetra-quarks. However, all of these states contained charm quarks and had therefore higher masses (around 4 GeV). Regarding the lightest quarks, no proof for exotic states could be found so far, even though there are several candidates.To shed light on this question, the GlueX experiment was build-up in the last years at the CEBAF accelerator at Jefferson Lab, USA. The GlueX experiment has the special ability to measure neutral and charged decay particles with a high angular and energy resolution. This poses an ideal setup to hunt for exotic states by systematically map the meson spectrum and search for hybrid states.During this fellowship, I want to analyse final states consisting of two neutral mesons like two eta mesons. With these final states, the same quantum numbers, which have been predicted for the lowest laying glueball, become available for the intermediate states. Measurements with photoproduction have been conducted before, however, they were not able use photon beams of these high energies and achieve such a precision and statistics as it is possible for the GlueX experiment. Additionally, linearly polarized photons are used to excite the nucleons. This allows to apply different constraints to the data and gives further options to identify the quantum numbers of the intermediate states.Within the scope of this fellowship I want to get to know the experimental setup of the GlueX experiment and to understand their analysis software. This will allow me to conduct my own analysis and to exert my previous knowledge about the extraction of different final states and the observables. I plan to join the GlueX collaboration and to extensively contribute to their project in the next years. My work at the GlueX experiment will contribute to the search for exotic states containing light mesons and hopefully help to answer this question.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom
• Host: Professor Dr. David Ireland