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Projects for undergrad students

Protons and neutrons (nucleons) constituents, the quarks and gluons, also known under the generic term “partons”, are seen as elementary bricks of matter. First experimental proof of this internal structure was provided in the 70's. Since then, many experiments have been developed and try to provide answers to questions such as why partons are confined in nucleons, how their distributions look like... Hadronic physics is a field close to nuclear and particle physics, aiming at understanding the properties of composite particles (made of several partons) from their constituents. Quantum Chromodynamic is a theory where gluons are described as fields, vectors of the “strong force”, responsible for the confinement. Many models have been developed, initially describing nucleons as made of 3 quarks, nowaday these models are more complex and describe the nucleons as made of a multitude of quarks, antiquarks and gluons (“cloud”). These models are used to interpret high energy particles scattering off nucleons, thanks to parametrizations of the distributions of partons in terms of position, momentum, spin.

In the past ~20 years, some reactions sensitive to the correlation between the longitudinal momentum and the transverse position of partons are studied. These reactions are called “exclusive” (all products are known) and are “inelastic” (particles are produced). The functions used in their parameterization and that can be extracted from experimental measurements can lead to descriptions of the nucleon internal structure such as “3D maps''. One example of such reactions is the emission of a high energy photon after an electron is scattered of a quark in a nucleon.

Below, we propose several projects, all involving the studies of one of these reactions. The students will read articles to understand the goals of such studies and they will perform basic kinematic calculations (particle's momenta, standard variables...). Then they will perform a short data analysis with simulations using C++/ROOT. Their goal is to explore the kinematics, determine where particles are scattered, how many events can be expected for a certain number of days if we are going to run an experiment... These exploratory studies will serve the purpose of developing new experiments at Jefferson Lab (Newport News, VA).

Electron-positron pair production off hydrogen target with a photon beam

This project will complement studies that were done in order to propose a new experiment at Jefferson Lab. The student will analyse data and tell what is the best way to separate them from the background, how long we should run our experiment to observe a significant amount of events... They will also set uncertainties for the observables that can be measured. One or two projects can be done with these data: 1) focus on the analysis method and the statistics, 2) focus on optimizing the kinematics for measuring asymmetries, for an experiment using a polarized photon beam.

Electron-positron pair production off deuterium target with a photon beam

The difference between this project and the above one is that we want to explore what we can get from events where the photon scattering occurs off the neutron (deuterium is made of proton+neutron), rather than off the proton. The students will analyse simulation and tell where the proton and the neutron are scattered after the reaction, where the electron-positron pair is emitted, and what is the ratio between events occurring off a neutron and off a proton. One or two possible projects are: 1) focus on the comparison of events off protons and neutrons and the statistics that can be expected for scattering of the neutron, 2) focus on the evolution and optimization of the kinematics for the purpose of measuring asymmetries for measurements using a polarized photon beam.

Muon pairs production in electron-proton scattering of hydrogen target

Students will analyse generated data and will tell where particles are emitted in the lab, where we should position our detector if we want to develop a new experiment, what is the kinematics of the emitted particles... This exploratory study will tell if an experiment will be feasible and if yes, how long it should run. The students will have the opportunity to get familiar with standard tools used in high energy physics as well as learning about this physics and about Jefferson Lab.

Initiation to data analysis: separation of meson from different species and exclusive reactions

Students will start by reading articles to understand the interest of measuring various exclusive reactions where mesons are produced. Mesons are particles made of a quark and an antiquark, their nature and their properties teach us different things about the proton content. The students will analyse generated data containing samples of various reactions, and they will have to find how to separate the different species. The goal is to figure out our ability to isolate the channel we are the most interested in, and provide an estimation of the remaining background (other reactions present in the sample).

Heavy meson production of polarized target using a photon beam

The students will analyse generated data and tell if decay products from heavy meson can be detected, what their kinematics are, how long we should run an experiment if we want to observe a significant amount of data... It is a feasibility study for potential future measurements that have never been done at such kinematics. Students will also have the opportunity to read articles in order to get familiar with this kind of physics.