This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.
This award will support a twenty-four-month research fellowship by Dr. Astrid Morreale to work with Dr. Fabienne Kunne at the French Atomic Energy Commission (CEA) in Saclay, France.
The proton is a composite particle made of more fundamental subatomic entities which are called quarks and gluons. While experiments can't study quarks and gluons directly, they can be studied within the confines of other particles, furthermore, the behavior of these internal constituents generates the observed quantum mechanical spin ½ properties. It is known now, that the spin of the quarks contributes surprisingly a very small fraction to the proton's spin, yet a puzzle still remains to be solved. Questions that linger in the field of nuclear spin physics, include the role played by the strong force mediators (gluons), the role of the virtual quark?antiquark pairs originating from the gluons' strong interaction field (sea quarks) and lastly the role of angular momentum to the nucleon spin. Discovering what contributes to nuclear spin, could lead in the future to discoveries on ways to better control matter, as spin ½ is one of the most important cases to explain electronic structure of atoms, and nuclear matter interactions. We would probably not exist, if nucleons would have different spin quantum number. This project aims to add more pieces of the puzzle of the quark and gluon contributions to the proton spin, and thus learn more about the matter we are made of, at the sub-atomic level. The objective of this research is to contribute to the the world data of nuclear spin studies while using data from a fixed target experiment presently in operation at CERN (European Laboratory for Particle Physics): the COmmon Muon and Proton Apparatus for Structure and Spectroscopy(COMPASS). The quest is to make the connection on how the nucleon's spin is distributed among the quarks and gluons (partons) by measuring final state hadrons (bound state of quarks held together by the strong force) coming from photon-gluon fusion processes from the COMPASS detector. The proposal is a new method of measuring these abundant and fully measurable processes at COMPASS by the calculation of spin-dependent asymmetries of final state hadrons in several intervals of transverse momentum. This new method allows for experimental comparisons to existing models and full incorporation to world efforts on solving the nucleon spin puzzle.
The results of the proposed measurement are long awaited, as much is still unknown of the internal constituent contributions to the proton's spin. Current world spin data have accessed gluon probes in a very limited kinematic region, thus only giving an emerging, partial picture of the proton. Clear knowledge of the proton spin can emerge, by a global effort on the analysis of the world data where many channels are studied across a wide kinematic region.
