RUI: Hadron Structure and Interactions

Seattle University, Seattle WA

Investigators

Abstract

A central problem for theoretical physics is the description of the structure of hadrons and their interactions.The building blocks of hadrons are quarks and gluons,among which the distribution of .avor,momentum,and spin is an area of intense study.This project will study two of the outstanding challenges to theory posed by recent experimental results:1) .avor asymmetry in the proton sea,measured by E866 at FermiLab,in which the excess of d -antiquarks (Pd )over u -antiquarks (Pu )for low values of x (the fraction of proton momentum carried by the antiquark),is replaced by a dominance of Pu over Pd for larger values of x ,and 2) the spin transfer measurements of PS185 at CERN,for Pff production from Pp collisions with a polarized proton target,which disagree with all theoretical predictions.These investigations will be extended to calculation of polarized .avor asymmetry in the proton sea,and to other antihyperon-hyperon (PYY )production reactions.A new area of research,singular potentials and limit cycles,will be studied in the context of e .ective .eld theory. Flavor asymmetry in the proton sea will be calculated in terms of a meson cloud model, in which the proton can .uctuate into meson-baryon states,whose quark distributions then contribute to the measured quark distributions of the proton.The quark and gluon degrees of freedom of the proton will also be included in a statistical model of the gbare proton, hthe leading term in the proton wave function.E .ects of charge symmetry violation,arising from di .erences in the masses of the Pd and the Pu ,will be included.The goal of this project is to explain the x -dependence of the experimentally determined unpolarized .avor asymmetry, and to predict the polarized asymmetry. High precision calculations of Ppp PYY will be carried out which will include:a)e .ective interactions that represent the leading contributions to Pqq annihilation and creation,b) an initial state interaction which has been determined by .t to PNN reaction data in the momentum region spanned by the strangeness production experiments,and c)a contribution to the reaction mechanism from a spin singlet term,for which there is evidence from the recent spin-transfer data.The goal of this project is to learn about the reaction mechanism and the otherwise unknown PYY interactions in the .nal state. The study of singular potentials and limit cycles will include investigation of real and complex potential regulators and their renormalization properties.Applications to cold atom scattering and problems in e .ective .eld theory will be made. This project has intellectual merit because,as described above,it addresses important problems in hadron structure and interactions for which there is signi .cant disagreement between nuclear theory and experiment.It extends prior work to new areas.The preliminary work necessary for the project has been successfully completed by the P.I. Broader impacts of the project include placing the research in an undergraduate setting, in which students are drawn from a diverse population (40%minority)with a high percent- age of women physics majors (40%).The student research experience will be complemen- tary to coursework,and provide an integration of classroom learning and the excitement of contemporary research.Students will receive training in research methods and scienti .c communication.They will work in teams,mentor younger students and present their work in papers,posters and talks at meetings of professional societies.In addition to presentation of research .ndings in journal articles and at scienti .c meetings,seminars and colloquia will be given at other undergraduate institutions.