RUI: Hadron Structure and Interactions

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A central problem for theoretical physics is the description of the structure of hadronsand their interactions.The building blocks of hadrons are quarks and gluons,among whichthe distribution of .avor,momentum,and spin is an area of intense study.This project willstudy 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 ofd -antiquarks (Pd )over u -antiquarks (Pu )for low values of x (the fraction of proton momentumcarried 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 apolarized proton target,which disagree with all theoretical predictions.These investigationswill be extended to calculation of polarized .avor asymmetry in the proton sea,and to otherantihyperon-hyperon (PYY )production reactions.A new area of research,singular potentialsand 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 thencontribute to the measured quark distributions of the proton.The quark and gluon degreesof freedom of the proton will also be included in a statistical model of the gbare proton, htheleading term in the proton wave function.E .ects of charge symmetry violation,arising fromdi .erences in the masses of the Pd and the Pu ,will be included.The goal of this project is toexplain the x -dependence of the experimentally determined unpolarized .avor asymmetry,and to predict the polarized asymmetry.High precision calculations of PppPYY will be carried out which will include:a)e .ectiveinteractions 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 themomentum region spanned by the strangeness production experiments,and c)a contributionto the reaction mechanism from a spin singlet term,for which there is evidence from therecent spin-transfer data.The goal of this project is to learn about the reaction mechanismand the otherwise unknown PYY interactions in the .nal state.The study of singular potentials and limit cycles will include investigation of real andcomplex potential regulators and their renormalization properties.Applications to cold atomscattering and problems in e .ective .eld theory will be made.This project has intellectual merit because,as described above,it addresses importantproblems in hadron structure and interactions for which there is signi .cant disagreementbetween nuclear theory and experiment.It extends prior work to new areas.The preliminarywork 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 excitementof contemporary research.Students will receive training in research methods and scienti .ccommunication.They will work in teams,mentor younger students and present their workin papers,posters and talks at meetings of professional societies.In addition to presentationof research .ndings in journal articles and at scienti .c meetings,seminars and colloquia willbe given at other undergraduate institutions.