PERSPECTIVES IN ELECTRO- AND PHOTO-NUCLEAR PHYSICS

By THOMAS LEE

CONTENTS QUARK MODELS OF HADRONS AND ISSUES IN QUARK DYNAMICS CHROMOSTATICS MESONS AS BOUND STATES FROM B¯B TO LIGHT ?AVOURS FLAVOUR MIXINGS BARYONS SPIN–?AVOUR CORRELATIONS SU(6) MULTIPLETS AND EXCITED MULTIPLETS ROLE OF Q2 AS A TEST OF DYNAMICS PENTAQUARKS AND EXOTIC BARYONS GLUONIC EXCITATIONS REFERENCES ELASTIC FORM FACTORS ELECTRON SCATTERING AND FORM-FACTOR MEASUREMENTS SPACE-LIKE NUCLEON FORM FACTORS MODEL CALCULATIONS OF NUCLEON FORM FACTORS TIME-LIKE NUCLEON FORM FACTORS THE PION FORM FACTOR THE AXIAL FORM FACTOR NUCLEON STRANGE FORM FACTORS OUTLOOK AND CONCLUSIONS ELECTROMAGNETIC EXCITATIONS OF NUCLEON RESONANCES ISSUES GENERAL FORMALISM THEORETICAL MODELS DATA AND RESULTS CONCLUDING REMARKS AND OUTLOOK MESON RADIATIVE DECAYS ELECTRON–POSITRON ANNIHILATION AND ? DECAY SINGLE-PHOTON TRANSITIONS BETWEEN MESONS TWO-PHOTON DECAYS OF MESONS INTERMEDIATE-ENERGY PHOTOPRODUCTION REGGE POLES PHOTOPRODUCTION OF PSEUDOSCALAR MESONS VECTOR-MESON PHOTOPRODUCTION EXOTIC MESONS CHIRAL PERTURBATION THEORY CHIRAL SYMMETRY EFFECTIVE ?ELD THEORY OF GOLDSTONE BOSONS MESONIC CHIRAL PERTURBATION THEORY INCLUDING NUCLEONS SPIN STRUCTURE FUNCTIONS LEPTOPRODUCTION STRUCTURE FUNCTIONS AND CROSS SECTION VIRTUAL PHOTON CROSS SECTIONS SYMMETRY PROPERTIES OF THE STRUCTURE FUNCTIONS POLARIZED LEPTOPRODUCTION THE PARTON MODEL PROPERTIES OF QUARK DISTRIBUTIONS QCD CORRECTIONS IN DEEP INELASTIC SCATTERING EVOLUTION EQUATIONS ONE-PARTICLE INCLUSIVE LEPTOPRODUCTION COLLINEAR PARTON DISTRIBUTIONS BOUNDS ON THE DISTRIBUTION FUNCTIONS TRANSVERSE MOMENTUM-DEPENDENT CORRELATION FUNCTIONS FRAGMENTATION FUNCTIONS INCLUSION OF SUBLEADING CONTRIBUTIONS COLOUR GAUGE INVARIANCE DIFFRACTION AND COLOUR DIPOLES DIFFRACTIVE PROCESSES THE DIPOLE FRAMEWORK LIGHT-CONE WAVE FUNCTIONS THE DIPOLE CROSS SECTION DIPOLE PHENOMENOLOGY CONCLUSIONS GENERALIZED PARTON DISTRIBUTIONS PROPERTIES AND PHYSICS OF GPDS DYNAMICS AND MODELS PROCESSES PHENOMENOLOGY OF COMPTON SCATTERING EXPERIMENTAL RESULTS ON DVCS EXPERIMENTAL RESULTS ON MESON PRODUCTION GPDS AND LARGE-ANGLE SCATTERING PROCESSES FUTURE FACILITIES FOR GPD PHYSICS OUTLOOK QUARK–HADRON DUALITY DUALITY IN HADRONIC REACTIONS BLOOM–GILMAN DUALITY DUALITY IN INCLUSIVE ELECTRON SCATTERING SCALING AND DUALITY IN DYNAMICAL MODELS DUALITY IN SPIN-DEPENDENT ELECTRON SCATTERING DUALITY IN SEMI-INCLUSIVE REACTIONS DUALITY IN EXCLUSIVE REACTIONS COLOUR TRANSPARENCY POINT-LIKE CON?GURATIONS SMALL-SIZED OBJECTS HAVE SMALL CROSS SECTIONS GENERIC COLOUR TRANSPARENCY SIMPLE EXAMPLES THE BEST CASE: DIJET PRODUCTION BY HIGH-ENERGY PIONS VECTOR-MESON PRODUCTION QUASI-ELASTIC NUCLEAR REACTIONS ASSESSMENT AND OUTLOOK QUARK MODELS OF HADRONS AND ISSUES IN QUARK DYNAMICS 1 1 CHROMOSTATICS THE DISCOVERY OF QUARKS IN INELASTIC ELECTRON SCATTERING EXPERIMENTS, FOLLOWING THEIR HYPOTHESIZED EXISTENCE TO EXPLAIN THE SPECTROSCOPY OF HADRONS, LED RAPIDLY TO THE QUANTUM CHROMODYNAMIC (QCD) THEORY AND THE STANDARD MODEL, WHICH HAS UNDERPINNED PARTICLE PHYSICS FOR THREE DECADES TODAY, ALL KNOWN HADRONS CONTAIN QUARKS AND/OR ANTIQUARKS THE QCD LAGRANGIAN IMPLIES THAT GLUONS ALSO EXIST, AND THE DATA FOR INELASTIC SCATTERING AT HIGH ENERGY AND LARGE MOMENTUM TRANSFER CON?RM THIS WHAT IS NOT YET ESTABLISHED IS THE ROLE THAT GLUONS PLAY AT LOW ENERGIES IN THE STRONG INTERAC- TION REGIME CHARACTERISTIC OF HADRON SPECTROSCOPY QCD IMPLIES THAT THERE EXIST ‘GLUEBALLS’, CONTAINING NO QUARKS OR ANTIQUARKS, AND ALSO QUARK–GLUON HYBRIDS THE ELECTROMAGNETIC PRODUCTION OF HYBRIDS IS ONE OF THE AIMS OF JLAB GLUEBALLS, ON THE OTHER HAND, ARE NOT EXPECTED TO HAVE DIRECT AF?NITY FOR ELECTROMAGNETIC INTERACTIONS; HENCE HADROPRODUCTION OF A MESON THAT HAS SUPPRESSED ELECTROMAGNETIC COUPLING IS ONE OF THE WAYS THAT SUCH STATES MIGHT BE IDENTI?ED QUARKS ARE FERMIONS WITH SPIN 2 AND BARYON NUMBER 3 A BARYON, WITH HALF-INTEGER SPIN, THUS CONSISTS OF AN ODD NUMBER OF QUARKS (Q) AND/OR ANTIQUARKS (¯Q), WITH A NET EXCESS OF THREE QUARKS MESONS ARE BOSONS WITH BARYON NUMBER ZERO, AND SO MUST CONTAIN THE SAME NUMBER OF QUARKS AND ANTIQUARKS THE SIMPLEST CON?GURATION TO MAKE A BARYON IS THUS THREE QUARKS, QQQ; A MESON MOST SIMPLY IS Q¯Q WITHIN THIS HYPOTHESIS WELL OVER TWO HUNDRED HADRONS LISTED BY THE PARTICLE DATA GROUP (PDG) [1] CAN BE DESCRIBED THE QUESTION OF WHETHER THERE ARE HADRONS WHOSE BASIC CONSTITUTION IS MORE COMPLICATED THAN THESE, SUCH AS MESONS MADE OF QQ¯Q¯Q OR BARYONS MADE OF QQQQ¯Q, IS AN ACTIVE AREA OF RESEARCH, WHICH WE SHALL SUMMARIZE LATER FIRST WE EXAMINE WHAT PROPERTY OF THE ATTRACTIVE FORCES CAUSES SUCH COMBINATIONS TO OCCUR AND THEN DISCUSS HOW THE MULTITUDE OF HADRONS ARE DESCRIBED THE FUNDAMENTAL THEORY OF THE STRONG FORCES BETWEEN QUARKS IS QCD THE DETAILS OF THIS THEORY AND RULES OF CALCULATION MAY BE FOUND IN DEDICATED TEXTS SUCH AS [2] A QUARK CARRIES ANY OF THREE COLOURS – WHICH WE LABEL RBG THEY ARE THE CHARGES THAT ARE THE SOURCE OF THE FORCE BETWEEN QUARKS THE RULES OF ATTRACTION AND REPULSION ARE AKIN TO THOSE OF ELECTROSTATICS WHERE LIKE REPEL AND UNLIKE ATTRACT ASSOCIATE POSITIVE CHARGES WITH QUARKS AND NEGATIVE WITH ANTIQUARKS THE ATTRACTION OF PLUS AND MINUS THEN NATURALLY LEADS TO THE Q¯Q CON?GURATIONS, THE MESONS, FOR WHICH THE COLOUR CHARGES HAVE COUNTERBALANCED IN QUANTUM ELECTRODYNAMICS, QED, THE ELECTROMAGNETIC FORCE IS TRANSMITTED BY PHOTONS; ANALOGOUSLY, IN QCD THE FORCES BETWEEN QUARKS ARE TRANSMITTED BY GLUONS THIS FAR IS ANALOGOUS TO THE FORMATION OF ELECTRICALLY NEUTRAL ATOMS THE NOVEL FEATURE ARISES FROM THE THREE DIFFERENT COLOUR CHARGES TWO IDENTICAL COLOURS REPEL ONE ANOTHER BUT TWO DIFFERENT, NAMELY RG, RB OR BG, CAN MUTUALLY ATTRACT A THIRD QUARK CAN BE MUTUALLY ATTRACTED TO THE INITIAL PAIR SO LONG AS ITS COLOUR DIFFERS FROM THAT PAIR THIS LEADS TO ATTRACTION BETWEEN THREE DIFFERENT COLOURS: RBG A FOURTH QUARK MUST CARRY THE SAME COLOUR CHARGE AS ONE THAT IS ALREADY THERE AND WILL BE REPELLED BY THAT, MEANWHILE BEING ATTRACTED TO THE DISSIMILAR PAIR THE ABOVE PEDAGOGIC ILLUSTRATION NEEDS BETTER SPECI?CATION THE RULES OF ATTRAC- TION AND REPULSION DEPEND ON THE SYMMETRY OF THE PAIR UNDER INTERCHANGE THUS SYMMETRIC COMBINATIONS REPEL, ANTISYMMETRIC ATTRACT TWO IDENTICAL COLOURS, BEING INDISTINGUISHABLE, ARE TRIVIALLY SYMMETRIC TWO DIFFERING COLOURS CAN BE EITHER SYM- METRIC OR ANTISYMMETRIC: [RB]S ? 2(RB + B R), (1 1) [RB]A ? 2(RB ?B R) (1 2) THUS ANY PAIR OF QUARKS IN A BARYON IS IN AN ANTISYMMETRIC SYMMETRY STATE FOR THE SATURATION OF THE ATTRACTIVE FORCES THE FULL WAVE FUNCTION FOR THE COLOUR OF A THREE-QUARK BARYON IS THUS 6 ((RB ?B R)G + (BG ?GB)R + (G R ?RG)B) (1 3) THE THREE COLOURS FORM THE BASIC 3 REPRESENTATION OF SU(3); THE THREE ‘NEGATIVE’ COLOURS OF ANTIQUARKS ARE THEN A ¯3 THE RULES OF COMBINING REPRESENTATIONS GIVE 3 ?¯3 = 1 ?8; 3 ?3 ?3 = 1 ?8 ?8 ?10 (1 4) PERSPECTIVES IN ELECTRO AND PHOTO NUCLEAR PHYSICS