Introduction

1. GPDs TAPS, 512 BaF2 elements Glasgow Photon Tagging Spectrometer 5x106γ/sec Crystal Ball, 672 NaI elements Hadron Physics Highlights Introduction Glasgow’s NPE research Group uses high precision electromagnetic probes to study the subatomic structure of matter. Alongside this we are involved in the preparation of future experiments with electron, photon and antiproton beams. Our work is best classified into four interdependent and overlapping physics themes (see Fig. 1). Within each of these themes, we make optimum use of the available experimental facilities throughout Europe and the USA by selecting the facility which best matches the physics requirements of each experiment. Each theme utilises multiple facilities to provide complementary data sets which combine to provide the maximum physics output. Short Range Nuclear Structure Concentration of strongly interacting matter inside the nucleus may lead to changes in the properties of hadronic matter. We will study variation in: • Charge distribution within the proton (JLab Hall A) • Nucleon polarisibilities (JLab Hall A) • Mass of the pion-pion (σ) system (MAMI A2) • Mass of the Ω meson within the nuclear medium. Meson exchange models do not describe the nucleon-nucleon interaction at short range properly. Two-nucleon- knockout reactions at MAMI A1, A2 and JLab Hall A provide input for nucleon-nucleon correlation based approaches. Figure 5: Short range nucleon interaction Nucleon Structure • The structure of the nucleon still poses significant questions: • What is the origin of its mass? The current quark mass accounts for approximately 2% of the nucleon mass, the remaining 98% is generated dynamically via strong interactions described by QCD. • What is the origin of the spin of the nucleon? In most accurate measurement to date, HERMES found that the quark spins contribute only 33% of the spin of the nucleon. What is the origin of the remaining 67%? Figure 6: Recent DVCS results showing limits on the total angular momentum of the up (Ju) and down (Jd) quark. Neutron data from Hall A, proton data from HERMES. Figure 1: Themes, Laboratories and Collaborations Nucleon Resonance Spectroscopy At the energy and distance scales typical of the nucleon, QCD is extremely challenging due to its non-perturbative nature. Nucleon resonance spectroscopy provides a key to unlocking this challenge. To disentangle the many overlapping resonances (Fig. 3) we measure differential cross sections and polarisation observables (Fig. 4) of π, η and K mesons. To achieve this we employ the JLab CLAS and MAMI A2 (Fig. 2) facilities, which are ideally suited to our requirements for large acceptance detector systems and polarised beams and targets. Generalised Parton Distributions describe the 3D structure of the nucleon Nucleon elastic form factor Pioneering measurements in MAMI A1, double polarisation JLab Hall A results challenge nucleon structure models Wide Angle Compton Scattering Polarised Compton Scattering in JLab Hall A provide first high precision measurements in the few GeV range. Hard exclusive meson production Analysis experience from HERMES will be used in new CLAS experiments Parton Distribution Functions (PDF) PDFs measured at HERMES form input for GPDs Deeply Virtual Compton Scattering (DVCS) Production of real photon in electron scattering from an individual quark in the nucleon. Pioneering HERMES expertise transferred to measurements at CLAS 12 & PANDA Figure 2: CB@MAMI detector setup in MAMI A2 • MAMI Highlights • Electromagnetic moments of baryon resonances • Elusive basic parameters of the P11(1440) resonance • First complete measurement of pseudoscalar meson photoproduction giving unambiguous decomposition of the resonance spectrum in π and η photoproduction New Forms of Hadronic Matter We commonly observe baryons, such as the nucleon, with three valence quarks and mesons, such as the pion, which contain a quark-antiquark pair. However, the theory of Quantum ChromoDynamics (QCD) allows any state that is colour neutral. To test this theory, we should search for other colour-neutral states which are predicted to exist but remain unobserved e.g. Glueballs and hybrids. The photon is an ideal source of energy for the excitation of exotic waves due to it’s spin and parity. This technique will be exploited to produce hybrids at: Figure 3: Meson photo-production from the proton • JLab HyCLAS • JLab GlueX • To produce Glueballs, it is necessary to provide a gluon rich environment and this is ideally provided by proton-antiproton annihilation at • PANDA JLab CLAS Highlights • Access to new resonances via polarisation observables in strangeness photoproduction • First complete measurements of strangeness photoproduction allowing unambiguous determination of the resonance spectrum in KΛ and K channels Figure 7: Diagrams of known and new forms of hadronic matter. Figure 4: Strangeness polarisation observables from JLab CLAS