Hadron physics Hadron physics Challenges and Achievements Mikhail Bashkanov University of Edinburgh UK Nuclear Physics Summer School I

OUTLINE OF THE COURSE Lecture 1: Hadron Physics. Experiments: new toys – new knowledge (progress in particle detector systems). Research areas: Hadron spectroscopy, meson rare decays (physics beyond SM), structure of hadrons. Lecture 2: Baryon spectroscopy, naïve quark model and beyond, molecular states, new horizons with precise measurements. Lecture 3: Using EM probes to learn about the nucleon. Nucleon form factors. Radius of the proton. 2

HADRON PHYSICS 3

ELECTROMAGNETIC INTERACTIONS 4 Ze

ELECTROMAGNETIC INTERACTIONS 5 Ze 2

EM -> STRONG INTERACTIONS 6 2 qq q q g

QUARKS 7

ENERGY DEPENDENCE OF THE COUPLING CONSTANT 8 q Bare quark

ENERGY DEPENDENCE OF THE COUPLING CONSTANT 9 q Dressed quark

ENERGY DEPENDENCE OF THE COUPLING CONSTANT 10 q Dressed quark Low energy probe

ENERGY DEPENDENCE OF THE COUPLING CONSTANT 11 q Dressed quark High energy probe

ELECTRON MICROSCOPY de Broglie wavelength of probe particle must be ~size of the object you wish to study 12

STRONG COUPLING CONSTANT 13

STRONG COUPLING CONSTANT Perturbative QCD Particle Physics Nonperturbative QCD Nuclear Physics 14

NUCLEAR VS PARTICLE PHYSICS Nuclear PhysicsParticle Physics Below charm thresholdAbove charm threshold Nucleon structureMesons with mass > 1.2 GeV Light quark baryons (without c/b quarks) 15 anticolor Meson Baryon color

MAJOR DIRECTIONS 16

RECENT PROGRESS IN NUCLEAR PHYSICS 17

BUBBLE CHAMBERS Gargamelle Bubble Chamber 18

MAGNETIC SPECTROMETERS 19 Time Of Flight->velocity

MODERN DETECTORS Large acceptance (close to 4  coverage) Charge and neutral particles Magnetic field, drift chambers Calorimeters High luminosity High rate, fast triggering Polarized beams/targets Polarimeters 20

MODERN DETECTORS KLOE WASA 21

PHOTONS Basics 22

WHY DO WE USE E/M PROBES? Pros: Interaction is understood (QCD) Beams are clean Beams can be polarized Targets can be polarized and dense Cons: Cross-sections are small Photon beams were(!) challenging Polarized targets are challenging Nucleon polarimetry is complicated 23

TYPES OF PHOTON POLARIZATION Linear polarization: (Electric field vector oscillates in plane) Circular polarization: (Electric field rotates Clockwise or anticlockwise) Both real and virtual photons can have polarization Determining azimuthal distribution of reaction products around these polarization directions gives powerful information. 24

HOW DO WE GENERATE INTENSE ELECTRON BEAMS Microtron: (MAMI, JLab) Electron beam accelerated by RF cavities. Tune magnetic field to ensure path through magnets multiple of Wavelength of accelerating field - electrons arrive back in phase with the accelerating field. Gives “continuous” beam (high duty factor) Stretcher ring: (ELSA, Spring8) Electron beams fed in from linac. Then accelerated and stored in ring. Useable beam bled off slowly Many stretcher rings built for synchrotron radiation – can exploit infrastructure for multiuse (e.g. Spring8) Tend to have poorer duty factors, less stable operation and poorer beam properties than microtrons. 25

REAL PHOTON BEAMS FROM ELECTRON BEAMS Wide range of photon energies Good time/position resolution for the tagger Small radiator-target distance Bremsstrahlung spectra 26

POLARIZATION IN REAL PHOTON BEAM Linear polarization: crystalline radiator, e.g. thin diamond. orient diamond to give polarised photons in certain photon energy ranges. Circular polarization: helicity polarised electrons. bremsstrahlung in amorphous radiator, e.g. copper. 27

COHERENT BREMSSTRAHLUNG 28

LINEAR POLARIZATION 29

COHERENT BREMSSTRAHLUNG 30

FROZEN SPIN TARGET 31

THE POLARIZED TARGET 32

NUCLEON POLARIMETER Polar angle distribution for unpolarized nucleons Analysing power Polarization 33

HADRON SPECTROSCOPY 34

REAL EXPERIMENT Diamond Target Polarimeter 35

INTERFERENCE 36

DECAY WIDTH 37 Decay width

NUCLEON EXCITED STATES 38

DOUBLE POLARIZATION EXPERIMENTS 39

POLARIZATION OBSERVABLES 40

RESONANCE HUNTING 41

MESON PHOTOPRODUCTION CROSS SECTIONS 42

RARE EVENTS The Standard Model and beyond 43

PRECISION IS POWER Testing Standard Model with precise measurements 44

ELECTRIC DIPOLE MOMENT 45

NEUTRON EDM 46

NEUTRON EDM SM SUSY 47

RARE DECAYS 48

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UNIVERSE CONTENT 50

SEARCH FOR DARK PHOTON Dark force: Dark photon 51

CONCLUSION Enormous progress in nuclear physics Precision is a new motto Acceptance Luminosity Polarization Photons are the best Experimentally clean Well understood theoretically 52