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I Hadron physics Challenges and Achievements Mikhail Bashkanov University of Edinburgh UK Nuclear Physics Summer School 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. 2 • Lecture 3: Using EM probes to learn about the nucleon. Nucleon form factors. Radius of the proton. 3 HADRON PHYSICS ELECTROMAGNETIC INTERACTIONS Ze 4 Ze ELECTROMAGNETIC INTERACTIONS 2 Ze 5 Ze 𝑒2 1 𝛼= ~ ℏ𝑐 137 EM -> STRONG INTERACTIONS q g q 2 𝑒 1 𝛼= ~ ℏ𝑐 137 𝛼𝑠 ~1 q 6 q 2 QUARKS 1 ) 2 7 • Fermions (spin 𝑆 = • 3 colors (red, green, blue) • Parity +1 ENERGY DEPENDENCE OF THE COUPLING CONSTANT Bare quark 8 q ENERGY DEPENDENCE OF THE COUPLING CONSTANT Dressed quark 9 q ENERGY DEPENDENCE OF THE COUPLING CONSTANT Δ𝑝 ∙ Δ𝑥 ≥ ℎ Dressed quark Low energy probe 10 q ENERGY DEPENDENCE OF THE COUPLING CONSTANT Δ𝑝 ∙ Δ𝑥 ≥ ℎ Dressed quark High energy probe 11 q ELECTRON MICROSCOPY 12 de Broglie wavelength of probe particle must be ~size of the object you wish to study 13 STRONG COUPLING CONSTANT STRONG COUPLING CONSTANT Perturbative QCD Particle Physics 14 Nonperturbative QCD Nuclear Physics NUCLEAR VS PARTICLE PHYSICS Nuclear Physics Particle Physics Below charm threshold Above charm threshold Nucleon structure Mesons with mass > 1.2 GeV Light quark baryons (without c/b quarks) Meson anticolor 15 color Baryon MAJOR DIRECTIONS • Hadron spectroscopy: • Hadron properties (mass, with, decay branching…) • Hadron structure (|𝒒𝒒𝒒 , |𝒒𝒒𝒒(𝒒𝒒) , |𝒒𝒒𝒒𝒈 , meson-baryon molecule…) • Precision tests of SM: • Neutron magnetic moment • Neutron electric dipole moment • Muon/electron magnetic moment (g-2) • Rare decays of mesons • … • Size and structure of nucleon 16 • Nucleon form factor • Nucleon radius 17 RECENT PROGRESS IN NUCLEAR PHYSICS BUBBLE CHAMBERS 18 Gargamelle Bubble Chamber MAGNETIC SPECTROMETERS 2 2 𝐸 =𝑝 +𝑚 2 Time Of Flight->velocity 1 − 𝑣2 19 𝑝= 𝑚𝑣 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 20 • Polarimeters MODERN DETECTORS WASA 21 KLOE PHOTONS Basics 22 WHY DO WE USE E/M PROBES? • • • • 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 Pros: TYPES OF PHOTON POLARIZATION • Both real and virtual photons can have polarization • Determining azimuthal distribution of reaction products around these polarization directions gives powerful information. Linear polarization: (Electric field vector oscillates in plane) Circular polarization: 24 (Electric field rotates Clockwise or anticlockwise) 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) • 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 Stretcher ring: (ELSA, Spring8) REAL PHOTON BEAMS FROM ELECTRON BEAMS Wide range of photon energies Good time/position resolution for the tagger Bremsstrahlung spectra Small radiator-target distance Θ𝑐 = 𝑚𝑒 [𝑀𝑒𝑉] [𝑟𝑎𝑑] 𝐸𝑒 [𝑀𝑒𝑉] 26 Ee = 855 MeV → Θ𝑐 = 0.6 𝑚𝑟𝑎𝑑 POLARIZATION IN REAL PHOTON BEAM 𝐸𝑒 = 1600 𝑀𝑒𝑉 Linear polarization: Circular polarization: • crystalline radiator, e.g. thin diamond. • helicity polarised electrons. • • bremsstrahlung in amorphous radiator, e.g. copper. 27 orient diamond to give polarised photons in certain photon energy ranges. 28 COHERENT BREMSSTRAHLUNG 29 LINEAR POLARIZATION 30 COHERENT BREMSSTRAHLUNG FROZEN SPIN TARGET • • • • • • available (Mainz) since 05.2010 Butanol(𝑪𝟒 𝑯𝟗 𝑶𝑯) or D-Butanol 3He/4He dilution refrigerator (50mK) Superconducting holding magnet Longitudinal or transverse polarizations are possible Maximal polarization for protons ~90%, for deuterons ~75% Relaxation time ~2000 hours 31 • 32 THE POLARIZED TARGET NUCLEON POLARIMETER 𝑛 Θ, 𝜙 = 𝑛0 (Θ)(1 + 𝐴(Θ)[𝑃𝑦 cos 𝜙 − 𝑃𝑥 sin(𝜙)]) Polarization Number of nucleons scattered in the direction Θ, 𝜙 Analysing power 𝐀𝐲 Polar angle distribution for unpolarized nucleons 𝝓 𝚯 33 𝒑 HADRON SPECTROSCOPY 34 REAL EXPERIMENT 𝐵 𝜸 +− 𝝅𝒑 𝝅 Θ, 𝜙, 𝐸 Diamond 𝛾𝑝 → 𝑝𝜋 + 𝜋 − Target Polarimeter 𝚯′ , 𝝓′ 35 𝑒− 36 INTERFERENCE DECAY WIDTH Mean life time 𝝉 = ℏ/𝚪 Decay width 37 Typical “strong” decay width Γ~100𝑀𝑒𝑉 𝜏~10−24 𝑠 38 NUCLEON EXCITED STATES 39 DOUBLE POLARIZATION EXPERIMENTS 40 POLARIZATION OBSERVABLES 41 RESONANCE HUNTING 42 MESON PHOTOPRODUCTION CROSS SECTIONS RARE EVENTS The Standard Model and beyond 43 PRECISION IS POWER Testing Standard Model with precise measurements • Neutron electric dipole moment • Muon magnetic moment (g-2) • 𝜼/𝝅𝟎 rare decays 44 • …. 45 ELECTRIC DIPOLE MOMENT 46 NEUTRON EDM NEUTRON EDM SM 47 SUSY RARE DECAYS 48 𝜂 → 𝜋 +𝜋 −𝑒 +𝑒 −: CP VIOLATION 49 𝐵𝑟 𝜂 → 𝜋 + 𝜋 − 𝑒 + 𝑒 − = 2.7 ∙ 10−4 50 UNIVERSE CONTENT Dark force: SEARCH FOR DARK PHOTON 𝜼/𝝅𝟎 51 Dark photon CONCLUSION • Enormous progress in nuclear physics • Precision is a new motto • Acceptance • Luminosity • Polarization • Photons are the best 52 • Experimentally clean • Well understood theoretically