Hadron physics Hadron physics Challenges and Achievements Mikhail Bashkanov University of Edinburgh...
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Transcript of Hadron physics Hadron physics Challenges and Achievements Mikhail Bashkanov University of Edinburgh...
Hadron physicsChallenges 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.
3
HADRON PHYSICS
4
ELECTROMAGNETIC INTERACTIONS
Ze
Ze
5
ELECTROMAGNETIC INTERACTIONS
Ze
Ze
2
6
EM -> STRONG INTERACTIONS
2qq
q q
g
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QUARKS• Fermions (spin )• 3 colors (red, green, blue)• Parity +1
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ENERGY DEPENDENCE OF THE COUPLING CONSTANT
q
Bare quark
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ENERGY DEPENDENCE OF THE COUPLING CONSTANT
q
Dressed quark
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ENERGY DEPENDENCE OF THE COUPLING CONSTANT
q
Dressed quarkΔ𝑝 ∙ Δ𝑥 ≥h
Low energy probe
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ENERGY DEPENDENCE OF THE COUPLING CONSTANT
q
Dressed quarkΔ𝑝 ∙ Δ𝑥 ≥h
High energy probe
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ELECTRON MICROSCOPYde Broglie wavelength of probe particle must be ~size of the object you wish to study
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STRONG COUPLING CONSTANT
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STRONG COUPLING CONSTANT
Perturbative QCDParticle Physics
Nonperturbative QCDNuclear Physics
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NUCLEAR VS PARTICLE PHYSICS
Nuclear Physics Particle PhysicsBelow charm threshold Above charm threshold
Nucleon structure Mesons with mass > 1.2 GeV
Light quark baryons (without c/b quarks)
anticolor
Meson Baryon
color
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MAJOR DIRECTIONS• Hadron spectroscopy:
• Hadron properties (mass, with, decay branching…)• Hadron structure (, , , 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
• Nucleon form factor• Nucleon radius
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RECENT PROGRESS IN NUCLEAR PHYSICS
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BUBBLE CHAMBERS
Gargamelle Bubble Chamber
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MAGNETIC SPECTROMETERS
𝐸2=𝑝2+𝑚2
Time Of Flight->velocity
𝑝=𝑚𝑣
√1−𝑣2
20
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
High precision
21
MODERN DETECTORS
KLOE
WASA
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PHOTONSBasics
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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
24
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.
25
HOW DO WE GENERATE INTENSE ELECTRON BEAMSMicrotron: (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.
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REAL PHOTON BEAMS FROM ELECTRON BEAMS
Wide range of photon energies
Good time/position resolution for the tagger
Small radiator-target distance
Bremsstrahlung spectra
Θ𝑐=𝑚𝑒[𝑀𝑒𝑉 ]𝐸𝑒[𝑀𝑒𝑉 ]
[𝑟𝑎𝑑]
E e=855MeV→Θ𝑐=0.6𝑚𝑟𝑎𝑑
27
POLARIZATION IN REAL PHOTON BEAM
Linear polarization:• crystalline radiator,
e.g. thin diamond.
• orient diamond to give polarised photons in certain photon energy ranges.
𝐸𝑒=1600𝑀𝑒𝑉
Circular polarization:• helicity polarised
electrons.
• bremsstrahlung in amorphous radiator, e.g. copper.
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COHERENT BREMSSTRAHLUNG
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LINEAR POLARIZATION
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COHERENT BREMSSTRAHLUNG
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FROZEN SPIN TARGET• available (Mainz) since
05.2010
• Butanol() 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
32
THE POLARIZED TARGET
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NUCLEON POLARIMETER𝑛 (Θ ,𝜙 )=𝑛0(Θ)(1+𝐴(Θ) [𝑃 𝑦 cos (𝜙 )−𝑃𝑥sin (𝜙)])
𝐀𝐲
𝚯�⃗�
𝝓
Number of nucleons scattered in the direction
Polar angle distribution for unpolarized nucleons
Analysing powerPolarization
34
HADRON SPECTROSCOPY
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REAL EXPERIMENT
𝑒−
�⃗�
Diamond
𝜸
Target
𝝅+¿ ¿𝝅−𝒑
Θ ,𝜙 ,𝐸
𝚯′ ,𝝓 ′
�⃗� �⃗�→ �⃗� 𝜋+¿𝜋 −¿ Polarimeter
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INTERFERENCE
37
DECAY WIDTH
Mean life time
Decay width
Typical “strong” decay width
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NUCLEON EXCITED STATES
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DOUBLE POLARIZATION EXPERIMENTS
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POLARIZATION OBSERVABLES
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RESONANCE HUNTING
42
MESON PHOTOPRODUCTION CROSS SECTIONS
43
RARE EVENTSThe Standard Model and beyond
44
PRECISION IS POWER
• Neutron electric dipole moment
• Muon magnetic moment (g-2)
• rare decays
• ….
Testing Standard Model with precise measurements
45
ELECTRIC DIPOLE MOMENT
46
NEUTRON EDM
47
NEUTRON EDM
SM
SUSY
48
RARE DECAYS
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: CP VIOLATION
𝐵𝑟 ¿
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UNIVERSE CONTENT
51
SEARCH FOR DARK PHOTONDark force:
Dark photon
𝜼 /𝝅𝟎
52
CONCLUSION
• Enormous progress in nuclear physics
• Precision is a new motto
• Acceptance• Luminosity• Polarization
• Photons are the best
• Experimentally clean• Well understood theoretically