Transcript electric beams

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