Тяжёлые адроны ФИАН / 2
.pdf
Theta-tau paradox ~ 1947-1953
Very close masses and lifetimes, but …
(Assuming l1=l2 = 0) |
(Assuming J = l = 0) |
P = (−1) (−1) (−1) = −1 |
P = (−1) (−1) = +1 |
How to measure l1, l2 ? Dalitz diagram / Dalitz plot
For 3-body decay M→123
Original idea: non-relativistic regime |
|
Q = energy release in the decay = M-m1-m2-m3 |
|
Q = T1+T2+T3 |
|
Why a point inside the triangle represents T1, T2, T3? |
|
What are X and Y ? |
|
Why circle is a boundary of allowed events? |
21 |
|
3-body decay
If the invariant amplitude is constant the Dalitz plot will be uniformly populated Non-uniformity in population of Dalitz plot gives information on final-state interactions.
22
3-body decay
More later, let’s go back to theta-tau
23
Theta-tau paradox ~ 1947-1953
− |
+ |
Idea: parity is not conserved in weak interactions… ?
How to test?
Nucleus spin is a pseudovector – does not change the direction under P transformation
why?
Momentum us true vector, p→−p
If parity is conserved, the Lagrangian should not contain terms depending on P X J |
|
→ Search for P-J correlations in nuclei decays |
24 |
Wu experiment
Cool 60Co atoms to near absolute zero (0.01K) Why?
Put them in strong magnetic field to polarize
60Co decays to unstable excited state of Ni, which then emits two photons
Photons are observed to be emitted isotropically, independently of the temperature
Electrons show asymmetry: more electrons emitted opposite to the nucleus spin
At the same time other experiments have shown parity non-conservation in pion decay
25
Wu experiment
Why mirror does not inverse vertical direction on the plot? (or, why is this mirror representative of P conjugation??)
26
Summary
αβγ decays
β decay puzzle and Pauli solution Parity
Parity violation
27
LHC
Largest particle collider 27 km underground tunnel from LEP
Run-1
7 TeV (2011)
8 TeV (2012)
Run-2
13 TeV (2016-2018)
Run-3
13.6 TeV (2022-2024?)
https://home.cern/science/accelerators/large-hadron-collider |
28 |
Brief summary of LHC Run-2
29
LHC experiments ATLAS and CMS
https://home.cern/science/experiments/cms
https://atlas.cern
30