1. CP Violation in Particle Physics违反
CP Violation in Particle Physics

2. Summary of Lecture 4
K0 and K0 mesons are not mass eigenstates; KS and KL are mass eigenstates
KL mesons discovered at Brookhaven Laboratory
a K0 will oscillate into a K0 and vice versa
neutral K mesons produced in f decay are ~100% “quantum correlated”
KS mesons are “regenerated” when a KL passes through matter _ _

3. My plan for week 2
Done
Week 2: Monday: The neutral K meson system: the KS and KL mass eigenstates
and K0-K0 mixing.
Wednesday: CP violation in KL decays; measurements
of CPV parameters;
Friday: Superweak or not superweak? Search for direct CP violation
in KL decay.

4. the search for CP violation

5. Properties of the Mass Matrix
-- slide from lecture 4 --
I ignore K0 life-time
terms (for now)
CPT symmetry requires:
CP symmetry says:
Let’s not use
this condition
& assume CP
is violated
Schrodinger’s equation
for energy eigenstates;

6. Hamiltonian operator with decays2
H=M - -- G -
-- now we will include decays --
Hermitian
Mass matrix
Decay matrix
CPT symmetry:
no assumptions about CP
Hermiticity:

7. Schrodinger’s Equation
-- allowing for CP violation and including decays --
to conform to the standard notation:
Schrodinger’s equation
for energy eigenstates;

8. Solutions for Y(t) eigenvalue equation: eigenvalues eigenstates
in terms of the
CP eigenstates:

9. Decay of the KL CP odd CP even CP even CP oddOK OK
CP even
CP odd
If CP is violated: KL contains a CP -even K1 component

10. Discovery of KL decays to p+p-

11. “Hint” for KLp+p- ?? a Bubble chamber in a neutral beam
at Brookhaven saw
some p+p- events
neutrons & KL’s
KLp+p-events or KLKS via regeneration

12. proposal

13. AGS Brookhaven’s 2nd HE accelerator
-- world’s first strong focusing accelerator, still running, more than 50 years later --
“Inner Mongolia”

14. BEPC—AGS see the differences?

15. AGS combined function magnets

16. Quadrupoles & dipoles
dipole
Quadrupole

17. the “inner Mongolia” beam line
shielding blocks
sweeping magnet
AGS accelerator magnets
Internal target

18. The Fitch-Cronin experiment
Helium gas
all KS have
decayed

19. Spark chamber

23. Data-taking and analysis

24.    

25. _______
____________________________

27. p+ cosq p+p- “invariant mass” M(p+p-)<M(KL) M(p+p-)=M(KL)
5211 KL  π+ + π- candidates remeasured on a commercial bubble chamber measuring machine
p+p- “invariant mass”
M(p+p-)<M(KL)
M(p+p-)=M(KL) p+ |
q=1o
p+p-)>M(KL)
cosq

29. Results

30. CP is violated!! James Cronin Val Fitch 1980 Nobel Prize for Physics
No prizes for Christenson or Turlay

31. 25 year anniversary reunion

32. Let’s look at e: what we know about p & q definition of e:
rewrite e in terms
that we know:

33. Some comments CP is only violated if the off-
diagonal terms are different
Hermiticity: M21=M12 & G12=G21
CPV only driven by imaginary terms * *
Latest numbers:
CPV is very small, ~10-3GF2, far from
the maximum that is possible
(unlike P and C violations)

34. virtual & on-shell K0--K0 couplings_
2nd-order quark-level
virtual |DS|=2 process
“short-distance processes”
On-shell pion-induced
|DS|=2 process
“long-distance processes”

35. Phase of e (h+-)

36. K0 -- K0 basis states with CPV_
Solve for K0 and K0 _
Please check
this for HW

37. The CPLEAR experiment

38. Strangeness-tagging at CPLEAR_ _

39. Time-dependence of K0(K0)p+p-_
KL(xh+-)

40. Phase of (h+-) from CPLEAR

41. Exploit KLKS regeneration
Need to know regeneration phase p- p+ p- p+

42. DM and f(h+-) measured via regeneration

43. K0 K0 oscillations (mixing);no CPVCPV_
eigenstates
start at t=0 with a K0:
then, at a later time t:
These are the
K0 and K0 rates
we measure
I0 = beam
intensity
(particles/s) _

44. K0 K0 in a neutral K beam no CPVCPV_ _
e=2.23
start with ≈75% K0 and ≈25% K0
(fe=400±40)
2Ree=
3.4±0.2x10-3

45. Neutral Kaon spectrometer @ CERN
expanded view of target region

46. Measurements of 2Ree (circa 1974)

47. Recent values of K-meson CPV parameters

48. Summary of Lecture 5
Discovery of KLp+p- decays proved that CP symmetry is violated
Measurements consistent with KL=K2+eK1; e= 2.2x10-3
Phase of e consistent with CPV originating from short-distance Mass-Matrix terms
Many beautiful, high-statistics measurements of CPV interference effects reported