part iii cp violation and k physics
DESCRIPTION
Part III CP Violation and K Physics . C hris P arkes. Outline. PHENOMENOLOGY AND EXPERIMENTS CP violation and Kaon physics T-violation: CPLEAR An angle (phase difference) measurement: CPLEAR ε ’ : NA48 Rare kaon decays CP violation and B physics CP Violation and D physics - PowerPoint PPT PresentationTRANSCRIPT
Chris Parkes 1
Part IIICP Violation and K Physics
Chris Parkes
Chris Parkes 2
Outline
PHENOMENOLOGY AND EXPERIMENTS
III. CP violation and Kaon physicsT-violation: CPLEAR
An angle (phase difference) measurement: CPLEAR
ε’ : NA48
Rare kaon decays
IV. CP violation and B physics
V. CP Violation and D physics
VI. Concluding remarksPresent status and future ahead
Mixing in theneutral kaon system
Chris Parkes 4
Neutral kaon system K0 – K0 in nature (1/2)
If CP was conserved:
In nature, CP violated:
oo
oo
KKK
KKK
212
1
2
1with 22
11
1
1
KKCP
KKCP
e quantifiesdegree of CP violation
flavour eigenstates, CP conjugated
1,2
1
qpqp
1qp
Chris Parkes 5
Neutral kaons “identity card”:
Branching fractions:
KS : pp 69% , p0p0 31% KL : p0p0p0 21% , ppp0 13% , pn 66%
Mixing parameters:
GeV10)009.0483.3(
s100014.05301.0=
s1004.017.51
s100008.08934.01
15
110
SL
8
LL
10
SS
mmm
Neutral kaon system K0 – K0 in nature (2/2)
~600 times larger!
21 95.0
Mx
KSpopo
KSp+p-
KLp+p-po
KLpopopo
CP=+1
CP=-1
Chris Parkes 6
d
su, c, t W
W_
s
d_u, c, t
d
s u, c, tW W
_
s
d_
u, c, t___
K0K0
Neutral kaon mixing - oscillations
K0 K0
Feynman (box) diagrams for neutral kaon mixing:
t=0:initial K0 beam
KS decay early Pure KL beamafter a while!
At t>0:superposition of states
Chris Parkes 7
CPLEAR T-invariance(can also think of it in terms of CP violation)
Rate difference Ko Ko Ko Ko is T violation
8
Experiment at LEAR ring at CERN 1990-1996
Pions from kaon decay
9
1) Identify Ko / Ko at production:produced in association with K+/K-
2) Identify Ko / Ko at decay from charge of lepton:
CPLEAR
pp
KKKK
pp0
0
)su(K
)su(K
measure
Get positron:
s
dKo
u
d
e+ν
W+
π -
d d
Or electron:
sKo
ue-
νW-
π+
Final states f, f are particle /anti-particles
Oscillation
10
t=0 t
K0
K0
K0
K0
K0
K0
Oscillation & Decay
11
t=0 t
K0
K0
K0
K0
K0
K0
s
dKo
u
d
e+ν
W+
π -
d d
sKo
ue-
νW-
π+
CPLEAR T-Invariance
12
T or equivalently CP is violated by this tiny amount
Chris Parkes 13
CPLEAR : decay to CP eigenstate- Illustrate 3 types of CP violation- Measuring an angle (phase difference)
14
1) Identify Ko / Ko at production:produced in association with K+/K-
2) Decay to π+π- final state reachable from Ko and Ko
CPLEAR – decay to π+π-
pp
KKKK
pp0
0
)su(K
)su(K
measure
Interference of route with/without oscillations
Same final state f in both cases
Oscillation
15
t=0 t
K0
K0
K0
K0
K0
K0
Oscillation & Decay
16
t=0 t
K0
K0
K0
K0
K0
K0
Amplitude
Amplitude
Rate
Rate
Three methods of CP Violation Revisited
Rates
17
1. CP violation in decay2. CP violation in mixing3. CP violation in interference mixing/decay
18
(since ) Hence we are measuring an angle ϕ+-
c.f. B system discussion later
19
NA48: Direct CP Violation
Chris Parkes 21
CP violation first seen though existence of decay modes
CP conservation would imply
…. but experimentally these parameters are found ~ 10-3
CP violation due solely to mixing would be independent of the decay to the final state
SW
LW
SW
LW
KH
KH
KH
KH00
00
00,pp
pp
pp
pp
00
The e and e’ parameters (1/2)
000
Chris Parkes 22
To separate CP violation in decay from CP violation in mixing, the following is introduced:
… to separate the channel-independent term e from the channel-dependent term e’
Measurement of rates
yields
The e and e’ parameters (2/2)
pppp
S
L2
KK
NN
00S
00L2
00 KK
pppp
NN
'2,' 00 eeee
Direct CP violation(i.e. in decay)
CP violationin mixing
KL/Ks rates:
Chris Parkes 23
The NA48 experiment at CERN (1/2)
Study of direct CP violation in the neutral kaon system
Chris Parkes 24
Start with a pure Ko beam After a few meters (short time) all Ks component decayed
Introduce slab of material in beam Several reactions can occur with the material:
1) elastic scattering
2) charge exchange
3) Hyperon production
Þ K0 absorbed more strongly!f amount of K0 absorbed,f amount of K0 absorbed
pKnK
nKpK
0
0
00 ppK
sL
emerge
KffKff
KfKfK
21
21
21 00
Neutral kaon regeneration
Ks regenerated!
A consequence of particle-antiparticle
mixing
Chris Parkes 25
Measurements of e’/e : Discovery of Direct CP violation
Average: 1.68 ± 0.14 10-3
Not easy to compare with SM theory
- CP violation frontier now in B and D
4
2
00
103.27.16
161Re
ee
Direct CP Violation
Rare kaon decays
Chris Parkes 27
Rare Kaon Decays
Look for extremely suppressed decays in SM – where new physics could contribute Precision currently at parts per trillion !
Some interesting modes
Standard Model New Physics ExampleSame experimental signature
Very light/massless neutralino – neutral SUSY particle
Chris Parkes 28
Mainly (and very) sensitive to Vtd Predicted B. R. ~ 8x10-11
nnp K
One such event
Enhancement over SM
of central value, but not significant
Chris Parkes 29
Rare kaon decays – NA62 (successor to NA48) NA62 at CERN’s SPS currently commissioning, to measureStart after CERN (LHC) accelerator shutdown
nnp K
K+ p+
n
n
~11 MHz of K+ decays
Expect
Also Koto expt, Japan
Chris Parkes 30
Key Points – Kaon section• Ks (short lived) , KL (long lived) are mixture of K1 (CP +ve), K2 (CP –ve)
• ε quantifies degree of CP violation
• CPLEAR measurement of T (or equiv. CP) Violation
• Ko Ko Ko Ko • CPLEAR CP violation in a CP eigenstate π+π-
• same final state f, defined Parameter η+-
• How to measure an angle
• NA48 Direct CP Violation
• Difference in CP violation in π+π-, π0π0
• Quantified by e’/e
• Rare Decays, extremely suppressed in SM, new physics can contribute
• NA62 nnp K
'2,' 00 eeee