Upload
bethanie-ellis
View
217
Download
0
Embed Size (px)
Citation preview
Oct 8th, 2003 Gerhard Raven 1
CP violation:CP violation:The difference between matter and The difference between matter and
antimatterantimatter
Gerhard Raven Vrije Universiteit Amsterdam, Subatomic Physics
& NIKHEF
Oct 8th, 2003 Gerhard Raven 2
AntimatterAntimatter
Westminster Abbey
1928: Dirac equation unifies Quantum Mechanics and
Special Relativity: 0i m
( )i p xu p e
1) Negative energy solutions can be seen as particles traveling backwards in time, equivalent to anti-particles traveling forward in time (Feynman & Stückelberg)
2) The # of particles is NOT conserved but #particles - #antiparticles is conserved)
Paul A.M. Dirac 2
Dirac Algebra:
g 2 2E p m
Oct 8th, 2003 Gerhard Raven 3
Discovery of the positronDiscovery of the positron
In 1932, Carl Anderson discovers the positron
Oct 8th, 2003 Gerhard Raven 4
E=mcE=mc22: creating Matter and Antimatter: creating Matter and Antimatter
When creating matter from energy, always create equal amount of antimatter
e e e e Z qq
Oct 8th, 2003 Gerhard Raven 5
Big Bang CosmologyBig Bang Cosmology
Equal amounts of matter & antimatter
Matter Dominates !
Oct 8th, 2003 Gerhard Raven 6
Searches for Antimatter in the UniverseSearches for Antimatter in the Universe
• Universe around us is matter dominated:– Absence of antinuclei amongst cosmic rays– Absence of intense ray emission due to annihilation of
distant galaxies in collision with antimatter
Alpha Magnetic Spectrometer
Oct 8th, 2003 Gerhard Raven 7
Searches for Antimatter in the UniverseSearches for Antimatter in the Universe
The visible universe is very much matter dominated
Oct 8th, 2003 Gerhard Raven 8
Where did the Antimatter go?Where did the Antimatter go?
0.4 100.3(6.5 ) 10baryons
photons
N
N
Almost all matter annihilated with antimatter, producing photons…
, ,lm lmaT Y
WMAP satellite
1 1,T 2 2,T
2.7248K 2.7252K
Cosmic Microwave Background
Angular Power Spectrum
l
Oct 8th, 2003 Gerhard Raven 9
Where did the Antimatter go?Where did the Antimatter go?
• In 1966, Andrei Sakharov showed that the generation of a net baryon number requires:1. Baryon number violating
processes (e.g. proton decay)2. Non-equilibrium state during the
expansion of the universe3. Violation of C and CP symmetry
• Standard Model of particle physics does allow for some CP-violation
• However, it is extremely unlikely to be sufficient to explain matter asymmetry in the universe– It means there must be
something beyond the SM in CP violation somewhere, so a good place for further investigation
Oct 8th, 2003 Gerhard Raven 10
Three Important Symmetries: C, P and T Three Important Symmetries: C, P and T
• Parity, P– Parity reflects a system through the origin. Converts
right-handed coordinate systems to left-handed ones.– Vectors change sign but axial vectors remain unchanged
• x x , p -p, but L=xp L
• Charge Conjugation, C
– Charge conjugation turns a particle into its anti-particle• e e K K
• Time Reversal, T– Changes, for example, the direction of motion of particles
• t t
• CPT Theorem– One of the most important and generally valid theorems in local quantum field theory.– All interactions are invariant under combined C, P and T– Implies particle and anti-particle have equal masses and lifetimes
Oct 8th, 2003 Gerhard Raven 11
““Weak” InteractionsWeak” Interactions
d
p u
u
d
u n
d
e
e
W
Oct 8th, 2003 Gerhard Raven 12
Weak Force breaks C, breaks P, is CP really Weak Force breaks C, breaks P, is CP really OK ?OK ?
• Weak Interaction breaks both C and P symmetry maximally!
• Despite the maximal violation of C and P symmetry, the combined operation, CP, seemed exactly conserved…
• But, in 1964, Christensen, Cronin, Fitch and Turlay observed CP violation in decays of Neutral Kaons!
(1980 Nobel prize)
W+
e+R
L
W+
e+L
R
W
eR
L
W
eL
R
P
C
LR spin
spin
Oct 8th, 2003 Gerhard Raven 13
The Standard Model and CP violationThe Standard Model and CP violation
• 1973: If there are at least 3 generations of quarks, the Standard Model of particle physics allows for CP asymmetry– All 3 generations have been
observed • c: 1974 (Nobel prize 1976)• : 1975 (Nobel prize 1995)• b: 1977• t: 1994• LEP: 1990 – 1995: there are 3 species of (light, left-handed) neutrinos
– With 3 generations, there is a single parameter in the SM responsible for all CP violating processes
– Very predictive! (in principle)• To explain the observed ratio of
baryons to photons, it falls short by ~8 orders of magnitude
• Ideal place for further research!
Oct 8th, 2003 Gerhard Raven 14
Matter-Antimatter OscillationsMatter-Antimatter Oscillations
0B
0B
0B
0B
Oscillation frequency:
0.5/ps,
Average B0 lifetime:
1.5 ps
Produce with =0.56,
and measure flight distance
(1ps ~ 150 m)t(ps)
mixA
At t=0 produce a B0 and B0 pairFor many such pairs, plot Amix asa function of the decaytime, t
0 0 0 0 0 0
0 0 0 0 0 0mix
N B B N B B N B BA
N B B N B B N B B
But B0 B0 goes as fast as B0B0…
Oct 8th, 2003 Gerhard Raven 15
Intermezzo: InterferenceIntermezzo: Interference
Interference allows one to determine phase-differences
Oct 8th, 2003 Gerhard Raven 16
Interference due to BInterference due to B00 B B00 oscillations oscillations
0B
0B 0SJ K
0SJ K
0t t
CP
0B2 sin
2i mtie
0B2 sin
2i mt
ie
0Bcos
2
mt
0Bcos
2
mt
Oct 8th, 2003 Gerhard Raven 17
Coherent Time Evolution at the Coherent Time Evolution at the (4S)(4S)
B-Flavor Tagging
Exclusive B Meson
Reconstruction
PEP-2 (SLAC)
Vertexing &Time DifferenceDetermination
Oct 8th, 2003 Gerhard Raven 18
BaBar Silicon Vertex DetectorBaBar Silicon Vertex Detector
Beam pipe
Layer 1,2Layer 3
Layer 4Layer 5
Beam bending magnets
Readoutchips
Oct 8th, 2003 Gerhard Raven 19
BaBar Detector BaBar Detector @ Stanford Linear Accelerator Center (SLAC)@ Stanford Linear Accelerator Center (SLAC)
Oct 8th, 2003 Gerhard Raven 20
Example of a fully reconstructed eventExample of a fully reconstructed event
(2S) Ks
+- +-
B0 D*+ -fast
D0+
soft
K-+
‘’fish eye’’ view
fast
soft
B0(t)
At t=0 (i.e. when the D* decay happened), the ‘CP’ B was/would have been a B0
EPR
!Kb
c s
In general, use charges of identified•leptons,•kaons,•soft pions
from the “the rest of the event” to tag B flavour
Oct 8th, 2003 Gerhard Raven 21
CP violation in the B system is not small!CP violation in the B system is not small!CP violation in B system not small!CP violation in B system not small!
caveat: 100 million (4S) decays needed…
sin2 0 79 0 11β . .
220 events
0 taggedB
0 taggedB
0B
0B
0B
0B
0B
0B
0SJ K
0SJ K
Oct 8th, 2003 Gerhard Raven 22
The Result & The Standard ModelThe Result & The Standard Model
Without using sin(2)
One solution for is consistent with the
prediction from the SM
The SM has successfully
survived its first precision test of CP violation!
Standard Model predicts two other distinct phase differences, and
Current research aims to measure using several redundant
methods
Oct 8th, 2003 Gerhard Raven 23
SummarySummary
•CP asymmetry is required to generate a universe with more than just photons…
•CP is included in the Standard Model of particle physics if particles come in (at least) 3 generations
•We have now observed all 3 generations!
•The Standard Model does not allow sufficient CP asymmetry to explain the observed baryon to photon ratio
•The Standard Model prediction for CP violation has survived its first experimental precision test
•Current research aimed at testing the Standard Model predictions in various ways
•Somewhere the Standard Model must be incomplete…
Oct 8th, 2003 Gerhard Raven 24
Escher on CP violation…Escher on CP violation…
P
P
C CCP
Oct 8th, 2003 Gerhard Raven 25
CollidersColliders
• First collider: 13 cm, 80 KeV, 1931• LHC: 27 km, 14 TeV, 2007