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((o)) ((o))
U
July 21, 2009 Lecture 3 of 4
@ ORICL Philosophical
Phil
hi l S
Society
i t
Yuri Kamyshkov
University of Tennessee
kamyshkov@utk.edu
Previous lectures are posted at
http://web.utk.edu/~kamyshko/ORICL/
matter
tt and
d anti-matter
ti
tt particles
ti l have
h
spin
i ½ X;
X
use the same forces for interactions
How quarks make protons, neutrons, and other particles
Baryons
Mesons
Nucleons
uc eo s
hadrons
π− = d u
K 0 = d s (strangeness +1)
π+ =u d
K 0 = s d (strangeness − 1)
( )
Cπ = du = du = π
−
uu − dd
π =
2
Cπ 0 = π 0
0
+
CK 0 = K 0
p = uud ; p = uud
Cp
p = p; Cpp = p
Cn = n ; Cn = n
(qq ) Mesons [using u, d , s, c]
(qqq ) Baryons [using u , d , s, c]
Constituents of atomic nuclei = nucleons
anti-nuclei = anti-nucleons
proton
quarks
neutron
baryons
anti-proton, antineutron → anti-baryons
Summary of terminology
Leptons: electron, positron, neutrino, anti-neutrino (3 families)
Quarks: do not exist as free objects, only inside hadrons
Hadrons: made of quarks - Baryons and Mesons
Baryons: objects made of 3 quarks ( qqq ) or ( qqq )
Mesons: objects made of quark and anti-quarks ( qq )
Pentaquarks: recently ? ( qqqqq ) ... not confirmed
Can anti-matter be stored?
Can not be stored like that
The Low Energy Antiproton Ring (LEAR) at CERN (Geneva, Switzerland)
The Antiproton Accumulator (AA) which has been
transformed into the Antiproton Decelerator (AD) in 1999
Anti--hydrogen storage at CERN (Antiproton Decelerator)
Anti
Three experiments:
p
ASACUSA " Atomic Spectroscopy and Collisions using Slow Antiprotons";
ATHENA "Antihydrogen Production and Precision Experiments" and
ATRAP "Cold Antihydrogen for Precise Laser Spectroscopy".
Penning Trap
Electron--Positron Annihilation
Electron
annihilation at rest
−
+
e + e → γ + γ + (γ )
+ −
e e scattering
e+
e+
γ
e−
e−
As more energy is available the annihilation of electron and positron
can lead to creation of many new particles, some more massive than
electron or positron (e.g. at Large Electron – Positron collider at CERN)
View of annihilation
☯
How will nucleon and antianti-nucleon annihilate ?
Nucleon + antianti-nucleon
annihilate mostly into
pions.
i
Average
A
number
b
of pions = 5
Pions and muons eventually
decay into stable particles:
electrons positrons,
electrons,
positrons
photons and neutrinos
(~ 60% of energy ultimately
is curried awayy byy neutrinos).
)
π + → μ + +ν
Antiproton annihilation in hydrogen bubble chamber
H
How
neutrino-antineutrino
i
i
i can annihilate?
ihil ?
If e+e− and pp― annihilate
annihilate,, why e− and p+ do not ?
i.e. why hydrogen atom is stable and there is no 1H (e−p+) → 2 γ ?
or why doesn’t proton decay p → e+ γ ?
Nucleons (p
(p, n) and other heavy 3-quark particles are called Baryons
e, ν, and other particles with similar properties are called Leptons
Stability
St
bilit off the
th matter
tt (at
( t the
th level
l l observed
b
d so far)
f ) can be
b
explained as a conservation of the global quantum numbers
called “baryon charge” and “lepton charge”.
Why baryon charge is conserved
conserved??
H. Weyl (1929)
H
(1929), E.
E Stueckelberg (1938)
(1938), E.
E Wigner (1949)
independently tried to postulate the conservation of nucleon
(baryon) charge by analogy with conservation of electric charge.
Test results confirm strict
conservation of electric charge
How do we know whether “baryonic photons” exist?
((Lee
ee & Yang,
ang, Pati
ati & Salam, Okun, Sakharov)
Sakha ov)
There are no reasons to believe that baryonic
y
charge
g can be
conserved for the same reason as electric charge , i.e. there is
no good explanation of baryon and lepton number conservation.
Sacred and Approximate Conservation Laws
Sacred: conservation of energy-momentum, angular momentum,
electric charge; casuality,
casuality Lorentz invariance,
invariance unitarity
unitarity, CPT symmetry
Approximate:
Left-Right symmetry
Particle-Antiparticle symmetry
CP-symmetry
y
y
T-symmetry
Lepton family number (Lμ ,Le)
Lepton number (L)
Baryon number (B)
(P-parity, fallen in 1956)
(C-parity, fallen in 1956)
((fallen in 1964))
(fallen in 1999)
(fallen in 1998)
hold (to be tested in 2β0ν expts)
hold (needs to be tested)
The Universe
Th
U i
provides
id us an evidence
id
that net baryon number is not conserved