weak decays beta decay ofneutron problem energy and momentum not conserved e n p
TRANSCRIPT
weak decays weak decays beta decay beta decay
of of neutron neutron
epn
problem energy and momentum not conserved
e
n
p
W. Pauli: 1930 Neutrino mass ~ m(e)
weak decays weak decays beta decay beta decay
of of neutron neutron
eepn
e
n p
e
direct interaction of four fermions
Enrico Fermi, ~1936
p
n
electron
antineutrino
251016637.1 GeVGF
weak interactions current-current interaction weak currents ~ lefthanded:
jjGL
xj
F
int
5 )1()(
lefthanded fermion
S= - 1/2
righthanded antifermion
S = + 1/2
maximal breaking of
parity
weak interaction of the quarks
beta – decay
d u
eepn
weak decays of strange particles
epe
( u d s ) ( u u d )
s u
Cabibbo angle:
)sincos( sdd
flavor mixing
)(xj
19
W(+) W(-) Z photon
rotation symmetry
spontaneous symmetry breaking in classical mechanics
spontaneous symmetry breaking baki
direction singled out rotation symmetry broken
Peter Higgs
Kibble Guralnik Hagen Englert Brout
potential
V
example 1: real scalar field
4
=> 2 ground states
example 2: complex scalar field
exact symmetry:
broken symmetry:
scalars:
doublet
degrees of freedom before symmetry breaking:
After symmetry breaking:
scalars:
triplet
„Higgs“ scalar
2)(
1)()(
2
13
R
eL
eY
YeY
YTQ
R
L
e
eRSinglet
eLDoublet
:
:
YB
iTW
bosonsgauge
ii
3,2,1
:4
RDiRLDiLL
GGFFL
f
iibg
4
1
4
1..
0
:
scalar
g
gangleweak
ggcouplingstwo
USU
w
tan:
,:
:)1()2(
photon
first term lefthanded
parity violation
neutral current interaction
parity violation
observed in atomic physics
neutrino massless
(only lefthanded component)
The masses of the weak bosons are predicted,
once the weak angle is measured. The electron mass cannot be
predicted( the coupling constant g is unknown ).
electroweak theory: mass generation by
??? SSB ???QCD: mass generation
by confinement
problem: mass generation
hypothetical hypothetical Higgs Higgs bosonboson
L3
I
ATLAS
CMS
LHCb
Alice
December 2011:
ATLAS and CMS report signal at 125 GeV decay into
Z + Z W + W, photon + photon
Real World 3 lepton-quark families
de
ue
s
c
b
t
mass
Real World 6 leptons – 6 quarks
2 x 3 doublets
ee
bsd
tcu
bsd
bsd
flavor mixing