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On a more fundamental level, beta decay of hadrons can be viewed as the
transforma:on of one type of quark to another through exchange of charged weak
currents (W bosons carry net charges; Z boson is neutral ‐ it is the source of neutral weak
current).
n
p e- νe
_
W-
e- ν
e- ν
Z0
The flavor of quarks is conserved in strong interac:ons. However, weak interac:ons
change flavor!
u→ d + e++ν
ed→ u+ e
−+ν
e
Beta decay: microscopic view
Three generations of matter
There are three "sets" of quark pairs and lepton pairs. Each "set" of these par:cles is called
a genera:on, or family. The up/down quarks are first genera:on quarks, while the
electron/electron neutrino leptons are first genera:on leptons.
up type (q=+2/3e)
down type (q=‐1/3e)
neutral
charged (q=‐e)
mass
par:cles of higher genera:ons to
decay to the first genera:on
(everyday maUer is made of
par:cles from the first genera:on)
http://phys.org/news/2012-12-particles-suffice-nature.html
12 matter particles suffice in nature?
The result of the sta:s:cal analysis is that the
existence of further fermions can be excluded with
a probability of 99.99999 percent (5.3 sigma). The
most important data used for this analysis come
from the recently discovered Higgs par:cle.
hUp://journals.aps.org/prl/abstract/10.1103/PhysRevLeU.109.241802
When a quark beta‐decays, the new quark does not have a definite flavor. For instance
(Cabibbo 1963): u→ d ' = d cosθ
c+ ssinθ
cCabibbo angle θc=13.02º
However, the observed weak transi:ons are between quarks of definite flavor. In general,
the strong‐interac:on quark eigenstates:
u
d
"
# $ $ %
& ' ' c
s
"
# $ $ %
& ' ' t
b
"
# $ $ %
& ' '
u
d'
"
# $ $ %
& ' ' c
s'
"
# $ $ %
& ' ' t
b'
"
# $ $ %
& ' '
are different from weak interac:on eigenstates:
A quark of charge +2/3 (u,c,t) is always transformed
to a quark of charge ‐1/3 (d,s,b) and vice versa. This
is because the transforma:on proceeds by the
exchange of charged W bosons, which must change
the charge by one unit.
Beta decay: mass and weak eigenstates
d '
s '
b '
!
"
###
$
%
&&&=
Uud
Uus
Uub
Ucd
Ucs
Ucb
Utd
Uts
Utb
!
"
####
$
%
&&&&
d
s
b
!
"
###
$
%
&&&
Cabibbo _Kobayashi-
Maskawa (CKM) matrix
For nuclear beta‐decay, we are mainly concerned with the transi:on between u‐ and d‐
quarks. As a result, only the product
enters into the process.
GV=G
Fcosθ
c
Kobayashi and Maskawa generalized the Cabbibo matrix into the Cabibbo–Kobayashi–
Maskawa matrix (or CKM matrix) to keep track of the weak decays of three genera:ons of
quarks
The current determination:
The choice of usage of down‐type quarks in the defini:on is purely arbitrary and does not
represent some sort of deep physical asymmetry between up‐type and down‐type quarks.
Beta decay: CKM Matrix
weak eigenstates mass eigenstates
! !
Observation of Neutrino Oscillations
Oscillation signal(Super)KamiokandeAtmospheric neutrinos
Oscillation signalLSNDAccelerator
Clear disappearance signalK2K
Clear disappearance signalKamLAND, CHOOZReactor
Ultimate “solar neutrino experiment”: proves the
oscillation of solar ν
Heavy water: SNO
Confirm disappearance of solar neutrinos
Water experiments:
(Super)Kamiokande, IMB
First observation of “neutrino disappearance” dates more than 20 years ago: “Solar neutrino problem”
Radio-chemical exp.: Homestake Cl exp., GALLEX, SAGE
Solar neutrinos
CommentsExperimentNeutrino source
Clear disappearance signalMINOS
much disputed
KARMEN and MiniBooNE refuted
Two-Flavor mixing:
Deviations around the
endpoint due to nonzero
neutrino mass…
KATRIN neutrino experiment hUp://www.katrin.kit.edu
hUps://www.youtube.com/watch?v=dmmVb779NP4