View
40
Download
0
Category
Tags:
Preview:
DESCRIPTION
1962 Lederman,Schwartz,Steinberger Brookhaven National Laboratory using a as a source of antineutrinos and a 44-foot thick stack of steel ( from a dismantled warship hull ) to shield everything but the ’s found 29 instances of + p + + n - PowerPoint PPT Presentation
Citation preview
1962 Lederman,Schwartz,Steinberger Brookhaven National Laboratory
using a as a source of antineutrinos
and a 44-foot thick stack of steel (from a dismantled warship hull) to shield everything but the ’s
found 29 instances of
+ p + + n
but none of
+ p e+ + n
1988 Nobel Prize in Physics
"for the neutrino beam method and the demonstration of the doublet structure of the leptons through the discovery of the muon neutrino"
Bep
The Nuclear pp cycle producing energy in the sun
6 protons 4He + 6+ 2e + 2p 26.7 MeV
Begins with the reaction
eedpp
0.26 MeV neutrinos
1967 •built at Brookhaven labs•615 tons of tetrachloroethylene•Neutrino interaction 37Cl37Ar(radioactive isotope, ½ = 35 days)Chemically extracting the 37Ar, its radioactivity gives the number of neutrino interactions in the vat(thus the solar neutrino flux). Results: Collected data 1969-1993 (24 years!!) gives a mean of 2.5±0.2 SNU while theory predicts 8 SNU (1 SNU = 1 neutrino interaction per second for 10E+36 target atoms). This is a neutrino deficit of 69%.
Homestake MineExperiment
The energy spectrum of solar neutrinos predicted by the BP04 solar model. For continuum sources, the neutrino fluxes are given in number of neutrinos cm-2s-1 MeV-1
at the Earth's surface. For line sources, the units are number of neutrinos cm-2s-1. Total theoretical uncertainties are shown for each source.
The difficulttodetect CNO neutrino fluxes have been omitted in this plot.
Solar models predict the spectrum and flux of solar neutrinos reaching the earth
The Solar Neutrino ProblemThe rate of detection of solar e’s from
ee
ArCl 3737is 3 smaller than expected!
Is the sun’s core cooler than we thought? 6%
Is it a different age than we had assumed?
New and extraordinarily precise measurements of “solar sound speeds”
1998
• small oscillations in spectral line strengths• studied by solar seismologists• due to pressure waves traversing the solar volume
confirm the predictions of internal temperature and pressure bystandard solar models to with 0.1%
Atmospheric Neutrino Detection
all showers start
e
(all Ks decaying rapidly into s)with s and Kaons
e
e
e
e
e
→ +
Each pion decays by
→ e + e +
and each muon decays by
Note: at sea level
N
Ne
= 2
MCee
DataeeR)/()(
)/()(
One detector measures this significantly more accurately than any otherSuperKamiokande
They find
Rsub-GeV = 0.63 0.06
Rmulti-GeV = 0.65 0.09
Given the time dilation of muon lifetimes (and the probabilisticnature of their decays) we can still calculate/simulate the ratiowe expect to observe at the ground, and compare:
The observed handedness of neutrinos is consistent with being massless
p
but in a framemoving faster than
the neutrino p
In quantum-field theoretical terms: overtaking a particle corresponds to the Lagrangian term:
)(LRRL
g
=g
=g
=g
=g g
initial R final L
a Dirac mass term!
† †
† †
† †
†
][ 00
LLRRPP
])()[( 00 LRRL
PPPP ][ 00
LRRLPP
)]([ 0
LR
We know the strong “mass” eigenstates of the quarksmix into the weak eigenstates.
dc = dcos + ssinDo the lepton families also mix?
What really distinguishes from ?
Both appear massless, chargeless…
Could ee
? Like the neutral kaons?
Could
e ? Like the Cabibbo mixed quark families?
If e state produced along with e in weak interactions
state produced along with in weak interactions
but these “weak-interaction” states e , , are actually
super-positions (linear combinations) of the
“mass” eigenstates1 ,2 ,3
For a (simple) example of 2-d mixing
2
1
cossin
sincos
e
Giving the states PRODUCED(initial state) by a weak decay
while the propagation through space-time is quantum mechanically determined by
/222
/111
)0()(
)0()(tiE
tiE
et
et
/222
/111
)0()(
)0()(tiE
tiE
et
et
Since these components of the weaklyproduced states must initially be
spacially coherent (have the same momentum)
Then, using for mi << Ei (but not zero)
p
m
iipE 2
2
22422 cpcmE
2
222 1p
mppmE
pmppp
m 2/)1( 222
2
And writing
21sincos
observed weakly interacting state
“mass” or vacuum states
)0(sin)0(cos)(21
21
tiEtiEeet
If, for example, we started with -type neutrinos at t = 0
then the probability of remaining a :
P ( )2
22 21 sincostiEtiE
ee
)()0( t
)0(|)(
t= | |2
and if the |i are orthogonal states 021
1ii
P ( ) tiEtiEtiEtiE
eeee 2121 2222 sincossincos
tEEitEEiee
)()(2244 2121cossinsincos
using eix=cosx + isinx
}cos{cossin2sincos21
2244 tEE
P ( ) }cos{cossin2sincos
21
2244 tEE
using 2244 cossin21sincos
along with the approximation pmpE 22
P ( )
t
pm2
222 cos1cossin21
and finally with 2sincossin21
2sin22cos1
P ( )
t
p
m
4sin2sin1
222
and of course, then
P ( )e
1 P ( )
=
The photon is masslessand has no antiparticle(is its own antiparticle)
But all the fundamental particles of matter do have antiparticles:
e+e
ee+ +
p p n n
du du The quark content of pions show
while other mesons are their own antiparticle
uu dd
1965 Gellmann & Paisnoted a 2nd order (~rare) weak interaction could induce the strangeness-violating transition of K
o K o
a particle becoming
its own antiparticle!
u u
s
d s
d
Ko
Ko
W
u
u
s
d s
d
Ko
Ko
W W
sd
sdK
The neutral kaon however is not its own antiparticle:
K
u
d
e
e
_uu
dd
eepn
W
enpe
e+
e
_
ud u
dd u
epne
but have never observed:
have observed:
Cowan & Reines: Savannah River
In many even-even nuclei, -decay is energetically forbidden.
This leaves -decay as the allowed decay mode.
76As33
76Ge32
76Se34
EndpointEnergy
2
0+
0+
2+
0+
Atomic mass (u)
76Ge32 75.92140276As33 75.92239376Se34 75.919913
ee
34
76
4232
76
44SeGe is observed!
If were its own antiparticle (or could oscillate into )
there could be a chance to observe neutrino-less double-beta decay events.
ee
34
76
4232
76
44SeGe the observed process
34
76
4232
76
44SeGe being searched for!
neutrino-less
Recommended