Double-Beta Decay and the Neutrino Steve Elliott Nuclear Physics.
Neutrino Physics - Double-Beta Decay Steve Elliott Los ...June 2007 Steve Elliott, FNAL Neutrino...
Transcript of Neutrino Physics - Double-Beta Decay Steve Elliott Los ...June 2007 Steve Elliott, FNAL Neutrino...
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Neutrino Physics - Double-Beta Decay
Steve ElliottLos Alamos National
Laboratory
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June 2007 Steve Elliott, FNAL Neutrino Summer School 2
Lecture Outline
• Double Beta Decay– Basic physics– General experimental techniques– The various experiments
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June 2007 Steve Elliott, FNAL Neutrino Summer School 3
Example Decay Scheme
2+
0+
0+
0+
2-
Ge76
As76
Se76
!!
In many even-even nuclei, β decay is energetically forbidden. This leaves ββ
as the allowed decay mode.
EndpointEnergy
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June 2007 Steve Elliott, FNAL Neutrino Summer School 4
ββ(2ν): Allowed weak decay
!
2n" 2p+ 2e#
+ 2$ e
e-
e-
Z+2Z+1
Zνe
νe
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June 2007 Steve Elliott, FNAL Neutrino Summer School 5
ββ(0ν): requires massive Majorana νOnly practical way to address the particle-antiparticle question
e-
e-
Z+2
Z+1
Z νe
n! p + e"+ #e
!e + n" p + e#
!
(RH "e )
!
(LH "e)
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June 2007 Steve Elliott, FNAL Neutrino Summer School 6
Energy Spectrum for the 2 e-
2.01.51.00.50.0
Sum Energy for the Two Electrons (MeV)
Two Neutrino Spectrum Zero Neutrino Spectrum
1% resolution!(2") = 100 * !(0")
EndpointEnergy
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June 2007 Steve Elliott, FNAL Neutrino Summer School 7
ββ History
• ββ(2ν) rate first calculated by Maria Goeppert-Mayer in 1935.
• First observed directly in 1987.• Why so long? Background
τ1/2(U, Th) ~ Tuniverse
τ1/2(ββ(2ν)) ~ 1010 Tuniverse
• But next we want to look for a process with:
τ1/2(ββ(0ν)) ~ 1017 Tuniverse
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June 2007 Steve Elliott, FNAL Neutrino Summer School 8
ββ Candidates
There are a lot of them!
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June 2007 Steve Elliott, FNAL Neutrino Summer School 9
How to choose a ββ isotope?
• Detector technology exists
• High isotopic abundance or an enrichedsource exists.
• High energy = fast rate
• High energy = above background
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June 2007 Steve Elliott, FNAL Neutrino Summer School 10
ββ CandidatesAbundance > 5%,Trans. Energy > 2 MeV
Frequently studied isotope.
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June 2007 Steve Elliott, FNAL Neutrino Summer School 11
ββ Decay Rates
!2" = G2" M2"
2
!0" = G0"M0"
2
m"2
G are calculable phase space factors.G0ν ~ Q5
|M| are nuclear physics matrix elements.Hard to calculate.
mν is where the interesting physics lies.
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June 2007 Steve Elliott, FNAL Neutrino Summer School 12
“Because Its Not There”
Larson
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June 2007 Steve Elliott, FNAL Neutrino Summer School 13
Neutrino Mass: What do we want to know?
Mas
sAbsolute
MassScale
RelativeMassScale
!"
!#
!#
!"
$
%
& & & & &
'
(
) ) ) ) )
or
!"
!#
$
% & &
'
( ) )
Dirac or Majoranaνe ν1 ν2 ν3
Ue1
2Ue2
2Ue3
2
Mixing
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June 2007 Steve Elliott, FNAL Neutrino Summer School 14
Neutrino Mass: How do we learn what we want toknow?
Absolute Mass Scale
Relative Mass Scale
Mixing Matrix
Elements
CP nature
of
, cosm. Oscil.
Need all 3 types of experiments.
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June 2007 Steve Elliott, FNAL Neutrino Summer School 15
Neutrino Masses: What do we know?
• The results of oscillation experiments indicate νdo have mass!, set the relative mass scale, and aminimum for the absolute scale.
• β decay experiments set a maximum for theabsolute mass scale.
50 meV < mν < 2200 meV
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June 2007 Steve Elliott, FNAL Neutrino Summer School 16
We also know ν mix.
!e!µ
!"
#
$
% %
&
'
( ( =
Ue1 Ue2 Ue3
Uµ1 Uµ2 Uµ3
U"1 U"2 U"3
#
$
% %
&
'
( (
!1!2!3
#
$
% %
&
'
( (
The weak interaction produces νe, νµ, ντ.
These are not pure mass states but a linearcombination of mass states.
Oscillation experiments indicate that ν mix and constrain Uαi.
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June 2007 Steve Elliott, FNAL Neutrino Summer School 17
Oscillations and HierarchyPossibilities
mass
Normal Invertedmsmallest1
2
312
3
49 meV
9 meV
νe is composed of a large fraction of ν1.
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June 2007 Steve Elliott, FNAL Neutrino Summer School 18
What about mixing, mν & ββ(0ν)?
m!! = Uei
2
mi
i=1
3
" #i
ε = ±1, CP cons.
Compare to β decay result:
m! = Uei
2
mi
2
i=1
3
"
virtual νexchange
real νemission
No mixing: m!! = m"e= m
1
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June 2007 Steve Elliott, FNAL Neutrino Summer School 19
Why does the CP parity appear in <mββ>?
Look at the critical part of this diagram.
A0ν ∼ Σin
n
p
p
W-
W-
νi
e-
Uei
Uei
e-
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June 2007 Steve Elliott, FNAL Neutrino Summer School 20
The crossed channel.
e+ e-
W- W+
νi
A! Uei
2e+W
"HSM
#i
i
$ #iHSMe"W
+
The 1st vertex creates the CP partnerof the particle needed by the 2nd vertex.
But CP !i= "
i!i
Upon substitution, the factor εi appears.
Vertex 1
Vertex 2
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June 2007 Steve Elliott, FNAL Neutrino Summer School 21
What can be learned from Oscillations & ββ?
• From oscillations, we have:Information on UeiInformation on δm2
• With <mββ> constraints, we can constrain m1:(2 flavor example)
!
m"" = Ue1
2m1+#
21Ue2
2m
1
2+$m
21
2
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June 2007 Steve Elliott, FNAL Neutrino Summer School 22
Min. <mββ> as a vector sum.General Case
m!! = Ue1
2
m1+ e
i!Ue2
2
m2+ e
i"Ue3
2
m3
!
"
Ue3
2m3
Ue2
2m2
Ue1
2m1
<mββ>
<mββ> is the modulus of the resultant.In this example, <mββ> has a min. It cannot be 0.
min
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June 2007 Steve Elliott, FNAL Neutrino Summer School 23
PlotThanks toPetr Vogel
More General: 3 ν
50 meV orfew x 1027 yr
msmallest
<mββ
>
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June 2007 Steve Elliott, FNAL Neutrino Summer School 24
More General
PlotThanks toPetr Vogel
50 meV orfew x 1027 yr
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June 2007 Steve Elliott, FNAL Neutrino Summer School 25
50 meVOr ~ 1027 yr
Normal
Inverted
0.1
1
10
100
1000Eff
ecti
ve !! M
ass
(m
eV
)
12 3 4 5 6 7
102 3 4 5 6 7
1002 3 4 5 6 7
1000
Minimum Neutrino Mass (meV)
Ue1
= 0.866 "m2
sol = 70 meV
2
Ue2
= 0.5 "m2
atm = 2000 meV
2
Ue3 = 0
Inverted
Normal
Degenerate
Solar Scale
Atmospheric Scale
KKDC Claim
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An exciting time for ββ!
< mββ > in the range of10 - 50 meV is very interesting.
For the next experiments:
For at leastone
neutrino:
!
mi > "matmos2
# 50meV
!
m"" # 50meV
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June 2007 Steve Elliott, FNAL Neutrino Summer School 27
The 1st Observation
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June 2007 Steve Elliott, FNAL Neutrino Summer School 28
The Heidelberg-Moscow Experiment
Foun
datio
ns o
f Phy
sics
, 32,
(200
2)
8”
~10 kg of 76Ge13 years of data
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June 2007 Steve Elliott, FNAL Neutrino Summer School 29
Elliott & VogelAnnu. Rev. Part. Sci. 2002 52:115
102
103
104
105
Mass L
imit
(m
eV
)
20202000198019601940
Year
Ge-76Ge-76
Te-128
Te-128
Se-82
Ge-76
Ge-76
Ca-48Nd-150
Nd-150
EXO-200
GERDA
MJ-120
CUORE
>3.6x1021 y150Nd
<(0.8-5.6) eV>4.5x1023 y136Xe
<(0.41-1.) eV>3.0x1024 y130Te
<(1.1-1.5) eV>7.7x1024 y128Te
<1.7 eV>1.7x1023 y116Cd
<(0.6-2.7) eV>5.8x1023 y100Mo
<(1.2-3.2) eV>2.1x1023 y82Se
=0.44 eV=1.2x1025 y76Ge
<(0.33-1.35) eV>1.6x1025 y76Ge
<0.35 eV>1.9x1025 y76Ge
<(7.2-44.7) eV>1.4x1022 y48Ca
m!! "1
M G0#$1 / 2
%
& ' '
(
) * *
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June 2007 Steve Elliott, FNAL Neutrino Summer School 30
An Ideal ExperimentMaximize Rate/Minimize Background
• Large Mass (~ 1 ton)• Good source radiopurity
• Demonstrated technology• Natural isotope
• Small volume, source = detector• Good energy resolution
• Ease of operation• Large Q value, fast ββ(0ν)
• Slow ββ(2ν) rate• Identify daughter
• Event reconstruction• Nuclear theory
m!! "b#E
Mtlive
$
% & &
'
( ) )
1
4
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June 2007 Steve Elliott, FNAL Neutrino Summer School 31
Great Number of Proposed Experiments
• Calorimeter– Semi-conductors– Bolometers– Crystals/nanoparticles immersed in scintillator
• Tracking– Liquid or gas TPCs– Thin source with wire chamber or scintillator
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“Found” PeaksPR
D45
, 254
8 (1
992)
A 2527-keV Ge-det. peak that was an electronic artifact.
A ~2528-keV Te-det.peak that was a 2σStatistical flucuation. N
P B3
5 (P
roc.
Sup
p.),
366
(199
4).
Need more thanone experiment
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June 2007 Steve Elliott, FNAL Neutrino Summer School 33
A Recent Claim for ββ(0ν)
Mod
. Phy
s. Le
tt. A
16, 2
409
(200
1)
20
15
10
5
0
Counts
20802060204020202000
Energy (keV)
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June 2007 Steve Elliott, FNAL Neutrino Summer School 34
The ROI
The “feature” at 2038keV is arguablypresent. This willprobably requireexperimental testing.
Background leveldepends on intensity fitto other peaks.
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June 2007 Steve Elliott, FNAL Neutrino Summer School 35
Future Data Requirements
Why wasn’t this claim sufficient to avoidcontroversy?
• Low statistics of claimed signal - hard torepeat measurement• Background model uncertainty• Unidentified lines• Insufficient auxiliary handles
Result needs confirmation or repudiation
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June 2007 Steve Elliott, FNAL Neutrino Summer School 36
Various Levels of Confidence
• A preponderance of the evidence: a combination of– Correct peak energy– Single-site energy deposit– Proper detector distributions (spatial, temporal)– Rate scales with isotope fraction
• Beyond a reasonable doubt: include the following– Observe the two-electron nature of the event– Measure kinematic dist. (energy sharing, opening angle)– Observe the daughter– Observe the excited state decay
• Open and shut case: the smoking gun– See the process in several isotopes
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June 2007 Steve Elliott, FNAL Neutrino Summer School 37
Classes of Background for ββ(0ν)
• ββ(2ν) tailNeed good energy resolution.
• Natural U, Th in source and shieldingPure materials, segmentation, pulse shape.
• Cosmic ray activationStore and prepare materials underground.
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June 2007 Steve Elliott, FNAL Neutrino Summer School 38
ββ(2ν) as a Background.Sum Energy Cut Only
next generationexperimentalgoal
10-4
10-3
10-2
10-1
100
101
102
103
<m
!!>
Sen
siti
vity
(meV
)
54321Resolution (%)
100Mo
136Xe
76Ge
130Te
2.0
1.5
1.0
0.5
0.0
dN
/d(K
e/Q
)
1.00.80.60.40.20.0Ke/Q
30
20
10
0
x1
0-6
1.101.000.90
Ke/Q
!
S
B=me
7Q" 6T1/ 2
2#
T1/ 2
0#
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June 2007 Steve Elliott, FNAL Neutrino Summer School 39
Natural Activity
• The Problem: τ(U, Th) ~ 1010 yearsGoal: τ(ββ(0ν)) ~ 1027 years
• Detector: Intrinsic Ge is very pure• Cryostat: Electro-formed Cu• Shielding: Roman Pb• Front End Electronics: behind shield
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June 2007 Steve Elliott, FNAL Neutrino Summer School 40
Cosmic Ray Induced Activity
• Material dependent.Lots of experience with Ge.
• Need for depth to avoid activation.
• Need for storage to allow activationto decay.
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June 2007 Steve Elliott, FNAL Neutrino Summer School 41
Pb(n,n’γ) and 76Ge: an example
206Pb 207Pb
3744 keV 3633 keV
1703 keV1467 keV1167 keV
803 keV
g.s.571 keV
g.s.
2041 keV
3062 keV
DEP of 3062line is at 2040
keV!!
Am
Be
stud
y at
LA
NL
n,n’
stu
dy a
t TU
NL