KATRIN: A next generation
neutrino mass experiment
Michelle Leber
For the KATRIN collaboration
University of Washington
7/19/2016
1
Outline
• What is a neutrino and why is its mass
interesting?
• What techniques can measure neutrino
mass?
• Overview of the KATRIN tritium -decay
experiment
– Principle of MAC-E filter
• Detector region design
– Backgrounds simulations for KATRIN
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2
1930: Missing Energy
Nuclear ß-decay:
•
•
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Two particles observed
in the final state
Energy and momentum
appear to not be
conserved
3
The Neutrino Postulated
Nuclear ß-decay:
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Pauli postulates a third
particle is emitted
•Electrically neutral
•Light:
•Spin 1/2
4
Standard Model of Particle
Physics
• Three flavors of neutrinos interact via the
weak interaction mediated by W+ and Z0
• Interaction projects out left-handed particle
states to violate parity maximally
• In SM neutrinos are only
left-handed and massless!
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5
However…
Solar and atmospheric neutrino experiments observe flavor
oscillations
If neutrinos have different mass and flavor eigenstates
(like CKM) then neutrinos can oscillate to other flavors
Oscillations show neutrinos are not massless!
But cannot measure the absolute mass scale
Figure from Scott Dodelson
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6
Why is neutrino mass
important?
• Particle Physics:
– Neutrino mass is much smaller than other fermion
masses
– Neutrinos are uncharged and have the possibility
to be their own antiparticle
– Do neutrinos acquire mass differently than other
particles?
– New physics?
Figure from APS “Neutrino Matrix”
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Why is neutrino mass
important? Matter distribution
• Cosmology
Cold Dark Matter
(no neutrino mass)
in the universe
Colombi, Dodelson, & Widrow 1995
– 109 more neutrinos than
baryons in the universe
– Large Scale Structure
– Leptogenesis
• Might be able to explain the
abundance of matter over
antimatter in the universe
– Supernovae
Hot + Cold Dark Matter
(non-zero neutrino mass)
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8
Measuring Neutrino Mass
• Cosmology:
– Massive neutrinos suppress
matter power spectrum at
small scales
– Model dependent
• Neutrinoless Double Beta
Decay:
Smaller scales
– If neutrinos are Majorana
particles
– Rate depends on effective mass
and nuclear matrix element
– Model dependent
Figure from Scott Dodelson
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9
Measuring Neutrino Mass:
Beta Decay
Neutrinos with mass modify the shape of
the electron’s energy spectrum near the
endpoint (18.6 keV)
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Beta Decay
Electron’s energy spectrum:
For degenerate neutrino mass region (3 flavors) measure
an effective mass:
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11
Constraints on  mass
What we know
Upper Bound
Tritium -decay
(Mainz)
Upper Bound
Cosmology
(WMAP, 2dF,
Lyman-)
 meV
Future Experiments
KATRIN
Tritium
-decay
Lower Bound
Atm.  (SuperK)
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12
Overview of KATRIN
70 m
Rear
Source
3H
β-decay
Transp/Pump
Pre-spectrometer
Main spectrometer
Detector
e
e-
e-
1010 e- /s
1010 e- /s
3He
e-
e-
103 e- /s
1 e- /s
3He
3He
3•10-3 mbar
± 1 kV
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10-11 mbar
18.4 kV
10-11 mbar
18.574 kV
13
Principle of a MAC-E Filter
Magnetic Adiabatic Collimation + Electrostatic Filter
• Two superconducting
solenoids make a guiding
magnetic field
• Electron source in left solenoid
• Electrons emitted in forward
direction are magnetically
guided
• Adiabatic transformation:
 Parallel beam at
analyzing plane
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Principle of a MAC-E Filter
Magnetic Adiabatic Collimation + Electrostatic Filter
U
•
Retarding
electrostatic potential
is an integrating highenergy pass filter
qU
•
Parallel energy
analysis
electrodes
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Main Spectrometer Delivery
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KATRIN’s Detector Region
30 kV post-acceleration
electrode
10-11 mBar
vacuum
3 Tesla magnet
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5 cm Silicon Detector
500 m thick
148 segments
17
Detector Background
Region Of
Interest (ROI)
depends on
• Postacceleration
• Energy
resolution
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Detector-related
background
18
Spectrometer-related
Background
Electrons
produced in
the
spectrometer
Mimics the signal
Position
determined by
postacceleration
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Detector-related
background
Spectrometer-related
background
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KATRIN Signal
Position
determined
by postacceleration
0-100 Hz rate
depending
on retarding
voltage
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Detector-related
background
Spectrometer-related
background
KATRIN signal
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KATRIN Signal
Signal rate:
0-100 Hz
Spectrometer
Background:
10 mHz
Detector
background:
1 mHz
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Detector-related
background
Spectrometer-related
background
KATRIN signal
ROI
21
Detector-related Backgrounds
• Sources
– Cosmic Rays
• Muons, protons, and neutrons
– Natural Radioactivity
•
238U, 232Th
– Cosmogenics
• Copper, Stainless Steel, Silicon, Ceramic
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Detector Area
Superconducting
Magnet Coils
Copper/
Lead
Shield
Scintillator
Beamline
Detector
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CF flange
23
Natural Radioactivity
Uranium Chain:
214Bi releases
0.7 gammas
per decay
above 1 MeV
Thorium Chain:
228Ac and 208Tl
release
0.5 gammas per
decay above
1 MeV
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Potassium-40
releases 0.1
gammas per
decay above
1 MeV
24
Backgrounds from Magnet
Coils
High energy photons compton
scatter within the detector
Activity Bq/kg
Rate 15.9-19.4
Uranium
0.74
0.023 + 0.006 mHz
Thorium
0.89
0.034 + 0.008 mHz
Potassium
3.0
0.01-0.02 mHz
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25
Simulation Detector
• 500 m, 5 cm radius Silicon Wafer
• Copper cooling ring
• Mounted on
CF flange
• Feed through
Insulators
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Feed-through Insulators
• Uranium:
– 6 s per decay
max endpoint ~3
MeV
• Thorium
– 4 s per decay
max endpoint ~2
MeV
• Potassium
– 1  per decay max
endpoint 1.5 MeV
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Feed-through Insulators
material
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kryoflex
Activity
Bq/kg
470 238U
Mass Rate 15.9g
19.4 mHz
3.2
5.6 + 0.1
glass
900 40K
3.2
1.5 + 0.2
28
Remaining Background Work
• Verification
– Short term:
• Detector response to photons (241Am)
• Measure the cosmic ray spectrum
• Electron Gun
– During Commissioning:
• Effect of magnetic field on detector
backgrounds
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Conclusions
• The KATRIN experiment will investigate
an interesting region of neutrino mass
• Largest detector backgrounds are
starting to be understood
– Cosmic Rays
– s originating close to the detector
• Neutrino mass measurements will start
end of 2009-2010
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30
Thanks!
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QuickTime™ and a
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QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
John Wilkerson, Peter Doe, Hamish Robertson, Joe
Formaggio, Markus Steidl, Ferenc Glück, Brent
VanDevender, Brandon Wall, Jessica Dunmore
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QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
7/19/2016
QuickTi me™ and a
TIFF ( Uncompressed) decompressor
are needed to see thi s pi ctur e.
QuickT ime ™an d a
TIFF ( Uncomp res sed) deco mpre ssor
ar e need ed to see this pictur e.
Qui ckTime™ and a
TIFF (U ncompr essed) decompressor
are needed to see thi s pi cture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
31
Parity Violation
• Polarized 60Co nuclei
ß-decay, emitting
electrons
preferentially away
from the magnetic
field
• Under parity, spin
does not change
sign, but the
electron’s momentum
does
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Figure from Los Alamos Science
32
Helicity vs. Chirality
• Helicity
Conserved
Frame dependent
Figure from Los Alamos Science
• Chirality
x
Frame independent
Not conserved
In the Standard Model, only massless, left-chirality neutrinos
exist.
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Current State of Neutrino
Physics
Oscillations show neutrinos are not massless!
But cannot measure the mass scale
Solar Experiments and
KamLAND measure
SNO Collaboration, Phys. Rev. C72 (2005)
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Atmospheric
Experiments
measure
Super Kamiokande Collaboration,
Phys. Rev. Lett. 93(2004)
34
Bounds from cosmology
S. Hannestad, Annu. Rev. Nucl. Part. Phys. (2006) 1
Bounds fluctuate because of model dependencies
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KATRIN’s Sensitivity
10101
0.2 eV (90% CL)
KKDC
0
claim
Mainz
limit
1100
m23
atm
0.0110-2
0.00110-3 -3
10
0.001
Heidelberg
-Moscow
0
limit
mi
Projected
KATRIN
limit
0.110-1
m12
solar
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Quasi-degenerate
-masses
mj [eV]
KATRIN will
probe the
degenerate
mass regions
with projected
sensitivity
m3
hierarchical
-masses
m2
m1
10-2
0.01
10-1
0.1
m1 [eV]
100
1
101
10
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