Direct Determination of Neutrino Mass Beta Decay –Tritium – 187 Re –Other ideas? Neutrino...
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Direct Determination of Neutrino Mass
• Beta Decay– Tritium– 187Re– Other ideas?
• Neutrino Oscillations• Supernova timing• Double beta decay• Cosmology• Z-bursts
Hamish Robertson -- Carolina Symposium 5/08
• The mass is needed for• Particle physics• Interpretation of supernova signal• Cosmology
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Masses linked by oscillations
PresentLab Limit2.3 eV
m232m12
2
Average mass > 20 meV ?
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Claim of Evidence for 0 in 76Ge
Single-site events in detectors 2, 3, 4, 5 (56.6 kg-y).H.V. Klapdor-Kleingrothaus, Int. J. Mod. Phys. E17, 505 (2008)
<m> ~ 0.2 to 0.3 eV
Looks good to me…
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Beta decay and neutrino mass
Task: Investigate 3H or 187Re endpoint with sub-eV precision
KATRIN Aim:Improve m sensitivity tenfold (2eV 0.2eV )
Requirements:
• Strong source
• Excellent energy resolution
• Small endpoint energy E0
• Long term stability
• Low background rate
3H
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What are we measuring?
Writing the transition probability as the matrix element of some operator T,
In the degenerate regime where all the masses are the same, the unitarity of U gives us back the original expression for a single massive neutrino, an “electron neutrino with mass”
€
∝ peE(E − E0)2 1−mν
2
(E − E0)2
⎡
⎣ ⎢
⎤
⎦ ⎥
1/ 2
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Final Mainz Result -- Kraus et al. hep-ex/0412056
Improved S/N tenfold over 1994 data
20 weeks of data in 1998, 1999, 2001
Stable background: pulsed RF clearing field applied at 20-s intervals
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Assemble everyone who has done a tritium experiment. Then…
aim : improve m by one order of magnitude (2 eV 0.2 eV )
requires : improve m by two orders of magnitude (4 eV2 0.04 eV2 )
problem : count rate close to ß-end point drops very fast (~E3)
• improve statistics :
- stronger tritium source (factor 80) (& large analysing plane, Ø=10m)
- longer measuring period (~100 days ~1000 days)
• improve energy resolution :
- large electrostatic spectrometer with E=0.93 eV (factor 4 improvement)
- reduce systematic errors :
- better control of systematics, energy losses (reduce to less than 1/10)
2
The next generation experiment
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TLK
~ 75 m long with 40 s.c. solenoids
KATRIN 5 countries13 institutions100 scientists
at Forschungszentrum Karlsruhe
unique facility for closed T2 cycle:
Tritium Laboratory Karlsruhe
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Windowless Gaseous T2 Source
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Adiabatic magnetic guiding of ´s along field lines in stray B-field of s.c. solenoids:Bmax = 6 TBmin = 3×10-4 T
Energy analysis bystatic retarding E-fieldwith varying strength:
High pass filter withintegral transmissionfor E>qU
Principle of MAC-E Filter
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1010 e- /s
e-
3•10-3 mbar- 1 ± 1 kV
Source
3H
β-decay
e
3He
Source: Provide the required tritiumcolumn density
70 m
10-11 mbar- 1 - 18.4 kV
Pre-spectrometer
103 e- /s
e-
Pre-spectrometer:Rejection of low-energy electrons and adiabatic guiding of electrons
1 e- /s
e-
10-11 mbar-1 - 18.574 kV
Main spectrometer
Main-spectrometer:Rejection of electronsbelow endpoint and adiabatic guiding ofelectrons
Detector
Detector:Count electrons and measure their energy
Rear
3He
Rear System:Monitor sourceparameters
Transp/Pump
3He
1010 e- /s
e-
Transp. & Pump system:Transport the electrons,adiabatically and reduce the tritium densitysignificantly
0 kV
KATRIN Experiment
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Parameters:•Length: 3.4 m (flange to flange)•Diameter:1.7 m•Vacuum: < 10-11 mbar•Material: Stainless steel•Magnets: 4.5 T
Status:•Vacuum 7•10-11 mbar (without getter)•Outgassing 7•10-14 mbar l/ s cm2
•Measurements in progress
Pre-spectrometer
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Tandem design: -- Pre-filter, Energy analysis
detector
Pre- spectrometerMain spectrometer
10 10 e -/sec
10 3 e -/sec
10 i e -/sec
Pre-spectrometerFilters low energy -decay electrons E<18.4 keVModerate energy resolution E80 eVTest bed for vacuum, electrode design, detector.
Main spectrometer23 m long, 10 m diameterHigh luminosity: dN/dt~Aspect.
high energy resolution: E/E~Aspect
Vacuum 3x10-11 mbar (reduce backgrounds)use non-evaporable getter pumps
Inner wire electrode (shape field, reduce backgrounds)External air coil - compensate for Earths magnetic field
Detector145 pixel Si PIN diode~1keV resolutionImage source systematics backgrounds
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assembly hall DWE
Danube
2 conical end pieces
1 cylindrical centre piece
Main Spectrometer Manufacture
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Voyage of the main spectrometer
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Arrival in Leopoldshafen: Nov 24, 2006
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Inside the Spectrometer
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Detector Section (Univ. of Washington, MIT)
Silicon PIN diode detector• 9 cm active diameter• 500 m thick• 148 segments
e-
“flux tube”
post-acceleration electrode
detector magnetB = 3-6 T
shielding & veto
pinch magnetB = 6 T
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Pixelized Detector Corrects Focal Plane Resolution
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• Improved over original design (7 m diameter main spectrometer, source luminosity)
• Reduction in background
• Only shows statistical uncertainty
KATRIN Statistical Sensitivity
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Optimized run time at each energy
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Tritium Beta Decay History
€
mv2 = 2Δσ 2
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A window to work in
Molecular Excitations
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preli
minary
preli
minary
preli
minary
Precision Voltage Divider test at PTB, 2006
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Improved sensitivity with larger system
Discovery
90% CL UL
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Mass Range Accessible
PresentLab Limit2.3 eV
m232m12
2
Average mass > 20 meV
KATRIN
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8751 hours x mg (AgReO4)
MIBETA: Kurie plot of 6.2 ×106 187Re ß-decay events (E > 700 eV)
10 crystals:
E0 = (2465.3 ± 0.5stat ± 1.6syst) eV
MANU2 (Genoa)metallic Rheniumm() < 26 eV
Nucl. Phys. B (Proc.Suppl.) 91 (2001) 293
MIBETA (Milano)AgReO4
m() < 15 eV
MARE (Milano, Como,Genoa, Trento, US, D)Phase I : m() < 2.5 eVm
2 = (-112 ± 207 ± 90) eV2
Nucl. Instr. Meth. 125 (2004) 125
hep-ex/0509038
Microcalorimeters for Microcalorimeters for 187187Re ß-decayRe ß-decay
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• KATRIN can measure neutrino mass directly via kinematics of beta decay -- model independent
• Improvement of order of magnitude over previous best
• Challenging goal of m < 0.2 eV (90% C.L.) looks achievable
• German funding (33.5 M€) is in place • US DOE funding ($2.6 M) is in place• Initial operation 2010.
KATRIN outlook
Thanks, Peter
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Fin
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Supernova Neutrino Time-of-flight
For a supernova at distance D (in 10 kpc) the time delay for a neutrino of mass m (eV) and energy E (MeV) is:
Beacom & Vogel hep-ph/9802424
The delay must be ~ the duration of the neutrino signal to avoid model dependence at short times and not to be drowned in background at long times. For a 1 eV result with 30-MeV neutrinos, need D = 175 Mpc. Scaling Kamiokande for the same rate as SN1987a, detector mass must be 12 Gt.
IceCube will be “only” 1 Gt, and not very sensitive at these low energies.
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Z-bursts
Hypothesis: the extreme-energy CR spectrum is produced by neutrinos from distant sources. The neutrinos can annihilate at the Z pole on relic neutrinos to produce the observable EE CR. (A GZK-style cutoff for neutrinos).
Gelmini, Varieschi & Weiler, hep-ph/0404272
If cutoff is at 2 x 1020 eV, then m > 20 eV, in disagreement with expt. EE CR thus likely not neutrino Z-burst debris.
Abbasi et al., PRL 92, 151101
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• Ultimate sensitivity of spectrometers– require instrumental resolution of ~
– Linear size X of instrument scales with resolution:• Differential spectrometers • Integral spectrometers
– spectral fraction per decay in the last mn of the spectrum is ~ (m/Eo )3
– source thickness is set by the inelastic scattering cross-section (3.4 x 10-18 cm2 ), n ≤ 1. Can’t make it thicker, only wider.
– If one wants ~1 event/day in last m of the spectrum
• for a 10 m magnetic spectrometer m ~ 1.7 eV
• for a 3 m dia. solenoid retarding field spectrometer m ~ 0.3 eV
€
X ∝ Ee /mν
€
X ∝ Ee /mν
KATRIN is probably the end of the road for tritium beta decay
€
Ee /mν
Future tritium measurements?
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Electron Gun
Cold Finger
TritiumGetter
Cryopump
CylindricalMirror Analyzer
SphericalDeflectingAnalyzer
Tritium Cell
Detector
Mu-Metal
Deflecting &FocusingAnalyzer
Liquid Nitrogen Baffles
Diffusion Pumps
NEXTEXNEXTEX
U of Texas (1 M$)
Pure electrostatics
Possibility for electron diffr.
no magnetic fields <0.1 mG
Sensitivity ~ 0.8 eV
Required funding 6.5M$
Not funded, it’s over
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Sensitivity with run time
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Systematic Uncertainties
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WGTSManufacturing Started
Delivery 2007
Main spectrometerFinal designs by MAN-DWEDelivered December 2006
Pre-spectrometer magnetsDelivered in February 2005
Pre-spectrometer Delivered in Oct. 2003Vacuum tests started May 2004El. mag. test start 2006
DPS2-FManufacturing startedDelivery 2007
Status of KATRIN Hardware Activities
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MC Using Stopping Power (M. Steidl)
Arrows show 99% intensity windows
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Figure-of-merit
“Better”
1 mHz
2 mHz
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QuickTime™ and a decompressor
are needed to see this picture.
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Final States
Red: 3HeT+ Blue: 3HeH+
1% uncertainty in rovib spectrum m2 = 6 x 10-3 eV2
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Even small m influences structure
0
0.5 eV
2.4 eV2DF Galaxy SurveyPRL 89 061301
LargeScale
SmallScale
m
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Mass (eV)
0.058
0.009
0
Minimum Neutrino Masses and Flavor Content
3
e mu tau
Atmospheric
21
Solar
Atmospheric
21
Solar
0 3
0.0500.049
? ?
m232
m122
Neutrino mass spectrum and flavor content