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
Masses linked by oscillations
PresentLab Limit2.3 eV
m232m12
2
Average mass > 20 meV ?
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…
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
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
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
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
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
Windowless Gaseous T2 Source
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
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
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
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
assembly hall DWE
Danube
2 conical end pieces
1 cylindrical centre piece
Main Spectrometer Manufacture
Voyage of the main spectrometer
Arrival in Leopoldshafen: Nov 24, 2006
Inside the Spectrometer
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
Pixelized Detector Corrects Focal Plane Resolution
• Improved over original design (7 m diameter main spectrometer, source luminosity)
• Reduction in background
• Only shows statistical uncertainty
KATRIN Statistical Sensitivity
Optimized run time at each energy
Tritium Beta Decay History
€
mv2 = 2Δσ 2
A window to work in
Molecular Excitations
preli
minary
preli
minary
preli
minary
Precision Voltage Divider test at PTB, 2006
Improved sensitivity with larger system
Discovery
90% CL UL
Mass Range Accessible
PresentLab Limit2.3 eV
m232m12
2
Average mass > 20 meV
KATRIN
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
• 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 ($2.6 M) is in place• Initial operation 2010.
KATRIN outlook
Thanks, Peter
Fin
Supernova Neutrino Time-of-flight
For a supernova at distance D (in 10 kpc) the time delay for a neutrino of mass m (eV) and energy E (MeV) is:
Beacom & Vogel hep-ph/9802424
The delay must be ~ the duration of the neutrino signal to avoid model dependence at short times and not to be drowned in background at long times. For a 1 eV result with 30-MeV neutrinos, need D = 175 Mpc. Scaling Kamiokande for the same rate as SN1987a, detector mass must be 12 Gt.
IceCube will be “only” 1 Gt, and not very sensitive at these low energies.
Z-bursts
Hypothesis: the extreme-energy CR spectrum is produced by neutrinos from distant sources. The neutrinos can annihilate at the Z pole on relic neutrinos to produce the observable EE CR. (A GZK-style cutoff for neutrinos).
Gelmini, Varieschi & Weiler, hep-ph/0404272
If cutoff is at 2 x 1020 eV, then m > 20 eV, in disagreement with expt. EE CR thus likely not neutrino Z-burst debris.
Abbasi et al., PRL 92, 151101
• Ultimate sensitivity of spectrometers– require instrumental resolution of ~
– Linear size X of instrument scales with resolution:• Differential spectrometers • Integral spectrometers
– spectral fraction per decay in the last mn of the spectrum is ~ (m/Eo )3
– source thickness is set by the inelastic scattering cross-section (3.4 x 10-18 cm2 ), n ≤ 1. Can’t make it thicker, only wider.
– If one wants ~1 event/day in last m of the spectrum
• for a 10 m magnetic spectrometer m ~ 1.7 eV
• for a 3 m dia. solenoid retarding field spectrometer m ~ 0.3 eV
€
X ∝ Ee /mν
€
X ∝ Ee /mν
KATRIN is probably the end of the road for tritium beta decay
€
Ee /mν
Future tritium measurements?
Electron Gun
Cold Finger
TritiumGetter
Cryopump
CylindricalMirror Analyzer
SphericalDeflectingAnalyzer
Tritium Cell
Detector
Mu-Metal
Deflecting &FocusingAnalyzer
Liquid Nitrogen Baffles
Diffusion Pumps
NEXTEXNEXTEX
U of Texas (1 M$)
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
Sensitivity with run time
Systematic Uncertainties
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
MC Using Stopping Power (M. Steidl)
Arrows show 99% intensity windows
Figure-of-merit
“Better”
1 mHz
2 mHz
QuickTime™ and a decompressor
are needed to see this picture.
Final States
Red: 3HeT+ Blue: 3HeH+
1% uncertainty in rovib spectrum m2 = 6 x 10-3 eV2
Even small m influences structure
0
0.5 eV
2.4 eV2DF Galaxy SurveyPRL 89 061301
LargeScale
SmallScale
m
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