Direct Determination of Neutrino Mass The mass is needed for Particle physics Interpretation of supernova n signal Cosmology Beta Decay Tritium 187Re Other ideas? Neutrino Oscillations Supernova timing Double beta decay Cosmology Z-bursts Hamish Robertson -- Carolina Symposium 5/08

Masses linked by oscillations Average mass > 20 meV Present Lab Limit 2.3 eV ? m232 m122

Claim of Evidence for 0 in 76Ge <m> ~ 0.2 to 0.3 eV Looks good to me… Single-site events in detectors 2, 3, 4, 5 (56.6 kg-y). H.V. Klapdor-Kleingrothaus, Int. J. Mod. Phys. E17, 505 (2008)

Beta decay and neutrino mass 3H Requirements: Strong source Excellent energy resolution Small endpoint energy E0 Long term stability Low background rate Task: Investigate 3H or 187Re endpoint with sub-eV precision KATRIN Aim: Improve mn sensitivity tenfold (2eV  0.2eV )

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”

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

The next generation experiment Assemble everyone who has done a tritium experiment. Then… aim : improve mn by one order of magnitude (2 eV ® 0.2 eV ) requires : improve mn by two orders of magnitude (4 eV2 ® 0.04 eV2 ) problem : count rate close to ß-end point drops very fast (~dE3) 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 DE=0.93 eV (factor 4 improvement) reduce systematic errors : - better control of systematics, energy losses (reduce to less than 1/10) 2

KATRIN 5 countries 13 institutions 100 scientists at Forschungszentrum Karlsruhe unique facility for closed T2 cycle: Tritium Laboratory Karlsruhe 5 countries 13 institutions 100 scientists TLK ~ 75 m long with 40 s.c. solenoids

Windowless Gaseous T2 Source

Principle of MAC-E Filter Adiabatic magnetic guiding of b´s along field lines in stray B-field of s.c. solenoids: Bmax = 6 T Bmin = 3×10-4 T Energy analysis by static retarding E-field with varying strength: High pass filter with integral b transmission for E>qU

KATRIN Experiment 70 m 10-11 mbar - 1 - 18.4 kV Pre-spectrometer Rear Rejection of low-energy electrons and adiabatic guiding of electrons Rear 3He Rear System: Monitor source parameters 1010 e- /s e- 3•10-3 mbar - 1 ± 1 kV Source 3H β-decay 3He Source: Provide the required tritium column density Transp/Pump 3He 1010 e- /s e- Transp. & Pump system: Transport the electrons, adiabatically and reduce the tritium density significantly 0 kV 1 e- /s e- 10-11 mbar -1 - 18.574 kV Main spectrometer Main-spectrometer: Rejection of electrons below endpoint and adiabatic guiding of electrons Detector Detector: Count electrons and measure their energy

Pre-spectrometer 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

Tandem design: -- Pre-filter, Energy analysis Pre-spectrometer Filters low energy -decay electrons E<18.4 keV Moderate energy resolution E80 eV Test bed for vacuum, electrode design, detector. detector Pre- spectrometer Main spectrometer 1010 e-/sec 103 e-/sec 10i e-/sec Detector 145 pixel Si PIN diode ~1keV resolution Image source  systematics  backgrounds Main spectrometer 23 m long, 10 m diameter High 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

Main Spectrometer Manufacture 2 conical end pieces Danube assembly hall DWE 1 cylindrical centre piece

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 detector magnet B = 3-6 T “flux tube” e- The last, but not least, part of our apparatus is the detector section, which is UW's contribution to the project. The detector itself is a 9 cm diameter silicon p-i-n diode, with 145 individual pixels. It sits at the end of the section, and is shown enlarged in the inset. Note that there is also a post acceleration electrode. This allows us the possibility to apply an additional accelerating field to enhance our signal to background to ratio. pinch magnet B = 6 T shielding & veto post-acceleration electrode

Pixelized Detector Corrects Focal Plane Resolution

KATRIN Statistical Sensitivity Improved over original design (7 m diameter main spectrometer, source luminosity) Reduction in background Only shows statistical uncertainty

Optimized run time at each energy

Tritium Beta Decay History

A window to work in Molecular Excitations

Precision Voltage Divider test at PTB, 2006 preliminary preliminary preliminary

Improved sensitivity with larger system Discovery 90% CL UL

Mass Range Accessible KATRIN Present Average mass > 20 meV Lab Limit 2.3 eV m232 m122

Microcalorimeters for 187Re ß-decay MIBETA: Kurie plot of 6.2 ×106 187Re ß-decay events (E > 700 eV) MANU2 (Genoa) metallic Rhenium m(n) < 26 eV Nucl. Phys. B (Proc.Suppl.) 91 (2001) 293 MIBETA (Milano) AgReO4 m(n) < 15 eV 10 crystals: 8751 hours x mg (AgReO4) Nucl. Instr. Meth. 125 (2004) 125 MARE (Milano, Como, Genoa, Trento, US, D) Phase I : m(n) < 2.5 eV E0 = (2465.3 ± 0.5stat ± 1.6syst) eV mn2 = (-112 ± 207 ± 90) eV2 hep-ex/0509038

KATRIN outlook 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. 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 Gelmini, Varieschi & Weiler, hep-ph/0404272 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). 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

Future tritium measurements? 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 KATRIN is probably the end of the road for tritium beta decay

NEXTEX Sensitivity ~ 0.8 eV Not funded, it’s over 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

Status of KATRIN Hardware Activities Pre-spectrometer magnets Delivered in February 2005 Main spectrometer Final designs by MAN-DWE Delivered December 2006 WGTS Manufacturing Started Delivery 2007 Pre-spectrometer Delivered in Oct. 2003 Vacuum tests started May 2004 El. mag. test start 2006 DPS2-F Manufacturing started Delivery 2007

MC Using Stopping Power (M. Steidl) Arrows show 99% intensity windows

Figure-of-merit 2 mHz “Better” 1 mHz

Final States Red: 3HeT+ Blue: 3HeH+ 1% uncertainty in rovib spectrum  m2 = 6 x 10-3 eV2

Even small mn influences structure 2DF Galaxy Survey PRL 89 061301 Smn 2.4 eV 0.5 eV Large Scale Small Scale

Neutrino mass spectrum and flavor content Minimum Neutrino Masses and Flavor Content Mass (eV) e mu tau Atmospheric n3 0.058 Solar 0.050 n2 0.049 n1 m232 Solar n2 0.009 Atmospheric m122 n1 0 0 n3 ? ?