Direct Determination of Neutrino Mass Beta Decay Tritium

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

Masses linked by oscillations Average mass > 20 me. V m 122 m 232 ? Present Lab Limit 2. 3 e. V

Claim of Evidence for 0 in 76 Ge <m> ~ 0. 2 to 0. 3 e. V Single-site events in detectors 2, 3, 4, 5 (56. 6 kg-y). Looks good to me… H. V. Klapdor-Kleingrothaus, Int. J. Mod. Phys. E 17, 505 (2008)

Beta decay and neutrino mass 3 H Requirements: • Strong source • Excellent energy resolution • Small endpoint energy E 0 • Long term stability • Low background rate Task: Investigate 3 H or 187 Re endpoint with sub-e. V precision KATRIN Aim: Improve m sensitivity tenfold (2 e. V 0. 2 e. V )

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 m by one order of magnitude (2 e. V 0. 2 e. V ) requires : improve m 2 by two orders of magnitude (4 e. V 2 0. 04 e. V 2 ) problem : count rate close to ß-end point drops very fast (~d. E 3) • improve statistics : - stronger tritium source (factor 80) (& large analysing plane, Ø=10 m) - longer measuring period (~100 days ~1000 days) • improve energy resolution : - large electrostatic spectrometer with E=0. 93 e. V (factor 4 improvement) - reduce systematic errors : - better control of systematics, energy losses (reduce to less than 1/10)

KATRIN at Forschungszentrum Karlsruhe unique facility for closed T 2 cycle: Tritium Laboratory Karlsruhe TLK ~ 75 m long with 40 s. c. solenoids 5 countries 13 institutions 100 scientists

Windowless Gaseous T 2 Source

Principle of MAC-E Filter Adiabatic magnetic guiding of ´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 transmission for E>q. U

KATRIN Experiment 70 m Rear Transp/Pump Source Pre-spectrometer Main spectrometer Detector 3 H β-decay e- e- 1010 e- /s 3 He Rear System: Monitor source parameters Source: Provide the required tritium column density e- 103 e- /s 1 e- /s 3 He 3 • 10 -3 mbar - 1 ± 1 k. V e- 0 k. V 10 -11 mbar - 18. 4 k. V Transp. & Pump system: Transport the electrons, adiabatically and reduce the tritium density significantly Pre-spectrometer: Rejection of low-energy electrons and adiabatic guiding of electrons 10 -11 mbar -1 - 18. 574 k. V Main-spectrometer: Rejection of electrons below endpoint and adiabatic guiding of electrons 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 cm 2 • Measurements in progress

Tandem design: -- Pre-filter, Energy analysis Pre 10 1 0 e -/ se -s pe ctr c 10 3 om ete r Pre-spectrometer Filters low energy -decay electrons E<18. 4 ke. V Moderate energy resolution E 80 e. V Test bed for vacuum, electrode design, detector. Ma in s e -/ se c Main spectrometer 23 m long, 10 m diameter High luminosity: d. N/dt~Aspect. high energy resolution: E/ E~Aspect pe ct rom ete r Detector 145 pixel Si PIN diode ~1 ke. V resolution Image source systematics backgrounds de tec tor 3 x 10 -11 Vacuum mbar (reduce backgrounds) use non-evaporable getter pumps Inner wire electrode (shape field, reduce backgrounds) External air coil - compensate for Earths magnetic field 10 i e -/ se c

Main Spectrometer Manufacture 2 conical end pieces e b anu D 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- pinch magnet B=6 T post-acceleration electrode shielding & veto

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 ry a in m li e r p ry lim e r p ina li e r p m ina ry

Improved sensitivity with larger system Discovery 90% CL UL

Mass Range Accessible KATRIN Average mass > 20 me. V m 122 m 232 Present Lab Limit 2. 3 e. V

Microcalorimeters for 187 Re ß-decay MIBETA: Kurie plot of 6. 2 × 106 187 Re ß-decay events (E > 700 e. V) MANU 2 (Genoa) metallic Rhenium m( ) < 26 e. V Nucl. Phys. B (Proc. Suppl. ) 91 (2001) 293 10 crystals: 8751 hours x mg (Ag. Re. O 4) MIBETA (Milano) Ag. Re. O 4 m( ) < 15 e. V Nucl. Instr. Meth. 125 (2004) 125 E 0 = (2465. 3 ± 0. 5 stat ± 1. 6 syst) e. V m 2 = (-112 ± 207 ± 90) e. V 2 MARE (Milano, Como, Genoa, Trento, US, D) Phase I : m( ) < 2. 5 e. V 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 e. V (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 (e. V) and energy E (Me. V) 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 e. V result with 30 -Me. V neutrinos, need D = 175 Mpc. Scaling Kamiokande for the same rate as SN 1987 a, detector mass must be 12 Gt. Ice. Cube 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 e. V, then m > 20 e. V, 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 cm 2 ), 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 e. V • for a 3 m dia. solenoid retarding field spectrometer m ~ 0. 3 e. V KATRIN is probably the end of the road for tritium beta decay

NEXTEX U of Texas (1 M$) Pure electrostatics Possibility for electron diffr. no magnetic fields <0. 1 m. G Sensitivity ~ 0. 8 e. V Required funding 6. 5 M$ Not funded, it’s over

Sensitivity with run time

Systematic Uncertainties

Status of KATRIN Hardware Activities Pre-spectrometer magnets Delivered in February 2005 WGTS Manufacturing Started Delivery 2007 DPS 2 -F Manufacturing started Delivery 2007 Main spectrometer Final designs by MAN-DWE Delivered December 2006 Pre-spectrometer Delivered in Oct. 2003 Vacuum tests started May 2004 El. mag. test start 2006

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

Figure-of-merit 2 m. Hz “Better” 1 m. Hz

Final States Red: 3 He. T+ Blue: 3 He. H+ 1% uncertainty in rovib spectrum m 2 = 6 x 10 -3 e. V 2

Even small m influences structure Sm 2 DF Galaxy Survey PRL 89 061301 2. 4 e. V 0. 5 e. V 0 Large Scale Small Scale

Minimum Neutrino and Flavor Content Neutrino mass. Masses spectrum and flavor content Mass (e. V) e mu tau Atmospheric 3 0. 058 0. 050 0. 049 m 232 2 1 Solar m 122 ? 0. 009 0 2 1 Atmospheric 0 3 ?