1. OUTLINE OF TALK Motivation General description of the experiment The KATRIN collaboration Crunch Areas of the Experiment and the UK role Tritium beta-decay experiments: a (p)review ORKATRIN A next generation experiment with sub-eV sensitivity for the electron neutrino mass M. Charlton 1, A.J. Davies 1, H.H. Telle 1, D.L. Wark 2, J. Tennyson 3, P.J. Storey 3 and P.T. Greenland 3 1 Department of Physics, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK 2 Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK 3 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

2. NEUTRINOS HAVE MASS Oscillations prove they are massive mass eigenvalues, m 1, m 2 and m 3 hierarchical or degenerate? m 1 << m 2 << m 3 or m 1 m 2 m 3 NO ABSOLUTE SCALE FROM m

3. AN ABSOLUTE SCALE ……. A finite measured value for m( e ) would be vitally important An improved limit as proposed by KATRIN – implications for cosmology and astrophysics OTHER POSSIBLE METHODS Astronomical Measurements Need model-dependent assumptions to arrive at mass Neutrinoless Double Beta-Decay Neutrino must be a Majorana particle for there to be mass sensitivity

4. THE PROCESS T 2 3 HeT + + e – + e (bar) The distortion of the beta-spectrum due to m( e ) 0 is only appreciable near the endpoint, E o since the count rate rises rapidly in this region, varying as dN/dE (E – E o ) 2

5. THE BETA-DECAY SPECTRUM OF TRITIUM

6. RECENT MAINZ DATA 10 -YEARS OF NEUTRINO MASS FROM TRITIUM EXPERIMENTS

7. THE CHALLENGE Measure the kinetic energy of an 18.6 keV electron with sub-eV resolution! So E/E o 5 x 10 -5 or better …… (NB normal electron spectrometers have resolutions of 10 -3 or worse) THE SOLUTION Magnetic Adiabatic Collimation with Electrostatic Filter - the MAC-E Filter Exploits the properties of charged particle orbits in slowly-varying (in magnitude) magnetic fields

8. CONSERVED QUANTITIES (adiabatic invariants - non.rel.) BA = constant E /B = constant B is magnetic field, A is the area enclosed by the orbit and E is the component of the kinetic energy perpendicular to B. ……. E/E o = B A /B max …so B A is the magnetic field in the analysing plane (5 x 10 -4 T and B max is the maximum field (10 T) E/E o = 5 x 10 -5 ……..as required

9. SCHEMATIC OF THE KATRIN EXPERIMENT

10. ESTIMATES OF THE SENSITIVITY OF KATRIN - New mode of operation under discussion; possible limit around 0.1 eV

11. KATRIN THE KATRIN COLLABORATION More than 50 scientists ( ) from Mainz, Karlsruhe, Fulda, Moscow/Dubna, Prague, Washington and the UK Development complete …. 2006 Testing starts ……………. 2007 Overall cost (excluding manpower) around 25M

12. CRUNCH AREAS OF THE EXPERIMENT (I) SOURCE Workhorse source will be the Windowless Gas Tritium Source Change conditions …e.g. pressure, local magnetic fields Modelling – most parameters can be measured or calculated with high precision and used to model many aspects of β-particle interactions Trapped ions/electrons; local potentials In-situ measurements with electrons (gun or 83 Kr) ….. ….. energy loss and scattering of β-particles UK INPUT Molecular physics – (Tennyson, UCL) Monitoring – (Telle, Swansea) Modelling – (various, UCL)

13. WINDOWLESS GAS TRITIUM SOURCE

14. ___________ Analysis of T 2 (KATRIN requirements) __________ ___________ Analysis of T 2 (KATRIN requirements) __________ For the KATRIN neutrino experiments T 2 gas of isotopic purity 0.99 is required (impurities constitute other H-isotopomers, contents of 3 He, 4 He have to be negligible) Monitoring and regulation of T 2 purity to about ±0.005-0.010 Measurement of feed gas impurity concentrations at the inlet to the T 2 source (at pressure of ~100-1,000mbar) For a mixture of say 99% T 2 and 1% H 2 on finds, at chemo-thermal equilibrium, fractional amounts of [T 2 ] ~ 0.9899, [HT] ~ 1.003 10 -2 and [H 2 ] ~ 7 10 -5 detection sensitivities of the order <10 -5 ( 10 -2 mbar) needed Analytical method of choice: RAMAN SPECTROSCOPY

15. _______ Raman analysis of T 2 (KATRIN requirements) _______ _______ Raman analysis of T 2 (KATRIN requirements) _______ Spectral pattern isotopomer species identification Spectral intensities quantitative information Detection limits realised by Karlsruhe group using ASER Raman set-up: ~1 10 -5 H 2 in D 2 (no T 2 measurements yet) at the borderline of requirement for purity control Estimated detection limit using proposed new set-up with pulsed laser: < 2 10 -6 H 2 in T 2 λ Laser Raman v=0 V=1 J J Raman excitation with J = 0, 2

16. ____________ Raman spectroscopy of H 2 / HT / T 2 _____________ ____________ Raman spectroscopy of H 2 / HT / T 2 _____________ CALCULATED RAMAN SPECTRA (for Laser =532nm, T=300K) [ nm ] Fraction 1 ~10 -2 <10 -4 Q O S Typical dynamic range of ICCD detectors ~64,000 the weakest H 2 lines would not be detected, or the strongest T 2 lines would be saturated Line widths of cw and pulsed Nd:YAG lasers (532nm) less than typical spectral resolution of an ICCD-coupled spectro- graph all rotational lines except in the Q-branch resolved

17. _____ Raman analysis of T 2 (initial attempt at Karlsruhe) _____ _____ Raman analysis of T 2 (initial attempt at Karlsruhe) _____ ASER = actively stabilised external resonator (used to enhance I Laser by ~ 250) Problems with this initial, complex set-up: (a) optical isolator needed to avoid laser damage by back reflections (b) modulator required for locking control of ASER (c) ASER difficult to keep in resonance in the long-term (d) large Rayleigh scattering background contribution to Raman signals

18. Need reliable model of 3 HeT + final state over wide (for molecules) energy range. Many issues covered by Froelich, Saenz & co-workers, but: Excitation to electronic continuum in both resonant and non-resonant processes must be considered. Nuclear motion continuum should be treated at better than the reflection approximation (particularly for resonances). Cross-section requirements for collisions arising in the source. Will be done theoretically. Question: Question: Is it possible to design experimental tests of theory? KATRIN - Molecular Physics issues

19. CRUNCH AREAS OF THE EXPERIMENT (II) SPECTROMETER(S) MAC-E filter type; very high energy resolution (~ 5 x 10 -5 ) Sources of background need to be understood – modelling of internal discharges Voltage standard needed (and stability) Calibration – stand-alone MAC-E filter for 83 Kr; electron gun for ( source spect ) UK INPUT Modelling – (Davies, Swansea)

20. SCHEMATIC VIEW OF THE KATRIN SPECTROMETERS

21. SWANSEA CONTRIBUTION TO THE MODELLING Design of spectrometer must eliminate electrical breakdown due to desorption of gas from surfaces and field emission. Great care to be taken in design and preparation of interior surfaces. Modelling at Swansea will involve evaluation of precise 3D electric and magnetic field distributions in critical regions, especially near interior surfaces. Simulation of low-pressure breakdown processes resulting from gaseous emission from interior surfaces will enable critical breakdown paths to be determined. Monte-Carlo techniques will also be used to investigate the interaction of beam electrons with the background gas. Simulation and modelling work at early stage of design will help minimise potential breakdown and background problems.

22. CONCLUDING REMARKS KATRIN will be sensitive to m( e ) to below 1 eV and maybe as low as 0.1 eV Hope for a factor of 10 improvement over current best direct limit of 2.2 eV It will be difficult and systematics will have to be chased hard KATRIN is most likely the end-of-the-road for this type of spectrometer-based experiment