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OUTLINE OF TALK Motivation  General description of the experiment The KATRIN collaboration

Tritium beta-decay experiments: a (p)review OR KATRIN 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

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OUTLINE OF TALK Motivation  General description of the experiment The KATRIN collaboration

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  1. Tritium beta-decay experiments: a (p)review OR KATRIN A next generation experiment with sub-eV sensitivity for the electron neutrino mass M. Charlton1, A.J. Davies1, H.H. Telle1, D.L. Wark2, J. Tennyson3, P.J. Storey3 and P.T. Greenland3 1Department of Physics, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK 2Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK 3Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK OUTLINE OF TALK Motivation  General description of the experiment The KATRIN collaboration Crunch Areas of the Experiment and the UK role

  2. NEUTRINOS HAVE MASS Oscillationsprove they are massive mass eigenvalues, m1, m2 and m3 hierarchical or degenerate? m1 << m2 << m3 or m1 m2 m3 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 T2 3HeT+ + e– + e(bar) The distortion of the beta-spectrum due to m(e)  0 is only appreciable near the endpoint, Eo since the count rate rises rapidly in this region, varying as dN/dE  (E – Eo)2

  5. THE BETA-DECAY SPECTRUM OF TRITIUM

  6. RECENT MAINZ DATA10-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/Eo  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/Eo = BA/Bmax …so BA is the magnetic field in the analysing plane (5 x 10-4 T and Bmax is the maximum field (10 T)  E/Eo = 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. 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 highprecision and used to model many aspects of β-particle interactions Trapped ions/electrons; local potentials In-situ measurements with electrons (gun or 83Kr) ….. ….. 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 T2 (KATRIN requirements) __________ • For the KATRIN neutrino experiments T2 gas of isotopic purity  0.99 • is required (impurities constitute other H-isotopomers, contents of • 3He, 4He have to benegligible) • Monitoring and regulation of T2 purity to about ±0.005-0.010 • Measurement of feed gas impurity concentrations at the inlet to the T2 source (at pressure of ~100-1,000mbar) • For a mixture of say 99% T2and 1% H2 on finds, at chemo-thermal equilibrium, fractional amounts of [T2] ~ 0.9899, [HT] ~ 1.00310-2 and [H2] ~ 710-5  detection sensitivities of the order <10-5 (10-2 mbar) needed • Analytical method of choice: • RAMAN SPECTROSCOPY

  15. _______ Raman analysis of T2 (KATRIN requirements) _______ λLaser λRaman J’ V’=1 J” v”=0 Spectral pattern  isotopomer species identification Spectral intensities  quantitative information Detection limits realised by Karlsruhe group using ASER Raman set-up: ~110-5 H2in D2 (no T2 measurements yet)  at the borderline of requirement for purity control Estimated detection limit using proposed new set-up with pulsed laser: <210-6 H2in T2 Raman excitation with J = 0, 2

  16. ____________ Raman spectroscopy of H2 / HT / T2 _____________ Typical dynamic range of ICCD detectors ~64,000  the weakest H2lines would not be detected, or the strongest T2 lines wouldbe saturated Line widths of cw and pulsed Nd:YAG lasers (532nm) less than typical spectral resolution of an ICCD-coupled spectro- graph  all rotationallines except in the Q-branch resolved Fraction 1 ~10-2 <10-4 Q S O [ nm ] CALCULATED RAMAN SPECTRA (for Laser=532nm, T=300K)

  17. _____ Raman analysis of T2 (initial attempt at Karlsruhe) _____ • ASER = actively stabilised external resonator • (used to enhance ILaser by ~250) • “Problems” with this initial, complex set-up: • optical isolator needed to avoid laser damage by back reflections • modulator required for locking control of ASER • ASER difficult to keep in resonance in the long-term • large Rayleigh scattering background contribution to Raman signals

  18. KATRIN - MolecularPhysicsissues • Need reliable model of 3HeT+ 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: Is it possible to design experimental tests of theory?

  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 83Kr; 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

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