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or evidence?

Three roads to neutrino masses. or evidence?. complementary. or evidence?. Absolute Neutrino Mass Measurements Beate Bornschein. Lecture I Introduction Electron neutrino mass measurements - methods Status at the begin of the 3rd millennium. sensitivity 0.2 eV/c 2.

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  1. Three roads to neutrino masses or evidence? complementary or evidence?

  2. Absolute Neutrino Mass MeasurementsBeate Bornschein Lecture I • Introduction • Electron neutrino mass measurements - methods • Status at the begin of the 3rd millennium sensitivity 0.2 eV/c2

  3. Absolute Neutrino Mass MeasurementsBeate Bornschein Lecture II • Future of Re experiments – MARE • Fixing the neutrino mass scale with KATRIN • Summary & Perspectives sensitivity 0.2 eV/c2

  4. Absolute neutrino masses ---Particle Data Group

  5. Absolute neutrino masses – PDG (May 2006)

  6. Absolute neutrino masses – the ‚traditional‘ way m(ne) : tritium ß-decay 3H → 3He + e- + ne m(nµ) : pion-decay p+ → µ+ + nµ m(nt) : tau hadr. decay t → 5p + nt kinematic phase space studies m(nm) < 190 keV (PDG2006) m(nt) < 18.2 MeV (PDG2006) m(ne) < 2 eV (PDG2006)

  7. Neutrino oscillations: linking -masses n-mass offset?

  8. Absolute neutrino masses – the ‚traditional‘ way m(ne) : tritium ß-decay 3H → 3He + e- + ne m(nµ) : pion-decay p+ → µ+ + nµ m(nt) : tau hadr. decay t → 5p + nt kinematic phase space studies neutrino oscillations with large mixing angles - all -masses are linked to lightest by oscillations m(nm) < 190 keV (PDG2006) m(nt) < 18.2 MeV (PDG2006) m(ne) < 2 eV (PDG2006)

  9. Absolute neutrino masses – the ‚traditional‘ way m(ne) : tritium ß-decay 3H → 3He + e- + ne m(nµ) : pion-decay p+ → µ+ + nµ m(nt) : tau hadr. decay t → 5p + nt kinematic phase space studies Therefore, concentration on m(e), especially -decay experiments m(nm) < 190 keV (PDG2006) m(nt) < 18.2 MeV (PDG2006) m(ne) < 2 eV (PDG2006)

  10. A short step into the past • myon neutrino mass • tau neutrino mass

  11. Myon neutrino mass Principle: Three different quantities needs to be measured with very high precision Done in three different experiments!

  12. Myon neutrino mass • Measurement of , with CPT theorem: = Pionic atom: negative pion is stopped in matter and captured by an atom. Example: Measurement of the 4f-3d transition in pionic 24Mg with a crystal spectrometer • Measurement of Jeckelmann et al., PhysLettB335 (1994)326 Mohr and Taylor, CODATA, RevModPhys 77 (2005)

  13. Myon neutrino mass • Measurement of at Paul-Scherrer Institute (PSI) Assamagan et al., PhyRevD 53 (1996)6065

  14. Setup at PSI Assamagan et al., PhyRevD 53 (1996)6065

  15. Different neutrino mass states i

  16. Myon neutrino mass PDG2006 PDG2006

  17. Tau neutrino mass Method:  Hadronic system is composed of 3, 5 or 6 pions  In tau rest frame energy of hadronic system is fixed:  m() can computed for given values of mhand Eh*  mhand Eh* are determined from the measured momenta of the particles composing the hadronic system

  18. Tau neutrino mass – ALEPH collaboration Barate et al., Eur. Phys. J. C2 (1998)395

  19. Tau neutrino mass PDG2006 (23 entries …)

  20. Absolute neutrino masses – the ‚traditional‘ way m(ne) : tritium ß-decay 3H → 3He + e- + ne m(nµ) : pion-decay p+ → µ+ + nµ m(nt) : tau hadr. decay t → 5p + nt kinematic phase space studies Therefore, concentration on m(e), especially -decay experiments m(nm) < 190 keV (PDG2006) m(nt) < 18.2 MeV (PDG2006) m(ne) < 2 eV (PDG2006)

  21. Electron neutrino mass - again a look into PDG2006

  22. Neutrino mass from SN1987A Time of flight measurement: SN1987A L  1.5 ∙ 1018 km  1.6 ∙ 105 light years One neutrino with m, E (m2 << E2) Two neutrinos with m, E1, E2

  23. Neutrino mass from SN1987A Time of flight measurement: One neutrino with m, E Two neutrinos with m, E1, E2 Dependent on SN model !

  24. Neutrino mass from SN1987A: results PDG2006 • T.J. Loredo et al., PRD65 (2002) 063002, 39 pp • improved SN model • improved data modeling

  25. Neutrino mass from SN20xx ??? • Actually no competition with -decay experiments: • not sensitive to sub-eV neutrino masses (uncertainty in emission time at SN) • galactic SN only expected every 40 years

  26. β-decay and neutrino mass

  27. ß-decay and neutrino mass kinematic measurement of electron neutrino mass m(ne):

  28. ß-decay and neutrino mass kinematic measurement of electron neutrino mass m(ne): scaling in ß-decay: experimental observable is mn2 n-mass eigenstates mi too close to be resolved experimentally with DE ~ 1 eV for single electrons at ß-decay endpoint • ß-decay & -oscillation experiments allow to fully reconstruct • mass eigenstates mj as -oscillations provide Uei and Δm2ij

  29. ß-decay and neutrino mass kinematic measurement of electron neutrino mass m(ne): 3H E0 = 18.57 keV T1/2 = 12.3 y superallowed ß-source requirements : • high ß-decay rate • low ß-endpoint energy E0 • no strongly forbidden transition • …, see further discussion, dependent on experiment E0 = 2.47 keV T1/2 = 43.2 Gy unique 1st forbidden 187Re calorimeter: source = detector ß-detection requirements : • - high resolution (DE< few eV) • - large solid angle (DW ~ 2p) • - low background spectrometer: source ≠ detector

  30. Electron analyzer Electron counter Source n T2 b excitation energies electron high activity • high efficiency • low background • high energy resolution • integral spectrum: select Ee > Eth spectrometersMAINZ-TROITSK KATRIN microcalorimetersMIBETA, MANU  MARE • high energy resolution • differential spectrum: dN/dE bolometer When in presence of decays to excited states, the calorimeter measures both the electron and the de-excitation energy Based on Andrea Giuliani, MARE collaboration

  31. Tritium β-decay experiment 3H  3He+ + e- + e with E0=18.6 keV Measurement of T2 β-decay spectrum in the region around the endpoint E0

  32. Why tritium? recoil energy and excitation neglected Fermi function nuclear matrix element Tritium: E0 = 18.6 keV, TH = 12.3 a • Superallowed transition:  matrix element M is not energy dependent • Low endpoint energy:  relative decay fraction at the endpoint is comparatively high • Short half life:  specific activity is high  low amount of source material  low fraction of inelastic scattered electrons • Hydrogen isotope:  simple atomic shell  final states precisely calculable

  33. Tritium β-decay experiment: basic requirements • very high energy resolution • very high luminosity L = ASeff/4 - large source area - large accepted solid angle • high -decay rate • very low background Best solution: tritium source combined with MAC-E filter

  34. Principle of an electrostatic filter withmagnetic adiabatic collimation (MAC-E) MAC-E Filter: • adiabatic guiding of  particles along the magnetic field lines • large accepted solid angle   2 • inhomogen B-Field: adiabatic transformation

  35. Principle of an electrostatic filter withmagnetic adiabatic collimation (MAC-E) MAC-E Filter: • adiabatic guiding of  particles along the magnetic field lines • large accepted solid angle   2 • inhomogen B-Field: adiabatic transformation • electrostatic retarding field: high pass filter ! • E = Bmin/Bmax E0

  36. Principle of an electrostatic filter withmagnetic adiabatic collimation (MAC-E) MAC-E Filter: • adiabatic guiding of  particles along the magnetic field lines • large accepted solid angle   2 • inhomogen B-Field: adiabatic transformation • electrostatic retarding field: high pass filter ! • E = Bmin/Bmax E0

  37. Principle of a MAC-E filter II MAC-E Filter - method • Scanning β spectrum and background region by varyingspectrometer voltage U0 • All β electrons with an energy higher than the filter energy –eU0 accepted and counted • Measuring time per data pointis experiment specificTypical values: 20 to 60 s per voltage set -eU0 E0

  38. Principle set-up of a tritium -decay experiment

  39. The Mainz neutrino mass experiment (1997-2001) • Detector • 5 segments • silicon • Molecular T2 source • T2 film at 1.9 K • Quench condensed on graphite (HOPG) • d  480Å (140 ML) A = 2 cm2 • 20 mCi activity • Spectrometer • 23 ring electrodes • 4.8 eV resolution • L = 4 m, Ø = 1 m • Vacuum better 10-10 mbar QCTS = Quench Condensed Tritium Source

  40. The Mainz neutrino mass experiment (1997-2001) KATRIN 2006 Mainz neutrinogroup 2001: J. Bonn B. Bornschein* L. Bornschein*B. FlattCh. KrausB. Müller **E.W. OttenJ.P. SchallTh. Thümmler**Ch. Weinheimer** *  FZ K + U Karlsruhe**  U Münster

  41. Source systematics • Quench Condensed Tritium Source QCTS, before 1997: • Source temperature 4.2K, 2.8 K • Roughening transition ! • Increased energy loss Investigation of source effect in Mainz: Entering the solid state physics…

  42. Stray light measurements

  43. Results of stray light measurements Fleischmann et al. Eur. Phys. J. B 16 (2000) 521 • Model of surface diffusion Δt ≈ Δt0  exp(Δ W / kT) (Arrhenius-law) Δt = characteristic dewetting time ΔW = activation energy • Dewetting time Δt (T=1.9 K) > 1.2 a (95% C. L.)  long term measurements are possible with quench condensed tritium films if T< 1.9 K Δt

  44. Source systematics & negative mass squares • Quench Condensed Tritium Source QCTS, before 1997: • Source temperature 4.2K, 2.8 K • Roughening transition ! • Increased energy loss

  45. Underestimated energy loss – the most often reason for negative mass squares If we have underestimated or just missed some energy loss mechanism, then the fit finds a too low endpoint which shifts the squared neutrino mass towards negative values (count rate “above” the endpoint)

  46. Results of neutrino mass measurements of last 2 decades • Long series of tritium -decay experiments • “Problem of negative mass squares” disappeared due to better understanding of systematic effects • Troitsk: Gaseous tritium source (WGTS) • Mainz: Quench condensed tritium source (QCTS)

  47. QCTS - investigations of systematic effects  Roughening transition of T2 film  Inelastic scattering Determination of cross section:σtot = (2.98±0.16) 10‑18 cm2 Det. of energy loss function V.N. Aseev et al., Eur. Phys.J. D10 (2000) 39 • Determination of dynamics: ΔE = (45±6) kBK • no roughening transition below 2 K • L. Fleischmann et al., J. Low Temp. Phys. 119 (2000) 615,L. Fleischmann et al., Eur. Phys. J. B16 (2000) 521  Self-charging of T2 film  Long time behavior of T2 film Rest gas condensation & evaporation =>Effect limits measurement time Determination of critical field: Ecrit = (63±4) MV/m=> slight broadening of energy resolution H. Barth et al., Prog. Part. Nucl. Phys. 40 (1998) 353B. Bornschein et al., J. Low Temp. Phys. 131 (2003) 69

  48. Self-charging of QCTS • First hint: shift of the β-endpoint energy (1997) • Idea: Charging of the tritium film (40 mCi ≈ 1.5E9 electrons/s) Measurement with Kr-83m conversion electrons

  49. Time dependencyof charging Assumption: tritium β-decay & existence of critical field

  50. Result of measurement Steady state is characterized by a practically constant, critical electric field strength Ecrit≈62 MV/m ≈20mV/monolayer over the film, at which the residual positive charges attain sufficient mobility to penetrate the film towards the conducting substrate. β-spectroscopy: Limits either resolution (in case of thick films) or count rate (in case of thin films). Reason for using gaseous source in KATRIN experiment! B. Bornschein et al., J. Low Temp. Phys. 131 (2003) 69

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