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/c2

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

Absolute neutrino masses --- Particle Data Group

Absolute neutrino masses – PDG (May 2006)

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)

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

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)

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)

A short step into the past myon neutrino mass tau neutrino mass

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

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)

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

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

Different neutrino mass states i

Myon neutrino mass PDG2006 PDG2006

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 mh and Eh*  mh and Eh* are determined from the measured momenta of the particles composing the hadronic system

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

Tau neutrino mass PDG2006 (23 entries …)

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)

Electron neutrino mass - again a look into PDG2006

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

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

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

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

β-decay and neutrino mass

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

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

ß-decay and neutrino mass kinematic measurement of electron neutrino mass m(ne): E0 = 18.57 keV T1/2 = 12.3 y superallowed 3H 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 ß-detection requirements : - high resolution (DE< few eV) - large solid angle (DW ~ 2p) - low background calorimeter: source = detector spectrometer: source ≠ detector

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

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

Why tritium? Tritium: E0 = 18.6 keV, TH = 12.3 a 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

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

Principle of an electrostatic filter with magnetic 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

Principle of an electrostatic filter with magnetic 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

Principle of an electrostatic filter with magnetic 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

Principle of a MAC-E filter II -eU0 MAC-E Filter - method Scanning β spectrum and background region by varying spectrometer voltage U0 All β electrons with an energy higher than the filter energy –eU0 accepted and counted Measuring time per data point is experiment specific Typical values: 20 to 60 s per voltage set E0

Principle set-up of a tritium -decay experiment

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

The Mainz neutrino mass experiment (1997-2001) KATRIN 2006 Mainz neutrino group 2001: J. Bonn B. Bornschein* L. Bornschein* B. Flatt Ch. Kraus B. Müller ** E.W. Otten J.P. Schall Th. Thümmler** Ch. Weinheimer** *  FZ K + U Karlsruhe **  U Münster

Source systematics Investigation of source effect in Mainz: 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…

Stray light measurements

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

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

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)

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)

QCTS - investigations of systematic effects  Roughening transition of T2 film  Inelastic scattering 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 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  Self-charging of T2 film  Long time behavior of T2 film Determination of critical field: Ecrit = (63±4) MV/m => slight broadening of energy resolution H. Barth et al., Prog. Part. Nucl. Phys. 40 (1998) 353 B. Bornschein et al., J. Low Temp. Phys. 131 (2003) 69 Rest gas condensation & evaporation =>Effect limits measurement time

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

Time dependency of charging Assumption: tritium β-decay & existence of critical field

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

Results of Mainz experiment (1998/1999 + 2001)

Results of Mainz experiment Data of 20 weeks run time added for evaluation With neighbour excitation from calculation (Kolos et al., Phys. Rev. A37 (1988) 2297) m2(n) = -1.2 ± 2.2 ± 2.1 eV2 Þ m(n) < 2.2 eV (95% C.L.) Ch. Weinheimer, Nucl. Phys. B (Proc. Suppl.) 118 (2003) 279, C. Kraus et al., Nucl. Phys. B (Proc. Suppl.) 118 (2003) 482 Neighbour excitation fitted from own data m2(n) = -0.6 ± 2.2 ± 2.1 eV2 Þ m(n)< 2.3 eV (95% C.L.) C. Kraus et al., Eur. Phys. J. C40 (2005) 447 PDG2006

Troitsk neutrino mass experiment = Windowless Gaseous Tritium Source & MAC-E Filter Dominant systematic uncertainty: Energy loss due to inelastic scattering of decay electrons

Troitsk setup WGTS 26-28 K L=3 m, Ø= 5 cm T2:HT:H2 = 6:8:2 column density: 1017cm‑2 Spectrometer 3 ring lectrodes 3.5 eV resolution L=6 m, Ø=1.2 m P = 10‑9 mbar Detector Si(Li)

Troitsk setup

Troitsk Anomaly Observation of an excess count rate (‘step’) close to the endpoint (equivalent to a mono energetic line in original β-spectrum) Location: 5 – 15 eV below E0, intensity: ≈ 10‑10 of total T2-decay rate Periodicity = 0.5 years ?

Troitsk Results Strong correlation between step parameters (anomaly) and m2 Requires description of anomaly phenomenologically by adding 2 additional fit parameters (standard: E0, m2, Amp, Bg): step_position, step_amplitude 1994-98 results (6 parameter fit): m2 = -1.9 ± 3.4 ± 2.2 eV2/c4 => m < 2.5 eV/c2 (95% C.L.) V. Lobashev et al., Phys. Lett. B 460 (1999) 227 1994-99/01 results (6 parameter fit): m2 = -2.3 ± 2.5 ± 2.0 eV2/c4 => m < 2.2 eV/c2 (95% C.L.) V. Lobashev, Proceedings 17th International Conference on Nuclear Physics in Astrophysics, Debrecen/Hungary, 2002, Nucl. Phys. A 719 (2003) 153 PDG2006

Coincident measurements in Troitsk and Mainz Mainz results: No significant change of 2 => no indication of an anomaly Troitsk anomaly is very likely an experimental artefact which is not present in Mainz

PDG2006

Electron neutrino mass PDG2006 ^

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

Additional transparencies

Model for charging electrons are leaving the T2 film pos. Ions are remaining in the film need charge compensating current from/to substrate mobility of charges: proportional to exp (-W/kT) T < 2 K  no mobility! Charging additional el. Field movement of charges at Ecrit