Direct Measurements of the Neutrino Mass. Klaus Eitel Forschungszentrum Karlsruhe Institute for Nuclear Physics

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1 Direct Measurements of the Neutrino Mass Klaus Eitel Forschungszentrum Karlsruhe Institute for Nuclear Physics

2 Direct Measurements of the Neutrino Mass neutrino masses in particle physics & cosmology (mass scenarios, ν s as HDM) micro-calorimeters (Mibeta: 187 Re in AgReO 4 ) electrostatic spectrometers (Mainz, Troitsk, KATRIN)

3 neutrino masses and schemes normal mass hierarchy m 1 <m 2 <m 3 quasi-degenerate first task: decide ν mass scenario hierarchical

4 neutrino masses and cosmology ρ [% of ρ cr ] second task: decide whether ν contribute as Hot Dark Matter ν s per flavor from BB! (without ν annihilation; astro-ph/ )

5 cosmology & structure formation Neutrino Mass Measurements Strategies 0νββ decay: 76 LNGS (71.7 kg y) 2νββ NEMO3 D.N. Spergel et al: S.W. Allen et al: Σm ν < 0.69 ev (95%CL) Σm ν = 0.56 ev (best fit) m ee = ev astrophysics: SN ToF measurements 187 Re β decay kinematics: microcalorimeters MAC-E spectrometers SuperK, SNO, OMNIS + grav.waves: potential for ~1eV sensitivity? 3 H

6 β decay kinematics phase space determines energy spectrum transition energy E 0 = E e + E ν (+ recoil corrections) dn/de = K F(E,Z) p E tot (E 0 -E e ) [ (E 0 -E e ) 2 m ν2 ] 1/2 rel. rate [a.u.] theoretical β spectrum near endpoint 1 0 m ν = 0eV m ν = 1eV E e -E 0 [ev] experimental observable strong source (high count rate near E 0 ) small endpoint energy E 0 excellent energy resolution long term stability low bg rate

7 β decay kinematics β-decay kinematics direct ν mass determination if ν masses are not resolved average neutrino mass and 0νββ decay 0νββ decay only possible for Majorana ν s coherent sum of mass EV s m 2 (ν e ) = Σ U ei2 m(ν i ) 2 m ee (ν) = Σ U ei 2 e iα(i) m(ν i ) incoherent sum, real average, since 0 U ei2 1 partial cancellation possible (not fully since SNO says: no max. solar mixing) m 2 (ν e ) vs. m ee (ν): complementary information, differences due to Dirac neutrino CP-phases Problems with nuclear matrix elements Other processes (right-handed currents, Susy-particles,...)

8 µ calorimeters for for 187 Re β decay 187 Re E 0 = 2.46 kev neutrino mass measurement with array of 10 AgReO 4 crystals lower pile up higher statistics MIBETA experiment (Milano, Como, Trento) M.Sisti et al, NIM A520(2004)125 A.Nucciotti et al, NIM A520(2004)148 C. Arnaboldi et al, PRL 91, (2003) MANU2 experiment (Genoa) F. Gatti, Nucl. Phys. B (Proc.Suppl.) 91 (2001) 293) T op ~ mK

9 µ calorimeters for for 187 Re β decay 187 Re Kurie plot of Re β decay events above 700 ev fit with function free fit parameters: β endpoint energy m ν 2 Mibeta β spectrum normal. pile-up amplitude background level

10 187 Re β decay endpoint and m ν E 0 = ± 0.5 stat ±1.6 syst ev (8751 h*mg, NIMA520, 2004) = ± 0.8 stat ±1.5 syst ev (4485 h*mg, PRL91,2003) fit range: 0.9 to 4 kev fit function m ν 2 = -112 ± 207 ± 90 ev 2 m ν < 15 ev (90%CL) future: proposal for a new calorimeter expt. with ~2-3 ev sensitivity foreseen 2007 (?) F. Gatti (ν 04): 0.5g Re ev sensitivity expected

11 principle of an electrostatic filter with magnetic adiabatic collimation (MAC-E)

12 principle of an electrostatic filter with magnetic adiabatic collimation (MAC-E) adiabatic magnetic guiding of β s along field lines in stray B-field of s.c. solenoids: B max = 6 T B min = T energy analysis by static retarding E-field with varying strength: high pass filter with integral β transmission for E>qU

13 magnetic spectrometers & MAC-E filters

14 latest results from the MAINZ experiment frozen T 2 on HOP graphite T=1.86K A=2cm 2, d~130ml (~45nm) 20mCi activity spectr.: l=2m, Ø=0.9m E=4.8eV condensed T 2 film neighbour excitations W.Kolos et al., PRA37(1988): a nex =5.9%; ε=14.6ev Mainz : a nex =(5±1.6±2.2)% with ε=16.1ev C. Kraus, Eur.Phys.J. C33, s01 (2004), ν 04 free fit for a nex, m ν2 for last 170eV improvements in systematics: roughening of T 2 film inelastic scattering self charging of T 2 film

15 From current to future experiments Mainz: Troitsk: m ν2 = -1.2(-0.7) ±2.2 ±2.1 ev 2 m ν2 = -2.3 ± 2.5 ± 2.0 ev 2 m ν < 2.2(2.3) ev (95%CL) m ν < 2.05 ev (95%CL) C. Weinheimer, Nucl. Phys. B (Proc. Suppl.) 118 (2003) 279 V. Lobashev, Nucl.Phys. A719 (2003) 153c C. Kraus, Eur.Phys.J. C33 (neighbour excit s self-consistent) (allowing for a step function near endpoint) aim: improvement of m ν by one order of magnitude (2eV 0.2eV ) improvement of uncertainty on m ν2 by 100 (4eV eV 2 ) statistics: stronger Tritium source (>>10 10 β s/sec) longer measurement (~100 days ~1000 days) energy resolution: E/E=B min /B max spectrometer with E=1eV Ø 10m UHV vessel

16 The KArlsruhe TRItium Neutrino Experiment Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft

17 KATRIN location at FZKarlsruhe KATRIN ~70 m beamline, 40 s.c. solenoids

18 Windowless Gaseous Tritium Source at Tritium Laboratory Karlsruhe single WGTS solenoid (l=1m) WGTS parameters: total length l = 10m, inner diam. Ø = 90mm, B source = 3.6T, isotopic purity > 95% T 2 T = (27± 0.03)K (l=10m)

19 WGTS source characteristics p inj = mbar ( at T=27K) q inj = 1.85 mbar l/s = mol./s = 4.7 Ci/s (~ 40g T 2 per day if no closed loop) isotopic purity (±2 ) monitored by Laser Raman spectroscopy

20 electrostatic spectrometers tandem design electrostatic pre-filtering & analysis of tritium ß-decay electrons ~10 10 β s/sec ~10 3 β s/sec ~10 β s/sec (qu=e 0-25eV) pre-spectrometer fixed retarding potential 18.45kV Ø = 1.7m; length = 3.5m E 60 ev main spectrometer variable retarding potential kv Ø = 10m; length = 24m E = 0.93 ev (18.575keV) detailed el.-magn. design!

21 KATRIN Main Spectrometer stainless steel vessel (Ø=10m & l=24m) on HV potential minimisation of bg UHV: p mbar massless inner electrode system Mainz V results UHV requirements: outgassing < mbar l/s inner surface ~ 800m 2 volume to pump ~ 1500m 3 intrinsic det. bg 1.6mHz 2.8mHz inner electrode installed in Mainz spectrometer for background tests

22 PIN diode array Detector concept the prespectrometer detector: prototype of KATRIN main detector T-structure multipixel PIN diode 8x8 Pin-Diode from Canberra SemiConductors segmented PIN-diode 44 x 44 mm² 64 segments 5x5 mm², bonded onto ceramics with FET stage backside of UHV flange, with board for 64 preamps 64 channel FET stage

23 KATRIN sensitivity & discovery potential statistical accuracy on m ν 2 design optimisation LoI 9/2001

24 KATRIN sensitivity & discovery potential statistical accuracy on m ν 2 design optimisation LoI 9/ stronger gaseous source (Ø=75mm Ø=90mm) required Ø=10m spectrometer) isotopic T purity 70% 95%

25 KATRIN sensitivity & discovery potential statistical accuracy on m ν 2 design optimisation LoI 9/ stronger gaseous source (Ø=75mm Ø=90mm) required Ø=10m spectrometer) optimised measuring point distribution (~5 ev below E 0 ) reference

26 KATRIN sensitivity & discovery potential statistical accuracy on m ν 2 design optimisation reference LoI 9/ stronger gaseous source (Ø=75mm Ø=90mm) required Ø=10m spectrometer) optimised measuring point distribution (~5 ev below E 0 ) active background reduction by inner electrode system, low background detector (needs further detailed tests)

27 KATRIN - systematic uncertainties 1. inelastic scatterings of ß s inside WGTS requires dedicated e-gun measurements, unfolding techniques for response fct. 2. HV stability of retarding potential required: ~ppm level precision HV divider (PTB), monitor spectrometer beamline 3. fluctuations of WGTS column density required < 0.1% stability rear detector, Laser-Raman spectroscopy, T=30K stabilisation, e-gun measurements 4. WGTS charging due to remaining ions (MC: φ<20mv) inject low energy mev electrons from rear side, diagnostic tools available 5. final state distribution reliable quantum chem. calculations unaccounted variances σ 2 lead to shift of m 2 : a few contributions with each m 2 ν ev 2

28 KATRIN sensitivity & discovery potential expectation: after 3 full beam years σ syst ~ σ stat 5σ m ν m ν = 0.35eV (5σ) = 0.3eV (3σ) discovery potential m ν < 0.2eV (90%CL) sensitivity

29 status of hardware activities pre-spectrometer pre-spec detector assembly WGTS differential pumping section

30 conclusions & outlook absolute neutrino mass of prime importance microcalorimeter (MIBETA 187 Re): m ν <15eV(90%CL) 2eV in 2007? MAC-E spectrometers (Mainz, Troitsk) m ν <2.3eV(95%CL) (sensitivity limit) KATRIN sensitivity m ν <0.2eV(90%CL) discovery potential m ν =0.35eV at 5σ design optimized; first components; commissioning in 2008