KATRIN a model independent experiment to determine the neutrino mass with 0.2 ev sensitivity

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1 Talk at the Institute of Particle and Nuclear Physics Faculty of Mathematics and Physics, Charles University, Prague, March 5, 2008 Otokar Dragoun, Nuclear Physics Institute AS CR Řež near Prague KATRIN a model independent experiment to determine the neutrino mass with 0.2 ev sensitivity

2 Outline of the lecture Neutrino mass and methods of its measurement 60 years of searching for massive neutrinos in β-spectra The Karlsruhe Tritium Neutrino Experiment Main components Calibration and monitoring of the energy scale including Czech contribution Measurement strategy and spectrum analysis m ν from β-spectrum of 187 Re Expectations about m ν in the next decade

3 What do we know about the neutrino mass? m ν is important for particle physics, astroparticle physics and cosmology m ν was not yet measured, only upper limits No reliable theoretical prediction, SM assumed m ν = 0 Neutrino oscillations (predicted by B. Pontecorvo 1957) Proved by measurements of atmospheric, solar, reactor and accelerator neutrinos m ν 0 the first experimental fact beyond the SM Observable neutrino states are superposition of mass eigenstates ν j > = Σ U ji ν i > m 3 or m 2 is 0 and > 0.05 ev either m 1 << m 2 << m 3 (e.g. m 1 0, m ev, m ev) or m 1 m 2 m 3 (e.g. m , m ev, m ev)

4 How do we try to measure m ν? Model independent methods, E 2 = p 2 c 2 + m 2 c 4 β-decay (m ν < 2.3 ev) (NPI ASCR Rez) π decay (m ν < 190 kev) τ decay (m ν < 18.2 MeV) Model dependent methods: T 1/2 (0νββ) depends on the nuclear models (IEAP Czech Tech Uni) time of flight depends on the supernova model anisotropy of the cosmic microwave background and the large scale structure of galaxies depends on the cosmological models Neutrino oscillations: not m ν but m i2 m j2 and ν mixing matrix (IPNP Charles Uni) No competition: to determine m i and U jk complementary methods are needed

5 60 years searching for massive neutrinos in β-ray spectra Enrico Fermi (1934): dn/de = K F(E,Z) p E tot (E 0 -E e ) [ (E 0 -E e ) 2 m ν2 ] 1/2 m ν2 = Σ U ei 2 m i 2 E 0 = 18.6 kev T 1/2 = 12,3 y In principle: ~E 0-3 m ν c 2 ΔM( 3 H 3 He) c 2 E β,max Mass spectroscopy β-ray spectroscopy Simultaneously: - high resolution - high luminosity - low background

6 Neutrino mass from the β-spectrum shape m ν < 5 kev 1948 Cook et al. (1948) 35 S E 0 =167 kev magnetic spectrometer, ΔE instr = 1,5 kev, Ω/4π = 0,1% m ν < 1 kev 1949 m ν 60 ev 1970 m ν 30 ev!? 1980 m ν 0 ev + 3% of m ν =17 kev?? 1985 m 2 ν 0?? 1990 m ν 2.3 ev (m ν2 = -0.7 ± 2.2 ± 2.1 ev 2 ) 2005 For details see PMFA 52(2007)

7 A new β-spectroscopic experiment Founded 2001 Now 120 researchers from 5 countries Running Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Nuclear Physics Institute AS CR Rez near Prague

8 Aim: m ν < 0.2 ev/c 2 at 90 % C.L. if no effect is observed m ν = 0.35 ev should be seen as 5σ effect In comparison with recent experiments at Mainz and Troitsk 10x better sensitivity on m ν (2eV 0.2 ev) 100 x better sensitivity on m ν2 (3eV eV 2 ) Improve both resolution and luminosity! Tool: extremely large β-ray spectrometer with a strong tritium windowless gaseous source Place: The Forschungszentrum Karlsruhe (FZK) Tritium Laboratory up to Bq (400 kci) Experience in superconducting magnets, vacuum technology, electronics and data processing, large scale experiments, astroparticle physics

9 FZK + Tech. Univ. Karlsruhe = KIT Karlsruhe Institute of Technology The research centre FZK at Karlsruhe, Germany including the Tritium Laboratory TLK and other research institutes

10 Tritium Laboratory Karlsruhe The only laboratory capable to supply KATRIN with necessary amount of chemically and isotopically pure tritium Two tritium systems: primary - UHV tight secondary glove boxes Adaptation of the tritium laboratory for its connection with KATRIN spectrometers

11 Scheme of the KATRIN experiment Tritium Laboratory Karlsruhe New buildings of the KATRIN experiment Windowless gaseous tritium source Electron pre-spectrometer Electron detector Differential and cryopumping of tritium Main electron spectrometer

12 Flux of β-particles in the KATRIN set-up In gaseous source of tritium molecules: E β = kev β /s Electron detector: PIN-Diode, 145 pixels ΔE=600 ev at 18.6 kev Bckg 0.01 /s ΔE=0.93eV at 18.6.keV After pre-spectrometer: E β = kev 10 3 β /s After energy analysis in the main spectrometer: 1 β /s

13 Windowless Gaseous Tritium Source (WGTS) WGTS tube: stainless steel,10 m length, 90 mm diameter Magnetic field: 3.6 Tesla (± 2%) Source tube temperature: 27 K (± 0.1% stable) 16 m T 2 injection rate: 1.8 cm 3 /s (± 0.1%) at pressure of mbar T 2 injection Isotopic purity >95% T 2 pumping Total pumping speed: l/s Probably the most complex cryostat ever built

14 Tritium part of the KATRIN experiment T=27 K R=10 7 T= 3 K R=10 7 T=77 K differential pumping gaseous tritium source differential pumping Requirements Activity: Bq ± 0,1 % tritium isotopic purity: > 95 % tritium flow: molecules/s ±0.1% column density r d: molecules/cm 2 ± 0.1% temperature stability: ± 0,1 % T=77 K magnetic field intensity: 3.6 T ± 2% in WGTS, 5.6 T in dif. and cryo pumping speed: l/s reduction of T 2 flow: cryogenic pumping 99% of tritium will circulate within internal loop of the gaseous source 1 % of tritium will be purified both chemically (from 3 He, N 2, CO, H 2 O, CH 4, ) and isotopically (from H 2, DT, HT, HD,..)

15 Retarding electrostatic filter with magnetic adiabatic collimation (MAC-E) Guiding magnetic field Developed independently at Mainz and Troitsk ΔE/E = B min /B max ΔΩ/4π = (1-cosθ max )/2 θ max = arcsin(b s /B max ) 1/2 KATRIN: B min = T, B max =6 T ΔE= 0,93 ev, E=18,6 kev θ max = 51º, ΔΩ/4π = 0,19 High-pass electrostatic filter: E e > e U ret

16 Electron spectrometers of MAC-E-Filter type Advantages: High luminosity and high resolution simultaneously No scattering on slits defining electron beam No high energy tail of the response function Disadvantages: Danger of magnetic traps for charged particles (bunches of background pulses) Integral spectra: low energy features superimposed on background from high energy part not important for endpoint region of β-spectrum 83 Rb/ 83m Kr Monoenergetic line at 17.8 kev

17 Tandem of electrostatic spectrometers pre-spectrometer fixed retarding potential 18.45kV Ø = 1.7m; length = 3.5m DE 60 ev main spectrometer variable retarding potential kv Ø = 10m; length = 23m DE = 0.93 ev at keV electrostatic pre-filtering & analysis of tritium ß-decay electrons ~10 10 b s/sec ~10 3 b s/sec ~10 b s/sec (qu=e 0-25eV)

18 Vacuum chamber of the main KATRIN spectrometer Diameter 10m Weight 200 t Volume 1240 m 3 Inner surface 690 m 2 Vacuum mbar Outgassing rate mbar l s -1 cm -2 baking up to 350ºC, 360 kw power Vessel on HV up to 35 kv 6 turbomolecular pumps: l s -1 3 km getter strips: l s-1 for H 2

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20 Vacuum test of the spectrometer chamber at a factory: Helium test O.K. p < mbar without baking

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22 9000 km on sea around Europe The last 7 km to the FZ Karlsruhe diameter 10 m length 23 m weight 200 t

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25 Bake out of the main spectrometer temperature Heating/cooling by thermo-oil 20 to +350ºC 360 kw power is needed homogeneous temperature distribution measured with 250 sensors 337 C expansion 10 cm Pressure of mbar and outgassing of mbar l cm -2 s -1 achieved with turbomolecular pumps Final pressure <10-11 mbar expected with 3km of getter strips

26 1 st HV test of the main spectrometer chamber -18,6 kv for 3 hours -36,0 kv for 15 minutes -45,0 kv for 1 minute without any discharge

27 KATRIN electron pre-spectrometer Aim: only uppermost part of β-spectrum into the main spectrometer b/s 10 3 b/s Vacuum chamber: 1.7 m in diameter, 3.4m in length Superconducting magnets 90 m of getter strips (Zr+V+Fe alloy) 0.5 m diameter, 1 m length mbar achieved Wire electrodes at negative potential to reduce background of secondary electrons knock out from the wall of vacuum chamber by cosmic muons and external gamma-rays.

28 Wire electrodes of the main KATRIN spectrometer s=25mm U 0-200V U 0-100V U 0 =-18.4kV r 1 r 2 e - d 2 =70mm d 1 =150mm Spectrometer wall Reduce background due to secondary electrons from the wall Secure precise form of the retarding electrostatic field no magnetic traps for e - and ions One of 240 modules with a transport frame Mounting positions on the rail system inside the spectrometer

29 Position sensitive detector of β-particles in the focal plane of the main spectrometer Correction for the radial change of retarding potential along the analysing plane of the main spectrometer 145 independent detectors resolution <600 ev at 18.6 kev time resolution <0.5 μs efficiency >90 % threshold 5 kev non magnetic (6 Tesla) low radioactivity (bckg< s -1 ) low degassing rate

30 How to avoid unrecognized shifts of the energy scale? MC simulations: unrecognized shift of U ret by 50 mv at 18.6 kv systematic error of m(ν e ) by 0.04 ev!! Diploma work by Jarek Kašpar, NIM 2004 Two ways of monitoring of the energy scale stability: a) Precise measurement of the retarding HV but no precision HV dividers for tens of kv on ppm level are commercially available b) Monitor spectrometer on the same HV + physical standard of monoenergetic electrons but no precision electron standards for tens of kev Reason: E kin = E exc - E bin E bin is sensitive to phys. & chem. environment

31 Precision HV power supply Voltage up to 35 kv TC: 2 ppm/k Stability: 2 ppm/8h Noise pp:20-50 mv Digital voltmeter Fluke 8508A precision at the 20V range: 2.7 ppm / year KATRIN precision HV divider 1. Precision primary divider 2. Secondary field shaping divider 3. Tertiary capacitive divider Voltage up to 35 kv Temperature coeff ppm/k Voltage dependence 0.03 ppm/kv Reproducibility 0.05 ppm/day Pre-aged resistors for next divider Uni Muenster + PTB Braunschweig

32 Monitor spectrometer on the same HV m(ν e ) 2.3 ev with 4.8 ev resolution Mainz MAC-E-Filter adjusted for 1 ev resolution

33 How to prepare electron sources with stable energy? Radioactive sources for the monitoring spectrometer: a narrow monoenergetic electron line E kin close to the endpoint energy E 0 = 18.6 kev extreme stability of the line energy ΔE kin 50 mev a) Condensed 83m Kr E kin is 750 ev below E o, Γ = 2.8.eV, T 1/2 = 1.8 h Uni Muenster b) Vacuum evaporated 83 Rb/ 83m Kr E kin is 750 ev below E 0, Γ = 2.8.eV, T 1/2 = 86 d NPI Řež c) Compact 241 Am/Co photoelectron source E kin is 60 ev above E 0, Γ = 1.3 ev, T 1/2 = 432 y NPI Řež

34 Czech electron spectroscopy of radioactive nuclei started in 1952 The first β-ray spectrometer constructed by Z. Plajner, the founder of the nuclear spectroscopy in our country Double focusing magnetic β-ray spectrometer (with upper iron pole piece removed) Monoenergetic conversion electrons emitted from atomic shells during nuclear deexcitation Computer control and a light pen introduced in 1972

35 Precision conversion electron and β-ray spectroscopy at NPI Řež The ESA12 high-resolution, low-transmission electrostatic electron spectrometer Zero-energy-loss peaks 1.9 kev conversion electrons from 99m Tc E ce = E γ E bin (ΔE) instr <1 ev Γ nat < 0.3 ev Our laboratory made HV dividers up to 11 kv temperature drift < 1 ppm/ ºC drift of dividing ratio < 3 ppm/month IEEE Transactions 2005 Vacuum < mbar Reliable operation for thousands of hours

36 Chemical and environmental shifts of E bin We measured: ΔE(TcO 2 TcO 4 ) = 3.00 ±0.46 ev ΔE(Tc metal TcO 4 ) = 5.61 ±0.15 ev ΔE(Tc metal Tc cluster ) = 0.44 ±0.07 ev Tc metal : ρ > 10-5 g cm -2 (> atoms cm -2 ) Tc cluster : ρ < 10-7 g cm -2 (< atoms cm -2 ) no radioactive standards of monoenergetic electrons Must be developed for KATRIN with <50 mev precision

37 Vacuum evaporated 83 Rb/ 83m Kr source 83 Rb produced by the nat Kr(p,xn) reaction at the Řež cyclotron Pressurized krypton gas target 83 Rb up to 12 MBq was evaporated on Al and C backings Vacuum coating system : 8 irradiations and chem. separations 18 vacuum evaporations of 83 Rb thousands of hours on our e - spectrometer

38 The 17.8 kev conversion electron line from the 83 Rb/ 83m Kr source measured with the MAC-E-Filter at the Mainz Uni E ce = E γ E bin Spectrometer resolution: 1.5 ev Accepted solid angle: 25 % of 4π Statistical uncertainty of the fitted line position: ±30 mev Is E bin stable enough during two months? Testing at NPI Řež MC simulation: 100 kbq 83 Rb/ 83m Kr source with no 83m Kr escape into the monitor spectrometer operating at 2 ev resolution: The 2 ppm shift of the energy scale (40 mev at 17.8 kev) will be recognized in 10 minutes exposure A part of 83m Kr escapes from the source at room temperature R&D at NPI Řež Our statistical method to test stability of the measurement conditions NIM 1997

39 241 Am/Co photoelectron source for checking stability of the KATRIN energy scale PhD thesis by J. Kašpar, kev γ-rays from 241 Am eject photoelectrons from a tin Co foil E kin = ±0.2 ev υ spectr 241 Am source of 1.1 GBq activity with Be window Co foil sputtered by Ar ions!! Only 60 ev above tritium E β max!! but effect/background = 1/8 small intensity of 26 kev photons Background from direct γ-rays suppressed 100x by tilting the source X-rays eject disturbing photoelectrons from Co L-shell

40 Do we need absolute energy calibration? E 0 is one of the fitted parameters MC simulations: m(ν e ) is not sensitive to energy bias 10 ev bias of energy scale 1 μev shift of fitted m(ν e ) Comparison of fitted E 0 with ΔM( 3 H 3 He) [±1.2 ev, better soon] important check for systematic errors Absolute calibration of the KATRIN energy scale using gaseous 83m Kr within gaseous tritium source energy measurement of the 32 kev transition in 83m Kr ±1.6 ev ±0.5 ev, Nucl. Instr. Meth determination of energy of K-shell electrons in gaseous krypton ±0.8 ev ±0.04 ev, Czech. J. Phys E ce = E γ E bin E cor KATRIN abs.calibration to ± 0.5 ev

41 β-spectrum of a tritium molecule: final states of daughter (THe) + dn/de = K F(E,Z) p E tot S P i (E 0 -V i -E e ) [ (E 0 -V i -E e ) 2 m n2 ] 1/2 P i Rotational-vibrational excitations above the electronic ground state Width of 0.36 ev limits the resolution attainable in β-decay of molecular tritium V i Electronic excited states; in 57% of β-decays, the ground electronic state is populated (THe) + and (HHe) + from gaseoust 2 and HT Theoretical spectra by Saenz et al., PRL 2000

42 How to learn most about m 2 (ν e )? On basis of extensive Monte Carlo simulations of the systematic and statistical effects: Measurements in the interval (E 0-30 ev, E 0 +5eV) for full 3 years (5 calendar years) when σ stat σ syst Distribution of measurement point optimized to determine 4 fitted parameters: intensity, bckg, E 0, m 2 (ν e ) Strong correlation: δm 2 (ν e ) = 2(E 0 E) δe E 0 from ΔM( 3 H 3 He)? No, mev precision is necessary, also in calibration of the spectrometer energy scale 5 largest σ syst,i identified: uncertainites in molecular final states, elastic and inelastic e - T 2 scattering, instabilities in retarding HV and T 2 column density ρd requesting Δm 2 (ν e ) < ev 2 for each σ syst,i and σ syst,tot = σ stat we get σ tot ev 2 and sensitivity m ν < 0.2 ev at 90% C.L.

43 KATRIN sensitivity & discovery potential Expectation: after 3 full beam years s syst ~ s stat 5s m ν = 0.35eV (5σ) m ν = 0.3eV (3σ) Discovery potential m n < 0.2eV (90%CL) Sensitivity

44 K(E) m ν from β-spectrum of 187 Re measured with cryogenic microcalorimeters 187 Re 187 Os + e + ν ẽ E 0 = 2,5 kev, T 1/2 = 4, r Kurie graph Rhenium crystal is simultaneously the source and calorimetric detector of all 187 Re β-particles Advantage: crystal absorbs all released energy except that of the neutrino Disadvantage: all β musí se měřit celé spektrum, only part in the uppermost 1 ev E (kev) Present limit: m ν < 15 ev at 28 ev resolution Pland of the MARE experiment: 1) 1300 detectors with 20 ev resolution, 2 ev sensitivity to m ν 2) detectors with 5 ev resolution, 0,2 ev sensitivity to m ν in 5 year exp. KATRIN a MARE do not compete but complement ear other there are totally different sources of systematic errors

45 What can we learn about m ν in the next decade? If m ν O(10-1 ) ev, it will be measured If m ν < O(10-1 ) ev, its upper limits will be improved: m β 0.2 ev model independent analysis of β-spectra m ββ 0.03 ev model dependent analysis of 0νββ Σm i 0.07 ev model dependent analysis of cosmological observations (CMB, LSS, SN20xx?) Czech physicists participate in three types of neutrino experiments: shape of tritium β spectrum KATRIN (NPI ASCR, Řež) search for 0νββ NEMO, TGV (IEAP Czech Tech Uni, Prague) reactor neutrino oscillations Daya Bay (IPNP Charles Uni, Prague)

46 Electron spectroscopy group at NPI Řež Fully concentrated on the KATRIN project: We are responsible for the Calibration and Monitoring Task ( ) We are working at Řež, at Uni Mainz and Uni Münster, since 2009 also at KIT (Karlsruhe Institute of Technology) We are members of the Czech Centrum for Astroparticle Nuclear Physics ( ) We are searching for younger experimental physicist Bc, Mgr, PhD students with a perspective to work for months or years at modern KIT, Germany