Neutrino Mass Determination from Tritium-  -decay : From Mainz to KATRIN Björn Flatt SLAC, Motivation Neutrino mass determination Tritium-  -decay Electrostatic spectrometers The Mainz Neutrino Mass Experiment The KATRIN Experiment

2 Neutrino mass oStandard Model:Neutrinos are massless oEvidence for massive neutrinos: oscillation experiments oAtmospheric neutrinos: SuperKamiokande (1998), … oSolar Neutrinos: Homestake, …, SNO Oscillations confirmed by KamLAND (reactor neutrinos)  m 2 solar  m 2 atmos Problem: sensitive to  m ij ²= m i ²- m j ² not to the absolute mass scale quasi degenerate hierarchical

3 Neutrinos in Cosmology & Astrophysics ocontribute to Dark Matter (N = 10 9 N B ) oinfluence structure formation in the universe oneutrinos from supernovae oneutrinos as origin of UHECR oDirect determination of the absolute neutrino mass scale needed! 

4 Neutrino mass determination Time of flight measurements of Supernovae ->but when??? Kinematics of  -decay: model independent: no cancellations m 2 ( e ) =  |U ei 2 | m 2 ( i ) : incoherent sum 0  decay : need:a) = (Majorana) b) helicity flip : m( )  0 (or other new physics) m ee ( ) = |  |U ei 2 | e ia(i) m( i )|

5 Direct neutrino mass determination oInvestigation of the endpoint region of the Tritium-  -spectrum dN/dE = K × F(E,Z) × p × E tot × (E 0 -E e ) × [ (E 0 -E e ) 2 – m 2 ] 1/2 strong source high luminosity high energy resolution long term stability low background rate observable

6 History of -mass from tritium-decay problem of early 90‘s: negative m ² -magnetic spectrometers yield negative results -electrostatic spectrometers has problems in the beginning (early 90‘s) -reason: underestimated energy losses -MAINZ: roughening transition inside the solid source  lower temperatur -TROITSK: energy loss due to scattering in the gaseous source

7 MAC-E-Filter Two superconducting solenoids compose magnetic guiding field Electron source (T 2 ) in left solenoid adiabatic transformation: µ= E ┴ /B = const.  parallel e - beam Energy analysis by electrostat. retarding field Energy resolution:  E = B min /B max  E 0

8 The Mainz -mass experiment source: frozen T 2 on HOP graphite T=1.86K A=2cm 2, d~130ML (~45nm) 20mCi activity spectrometer: l=4m, Ø=0.9m  E=4.8eV

9 Higher spectrometer energy resolution  E: 6.5 eV  4.8 eV More stable background: HF-Pulses on electrode inbetween measurements Lower T 2 film temperature: T = 1.86K (instead former > 3K) (undefined losses) (problems in 1991 and 1994) (  negative m²( ) problem) L. Fleischmann et al., J. Low. Temp. Phys. 119 (2000) 615, L. Fleischmann et al., Eur. Phys. J. B16 (2000) 521 Measurements month measurement time improvement of signal: * 5 reduction of background: * 2   Signal/background 10 times higher

10 Results from Mainz 1998/1999/2001:m²( ) = -0.6 ± 2.2 ± 2.1 eV²  m( )< 2.3 eV (95% C.L.)  sensitivity limit reached C.Kraus, …, B. Flatt, …,et al. accepted by Eur. Phys. J C, hep-ex/ ,

11 Trend towards „negative m 2 ( )“  missing energy loss Former problem of negative m²( )

12 Former problem of negative m²( ) Trend towards „negative m 2 ( )“ not in 1998/1999 data anymore,  missing energy lossroughening transition avoided by T < 2 K  No problem in Mainz data (from Q5/1998)

13 C.Kraus, EPS HEP03, Aachen, July 2003 B. Bornschein et al., J. Low Temp. Phys., 131 (2003) 69 Determination of neighbour excitation from Mainz tritium data NEW Investigation and improvement of systematics

14 The Troitsk Neutrino Mass Experiment Gaseous T 2 source MAC-E-Filter energy resolution :  E = 3.5eV 3 electrode system in 1.5m diameter UHV vessel (p<10 -9 mbar) column density: cm -2 luminosity: L = 0.6cm 2 (L =  * A source )

15   qU Troitsk anomaly: step in countrate a few eV below endpoint = monoenergetic line in  spectrum - rel. amplitude position varies with 0.5y - period (up to 2000) The Troitsk anomaly Describing anomaly phenomenologically by additional line, different run-by-run Troitsk ,2001 data: m²( ) = -2.3 ± 2.5 ± 2.0 eV 2  m( )< 2.05 eV (95% C.L.) (step effect without additional systematic uncertainty) V.M. Lobashev et al., Phys. Lett. B460 (1999) 227 not confirmed by Mainz Simultanous measurements and Signal for anomaly in Troitsk, but not in Mainz  experimental artefact

16 Parallel measurements in 2000 No hint in Mainz data  must be apparative effect (local in Troitsk)

17 Summary osensitivity limit reached oupper limit: 2.3 eV (95% C.L.) osystematic effects understood otroitsk anomaly must be apparative effect opublication coming soon (hep-ex/ )

18 From current to future experiments Mainz:Troitsk: m 2 = -0.6 ± 2.2 ± 2.1 eV 2 m 2 = -2.3 ± 2.5 ± 2.0 eV 2 m < 2.3 eV (95%CL) m < 2.1 eV (95%CL) V. Lobashev, private communication (allowing for a step function near endpoint) aim:improvement of m by one order of magnitude (2eV  0.2eV )  improvement of uncertainty on m 2 by 100 (4eV 2  0.04eV 2 ) statistics: stronger Tritium source (>>10 10  ´s/sec) longer measurement (~100 days  ~1000 days) energy resolution:  E/E=B min /B max  spectrometer with  E=1eV  Ø 10m UHV vessel

19 owindowless, gaseous tritium source o  9cm,  d = 5  molecules/cm 2, B s = 5,6T  90% of saturation (limited by inelastic scattering) oprespectrometer oreduction of countrate in the mainspectrometer omoderate resolution, high pass filter  MAC-E-Filter omain spectrometer oenergy analysis with high resolution  E  0.93 eV, B min  T  MAC-E-Filter odimensions are given by conservation of magnetic flux Aim: sensitivity on m( e ) in sub-eV range model independent! The KArlsruhe TRItium Neutrinoexperiment KATRIN

20 Forschungs Zentrum Karlsruhe ~70 m beamline, 40 s.c. solenoids

21 Windowless gaseous tritium WGTS parameters: total length l = 10m, inner diam. Ø = 90mm, B source = 3.6T, isotopic purity > 95% T 2 T = (27± 0.03)K

22 WGTS parameters p inj = 3.0 × 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

23 Electrostatic spectrometers electrostatic pre-filtering & analysis of tritium ß-decay electrons ~10 10  ´s/sec ~10 3  ´s/sec ~10  ´s/sec (qU=E 0 -25eV)

24 The main spectrometer o stainless steel vessel (Ø=10m & l=22m) on HV potential o minimisation of bg  UHV: p ≤ mbar  „massless“ inner electrode system UHV requirements: outgassing < mbar l/s inner surface ~ 800m 2 volume to pump ~ 1500m 3

25 KATRIN sensitivity 2× 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) design optimisation ´01  ´03 

26 Discovery potential m < 0.2eV (90%CL) m = 0.35eV (5  ) m = 0.3eV (3  ) sensitivity discovery potential expectation: after 3 full beam years  syst ~  stat

27 Background in MAC-E-Filters MAC-E-Filter collects low energetic e - at detector e - are created (with low energy E S ) at potential U S background: E S + qU S  qU A signal: E ≥ qU A impossible to distinguish signal from background electrons! (due to limited energy resolution of detector) E S, U S

28 Origin of background electrons oelectrode surface osecondary electrons ocosmic rays oradioactive inclosures… ofield emission, discharges magnetic and active elektric shielding ospectrometer volume otritium decay in the spectrometer oscattering of ß-electrons on residual gas oscattering of trapped electrons on residual gas good vacuum, avoid traps, remove electrons from traps

29 Magnetic shielding adiabatic movement of electrons: guidance along magnetic field lines magnetic mirror  intrinsic background supression not completely: shown by experiment: missing supression  reason: deviation from axi-symmetry in setup (numeric investigations: F.Glück)  U e-e- B 

30 New: electric shielding   U-  U U e-e- secondaries from the electrode surface (cosmic muons, radioactive inclosures,…) are shielded by a grid on a slightly more negative potential than the electrode First realization 2002 Background reduction by factor 3 X-ray induced background Screen potential 100V X-ray induced background no shielding Detektorsegment 3 18,6 keV

31 Modification of the Mainz setup: Mainz V (almost) complete coverage of solid electrodes by wire elctrodes can be used in dipolar mode electrodes on ground potential 142 wires,  0,2 mm, 2 cm distance l=264,8 cm r 1 =19,7 cm r 2 =41,5 cm

32 Die Mainz V Elektrode 5 cm

33 background measurements with Mainz V ovariation of shielding potential odependence on magnetic feild oB = 1,7 T: 4.1 mHz oB = 5,1 T: 2.8 mHz odetector background: 1.6 mHz  background from spectrometer : 1.2 mHz lowest background rate in a MAC-E-Filter! B.Flatt et al. publication in preperation

34 Electrodes for the prespectrometer built at University of Washington split electrodes, useable in dipolar mode (remove trapped particles)

35 The prespectrometer

36 Summary technical design report available for download : www-ik.fzk.de/katrin/publications/index.html o absolute neutrino mass of prime importance o MAC-E spectrometers (Mainz, Troitsk) o m <2.3eV(95%CL) (sensitivity limit) o KATRIN sensitivity m <0.2eV(90%CL) o discovery potential m =0.35eV at 5  o design optimized; first components; o commissioning in 2008

37 The KArlsruhe TRItium Neutrinoexperiment KATRIN Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft