1. HQL2004 June 1. Jochen Bonn Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz, Evidence for neutrino masses Neutrino mass measurements Tritium β decay The experiments in Mainz and Troitsk The MAC-E-spectrometer Results The next generation experiment KATRIN Parameters of KATRIN Present status Jochen.Bonn@uni-mainz.de "Neutrino Mass: Tritium Beta Decay".

2. Based on the detection of solar and atmospheric neutrinos Evidence for -masses Mz limit KATRIN Limits from T- ß- decay Mainz KATRIN

5. Direct measurement of m( e ) super-allowed E 0 = 18.6 keV t 1/2 = 12.3 a Tritium  decay: 3 H  3 He + + e - + e _ Need very high energy resolution and very high luminosity  MAC-E-Filter

6. Principle of the MAC-E-Filter Magnetic Adiabatic Collimation + Electrostatic Filter (A. Picard et al., Nucl. Instr. Meth. 63 (1992) 345)  Two supercond. solenoids compose magnetic guiding field  Electron source (T 2 ) in left solenoid  e - in forward direction: magnetically guided  adiabatic transformation:  = E  /B = const.  parallel e - beam  Energy analysis by electrostat. retarding field  E = E  B min /B max = E  A s,eff /A analyse  4.8 eV (Mainz)

7. Mainz Neutrino Mass Experiment (1997-2001) Mainz 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 Karlsruhe **  Univ. Bonn T 2 Film at 1.86 K quench-condensed on graphite (HOPG) 45 nm thick (  130ML), area 2cm 2 Thickness determination by ellipsometry

8. Mainz data of 1998 - 2001 9 month measurement time (only possible with remote experiment control) Improvement of signal: * 5 Reduction of background: * 2 Fit range „lower limit of fit“   Signal/background 10 times higher

9. Statistical and systematic uncertainies Mainz 1998-2001 data  m 2 [eV 2 ]

10. (Final) Mainz results Improvement of S/Bg by factor 10 Longterm measurements in 1998,1999,2001 (analysed:  t = 20 weeks) Using neighbour excitation from calculation (Kolos et al., Phys. Rev. A37 (1988) 2297) m 2 ( ) = -1.2 ± 2.2 ± 2.1 eV 2  m( )< 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 amplitude from own tritium  spectrum m 2 ( ) = -0.7 ± 2.2 ± 2.1 eV 2  m( )< 2.3 eV (95% C.L.) C. Kraus, EPS HEP03, Aachen, July 2003

11. 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: 10 17 cm -2 luminosity: L = 0.6cm 2 (L =  /2  * A source )

12.   qU Troitsk anomaly: step in countrate a few eV below endpoint = monoenergetic line in  spectrum rel. amplitude 10 -10 position varies with 0.5y period (up to 2000) The Troitsk anomaly Describing anomaly phenomenologically by additional line, different run-by-run Troitsk 1994-1999,2001 data: m²( ) = -2.3 ± 2.5 ± 2.0 eV 2  m( )< 2.2 eV (95% C.L.) V.M. Lobashev et al., Phys. Lett. B460 (1999) 227

13. Status of the experiments in Mainz and Troitsk both experiments have practically reached their sensitivity limit Mainz –Limit on neutrino mass 2.3 eV –Systematic and statistical uncertainties about equal i.e. sensitivity limit almost reached –On the level of its sensitivity no apparent problems with systematics –Spectrometer modified for tests to prepare KATRIN Background reduced from 15mHz to 1.3mHz –Experiments to prepare KATRIN funded Troitsk –Limit on neutrino mass 2.2 eV but after corrections for step and from a negative mean value –Some problems with systematics –Attempts to clarify step problem

14. The Karlsruhe Tritium Neutrino experiment KATRIN }  10m (hep-ex/0109033) Physics aim: Sensitivity on neutrino mass scale: m( ) << 1eV  Higher energy resolution:  E  1eV since E/  E ~ A spectrometer  larger spectrometer  Relevant region below endpoint is smaller even less count rate dN/dt ~ A spectrometer  larger spectrometer

15. Molecular tritium sources WGTS:  9cm, length: 10m, T = 30 K allows to measure with near to maximum count rate using  d = 5  10 17 /cm 2 with small systematics QCTS:  8cm, T=1.6 K, d = 35 nm presently limited by self-charging Standard source: Alternative Source: T2T2

16. transport magnet s spectrometer solenoi ds 10 10 e - /s 10 3 e - /s Pre and main spectrometer Main spectrometer: Energy resolution:  E = 1eV high luminosity: L = A Seff  /4  = A analyse  E/(2E) = 20 cm 2 Ultrahigh vacuum requirements (Background) p < 10 -11 mbar „simple“ construction: vacuum vessel at HV = electrode An industry study was done Pre spectrometer: Transmission of electron with highest energy only (10 -7 part in last 100 eV)  Reduction of scattering probaility in main spectrometer  Reduction of background only moderate energy resolution required:  E = 50 eV Test of new ideas (XHV, shape of electrodes, avoid and remove of trapped particles,...) air coil  10m, l=22m

17. KATRIN Pre-Spectrometer

18. Sensitivity of KATRIN KATRIN 4 th collaboration meeting in Prag, June 2003: -optimised measurement point distribution -smaller sys. uncertainties  sensitivity on m( e )  0.20 eV/c 2 (about equal contributions from stat. and sys. uncertainties) (90% C.L. upper limit for m( e )=0) m( e ) = 0.30eV observable with 3  m( e ) = 0.35eV observable with 5   m stat ( ) 2 [eV 2 ] LoI Opt. of meas. points tritium purity 10m spectr. + optim. background = 1mHz?

19. Technical challenges Recirculation and purification of tritium to a large extent (kCi)  30 superconducting solenoids UHV (< 10 -11 mbar) in huge volume (1000m 2 ) HV calibration and stability on ppm level High resolution detectors....  ideal place: Forschungszentrum Karlsruhe/Germany Inst. f. Kernphysik (IK) Institut für Technische Physik (ITP) Tritiumlabor Karsruhe (TLK) Inst. f. Prozessdaten- verarbeitung und Elektronik (IPE)

20. August 2003: first successful vacuum tests at company Arrival of pre spectrometer vessel: Oct 1, 2003 Refurbished hall, superconducting magnets will arrive in Oct 2003, too