Current status and future prospects of direct neutrino mass experiments

Transcription

1 Current status and future prospects of direct neutrino mass experiments Christine Kraus, Johannes Gutenberg-University Mainz Motivation Current tritium-β-decay experiments: Mainz, Troitsk Rhenium experiments Future tritium-β-experiment: KATRIN NOON , Tokyo

2 Absolute values of neutrino masses Fundamental ν-mass scale of key importance for Cosmology (ν hot dark matter) & particle physics (hierarchical/quasi-degenerate models) indirect approaches Cosmology: LSS & CMBR depends on priors 0νββ Majorana: m ee (ν), CP-phases Direct measurements Supernova ToF waiting for SN20xx Kinematics of particle decays Ε 2 = p 2 c 2 + m 2 c 4

3 Fermi theory of β-decay and ν-mass recoil energy and excitation neglected N( E) = const M F( Z, E) p( E + mec )( E0 E) ( E0 E) mν c count rate [a.u.] tritium β- spectrum energy E [ev] N [a.u.] m ν = 1 ev experimental observable m ν2 = Σ U ei2 m i 2 m ν = 0 ev * E - E 0 [ev] Need: high luminosity, high energy resolution and low background

4 Two supercond. solenoids compose magnetic guiding field Electron source (T 2 ) in left solenoid Principle of the MAC-E-Filter Magnetic Adiabatic Collimation + Electrostatic Filter (A. Picard et al., Nucl. Instr. Meth. 63 (1992) 345)

5 Two supercond. solenoids compose magnetic guiding field Electron source (T 2 ) in left solenoid e - in forward direction: magnetically guided adiabatic transformation: µ = E /B = const. parallel e - beam Principle of the MAC-E-Filter Magnetic Adiabatic Collimation + Electrostatic Filter (A. Picard et al., Nucl. Instr. Meth. 63 (1992) 345)

6 Principle of the MAC-E-Filter Two supercond. solenoids compose magnetic guiding field Electron source (T 2 ) in left solenoid e - in forward direction: magnetically guided adiabatic transformation: µ = E /B = const. parallel e - beam Magnetic Adiabatic Collimation + Electrostatic Filter (A. Picard et al., Nucl. Instr. Meth. 63 (1992) 345)

7 Principle of the MAC-E-Filter Two supercond. solenoids compose magnetic guiding field Electron source (T 2 ) in left solenoid e - in forward direction: magnetically guided adiabatic transformation: µ = 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) Magnetic Adiabatic Collimation + Electrostatic Filter (A. Picard et al., Nucl. Instr. Meth. 63 (1992) 345)

8 Principle of the MAC-E-Filter Magnetic Adiabatic Collimation + Electrostatic Filter (A. Picard et al., Nucl. Instr. Meth. 63 (1992) 345) sharp integrating transmission function without tails: Mainz E = E B min /B max = E A s,eff /A analyse 4.8 ev (Mainz)

9 Mainz Neutrino Mass Experiment ( ) T 2 Film at 1.86 K quench-condensed on graphite (HOPG) 45 nm thick ( 130ML), area 2cm 2 Thickness determination by ellipsometry

10 Mainz data of month measurement time (only possible with remote experiment control) 119 days analysed data Fit range 2001 lower limit of fit

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

12 Fit of neighbour excitation β-decay: neighbour molecules can be excited former: only one calculation (W. Kolos et al., Phys. Rev A37 (1988) 297): a nex = 5.6%, E nex = 14.6eV (energy states like gaseous, dense crystal) Mainz: tritium films are porous & differences in energy loss for gaseous and solid T 2 a nex = 4.6%, E nex = 16.1eV but criticized (for example by Troitsk-group) new: Mainz has enough statistic (tritium data) for fitting a nex : a nex = 5.0 ± 1.6 stat ± 2.2 sys % (in good agreement!) Consistent description of system. Uncert. m 2 ν = -0.7 ± 2.2 ± 2.1 ev 2 /c 4 m ν 2.3 ev/c 2 sensitivity limit reached, final result publication in preparation first presented EPS HEP03, Aachen, Juli 2003

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

14 The Troitsk anomaly qu Troitsk anomaly: step in countrate a few ev below endpoint = monoenergetic line in β spectrum - rel. amplitude position varies with 0.5y - period (up to 2000) V.M. Lobashev et al., Phys. Lett. B460 (1999) 227 Decribing anomaly phenomenologically by additional line, different run-by-run Troitsk ,2001 data: m²(ν) = -2.3 ± 2.5 ± 2.0 ev 2 m(ν)< 2.05 ev (95% C.L.) Simultanous measurements and Signal for anomaly in Troitsk, but not in Mainz experimental artefact not confirmed by Mainz

15 Cryo bolometer experiments with 187 Re Multi-purpose, scalable new detector technology Basic idea: β emitting crystal = cryodetector single final state: excitation by excited electronic states and inelastic scattering is collected free choice of β emitter: 187 Re: E 0 = 2.5keV (t 1/2 = y) Current experiments: NU2 (F. MAGatti et al., Genova) - Re metallic crystal (1.5 mg) - BEFS measured (F.Gatti et al., Nature 397 (1999) 137) - current: m(ν) < 26 ev near future: future: sensitivity of 10 ev expected ev resolution by s.c. sensors typical E = 30 ev MiBeta (E. Fiorini et al., Milano,Como) - AgReO 4 ( mg) - current: m(ν) < 22 ev Future: sensitivity 1-10 ev expected Need: higher resolution + larger arrays

16 The Karlsruhe Tritium Neutrino experiment KATRIN Physics aim: Sensitivity on neutrino mass scale: m(ν) << 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 } 10m new, since 12/2002 (hep-ex/ )

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

18 standard source: Molecular tritium sources alternative source: T 2 WGTS: QCTS: 9cm, length: 10m, T = 30 K allows to measure with near to maximum count rate using ρd = /cm 2 ; with small systematics 8cm, T=1.6 K, d = 35 nm presently limited by self-charging

19 Pre and main spectrometer air coil 10m, l=22m transport magnets spectrometer solenoids e - /s 10 3 e - /s Pre spectrometer: Main spectrometer: Transmission of electron with highest Energy resolution: E = 1eV energy only (10-7 part in last 100 ev) High luminosity: reduction of scattering probability L = A Seff Ω/4π = A analyse E/(2E) = 20 cm 2 in main spectrometer Ultrahigh vacuum requirements reduction of background (Background) p < mbar Only moderate energy resolution: Simple construction: vacuum vessel at HV E = 50 ev = electrode Test of new ideas (XHV, shape of electrodes, avoid and remove of trapped particles,...)

20 Place and time schedule ideal place: Forschungszentrum Karlsruhe/Germany 2002 very positive response by International Review Panel first, but significant funding by BMBF, FZKarlsruhe 2003 application for major funding, Pre spectrometer at FZK background investigations at Mainz set up of main componentes: sources, main spectrometer, 2008 start of data taking

21 Pre spectrometer at FZK magnet for pre spectrometer arrival at FZK, oktober 2003 vacuum: mbar reached heating-cooling system mounted test measurements started

22 KATRIN collaboration 4. Project organisation

23 Coincident measurementstroitsk and Mainz Dec Dec Troitsk: 2 times sizeable anomaly Mainz: no significant E step -E 0 change [ev] of χ 2 no indication E step of -E 0 an [ev] anomaly

24 m ν 2 [ev 2 ] Statistical and systematic uncertainies Mainz data

25 Systematic uncertainties As smaller m(ν), as smaller the region of interest below endpoint E 0 Excited electronic final states does not play a role ( E exc > 27 ev) Inelastic scattering in T 2 is small ( E inel. > 12eV largest interval 25eV: 2%) One well-defined final state (similiar to cryo detectors) Is only true, since MAC-E-Filter response function has no tails 1eV Systematic uncertainties Rotation-vibration excitation of final state Inelastic scattering (systematic uncertainty: Troitsk 2%, Mainz 6%, KATRIN 0.x%) electrical potential distribution over source Solid state effects (for QCTS only) Stability of parameters (HV, T partial pressure, T 2 2 purity,...)

26 KATRIN Pre-Spectrometer