hql2004 june 1. jochen bonn institut für physik, johannes gutenberg-universität, 55099 mainz,...
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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".
Based on the detection of solar and atmospheric neutrinos
Evidence for -masses
25.
2 10.7 eVm sol
24.
2 105.2 eVm atmMz limit
KATRIN Limits from T- ß- decay
Mainz
KATRIN
Direct measurement of m(e)
super-allowedE0 = 18.6 keVt 1/2 = 12.3 a
Tritium decay: 3H3He+ + e-+ e _
Need very high energy resolution and very high luminosity MAC-E-Filter
Principle of the MAC-E-Filter Magnetic Adiabatic Collimation + Electrostatic Filter
(A. Picard et al., Nucl. Instr. Meth. 63 (1992) 345)
Two supercond. solenoidscompose magneticguiding field
Electron source (T2)
in left solenoid e- in forward direction:
magnetically guided adiabatic transformation:
= E/B = const.
parallel e- beam Energy analysis by
electrostat. retarding fieldE = EB
min/B
max
= EAs,eff
/Aanalyse
4.8 eV (Mainz)
Mainz Neutrino Mass Experiment (1997-2001)Mainz group
2001:
J. BonnB. Bornschein*L. Bornschein*B. FlattCh. KrausB. Müller**E.W. OttenJ.P.SchallTh. Thümmler**Ch. Weinheimer**
* FZ Karlsruhe** Univ. Bonn
• T2 Film at 1.86 K
• quench-condensed on graphite (HOPG)• 45 nm thick (130ML), area 2cm2
• Thickness determination by ellipsometry
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
(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)
m2() = -1.2 ± 2.2 ± 2.1 eV2 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 spectrumm2() = -0.7 ± 2.2 ± 2.1 eV2 m()< 2.3 eV (95% C.L.)C. Kraus, EPS HEP03, Aachen, July 2003
The Troitsk Neutrino Mass ExperimentGaseous T2 source MAC-E-Filter
energy resolution: E = 3.5eV
3 electrode system in 1.5m
diameter UHV vessel (p<10-9 mbar)
column density: 1017 cm-2
luminosity: L = 0.6cm2
(L = /2 * Asource
)
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-runTroitsk 1994-1999,2001 data: m²() = -2.3 ± 2.5 ± 2.0 eV2 m()< 2.2 eV (95% C.L.)
V.M. Lobashev et al., Phys. Lett. B460 (1999) 227
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
The Karlsruhe Tritium Neutrino experiment KATRIN
}10m
(hep-ex/0109033)
Physics aim: Sensitivity on neutrino mass scale: m() << 1eV
Higher energy resolution: E 1eVsince E/E ~ A
spectrometer larger spectrometer
Relevant region below endpoint is smallereven less count rate dN/dt ~ A
spectrometer larger spectrometer
Molecular tritium sources
WGTS: 9cm, length: 10m, T = 30 Kallows to measure with near to maximum count rate using d = 5 1017/cm2
with small systematicsQCTS: 8cm, T=1.6 K, d = 35 nm
presently limited by self-charging
Standard source: Alternative Source:
T2
transportmagnets
spectrometersolenoids1010 e-/s
103 e-/s
Pre and main spectrometer
Main spectrometer:• Energy resolution:
E = 1eV• high luminosity:
L = ASeff
/4 = Aanalyse
E/(2E) = 20 cm2
• 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
Sensitivity of KATRIN KATRIN 4th collaboration
meeting in Prag, June 2003:
-optimised measurement point distribution
-smaller sys. uncertainties
sensitivity on m(e)
0.20 eV/c2
(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
mst
at(
)2
[eV
2 ]
LoI
Opt. of meas. points
tritium purity
10m spectr. + optim.
background = 1mHz?
Technical challenges• Recirculation and purification of tritium to a large extent (kCi)• 30 superconducting solenoids• UHV (< 10-11 mbar) in huge volume (1000m2)• HV calibration and stability on ppm level• High resolution detectors• ....
ideal place: Forschungszentrum Karlsruhe/Germany
Inst. f. Kernphysik(IK)
Institut für TechnischePhysik (ITP)
TritiumlaborKarsruhe (TLK)
Inst. f. Prozessdaten-verarbeitung
und Elektronik (IPE)
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