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

Statistical and systematic uncertainiesMainz 1998-2001 data

m

2 [e

V2 ]

(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)

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