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Status of the KATRIN experiment

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The aim of the Karlsruhe Tritium Neutrino experiment-KATRIN-is the direct measurement of the anti-neutrino mass with a sensitivity of 200 meV/c 2 (90% C.L.). It is based on the study of the endpoint region of tritium β decay where a non-vanishing anti-neutrino mass causes a distortion of the β spectrum. KATRIN will allow to probe a part of the cosmology-relevant neutrino mass parameter space and hence further constrain cosmological models and help to clarify the role of neutrinos as dark matter. KATRIN uses a windowless gaseous tritium source for production of β electrons in combination with an electrostatic filter for energy analysis. An overview of the status of the KATRIN experiment will be given.
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PoS(EPS-HEP2011)097
Status of the KATRIN experiment
Sebastian Fischer
Karlsruhe Institute of Technology, Germany
E-mail: sebastian.fischer@kit.edu
The aim of the Karlsruhe Tritium Neutrino experiment - KATRIN - is the direct measurement of
the anti-neutrino mass with a sensitivity of 200 meV/c2(90% C.L.). It is based on the study of the
endpoint region of tritium βdecay where a non-vanishing anti-neutrino mass causes a distortion
of the βspectrum. KATRIN will allow to probe a part of the cosmology-relevant neutrino mass
parameter space and hence further constrain cosmological models and help to clarify the role of
neutrinos as dark matter. KATRIN uses a windowless gaseous tritium source for production of β
electrons in combination with an electrostatic filter for energy analysis.
An overview of the status of the KATRIN experiment will be given.
The 2011 Europhysics Conference on High Energy Physics-HEP 2011,
July 21-27, 2011
Grenoble, Rhône-Alpes France
Speaker.
for the KATRIN collaboration
c
Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/
PoS(EPS-HEP2011)097
Status of the KATRIN experiment Sebastian Fischer
1. Introduction
Cosmological observations and the detection of neutrino flavour oscillations have shown that
neutrinos are massive particles. Although the mass splittings between the neutrino mass eigenstates
are known to be |m312|= (2.32+0.12
0.08)×103eV2/c4[1] and m21 2= (7.41+0.21
0.19 )×105eV2/c4
[2], the overall mass scale is still unknown. A complementary approach is the study of the endpoint
region of tritium βdecay 3H3He +e+¯
νewhere a non-zero anti-neutrino mass mνcauses a
distortion of the βspectrum
d2N
dE dt p(E+mec2)(E0E)q(E0E)2m2
νc4with mν=
3
i=1
|Uei |2mi2
.(1.1)
This measurement allows a direct and model-independent determination of mνand based on the
results of the Mainz [4] and Troitsk [5] experiments an upper limit of 2 eV/c2(95 % C.L.) can be
deduced [6]. The aim of the KArlsruhe TRItium Neutrino (KATRIN) experiment is the measure-
ment of mνwith 200 meV/c2design sensitivity (90% C.L.) [3]. By improving the sensitivity by
one order of magnitude in comparison to foregoing experiments, KATRIN will probe a cosmology-
relevant part of the neutrino mass parameter space.
2. The KATRIN experiment: Principle and status of the main components
The KATRIN experiment consists of four main sections (figure 1): The windowless gaseous
tritium source (1) in which the βelectrons are produced. The transport section (2) which reduces
the tritium flow rate by 14 orders of magnitude and adiabatically guides the electrons to the spec-
trometer and detector section (3) where the energy analysis is performed. The calibration and
monitoring system (4) monitors the activity of the WGTS and performs systematic studies. An
overview of the status of these main sections will be given in the following.
2.1 Status of the windowless gaseous tritium source
The main parameters of the windowless gaseous tritium source (WGTS), i.e. the source tem-
perature, the gas inlet and outlet flow rate and the isotopic composition of the inlet gas, have to
be stabilized to the 103level and accordingly monitored in order to reach the design sensitivity
of 200 meV/c2. The test experiment Demonstrator has proven that cooling concept of the WGTS
WGTS Cryostat Calibration
and
monitoring
Section
DPS2-F CPS Main Spectrometer Detector
Pre-Spectrometer
Transport Section Spectrometer and detector section
DPS1-F
Figure 1: Overview of the KATRIN experiment. The tritium loop system of the WGTS are not shown. For
further details see main text.
2
PoS(EPS-HEP2011)097
Status of the KATRIN experiment Sebastian Fischer
cryostat can achieve a temperature stabilization of the 30 K beam tube in the mK range (Require-
ment: 30 mK stability). After completing the tests, the Demonstrator will be upgraded to the final
WGTS by installing the tritium related parts and the magnets for electron guiding.
The precise knowledge of the composition of the tritium inlet gas of the WGTS is necessary to
account for systematic effects in the WGTS, e.g. Doppler broadening, elastic scattering, nuclear re-
coil and the final state distribution of the (3HeT)+daughter molecules. Laser Raman spectroscopy
(LARA) is the method of choice for the monitoring of the gas composition in KATRIN since it
allows the simultaneous monitoring of all hydrogen isotopologues (T2, DT, HT, D2, HD, H2) [7].
Laser Raman spectroscopy is based on Raman scattering, i.e. the inelastic scattering of photons
on molecules. In this process the wavelength of the scattered light changes due to the rotational-
vibrational (de-)excitation of the molecule which produces characteristic spectra for each hydrogen
isotopologue. As an optical method, Raman spectroscopy is non-invasive, i.e. no samples have to
be taken and hence no radioactive waste is produced.
The test of the LARA system in the closed tritium loop LOOPINO during 3 weeks of non-stop
operation showed that the required 0.1% precision is achieved under KATRIN-like conditions [8].
Further improvement of precision due to an optimisation of the laser beam path and the read-out
mechanism of the optical detector are expected. Experimental tests of calculated Raman scattering
cross-sections of all hydrogen isotopologues were made to improve the accuracy of the LARA
measurements.
2.2 Status of the transport section
The transport section consists of the differential pumping sections (DPS1-F and DPS2-F) and
the cryogenic pumping section (CPS). After commissioning of the DPS2-F, the gas reduction factor
has been measured for D2, He and other noble gases at room temperature. The measured reduction
factors vary between (1.86 ±0.37)×104(for D2) and (5.6±1.1)×104(for Kr) [9]. A further
improvement of the gas reduction factor is expected when the complete beam tube instrumentation
of the DPS2-F is installed. The manufacturing of the CPS is ongoing and the delivery to KIT is
expected for 2012.
2.3 Status of the spectrometer and detector section
Two electrostatic filters, based on the MAC-E [10] principle, are used for energy analysis:
The pre-spectrometer will reject most of the electrons which have energies less than about 300 eV
below the endpoint, i.e. which do not contain information on the anti-neutrino mass. The retarding
potential of the main spectrometer will be varied to measure the spectrum in the last 30 eV below
the endpoint. The pre-spectrometer has been operated as a prototype for systematic investigations
and hardware developments which are also relevant for the main spectrometer. A radon induced
background signal, emerging from the material of vacuum getter strips, has been identified and
suitable experimental measures for suppression were found [11]. The test operation of the pre-
spectrometer is finished and it is ready for its final integration into the KATRIN setup.
The installation of the wire frame modules [12] in the main spectrometer, which are used for
reduction of muon induced electron background, is completed. The detector system has arrived
in Karlsruhe in summer 2011 and has been commissioned. The commissioning and first measure-
ments of the main spectrometer are scheduled for 2012.
3
PoS(EPS-HEP2011)097
Status of the KATRIN experiment Sebastian Fischer
2.4 Status of the calibration and monitoring system
The feasibility of source activity monitoring using βinduced X-ray spectroscopy has been
successfully demonstrated at Tritium Laboratory Karlsruhe. A technical design of the calibration
and monitoring section has been developed.
3. Conclusions
Test measurements of several main components of KATRIN have been successfully performed
and important milestones were achieved. The LARA system has reached 0.1% precision (1σ) under
KATRIN-like conditions and further imrovements are expected. With the upcoming measurements
at the main spectrometer in 2012 the commssioning of KATRIN main components will continue.
References
[1] P. Adamson et al., Measurement of the Neutrino Mass Splitting and Flavor Mixing by MINOS, Phys.
Rev. Lett. 106, 181801 (2011), doi:10.1103/PhysRevLett.106.181801.
[2] B. Aharmim et al., Combined Analysis of all Three Phases of Solar Neutrino Data from the Sudbury
Neutrino Observatory, arXiv:1109.0763v1 [nucl-ex] (2011).
[3] KATRIN Collaboration, KATRIN Design Report 2004, FZKA 7090 (2005).
[4] Ch. Kraus et al., Final Results from phase II of the Mainz Neutrino Mass Search in Tritium βDecay,
Eur. Phys. J. C 40 (2005) 447-468.
[5] V.M. Lobashev et al., Direct search for mass of neutrino and anomaly in the tritium beta-spectrum,
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[6] C. Amsler et al. (Particle Data Group), Review of Particle Physics, Phys. Lett. B 667 (2008) and 2009
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[7] M. Sturm et al., Monitoring of All Hydrogen Isotopologues at Tritium Laboratory Karlsruhe Using
Raman Spectroscopy, Laser Phys. 20 2 (2010).
[8] S. Fischer et al., Monitoring of tritium purity during long-term circulation in the KATRIN test
experiment LOOPINO using laser Raman spectroscopy, Fusion Sci. Technol. 60 3 (2011) 925-930.
[9] S. Lukic et al., Measurement of the gas-flow reduction factor of the KATRIN DPS2-F differential
pumping section, arXiv:1107.0220v1 [physics.ins-det] (2011).
[10] P. Kruit, F. H. Read, Magnetic field paralleliser for 2πelectron-spectrometer and electron-image
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[11] F.M. Fränkle et al., Radon induced background processes in the KATRIN pre-spectrometer, Astropart.
Phys. 35 3 (2011) 128-134doi:10.1016/j.astropartphys.2011.06.009.
[12] K. Valerius, The wire electrode system for the KATRIN main spectrometer, Progress in Particle and
Nuclear Physics 64 2 291-293 (2010) doi:10.1016/j.ppnp.2009.12.032.
4
... The KArlsruhe TRitium Neutrino mass experiment (KATRIN) will have a sensitivity on the electron neutrino effective mass, m β = i |U ei | 2 m 2 i , of 0.2 eV at 95% CL [42]. Cosmological limits today still allow for quasi-degenerate neutrino masses; however, this possibility will soon be confirmed or ruled out. ...
... The region allowed by the normal (inverted) mass ordering is in blue (red), the recent limit on |m ee | given by KamLAND-Zen [39] in gray and the region excluded by cosmology [41] in magenta. We also show the reach expected for the beta decay experiment Katrin [42], as well as the ultimate reach aimed by the neutrinoless double beta decay experiments GERDA and CUORE according to ref. [40]. ...
... The region allowed by the normal (inverted) mass ordering is in blue (red), and the recent limit on |m ee | given by KamLAND-Zen [39] in gray. We also show the reach expected for the beta decay experiment Katrin [42], as well as the ultimate reach aimed by the neutrinoless double beta decay experiments GERDA and CUORE according to ref. [40]. ...
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