katrin - the karlsruhe tritium neutrino experiment the karlsruhe tritium neutrino experiment h.h....
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KATRIN - KATRIN -
The The KaKarlsruhe rlsruhe TriTritium tium NNeutrino Experimenteutrino Experiment
H.H. Telle
Department of Physics, University of Wales SwanseaSingleton Park, Swansea SA2 8PP
HHT – UK HEP “Dark Matter” (15/05/05) 1
What is KATRINWhat is KATRIN
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The KATRIN experiment is designed to measure the mass of
the electron neutrino directly with a sensitivity of 0.2 eV.
It is a next generation tritium beta-decay experiment scaling
up the size and precision of previous experiments by an order
of magnitude as well as the intensity of the tritium beta
source.
10 m
Who and WhereWho and Where
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KATRIN is a joint effort of several European and U.S.
institutions.
Currently there are about 100 scientists, engineers,
technicians and students involved, including most of the
groups that have worked on tritium beta-decay experiments in
recent years.
KATRIN is being built at Forschungszentrum Karlsruhe in
Germany where much of the required technical infra-structure
is already available, especially for the tritium source.
WhyWhy
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The widely-used Standard Model (SM) of particle physics
originally assumed neutrinos to be mass-less.
However, actual investigations of neutrinos from the sun and of
neutrinos created in the atmosphere by cosmic rays have given
strong evidence for massive neutrinos indicated by neutrino
oscillations.
Neutrino oscillations imply that a neutrino from one specific
weak interaction flavour, e.g. a muon neutrino νµ, transforms
into another weak flavour eigenstate, i.e. an electron neutrino νe
or a tau neutrino ντ , while travelling from the source to the
detector.
Neutrino mass determination methodsNeutrino mass determination methods
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Neutrino mass: a source for “hot” dark matter (HDM)Neutrino mass: a source for “hot” dark matter (HDM)
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The contribution Ων from neutrino HDM to the total matter energy density Ω of the universe spans two orders of magnitude. The lower bound on Ων comes from the analysis of oscillations of atmospheric ν’s. The upper bound stems from current tritium β-decay experiments and studies of structure formation.
Overview of KATRIN set-upOverview of KATRIN set-up
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1 2 3 4 5
scale
Overview of the KATRIN setup. The electron path is from left to
right. To minimise background, an ultra high vacuum of better than
10-11 mbar is necessary.
2 – the transport section2 – the transport section
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The electron transport
system adiabatically guides
beta decay electrons from
the tritium source to the
spectrometer, while at the
same time eliminating any
tritium flow towards the
spectrometer, which has to
be kept practically free of
tritium for background and
safety reasons.
3 – the pre-spectrometer3 – the pre-spectrometer
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Between the tritium sources and the main spectrometer a pre-
spectrometer of MAC-E-Filter type will be inserted, acting as
energy pre-filter to reject all β electrons except the ones in the
region of interest close to the endpoint E0.
The MAC-E filterThe MAC-E filter
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MAC-E-Filter = Magnetic Adiabatic Collimation combined
with an Electrostatic Filter
Varying the electrostatic
retarding potential allows
to measure the beta
spectrum in an integrating
mode.
The hardware status of the pre-spectrometerThe hardware status of the pre-spectrometer
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4 – the main spectrometer (1)4 – the main spectrometer (1)
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A key component of the new experiment will be the large
electrostatic spectrometer with a diameter of 10m and an
overall length of about 23m.
This high resolution MAC-E-Filter will allow to scan the tritium
endpoint with increased luminosity at a resolution of < 1eV,
which is a factor of 4 better than present MAC-E Filters.
5 – the detector (1)5 – the detector (1)
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All β particles passing the retarding potential of the MAC-E-
Filter will be guided by a magnetic transport system to the
detector.
The detector requirements are the following:
high efficiency for e-detection and simultaneously low
background,
energy resolution of ΔE < 600 eV for 18.6 keV electrons to
suppress background events at different energies,
operation at high magnetic fields,
5 – the detector (2)5 – the detector (2)
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position resolution to map the source profile, to localize
the particle track within the spectrometer (for compensation of
inhomogeneities of electric potential and magnetic field in the
analyzing plane), and to suppress background originating
outside the interesting magnetic flux (e.g. coming from the
electrodes of the spectrometer),
for a measurement in a MAC-E-TOF mode, a reasonable
time resolution < 100 ns),
for test and calibration measurements ready to take high
count rates (up to total rate of order 1 MHz)
Time scheduleTime schedule
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Numerous parts have been delivered and are under test
All major components (source and main spectrometer) have
been ordered
Work on new buildings commenced
Full commissioning and test of whole assembly in late 2007
Start of measurements: 2008
Duration of measurements: 3-5 years
CostsCosts
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Capital investment – about € 32 M
(mostly provided by the Helmholtz Gesellschaft and the
German Federal Government)
Operating costs from 2007/8 onwards – about € 1.5 M p.a.
(to be shared by the participating countries)
The scientific contribution from the UKThe scientific contribution from the UK
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Swansea
Development of a monitoring system for T2 purity
Calculation of trajectory distortion of -particles from
space charge and electrode edges
University College London
Calculation of final molecular state distributions in the
WGTS
CCLRC Daresbury
expertise in XUHV
Requirements for TRequirements for T22 analysis analysis
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KATRIN requires T2 gas of high (>95%) purity.
Impurities include the other hydrogen isotopomers (H2, HT,
D2, DH, DT) and possibly small amounts of methane
isotopes CHxRy (R=H,D,T) from chemical reactions.
In the long-term, knowledge of the T2 purity to within ±0.1%
is needed, with Raman spectroscopy providing quantitative
information about the impurities.
Measurements of impurities to be done at the inlet* to the T2
source at a total pressure of ~10mbar
* Identified as the most convenient location for continuous
in-line analysis
Principles of Raman spectroscopyPrinciples of Raman spectroscopy
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v=0
v=1
excited state
J
J
0
0
1
1
2
2
Vibrational states: v=0,1,2,3…
Rotational states: J=0,1,2,3…
Laser excites the molecule to an excited state which scatters:
either
to the same initial vibrational state, with J = 0,+2
or
to a higher vibrational state, with J = 0, ±2
las
er
ro
t
ro
-vib
Raman spectroscopy of HRaman spectroscopy of H22
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~550,000
rotational ro-vibrational
S0 O1 Q1 S1
H2
Proposed experimental set-up at FZKProposed experimental set-up at FZK
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WGTS
Monitoring Gas Cell
By-Pass
180cm
120cm
Area Allocated To
Raman Monitoring
T2 safety enclosure
Experimental set-up for realisation of HExperimental set-up for realisation of H22 / D / D22 / T / T22 Raman Raman
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The test set-up for HThe test set-up for H22 / D / D22 Raman Raman
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Test – Raman of ambient air (8mW laser)Test – Raman of ambient air (8mW laser)
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Test – Raman of DTest – Raman of D2 2 (8mW laser)(8mW laser)
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S1(Q) D2
S1(
Q)
N2
S1(
Q)
O2
S0(S) D2
Nd
:YA
G
Test – Raman of HTest – Raman of H22+D+D2 2 mixture (8mW laser)mixture (8mW laser)
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Not yet sufficient resolution to follow rotational population of all isotopomers
Estimates for estimated Raman sensitivitiesEstimates for estimated Raman sensitivities
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The remit of KATRINThe remit of KATRIN
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KATRIN is expected to achieve the following sensitivities for the mass of the electron neutrino:
Sensitivity:
(90% upper limit if neutrino mass is zero)0.2 eV
with about equal contributions of statistical and systematical errors.
Discovery potential:
A neutrino mass of 0.35 eV would be discovered with 5 sigma significance.A neutrino mass of 0.30 eV would be discovered with 3 sigma significance.
Accuracy on mAccuracy on mνν22 for 3-year data taking (calculation -1) for 3-year data taking (calculation -1)
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.
Accuracy on mAccuracy on mνν22 for 3-year data taking (calculation-2) for 3-year data taking (calculation-2)
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.
Systematic uncertainties are expected to amount to an equal size as the statistical errors after a measuring time of 3 full years, using an analyzing interval of 30 eV below the endpoint. These are especially:
• Time variation of parameters of the Windowless Gaseous Tritium Source (WGTS),
• description of space charging within the WGTS,
• determination of scattering probabilities of β-electrons within the WGTS,
• description of the final state distribution of (3HeT)+ ions after tritium decay,
• variations of the retarding potential,
• and the limited uniformity of the magnetic and electrostatic fields in the spectrometer analyzing plane.