KATRIN - The Karlsruhe Tritium Neutrino Experiment The Karlsruhe Tritium Neutrino Experiment H.H. Telle Department of Physics, University of Wales Swansea Singleton Park, Swansea SA2 8PP HHT – UK HEP “Dark Matter” (15/05/05) 1

What is KATRIN What is KATRIN HHT – UK HEP “Dark Matter” (15/05/05) 2 The KATRIN experiment is designed to measure the mass of the electron neutrino directly with a sensitivity of 0.2 eV.sensitivity 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 Where Who and Where HHT – UK HEP “Dark Matter” (15/05/05) 3 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.

The location The location HHT – UK HEP “Dark Matter” (15/05/05) 4

Why Why HHT – UK HEP “Dark Matter” (15/05/05) 5 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 ν µ, transforms into another weak flavour eigenstate, i.e. an electron neutrino ν e or a tau neutrino ν τ, while travelling from the source to the detector.

Neutrino mass determination methods Neutrino mass determination methods HHT – UK HEP “Dark Matter” (15/05/05) 6

Neutrino mass: a source for “hot” dark matter (HDM) Neutrino mass: a source for “hot” dark matter (HDM) HHT – UK HEP “Dark Matter” (15/05/05) 7 The contribution Ω ν from neutrino HDM to the total matter energy density Ω of the universe spans two orders of magnitude. The lower bound on Ω ν 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.

The experiment The experiment HHT – UK HEP “Dark Matter” (15/05/05) 8

Overview of KATRIN set-up Overview of KATRIN set-up HHT – UK HEP “Dark Matter” (15/05/05) scale Overview of the KATRIN setup. The electron path is from left to right. To minimise background, an ultra high vacuum of better than mbar is necessary.

1 – the source 1 – the source HHT – UK HEP “Dark Matter” (15/05/05) 10 T 2 injection

2 – the transport section 2 – the transport section HHT – UK HEP “Dark Matter” (15/05/05) 11 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-spectrometer 3 – the pre-spectrometer HHT – UK HEP “Dark Matter” (15/05/05) 12 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 E 0.

The MAC-E filter The MAC-E filter HHT – UK HEP “Dark Matter” (15/05/05) 13 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-spectrometer The hardware status of the pre-spectrometer HHT – UK HEP “Dark Matter” (15/05/05) 14

4 – the main spectrometer (1) 4 – the main spectrometer (1) HHT – UK HEP “Dark Matter” (15/05/05) 15 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.

4 – the main spectrometer (2) 4 – the main spectrometer (2) HHT – UK HEP “Dark Matter” (15/05/05) 16

5 – the detector (1) 5 – the detector (1) HHT – UK HEP “Dark Matter” (15/05/05) 17 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) HHT – UK HEP “Dark Matter” (15/05/05) 18 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 schedule Time schedule HHT – UK HEP “Dark Matter” (15/05/05) 19 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

Costs Costs HHT – UK HEP “Dark Matter” (15/05/05) 20 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 UK The scientific contribution from the UK HHT – UK HEP “Dark Matter” (15/05/05) 21 Swansea Development of a monitoring system for T 2 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 T 2 analysis Requirements for T 2 analysis HHT – UK HEP “Dark Matter” (15/05/05) 22 KATRIN requires T 2 gas of high (>95%) purity. Impurities include the other hydrogen isotopomers (H 2, HT, D 2, DH, DT) and possibly small amounts of methane isotopes CH x R y (R=H,D,T) from chemical reactions. In the long-term, knowledge of the T 2 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 T 2 source at a total pressure of ~10mbar * Identified as the most convenient location for continuous in-line analysis

Principles of Raman spectroscopy Principles of Raman spectroscopy HHT – UK HEP “Dark Matter” (15/05/05) 23 v=0 v=1 excited state J J 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 laser rot ro-vib

Raman spectroscopy of H 2 Raman spectroscopy of H 2 HHT – UK HEP “Dark Matter” (15/05/05) 24 ~550,000 rotational ro-vibrational S 0 O 1 Q 1 S 1 H2H2

Proposed experimental set-up at FZK Proposed experimental set-up at FZK HHT – UK HEP “Dark Matter” (15/05/05) 25 WGTS Monitoring Gas Cell By-Pass 180cm 120cm Area Allocated To Raman Monitoring T 2 safety enclosure

Experimental set-up for realisation of H 2 / D 2 / T 2 Raman Experimental set-up for realisation of H 2 / D 2 / T 2 Raman HHT – UK HEP “Dark Matter” (15/05/05) 26

The test set-up for H 2 / D 2 Raman The test set-up for H 2 / D 2 Raman HHT – UK HEP “Dark Matter” (15/05/05) 27

Test – Raman of ambient air (8mW laser) Test – Raman of ambient air (8mW laser) HHT – UK HEP “Dark Matter” (15/05/05) 28

Test – Raman of D 2 (8mW laser) Test – Raman of D 2 (8mW laser) HHT – UK HEP “Dark Matter” (15/05/05) 29 S 1 (Q) D 2 S 1 (Q) N 2 S 1 (Q) O 2 S 0 (S) D 2 Nd:YAG

Test – Raman of H 2 +D 2 mixture (8mW laser) Test – Raman of H 2 +D 2 mixture (8mW laser) HHT – UK HEP “Dark Matter” (15/05/05) 30 Not yet sufficient resolution to follow rotational population of all isotopomers

Estimates for estimated Raman sensitivities Estimates for estimated Raman sensitivities HHT – UK HEP “Dark Matter” (15/05/05) 31

The remit of KATRIN The remit of KATRIN HHT – UK HEP “Dark Matter” (15/05/05) 32 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 m ν 2 for 3-year data taking (calculation -1) Accuracy on m ν 2 for 3-year data taking (calculation -1) HHT – UK HEP “Dark Matter” (15/05/05) 33.

Accuracy on m ν 2 for 3-year data taking (calculation-2) Accuracy on m ν 2 for 3-year data taking (calculation-2) HHT – UK HEP “Dark Matter” (15/05/05) 34. 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 ( 3 HeT) + ions after tritium decay, variations of the retarding potential, and the limited uniformity of the magnetic and electrostatic fields in the spectrometer analyzing plane.

Summary of expectation from KATRIN Summary of expectation from KATRIN HHT – UK HEP “Dark Matter” (15/05/05) 35 originally now