OUTLINE OF TALKMotivation 

General description of the experimentThe KATRIN collaboration

Crunch Areas of the Experiment and the UK role

Tritium beta-decay experiments: a (p)reviewTritium beta-decay experiments: a (p)reviewOROR

KATRINKATRINA next generation experiment A next generation experiment

with sub-eV sensitivity for the electron neutrino masswith sub-eV sensitivity for the electron neutrino mass

M. Charlton1, A.J. Davies1, H.H. Telle1, D.L. Wark2, J. Tennyson3, P.J. Storey3 and P.T. Greenland3

1Department of Physics, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK2Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK

3Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

NEUTRINOS HAVE MASS

Oscillations prove they are massive

 mass eigenvalues, m1, m2 and m3

hierarchical or degenerate? m1 << m2 << m3 or m1 m2 m3

NO ABSOLUTE SCALE FROM m

AN ABSOLUTE SCALE ……. 

A finite measured value for m(e) would be vitally important 

An improved limit as proposed by KATRIN – implicationsfor cosmology and astrophysics

OTHER POSSIBLE METHODS 

Astronomical Measurements Need model-dependent assumptions to arrive at mass  

Neutrinoless Double Beta-Decay Neutrino must be a Majorana particle for there to be mass sensitivity

THE PROCESS

T2 3HeT+ + e– + e(bar)

The distortion of the beta-spectrum due to m(e) 0

is only appreciable near the endpoint, Eo since the count rate rises rapidly in this region, varying as

dN/dE (E – Eo)2

THE BETA-DECAY SPECTRUM OF TRITIUM

RECENT MAINZ DATA 10 -YEARS OF NEUTRINO MASS FROM TRITIUM

EXPERIMENTS

THE CHALLENGE

Measure the kinetic energy of an 18.6 keV electron with sub-eV resolution!

So E/Eo 5 x 10-5 or better ……

(NB “normal” electron spectrometers have resolutions of 10-3 or worse)

THE SOLUTION

Magnetic Adiabatic Collimation with Electrostatic Filter - the MAC-E Filter

Exploits the properties of charged particle orbits in slowly-varying (in magnitude) magnetic fields

CONSERVED QUANTITIES (adiabatic invariants - non.rel.)

BA = constant

E/B = constant

B is magnetic field, A is the area enclosed by the orbit and E is the component of the kinetic energy perpendicular to B.

……. E/Eo = BA/Bmax …so BA is the magnetic field in the analysing plane (5 x 10-4 T and Bmax is the maximum field (10 T)

E/Eo = 5 x 10-5 ……..as required

SCHEMATIC OF THE KATRIN EXPERIMENT

ESTIMATES OF THE SENSITIVITY OF KATRIN - New mode of operation under discussion; possible limit around 0.1 eV

THE KATRINKATRIN COLLABORATION 

More than 50 scientists ()from 

Mainz, Karlsruhe, Fulda, Moscow/Dubna, Prague, Washington and the UK

 Development complete …. 2006Testing starts ……………. 2007

 Overall cost (excluding manpower) around €25M

 

CRUNCH AREAS OF THE EXPERIMENT (I) 

SOURCE

Workhorse source will be the Windowless Gas Tritium Source

Change conditions …e.g. pressure, local magnetic fields

Modelling – most parameters can be measured or calculated with high precision and used to model many aspects of β-particle interactions

Trapped ions/electrons; local potentials

In-situ measurements with electrons (gun or 83Kr) ….. ….. energy loss and scattering of β-particles UK INPUT

Molecular physics – (Tennyson, UCL)

Monitoring – (Telle, Swansea)

Modelling – (various, UCL)

WINDOWLESS GAS TRITIUM SOURCE

___________ Analysis of T___________ Analysis of T2 2 (KATRIN requirements) __________ (KATRIN requirements) __________

For the KATRIN neutrino experiments T2 gas of isotopic purity 0.99

is required (impurities constitute other H-isotopomers, contents of 3He, 4He have to be negligible)

Monitoring and regulation of T2 purity to about ±0.005-0.010

Measurement of feed gas impurity concentrations at the inlet to the T2

source (at pressure of ~100-1,000mbar)

For a mixture of say 99% T2 and 1% H2 on finds, at chemo-thermal

equilibrium, fractional amounts of [T2] ~ 0.9899, [HT] ~ 1.00310-2

and [H2] ~ 710-5

detection sensitivities of the order <10-5 ( 10-2 mbar) needed

Analytical method of choice:

RAMAN SPECTROSCOPYRAMAN SPECTROSCOPY

_______ Raman analysis of T_______ Raman analysis of T2 2 (KATRIN requirements) _______ (KATRIN requirements) _______

Spectral pattern isotopomer species identification

Spectral intensities quantitative information

Detection limits realised by Karlsruhegroup using ASER Raman set-up: ~110-5 H2 in D2 (no T2 measurements yet)

at the borderline of requirement for purity control

Estimated detection limit using proposednew set-up with pulsed laser: < 210-6 H2 in T2

λLaser λRaman

v”=0

V’=1

J”

J’

Raman excitation with J = 0, 2

____________ Raman spectroscopy of H____________ Raman spectroscopy of H22 / HT / T / HT / T2 2 _____________ _____________

CALCULATED RAMAN SPECTRA (for λLaser=532nm, T=300K)

[ nm ]

Fraction

1

~10-2

<10-4

Q

OS

Typical dynamic range of ICCD detectors ~64,000

the weakest H2 lines would not be detected, or the strongest T2 lines would be saturated

Line widths of cw and pulsedNd:YAG lasers (532nm) lessthan typical spectral resolutionof an ICCD-coupled spectro-graph

all rotational lines except in the Q-branch resolved

_____ Raman analysis of T_____ Raman analysis of T22 (initial attempt at Karlsruhe) _____ (initial attempt at Karlsruhe) _____

ASER = actively stabilised external resonator (used to enhance ILaser by ~ 250)

“Problems” with this initial, complex set-up:

(a) optical isolator needed to avoid laser damage by back reflections(b) modulator required for locking control of ASER(c) ASER difficult to keep in resonance in the long-term (d) large Rayleigh scattering background contribution to Raman signals

ASER

Czerny-Turnerspectrograph

ICCD

computercontrol

control

modulation

spectrumtransfer

Nd:YAG laser532nm (3W cw)

modulatoroptical isolator

IRaman

~ NILaser

ASERASER

Czerny-Turnerspectrograph

ICCD

computercontrol

control

modulation

computercontrol

control

modulation

spectrumtransfer

Nd:YAG laser532nm (3W cw)

modulatoroptical isolator

IRaman

~ NILaser

Need reliable model of 3HeT+ final state over wide (for molecules) energy range.

Many issues covered by Froelich, Saenz & co-workers, but:

• Excitation to electronic continuum in both resonant and non-resonant processes must be considered.

• Nuclear motion continuum should be treated at better than the reflection approximation (particularly for resonances).

• Cross-section requirements for collisions arising in the source.

Will be done theoretically.

Question:Question: Is it possible to design experimental tests of theory?

KATRIN - Molecular Physics issues

CRUNCH AREAS OF THE EXPERIMENT (II) SPECTROMETER(S)

MAC-E filter type; very high energy resolution (~ 5 x 10-5)

Sources of background need to be understood – modelling of internal discharges

Voltage “standard” needed (and stability)

Calibration – stand-alone MAC-E filter for 83Kr; electron gun for (source − spect)

   UK INPUT

Modelling – (Davies, Swansea)

SCHEMATIC VIEW OF THE KATRIN SPECTROMETERS

SWANSEA CONTRIBUTION TO THE MODELLING

• Design of spectrometer must eliminate electrical breakdown due to desorption of gas from surfaces and field emission. Great care to be taken in design and preparation of interior surfaces.

• Modelling at Swansea will involve evaluation of precise 3D electric and magnetic field distributions in critical regions, especially near interior surfaces.

• Simulation of low-pressure breakdown processes resulting from gaseous emission from interior surfaces will enable critical breakdown paths to be determined.

• Monte-Carlo techniques will also be used to investigate the interaction of beam electrons with the background gas.

• Simulation and modelling work at early stage of design will help minimise potential breakdown and background problems.

CONCLUDING REMARKS

KATRIN will be sensitive to m(e) to below 1 eV and maybe

as low as 0.1 eV

Hope for a factor of 10 improvement over current best direct limit of 2.2 eV

It will be difficult and systematics will have to be chased hard

KATRIN is most likely the “end-of-the-road” for this type of spectrometer-based experiment