direct neutrino mass determination: status and prospects hannen, taup 2011 conference, 7.9.2011 1...

Volker Hannen, TAUP 2011 conference, 7.9.2011 1

V.M. Hannen for the KATRIN collaboration

Institut für Kernphysik,

Westfälische Wilhelms-Universität Münster

Direct neutrino mass determination: Status and prospects

2Volker Hannen, TAUP 2011 conference, 7.9.2011

Contents

Introduction

● Neutrino mass in particle physics / cosmology● Current knowlegde● Experimental methods

Upcoming experiments

● MARE● KATRIN

New ideas

● Project 8● ECHO

Summary


Neutrino mass in particle physics

● Nature of the neutrino: Majorana or Dirac particle, i.e. is the neutrino it's own anti-particle ?

● How to explain the many orders of magnitude difference between neutrino mass limits and masses of the charged fermions of the standard model→ sea-saw type I and type II

mechanisms

● Possible connection to the generation of the observed matter - antimatter asymmetry in the universe → leptogenesis


KATRIN

Mainz / Troitsk

ν - oscillations

dark energy

dark matter

baryons

stars / gas

Neutrino mass in cosmology

● Neutrinos are (after γ's) the second most abundant particle species in the universe

● As part of the hot dark matter, neutrinos have a significant influence on structure formation

● For large Σmν values fine grained

structures are washed out by the free streaming neutrinos

Ʃ Ʃ

Ʃ ƩChung-Pei Ma 1996


Current knowlegde and open questions

What we know (from ν oscillations):

● Neutrino flavour eigenstates differ from their mass eigenstates

● Neutrinos oscillate, hence they must have mass

● Mixing angles and Δm2 values known (with varying accuracies)

What we don't know :

● Normal or inverted hierachy ?● Dirac or Majorana particle ?● CP violating phases in mixing

matrix ?● No information about absolute

mass scale ! (only upper limits)● Existence of sterile neutrinos ?

normalhierachy

invertedhierachy

absolutescale ?


β-decay: absolute ν-massmodel independent, kinematicsstatus: m

ν < 2.3 eV

potential: mν ≈ 200 meV

e.g.: KATRIN, MARE-II

0νββ-decay: eff. Majorana massmodel-dependent (CP-phases)status: mββ < 0.35 eV (evidence?)

potential: mββ ≈ 20-50 meV

e.g.: GERDA, CUORE, EXO, SNO+, Majorana, Nemo 3, COBRA, KamLAND-Zen

cosmology: ν hot dark matter Ων

model dependent, analysis of LSS datastatus: Σm

ν < 0.44 eV (Hannestad et al.,

JCAP08(2010)001)

potential: Σmν ≈ 20-50 meV

e.g.: WMAP, SDSS, LSST, Planck

neutrino massmeasurements

mν mββ

Σmi

Search for neutrino mass


(modified by final states, recoil corrections, radiative corrections, ...)

T-decay

C=GF

2

23cos2

C∣M∣2

d dE

=C p EmeE0−E E o−E 2−me

2 F Z1, E E0−E−meS E

Kinematic determination of m(νe)

Suitable β emitters:

Tritium● E

0 = 18.6 keV, T

1/2 = 12.3 a

● S(E) = 1 (super-allowed)

Rhenium● E

0 = 2.47 keV, T

1/2 = 43.2 Gy

alternative approach:

Holmium (EC decay)● Q

EC ≈ 2.5 keV, T

1/2 = 4570 y

me=∑

i=1

3

∣U ei∣2mi

2


(Main) experimental approaches

calorimeter approach (MARE) spectrometer approach (KATRIN)

source

activity

technique single crystal bolometers electrostatic spectrometer

solid angle

response

interval entire spectrum

method differential energy spectrum integrated energy spectrum

setup modular size, scalable integral design, size limits

resolution

metallic Re / dielectric AgReO4

high purity T2

low : < 105 β/s, ≈ 1Bq/mg Re high: ≈ 105 β/s, 4.7 Ci/s injection

4π (source = detector) 40% of 2π (max. forw. angle 51º)

entire β-decay energy kinetic energy of β-decay electrons

narrow interval close to E0

ΔE ~ 11-25 eV (FWHM) ΔE ~ 0.93 eV (100%)

Detector requirements:

● large solid angle● high energy resolution● low background● low dead time / no pile up

effect of :● background● pile up● fluctuations


Microcalorimeter Arrays for a Rhenium Experiment

187Re as ß-emitter:

● E0 = 2.47 keV, T

1/2 = 4·1010 y

● isotopic abundance 63%→ 1mg Re ≈ 1 decay/s

● slow decay time of signals → large number of small detectors

required to minimize pile-up

dielectric AgReO4 crystal

Precursor experiments:Genoa: metallic Re (MANU), Milano: AgReO4 (MIBETA, 10 crystals)

6.2 ×106 events: m(ν) < 15 eV

MARE

M. Sisti et al., NIM A 520 (2004), 125


MARE phase 1 / phase 2 objectives

Angelo Nucciotti, Meudon 2011

MARE-1 : - collection of activities aiming at isotope / technique selection - setup of a 187Re experiment with few eV light ν sensitivity

MARE-2 : - full scale experiment with several 104 -105 detector pixels aiming at 0.1 eV - 0.2 eV statistical sensitivity


MARE-1: TES and thermistor arrays

Angelo Nucciotti, Meudon 2011

MARE-1 @ Milano-Bicocca

● 6x6 array of Si-implanted thermistors (NASA/GSFC)

● 0.5 mg AgReO4 crystals

● ΔE ≈ 25 eV, τ

R ≈ 250 μs

● experimental setup for upto 8 arrays completed

● starting with 72 pixels in 2011

● up to 1010 events in 4 years→ ~ 4 eV sensitivity

MARE-1 @ Genoa

● R&D effort for Re single crystals on transition edge sensors (TES)→ improve rise time to ~ μs and energy resolution to few eV

● large arrays (≈103 pixels) for 104-105 detector experiment

● high bandwidth, multiplexed SQUID readout

● also used with 163Ho loaded absorbers

Re crystal

36x36 TES array(NASA/GSFC)


Temperature T [mK] S

peci

fic h

eat

C

[

10−4

J m

ol−1

K−1

]

Inverse Temperature T−1 [K −1]

Mag

net

izat

ion

M

[A/m

]

Au:Er paramagnetic sensor● Development at Uni Heidelberg● Strong dependence of magnetization

upon temperature changes● Fast energy thermalization / small spec. heat

Within MARE-1● Optimization of MMCs with superconducting

Re absorbers (rise time, energy resolution)● Investigation of 163Ho loaded absorbers● Development of micro-structured MMCs for

ion implantation at ISOLDE-CERN● Microwave SQUID multiplexing for MMCs

Mare-1: Metallic Magnetic Calorimeters

courtesy L. Gastaldo, Angelo Nucciotti

S ∝ ∂M∂T

T S ∝ ∂M∂T

EC sensC abs


● adiabatic transport → μ = E⊥/ B = const.

● B drops by 2·104 from solenoid to analyzing plane → E ⊥ → EII

● only electrons with EII > eU0 can pass the retardation potential

● Energy resolution ΔE = E ,max, start⊥ · Bmin

/ Bmax

< 1 eV

KATRIN: MAC-E filter concept

Magnetic Adiabatic Collimation with Electrostatic Filter

A. Picard et al., NIM B 63 (1992)


KATRIN experiment at KIT

Pre-SpectrometerTritium source Transport section Spectrometer Detector

70 m


WGTS demonstrator tests● on-site since April 2010● cool-down to 30 K successful● test of 2-phase liquid Neon cooling

→ temperature stability 4 mK (1σ) over 24 h

● Next steps: completion of demonstrator to full WGTS

Some KATRIN highlights

Laser Raman spectroscopy● monitoring of T

2 purity

● 0.1% precision (1σ)

T2 inner loop

● successfully comissioned at the TLK ● Pressure fluctuations < 0.02%

→ 5 times better than specified



Cryogenic Pumping Section (CPS)● all magnet modules cold tested at ASG● successful pressure and integral leak

tests of LN2 thermal shield and cryostat● delivery to KIT spring 2012

Differential Pumping Section (DPS2-F)● Arrival at KIT July 2009● Acceptance tests completed● Test measurements yield a reduction

factor for Argon of 5·10-4

Pre-Spectrometer● background down to ~ 10 mHz

- removal of Penning traps (improved electrode design)- elimination of Radon induced background from NEG strips

● many lessons learned for main spectrometer



Main spectr. inner wire electrode

● Purpose: - electrostatic shielding of background electrons - shaping of eletric fields - removal of trapped particles

● 224 of 248 double layer wire modules installed● last 24 modules to be installed after preparation

of the pump port region in fall 2011● main spectrometer commissioning spring 2012


PINCH MAGNET

DETECTOR MAGNET

DETECTOR

SUPPORT STRUCTURE

VACUUM, CALIBRATION SYSTEM

ELECTRONICS

electrons →


Focal plane detection system

● segmented Si PIN diode:90 mm Ø, 148 pixels, 50 nm dead layer

● energy resolution ≈ 1 keV● pinch and detector magnets up to 6 T● post acceleration up to 30kV● active veto shield● on-site since june 2011● magnets successfully tested● currently bake-out of detector chamber● detector commissioning at KIT: fall 2011

pre-amplifier wheel

segmented Si-PIN wafer

detector magnets at KIT


precision HV dividers (with PTB)error budget: Δm2

U < 0.0075 eV2/c4 → σ

U < 60 mV @ 18.6 kV

83mKr conversion electronsnatural standard via 17.8 keV conversion electrons from 83mKr

monitor spectrometer

D. Venos, arXiv 0902.0291;

M. Rasulbaev et al.,

Appl. Rad. Iso., 66 (2008) 1838

Spectrometer calibration and monitoring

T2 β-decay electrons

●HV-supplies● up to 35 kV● 5 ppm/8h

T. Thümmler et al., New Jour. Phys.

11, 103007 (2009)

83mKr conv. electrons

electron gun


Monte Carlo framework KASSIOPEIA

● KATRIN requires precise numerical simulations of all experiment components to minimize systematic uncertainties

● many software packages have been written for the individual subsystems→ need a coherent framework to unify these efforts→ development of a global simulation package: KASSIOPEIA

● tailored to the special needs of the KATRIN experiment:- ultra high precision- calculation of electromagnetic fields- particle generation / tracking / scattering- inclusion of a realistic geometrical model of the experiment- compatibility with KATRIN database and DAQ


1. Inelastic scattering of ß´s in the source (WGTS) - calibration measurements with e-gun necessary - deconvolution of electron energy loss function

2. Fluctuations of WGTS column density (required < 0.1%) - rear wall detector, Laser - Raman spectroscopy, T=30K stabilization, e-gun measurements

3. Transmission function - spatially resolved e-gun measurements 4. WGTS charging due to decay ions (MC: φ < 20mV) - Injection of low energy (meV) electrons from the rear end, diagnostic tools available 5. Final state distribution - reliable quantum chem. calculations

6. HV stability of retarding potential on 3ppm level required - precise HV-Divider (PTB), monitor spectrometer, calibration sources

allow only few contributions with Δm

ν2

≤ 0.007 eV2

⇔ σ < 60 meV

⇒ 3 ppm long term stability

fluctuations σ2 lead to a downward shift in m

ν2

UU

=0.06

18575≈3⋅10−6

m2=−22

Systematic effects and error budget


1. Inelastic scattering of ß´s in the source (WGTS) - calibration measurements with e-gun necessary - deconvolution of electron energy loss function

2. Fluctuations of WGTS column density (required < 0.1%) - rear wall detector, Laser - Raman spectroscopy, T=30K stabilization, e-gun measurements

3. Transmission function - spatially resolved e-gun measurements 4. WGTS charging due to decay ions (MC: φ < 20mV) - Injection of low energy (meV) electrons from the rear end, diagnostic tools available 5. Final state distribution - reliable quantum chem. calculations

6. HV stability of retarding potential on 3ppm level required - precise HV-Divider (PTB), monitor spectrometer, calibration sources

allow only few contributions with Δm

ν2

≤ 0.007 eV2

⇔ σ < 60 meV

⇒ 3 ppm long term stability

fluctuations σ2 lead to a downward shift in m

ν2

UU

=0.06

18575≈3⋅10−6

Systematic effects and error budget

statistical uncertainty σstat

≈ 0.018 eV2

systematic uncertainty σsys,tot

≈ 0.017 eV2

→ sensitivity for upper limit: 200 meV/c2 (90% C.L.)

m(νe) = 0.35 eV observable with 5σ

KATRIN sensitivity: 5 year measurement

(eff. 3 y of data)

m2=−22


B. Monreal and J. Formaggio, PRD 80:051301, 2009

● Source = KATRIN tritium source technology :- uniform B field- low pressure T2 gas

● β electrons radiate coherent cyclotron radiation with frequency:

● Antenna array for cyclotron radiation detection

courtesy J. Formaggio

Measurement of coherent cyclotron radiation of tritium electrons

New developments: Project 8

=0

=

e BEkme

combined antenna signal


rare high-energyelectrons

many overlapping

low-energy electrons

courtesy J. Formaggio

New developments: Project 8● Frequency measurement

→ resolution depends on measurement time: Δω~1/T→ 30 μs observation time per electron required for ΔE = 1eV

● Simulated microwave spectrum of 105 decays within 30 μs in a 10 m source:

● Need to consider new systematics (Doppler shift, magnetic field drifts / inhomogeneities, scattering, pile-up, ...)→ lots of R&D work necessary !

● A small prototype experiment is currently being set up at the University of Washington in Seattle (1 T magnet, measurement of 83mKr spectrum)

17.6 keV e-


New developments: ECHO

Electron Capture 163Ho Experiment(Uni Heidelberg, MPIK Heidelberg, Saha Inst. of Nucl. Phys., ISOLDE CERN, Petersburg Nucl. Phys. Inst.)

A non-zero neutrino mass affects the de-excitation spectrum of electron capture decays

→ calorimetric measurement of the de-excitation energy spectrum

Suitable candidate: 163Ho → QEC

≈ 2.5 keV

T1/2

≈ 4570 y

courtesy L. Gastaldo


New developments: ECHO

● Position of the peaks in agreement with theory

● Extracted end-point value Q

EC = (2.8 ±0.1) keV

● First micro-fabricated MMC with 163Ho implanted at ISOLDE-CERN has been tested

● Purity of the beam: presence of 147Gd chain and 144Pm

● Magnetic and thermal properties as expected ● Good energy resolution: ΔE

FWHM = 11.8 eV,

latest designs: ΔEFWHM

< 3 eV

● Fast rise-time τR = 90 ns

163Ho implanted

group of Ch. Enss, HDcourtesy L. Gastaldo


Summary

● Studies of β-decay kinematics offer a model-independent way to determine the neutrino mass, complementary to cosmology and 0νββ searches.

● KATRIN will probe the cosmologically relevant neutrino mass range down to 200 meV, however, KATRIN cannot be enlarged significantly to go beyond 100 meV.

● Calorimetric experiments (MARE, ECHO) will provide an independent look at kinematical neutrino mass limits. The scalable approach and further R&D work will allow to reach a competitive level of sensitivity.

● New ideas and a lot of R&D work are required to go beyond 100 meV !

● KATRIN next steps:

- many components on-site and working (inner loop, LARA, pre-spec, monitor spectr., air-coils, ...)- focal plane detector commissioning fall 2011- main spectrometer commissioning beginning of 2012- DPS2F testing ongoing, delivery of CPS spring 2012- source demonstrator tested, next: upgrade to full WGTS

direct neutrino mass determination: status and prospects hannen, taup 2011 conference, 7.9.2011 1...

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