Detecting Neutrinos

Hamish Robertson, INT Summer School, Seattle 2009

2

A Brief History of Neutrinos

• 1930 – Pauli’s ‘desperate remedy’.

• 1938 – Bethe & Critchfield explain the sun’s power.

•  1956 – Parity violation discovered in β decay

• 1956 – The neutrino observed.

•  1958 – Neutrino helicity measured.

•  1961 – The µ neutrino discovered.

• 1975 – the τ neutrino makes 3.

3

“I have created a particle that can never be detected…” W. Pauli

€

ν e + p→ e+ + n

Reines and Cowan’s Telegram to Pauli

Professor W. Pauli 14 June 1956 Zurich University

Switzerland

We are happy to inform you that we have definitely detected neutrinos from fission fragments by observing inverse beta decay of protons. Observed cross section agrees well with expected six times ten to minus forty-four square centimeters.

Frederick Reines & Clyde Cowan Box 1663 Los Alamos, New Mex

Nite letter

Ooops! He was at ETH.

5

Pauli’s answer…

6 x 10-44 cm2

‘t Hooft, PLB37, 195 (1971)

€

σν ,e ∝T

NOT Detecting Neutrinos

Helicity -- the Goldhaber-Grodzins-Sunyar experiment.

Mass from the electron spectrum in beta decay.

Neutrinoless Double Beta decay and the question of whether the neutrino and antineutrino are the same or different.

Helicity of the neutrino

152mEu source

γ detector

Pb

Sm2O3

ν

γ

Fe Coil

152mEu

0-

152Sm

1-

2+

0+

Electron capture

961

837

30 fs

Goldhaber , Grodzins, & Sunyar, PR 109, 1015 (1958)

The neutrino is left-handed:

€

σ • ˆ p = −1

Mass confusion

10

Fermi 1932: Neutrinos could have mass, just like electrons, but seems much less.

Hanna & Pontecorvo 1949: Neutrino mass < 1/1000 electron mass.

Glashow, Weinberg, Salam late 1960’s: Can’t understand these things unless mass = 0. So, no RH neutrinos in the SM.

1950’s: Parity violation discovered. Neutrino directly observed. Neutrino helicity measured. PV attributed to neutrinos.

Determination of Neutrino Mass

•  Neutrino Oscillations •  Beta Decay

–  Tritium –  187Re

•  Double beta decay •  Cosmology

•  The mass is needed for •  Particle physics •  Cosmology

12

Direct Mass Limits: the History M

ass

Lim

it (e

V, k

eV, o

r MeV

)

Why is neutrino mass so small?

Neutrino mass is not a feature of

the SM

A signal of unification? See-

saw model:

€

mν =mD2

M

€

ν 3 : 3×10−6

ν 2 :1×10−8

ν1 : 3×10−13

eV

The Universe -- A very odd place

And why is there matter but no antimatter? Sakharov’s criteria: Baryon number not conserved… CP violated… Universe not in equilibrium at some point…

Neutrinos and cosmology

•  Minimum mass: Σmν > 55 meV (oscillations)

(total about 20% of the mass of stars)

•  Maximum mass: Σmν < 6900 meV (tritium), about 8% of closure.

Even small mν influences structure

Σmν

280 meV

1500 meV

3000 meV

Barger et al. hep-ph/0312065

SDSS + 2dFGRS

•  Minimum mass: Σmν > 60 meV (oscillations)

Fogli et al. Phys.Rev.D75:053001,2007 Σmν, eV2

KATRIN

Planck will provide 3 separate ΛCDM constraints on Σmν: 1.  Planck + SDSS 0.2 eV 2.  Planck only 0.26 eV 3.  CMBR + grav. lensing 0.15 eV

From Planck “Bluebook”

Planck Launched May 15, 2009

β-decay electron spectrum…

… shape determines the absolute neutrino mass squared:

i

K ~ [ gv2|MF|2 + gA

2|MGT|2 ] F(E,Z) = Fermi function mν = “mass” of electron (anti-)neutrino = Σi|Uei|2 mi = mν in quasi-degenerate region.

Present Limit: 2.3 eV (95% CL) Kraus et al. hep-ex/0412056

The Mainz Neutrino Mass Experiment Phase 2: 1997-2001

After all critical systematics measured by own experiment (inelastic scattering, self-charging, neighbor excitation):

m2(ν) = -0.6 ± 2.2 ± 2.1 eV2 ⇒ m(ν)< 2.3 eV (95% C.L.)‏

C. Kraus et al., Eur. Phys. J. C 40 (2005) 447

⇓

Kinematics of β-decay

Model-independent determination of mass. Independent of:

•  whether neutrinos Dirac or Majorana, •  nuclear matrix elements, •  phases, •  cosmological models.

What are we measuring?

Writing the transition probability as the matrix element of some operator T,

In the degenerate regime where all the masses are the same, the unitarity of U gives us back the original expression for a single massive neutrino, an “electron neutrino with mass”

€

∝ peE(E − E0)2 1− mν

2

(E − E0)2

1/ 2

In fact, because Ue3 is so small, this expression is good all the way down to about 10 meV!

TLK

~ 75 m long with 40 s.c. solenoids

KATRIN 5 countries 13 institutions 100 scientists

at Forschungszentrum Karlsruhe unique facility for closed T2 cycle: Tritium Laboratory Karlsruhe

Mass Range Accessible

Present Lab Limit 2.3 eV

Δm232 Δm12

2

Average mass > 20 meV

KATRIN

25

1010 e- /s e-

3•10-3 mbar - 1 ± 1 kV

Source

3H

β-decay

eν

3He

Source: Provide the required tritium column density

70 m

10-11 mbar - 1 - 18.4 kV

Pre-spectrometer

103 e- /s e-

Pre-spectrometer: Rejection of low-energy electrons and adiabatic guiding of electrons

1 e- /s

e-

10-11 mbar -1 - 18.574 kV

Main spectrometer

Main-spectrometer: Rejection of electrons below endpoint and adiabatic guiding of electrons

Detector

Detector: Count electrons and measure their energy

Rear

3He

Rear System: Monitor source parameters

Transp/Pump

3He

1010 e- /s e-

Transp. & Pump system: Transport the electrons, adiabatically and reduce the tritium density significantly

0 kV

Experimental Arrangement

26

Arrival in Leopoldshafen: Nov 24, 2006

Voyage of the main spectrometer

Adiabatic magnetic guiding of β´s along field lines in stray B-field of s.c. solenoids: Bmax = 6 T Bmin = 3×10-4 T

Energy analysis by static retarding E-field with varying strength:

High pass filter with integral β transmission for E>qU

  ΔE = E⋅Bmin/Bmax = E⋅As,eff/Aanalyse = 0.93 eV, KATRIN (4.8 eV, Mainz)‏

0.93 eV

KATRIN

⇒ sharp integrating transmission function without tails:

Magnetic Adiabatic Collimation + Electrostatic Filter (A. Picard et al., Nucl. Instr. Meth. 63 (1992) 345)‏

Principle of the MAC-E-Filter

Conversion electrons from 83mKr

(e.g. A. Picard et al., Z. Phys. A 342 (1992) 71)

Check of transmission function (Mainz Expt.)

qU – Ee [keV]

transmission function convoluted with Lorentzian (Γ = 2.83 eV)‏

A window to work in

Molecular Excitations

Systematic Uncertainties

5σ

sensitivity: mν < 0.2eV (90%CL) ‏

Expectation for 3 full beam years: σsyst ~ σstat

discovery potential: mν = 0.35eV (5σ) ‏mν = 0.3eV (3σ) ‏

⇒ KATRIN will search 1 order of magnitude below present upper bound.

KATRIN: sensitivity and discovery potential

Sensitivity with run time

Mass Range Accessible

Present Lab Limit 2.3 eV

Δm232 Δm12

2

Average mass > 20 meV

KATRIN

The Last Order of Magnitude

If the mass is NOT in the 200-2200 meV window, but the 20-200 meV window instead, how can we measure it? KATRIN may be the largest such experiment possible.

σ = 0.36 eV

Size of experiment now: Diameter 10 m.

Rovibrational states of THe+, HHe+ molecule

Source T2 column density near max

Next diameter: 300 m!

8751 hours x mg (AgReO4)

MIBETA: Kurie plot of 6.2 ×106 187Re ß-decay events (E > 700 eV)

10 crystals:

E0 = (2465.3 ± 0.5stat ± 1.6syst) eV

MANU2 (Genoa) metallic Rhenium m(ν) < 26 eV Nucl. Phys. B (Proc.Suppl.) 91 (2001) 293

MIBETA (Milano) AgReO4 m(ν) < 15 eV

MARE (Milano, Como, Genoa, Trento, US, D) Phase I : m(ν) < 2.5 eV mν

2 = (-112 ± 207 ± 90) eV2

Nucl. Instr. Meth. 125 (2004) 125

hep-ex/0509038

The Last Order of Magnitude

KATRIN-type experiment limit: Source and detector are separate. Can evade by making them the same. MARE 187Re uses microcalorimeters: source=detector. BUT pileup limits size of each to ~ 100 µg.

Tritium 187Re Endpoint 18.58 keV 2.47 keV

Branch to last eV 2 x 10-13 6 x 10-11

Half-life 12.32 y 4.32 x 1010 y

Mass (1 dis/d in last 200 meV)

20 µg 13 kg

Mass (1 dis/d in last 20 meV)

20 mg 13000 kg

New schemes

 Decay of 187Re (Q = 2.47 keV) observed in bolometers. • For 20 meV, need 13 T of Re or 20 mg of 3H.

 Atomic T in a trap, full kinematic reconstruction: arXiv 0901:3111

• For 200 meV, need 1,000’s of separate sources.

 Decay of radioactive ions in a storage ring at a specific momentum: arXiv 0904:1089

• For 200 meV, need 1018 – 1020 decays in beam.

 Detection of RF cyclotron radiation from β orbiting in B-field: arXiv 0904:2860

• ? Needs further thought, might be feasible.

Cyclotron motion of electrons in B field

B. Monreal, J. Formaggio, MIT: arXiv:0904.2860 [nucl-ex]