Direct Measurement of Neutrino Mass -2 Flavio Gatti University and - - PowerPoint PPT Presentation

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Direct Measurement of Neutrino Mass -2 Flavio Gatti University and - - PowerPoint PPT Presentation

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Direct Measurement of Neutrino Mass -2 Flavio Gatti University and INFN of Genoa E.Fermi School, ISAPP 2011 Varenna August 2nd, 2011 1 Calorimetric spectroscopy Initial motivation: perform a model independent measurement. External

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Direct Measurement of Neutrino Mass -2

Flavio Gatti University and INFN of Genoa E.Fermi School, ISAPP 2011 Varenna August 2nd, 2011

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Calorimetric spectroscopy

Initial motivation: perform a model independent measurement.

External source spectrometers need a precise model of the atom- molecule to calculate in particular the so called “final states effect”

External source spectrometers need also a model of the energy losses in the source material, scattered trajectories,…

Models contains unknown systematics (see problem of m2 <0

  • f the years ’90  1996 PDG

excluded all these determinations)

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ßi, dN/A 

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Principles of the calorimetric method

In a calorimeter the energy Ei= E(bi)+Di is measured for each event

Then the spectrum become dN(E) = A Si wi (Ei-E0)2dE

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Principles of the calorimetric method

Advantages:

no model dependent corrections for atomic and molecular final states.

no correction for nuclear recoil energy and for electron energy losses. Drawbacks:

Beta source inside the detector: whole spectrum must be acquired and the interesting area is proportional only to (mc2/E0 )3

Needed to work with Low Q Value Isotopes

 187Re : lowest Q ~ 2.5 keV.  187Re: (mc2/E0 )3 ~1/400 of H3

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Simple analytical estimation of the sensitivity

 Counts in DE below the

end-point E0 at fixed mn

 Counts at mn=0  Counts at mn≠0  Pileup counts  Sensitivity

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MC simulation tested on pilot experiments and extrapolated to a very high statistics experiments

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Few historical notes

 The first calorimetric experiment applied to the beta

decay has been made by Ellis and Wooster in 1927

 At that time it was established that “a-ray” were

emitted as mono-energetic lines by nuclei, as expected within the general framework of the quantum theory of the “disintegration of the bodies”

 But the “b-ray” behavior is in sharp contrast to this:

the kinetic energy spectrum is widely distributed.

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Further Notes

 “ b-spectrum is continuum because of the slowing down in the

material” (Lisa Meitner) or “in collision with atomic electron” (E.Rutherford)

 The results was <E> calorimeter= 0.33±0.03 MeV/atom against

Emax=1.05 MeV/atom

 ”Not conservation of energy” (N.Bohr)   Emax-<E> “carried out by escaping particle” (Heisemberg)  Pauli conjecture of the neutrino (1930)

 First fully calorimetric detector for b-decay even if not able to detect single particle.

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Single particle detection with thermal detector in1949: a technique incredibly similar to the present one

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The beginning of the calorimetric beta spectroscopy

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The “Simpson” experiment

Apparatus

S(E)=∫ R(E)Ob(E)

R(E)

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Initial state: implanted 3H moves under the effect of channeling and places as neutral atoms in the tetragonal structure od Si  atomic

3H in well defined site. 

Final state: 3He+ in 1s or 2s (+ possible shake-off processes)  recombination processes:

(a) second electron in 1s (1S0)(<10ns),

(b) in 2s (meta-stable if free) but it decays faster (radiatively) , due to screening of Si electrons and/or via Stark mixing with 2p1/2 to 1S in t<ns (58,4 nm emission).

The main de-excitation processes involves emission of several tens

  • f eV (20 eV 1s2p-1s1s), while the energy gap of silicon is 1.1 eV ,

w=3.66 eV (F.Sholze, JAP(1998)),

It can be considered an Energy Dispersive “charge calorimeter” for beta decay.

The “Simpson” experiment: how to check that it was “calorimetric”

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First steps towards “pure” thermal calorimetric beta spectroscopy

1985 – Dan Mc Cammon (Univ.

  • f Wisconsin) proposed to adopt

a fast thermal calorimeter to tritium beta decay spectroscopy (AIP Conf. Proc. 1985)

1985 - First conceptual proposal

  • f approach to the calorimetric

spectroscopy method of determining neutrino mass by using 187-Re (S.Vitale, Univ. INFN Genova) INFN Report /BE- 85/2)

185Re75 5/2+ 187Os76, 1/2-

b-

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How a calorimeter works

b

R V I 

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187-Re decay in a crystal: is it a true calorimeter?.

 HCP lattice  Tc=1.69 K   = 21 g/cm3  T(Debye)= 460 K  M.P.=3000 K  Z=75  A=185(37%), 187(63%)  1/2 Re-187=4x1010 y

Initial and final states are in the crystal

The spectrum end-point energy is lower than the one of isolated isotope.

Eendpoint=(Q-mec2)-(ef+EFermi)-DBlattice where

EFermi =11.2 eV,

Work function f =5.1 eV

Crystal binding energy Blattice = 16.9 eV

Change of binding from Re->Os DBlattice =2.7% Blattice

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187-Re decay in a crystal: case of Rhenium Metal.

75 Re [Xe] 4f14 5d5 6s2 , Etot= -429402.3 eV

76 Os+ [Xe] 4f14 5d6 6s1, Etot= -443164.5 eV

76 Os [Xe] 4f14 5d6 6s2 Etot=-443172.8 eV

DBcoul =13.7KeV greater than DEnucl

the bare 187-Re cannot undergo continuum b-decay. Bound state decay of 187Re75+ has been observed in storage ring having 32 y half life and 63KeV Q value

During the decay the beta particle pass through the atom. The electron may not have the time to rearrange the electrons, the atomic binding energy difference Re-Os+ is very close to the binding energy difference of the initial end final atomic state

Being the energy of the final state Os+ after the decay almost that one of the ground state of Os+, high excited state of te final atom are very unlikely

Further, due to the very similar atomic wave-function the probability of a transition toward an excited state is very small being Os eigenstate

  • rthogonal to the one of Re. A first evaluation of this probability is 7x10-5.
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187-Re decay in a crystal: case of Rhenium Metal.

 Recoil energy at level of few meV respect to several eV per

dislocations; recoil contribute directly to the generation of phonon of elastic branch.

 Recoil free beta decay (not yet observed) but extending

Mossbauer and tacking into account the so small recoil effect, this should be negligible.

 Shake off probability at 1% level only for N and O shells, that

can emits photons of 50 eV (avg) or Auger electron. They are fully absorbed in hundreds of Ang.

 Inner Bremsstrahlung: same Q value but larger penetration

depth, however at um level

 Esternal Bremsstrahlung: can be fully contained as before  Collective excitation based on long living quasi-particle states

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Collective Excitations: Phonon and qp after the primary events: simulation at 6keV

Heat promtly read out by calorimeter Energy trapped in qp. Recondense from us to 100 ms depending on T/Tc What is the prompt thermalization efficiency?  Ecal/Eparticle

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There are mechanism that speed up the thermalization of qp

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First pilot experiment (Genoa)

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Another solid state effect: Beta Environmental Fine Structure (BEFS)

Residuals from spectrum fitting

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BEFS

Eb >>E(Fermi)  beta electrons interacts with atomic cores.

k2=2m(E(b)-V)/h2 ,,

If V ~ -15 eV l(100 eV) ~ 0.2A, l(1000) ~0.04A

a=2.76A, c=4.45 A, c/a=1.61A (1.63 A).

Self interference of outgoing and reflected waves from atomic shells:

Oscillation  (backscattering amplitude) x (self- interference amplitude on Re nucleus from each atomic shell) x (number of atoms of shell)

Thermal motion energy: T0 ~ exp( 2k2 /MQD)

b wave attenuation (“range”): ~ exp(-gR), g ~3-20 A

First hypothesis: S.E.Koonin in 91(Nature 354,486), never observed.

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Second Pilot expriment (Milan)

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Microcalorimeter: some details

Thermal model contains non- linear terms

Linearized equations give simple exponential thermal response

C(T)

G(T,Tb) Tb

R(T) Pg Plin

k .

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Sensor: case of superconducting Transition Edge Sensor (TES)

Insert Sensor Model

Insert bias power for sensor readout

Improve the model taking into account of all C and G terms including their models

Set of non-linear equation…

2 2

( ) 1 1

T T T T s

R T R R e H e

 

     

          

 

 

   

 

 

2 2 1 2 n n n n TES TES Abs TES TES h x TES b n n Abs Abs Abs TES b st b x TES b p b

dT C K T T K T T R T I dt dT C K T T P t dt dI q R I t I R T I L dt C dq I dt

b

 

    -

  

      

a= (T/R) dR/dT Sensor sensitivity

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Electro-thermal feedback

Main concept of the whole dynamic response of the TES coupled calorimeter: the bias power act as negative feedback reducing thermal swing and time response  more linear and fast response

Parameter of ETF : L = aPbias /GTb   =(C/G) 1(1+L)

L range: 10-102

, , , ,  y0b S1    y1b S1    Ib S1   

2 .10 5 4 .10 5 6 .10 5 8 .10 5 1 .10 4 0.0829 0.0831 0.0833 0.0835 0.0837 0.0839

TES w ETF Abs w ETF TES absorber

t [s] T [K]

ETF effect

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Intrinsic energy resolution

 Temperature fluctuations are caused by the

phonon brownian motion between the two bodies

 Average phonons <N>= U/kT = CT/kT  Internal energy fluctuation DUrms= (N)1/2 x kT=

(kT2C)1/2

 RMS Intrinsic Energy Noise = (kT2C)1/2  Ex: T=0.1 K, C=10-13 J/K  DUrms≈ 1eV

T G Tb Phonon casual motion

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Whole model for energy resolution

Including all the noise sources (Phonon, Johnson…), the intrinsic thermal resolution contains sensor and conductance parameters: a and n (G~Tn).

Values better than 1 eV are predicted

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Re-187 detector needs further tech improvements

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The Group of MILAN is testing operation with array

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NASA-Goddard developments

Mo/Au TES  Electron-beam deposited  Tc ~ 0.1 K  Noise-mitigating normal-metal stripes Absorbers joined to TES in micro- fabrication  “Mushroom” shaped to cover the gaps Emphasis on absorbers needed for Constellation-X reference design  0.25 mm pitch (TES is 0.13 mm wide)  92% fill factor  95% QE at 6 keV

Bi Cu nitride

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NASA-Goddard has developed highly packed array with 2 eV resolution metallic calorimeter

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Heildeberg developed Metallic Magnetic Calorimeter

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A second isotope for neutrino mass calorimetric measurements: 163-Ho  allow the use of metallic calorimeter

 163Ho 163Dy* + ne 

We have already (10 year ago) performed some test experiment with EC capture decay of Fe-55 (g-g), Ho-163(g-g) (1997), and Be- 7(g-e,g)

The major problem has been the preparation of the absorbers for such kind of materials that easily form oxides.

Ho-oxide

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MC for sesitivity prediction

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Ho-163 production

Needed a dedicated Ho-163 production

There are several nuclear reaction

Er-162(nth,g)Er-163Ho-163 has 480 barn (good!)

Er-162 have 0.2% natural abundance

Needed enriched Er-162 at level

  • f 20%-40%

Needed pure sample of Er (oxide)

Other stable isotopes: 164,166,167,168 don’t give out long lived radioactive contaminant

Yield: 2x1011 Ho-163/3x1015 Er- 162 (100h irradiation in 1MW reactor)

First production has been tested using a calorimeter as external detector for simplicity

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Si Ir Bi

Drop of Ho-Cl

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Ho-163 Goddard type Array

TES array NASA/GSFC type

163Ho

In the next months one of these array will be charged with Ho-163 for preliminary test

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Summary

 MARE experiment is moving towards the Ho-163 isotope

because, at the present status of the art, it match better with the available technologies:

 detectors with 1-2 eV FWHM in array of 32x32 pixels

are already developed (only five array needed for 0.2 eV/c2 sensitivity)

 Ho-163 embedding process (under study) doesn’t

require major changes in detector architecture

 Readout is already developed and tested as prototype 

Ho-163 production with low content of radioactive impurities has been demonstrated

 We can seriously start producing the TDR for

funding request!

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