Investigating Methods of Neutrinoless Double-Beta Decay Detection Matthew Rose Supervisor: Dr. R....
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![Page 1: Investigating Methods of Neutrinoless Double-Beta Decay Detection Matthew Rose Supervisor: Dr. R. Saakyan 4C00 Project Talk 13th March 2007.](https://reader036.fdocuments.in/reader036/viewer/2022062511/551afea8550346f70d8b54bc/html5/thumbnails/1.jpg)
Investigating Methods of Neutrinoless Double-Beta
Decay Detection
Matthew Rose
Supervisor: Dr. R. Saakyan
4C00 Project Talk
13th March 2007
![Page 2: Investigating Methods of Neutrinoless Double-Beta Decay Detection Matthew Rose Supervisor: Dr. R. Saakyan 4C00 Project Talk 13th March 2007.](https://reader036.fdocuments.in/reader036/viewer/2022062511/551afea8550346f70d8b54bc/html5/thumbnails/2.jpg)
Matthew Rose 4C00 Project Talk 2
Talk Overview
• An explanation of 0 decay. • What can be learnt from 0 decay?• The Super-NEMO detector & Calorimeter design.• Why is Energy Resolution Important?• How do we improve Energy Resolution?• Studying Scintillators & Photomultipliers.• Results & Achieved Energy Resolutions.• Applications.• Comparison with Previous Results.
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Matthew Rose 4C00 Project Talk 3
2 decay is the simultaneous decay of
two neutrons to two protons, by emission of
2 e- and 2 e.
decay
0 decay does the same, but by
simultaneous emission of a e and absorption of a e, to conserve lepton
number.
![Page 4: Investigating Methods of Neutrinoless Double-Beta Decay Detection Matthew Rose Supervisor: Dr. R. Saakyan 4C00 Project Talk 13th March 2007.](https://reader036.fdocuments.in/reader036/viewer/2022062511/551afea8550346f70d8b54bc/html5/thumbnails/4.jpg)
Matthew Rose 4C00 Project Talk 4
What can 0 decay teach us?
• Nature of the (Majorana or Dirac)• Place limits on the effective mass of the
, h m i, by finding the half life of 0 events.
(T1/20)-1 = (h mi /me)2G0 |M0|2 / log(2)
(uncertainties depend on matrix element calculations)
T1/20 / h m i-2
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Matthew Rose 4C00 Project Talk 5
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Why is 0 so hard to find?
• 0 is very rare (T1/2
0> 1025yr), only ~1 in 105 events is estimated to be a 0
• The energies of 2 and 0are quite distinct, however…
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Matthew Rose 4C00 Project Talk 6
Why is 0 so hard to find?
Tiny energy signature, easily lost amongst background radiation
![Page 7: Investigating Methods of Neutrinoless Double-Beta Decay Detection Matthew Rose Supervisor: Dr. R. Saakyan 4C00 Project Talk 13th March 2007.](https://reader036.fdocuments.in/reader036/viewer/2022062511/551afea8550346f70d8b54bc/html5/thumbnails/7.jpg)
Matthew Rose 4C00 Project Talk 7
Detecting Events - Super-NEMO
• Super-NEMO will look for 0 decays
• source foil surrounded by tracking volume and Calorimeter (PMTs and Scintillators)
Light output (Nph)/ Ee
Nph x Q.E. = Npe
![Page 8: Investigating Methods of Neutrinoless Double-Beta Decay Detection Matthew Rose Supervisor: Dr. R. Saakyan 4C00 Project Talk 13th March 2007.](https://reader036.fdocuments.in/reader036/viewer/2022062511/551afea8550346f70d8b54bc/html5/thumbnails/8.jpg)
Matthew Rose 4C00 Project Talk 8
E/E, the Energy Resolution
• Npe follows a poisson distribution, so
EE
=FWHM
E=
2.35σ
E
σ = mean = N pe
EE
=2.35
N pe
• The energy resolution is related to the spread of the energy spectrum.
• Current E/E = 14% at 1 MeV.
• Aiming for 7% at 1 MeV, need an improvement in Npe by a factor of 4.
![Page 9: Investigating Methods of Neutrinoless Double-Beta Decay Detection Matthew Rose Supervisor: Dr. R. Saakyan 4C00 Project Talk 13th March 2007.](https://reader036.fdocuments.in/reader036/viewer/2022062511/551afea8550346f70d8b54bc/html5/thumbnails/9.jpg)
Matthew Rose 4C00 Project Talk 9
PMTs & Scintillators
• Must match Q.E. to wavelength of maximum emission.
• To do so, need to accurately know the emission spectra of the scintillators.
• Using a miniature spectrometer, can achieve this.
• First, does the spectrometer work?• Can Laser or X-rays be used to approximate
decays?• What are the W.O.M.E. for the scintillators?
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Matthew Rose 4C00 Project Talk 10
Spectrometer range = 340-1000nm?
• Spectra of LEDs taken to test sensitivity around the 400-500nm region (region of scintillators)
• Consistent results give confidence in the sensitivity of spectrometer at these wavelengths.
• Now can take spectra of Scintillators…
470nm470nm
403.5nm403.5nm
475nm475nm
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Matthew Rose 4C00 Project Talk 11
Spectrometer Setup
• Laser hits scintillator, produces light• Light travels along fibre to spectrometer• Data from spectrometer is stored on Laptop• Data analysed using ROOT• Four different scintillator samples studied - Bicron
because of high light output.• >80 spectra were taken for laser results alone, with
various orientations of laser and scintillator.
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Matthew Rose 4C00 Project Talk 12
Laser Spectra
Each has 5 unscaled spectra, they are so similar that any onecan be used for analysis. Background light is negligible.
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Matthew Rose 4C00 Project Talk 13
Laser vs. X-ray spectra
• Repeated with X-rays for all but BC-408.• Little difference between the spectra produced.• Decided that Laser can be used to simulate
ionizing radiation.• Can therefore take wavelengths of maximum
emission from Laser plots.
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Matthew Rose 4C00 Project Talk 14
Final Emission Spectra
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Matthew Rose 4C00 Project Talk 15
Finding E/E
• A fit accounting for the K, L and M energies gives us σK and EK.
• 207Bi is used to produce particles, as it has 2 conversion electrons at 494 and 967 keV.
• 207Bi is a AND source.• can be stopped easily, so
+ and are taken.
• The two spectra are normalised about the region of only. Subtracting the spectra should now give the energy spectrum.
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Matthew Rose 4C00 Project Talk 16
Finding E/E
2.35σ K
EK
=7.90%2.35σ K
EK
=819%
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Matthew Rose 4C00 Project Talk 17
Finding E/E
2.35σ K
EK
=104%
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Matthew Rose 4C00 Project Talk 18
Results
Scintillator
of max emission (nm) E/E (%)
(with Hamamatsu R6233MOD PMT)Bicron Measured
BC-404 408 414-420 7.8
BC-408 425 426-468 8.2
BC-412 434 432-436(424-8 also noted)
10.4
Karkhov - 418-425 -
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Matthew Rose 4C00 Project Talk 19
Comparison with Previous Results
Scintillator Coating E/E, %
BC-404 None 9.4
BC-404 Mylar 7.8
BC-404 Tyvec 8.2
BC-404 Mylar/Tyvec 7.4
BC-408 None 9.7
BC-408 Mylar 8.2
BC-408 Tyvec 8.5
BC-408 Mylar/Tyvec 7.7
• Previous investigations have seen better E/E with other coverings.
• Have only investigated Mylar covering, variations may further improve E/E.
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Matthew Rose 4C00 Project Talk 20
Results
• Target E/E of 7% at 1 MeV seems within reach.
• The R6233 used has Q.E.max of 34.9% at 350 nm.
• Multiplying normalised spectra by Q.E. and Light Outputs can give interesting plots.
• The integral of this plot is proportional to Npe.
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Matthew Rose 4C00 Project Talk 21
Using the Integrals E/E / (Npe)-1/2; I = N£ Q.E. = Npe
E/E £ (Npe)1/2 = constant
Should find:
I404 ' I408 because E/E404 ' E/E408
I404 > I412 because E/E404 < E/E412
Using measured Karkhov spectra, can find light output (55 % Anthracene) and use this to scale
the spectrum before multiplying by Q.E.
Can get a (very) rough idea of E/Ekarkhov using mean of constants.
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Matthew Rose 4C00 Project Talk 22
Using the Integrals
ScintillatorLight Output
(% Anthracene)E/E (%)
Integral
(I / Npe)E/E * (I)1/2
BC-404 68 7.8 17.183 32.33
BC-408 64 8.2 17.283 34.09
BC-412 60 10.4 12.819 37.24
Karkhov from spectra = 55 9.1 14.261 mean = 34.55
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Matthew Rose 4C00 Project Talk 23
Comparing integrals ( ?)
8.5%, 13.2%, 5.2% differences, acceptable for rough estimate of E/E:
E/Ekarkhov' 9.25§0.65%
E / E408
ΔE / E412
= 0.788,N pe412
N pe408
= 0.861
E / E404
ΔE / E412
= 0.750,N pe412
N pe404
= 0.864
E / E404
ΔE / E408
= 0.951,N pe408
N pe404
= 1.003
E/E (A)
ΔE/E (B)=
N pe(B)
N pe(A)
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Matthew Rose 4C00 Project Talk 24
Summary• Aiming for 7% E/E at 1 MeV.• Have achieved 7.8% at 967 keV.• This can be improved with change of
scintillator covering and possibly through use of a Green-extended PMT.
• Have a convenient & quick way to verify emission spectra of scintillators.
• Can estimate E/E with reasonable precision from emission & Q.E. spectra, which can be used to pre-judge suitability of scintillators before testing and also to check results.