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Investigating Methods of Neutrinoless Double-Beta Decay Detection Matthew Rose Supervisor: Dr. R. Saakyan 4C00 Project Talk 13th March 2007.

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Presentation on theme: "Investigating Methods of Neutrinoless Double-Beta Decay Detection Matthew Rose Supervisor: Dr. R. Saakyan 4C00 Project Talk 13th March 2007."— Presentation transcript:

1 Investigating Methods of Neutrinoless Double-Beta Decay Detection Matthew Rose Supervisor: Dr. R. Saakyan 4C00 Project Talk 13th March 2007

2 Matthew Rose 4C00 Project Talk2 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.

3 Matthew Rose 4C00 Project Talk3 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.

4 Matthew Rose 4C00 Project Talk4 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. (T 1/2 0 ) -1 = (h m i /m e ) 2 G 0 |M 0 | 2 / log(2) (uncertainties depend on matrix element calculations) T 1/2 0 / h m i -2

5 Matthew Rose 4C00 Project Talk5 Why is 0  so hard to find? 0  is very rare (T 1/2 0  > 10 25 yr), only ~1 in 10 5  events is estimated to be a 0  The energies of 2  and 0  are quite distinct, however…

6 Matthew Rose 4C00 Project Talk6 Why is 0  so hard to find? Tiny energy signature, easily lost amongst background radiation

7 Matthew Rose 4C00 Project Talk7 Detecting Events - Super-NEMO Super-NEMO will look for 0  decays  source foil surrounded by tracking volume and Calorimeter (PMTs and Scintillators) Light output (N ph )/ E e N ph x Q.E. = N pe

8 Matthew Rose 4C00 Project Talk8  E/E, the Energy Resolution N pe follows a poisson distribution, so 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 N pe by a factor of 4.

9 Matthew Rose 4C00 Project Talk9 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?

10 Matthew Rose 4C00 Project Talk10 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… 470nm 403.5nm 475nm

11 Matthew Rose 4C00 Project Talk11 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.

12 Matthew Rose 4C00 Project Talk12 Laser Spectra Each has 5 unscaled spectra, they are so similar that any one can be used for analysis. Background light is negligible.

13 Matthew Rose 4C00 Project Talk13 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.

14 Matthew Rose 4C00 Project Talk14 Final Emission Spectra

15 Matthew Rose 4C00 Project Talk15 Finding  E/E A fit accounting for the K, L and M energies gives us  K and E K. 207 Bi is used to produce  particles, as it has 2 conversion electrons at 494 and 967 keV. 207 Bi 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.

16 Matthew Rose 4C00 Project Talk16 Finding  E/E

17 Matthew Rose 4C00 Project Talk17 Finding  E/E

18 Matthew Rose 4C00 Project Talk18 Results Scintillator  of max emission (nm)  E/E (%) (with Hamamatsu R6233MOD PMT) BicronMeasured BC-404408414-4207.8 BC-408425426-4688.2 BC-412434 432-436 (424-8 also noted) 10.4 Karkhov-418-425-

19 Matthew Rose 4C00 Project Talk19 Comparison with Previous Results ScintillatorCoating  E/E, % BC-404None9.4 BC-404Mylar7.8 BC-404Tyvec8.2 BC-404 Mylar/Tyvec 7.4 BC-408None9.7 BC-408Mylar8.2 BC-408Tyvec8.5 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.

20 Matthew Rose 4C00 Project Talk20 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 N pe.

21 Matthew Rose 4C00 Project Talk21 Using the Integrals  E/E / (N pe ) -1/2 ;I = N  £ Q.E. = N pe  E/E £ (N pe ) 1/2 = constant Should find: I 404 ' I 408 because  E/E 404 '  E/E 408 I 404 > I 412 because  E/E 404 <  E/E 412 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/E karkhov using mean of constants.

22 Matthew Rose 4C00 Project Talk22 Using the Integrals Scintillator Light Output (% Anthracene)  E/E (%) Integral (I / N pe )  E/E * (I) 1/2 BC-404687.817.18332.33 BC-408648.217.28334.09 BC-4126010.412.81937.24 Karkhov from spectra = 559.114.261 mean = 34.55

23 Matthew Rose 4C00 Project Talk23 Comparing integrals ( ?) 8.5%, 13.2%, 5.2% differences, acceptable for rough estimate of  E/E:  E/E karkhov ' 9.25§0.65%

24 Matthew Rose 4C00 Project Talk24 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.

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