Development of a Liquid Scintillator and of Data ... - Borexino - Infn

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5 Particle Identification with a Neural Network 5.3.2 Data from CTF2 I tested the neural network also with real CTF data to see if in the case of real, more noisy spectra the NN would be superior to the tail-to-total method. Not for all CTF2 runs flash ADC data are available. To have a sufficiently high statistics for the training of the net, I chose one of the source runs, run 793. In this run, all the Bi and Po events occurred at the same position, i.e. the center of the Inner Vessel. In this case, the pulse shape is not further broadened by the time of flight differences to the different PMTs, so that the pulse shape discrimination should yield better results than for randomly distributed events. Fig. 5.9 shows a typical Bi beta and a Po alpha pulse. A total sample of 2360 events was available from run 793. The sample was too small to reduce it further by restricting the energy of the Bi events to the same energy range as the Po events, which would have been the case for only events. Giving the energy of the event as input parameter for the NN could lead to the unwanted case, that the NN uses the energy as decision criterium: high energy beta events, low energy alpha events. Hence I took as input parameter only the normalized flash ADC spectrum (100 bins = 250 ns). 1000 events were chosen as training set for the NN. The other 1360 events are the validation set. The training process continued 5000 epochs, until the error function became flat. The results of the NN algorithm are shown in fig. 5.10. From 680 beta events only 26 were misidentified as alpha events. From 680 alpha events 22 were misidentified as beta events. This means, that for 96.2 % beta identification efficiency, 96.7 % of the alpha events are rejected. For a comparison I tested the pulse shape discrimination using the tail-to-total ratio (with the tail starting after 48 ns) on the same data sample. For a beta identification efficiency of 96 %, an alpha rejection efficiency of 84.9 % is obtained (see fig. 5.11). In this case, the neural network is clearly better than the simple tail-to-total ratio. These results are encouraging for BOREXINO, but data samples with a higher statistics and further systematic tests are needed. 72
5.3 Results Figure 5.9: The flash ADC spectra of a typical Bi beta and a Po alpha pulse from run 793 ( Rn source in the center). 73
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Fakultät für Physik der Technisch
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Abstract The first chapter contains
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Übersicht an Radionukliden in BORE
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Contents 3 The Counting Test Facili
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Contents viii
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1 Solar Neutrinos Figure 1.1: The p
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1 Solar Neutrinos 1.2 Detection of
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1 Solar Neutrinos With this detecti
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1 Solar Neutrinos 1.2.3 Future Expe
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1 Solar Neutrinos 1.3.2 Astrophysic
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1 Solar Neutrinos Using the unitari
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1 Solar Neutrinos km in the earth.
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1 Solar Neutrinos 16 Solution ¡Ñ
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2 The Borexino Experiment The relat
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2 The Borexino Experiment Figure 2.
Page 32 and 33: 2 The Borexino Experiment 2.2 The D
Page 34 and 35: 2 The Borexino Experiment 2.3 Detec
Page 36 and 37: 2 The Borexino Experiment 2.3.2 Anc
Page 38 and 39: 2 The Borexino Experiment which per
Page 40 and 41: 2 The Borexino Experiment 2.4 Backg
Page 42 and 43: 2 The Borexino Experiment ns; Rn-
Page 44 and 45: 2 The Borexino Experiment volume wo
Page 46 and 47: 3 The Counting Test Facility (CTF)
Page 56 and 57: 4 Position Reconstruction of Scinti
Page 72 and 73: 5 Particle Identification with a Ne
Page 86 and 87: 6 Test of a PXE based scintillator
Page 108 and 109: 7 The Source Runs in CTF2 transpare
Page 110 and 111: 7 The Source Runs in CTF2 7.3 The S
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Page 114 and 115: 7 The Source Runs in CTF2 7.4 Analy
Page 116 and 117: 7 The Source Runs in CTF2 7.4.2 Rec
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Page 122 and 123: 7 The Source Runs in CTF2 112 reemi
Page 124 and 125: Summary and Outlook possible to dis
Page 126 and 127: Bibliography [Ade98] E. G. Adelberg
Page 128 and 129: Bibliography [Bra00] L. De Braeckel
Page 130 and 131: Bibliography [Lom97] P. Lombardi, D
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Bibliography [Vog96] R. B. Vogelaar
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Danksagung An dieser Stelle möchte
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Development of a Liquid Scintillator and of Data ... - Borexino - Infn

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