Setup of a Drift Tube Muon Tracker and Calibration of Muon ...

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eeSurvival probability for ν e, P0.80.70.60.50.4P ee for LMA7Be: Borexino8B: Borexino, (> 3 MeV)8B: Borexino (> 5 MeV)8B: SNO (> 4 MeV)pp: all solar ν experiments0.30.2-110 1 10E ν[MeV]Figure 4.10: Survival probability P ee for different neutrino energies as measured byseveral solar neutrino experiments. The pink line shows the expected survival probabilityfrom the MSW-LMA predictions. The data points cover, very interestingly,the transition area between matter dominated and vacuum dominated neutrino oscillations.Figure from [75].Very conveniently, there are no near-by nuclear reactors to the LNGS undergroundlaboratory. The mean baseline to distant nuclear reactors is approximately 1000 km.Nevertheless, the contribution of reactor neutrinos is not negligible. The main contributioncomes from 194 reactors in Europe, whereas the remaining 245 reactorsaround the world contribute only 2.5% of the nuclear ¯ν e flux at Gran Sasso. Theexpected neutrino signal from nearby reactors has been carefully investigated by adetailed analysis of their power time profiles and nuclear fuel composition.No significant flux of geo-neutrinos with an energy above 3.272 MeV is expected(cf. Section 2.4.4). This corresponds to a visible energy of approximately 2.6 MeV or1300 p.e. in Borexino. Reactor neutrinos, however, can easily reach energies up to8MeV. In the geo-neutrino window, 5.0±0.3 events from reactors are expected. Sincethe neutrinos in the energy regime leading to a light yield above 1300 p.e. originatesolely from nuclear reactors, this region can be used to confirm the assumptions madefor the reactor neutrino flux. The collected data is presented in Fig. 4.11. A fit hasbeen done for the contributions of geo-neutrinos, reactor neutrinos and backgroundto the spectrum. The best estimates are N geo = 9.9 +4.1−3.4 and N react = 10.7 +4.3−3.4 at68.3 %C.L., the hypothesis of no geo-neutrinos being observed is rejected at 99.997 ˙%C.L. The measurement also rejects the hypothesis of an active geo-reactor in theEarth’s core with a power above 3 TW at 95 %C.L.4.5 pep and CNO NeutrinosThe results from the Borexino 7 Be and 8 B neutrino measurements combined withother solar neutrino experiments show that the LMA-MSW oscillation predictionsare in good agreement with the observations. However, the energy region between66
Figure 4.11: Light yield spectrum for the positron prompt events of the ¯ν e candidatesobserved in Borexino. Figure taken from [50]. The dotted red line shows the fit forthe geo-neutrino contribution.the 7 Be neutrinos of 0.862 MeV and the lower threshold of the 8 B measurementsof 3 MeV has not yet been thoroughly investigated. This is exactly the region atwhich the transition between vacuum and matter dominated oscillations occurs.pep neutrinos are mono-energetic with an energy of 1.442 MeV. CNO neutrinos canreach energies up to 1.732 MeV. The observation of pep and CNO neutrinos couldthus be used to probe this region.The CNO neutrino flux is still one of the major uncertainties in the standardsolar models. Measuring it would allow to improve the predictions for the Sun’smetallicity Z. Like the 7 Be neutrinos, pep neutrinos could be easily identified bya Compton-like edge in the energy spectrum. Their flux is directly correlated tothe pp neutrino flux. Measuring the pep neutrino flux would thus allow to drawconclusions on the fundamental pp fusion reaction. Besides the impact on soalrphysics, measuring the CNO neutrino flux also allows for testing the intemediateenergy regime of the transition region of the MSW effect.The combined flux of pep and CNO neutrinos is predicted to be of the orderof 7 × 10 8 cm −2 s −1 , almost one order of magnitude below the lower energetic 7 Beneutrino flux but more than one order of magnitude above the higher energetic8 B neutrino flux. Neutrinos from these two sources have already successfully beendetected, hence it should also be possible to observe pep and CNO neutrinos. Unfortunately,the energy region of interest is dominated by the uncorrelated 11 C cosmogenicbackground, caused by cosmic muons passing the detector. The expected rateof 11 C events in Borexino is expected to be approximately five times higher than theneutrino signal. It is thus utterly important to find a way to sufficiently suppressthis background. It has been shown in Section 4.3.3 that the three fold coincidenceis used for this task. It relies on a precise muon tracking to avoid excluding largevolumes from the fiducial value. The CMT can perform this kind of measurement,however, the detector is not capable to cover all of Borexino. Nevertheless it can beused to improve the 11 C tagging. By comparing results of tracks reconstructed by67
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Setup of a Drift Tube Muon Trackera
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AbstractIn this work the setup and
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3.5.5 Pattern Recognition . . . . .
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viii
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essential for vetoing these events.
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Chapter 2NeutrinosThe standard mode
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However, it did not yet deliver an
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Table 2.1: Neutrino oscillation par
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this assumption, the Standard Solar
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Figure 2.1: Neutrino flux at Earth
Page 23 and 24: asymmetry between neutrino and anti
Page 25 and 26: Figure 2.3: Expected ¯ν e energy
Page 27: Nb neutrino/fission-11010-2Neutrino
Page 30 and 31: 108−dE/dx (MeV g −1 cm 2 )65432
Page 32 and 33: Figure 3.3: Setup of the muon track
Page 34 and 35: zyxModule b.0Module a.0Module b.1Mo
Page 36 and 37: Figure 3.6: Display of the slow con
Page 38 and 39: plastic scintillators. To avoid all
Page 40 and 41: N hitsHitmap Plane 06000h_hitmap0En
Page 42 and 43: Table 3.4: Data structure for calib
Page 44 and 45: TDC SpectrumN/[2 Channels]1000800H_
Page 46 and 47: Table 3.5: List of variables calcul
Page 48 and 49: with ∆⃗q = ⃗q n − ⃗q n−
Page 50 and 51: N [a.u.]∆ α (x)2200020000da0Entr
Page 52 and 53: d[mm]Reco Drift Distances201816H_RE
Page 54 and 55: N [a.u.]Real DataReal data0.06MCh1E
Page 56 and 57: χ 2N [a.u.]Probability103×10hc2p0
Page 58 and 59: N [a.u]Residuals20001800h0Entries 3
Page 60 and 61: Counts/(10 keV × day × 100 tons)1
Page 62 and 63: 4.1.3 Čerenkov LightČerenkov dete
Page 64 and 65: 4.2 The Borexino DetectorThe Borexi
Page 66 and 67: muons, is reduced by going deep und
Page 68 and 69: (typically below 50 cm), the locati
Page 70 and 71: 510Counts/(10 keV x day x 100 tons)
Page 72 and 73: counts/days*4 hitsDay (Red) and Nig
Page 76 and 77: the CMT to the Borexino tracking, t
Page 78 and 79: P C P DSCINT C SCINT DySCINT BSCINT
Page 80 and 81: Figure 5.2: The CMT setup on top of
Page 82 and 83: Angular AcceptanceAngular Acceptanc
Page 84 and 85: Comparison nhits=3 vs nhits=4N [a.u
Page 86 and 87: Table 5.3: Overview of all muon run
Page 88 and 89: N/dayAll Triggers vs Time12000h_tim
Page 90 and 91: Reco Hits in Scintillatory [mm]1000
Page 92 and 93: PMTPMTScintillatorPMTPMTFigure 5.16
Page 94 and 95: the CMT data file and the Borexino
Page 96 and 97: Zenith Angle CMT and BX-GL Tracks h
Page 98 and 99: Lateral x Resolution CMT - IDhlatx_
Page 100 and 101: Distance d between CMT and BX-GL Tr
Page 102 and 103: Angular difference αN [arbitrary u
Page 104 and 105: [m]z bxTrack Position in BX x=0 Pla
Page 106 and 107: N [arbitrary units]∆y all data200
Page 108 and 109: To determine the Borexino tracking
Page 110 and 111: Table A.1: Variables that can be se
Page 112 and 113: espectively. The channel numbers ar
Page 114 and 115: xyϕϕ ′βx ′µFigure C.2: Rela
Page 116 and 117: the z-coordinate z op,0 of the firs
Page 118 and 119: xyEvent: 470, Entry: 470, Time Tue
Page 120 and 121: [14] Ch. Kraus et al. Final Results
Page 122 and 123: [49] T. Araki et al. Experimental i
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Jan Lenkeit und Björn Wonsak sowie
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