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

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4.1.3 Čerenkov LightČerenkov detectors are well suited for the detection of high energetic charged particles.Relativistic particles traveling through a medium with refractive index n at aspeed faster than the speed of light within this medium (β ≥ c n) generate light in aconical shape. It is emitted at an angle αcos α = 1βn .Since only particles with high velocities produce Čerenkov radiation, such a detectorcan only be used for high energetic particles. Applying photo multipliers around thedetection volume allows to observe the Čerenkov light. A particle whose track iscontained in the target can be identified by a light ring whereas a passing particleproduces a disk like shape. Shape and dimensions of these structures can be usedto obtain information on the direction and energy of the particle. The Borexinoexperiment is surrounded by a large water tank acting both as a passive shieldingagainst external background sources as well as a Čerenkov veto for cosmic muons.The signals recorded in this tank are also used for muon tracking. Čerenkov light isnot only emitted in the water tank, it also occurs when high energetic particles likecosmic muons cross the scintillator.4.1.4 Background in Liquid Scintillator DetectorsElastic scattering and inverse β decay offer excellent detection methods of low energeticneutrinos in liquid scintillators. Unfortunately, their signatures can be mimickedby different sources of background. These originate either from radioactivecontaminations within the scintillator or the surrounding materials, or they arecaused by external radiation penetrating the detector.The dominating internal background source is 14 C which is intrinsic to the scintillator.14 C decays through a β − decay and has a half-life of 5730 years. Its naturalabundance on earth is of the order of 10 −12 . The β − decay has an end point energyof 156.475 keV. Despite the small abundance of 14 C, neutrino detection below thisthreshold is not possible.The decay of 14 C is not the only challenge when building a liquid scintillatordetector. Since it is virtually impossible to create a 100% pure scintillator, allbackground created by natural radioactivity and the abundances of radioactive elementshave to be understood and effectively reduced. The main internal backgroundsources besides 14 C are 238 U, 232 Th and 40 K as well as 222 Rn and its daughters.Furthermore, muons from the cosmic radiation create radionuclides by spallationprocesses with long half-lives. Despite the Čerenkov muon veto, the decay of theseradionclides cannot be simply vetoed since they occur long after the incident particlehas passed the detector. Due to the statistic process of radioactive decays, thetime after which the decay takes place cannot be directly correlated to the muon.The most prominet example for this cosmogenic background in liquid scintillatoris the production of 11 C, which is a β + emitter with a half-life of approximately20 minutes. As will be shown in Section 4.3, a high radio purity has been achievedfor Borexino. It will also be shown how cosmogenic events can mostly be controlled.54
Borexino DetectorExternal water tankStainless Steel SphereWaterNylon Outer VesselRopesNylon Inner VesselFiducial volumeInternalPMTsSteel platesfor extrashieldingBufferScintillatorMuonPMTsFigure 4.3: Onion-like structure of Borexino (Figure from [68]). The target scintillatoris located in the center. It is surrounded by two layers of non scintillating bufferliquid, shielding the target from external background sources. The scintillator and thefirst buffer layer are each contained in a thin nylon sphere. Both the buffer and thescintillator are located inside a stainless steel sphere (SSS) equipped with 2212 inwardfacing PMTs to measure the scintillation light. This inner detector is shielded by anexternal water tank serving as both a passive shielding and an active Čerenkov veto.208 additional PMTs mounted on the outer SSS and the bottom of this outer detectorare able to detect the Čerenkov light. 55
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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.
Page 13 and 14: Chapter 2NeutrinosThe standard mode
Page 15 and 16: However, it did not yet deliver an
Page 17 and 18: Table 2.1: Neutrino oscillation par
Page 19 and 20: this assumption, the Standard Solar
Page 21 and 22: 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 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 74 and 75: eeSurvival probability for ν e, P0
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
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espectively. The channel numbers ar
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xyϕϕ ′βx ′µFigure C.2: Rela
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the z-coordinate z op,0 of the firs
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xyEvent: 470, Entry: 470, Time Tue
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[14] Ch. Kraus et al. Final Results
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[49] T. Araki et al. Experimental i
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Jan Lenkeit und Björn Wonsak sowie
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