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

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Reco Hits in Scintillatory [mm]1000800600108400620040-2002-400-400 -200 0 200 400 600 800 1000x [mm]0Figure 5.15: Intersection of reconstructed events with the x−y-plane at z = 227mm.This plane represents the trigger scintillator layer. The single scintillators are representedby the black rectangles (compare Fig. 5.1). Tracks intersect the plane at theblack dots. The colored areas depict the number of tracks per 25cm 2 . One can clearlysee a lower density at the larger scintillators, especially the lower right one. Also, thetracks are not distributed homogeneously within all scintillators. This leads to theassumption that some of the scintillators are malfunctioning.smears out which is expected for inclined tracks. The number of hits then show ahomogeneous distribution for the second module of the plane. However, the averagenumber of hits of approximately 45 is below the according value of the y − z-plane,which has an average of 60 hits per tube. Since the latter plane is further away fromthe scintillator, less events would actually be expected here. This strengthens thehypothesis of a malfunctioning trigger scintillator. Scintillators C and D are spreadhomogeneously across the modules of the y − z-plane. Although they contribute toonly 22% of the trigger surface, they seem to account for the majority of events.Comparing the the peaks of the first module in the hitmap of the x − z-plane withthe level for the second module, one can estimate a reduction of the trigger rate byroughly a factor of three for the scintillators A and B. An efficiency of only one thirdof the two larger scintillators (accounting for 78% of the trigger surface) would leadto an overall efficiency of only 1 3× 0.78 + 0.22 = 0.48.The assumption of a poor trigger efficiency can be confirmed by consideringreconstructed tracks. The x and y coordinates at the level of the trigger plane (z =227 mm) were calculated and drawn in a scatter plot. The result is shown in Fig. 5.15.It shows the distribution of reconstructed tracks in the trigger scintillator plane.One can clearly see that the events are not distributed homogeneously. Obviously82
Table 5.4: Comparison of simulated and real events for the 197.68 days of data taking.Values are presented for the requirement of at least 3 and 4 hits as well as a track inBorexino.n events,4 n events,3 n events,BXReal data 788 1647 392MC data 1182 2372 897Ratio 66.7% 69.4% 43.7%one or more trigger scintillators are not working properly. This can be due tomalfunctioning PMTs, broken light guides or a broken scintillator itself. Due to theextremely low muon flux inside the LNGS tunnel, it is hard to find the exact sourceof error. The smaller scintillators seem to perform much better than the larger ones.This is no surprise, since the latter ones are much older. The trigger efficiency canbe deduced from a comparison of simulated and real events. The data presented inTab. 5.3 corresponds to 197.68 days of data taking. The corresponding rates havebeen calculated for the simulated data presented in Section 5.1.3 and are comparedin Tab. 5.4. Trigger efficiencies of 66.7% and 69.4% are found from data with a leastfour and three hits, respectively. This values are overestimated, since the numberof hits in the real data includes also cross talk and hits from δ electrons as well ascertain noise patterns (cf. Fig. E.2 in Appendix E) and only give an upper limit.Therefore, a third comparison has been made with the number of reconstructedevents that go through both the CMT and Borexino. In this case, an efficiencyof 43.7% is obtained. This value, on the other hand, now underestimates the trueefficiency, since the reconstruction still lacks a sufficient calibration and can thusonly be taken as a lower limit. Due to the poor trigger performance, it has beendecided to completely replace the trigger by a new one as will be described brieflyin Section 5.2.3.5.2.3 Trigger UpgradeDue to the poor performance of the current trigger system, a trigger update isnecessary. It has been decided to use only one large, unsegmented plastic scintillator.To suppress false triggers from PMT dark noise, a coincidence of up to four PMTswill be used, each mounted on one corner of the scintillator. The basic layout ofthe new trigger is depicted in Fig. 5.16. For the scintillator, a polyvinyltoluenebasedplastic has been chosen. The foreseen BC-408 scintillator from Saint GobainCrystals is 116×120cm 2 ×2cm in dimensions. On each corner, Hamamatsu R8900Uphoto multipliers will be attached. The PMTs have a squared surface of 23.5 mmside length. At the time of writing, all components have been delivered and arecurrently prepared for installation. After thorough tests in Hamburg, a setup atGran Sasso is foreseen for spring 2011.83
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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
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asymmetry between neutrino and anti
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Figure 2.3: Expected ¯ν e energy
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Nb neutrino/fission-11010-2Neutrino
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108−dE/dx (MeV g −1 cm 2 )65432
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Figure 3.3: Setup of the muon track
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zyxModule b.0Module a.0Module b.1Mo
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Figure 3.6: Display of the slow con
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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 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 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
Page 124 and 125: 116
Page 126: Jan Lenkeit und Björn Wonsak sowie
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