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

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(typically below 50 cm), the location of the cosmogenic induced carbon nuclei canbe found in the intersection of a sphere around the location of the neutron captureand a cylinder around the muon track. Any signal occurring within this regionduring a few half-lives of the 11 C can now be vetoed thus reducing the cosmogenicbackground. However, it is desirable to keep the excluded region of fiducial volumesmall, in order to not reduce the overall statistics too much. Therefore, a goodmuon tracking is needed. Fig. 4.4 shows the schematic principle of the three foldcoincidence. For a detailed description see [72].4.3.4 Muon Identification and TrackingMuons crossing Borexino are identified using several techniques. Light from the outerdetector Čerenkov veto is a strong indicator for muons. Also the inner detector canbe used by performing a pulse shape and timing analysis of the PMT signals: muonpulses feature longer rise and decay times than neutrino events of comparable energy.Thus, the outer and inner detector provide two independent and yet redundant tagsfor cosmic muons.For the reconstruction of muon tracks, two different algorithms are used. One isbased on the data from the outer detector and the other uses the information fromthe inner detector. A combination of the OD and ID fits is then further used for athird, global tracking. A brief overview of the tracking algorithms is presented here.The characteristic light patterns created by muons crossing Borexino are usedto reconstruct the muon tracks. For the OD tracking, the disk-like shapes from theČerenkov cone of a crossing muon are identified by the PMTs close to the muon’sentry point to the detector and after a time delay also close to the exit point.PMTs close to the entry point show significantly more photons registered than thosefurther away. Also, the Čerenkov light reaches these PMTs earlier. Depending onthe inclination of the track, the time profile of the hits corresponds to a circle or anellipse around the entry point. Once the two clusters of PMTs indicating a crossingmuon have been identified, the entry and exit points are determined by the chargebarycenters of these clusters. A detailed description of the tracking algorithm ispresented in [71].The inner detector tracking relies mainly on the distinct patterns of the photonarrival times at the PMTs. Due to the high light output from crossing muons, thecharge distribution of the PMTs cannot be used for the track reconstruction. Amuon crossing the inner detector produces both scintillation and Čerenkov light.The Čerenkov light is emitted as the typical forward bound Čerenkov cone whereasthe scintillation light evolves in all directions. First, the entry point is identified bythe backward running scintillation light. For a first approximation, the time patternof the hits registered within the first 5 ns of the event is analyzed. The exit pointis then identified by determining the symmetry plane dividing the photon arrivalpattern of the PMTs in half. This plane has to go through both the entry andexit point of the tracks, as well as through the center of the SSS, of which two arealready known. Having found this plane already allows a rough determination ofthe azimuth angle of the muon track. To get an even better result, twelve planesperpendicular to the symmetry plane in rising distance from the entry point areinvestigated. The arrival times at the PMTs in each plane show a minimum aroundthe track’s azimuth angle ϕ when plotted against the azimuth location of the PMT.60
Counts/(5 photoelectrons × day × 100 tons)51010 431010 210110 -110 -2-3All dataAfter fiducial cut and removal of Rn daughtersAfter statistical subtraction of αʻs100 200 400 600 800 1000Charge [photoelectrons]Figure 4.5: Raw photo electron spectrum after 192 days of data taking. The blackline shows all data, whereas the blue and red lines show the data after the applicationof some basic cuts. The Compton like edge from the 7 Be neutrinos can be clearly seenaround 300 photo electrons. Furthermore the impact of cosmogenic 11 C leaves a clearimpact in the region between 400 and 800 photo electrons. The peak around 200 photoelecrons is caused by the decay of polonium. Figure from [69]A fit is done for all twelve planes and the mean value of the obtained minimums isused as ϕ. For the exit point identification, the arrival times at the PMTs in thesymmetry plane in dependence of their polar coordinate are investigated. They showa clear minimum at the entry point and another local minimum at the exit point.Having found both entry and exit point, the polar angle θ can easily be determined.A detailed description of the inner tracking can again be found in [71]. The angularresolution of the muon tracking is estimated to be in the order of a few degreesand the spacial resolution is better than 50 cm. However, to obtain a more profoundestimate of the tracking’s resolution, one has to know the exact muon coordinates tobe able to compare them with the reconstructed values. The compact muon trackerintroduced in Chapter 3 is capable of performing this task. It can thus be used toprobe the quality of the Borexino muon tracking as will be presented in Chapter 5.4.4 Borexino ResultsThe Borexino experiment has been taking data since May 16 th 2007. The successfuldetection of solar 7 Be neutrinos was reported already a little over a year after that.Since then, also solar 8 B and geo-neutrinos have been observed. This section brieflysummarizes the first Borexino results.4.4.1 7 Be NeutrinosThe successful detection of the 0.862 MeV 7 Be solar neutrinos in Borexino has firstbeen reported in August 2008 [67]. The results are based on 192 online days of datataking. The interaction rate was found to be 49 ± 3 stat ± 4 syst counts per day and61
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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
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 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 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
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
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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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Setup of a Drift Tube Muon Tracker and Calibration of Muon ...

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