the CMT data file <strong>and</strong> the Borexino text file is now done simultaneously. For eachiteration the timestamps t CMT,i <strong>and</strong> t BX,j for the ith CMT <strong>and</strong> the jth Borexinoevent are compared, starting at the first events i = j = 0. The event numberfor the data set with the smaller timestamp is increased for the next iteration. Ifthe two timestamps match within one second, the combined event data is writtento file. The timestamps do not necessarily have to be identical, since the CMTtimestamp is only taken once per second whereas Borexino uses a GPS timestamp.However, considering the low event rates, requiring a maximum difference <strong>of</strong> 1 secondis sufficient for a correct data matching.The number <strong>of</strong> Borexino events with CMT flag does not necessarily match thenumber <strong>of</strong> CMT events. A muon might pass the CMT trigger <strong>and</strong> then bypass theCMT before crossing Borexino, causing a BX CMT flag <strong>and</strong> an empty (nhits=0)CMT event. On the other h<strong>and</strong>, tracks that also go through Borexino can occur inthe CMT without a corresponding flag in Borexino, e.g. when the Borexino DAQ is<strong>of</strong>fline while the CMT is taking data.The combined data is written into a new ROOT file with the same tree structure<strong>of</strong> TData as described in Section 3.5. However, the tree is extended by two branchesbxrun <strong>and</strong> bxevent, namely the Borexino run <strong>and</strong> event number.The combined data file can now be reconstructed using cmtrack. A specialparameter tells the program to keep the Borexino event information during thereconstruction <strong>and</strong> to include it in the output file. Only events that can be fullyreconstructed are written to file.A ROOT macro is now used to create a script which can then be launched to processall corresponding Borexino events on the Borexino cluster. Each single eventis retrieved from the Borexino data storage <strong>and</strong>—in a first step—saved to a singlefile, keeping the specific Borexino data structure (see [78] for details). After allevents have been processed, the single files are merged, together with the reconstructedCMT data. Thus, all information for common Borexino <strong>and</strong> CMT eventsare gathered in one file which can now easily be used for analysis.A total number <strong>of</strong> 392 common events could be reconstructed. Tab. 5.5 showsthe number <strong>of</strong> events for which there was also a muon track reconstructed by one<strong>of</strong> the Borexino muon tracking algorithms. Typical common events are depicted inFig 5.19. Most events show a good agreement for the different trackings. However,also differences can be observed. These are mainly seen in events where the Borexinotracking shows ambiguities in the different tracking algorithms. Very interestingly,for some events a parallel track is reconstructed by the CMT with respect to theBorexino tracking. This occurs when two muons from a shower hit the detectors.These muons are correlated <strong>and</strong> in general point in a similar direction. One hitsBorexino, whereas the second one hits the CMT <strong>and</strong> misses Borexino. A detailedcomparison <strong>of</strong> common events will be presented in the next chapter.5.4 Comparison <strong>of</strong> CMT <strong>and</strong> Borexino <strong>Muon</strong> TracksOnce the CMT <strong>and</strong> Borexino data are matched, a comparison <strong>of</strong> reconstructed tracksis possible. As described in Section 4.3.4, three methods to reconstruct muon tracksare used in Borexino: tracking with the outer detector only (OD tracking), theinner detector only (ID tracking) <strong>and</strong> a combined analysis (global tracking). The86
Table 5.5: Number <strong>of</strong> reconstructed events for different coincidence criteria withBorexino.Criteria NBX flag 392OD track 125ID track 82Global track 125(a) Common Track(b) False Tracking(c) Dimuon TrackingFigure 5.19: Common event display <strong>of</strong> Borexino <strong>and</strong> CMT tracks. The black lineis the track as reconstructed by the CMT. The colored lines correspond to the differentBorexino trackings (blue: OD tracking, red: ID tracking, pink: global tracking).Figure (a) shows a good agreement between tracks. This is the case for most events.However, events with large difference also occur. They result mainly from errors inthe Borexino tracking (Fig. (b)) where one <strong>of</strong> the trackings reconstructs the right coordinateswhereas the other tracking fails or from multi muon events (Fig. (c)), wherethe CMT sees a parallel track to that reconstructed by Borexino.87
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