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

the CMT data file and the Borexino text file is now done simultaneously. For eachiteration the timestamps t CMT,i and t BX,j for the ith CMT and 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 of 1 secondis sufficient for a correct data matching.The number of Borexino events with CMT flag does not necessarily match thenumber of CMT events. A muon might pass the CMT trigger and then bypass theCMT before crossing Borexino, causing a BX CMT flag and an empty (nhits=0)CMT event. On the other hand, tracks that also go through Borexino can occur inthe CMT without a corresponding flag in Borexino, e.g. when the Borexino DAQ isoffline while the CMT is taking data.The combined data is written into a new ROOT file with the same tree structureof TData as described in Section 3.5. However, the tree is extended by two branchesbxrun and bxevent, namely the Borexino run and 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 and 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 and—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 and CMT eventsare gathered in one file which can now easily be used for analysis.A total number of 392 common events could be reconstructed. Tab. 5.5 showsthe number of events for which there was also a muon track reconstructed by oneof 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 and in general point in a similar direction. One hitsBorexino, whereas the second one hits the CMT and misses Borexino. A detailedcomparison of common events will be presented in the next chapter.5.4 Comparison of CMT and Borexino Muon TracksOnce the CMT and Borexino data are matched, a comparison of 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) and a combined analysis (global tracking). The86