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

Table 5.8: Spatial resolution of the Borexino global muon tracking. The results getbetter for high energetic muons. Also, taking only IV muons (nhits>7000) improvesthe resolution.Value Cut σ [m]∆y - 0.963∆z - 1.125∆y p > 50 GeV 0.513∆z p > 50 GeV 0.828∆y p > 50 GeV, nhits>7000 0.377∆z p > 50 GeV, nhits>7000 0.553almost perpendicularly. Fig. 5.30 shows the intersections of muons within this planeas reconstructed by both the OPERA detector (black dots) and Borexino (red dots).The depiction resembles a view along the CNGS beam direction. Most muons travelin a direction close to the CNGS beam axis. One can clearly recognize both theBorexino sphere and the shape of the OPERA detector in the muon light.For a more qualitative analysis, the differences of the y and z coordinates forboth track reconstructions are taken into account. The distributions of ∆y and ∆zare shown in Fig. 5.31. Besides the spatial resolution one can also deduce a possiblemisalignment of both detectors from these values. A shift in y and z simply movesthe mean value of the corresponding distributions. Due to the small inclinationangle of ∼ 3.5 ◦ of a typical rock muon track and the large distance of approximately60 m between the detectors, the method is not sensitive to a possible shift in x. Thedistribution could be fitted by a Voigtian, i.e. a convolution of a Gaussian and aBreit-Wigner distribution. The spatial resolution is then given by the FWHM/2.35.An even larger dependency of the muon’s momentum can be observed for thespatial resolution as can be seen in Fig. 5.31. The results are much improved by onlyconsidering muons that passed the Borexino inner vessel (nhits>7000 in Borexino).All values are summarized in Tab. 5.8. Comparing the results to the values obtainedfrom the CMT analysis shows a good agreement for all trackings.5.6 Future AnalysisThe presented analysis shows the basic functionality of both the CMT and the Borexinotracking. Once the CMT trigger is replaced and enough statistics are gatheredfor a better calibration, the analysis of common events will improve significantly. Itis foreseen to include the CMT data directly in the Borexino reconstruction. Oncethe CMT yields satisfactory results, further studies on the Borexino tracking canbegin. The reason for different results of the three Borexino trackings can be investigatedwhen the true track is known. CMT tracks that go through Borexino withouta Borexino track reconstruction can be used to identify why no reconstruction wasdone and thus improve the Borexino tracking efficiency.97