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

TDC SpectrumN/[2 Channels]1000800H_TDC_ALLEntries 116351Mean 1549RMS 511.960040020000 500 1000 1500 2000 2500 3000 3500 4000TDC ChannelFigure 3.9: Initial TDC spectrum from raw data. Large TDC channels mean smalldrift distances. The steep edge around channel 2100 hence corresponds to hits nearthe anode wire.First, the peak of the spectrum is located and its value n m determined. For the upperboundary t c,max , all following channels are investigated. As soon as the averagefrom three consecutive channels is below a certain number of entries n l , the smallestchannel is taken as the upper boundary. In an ideal case, n l would just be zero.Since remaining noise cannot be excluded this limit has to be raised, especially forlarge data samples. For the determination of t c,max it has been found useful to usen l = nm900. The lower boundary is determined in a similar way, with the exceptionthat four consecutive bins are considered. The boundaries are written to a root treecalled TBound, which has two branches min and max and only one entry. The tree issaved in the file calib.root.3.5.3 Initial CalibrationAn initial calibration can be derived directly from the raw data. It can be assumedthat random cosmic muon tracks are distributed homogeneously in space, i.e. takinginto account a reasonable large number of tracks in a given drift tube all possibledrift distances occur equally often. Thus, from the TDC spectrum, the TDC countto distance relation can be derived. TDC counts can be directly associated todrift distances. It is hence not necessary to convert TDC counts to real times.As described in Section 3.3, large TDC values mean small drift distances.For a given TDC channel t c with N i entries, the distance r is hence given byr(t c ) = r max ×4095 ∑N ii=t c4095∑i=0N i= r max ×4095 ∑i=t cN iN Entries, (3.3)with r max = 18.15 mm being the inner tube radius. Fig. 3.10 shows the initial TDCcount to distance relation.36