Alignment of CASTOR with 2013 pA TOTEM-Data

The CASTOR very forward calorimeter of CMS is the most forward subdetector for charged particle characterization at LHC. Due to its location within the forward shielding of CMS various specific problems arise. One of them is the precise alignment of the detector with respect to the LHC beam. During the magnet ramp up the CMS forward area, including CASTOR, slightly moves. Thus, only a precise alignment during data taking conditions can provide a reliable measurement. In this analysis the fact is exploited that in front of CASTOR there is the T2 tracking telescope of the TOTEM collaboration. With the help of online trigger exchange and offline event merging a data set is produced that combines event data including both, the T2 and CASTOR detectors. For this data a dedicated L1 trigger was developed and used, which selects pure electromagnetic isolated clusters in CASTOR gated with a low track multiplicity in T2. These data comprises of isolated electron candidates, which is used for this precise alignment.