Time of Arrival calibration of HGCAL prototype modules using charge injection

As of January 2019 the Large Hadron Collider (LHC) has entered its second long shutdown (LS2) and is under maintenance. During Run 2 the collision centre-of-mass energy was 13 TeV with an instantaneous lumi-nosity of ∼ 1 · 1034 cm−2 s−1. This corresponds to an average of 40 simultaneous inelastic interactions per 25 ns-spaced bunch crossing, and these interactions are referred to as ‘pileup’. After the next long shutdown (LS3), the High Lumi-nosity LHC (HL-LHC) will start, increasing the instan-taneous luminosity of about 5 times. This increase of instantaneous luminosity is a challenge for detector radiation tolerance and for the mitigation of the extreme pileup where up to 200 collisions per bunch crossing are expected. For the detectors at the centre of which the collision happen, this increase requires material that can both be resistant to radiation and deliver precise measurements. To cope with these conditions the CMS collaboration [1] is in the middle of an extensive R&D programme to upgrade many parts of the detec-tor, including the replacement of its calorimeter endcaps. One of the key parameters for the new endcap calorimeter is a good timing resolution for the pileup mitigation and tracking efficiency. The CMS collaboration chose a High Granularity Calorimeter (HG-CAL) endcaps to cope with these conditions [2]. At this moment the HGCAL is in the final research and designing phase, the first prototypes of silicon modules have been assembled and tested, but further upgrades will be incorporated. Module performance, including timing resolution, has been tested with beams at CERN, DESY and Fermilab, the results have been summarised in [3].