First Results of the 2021 FASER Calorimeter Test Beam Charlotte Cavanagh, University of Liverpool FASER is a new experiment at CERN designed to complement the LHC's ongoing physics programme, extending its discovery potential to light and weakly-interacting particles such as long-lived dark photons (A’). These are characterised by a signature with two oppositely-charged tracks or two photons with very high energy (∼TeV) that emanate from a common vertex inside the detector. The FASER tracker consists of 72 double-sided silicon microstrip modules. • A 150 GeV muon beam with approx. 3.5M tracks was used to study local alignment in middle layer of 1 station • Local x and y residuals before (after) alignment shown in red (blue) displaying the results after alignment • Global alignment results are in progress • The test beam saw efficient data taking with good overall beam quality and purity • The relative calorimeter response to different electron energies and MIPs (high energy muons) were measured • Tracking studies have provided local alignment results • Preliminary results have been compared to simulation and fair agreement has been found in terms of energy resolution • Raw calorimeter data has been analysed and corrected to account for pre-shower, improving resolution • Analysis continues as an ongoing process, more than 150 million events were recorded during the week of the test beam • Detector once again situated in TI12, ready for data taking during Run 3 Experiment The main aims of the 2021 Test Beam are: • Calibration of calorimeter using electron (5-300 GeV) and muon (150 GeV) beams, scanning through 24 spatial points across 6 modules • Study uniformity of MIP response and pion scan Setup consists primarily of the tracking stations, the preshower and the calorimeter. Test Beam Tracking Studies • When the pre-shower sees more charge, the calorimeter sees less charge • A correction factor was derived and applied to calorimeter energy measurements to account for this imbalance in charge • The resulting calorimeter response increases mean charge/energy deposition and improves resolution Pre-shower Correction Outlook A full simulation of the calorimeter system is implemented in FASER’s Calypso framework. • Specific test beam geometry designed to compare simulation to data • Crystal ball fitted to distributions to extract μ and σ, where σ is derived from width of crystal ball, converting to energy resolution (σ/E) allows for direct comparison (see table) Corrected data - includes pre-shower correction, removal of noisy channels, 5 + 10 GeV data points excluded (limit of beam) to further reduce resolution Raw data - no corrections, event selection applied to waveform, μ = deposited charge/beam energy Simulated data - no pre-shower correction, comparable to raw data, μ = fraction of energy deposited in calorimeter Previous LHCb results - 2004 test beam extending to 100 GeV, using same ECAL modules but without a pre-shower, comparable to corrected data Next stage: calibrate response of calorimeter in terms of energy. Calorimeter Performance Tracking stations = 3 Planes per station = 3 Modules per plane = 8 FASER is supported by: Errors on plot are too small to be visible at this scale. Test Beam setup and event display.