Test beam characterization of sensor prototypes for the CMS Barrel MIP Timing Detector

Abstract

The MIP Timing Detector will provide additional timing capabilities for detection of minimum ionizing particles (MIPs) at CMS during the High Luminosity LHC era, improving event reconstruction and pileup rejection. The central portion of the detector, the Barrel Timing Layer (BTL), will be instrumented with LYSO:Ce crystals and Silicon Photomultipliers (SiPMs) providing a time resolution of about 30 ps at the beginning of operation, and degrading to 50-60 ps at the end of the detector lifetime as a result of radiation damage. In this work, we present the results obtained using a 120 GeV proton beam at the Fermilab Test Beam Facility to measure the time resolution of unirradiated sensors. A proof-of-concept of the sensor layout proposed for the barrel region of the MTD, consisting of elongated crystal bars with dimensions of about 3 × 3 × 57 mm 3 and with double-ended SiPM readout, is demonstrated. This design provides a robust time measurement independent of the impact point of the MIP along the crystal bar. We tested LYSO:Ce bars of different thickness (2, 3, 4 mm) with a geometry close to the reference design and coupled to SiPMs manufactured by Hamamatsu and Fondazione Bruno Kessler. The various aspects influencing the timing performance such as the crystal thickness, properties of the SiPMs (e.g. photon detection efficiency), and impact angle of the MIP are studied. A time resolution of about 28 ps is measured for MIPs crossing a 3 mm thick crystal bar, corresponding to a most probable value (MPV) of energy deposition of 2.6 MeV, and of 22 ps for the 4.2 MeV MPV energy deposition expected in the BTL, matching the detector performance target for unirradiated devices.

Precision Timing with the CMS MTD Barrel Timing Layer for HL-LHC

“…The most important figure of merit of the performance of the MTD is the time resolution and must be evaluated very carefully. A 120 GeV proton beam at the Fermilab Test Beam Facility [3] has been used to measure the time resolution of unirradiated sensors. The layout of the test beam consisted of a scintillation counter for trigger purposes, a silicon tracker telescope, and a Photek 240 Micro Channel Plate-PMT (MCP-PMT) to measure a reference time (Fig.…”

Comparative characterization study of LYSO:Ce crystals for timing applications

“…For this purpose, the CMS experiment at the Large Hadron collider (LHC) chose LYSO:Ce crystals coupled to Silicon Photomultipliers (SiPMs) to design the sensor unit for the barrel part (BTL) of its timing layer, the MIP Timing Detector [10]. With this layout, the BTL will be able to provide precision timing of minimum ionizing particles with a resolution of 30-60 ps [11], restoring the event reconstruction performance of the pre-high-luminosity era.…”

CMS MTD Barrel Timing Layer: Precision Timing at the HL-LHC

“…Each tray has a row of six Readout Units (RUs), every RU is made of twelve Front-End (FE) boards connected to a Concentrator Card (providing low voltage power, bias voltage, and three lpGBTs), and to every FE a module made of two LYSO:Ce arrays (16 crystals and 32 SiPMs each) is connected. LYSO:Ce crystals were chosen because of the high density (7.1 g/cm 3 , most probable value of energy deposit by a MIP ∼0.86 MeV/mm), high light yield (∼40000 photons/MeV), fast scintillation rise time (<100 ps), short decay time (∼40 ns) and very high radiation tolerance (less than few percent transmission loss at the end of HL-LHC). In addition, LYSO:Ce crystals have the scintillation light at 420 nm wavelength, matching perfectly with the SiPMs sensitivity.…”