Abstract
The increase in instantaneous luminosity during the high-luminosity phase of the LHC represents a significant challenge for future detectors. A strategy to cope with high-pileup conditions is to add a fourth dimension to the measurements of the hits, by exploiting the time separation of the various proton–proton primary collisions. According to LHCb simulation studies, resolutions of about 10–20 picoseconds, at least an order of magnitude shorter than the average time span between primary interactions, would be greatly beneficial for the physics reach of the experiment. Microchannel plate (MCP) photomultipliers are compact devices capable of measuring the arrival time of charged particles with the required resolution. The technology of large-area picosecond photodetectors (LAPPDs) is under investigation to implement a timing layer that can be placed within a sampling calorimeter module with the purpose of measuring the arrival time of electromagnetic showers. LAPPD performances, using a Gen-I tile with a delay-line anode and a Gen-II with a capacitively coupled anode, have been measured thoroughly both with laser (wavelength of 405 nm and pulse width of 27.5 ps FWHM) and high-energy electron (1–5.8 GeV) beams. Time resolutions of the order of 30 ps for single photoelectrons and 15 ps for electromagnetic showers initiated by 5-GeV electrons, as measured at the shower maximum, are obtained.
Highlights
The aim of the LHCb experiment in its Upgrade-2 incarnation [1,2] is to pursue extreme-precision measurements in quark-flavour physics during LHC operation beyond 2030 [3]
Studies conducted to explore the suitability of Microchannel plate (MCP)-based devices to build a timinglayer detector for the LHCb electromagnetic calorimeter (ECAL) Upgrade-2 have been presented
The idea consists of placing the timing layer between two sections of a longitudinally segmented ECAL, to sample the charged component of electromagnetic showers and measure the arrival time of photons, electrons and positrons with a resolution of 10–20 ps
Summary
The aim of the LHCb experiment in its Upgrade-2 incarnation [1,2] is to pursue extreme-precision measurements in quark-flavour physics during LHC operation beyond 2030 [3]. According to simulations, the electromagnetic calorimeter (ECAL) will have to measure the arrival time of electrons, positrons and photons in the 5–100 GeV range with resolutions of 10–20 picoseconds [2]. To achieve this level of precision, the implementation of a dedicated timing layer based on microchannel plates (MCPs) is being investigated. The two LAPPDs were tested with electrons of energies between 1 and 5.8 GeV at the DESY beamtest facility [9] In these tests, each LAPPD was inserted between two sections of an ECAL module [2], longitudinally segmented approximately in correspondence of the shower maximum (after about 6 radiation lengths). Avoiding the use of the PC helps prolong the lifetime of the timing-layer detector, leading in addition to a relevant simplification in its design and realisation, with consequent reduction of costs
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