Abstract
Recent interest in pile-up mitigation through fast timing at the HL-LHC has focused attention on technologies that now achieve minimum ionising particle (MIP) time resolution of 30 picoseconds or less. The constraints of technical maturity and radiation tolerance narrowed the options in this rapidly developing field for the ATLAS and CMS upgrades to low gain avalanche detectors and silicon photomultipliers. In a variety of applications where occupancies and doses are lower, devices with pixel elements of order 1 cm$^2$, nevertheless achieving 30 ps, would be attractive. In this paper, deep diffused Avalanche Photo Diodes (APDs) are examined as candidate timing detectors for HL-LHC applications. Devices with an active area of $8 \times 8$ mm$^2$ are characterised using a pulsed infrared laser and, in some cases, high energy particle beams.The timing performance as well as the uniformity of response are examined. The effects of radiation damage on current, signal amplitude, noise, and timing of the APDs are evaluated using detectors with an active area of $2 \times 2$ mm$^2$. These detectors were irradiated with neutrons up to a a 1-MeV neutrons fluence $\Phi_{eq} = 10^{15}$ cm$^{-2}$. Their timing performance was characterised using a pulsed infrared laser. While a time resolution of $27 \pm 1$ ps was obtained in a beam test using an $8 \times 8$ mm$^2$ sensor, the present study only demonstrates that gain loss can be compensated by increased detector bias up to fluences of $\Phi_{eq} = 6 \cdot 10^{13}$ cm$^{-2}$. So it possibly falls short of the $\Phi_{eq} = 10^{14}$ cm$^{-2}$ requirement for the CMS barrel over the lifetime of the HL-LHC.
Highlights
The high luminosity upgrade of the CERN Large Hadron Collider (HL-LHC) foreseen to start in 2026 will provide an instantaneous luminosity of up to 5 ⋅ 1034 cm−2s−1 with a bunch spacing of 25 ns, and an average pile-up of up to 200 collisions per bunch crossing [1]. This value of pile-up presents a challenge for the experiments, as currently ATLAS and CMS have reached a typical number of concurrent interactions within the same bunch crossing of approximately 35 [2,3]
This paper summarises the characterisation of deep diffused Avalanche Photo Diodes (APDs) produced by Radiation Monitoring Devices [6] used as timing detectors for charged particles
Deep diffused APDs with an active area of 2 × 2 mm2 produced by RMD were irradiated with reactor neutrons up to a fluence of Φeq = 1015 cm−2
Summary
The high luminosity upgrade of the CERN Large Hadron Collider (HL-LHC) foreseen to start in 2026 will provide an instantaneous luminosity of up to 5 ⋅ 1034 cm−2s−1 with a bunch spacing of 25 ns, and an average pile-up of up to 200 collisions per bunch crossing [1]. This value of pile-up presents a challenge for the experiments, as currently ATLAS and CMS have reached a typical number of concurrent interactions within the same bunch crossing (pile-up) of approximately 35 [2,3]. The pile-up at HL-LHC will pose a challenge to this method, as a significant fraction of the primary vertices will have a distance smaller than the resolution of the vertex detectors, making an association to the reconstructed physics objects impossible
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