A High Granularity Timing Detector for the ATLAS Detector Phase-II Upgrade

Abstract

To boost the performance of the Large Hadron Collider and increase the potential of discoveries after 2027, the High Luminosity LHC project has been announced, with the aim of increasing the luminosity by a factor of 10 above the design value of the LHC. This will lead to an increase of the pileup interactions and will negatively impact the reconstruction of objects in the ATLAS detector, as well as its triggering performance. In particular at the forward region, where the inner detector has a lower momentum resolution and the electromagnetic calorimeter has a coarser granularity. Therefore, a high granularity timing detector has been proposed to mitigate the pile-up effect; complementing the inner tracker and providing a luminosity measurement, it will be located in front of the LAr end-cap calorimeter.The HGTD will cover the pseudo-rapidity region between 2.4 and 4.0, with two layers of double-sided silicon sensors that will provide a time resolution of 30 ps per track. Each readout cell has a cross-section of 1.3 mm x 1.3 mm ensuring a high granular detector with 3.7 million channels. To achieve the required high signal-to-noise ratio and provide sufficient gain, Low Gain Avalanche Detector technology was chosen.The general specifications and requirements of LGAD will be outlined, as well as the technical design and status of the project. The ongoing R&D effort to study the sensors, readout ASIC, and other components, supported by laboratory and test beam results will also be presented, in addition to some physics and performance results.

Analysis of the performance of low gain avalanche diodes for future particle detectors

“…The HPK-P2-W25-1 × 1 sensor (Ch2) irradiated by 0.8 × 10 15 n eq /cm 2 was measured at two different bias voltages (−500 V and −510 V) at −30 • Cand the resulted time resolutions were 40.19 and 40.80 ps for −500 and −510 V bias voltages, respectively. The HPK-P2-W25-2 × 2 sensor (Ch2) irradiated by 1.5 × 10 15 n eq /cm 2 was also measured at different bias voltages (from −500 V to −600 V) at −30 • C and figure 16 shows its calculated time resolution values as a function of the bias voltage. Time resolution of this specific LGAD was found to increase from 44 to 82 ps after irradiation.…”

“…In order to distinguish between the numerous interactions happening within a single bunch crossing at slightly different times, in the order of tens of picoseconds, certain aspects of the present detector technology must be improved, including granularity and read-out speed. This improvement will involve a complete upgrade of the ATLAS inner tracker, along with all its silicon sensors, as part of the transition towards "4D" tracking [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15].…”

“…Upgrades to CERN's ATLAS and CMS detectors, as well as the future High Energy Physics (HEP) experiments, must consider sensors with fast timing properties and increased radiation hardness [1][2][3][4][5][15][16][17][18]. To address the anticipated pile-up problem, several teams around the world began developing devices with fine granularity and good timing resolutions (in the order of tens of picoseconds).…”

“…This type of silicon sensor will be used in the timing detectors of both CMS and ATLAS. LGADs for ATLAS have a thickness of about 50 μm and a pad area of 1.3 × 1.3 mm 2 , and they have demonstrated the fulfilment of the required timing performance and radiation hardness [1][2][3][4][5][19][20][21][22][23][24][25].…”

Advances in nuclear detection and readout techniques

“…The high luminosity physics experiments increase the number of collisions in each bunch crosses dramatically. The Reproduced from [80] LGAD, invented by the Centro Nacional de Microelectronica (CNM), Barcelona, Spain, with the support of the CERN-RD50 community [82], can provide a time resolution better than 40 ps and becomes an excellent choice of solid-state timing detectors [83]. Combined with the 3D position information, LGAD-based detectors are considered suitable for tracking.…”