Fabio Ravera

In this paper we report on the timing resolution obtained in a beam test with pions of 180 GeV/c momentum at CERN for the first production of 45 µm thick Ultra-Fast Silicon Detectors (UFSD). UFSD are based on the Low-Gain Avalanche Detector (LGAD) design, employing n-on-p silicon sensors with internal charge multiplication due to the presence of a thin, low-resistivity diffusion layer below the junction. The UFSD used in this test had a pad area of 1.7 mm2. The gain was measured to vary between 5 and 70 depending on the sensor bias voltage. The experimental setup included three UFSD and a fast trigger consisting of a quartz bar readout by a SiPM. The timing resolution was determined by doing Gaussian fits to the time-of-flight of the particles between one or more UFSD and the trigger counter. For a single UFSD the resolution was measured to be 34 ps for a bias voltage of 200 V, and 27 ps for a bias voltage of 230 V. For the combination of 3 UFSD the timing resolution was 20 ps for a bias voltage of 200 V, and 16 ps for a bias voltage of 230 V.

Low-Gain Avalanche Diodes (LGAD) are silicon detectors with output signals that are about a factor of 10 larger than those of traditional sensors. In this paper we analyze how the design of LGAD can be optimized to exploit their increased output signal to reach optimum timing performances. Our simulations show that these sensors, the so-called Ultra-Fast Silicon Detectors (UFSD), will be able to reach a time resolution factor of 10 better than that of traditional silicon sensors.

In this contribution we will review the progresses toward the construction of a tracking system able to measure the passage of charged particles with a combined precision of ∼10 ps and ∼10 μm, either using a single type of sensor, able to concurrently measure position and time, or a combination of position and time sensors.

Is it possible to design a detector able to concurrently measure time and position with high precision? This question is at the root of the research and development of silicon sensors presented in this contribution. Silicon sensors are the most common type of particle detectors used for charged particle tracking, however their rather poor time resolution limits their use as precise timing detectors. A few years ago we have picked up the gantlet of enhancing the remarkable position resolution of silicon sensors with precise timing capability. I will be presenting our results in the following pages.

We review the progress toward the development of a novel type of silicon detectors suited for tracking with a picosecond timing resolution, the so called Ultra-Fast Silicon Detectors. The goal is to create a new family of particle detectors merging excellent position and timing resolution with GHz counting capabilities, very low material budget, radiation resistance, fine granularity, low power, insensitivity to magnetic field, and affordability. We aim to achieve concurrent precisions of ∼ 10 ps and ∼ 10 μm with a 50 μm thick sensor. Ultra-Fast Silicon Detectors are based on the concept of Low-Gain Avalanche Detectors, which are silicon detectors with an internal multiplication mechanism so that they generate a signal which is factor ∼ 10 larger than standard silicon detectors.

The CMS-TOTEM Precision Proton Spectrometer (CT-PPS) detector will be installed in Roman pots (RP) positioned on either side of CMS, at about 210 m from the interaction point. This detector will measure leading protons, allowing detailed studies of diffractive physics and central exclusive production in standard LHC running conditions. An essential component of the CT-PPS apparatus is the tracking system, which consists of two detector stations per arm equipped with six 3D silicon pixel-sensor modules, each read out by six PSI46dig chips. The front-end electronics has been designed to fulfill the mechanical constraints of the RP and to be compatible as much as possible with the readout chain of the CMS pixel detector. The tracking system is currently under construction and will be installed by the end of 2016. In this contribution the final design and the expected performance of the CT-PPS tracking system is presented. A summary of the studies performed, before and after irradiation, on the 3D detectors produced for CT-PPS is given.

The Ultra Fast Silicon Detectors (UFSD) are a novel concept of silicon detectors based on the Low Gain Avalanche Diode (LGAD) technology, which are able to obtain time resolution of the order of few tens of picoseconds. First prototypes with different geometries (pads/pixels/strips), thickness (300 and 50 μm) and gain (between 5 and 20) have been recently designed and manufactured by CNM (Centro Nacional de Microelectrónica, Barcelona) and FBK (Fondazione Bruno Kessler, Trento). Several measurements on these devices have been performed in laboratory and in beam test and a dependence of the gain on the temperature has been observed. Some of the first measurements will be shown (leakage current, breakdown voltage, gain and time resolution on the 300 μm from FBK and gain on the 50 μm-thick sensor from CNM) and a comparison with the theoretically predicted trend will be discussed.

During the high luminosity phase of the LHC (HL-LHC), the machine is expected to deliver an instantaneous luminosity of 5×1034cm−2s−1. A total of 3000 fb−1 of data is foreseen to be delivered, with the opening of new physics potential for the LHC experiments, but also new challenges from the point of view of both detector and electronics capabilities and radiation hardness. In order to maintain its physics reach, CMS will build a new Tracker, including a completely new Pixel Detector and Outer Tracker. The ongoing R&D activities on both pixel and strip sensors will be presented. The present status of the Inner and Outer Tracker projects will be illustrated, and the possible perspectives will be discussed.

The development of Low-Gain Avalanche Diodes (LGADs) has made possible to manufacture silicon detectors with output signals that are about a factor of 10 larger than those of traditional sensors.This increased output brings many benefits such as the possibility of developing thin detectors with large enough signals, a good immunity towards low charge collection efficiency and it is key for excellent timing capabilities.In this paper, we report on the development of silicon sensors based on the LGAD design optimized to achieve excellent timing performance, the so-called Ultra-Fast Silicon Detectors (UFSDs).In particular, we demonstrate the possibility of obtaining ultra-fast silicon detectors with time resolution of less than 30 picosecond.

to the Level-1 trigger, allowing trigger rates to be kept at a sustainable level without sacrificing physics potential. For this, the OT will be made of modules that have two closely spaced sensors read out by the same electronics, which can correlate hits in the two sensors creating short track segments called ”stubs”. The stubs will be used for tracking at 40 MHz. In this contribution, the design of the CMS Phase-2 OT, the technological choices, and highlights of research and development activities are reported.

to the Level-1 trigger, allowing trigger rates to be kept at a sustainable level without sacrificing physics potential. For this, the OT will be made of modules that have two closely spaced sensors read out by the same electronics, which can correlate hits in the two sensors creating short track segments called ”stubs”. The stubs will be used for tracking at 40 MHz. In this contribution, the design of the CMS Phase-2 OT, the technological choices, and highlights of research and development activities are reported.

The High-Luminosity LHC (HL-LHC) upgrade of the CMS pixel detector will require the development of novel pixel sensors which can withstand the increase in instantaneous luminosity to L=5×1034 cm−2s−1 and collect ∼ 3000 fb−1 of data. The innermost layer of the pixel detector will be exposed to doses of about 1016 neq/ cm2. Hence, new pixel sensors with improved radiation hardness need to be investigated. A variety of silicon materials (Float-zone, Magnetic Czochralski and Epitaxially grown silicon), with thicknesses from 50 μm to 320 μm in p-type and n-type substrates have been fabricated using single-sided processing. The effect of reducing the sensor active thickness to improve radiation hardness by using various techniques (deep diffusion, wafer thinning, or growing epitaxial silicon on a handle wafer) has been studied. The results for electrical characterization, charge collection efficiency, and position resolution of various n-on-p pixel sensors with different substrates and different pixel geometries (different bias dot gaps and pixel implant sizes) will be presented.

In this paper we report on the timing resolution of the first production of 50 micro-meter thick Ultra-Fast Silicon Detectors (UFSD) as obtained in a beam test with pions of 180 GeV/c momentum. UFSD are based on the Low-Gain Avalanche Detectors (LGAD) design, employing n-on-p silicon sensors with internal charge multiplication due to the presence of a thin, low-resistivity diffusion layer below the junction. The UFSD used in this test belongs to the first production of thin (50 {\mu}m) sensors, with an pad area of 1.4 mm2. The gain was measured to vary between 5 and 70 depending on the bias voltage. The experimental setup included three UFSD and a fast trigger consisting of a quartz bar readout by a SiPM. The timing resolution, determined comparing the time of arrival of the particle in one or more UFSD and the trigger counter, for single UFSD was measured to be 35 ps for a bias voltage of 200 V, and 26 ps for a bias voltage of 240 V, and for the combination of 3 UFSD to be 20 ps for a bias voltage of 200 V, and 15 ps for a bias voltage of 240 V.

The CMS-TOTEM Precision Proton Spectrometer allows extending the LHC physics program by measuring protons in the very forward regions of CMS.Tracking and timing detectors have been installed along the beam pipe at ∼ 210 m from the CMS interaction point on both sides of the LHC tunnel.The tracking system consists of a station of silicon strip detectors and one of silicon pixel detectors on each side.The latter is composed of six planes of 3D silicon pixel sensors bumpbonded to the PSI46dig ROC developed for the CMS Phase I Pixel Tracker upgrade.A track resolution of ∼ 10 µm is obtained.The future goal is to replace the present strip stations with pixel ones in order to ensure better multi-track reconstruction.Each timing station is made of three planes of diamond detectors and one plane equipped with an Ultra-Fast Silicon Detector (UFSD).A timing resolution of a few tens of picoseconds can be achieved with the present detector; a large R&D effort is ongoing to reach the 10 ps target resolution.This contribution describes the hardware characteristics and the present status of the CT-PPS project.The operational experience during the 2017 data taking is also presented.

The LHC will be upgraded to the High Luminosity LHC (HL-LHC) in the late 2020s in order to reach an instantaneous luminosity as high as 7 × 10 34 cm -2 s -1 , hence increasing the discovery potential of the machine.In order to preserve physics object performance in spite of large pile-up, the CMS detector will be significantly upgraded.A key component of the upgrade is the Outer Tracker detector that will be able to identify tracks with transverse momentum above ∼ 2 GeV/c and provide them to the Track Finder boards, thus maintaining manageable trigger rates and good performance.One of the main challenges of the Level-1 track finding is being able to reconstruct charged particles trajectories from a 40 MHz collision rate with a few microsecond latency budget.Dedicated FPGA hardware systems have been developed for track finding to address this challenge.Another stringent requirement on the Tracker DAQ system is set by the unprecedented number of channels, reaching two billions for the Inner Tracker only.To handle this, the Tracker DAQ back-end boards will be equipped with commercial CPUs that will guarantee the system scalability and ensure an effective monitoring of the detector conditions.The DAQ proposal to handle this distributed computational power as well as the design choices of the Level-1 track finding are presented.

Based on curvature representation, a fuzzy Kohonen self-organizing feature mapping is combined with the fuzzy delta rule to recognize partially occluded objects. Because of learning and tolerant performance as well as fuzzy membership function, the fuzzy hybrid neural networks can recognize the objects with higher precision.