Development of a timing detector for the TOTEM experiment at the LHC

Abstract

he LHC is at present the world's largest and highest-energy particle accelerator, hosted at CERN, the European particle physics laboratory near Geneva. The TOTEM experiment was designed to measure the total pp cross section and to study elastic scattering and diffractive dissociation at LHC. The protons that underwent elastic interaction are lightly deflected and, to detect them, TOTEM has installed silicon strip detectors at more than 200 m from the interaction point that can transversally approach the beam down to few millimetres, thanks to a movable piece of the vacuum chamber called Roman Pot.During the first period of operation of the LHC, the TOTEM run campaigns were accomplished during low luminosity dedicated data taking. However, to allow the investigation of rare phenomena, an upgrade program has been proposed by the TOTEM Collaboration, to make possible the data taking at higher luminosities. In particular, a cornerstone of the upgrade program is the inclusion of a fast timing detector in the experimental apparatus to improve the capability of the apparatus to work in high pileup conditions.The main topic of this thesis is the design and the characterization of a fast timing detector for high energy protons. After a survey of the most promising sensor technologies available for fast timing measurements, it was proved, thanks to an extensive campaign of tests using particle beams, that the needed resolution, below 100 ps, was achievable using diamond sensors. In particular, different approaches for the front-end electronics were investigated: some commercially available amplifiers and the timing detector designed by the HADES Collaboration were characterized.Then, a diamond detector, fully compliant with the TOTEM requirements, was designed, tested and prepared for the installation in the RP system. In parallel, 13Introduction other solutions were investigated, such as 3D graphitized diamond sensors and an amplitude dependent amplifier, designed to increase the signal to noise ratio: the gain of the amplifier is small for low amplitude input (noise) and higher in presence of a signal.In particular, the first chapter describes the TOTEM experiment and the main physics results obtained during the first run of the LHC. Then, the physics motivation and the technological challenges of the consolidation and upgrade programs are discussed. Particular attention is given to the impedance optimization of the Roman Pot, described in the second chapter. In fact, the Roman Pot creates a cavity inside the primary vacuum that can resonate at the passage of the beam.This resonance can introduce instabilities in the beam and can, in the worst cases, damage the detector because of the excessive heat generated. The Roman Pot has been optimized in this sense and two new shapes have been designed and realized and, only thanks to this optimization, the Roman Pot can be safely inserted at few millimetres from the beam even at the highest intensities foreseen for the LHC.In the third chapter, the properties of diamond are dis...

Diamond Detectors for Timing Measurements in High Energy Physics

“…The shape of the signal induced on the electrodes can be derived using the Shockley-Ramo theorem [22]. In particular, assuming a constant and uniform electric field in the crystal (or a regime of saturated velocity) and that the charge carriers drift with the same velocity, it can be shown [23] that the signal generated at the passage of a particle is:…”

“…This section describes the main concepts needed to design a front-end amplifier for a diamond detector, with particular focus on timing applications. More detailed studies are discussed in [23] and [35].…”

Development of a timing detector for the TOTEM experiment at the LHC

“…The optimization was focused on the improvement of the signal-to-noise ratio (SNR) keeping as fast as possible the signal. In fact, a quick rule of thumb to estimate the time precision of a detector is [1]:…”

Measurements of timing resolution of ultra-fast silicon detectors with the SAMPIC waveform digitizer

“…We start by considering the signal average in usually negligible for fast timing, the time walk is assumed to be corrected and the jitter depends on the noise and the slope of the signal as shown in Equation 2. More details can be found in chapter 6 of [30]. The jitter from the TCD is assumed to be uncorrelated.…”