Diamond detectors for the TOTEM timing upgrade

Abstract

This paper describes the design and the performance of the timing detector developed by the TOTEM Collaboration for the Roman Pots (RPs) to measure the Time-Of-Flight (TOF) of the protons produced in central diffractive interactions at the LHC. The measurement of the TOF of the protons allows the determination of the longitudinal position of the proton interaction vertex and its association with one of the vertices reconstructed by the CMS detectors. The TOF detector is based on single crystal Chemical Vapor Deposition (scCVD) diamond plates and is designed to measure the protons TOF with about 50 ps time precision. This upgrade to the TOTEM apparatus will be used in the LHC run 2 and will tag the central diffractive events up to an interaction pileup of about 1. A dedicated fast and low noise electronics for the signal amplification has been developed. The digitization of the diamond signal is performed by sampling the waveform. After introducing the physics studies that will most profit from the addition of these new detectors, we discuss in detail the optimization and the performance of the first TOF detector installed in the LHC in November 2015.

The multilayer structure of protons

“…It is claimed in Ref. [1] that at the largest transferred momenta from 2.1 GeV 2 to 4 GeV 2 the power law favored by the quark counting rules can be adopted with the exponent of the order of 10. However, the measured angles are less than 3·10 −4 , i.e., too small for these rules to be applicable there.…”

“…More surprising is the behavior of the cross section at somewhat larger transferred momenta 0.7 < |t| < 3.83 GeV 2 (see Fig. 8 and Tables 9 and 10 in [1]). It shows also the exponential decrease albeit with the much smaller exponent…”

“…PACS numbers: 13.75.Cs; 13.85.Dz; 14.20.Dh The collaboration TOTEM published the data on the differential cross section of elastic scattering of protons at the energy 13 TeV [1,2]. It decreases approximately exponentially (with slight oscillations as seen in the insert in…”

Proton structure and hollowness from Lévy imaging of pp elastic scattering

“…The first and most precise measurements of the total, elastic and differential cross sections of elastic pp collisions has recently been performed by the TOTEM Collaboration at the Large Hadron Collider (LHC) at CERN at the highest energy frontier of √ s = 13 TeV (for recent TOTEM publications, see Refs. [10][11][12][13][14]). The large range in momentum transfer squared and very high precision of this set of data becomes a big challenge for a statistically acceptable description that is necessary for a reliable extraction of any physics information from such data with an appropriate statistical significance.…”

“…The TOTEM Collaboration has established [13,21] that at low values of the fourmomentum transfer squared t = (p 1 − p 3 ) 2 the differential elastic cross-section for pp collisions differs from a conventionally assumed naive exponential form, dσ/dt = A exp(−B|t|), -a subtle but significant deviation. A minimal way to parametrize such a deviation is to introduce a single parameter α into the exponent as dσ/dt = A exp [−(R 2 |t|) α ], to the leading order.…”