Federica Maria Simone

Abstract The High-Luminosity LHC will deliver proton-proton collisions at 5.0–7.5 times the nominal LHC luminosity, with an expected number of 140–200 pp-interactions per bunch crossing. To maintain the performance of muon triggering and reconstruction under high background, the forward part of the Muon spectrometer of the CMS experiment will be upgraded with Gas Electron Multipliers (GEM) and improved Resistive Plate Chambers detectors. Particularly challenging is the extension of the pseudorapidity of the muon system up to | η | < 2.8 with a 6-layer station, named ME0, that will be installed behind the new high granularity calorimeter and that will see particle rates up to 150 kHz/cm 2 and integrate a dose of 250 krad by the end of the High Luminosity phase of the LHC. In this contribution we will present the major design changes of the Triple-GEM detectors to adapt them for the harsh radiation environment and the high particle rate. We shall summarize the performance of prototype Triple-GEM detectors measured with X-rays and gamma at the CERN GIF++ irradiation facility.

The project of a Multi-TeV Muon Collider represents a unique opportunity to explore the high energy physics frontier and to measure with high precision the Higgs coupling with the other particles of the Standard Model as well as the trilinear and quadrilinear Higgs self-coupling, leading to a precise determination of the Higgs potential, in order to confirm the theoretical predictions of the SM and possibly to find evidences for new physics. One of the major challenges for the design and optimization of the technologies suitable for a Muon Collider experiment is represented by the high background induced by the decay of the muons coming from the beam. This contribution present the design of an innovative MPGD-based hadronic calorimeter (HCAL). The detector consists of a sampling calorimeter exploiting the Micro Pattern Gas Detectors (MPGDs) as active layers: MPGDs offer a fast and robust technology for high radiation environments and a high granularity for precise spatial measurements. Moreover, the detector is designed to optimize the jet reconstruction and for background suppression. The calorimeter is simulated using the Geant4 toolkit to support the detector R&D. The detector design and layout optimization supported by the simulation is described.

Abstract The present generation of Micro-Pattern Gaseous Detectors (MPGDs) are radiation hard detectors, capable of detecting effciently particle rates of several MHz/cm 2 , while exhibiting good spatial resolution (≤ 50 µm) and modest time resolution of 5-10 ns, which satisfies the current generation of experiments (High Luminosity LHC upgrades of CMS and ATLAS) but it is not sufficient for bunch crossing identification of fast timing systems at FCC-hh. Thanks to the application of thin resistive films such as Diamond-Like Carbon (DLC) a new detector concept was conceived: Fast Timing MPGD (FTM). In the FTM the drift volume of the detector has been divided in several layers each with their own amplification structure. The use of resistive electrodes makes the entire structure transparent for electrical signals. After some first initial encouraging results, progress has been slowed down due to problems with the wet-etching of DLC-coated polyimide foils. To solve these problems a more in-depth knowledge of the internal stress of the DLC together with the DLC-polyimide adhesion is required. We will report on the production of DLC films produced in Italy with Ion Beam Sputtering and Pulsed Laser Deposition, where we are searching to improve the adhesion of the thin DLC films, combined with a very high uniformity of the resistivity values.

Neural learning algorithms based on criterion optimization over differential manifolds have been devised over the few past years. Such learning algorithms mainly differ by the way the single learning steps are affected on the neural system's parameter space. The paper introduced a unifying view of these algorithms by recalling from the literature of differential geometry the concept of retraction on manifolds. It provides a general way of acting upon neural system's learnable parameters for learning criteria optimization purpose.

During Run-2 the Large Hadron Collider (LHC) has delivered instantaneous luminosities up to 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , being twice the design Luminosity. During the second Long Shutdown (LS2) the accelerator complex will be upgraded for the next Run-3 and anticipating the future High Luminosity LHC (HL- LHC) which will start taking data in 2025 with an instantaneous luminosity of 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> or even 7.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in the ultimate performance scenario. To cope with the corresponding increase in background rates in the forward muon system of CMS and to improve the trigger capabilities to keep the trigger rate at an acceptable level while not compromising the physics potential, the forward muon system of the CMS experiment will be upgraded with Gas Electron Multiplier (GEM) and Resistive Plate Chamber (RPC) detectors. In 2019 triple-GEM detectors will be installed in the first station of the muon detector, while a second station will be installed in 2022. Furthermore to enlarge the acceptance of the muon spectrometer a new station is considered to be installed directly behind the new High-Granularity Calorimeter during LS3 (2023-2024). We will present an overview of the CMS muon detector upgrade with Triple-GEM detectors: operational experience obtained from a test-slice installation in 2017, the production and quality control of the 144 Triple-GEM chambers for the first station, together with the design and prototyping of the Triple-GEM upgrades envisioned until 2024 along with the schedule for their production and quality control.

An estimate of environmental background hit rate on triple-GEM chambers is performed using Monte Carlo (MC) simulation and compared to data taken by test chambers installed in the CMS experiment (GE1/1) during Run-2 at the Large Hadron Collider (LHC). The hit rate is measured using data collected with proton-proton collisions at 13 TeV and a luminosity of 1.5$\times10^{34}$ cm$^{-2}$ s$^{-1}$. The simulation framework uses a combination of the FLUKA and Geant4 packages to obtain the hit rate. FLUKA provides the radiation environment around the GE1/1 chambers, which is comprised of the particle flux with momentum direction and energy spectra ranging from $10^{-11}$ to $10^{4}$ MeV for neutrons, $10^{-3}$ to $10^{4}$ MeV for $\gamma$'s, $10^{-2}$ to $10^{4}$ MeV for $e^{\pm}$, and $10^{-1}$ to $10^{4}$ MeV for charged hadrons. Geant4 provides an estimate of detector response (sensitivity) based on an accurate description of detector geometry, material composition and interaction of particles with the various detector layers. The MC simulated hit rate is estimated as a function of the perpendicular distance from the beam line and agrees with data within the assigned uncertainties of 10-14.5%. This simulation framework can be used to obtain a reliable estimate of background rates expected at the High Luminosity LHC.

Among the post-LHC generation of particle accelerators, the muon collider represents a unique machine with capability to provide very high energy leptonic collisions and to open the path to a vast and mostly unexplored physics programme. However, on the experimental side, such great physics potential is accompanied by unprecedented technological challenges, due to the fact that muons are unstable particles. Their decay products interact with the machine elements and produce an intense flux of background particles that eventually reach the detector and may degrade its performance. In this paper, we present technologies that have a potential to match the challenging specifications of a muon collider detector and outline a path forward for the future R&D efforts.

In this paper we report on the current status of studies on the expected performance for a detector designed to operate in a muon collider environment. Beam-induced backgrounds (BIB) represent the main challenge in the design of the detector and the event reconstruction algorithms. The current detector design aims to show that satisfactory performance can be achieved, while further optimizations are expected to significantly improve the overall performance. We present the characterization of the expected beam-induced background, describe the detector design and software used for detailed event simulations taking into account BIB effects. The expected performance of charged-particle reconstruction, jets, electrons, photons and muons is discussed, including an initial study on heavy-flavor jet tagging. A simple method to measure the delivered luminosity is also described. Overall, the proposed design and reconstruction algorithms can successfully reconstruct the high transverse-momentum objects needed to carry out a broad physics program.

The muon system of the CMS experiment has been instrumented with a new station of triple-GEM detectors in order to ensure redundancy in the pseudo-rapidity region 1.55< || <2.18, keeping the trigger rate at an acceptable level while not compromising the CMS physics potential in Run 3 of the LHC.The station, named GE1/1, provides two additional muon track hit measurements which will improve the muon tracking and triggering performance in combination with the existing CSC detectors.As the commissioning phase of the detector is ongoing, prompt assessment of the muon detection performance is crucial for adjusting the operating parameters of the detector and its electronics.This contribution will present a set of analysis tools developed for the detector performance monitoring based on tools common to all the CMS muon subdetectors.Validation of the analysis based on simulations will be discussed, together with preliminary results obtained from cosmic-ray events.

During Run 3 the LHC will deliver instantaneous luminosities in the range 5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> to 7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . To cope with the high background rates and to improve the trigger capabilities in the forward region, the muon system of the CMS experiment has been upgraded with two new stations of detectors (GE1/1), one in each endcap, based on triple-GEM technology. The system was installed in 2020 and consists of 72 ten-degree chambers, each made up of two layers of triple-GEM detectors. GE1/1 provides two additional muon hit measurements which will improve muon tracking and triggering performance. We report on the status of the ongoing commissioning phase of the detector and present preliminary results obtained from cosmic-ray events. We discuss detector and readout electronics operation, stability and performance, and preparation for Run 3 of the LHC.