A. Levin

Abstract Addressing the mass origin and properties of neutrinos is of strong interest to particle physics, baryogenesis and cosmology. Popular explanations involve physics beyond the standard model, for example, the dimension-5 Weinberg operator or heavy Majorana neutrinos arising from ‘seesaw’ models. The current best direct limits on the electron neutrino mass, derived from nuclei beta decay or neutrinoless double beta decay processes, are at the sub-electronvolt level. Here we propose a novel neutrino–neutrino collider where the neutrino beam is generated from TeV scale muon decays. Such collisions can happen between either neutrinos and anti-neutrinos, or neutrinos and neutrinos. We find that with a tiny integrated luminosity of about 10 −5 fb −1 we can already expect to observe direct neutrino anti-neutrino annihilation, <?CDATA $\nu \bar{\nu }\to {\rm{Z}}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ν</mml:mi> <mml:mover accent="true"> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> <mml:mo>→</mml:mo> <mml:mi mathvariant="normal">Z</mml:mi> </mml:math> , which also opens the door to explore neutrino related resonances <?CDATA $\nu \bar{\nu }\to {\rm{X}}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ν</mml:mi> <mml:mover accent="true"> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> <mml:mo>→</mml:mo> <mml:mi mathvariant="normal">X</mml:mi> </mml:math> . The low luminosity requirement can accommodate a relatively large emittance muon beam. Such a device would also allow for probing heavy Majorana neutrino and effective Majorana neutrino mass through ν ν → HH to a competitive level, for both electron and muon types.

An electron-muon collider with an asymmetric collision profile targeting multi-ab-1 integrated luminosity is proposed. This novel collider, operating at collision energies of, e.g., 20–200 GeV, 50–1000 GeV, and 100–3000 GeV, would be able to probe charged lepton flavor violation and measure Higgs boson properties precisely. The collision of an electron and muon beam leads to less physics background compared with either an electron-electron or a muon-muon collider, since electron-muon interactions proceed mostly through higher-order vector boson fusion and vector boson scattering processes. The asymmetric collision profile results in collision products that are boosted towards the electron beam side, which can be exploited to reduce beam-induced background from the muon beam to a large extent. With this in mind, one can imagine a lepton collider complex, starting from colliding order 10 GeV electron and muon beams for the first time in history and to probe charged lepton flavor violation, then to be upgraded to a collider with 50-100 GeV electron and 1-3 TeV muon beams to measure Higgs properties and search for new physics and finally to be transformed to a TeV-scale muon-muon collider. The cost should vary from order 100 million to a few billion dollars, corresponding to different stages, which make the funding situation more practical.

We consider a mechanism of dark matter production in the course of first order phase transition. We assume that there is an asymmetry between X- and anti-X-particles of dark sector. In particular, it may be related to the baryon asymmetry. We also assume that the phase transition is so strongly first order, that X-particles do not permeate into the new phase. In this case, as the bubbles of old phase collapse, X-particles are packed into Q-balls with huge mass defect. These Q-balls compose the present dark matter. We find that the required present dark matter density is obtained for the energy scale of the theory in the ballpark of 1-10 TeV. As an example we consider a theory with effective potential of one-loop motivated form.

The series of upgrades to the Large Hadron Collider, culminating in the High Luminosity Large Hadron Collider, will enable a significant expansion of the physics program of the CMS experiment. However, the accelerator upgrades will also make the experimental conditions more challenging, with implications for detector operations, triggering, and data analysis. The luminosity of the proton-proton collisions is expected to exceed $2-3\times10^{34}$~cm$^{-2}$s$^{-1}$ for Run 3 (starting in 2022), and it will be at least $5\times10^{34}$~cm$^{-2}$s$^{-1}$ when the High Luminosity Large Hadron Collider is completed for Run 4. These conditions will affect muon triggering, identification, and measurement, which are critical capabilities of the experiment. To address these challenges, additional muon detectors are being installed in the CMS endcaps, based on Gas Electron Multiplier technology. For this purpose, 161 large triple-Gas Electron Multiplier detectors have been constructed and tested. Installation of these devices began in 2019 with the GE1/1 station and will be followed by two additional stations, GE2/1 and ME0, to be installed in 2023 and 2026, respectively. The assembly and quality control of the GE1/1 detectors were distributed across several production sites around the world. We motivate and discuss the quality control procedures that were developed to standardize the performance of the detectors, and we present the final results of the production. Out of 161 detectors produced, 156 detectors passed all tests, and 144 detectors are now installed in the CMS experiment. The various visual inspections, gas tightness tests, intrinsic noise rate characterizations, and effective gas gain and response uniformity tests allowed the project to achieve this high success rate.

In the wake of a severe recession and a sluggish recovery, labor market slack cannot be gauged solely in terms of the conventional measure of the unemployment rate (that is, the number of individuals who are not working at all and actively searching for a job).Rather, assessments of the employment gap should reflect the incidence of underemployment (that is, people working part time who want a full-time job) and the extent of hidden unemployment (that is, people who are not actively searching but who would rejoin the workforce if the job market were stronger).In this paper, we examine the evolution of U.S. labor market slack and show that underemployment and hidden unemployment currently account for the bulk of the U.S. employment gap.Next, using state-level data, we find strong statistical evidence that each of these forms of labor market slack exerts significant downward pressure on nominal wages.Finally, we consider the monetary policy implications of the employment gap in light of prescriptions from Taylor-style benchmark rules.

Studying the longitudinally polarized fraction of ${W}^{\ifmmode\pm\else\textpm\fi{}}{W}^{\ifmmode\pm\else\textpm\fi{}}$ scattering at the LHC is crucial to examine the unitarization mechanism of the vector boson scattering amplitude through Higgs and possible new physics. We apply here for the first time a deep neural network classification to extract the longitudinal fraction. Based on fast simulation implemented with the Delphes framework, significant improvement from a deep neural network is found to be achievable and robust over all dijet mass region. A conservative estimation shows that a high significance of four standard deviations can be reached with the High-Luminosity LHC designed luminosity of $3000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$.

Triple-GEM detector technology was recently selected by CMS for a part of the upgrade of its forward muon detector system as GEM detectors provide a stable operation in the high radiation environment expected during the future High-Luminosity phase of the Large Hadron Collider (HL-LHC). In a first step, GEM chambers (detectors) will be installed in the innermost muon endcap station in the $1.6<\left|\eta\right|<2.2$ pseudo-rapidity region, mainly to control level-1 muon trigger rates after the second LHC Long Shutdown. These new chambers will add redundancy to the muon system in the $\eta$-region where the background rates are high, and the bending of the muon trajectories due to the CMS magnetic field is small. A novel construction technique for such chambers has been developed in such a way where foils are mounted onto a single stack and then uniformly stretched mechanically, avoiding the use of spacers and glue inside the active gas volume. We describe the layout, the stretching mechanism and the overall assembly technique of such GEM chambers.

Measuring longitudinally polarized vector boson scattering in the ZZ channel is a promising way to investigate unitarity restoration with the Higgs mechanism and to search for possible new physics. We investigated several deep neural network structures and compared their ability to improve the measurement of the longitudinal fraction ${\mathrm{Z}}_{\mathrm{L}}{\mathrm{Z}}_{\mathrm{L}}$. Using fast simulation with the Delphes framework, a clear improvement is found using a previously investigated ``particle-based'' deep neural network on a preprocessed dataset and applying principle component analysis to the outputs. A significance of around 1.7 standard deviations can be achieved with the integrated luminosity of $3000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ that will be recorded at the High-Luminosity LHC. The technique developed in this article is also useful to other LHC analyses involving helicity fraction measurement.

We consider Friedberg-Lee-Sirlin Q-balls in a (3+1)-dimensional model with vanishing scalar potential of one of the fields. The Q-ball is stabilized by the gradient energy of this field and carries scalar charge, over and beyond the global charge. The latter property is inherent also in a model with the scalar potential that does not vanish in some finite field region near the origin.

We project the performance of the ATLAS liquid argon endcap and forward calorimeters at the planned high luminosity LHC option HL-LHC by exposing small calorimeter modules of the electromagnetic, hadronic, and forward calorimeters to high intensity beams at IHEP/Protvino. The beam intensity extends well beyond the maximum expected for these calorimeters at HL-LHC. The signal reconstruction and calorimeter performance have been studied in full detail.

The high-luminosity phase of the Large Hadron Collider (HL-LHC) will result in ten times higher particle background than measured during the first phase of LHC operation. In order to fully exploit the highly-demanding operating conditions during HL-LHC, the Compact Muon Solenoid (CMS) Collaboration will use Gas Electron Multiplier (GEM) detector technology. The technology will be integrated into the innermost region of the forward muon spectrometer of CMS as an additional muon station called GE1∕1. The primary purpose of this auxiliary station is to help in muon reconstruction and to control level-1 muon trigger rates in the pseudo-rapidity region 1.6≤|η|≤2.2. The new station will contain trapezoidal-shaped GEM detectors called GE1∕1 chambers. The design of these chambers is finalized, and the installation is in progress during the Long Shutdown phase two (LS-2) that started in 2019. Several full-size prototypes were built and operated successfully in various test beams at CERN. We describe performance measurements such as gain, efficiency, and time resolution of these prototype chambers, developed after years of R&D, and summarize their behavior in different gas compositions as a function of the applied voltage.

During the first run, CMS collected and processed more than 10B data events and simulated more than 15B events. Up to 100k processor cores were used simultaneously and 100PB of storage was managed. Each month petabytes of data were moved and hundreds of users accessed data samples. In this document we discuss the operational experience from this first run. We present the workflows and data flows that were executed, and we discuss the tools and services developed, and the operations and shift models used to sustain the system. Many techniques were followed from the original computing planning, but some were reactions to difficulties and opportunities. We also address the lessons learned from an operational perspective, and how this is shaping our thoughts for 2015.

A model for thermopile detectors is developed using a MatLab based numerical simulation. The model uses geometry and physical parameters of thermopile materials as input data and calculates the main characteristics of the detector. The numerical results closely agree with experimentally determined parameters. The influence of several input parameters on the detector's performance is studied. Using this approach the output signal of the Dexter Research ST150 detector is improved by 30%. A new model of a CMOS based detector for gas analysis is optimized. The simulation results show significant improvement in the detector's performance when poly-Si/Al materials are substituted by n-poly-Si/p-poly-Si materials. The model predicts D* = 2.5/spl times/10/sup 8/ cmHz/sup 1/2//W with a time constant of 17 ms.

Abstract This chapter examines the evolution of long-run inflation expectations and models the stance of US monetary policy from 1960 to 1980. It begins by considering several distinct measures of long-run inflation expectations, which indicate that such expectations rose markedly during the late 1960s, remained elevated at that plateau through the mid-1970s, and then rose at an alarming pace from 1977 until mid-1980. The chapter then considers the stance of monetary policy in terms of the ex ante short-term real interest rate; that is, the federal funds rate less the Livingston Survey of one-year-ahead expected inflation. Next, it analyzes the behavior of real interest rates and shows that the course of monetary policy during the Great Inflation period can be represented as a series of stop–start episodes which occurred in 1968 to 1970, 1974 to 1976, and 1979 to 1980. In each case, policy tightening induced a contraction in economic activity, but that policy was not maintained long enough to induce a sustained decline in the inflation rate.

FRB/Global is a large-scale macroeconomic model developed and maintained by the Board&amp;#x27;s staff. This article provides a historical perspective on the development of the model, gives an overview of its structure, and highlights its dynamic properties with three simulation experiments: a reduction in U.S. government purchases; a depreciation of the U.S. dollar; and an increase in the price of oil exported by OPEC. The article illustrates other uses of FRB/Global by examining the spillover effects of fiscal and monetary policy under alternative European monetary policy regimes.

In recent years, many Low-Income Countries (LICs) have implemented substantial reforms to their monetary policy frameworks, but existing economic research has not provided a clear rationale to guide those efforts.In this paper we analyze the role of monetary policy frameworks in the propagation of aggregate shocks, using a large panel dataset of 79 LICs over the period 1990-2015 as well as event study analysis for a group of 28 sub-Saharan African LICs.We find highly significant differences in the propagation of external shocks between the LICs that target monetary aggregates or inflation compared to those that maintain rigid nominal exchange rates as a nominal anchor.We also find that the large surprise devaluation of the Central African Franc (CFA) in January 1994 had highly significant effects on the GDP growth of 10 CFA countries compared to 18 similar countries that were outside the CFA zone.Our empirical analysis provides strong support for the role of monetary policy frameworks in facilitating macroeconomic stability in LICs-a conclusion that is particularly relevant as LICs now face a multitude of similar shocks associated with the global COVID-19 pandemic.

In this paper it is shown that a measurement of the relative luminosity changes at the LHC may be obtained by analysing the currents drawn from the high voltage power supplies of the electromagnetic section of the forward calorimeter of the ATLAS detector. The method was verified with a reproduction of a small section of the ATLAS forward calorimeter using proton beams of known beam energies and variable intensities at the U-70 accelerator at IHEP in Protvino, Russia. The experimental setup and the data taking during a test beam run in April 2008 are described in detail. A comparison of the measured high voltage currents with reference measurements from beam intensity monitors shows a linear dependence on the beam intensity. The non-linearities are measured to be less than 0.5 % combining statistical and systematic uncertainties.

Gas Electron Multiplier (GEM) technology, in particular triple-GEM, was selected for the upgrade of the CMS endcap muon system following several years of intense effort on R&D. The triple-GEM chambers (GE1/1) are being installed at station 1 during the second long shutdown with the goal of reducing the Level-1 muon trigger rate and improving the tracking performance in the harsh radiation environment foreseen in the future LHC operation [1]. A first installation of a demonstrator system started at the beginning of 2017: 10 triple-GEM detectors were installed in the CMS muon system with the aim of gaining operational experience and demonstrating the integration of the GE1/1 system into the trigger. In this context, a dedicated Detector Control System (DCS) has been developed, to control and monitor the detectors installed and integrating them into the CMS operation. This paper presents the slice test DCS, describing in detail the different parts of the system and their implementation.

The CMS muon system in the region with 2.03<|η|<2.82 is characterized by a very harsh radiation environment which can generate hit rates up to 144 kHz/cm2 and an integrated charge of 8 C/cm2 over ten years of operation. In order to increase the detector performance and acceptance for physics events including muons, a new muon station (ME0) has been proposed for installation in that region. The technology proposed is Triple—Gas Electron Multiplier (Triple-GEM), which has already been qualified for the operation in the CMS muon system. However, an additional set of studies focused on the discharge probability is necessary for the ME0 station, because of the large radiation environment mentioned above. A test was carried out in 2017 at the Cern High energy AcceleRator Mixed (CHARM) facility, with the aim of giving an estimation of the discharge probability of Triple-GEM detectors in a very intense radiation field environment, similar to the one of the CMS muon system. A dedicated standalone Geant4 simulation was performed simultaneously, to evaluate the behavior expected in the detector exposed to the CHARM field. The geometry of the detector has been carefully reproduced, as well as the background field present in the facility. This paper presents the results obtained from the Geant4 simulation, in terms of sensitivity of the detector to the CHARM environment, together with the analysis of the energy deposited in the gaps and of the processes developed inside the detector. The discharge probability test performed at CHARM will be presented, with a complete discussion of the results obtained, which turn out to be consistent with measurements performed by other groups.

We propose a neutrino lepton collider where the neutrino beam is generated from TeV scale muon decays. Such a device would allow for a precise measurement of the W mass based on single W production [Formula: see text]. Although it is challenging to achieve high instantaneous luminosity with such a collider, we find that a total luminosity of 0.1[Formula: see text][Formula: see text] can already yield competitive physics results. In addition to a W mass measurement, a rich variety of physics goals could be achieved with such a collider, including W boson precision measurements, heavy leptophilic gauge boson searches and anomalous [Formula: see text] coupling searches. A neutrino lepton collider is both a novel idea in itself, and may also be a useful intermediate step, with less muon cooling required, towards the muon–muon collider already being pursued by the energy frontier community. A neutrino neutrino or neutrino proton collider may also be interesting future options for the high energy frontier.

We study the ionic distribution near a charged surface. A new method for performing Monte Carlo simulations in this geometry is discussed. A theory is then presented that allows us to accurately reproduce the density profiles obtained in the simulations. In the weak-coupling regime, a theory accounts for the ion-image interactions, leading to a modified Poisson-Boltzmann equation. When the correlations between the ions are significant, a strong-coupling theory is used to calculate the density profiles near the surface and a Poisson-Boltzmann equation with a renormalized boundary condition to account for the counterion distribution in the far-field.

The upgrade of the CMS detector for the high luminosity LHC (HL-LHC) will include gas electron multiplier (GEM) detectors in the end-cap muon spectrometer. Due to the limited supply of large area GEM detectors, the Korean CMS (KCMS) collaboration had formed a consortium with Mecaro Co., Ltd. to serve as a supplier of GEM foils with area of approximately 0.6 m2. The consortium has developed a double-mask etching technique for production of these large-sized GEM foils. This article describes the production, quality control, and quality assessment (QA/QC) procedures and the mass production status for the GEM foils. Validation procedures indicate that the structure of the Korean foils are in the designed range. Detectors employing the Korean foils satisfy the requirements of the HL-LHC in terms of the effective gain, response uniformity, rate capability, discharge probability, and hardness against discharges. No aging phenomena were observed with a charge collection of 82 mC cm−2. Mass production of KCMS GEM foils is currently in progress.

Abstract The Gas Electron Multiplier (GEM) detectors of the GE1/1 station of the CMS experiment have been operated in the CMS magnetic field for the first time on the 7 th of October 2021. During the magnetic field ramps, several discharge phenomena were observed, leading to instability in the GEM High Voltage (HV) power system. In order to reproduce the behavior, it was decided to conduct a dedicated test at the CERN North Area with the Goliath magnet, using four GE1/1 spare chambers. The test consisted in studying the characteristics of discharge events that occurred in different detector configurations and external conditions. Multiple magnetic field ramps were performed in sequence: patterns in the evolution of the discharge rates were observed with these data. The goal of this test is the understanding of the experimental conditions inducing discharges and short circuits in a GEM foil. The results of this test lead to the development of procedure for the optimal operation and performance of GEM detectors in the CMS experiment during the magnet ramps. Another important result is the estimation of the probability of short circuit generation, at 68 % confidence level, p short HV OFF = 0.42 -0.35 +0.94 % with detector HV OFF and p short HV OFF &lt; 0.49% with the HV ON. These numbers are specific for the detectors used during this test, but they provide a first quantitative indication on the phenomenon, and a point of comparison for future studies adopting the same procedure.

We conduct a systematic analysis of the costs and benefits of large-scale securities purchases, using the Federal Reserve's QE4 program as a concrete example.This program was initiated at the onset of the pandemic in March 2020 and continued for two years, leading to a doubling of the Fed's securities holdings to about $8.5 trillion as of March 2022.QE4 was initially aimed at mitigating strains in markets for Treasuries and agency mortgage-backed securities but was subsequently aimed more broadly at supporting market functioning and providing monetary stimulus.Nonetheless, QE4 did not have any notable benefits in reducing term premiums.Moreover, since the securities purchases were financed by expanding the Fed's short-term liabilities, QE4 amplified the interest rate risk associated with the publicly-held debt of the consolidated federal government.Our simulation analysis indicates that QE4 is likely to reduce the Federal Reserve's remittances to the U.S.

Abstract A temperature monitoring system based on fibre Bragg grating (FBG) fibre optic sensors has been developed for the gas electron multiplier (GEM) chambers of the Compact Muon Solenoid (CMS) detector. The monitoring system was tested in prototype chambers undergoing a general test of the various technological solutions adopted for their construction. The test lasted about two years and was conducted with the chambers being installed in the CMS detector and operated during regular experimental running. In this paper, we present test results that address the choice of materials and procedures for the production and installation of the FBG temperature monitoring system in the final GEM chambers.

We present analytical calculations, Finite Element Analysis modelling, and physical measurements of the interstrip capacitances for different potential strip geometries and dimensions of the readout boards for the GE2/1 triple-Gas Electron Multiplier detector in the CMS muon system upgrade. The main goal of the study is to find configurations that minimize the interstrip capacitances and consequently maximize the signal-to-noise ratio for the detector. We find agreement at the 1.5–4.8% level between the two methods of calculations and on the average at the 17% level between calculations and measurements. A configuration with halved strip lengths and doubled strip widths results in a measured 27–29% reduction over the original configuration while leaving the total number of strips unchanged. We have now adopted this design modification for all eight module types of the GE2/1 detector and will produce the final detector with this new strip design.

An uncooled linear array of 66 infrared elements has been designed, simulated, and fabricated using MEMS techniques. CMOS compatible poly-Silicon thermoelectric materials are utilized. Numerical simulations optimize the geometry and physical parameters for the thermopile materials. The pixel dimensions are 2.0 mm x 0.45 mm with 0.5 mm pitch. Excellent performance has been obtained in Nitrogen environment: D* = 1.2 x 10⁸ cm &radic;Hz/W; &iota; = 31 ms; and cross talk of &lt;15%. Measured performance is comparable to, and in some respects exceeds, the performance of thermopile linear arrays based on Bi and Sb materials. The arrays are packaged for integration with an existing dispersive infrared spectrometer.

Trials results of the universal berry-harvesting combine 'Uoonas-2000 in sea-buckthorn plantations are presented in the paper

We propose a neutrino lepton collider where the neutrino beam is generated from TeV scale muon decays. Such a device would allow for a precise measurement of the W mass based on single W production: nu l to W. Although it is challenging to achieve high instantaneous luminosity with such a collider, we find that a total luminosity of 0.1/fb can already yield competitive physics results. In addition to a W mass measurement, a rich variety of physics goals could be achieved with such a collider, including W boson precision measurements, heavy leptophilic gauge boson searches, and anomalous Znunu coupling searches. A neutrino lepton collider is both a novel idea in itself, and may also be a useful intermediate step, with less muon cooling required, towards the muon-muon collider already being pursued by the energy frontier community. A neutrino neutrino or neutrino proton collider may also be interesting future options for the high energy frontier.

Addressing the mass origin and properties of neutrinos is of strong interest to particle physics, baryogenesis and cosmology. Popular explanations involve physics beyond the standard model, for example, the dimension-5 Weinberg operator or heavy Majorana neutrinos arising from ``seesaw'' models. The current best direct limits on the electron neutrino mass, derived from nuclei beta decay or neutrinoless double beta decay processes, are at the sub-electronvolt level. Here we propose a novel neutrino neutrino collider where the neutrino beam is generated from TeV scale muon decays. Such collisions can happen between either neutrinos and anti-neutrinos, or neutrinos and neutrinos. We find that with a tiny integrated luminosity of about $10^{-5}$/fb we can already expect to observe direct neutrino anti-neutrino annihilation, $\nu\bar{\nu}\rightarrow {\rm Z}$, which also opens the door to explore neutrino related resonances $\nu\bar{\nu}\rightarrow {\rm X}$. The low luminosity requirement can accommodate a relatively large emittance muon beam. Such a device would also allow for probing heavy Majorana neutrino and effective Majorana neutrino mass through $\nu\nu\rightarrow {\rm H H}$ to a competitive level, for both electron and muon types.

An electron-muon collider with an asymmetric collision profile targeting multi-ab$^{-1}$ integrated luminosity is proposed. This novel collider, operating at collisions energies of e.g. 20-200 GeV, 50-1000 GeV and 100-3000 GeV, would be able to probe charged lepton flavor violation and measure Higgs boson properties precisely. The collision of an electron and muon beam leads to less physics background compared with either an electron-electron or a muon-muon collider, since electron-muon interactions proceed mostly through higher order vector boson fusion and vector boson scattering processes. The asymmetric collision profile results in collision products that are boosted towards the electron beam side, which can be exploited to reduce beam-induced background from the muon beam to a large extent. With this in mind, one can imagine a lepton collider complex, starting from colliding order 10 GeV electron and muon beams for the first time in history and to probe charged lepton flavor violation, then to be upgraded to a collider with 50-100 GeV electron and 1-3 TeV muon beams to measure Higgs properties and search for new physics, and finally to be transformed to a TeV scale muon muon collider. The cost should vary from order 100 millions to a few billion dollars, corresponding to different stages, which make the funding situation more practical.

The Phase-II high luminosity upgrade to the Large Hadron Collider (LHC) is planned for 2023, significantly increasing the collision rate and therefore the background rate, particularly in the high $\eta$ region. To improve both the tracking and triggering of muons, the Compact Muon Solenoid (CMS) Collaboration plans to install triple-layer Gas Electron Multiplier (GEM) detectors in the CMS muon endcaps. Demonstrator GEM detectors were installed in CMS during 2017 to gain operational experience and perform a preliminary investigation of detector performance. We present the results of triple-GEM detector performance studies performed in situ during normal CMS and LHC operations in 2018. The distribution of cluster size and the efficiency to reconstruct high $p_T$ muons in proton--proton collisions are presented as well as the measurement of the environmental background rate to produce hits in the GEM detector.

Abstract In 2018, a system of large-size triple-GEM demonstrator chambers was installed in the CMS experiment at CERN's Large Hadron Collider (LHC). The demonstrator's design mimicks that of the final detector, installed for Run-3. A successful Monte Carlo (MC) simulation of the collision-induced background hit rate in this system in proton-proton collisions at 13 TeV is presented. The MC predictions are compared to CMS measurements recorded at an instantaneous luminosity of 1.5 ×10 34 cm -2 s -1 . The simulation framework uses a combination of the FLUKA and GEANT4 packages. FLUKA simulates the radiation environment around the GE1/1 chambers. The particle flux by FLUKA covers energy spectra ranging from 10 -11 to 10 4 MeV for neutrons, 10 -3 to 10 4 MeV for γ's, 10 -2 to 10 4 MeV for e ± , and 10 -1 to 10 4 MeV for charged hadrons. GEANT4 provides an estimate of the detector response (sensitivity) based on an accurate description of the detector geometry, the material composition, and the interaction of particles with the detector layers. The detector hit rate, as obtained from the simulation using FLUKA and GEANT4, is estimated as a function of the perpendicular distance from the beam line and agrees with data within the assigned uncertainties in the range 13.7-14.5%. This simulation framework can be used to obtain a reliable estimate of the background rates expected at the High Luminosity LHC.