The CMS Collaboration intends to pursue the study of central exclusive production (CEP) events, pp $\to$ pXp, at the High-Luminosity LHC (HL-LHC) by means of a new near-beam proton spectrometer. In CEP events, the state X is produced at central rapidities, and the scattered protons do not leave the beam pipe. The kinematics of X can be fully reconstructed from that of the protons, which gives access to final states otherwise not visible. CEP allows unique sensitivity to physics beyond the standard model, e.g. in the search for anomalous quartic gauge couplings, axion-like particles, and in general new resonances. CMS has been successfully operating the Precision Proton Spectrometer (PPS), initially a joint CMS and TOTEM project, since 2016. The present document outlines the physics interest of a new PPS at the HL-LHC, and explores its feasibility and expected performance. Discussions with the machine groups led to the identification of four locations suitable for the installation of movable proton detectors: at 196, 220, 234, and 420 m from the interaction point, on both sides. Acceptance studies indicate that having the beams cross in the vertical plane at the interaction point, as implemented after Long Shutdown 3, is preferable over the present horizontal crossing. This gives access to states X in the mass range 133 GeV$-$2.7 TeV with the stations at 196, 220, and 234 m. The lower mass limit becomes 43 GeV if the 420 m station is included, which makes it possible to study central exclusive production of the 125 GeV Higgs boson. This is a major improvement with respect to the current mass range of 350 GeV$-$2 TeV. The project and its costs can easily be staged; the 420 m station can be addressed in a second step. In summary, a new near-beam proton spectrometer for operation at the HL-LHC appears feasible. It would greatly extend the CMS physics reach with a limited investment.
We plan to add high precision tracking- and timing-detectors at z = +/- 240 m to CMS to study exclusive processes p + p -- p + X + p at high luminosity. This enables the LHC to be used as a tagged photon-photon collider, with X = l+l- and W+W-, and as a "tagged" gluon-gluon collider (with a spectator gluon) for QCD studies with jets. A second stage at z = 240 m would allow observations of exclusive Higgs boson production.
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 GE11. The primary purpose of this auxiliary station is to help in muon reconstruction and to control le…
The CMS detector at the LHC is in the final stages of preparation. The high resolution Electromagnetic Calorimeter, which consists of nearly 76000 lead tungstate crystals, will play a crucial role in the coming physics searches undertaken by CMS. The design, status, and initial performance of the calorimeter, in test beams and with cosmic rays, will be reviewed.
The Resistive Plate Chambers (RPCs) are employed in the CMS experiment at the LHC as dedicated trigger system both in the barrel and in the endcap. This note presents results of the radiation background measurements performed with the 2011 and 2012 proton-proton collision data collected by CMS. Emphasis is given to the measurements of the background distribution inside the RPCs. The expected background rates during the future running of the LHC are estimated both from extrapolated measurements and from simulation.
While the CMS experiment is currently harvesting LHC collision data at CERN, the performance of its electromagnetic calorimeter (ECAL) is being constantly monitored, and work has started to assess the need for changes to the detector to ensure an adequate performance for High-Luminosity LHC (HL-LHC) running, which is planned for 2022 and beyond. In this paper, results from CMS running, beam tests and laboratory measurements are combined to anticipate the detector performance evolution at the HL-LHC. Further, various R&D studies are illustrated, that will provide a useful choice for electromagn…
The CMS collaboration used the past year to greatly improve the level of detector readiness for the first collisions data. The acquired operational experience over this year, large gains in understanding the detector and improved preparedness for early physics will be instrumental in minimizing the time from the first collisions to first LHC physics. The following describes the status of the CMS experiment and outlines early physics plans with the first LHC data.
The electronics of the CMS Drift Tube (DT) chambers need to be replaced during Long Shutdown 3 to tolerate the High Luminosity LHC (HL-LHC) data taking conditions. The first DT prototypes of the HL-LHC electronics, the on-detector board (OBDT), have been installed in the DT chambers of one sector, out of 60 sectors, and integrated into the central data acquisition and trigger systems. The signals from the chambers are split and reach both the legacy and Phase-2 demonstrator chains, which will allow them to operate in parallel during LHC collisions.
The Level-1 trigger of the CMS experiment at CERN has been designed to select proton-proton interactions whose final state includes signatures of new physics in the form of high transverse energy electrons, photons, jets, or high missing transverse energy. The Level-1 trigger system process data in a pipeline fashion at a rate of 40 MHz, has a design latency of 128 bunch crossings and an output rate of 100 KHz. The design of this system is presented with emphasis on the calorimeter triggers. After a long period of testing and validation of its performance the Level-1 trigger system has been in…
With the planned addition of tracking information to the Compact Muon Solenoid (CMS) Level-1 trigger for the High-Luminosity Large Hadron Collider (HL-LHC), the trigger algorithms can be completely reconceptualized. We explore the feasibility of using particle flow-like reconstruction and pileup per particle identification (PUPPI) pileup mitigation at the hardware trigger level. This represents a new type of multi-subdetector pattern recognition challenge for the HL-LHC. We present proof-of-principle studies on both physics and hardware-resource performance of a prototype algorithm for use by …
The muon spectrometer of the CMS (Compact Muon Solenoid) experiment at the Large Hadron Collider (LHC) is equipped with a redundant system made of Resistive Plate Chambers and Drift Tube in barrel and RPC and Cathode Strip Chamber in endcap region. In this paper, the operations and performance of the RPC system during the first three years of LHC activity will be reported. The stability of RPC performance, such as efficiency, cluster size and noise, will be reported. Finally, the radiation background levels on the RPC system have been measured as a function of the LHC luminosity. Extrapolation…
In the upcoming years, with the upgrade of the LHC to higher luminosities, CMS will be subject to an increasing flux of particles, especially in its most forward region, at | η| > 1.6. To consolidate the muon spectrometer of CMS and increase redundancy, the CMS GEM collaboration proposes to instrument the 1.6 < | η| < 2.1 region, originally foreseen to be equipped with RPC, with Triple-GEM detectors. This technology has proven to remain efficient under high fluxes and meets the requirements of CMS. This work, using simulations, studies three track reconstruction algorithms intended to be insta…
The Resistive Plate Chambers detector system at the CMS experiment at the LHC provides robustness and redundancy to the muon trigger. A total of 1056 double-gap chambers cover the pseudo-rapidity region < 1.6. The main detector parameters and environmental conditions are constantly and closely monitored to achieve operational stability and high quality data in the harsh conditions of the second run period of the LHC with center-of-mass energy of 13 TeV. First results of overall detector stability with 2015 data and comparisons with data from the LHC RUN-1 period at 8 TeV are presented.
High-Luminosity running at the LHC, which is planned for 2022 and beyond, will imply an order of magnitude increase in radiation levels and particle fluences with respect to the present LHC running conditions. The performance evolution of the CMS electromagnetic calorimeter (ECAL), comprising 75,848 scintillating lead tungstate crystals, indicates that an upgrade of its endcaps will be needed for HL-LHC running, to ensure an adequate performance. Results from LHC collision periods, beam tests and laboratory measurements of proton-irradiated crystals are combined to predict the performance of t…
The CMS inner pixel detector system is planned to be replaced during the first phase of the LHC luminosity upgrade. The plans foresee an ultra low mass system with four barrel layers and three disks on either end. With the expected increase in particle rates, the electronic readout chain will be changed for fast digital signals. An overview of the envisaged design options for the upgraded CMS pixel detector is given, as well as estimates of the tracking and vertexing performance.
The second LHC long shutdown period (LS2) is an important opportunity for the CMS Resistive Plate Chambers (RPC) to complete their consolidation and upgrade projects. The consolidation includes detector maintenance for gas tightness, HV (high voltage), LV (low voltage) and slow control operation. All services for the RPC Phase-2 upgrade, namely RE3/1 and RE4/1, were anticipated for installation to LS2. This paper summarises the RPC system maintenance and upgrade activities.
The CMS Resistive Plate Chamber (RPC) system has been certified for 10 years of LHC operation. In the next years, during the High luminosity LHC (HL-LHC) phase, the LHC instantaneous luminosity will increase to a factor five more than the existing LHC luminosity. This will subject the present CMS RPC system to background rates and operating conditions much higher with respect to those for which the detectors have been designed. Those conditions could affect the detector properties and introduce nonrecoverable aging effects. A dedicated longevity test is set up in the CERN Gamma Irradiation Fac…
The LHC machine is planning an upgrade program, which will smoothly bring the instantaneous luminosity to about $5-7.5\times10^{34}~\mathrm{cm}^{-2}\mathrm{s}^{-1}$ in 2028, to possibly reach an integrated luminosity of 3000-4500 fb$^{-1}$ by the end of 2039. This High-Luminosity LHC scenario, HL-LHC, will require a preparation program of the LHC detectors known as Phase-2 upgrade. The current CMS Outer Tracker, already running beyond design specifications, and the recently installed CMS Phase-1 Pixel Detector will not be able to survive the HL-LHC radiation conditions. Thus, CMS will need com…
At the High Luminosity LHC (HL-LHC), the CMS experiment will face a harsh environment with a high instantaneous luminosity up to 7x10$^{34}$/cm$^2$/s corresponding to an average of 140-200 multiple proton-proton collisions per bunch crossing. The main goal of the CMS Level 1 (L1) trigger upgrade for the HL-LHC is to maintain trigger thresholds that are as low as possible and comparable to those currently in use at the LHC, and to possibly include new triggers that were not feasible at the LHC. This will be achieved by upgrading the detector readout electronics, to allow a much larger L1 trigge…
The 2009 run provided the first proton-proton collisions from the Large Hadron Collider (LHC) at center of mass energies of 900 GeV and 2.36 TeV. The Compact Muon Solenoid (CMS) experiment has recorded a large sample of minimum bias events from these collisions. We present results from the all silicon tracking detectors from this run. The performance of the tracker and track reconstruction algorithms are considered including signal-to-noise, efficiencies and comparisons to simulation for track parameter and resonance reconstruction performance.
The strategies for and the performance of the CMS tracker alignment during the 2021-2022 LHC commissioning preceding the Run 3 data-taking period are described. The results of the very first tracker alignment after the pixel reinstallation, performed with cosmic ray muons recorded with the solenoid magnet off are presented. Also, the performance of the first alignment of the commissioning period with collision data events, collected at center-of-mass energy of 900 GeV, is presented. Finally, the tracker alignment effort during the final countdown to LHC Run 3 is discussed.
The CMS experiment collected around 150 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}$ = 13 TeV during the Run-2 data taking period of LHC. The CMS RPC system provided redundant information for robust muon triggering, reconstruction and identification. To ensure stable data taking, the CMS RPC collaboration has performed detector operation, calibration and performance studies. After the end of Run-2, it was started the second LHC long shutdown period (LS2), an important opportunity for maintenance and preparation for the next data taking period (Run-3) and the installation of services…
We discuss a CMS eXtension for Studying Energetic Neutrinos (CMS-XSEN). Neutrinos at the LHC are abundant and have unique features: their energies reach out to the TeV range, and the contribution of the τ flavour is sizeable. The measurement of their interaction cross sections has much physics potential. The pseudorapity range 4<|η|<5 is of particular interest since leptonic W decays provide an additional contribution to the neutrino flux from b and c production. A modest detector of 4.1x$10^{27}$ nucleons/cm$^{2}$, placed in the LHC tunnel, 25 m from the interaction point, around the focusing…
The Precision Proton Spectrometer (PPS) started operating in 2016 and has collected more than 110 fb$^{-1}$ of data over the course of the LHC Run 2, now fully available for physics analysis. This contribution covers the key features of the PPS alignment and optics calibration, which have been developed from scratch. The reconstructed proton distributions, the performance of the PPS simulation and finally the validation of the full reconstruction chain with physics data (dilepton events) are also illustrated.
The CMS experiment, located at the Large Hadron Collider (LHC) in CERN, has a redundant muon system composed by three different gaseous detector technologies: Cathode Strip Chambers (in the forward regions), Drift Tubes (in the central region), and Resistive Plate Chambers (both its central and forward regions). All three are used for muon reconstruction and triggering. The CMS RPC system confers robustness and redundancy to the muon trigger. The RPC system operation in the challenging background and pileup conditions of the LHC environment is presented. The RPC system provides information to …
A wealth of physics results have already been obtained from the LHC, due to the excellent performance of the collider and its experiments. Even more results are expected to be achievable in the phase of the high-luminosity LHC (HL-LHC). It is foreseen to deliver a ten times higher LHC design luminosity resulting in about 4000 fb-1 within ten years of operation. The upgrade of the LHC is driven by the prospect to observe and measure rare processes. High particle production rates and radiation doses result in a challenging environment for the collider experiments. The ATLAS and CMS experiments a…
The first LHC pp collisions at centre-of-mass energies of 0.9 and 2.36 TeV were recorded by the CMS detector in December 2009. The trajectories of charged particles produced in the collisions were reconstructed using the all-silicon Tracker and their momenta were measured in the 3.8 T axial magnetic field. Results from the Tracker commissioning are presented including studies of timing, efficiency, signal-to-noise, resolution, and ionization energy. Reconstructed tracks are used to benchmark the performance in terms of track and vertex resolutions, reconstruction of decays, estimation of ioniz…
The strategies for and the performance of the CMS silicon tracking system alignment during the 2015-2018 data-taking period of the LHC are described. The alignment procedures during and after data taking are explained. Alignment scenarios are also derived for use in the simulation of the detector response. Systematic effects, related to intrinsic symmetries of the alignment task or to external constraints, are discussed and illustrated for different scenarios.
The Compact Muon Solenoid (CMS) is one of two general-purpose detectors that reconstruct the products of high energy particle interactions at the Large Hadron Collider at CERN. The silicon pixel detector is the innermost component of the CMS tracking system. It determines the trajectories of charged particles originating from the interaction region with high resolution enabling precise momentum and impact parameter measurements in the tracker. It is designed to operate in the high particle density environment of the LHC. The calibration of the pixel detector plays an important role in its perf…
The CMS electromagnetic calorimeter (ECAL) is a high-resolution, hermetic, and homogeneous calorimeter made of 75,848 scintillating lead tungstate crystals. Following the discovery of the Higgs boson, the CMS ECAL is at the forefront of precision measurements and the search for new physics in data from the LHC, which recently began producing collisions at the unprecedented energy of 13 TeV. The exceptional precision of the CMS ECAL, as well as its timing performance, are invaluable tools for the discovery of new physics at the LHC Run 2. The excellent performance of the ECAL relies on precise …
As part of the Phase II upgrade program, the Compact Muon Solenoid (CMS) detector will incorporate a new timing layer designed to measure minimum ionizing particles (MIPs) with a time resolution of $\sim$30 ps. Precision timing will mitigate the impact of the challenging levels of pileup expected at the High Luminosity LHC. The time information assigned to each track will enable the use of 4D-vertexing which will render a 5-fold pile-up reduction, thus recovering the current conditions. Precision timing will also enable new time-based isolations and improved $b$-tagging algorithms. All of this…
The high pseudorapidity ($η$) region of the Compact Muon Solenoid (CMS) muon system is covered by Cathode Strip Chambers only and lacks redundant coverage despite the fact that it is a challenging region for muons in terms of backgrounds and momentum resolution. During the annual Year-End Technical Stops 2022 & 2023, two new layers of improved Resistive Plate Chambers (iRPC) will be added, RE3/1 & RE4/1, which will completely cover the region of $1.8 < |η| < 2.4$ in the endcap. Thus, the additional new chambers will lead to increase efficiency for both trigger and offline reconstruction in the…
Charged hadron production in hadron-hadron collisions with longitudinal momentum fraction Feynman-x, x_F, between 0.1 and 0.9 has not been measured above square root s = 63 GeV at the CERN Intersecting Storage Rings. I discuss a way to measure this at the Large Hadron Collider at square root s = 13 TeV, which is 40,000 times higher in equivalent fixed target energy, and important for understanding cosmic ray showers.
The central component of the CMS detector is the largest silicon tracker ever built. The precise alignment of this complex device is a formidable challenge, and only achievable with a significant extension of the technologies routinely used for tracking detectors in the past. This article describes the full-scale alignment procedure as it is used during LHC operations. Among the specific features of the method are the simultaneous determination of up to 200,000 alignment parameters with tracks, the measurement of individual sensor curvature parameters, the control of systematic misalignment ef…
The High Luminosity LHC (HL-LHC) will integrate 10 times more luminosity than the LHC, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry, and hallmarks the issue for future colliders. As part of its HL-LHC upgrade program, the CMS collaboration is designing a High Granularity Calorimeter to replace the existing endcap calorimeters. It features unprecedented transverse and longitudinal segmentation for both electromagnetic (ECAL) and hadronic (HCAL) compartments. This will facilitate particle-flow calorimetry, where the fine …
With the High Luminosity LHC upgrades, incorporating tracking information into the CMS Level-1 trigger becomes necessary in order to maintain a manageable trigger rate and good trigger performance e.g. to retain thresholds for electroweak physics. The main challenges Level-1 track finding faces are the large data throughput from the detector at a collision rate of 40 MHz and a 4 microsecond latency budget to reconstruct charged particle tracks with sufficiently low transverse momentum to be used in the Level-1 trigger decision. Dedicated all-FPGA hardware systems with time-multiplexed architec…
The electromagnetic ealorimeter (ECAL) of the CMS detector has played an important role in the physics program of the experiment, delivering outstanding performance throughout data taking. The High-Luminosity LHC will pose new challenges. The four to five-fold increase of the number of interactions per bunch crossing will require superior time resolution and noise rejection capabilities. For these reasons the electronics readout has been completely redesigned. A dual gain trans-impedance amplifier and an ASIC providing two 160 MHz ADC channels, gain selection, and data compression will be used…
The High Luminosity LHC (HL-LHC) will integrate 10 times more luminosity than the LHC, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry, and hallmarks the issue for future colliders. As part of its HL-LHC upgrade program, the CMS collaboration is designing a High Granularity Calorimeter to replace the existing endcap calorimeters. It features unprecedented transverse and longitudinal segmentation for both electromagnetic (ECAL) and hadronic (HCAL) compartments. This will facilitate particle-flow calorimetry, where the fine …
The CMS detector at the CERN LHC features a silicon pixel detector as its innermost subdetector. The original CMS pixel detector has been replaced with an upgraded pixel system (CMS Phase-1 pixel detector) in the extended year-end technical stop of the LHC in 2016/2017. The upgraded CMS pixel detector is designed to cope with the higher instantaneous luminosities that have been achieved by the LHC after the upgrades to the accelerator during the first long shutdown in 2013-2014. Compared to the original pixel detector, the upgraded detector has a better tracking performance and lower mass with…
During the High Luminosity LHC, the CMS detector will need charged particle tracking at the hardware trigger level to maintain a manageable trigger rate and achieve its physics goals. The tracklet approach is a track-finding algorithm based on a road-search algorithm that has been implemented on commercially available FPGA technology. The tracklet algorithm has achieved high performance in track-finding and completes tracking within 3.4 $μ$s on a Xilinx Virtex-7 FPGA. An overview of the algorithm and its implementation on an FPGA is given, results are shown from a demonstrator test stand and s…
The Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) is undergoing an extensive Phase II upgrade program to prepare for the challenging conditions of the High-Luminosity LHC (HL-LHC). A new timing layer is designed to measure minimum ionizing particles (MIPs) with a time resolution of 30 ps and a hermetic coverage up to a pseudo-rapidity of $|η|$ = 3. This MIP Timing Detector(MTD) will consist of a central barrel region based on LYSO:Ce crystals read out with SiPMs and two end-caps instrumented with radiation-tolerant Low Gain Avalanche Diodes (LGADs). The precision…
The challenging conditions of the High-Luminosity LHC require tailored hardware designs for the trigger and data acquisition systems. The Apollo platform features a "Service Module" with a powerful system-on-module computer that provides standard ATCA communications and application-specific "Command Module"s with large FPGAs and high-speed optical fiber links. The CMS version of Apollo will be used for the track finder and the pixel readout. It features up to two large FPGAs and more than 100 optical links with speeds up to 25\,Gb/s. We study carefully the design and performance of the board b…
The two Zero Degree Calorimeters (ZDCs) of the CMS experiment are located at $\pm 140~$m from the collision point and detect neutral particles in the $|η| > 8.3$ pseudorapidity region. This paper presents a study on the performance of the ZDC in the 2016 pPb run. The response of the detectors to ultrarelativistic neutrons is studied using in-depth Monte Carlo simulations. A method of signal extraction based on template fits is presented, along with a dedicated calibration procedure. A deconvolution technique for the correction of overlapping collision events is discussed.
In preparation for the High Luminosity LHC, the entire tracker detector of the CMS experiment will be exchanged as part of the Phase-2 Upgrade. The new Outer Tracker will comprise approximately 13,000 silicon sensor modules, of which 7608 are "2S modules" consisting of two parallel mounted silicon strip sensors, and 5592 are "PS modules" consisting of one pixel and one strip sensor in a single module. These modules provide tracking information to the Level 1 trigger by correlating the hit information of both sensor layers, allowing discrimination of particle tracks by their transverse momentum…
As part of its HL-LHC upgrade program, CMS is developing a High Granularity Calorimeter (HGCAL) to replace the existing endcap calorimeters. The HGCAL will be realised as a sampling calorimeter, including an electromagnetic compartment comprising 28 layers of silicon pad detectors with pad areas of 0.5 - 1.0 cm2 interspersed with absorbers. Prototype modules, based on 6-inch hexagonal silicon pad sensors with 128 channels, have been constructed and include many of the features required for this challenging detector. In 2016, beam tests of sampling configurations made from these modules have be…
The CMS muon system at the LHC is built of different detector technologies. The measurement of the background hit rates in the different muon detectors during the LHC Run-2 is of prime importance for an assessment of the longevity of the chambers and their on-board electronics, and therefore for the expected performance of the system at HL-LHC. Moreover, an accurate modelling of the backgrounds using simulations is also critical, as an estimation of the expected radiation background for the Phase-2 upgrade can only rely on Montecarlo-based predictions in the regions where new detectors are bei…
I describe a possible Forward Multiparticle Spectrometer (FMS) that could be installed downstream of the superconducting recombination dipole D1 in Run 4, from z = 96 m - 126 m to measure multi-TeV hadron spectra in low luminosity p + p collisions at Rt(s) = 14 TeV, as well as p + O and O + O collisions as relevant for cosmic ray showers. Light antinuclei and charmed hadrons at high Feynman xF can be measured, both of importance for astrophysics. At the full high luminosity HL-LHC a search for new long-lived neutral particles (LLPs) decaying in a 20 m long, 70 cm diameter vacuum pipe to visibl…
