Forward physics with CMS at the LHC covers a wide range of physics subjects, including very low-x QCD, underlying event and multiple interactions characteristics, gamma-mediated processes, shower development at the energy scale of primary cosmic ray interactions with the atmosphere, diffraction in the presence of a hard scale and even MSSM Higgs discovery in central exclusive production. We describe the forward detector instrumentation around the CMS interaction point and present selected feasibility studies to illustrate their physics potential.
The Compact Muon Solenoid (CMS) Experiment is a general purpose particle detector experiment located at the Large Hadron Collider (LHC) at CERN. In 2008, the LHC beam was commissioned and successfully steered through the CMS detector. First results from CMS with beam data are described, focusing on detector commissioning with beam data, from beam halo studies with the endcap muon system to displays of "beam splash" events, in which the proton beam was stopped by an upstream collimator.
This paper describes latest results on lepton (electron, muon and tau) and photon particle identification at the ATLAS and CMS experiments, with emphasis on how the particle identification can be validated and its performance determined using early LHC data.
Charm physics has been established at the LHC based on several high-precision measurements. The future of charm physics at the LHC experiments is discussed in detail. The bulk of the charm physics programme will be performed by LHCb and the LHCb upgrade. In particular, the impact of the LHCb upgrade on mixing and \CP violation measurements is presented.
A brief review of the discovery potential of the ATLAS and CMS experiments to search for signals from extra dimensions in different luminosity scenarios is given.
The capabilities of the ATLAS, CMS and LHCb detectors to reconstruct jets at forward rapidities (|η|> 3) in p-p collisions at the CERN Large Hadron Collider are reviewed. The QCD and Higgs physics motivations for such measurements are summarised. Details are given on studies that provide information on the parton structure and evolution at small values of fractional momenta in the proton.
Natural SUSY suggests the existence of light stop quarks, accessible at the LHC, which are the focus of a dedicated CMS search program. I present two inclusive CMS searches that look for TeV scale colored sparticles in final states with jets, b-tagged jets and missing transverse energy performed using up to 19.4fb-1 of 8TeV LHC proton-proton data. No deviation from the Standard Model was observed in these searches, and the implications for this was shown for several simplified model scenarios and phenomenological MSSM.
Selected results of searches for neutral long-lived particles with displaced and delayed jets, trackless jets and emerging jets, as well as displaced muons, obtained with data recorded at a centre-of-mass energy of 13 TeV by the ATLAS and CMS Collaborations during LHC's Run 2 are presented, as well as challenges and techniques.
A brief summary of the CMS discovery potential for the Standard Model Higgs boson in the H->gamma+gamma channel is presented. We review both a standard cut-based search and a more optimized analysis that takes advantage of the wide range of signal/background expectations as function of the possible selection cuts. As the Higgs discovery in this channel will rely heavily on performance of the CMS electromagnetic calorimeter, the relevant aspects of its design and operation in situ at the LHC are also briefly discussed.
Photon bremsstrahlung is studied for identifying elastic proton-proton interactions in the CMS experiment at the LHC. In addition to measurement of the elastic pp cross section (assuming that the elastic slope is known) the bremsstrahlung photons will allow evaluation of the total pp cross section, luminosity and alignment of the Zero Degree Calorimeters (ZDCs).
The physics reach of the CMS detector achievable with 300(0) inverse femtobarns of proton-proton collisions recorded at sqrt(s)=14 TeV is presented. Ultimate precision on measurements of Higgs boson properties, top quark physics, and electroweak processes are discussed, as well as the discovery potential for new particles beyond the standard model. In addition, the potential for future heavy ion physics is presented. This document has been submitted as a white paper to the Snowmass process, an exercise initiated by the American Physical Society's Division of Particles and Fields to assess the …
Physical possibility for bending the LHC protons (or ions) a huge angle of 1-20 degrees in the energy range of 0.45 to 7 TeV by means of a bent channeling crystal of Silicon or Germanium is demonstrated. Such an application can be useful for calibration of CMS (or ATLAS) calorimeters in situ by the LHC beam of precisely known energy. We show by simulations that such an application would be feasible at the LHC, and report the experience of IHEP Protvino in bending 70 GeV protons by 9 degrees (150 mrad) during 10 years in 1994-2004 experiments.
We report on the status and history of the CMS commissioning, together with selected results from cosmic-ray muon data. The second part focuses on strategies for optimizing the reconstruction of jets, missing transverse energy and photons for early standard model measurements at ATLAS and CMS with the first collision data from the Large Hadron Collider at CERN.
Measurements of the top quark mass are presented, obtained from CMS data collected in proton proton collisions at the LHC at centre-of-mass energies of 7 TeV and 8 TeV. The mass of the top quark is measured using several methods and channels, including the reconstructed invariant mass distribution of the top quark as well as measurements based on charged particle information. The dependence of the mass measurement on the kinematic phase space is investigated. The results of the various channels are combined and compared to the world average. The top mass is extracted from the inclusive top qua…
In January 2007 the CERN director general announced the plan for the staged upgrade of the LHC luminosity. The plan foresees a phase 1 upgrade reaching a peak luminosity of $3 \times 10^{34}$ cm$^{-2}$s$^{-1}$ followed by phase reaching up to $ 10^{35}$ cm$^{-2}$s$^{-1}$. We discuss the physics potential and the experimental challenges of an upgraded LHC running. The detector R&D needed to operate ATLAS and CMS in a very high radiation environment and the expected detector performance are also discussed.
This note presents selected measurements of W and Z boson production, carried out with the CMS experiment at the LHC, based on samples of events collected during 2015-2018 physics runs. W boson events were selected containing an isolated, energetic electron or muon, while Z boson events were selected containing a pair of isolated, energetic electrons or muons. Presented results include searches for rare decays of W bosons to pions.
We present an overview of measurements of electroweak vector boson pair production and anomalous Triple Gauge Couplings (aTGC), with semileptonic and fully leptonic final states. The data analyzed were taken at center of mass energy of 7 & 8 TeV by the CMS detector at the Large Hadron Collider. The cross-section measurements are important because they are test of the Standard Model predictions, while these processes serve as background for Higgs searches and various other processes.
The measurement of the inclusive cross section for Wgamma production is presented based on 36/ pb of data acquired with the CMS detector from 7 TeV LHC collisions in 2010. Comparisons are made with the predictions of the standard model. The W bosons are identified through their leptonic decays to electrons and muons. The Wgamma cross section is sensitive to anomalous triple-gauge couplings and hence this measurement probes physics beyond the standard model.
Searches for high-mass resonances decaying to pairs of standard model bosons using ATLAS and CMS detectors are presented. The searches use 15 - 36 $\textrm{fb}^{-1}$ of proton-proton collision data collected at the centre-of-mass energy of 13 TeV at the LHC. Many different final states have been considered and the results are interpreted in a range of theories beyond the standard model of particle physics, most common being heavy vector triplet and warped extra dimensions.
In this paper, a brief outlook on the measurements of the total and differential cross-sections of vector bosons production associated with heavy flavor quarks performed using CMS proton-proton collision data taken at center of mass energies of 7, 8, and 13 TeV is presented. Obtained results are compared with predictions of various state-of-the-art Monte-Carlo generators.
Recent CMS results on Forward and Small-x QCD Physics are presented. Those include the measurement of the Underlying Event activity and the study of jet production at large rapidity separation.
The forward physics program of the CMS experiment at the LHC spans a broad range of diverse physics topics including studies of low-x QCD and diffractive scattering, multi-parton interactions and underlying event structure, gamma-mediated processes and luminosity determination, Monte Carlo tuning and even MSSM Higgs discovery in central exclusive production. In this article, the forward detector instrumentation around the CMS interaction point is described and the prospects for diffractive and forward physics using the CMS forward detectors are summarized. In addition, first observation of for…
The latest results on searches for production of two Higgs bosons with the CMS detector using the 2016 CERN LHC dataset are presented, as shown at the LHCP 2017 conference.
We present the results of the Model Unspecific Search in CMS (MUSiC), which systematically scans the data taken by the CMS detector for deviations from the Standard Model predictions. Due to the minimal theoretical bias this approach is sensitive to a variety of models for new physics. Events containing at least one electron or muon are classified according to their content of reconstructed objects (muons, electrons, photons, jets and missing transverse energy). A broad scan of three kinematic distributions in those classes is performed by identifying deviations from Standard Model expectation…
We report on potential for measurement of inclusive W and Z boson production cross section using initial data from the LHC. We have designed W and Z triggers, selection algorithms, and event reconstruction techniques for both muon and electron decay modes, for low luminosity operation of the LHC integrating up to about 10 pb-1. Initial calibrations and alignment accuracies are assumed. While the accuracy of the cross section extracted will be dominated by the integral luminosity measurement, ratios of W and Z production, and asymmetry distributions will be important early measurements from LHC…
We present measurements of the forward (3 < |eta| < 5) energy flow in minimum bias events and in events with either hard jets or W and Z bosons produced at central rapidities together with first measurements of the inclusive forward jet cross section and central forward jet correlations. Results are compared to MC models with different parameter tunes for the description of the underlying event.
The Large Hadron Collider (LHC), scheduled to start operation in 2006, is foreseen to provide in the first year of running a total of $\sim 10^{12}$ $τ$ leptons. CMS (Compact Muon Solenoid) is a general-purpose experiment designed to study proton-proton and heavy-ion collisions at LHC. Even if the Susy particles and Higgs searches togheter with the B-physics present its main goal, the large amount of $τ$-lepton, could allow a systematic study of tau-physics. We have performed a full simulation of CMS using GEANT 3 package and the object-oriented reconstruction program ORCA to study the sensiti…
State-of-the-art theoretical predictions accurate to next-to-leading order QCD interfaced with {\sc pythia} and {\sc herwig} are tested by comparing the unfolded $t\bar{t}$ differential data collected with the CMS detector at 8 TeV and 13 TeV. These predictions are also compared with the measurements of underlying event activity distributions accompanying ${\rm t\bar{t}}$ events. Furthermore, predictions of beyond NLO accuracy in QCD are compared with the data.
The possibility to observe a Higgs boson having a mass between 300 and 600 GeV and to measure its couplings to vector bosons and top quark with CMS at the LHC is studied. Six different signatures are analyzed. The possibility to separate the Higgs events produced through weak boson fusion from the Higgs produced through gluon fusion using the forward going jets emitted in the weak boson fusion process is discussed for each of these different channels. The results are then used to determine the possible statistical errors on the ratio between the two Higgs decay branching fractions when it deca…
Results are presented for the search for invisible Higgs boson production using the full LHC dataset corresponding to integrated luminosity of 5.1 fb^-1 and 19.6 fb^-1 of proton-proton collision data at sqrt(s)= 7 TeV and 8 TeV (respectively) collected by the CMS detector. The invisible Higgs is searched for in final states of missing transverse energy, with two leptons from a recoiling Z boson. No significant excess is found beyond standard model predictions, and limits are obtained on the branching fraction of the Higgs boson to invisible particles.
The latest measurements of the top quark mass obtained by the ATLAS and CMS experiments at the LHC for centre-of-mass energies of 7 and 8 TeV are presented. The mass of the top quark is measured using several methods and channels, including the reconstructed invariant mass distribution of the top quark and shapes of top quark decay distributions. Measurements based on the inclusive tt-bar cross section and novel observables based on the differential cross section in the tt-bar + 1 jet channel are also discussed. The results of the various channels are combined and compared to the world average…
Results are summarized from searches for the standard model Higgs boson in pp collisions at sqrt(s) = 7 and 8 TeV in the CMS experiment at the LHC. The measurements of mass, cross section, and properties of the narrow resonance recently observed are presented. The searches beyond standard model Higgs boson, in the CMS experiment at the LHC, are highlighted.
We report on potential for measurement of W and Z boson production, as well as the production in association with jets. Of particular interest are jet multiplicity and $P_{\rm T}$ distributions. The 10 to $100 {\rm pb}^{-1}$ datasets expected in the startup year of operation of LHC are likely to already provide information beyond the reach of the Tevatron collider both in jet multiplicity and $P_{\rm T}$ range. We are especially interested in understanding the ratios of W+jets to Z+jets distributions by comparing them to next-to-leading order Monte Carlo generators, as these processes present …
A summary of the sensitivity of the ATLAS and CMS experiments at the LHC to discover a Standard Model Higgs boson is presented. Some prospects for Minimal Supersymmetric Standard Model Higgs searches at LHC are also included.
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 path taken by the LHC team to reach 3.6 10$^{33}$ cm$^{-2}$ s$^{-1}$ instantaneous luminosity, and to deliver 5.6 fb$^{-1}$ per experiment is summarized. The main performances of the two experiments are highlighted, in particular the way they managed to cope with the already high level of "pile-up". Selected Standard Model and top physics results are given, and the status of the limits on the Higgs boson search by each experiment is summarized. A brief overview of the search for supersymmetry and exotic phenomena is made at the end.
When the LHC starts its operation, CMS will have a unique opportunity to study q uarkonium production in pp collisions and later in PbPb collisions. Here we report on the methods and plans for measuring the differential pT Jpsi->mu+mu- production cross section, using data to be collected in the first LHC run by the CMS detector. Furthermore we discuss the performance of the CMS detector for quarkonium measurements in PbPb collisions.
The observation of inclusive diffraction with the CMS detector at the LHC is presented for centre-of-mass energies \sqrt s = 0.9 TeV and 2.36 TeV. Diffractive events are selected by the presence of a Large Rapidity Gap in the forward region of the CMS detector and uncorrected data are compared with Monte Carlo simulations based on the event generators PYTHIA and PHOJET. The measurement of the forward energy flow, in the pseudorapidity region 3.15 < |η| < 4.9, is also presented at \sqrt s = 0.9 TeV, 2.36 TeV and 7 TeV. Uncorrected data are compared with Monte Carlo simulations based on PYTHIA.
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.
The very-forward energy production in hadron collisions is of paramount importance for the understanding of ultra-high energy cosmic ray air showers. The CASTOR calorimeter of CMS is located at $-6.6 < η< -5.2$ in the phase-space where the peak of energy is deposited at LHC. The composition and characteristics of the particles in this phase-space have a determining impact on the formation of air shower cascades. An overview of various energy measurements performed with CASTOR is reported and possible implications for cosmic ray physics are outlined.
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…
A search for a heavy Higgs boson in the $H\rightarrow ZZ\rightarrow 2\ell2ν$ decay channel, where $\ell$ = e or $μ$, in pp collisions at a centre-of-mass energy of 7 and 8 TeV is presented. The search is optimized separately for the vector boson fusion and the gluon fusion production processes. No significant excess is observed above the background expectation. A re-interpretation of the results as a search for an electroweak singlet extension of the Standard Model is also presented.
Studies of forward processes are important tests of the standard model and inputs for Monte Carlo tuning. A measurement of the energy flow in the forward pseudorapidity region of CMS, $3.15 < \vert η\vert < 4.9$, is presented for 3 values of the centre-of-mass energy $\sqrt{s}$ = 0.9 TeV, 2.36 TeV and 7 TeV. The forward energy flow is measured for minimum bias events and for events with a central dijet system the transverse energy of which provides a hard scale. The energy flow is compared to various Monte Carlo models with different multiparton interaction schemes. A study of forward jets in …
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.
We report on the recent CMS measurements of soft hadron-hadron production, including the measurements of inclusive single- and double-diffractive cross sections, as well as the measurement of pseudorapidity distributions, and of the leading charged particle and leading jet cross sections. We present the cross sections for low-pT forward jets production, and production of dijets with large rapidity separation (central-forward, and forward-backward jets). Studies of double parton scattering using four-jet and W+2-jet events, and the cross sections for Drell-Yan with associated jet production are…
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…
An overview of minimum bias and underlying event studies at the LHC with the ATLAS and CMS detectors is presented. Current uncertainties in the modeling of soft pp inelastic interactions at the LHC energy scale are discussed. Triggers used to select inelastic interactions at ATLAS and CMS are described and compared. A summary of some of the ongoing minimum bias and underlying event analyses by the ATLAS and CMS collaborations is given.
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 LHC has delivered several fb-1 of data in spring and summer 2011, opening new windows of opportunity for discovering phenomena beyond the Standard Model. A summary of the searches conducted by the ATLAS and CMS experiments based on about 1 fb-1 of data is presented.
We report on a precision measurement of the effective weak mixing angle using the forward-backward asymmetry, $A_{FB}$, in Drell-Yan ($ee$ and $μμ$) events in pp collisions at $\sqrt{s}=8~\mathrm{TeV}$ at the CMS experiment at the Large Hadron Collider (LHC). The results are compared to other hadron collider measurements published by ATLAS, LHCb, CDF, D0 and Tevatron combination.
Forward (di)jet measurements are a useful tool to constrain the Parton Distribution Functions (PDFs) at low values of parton momentum fraction x, and to study the possible onset of BFKL or gluon saturation QCD evolutions in the proton. We present studies of jet reconstruction capabilities in the CMS Hadron Forward (HF) calorimeter (3<|eta|<5). The expected sensitivity of the inclusive forward jet p_T spectrum to the proton PDF, as well as the azimuthal decorrelation of Mueller-Navelet jets with a large rapidity separation are presented for p-p collisions at sqrt{s} = 14 TeV.
The CMS and ATLAS collaborations searched for Dark Matter (DM) particles directly produced in pair. The searches are performed using the full LHC Run-I dataset recorded with the CMS and ATLAS detectors in proton-proton collisions at a center-of-mass energy of 8 TeV. Signatures considered include those yielding energetic jets and large missing transverse momentum as well as electroweak bosons and heavy flavour quarks plus missing transverse energy. No deviation from SM background expectation was found and exclusion limits on DM production cross section were set.
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…
