Compact Muon Solenoid Detector Research Articles

Thermal Conductance of a Multilayer Drift Chamber: An Experimental Approach

Drift chambers in the compact muon solenoid (CMS) detector are piled modular structures joined together by a structural adhesive. This structure is used for the detection and tracking of high energy particles—particularly muons. According to Fourier’s law, the conductance of a multilayered drift chamber prototype can be measured using a simple device based on the thermal transience between two heat sinks. The heat gradients in the global CMS detector in operation at the European Council for Nuclear Research are estimated in this way. The resultant values are used to determine whether to include a forced cooling device in the CMS.

Optimization of the analysis of single top-quark production at the Large Hadron Collider (LHC)

Several steps of an investigation of single top-quark production at the Large Hadron Collider (LHC) are discussed. A number of general problems associated with basic steps of this analysis are discussed. The investigations are performed for the CMS (Compact Muon Solenoid detector) Collaboration, and detailed results will be presented in CMS publications. Three event generators used by the CMS Collaboration in simulating single top-quark production (SingleTop, MC@NLO, and a generator based on the MadGraph package) are compared in the present study. Schemes for optimizing the observation of a single top quark on the basis of the neural-network method are presented. The first steps in searches for possible anomalous vector couplings in the Wtb vertex that manifest themselves in processes of single top-quark production are described.

The CMS Magnetic Field Map Performance

The Compact Muon Solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in the CMS detector is required. During two major tests of the CMS magnet the magnetic flux density was measured inside the coil in a cylinder of 3.448 m diameter and 7 m length with a specially designed field-mapping pneumatic machine as well as in 140 discrete regions of the CMS yoke with NMR probes, 3-D Hall sensors and flux-loops. A TOSCA 3-D model of the CMS magnet has been developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. A volume based representation of the magnetic field is used to provide the CMS simulation and reconstruction software with the magnetic field values. The value of the field at a given point of a volume is obtained by interpolation from a regular grid of values resulting from a TOSCA calculation or, when available, from a parameterization. The results of the measurements and calculations are presented, compared and discussed.

Laser monitoring for the CMS ECAL

The Compact Muon Solenoid (CMS) detector at the LHC is equipped with a high precision lead tungstate crystal electromagnetic calorimeter (ECAL). To ensure the stability of the calorimetric response at the level of a few per mille, every channel of the detector is monitored with a laser system. This system enables corrections for fluctuations in the detector response with high precision, in particular the expected radiation induced changes in the crystal transparency. We describe the implementation of the laser monitoring system and report results from tests on the fully equipped supermodules of the ECAL. Specifically, we discuss results concerning the dynamics of crystal transparency change from dedicated irradiation studies in test beams.

The ECAL online software in the commissioning of the CMS detector

The Electromagnetic Calorimeter (ECAL) of the Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) is a crystal homogeneous calorimeter made of about 76 000 lead tungstate crystals. The detector was installed in the CMS experimental cavern in 2007 and 2008 and was commissioned with cosmic rays and with LHC beams in 2008. The trigger and data acquisition system of the CMS ECAL comprises 35 000 Front End ASICs and 170 Off Detector VME Boards. The operation of the system, performed by the ECAL online software, requires the configuration of O ( 10 7 ) parameters and the realtime monitoring of O ( 10 5 ) registers. In this paper we discuss the design and architecture of the ECAL online software and its performances in cosmic ray runs and with the first LHC beams.

Model discrimination at the LHC: A case study

We investigate the potential of the compact muon solenoid detector at the CERN Large Hadron Collider (LHC) to discriminate between two theoretical models predicting anomalous events with jets and large missing transverse energy, minimal supersymmetry, and little Higgs with T parity. We focus on a simple test-case scenario, in which the only exotic particles produced at the LHC are heavy color-triplet states (squarks or T quarks), and the only open decay channel for these particles is into the stable missing-energy particle (neutralino or heavy photon) plus a quark. We find that in this scenario, the angular and momentum distributions of the observed jets are sufficient to discriminate between the two models with a few inverse femtobarns of the LHC data, provided that these distributions for both models and the dominant standard model backgrounds can be reliably predicted by Monte Carlo simulations.

Search for Stueckelberg Z′ at LHC

We present the discovery potential for heavy Z′ gauge bosons in the Z′→e + e − decay channel at the Large Hadron Collider. The analysis focuses on the direct search for the massive Z′ bosons predicted by the Stueckelberg extension of the Standard Model. Using signal and background simulated events, and taking into account the basic parameters of the Compact Muon Solenoid detector, the discovery reach for the Stueckelberg Z′ is found to be in the range between 800 and 900 GeV/c2 for an integrated luminosity of 30 fb−1.

Avalanche photodiodes and vacuum phototriodes for the electromagnetic calorimeter of the CMS experiment at the Large Hadron Collider

The homogeneous lead tungstate electromagnetic calorimeter for the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider operates in a challenging radiation environment. The central region of the calorimeter uses large-area avalanche photodiodes to detect the fast blue-violet scintillation light from the crystals. The high hadron fluence in the forward region precludes the use of these photodiodes and vacuum phototriodes are used in this region. The constructional complexity of the calorimeter, which comprises 75848 individual crystals, plus the activation of material make repair during the lifetime of the detector virtually impossible. We describe here the key features and performance of the photodetectors and the quality assurance procedures that were used to ensure that the proportion of photodetectors that fail over the lifetime of CMS will be limited to a fraction of a percent.

Development of RE1/1 RPCs for the CMS muon trigger system

The first six Resistive Plate Chambers (RPCs) of RE1/1 in the forward region of the Compact Muon Solenoid (CMS) detector were constructed and are being tested. These RPCs cover the pseudo-rapidity region from 1.6 to 2.1 and will serve as the base detector for the CMS RPC muon trigger. We report that these six RPCs are being tested with the CMS RPC quality certification procedures and that a full measurement of a chamber efficiency of 95 ± 4 % has been achieved at an operating voltage of 9.4 kV. This performance demonstrates that the RPC is qualified to be tested at the closest distance to the beam pipe as the muon trigger detector at the full LHC design luminosity.

The CMS experiment at the CERN LHC

The Compact Muon Solenoid (CMS) detector is described. Thedetector operates at the Large Hadron Collider (LHC) at CERN. It wasconceived to study proton-proton (and lead-lead) collisions at acentre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and atluminosities up to 1034 cm−2 s−1 (1027 cm−2 s−1). At the core of the CMS detector sits ahigh-magnetic-field and large-bore superconducting solenoidsurrounding an all-silicon pixel and strip tracker, a lead-tungstatescintillating-crystals electromagnetic calorimeter, and abrass-scintillator sampling hadron calorimeter. The iron yoke of theflux-return is instrumented with four stations of muon detectorscovering most of the 4π solid angle. Forward samplingcalorimeters extend the pseudorapidity coverage to high values(|η| ⩽ 5) assuring very good hermeticity. The overalldimensions of the CMS detector are a length of 21.6 m, a diameter of14.6 m and a total weight of 12500 t.

Measurement of the CMS Magnetic Field

The measurement of the magnetic field in the tracking volume inside the superconducting coil of the Compact Muon Solenoid (CMS) detector under construction at CERN is done with a fieldmapper designed and produced at Fermilab. The fieldmapper uses 10 3-D B-sensors (Hall probes) developed at NIKHEF and calibrated at CERN to precision 0.05% for a nominal 4 T field. The precise fieldmapper measurements are done in 33840 points inside a cylinder of 1.724 m radius and 7 m long at central fields of 2, 3, 3.5, 3.8, and 4 T. Three components of the magnetic flux density at the CMS coil maximum excitation and the remanent fields on the steel-air interface after discharge of the coil are measured in check-points with 95 3-D B-sensors located near the magnetic flux return yoke elements. Voltages induced in 22 flux-loops made of 405-turn installed on selected segments of the yoke are sampled online during the entire fast discharge (190 s time-constant) of the CMS coil and integrated offline to provide a measurement of the initial magnetic flux density in steel at the maximum field to an accuracy of a few percent. The results of the measurements made at 4 T are reported and compared with a three-dimensional model of the CMS magnet system calculated with TOSCA.

Total calculation of electroweak corrections to the Drell-Yan process for LHC

A complete calculation of \( \mathcal{O} \)(α) electroweak radiative corrections to the Drell-Yan process for future experiments at the Large Hadron Collider (LHC) is performed. All contributions to cross sections and kinematical constraints are presented; in calculations and in order to simplify programming, the formalism of theta and delta functions is extensively used in numerical estimations. The independence of the results from unphysical parameters is tested, the independence from the parameter separating the regions of soft and hard photons being proven analytically. A numerical analysis of hypothesized effects is performed by means of the READY code in the FORTRAN language with allowance for experimental constraints at the Compact Muon Solenoid (CMS) detector. The electroweak corrections in question prove to be significant in the region of large dilepton invariant masses M, reducing substantially the differential cross section with respect to M and forward-backward asymmetry.

Aging Study with High-Level Radiation Sources for the CMS Forward RPCs

An aging study with intensive radiation sources was performed for the forward resistive plate chambers (RPCs) of the Compact Muon Solenoid (CMS) detector in the Large Hadron Collider experiment (LHC). The expected rate of the radiation background to be induced in the forward RPCs ranges from a few tens of Hz/cm to as much as ∼1 kHz/cm. Therefore, the radiation hardness for the forward RPCs should be sufficient to ensure the safe operation of the CMS and successful achievement of the LHC physics. Two oil-coated and one plain double-gap RPCs were manufactured and tested with the neutron beam provided by the MC50 cyclotron of the Korea Institute of Radiological and Medical Science (KIRAMS) and with gamma rays from a 200-mCi Cs source. The estimated radiation dose induced by the fast neutrons was approximately 50 Gy. No significant aging effect was found to be a consequence of the neutron irradiation, However, a degradation of the RPC performance was observed after intense gamma irradiation for a total of 32.5 days. The mean gamma-signal rate drawn in each RPC was 4.0 kHz/cm, which was approximately two times the maximum rate expected in the highest η-region covering the particle trigger. Increases in the noise rates and the currents accounted for the degradation in the efficiencies for the RPCs. As a result, safe operation of the forward RPCs in the avalanche mode was ensured for signal rates up to 2 kHz/cm.

Reconstructing Jets and Missing Transverse Energy using the CMS Detector

In 2007, the Large Hadron Collider (LHC) will circulate and collide proton-proton beams for the first time. The Compact Muon Solenoid (CMS) is one of four experiments at the LHC and is entering the final phases of construction and initial phases of commissioning. This report discusses the expected performance of reconstructing jets and missing transverse energy using the CMS Detector. In addition, strategies for calibrating the energy scale using real data are presented.

The production of radiation tolerant vacuum phototriodes and their HV filters for the Compact Muon Solenoid endcap electromagnetic calorimeter

Particle detectors which will operate at the Large Hadron Collider face unprecedented challenges in both the number of active detector elements and in operating without maintenance in a high radiation environment for many years. In the Compact Muon Solenoid (CMS) detector the scintillating crystal electromagnetic calorimeter uses vacuum photodetectors in the endcap where the lifetime neutron and hadron fluence is too high for the silicon avalanche photodiodes used in the barrel. Over 15000 radiation tolerant vacuum phototriodes (VPT) have been now been produced by industry for the endcap calorimeter. The VPT have to operate in an environment which has both a significant lifetime dose (up to 50 kGy) from electrons and gamma rays and a high neutron fluence (up to nearly 10 15 n.cm −2 for E > 100 keV). This paper discusses the steps taken during both the development and production of the VPT to ensure that the response to the scintillation light from the lead tungstate scintillator will not be significantly degraded during the operational lifetime of the experiment. Data from the quality assurance procedures and radiation induced degradation of complete VPT devices is presented. Other components of the endcap calorimeter are also exposed to a similarly intense radiation field. The quality assurance procedure used to select the passive components (resistors and capacitors) used in the high-voltage filter cards is described.

Muon Reconstruction and Identification at CMS

The Compact Muon Solenoid (CMS) is a general purpose detector currently being constructed for operation at the Large Hadron Collider (LHC) at CERN. One of the main goals of the CMS design is to ensure efficient and accurate identification and reconstruction of muons. This contribution describes two software algorithms that have been developed for reconstructing muons in the CMS experiment. In one approach stand-alone muons are reconstructed in the muon system and matched to a track in the central detector. The other technique starts from central tracks and extrapolates them toward the outer detector to look for compatible muon signatures in the calorimeter and muon chambers. Both approaches are complementary. The expected performance has been studied in detail using Monte Carlo simulation. During the recent Magnet Test and Cosmic Challenge (MTCC) the muon reconstruction was employed successfully to reconstruct cosmic muons traversing a full slice of the CMS detector.

Synchronization methods for the PAC RPC trigger system in the CMS experiment

The PAC (pattern comparator) is a dedicated muon trigger for the CMS (Compact Muon Solenoid) experiment at the LHC (Large Hadron Collider). The PAC trigger processes signals provided by RPC (resistive plate chambers), a part of the CMS muon system. The goal of the PAC RPC trigger is to identify muons, measure their transverse momenta and select the best muon candidates for each proton bunch collision occurring every 25 ns. To perform this task it is necessary to deliver the information concerning each bunch crossing from many RPC chambers to the trigger logic at the same moment. Since the CMS detector is large (the muon hits are spread over 40 ns), and the data are transmitted through thousands of channels, special techniques are needed to assure proper synchronization of the data. In this paper methods developed for the RPC signal synchronization and synchronous transmission are presented. The methods were tested during the MTCC (magnet test and cosmic challenge). The performance of the synchronization methods is illustrated by the results of the tests.

Search for a neutral Higgs boson with WH/ZH, H → γγ channel with the CMS detector at the LHC

A prospective analysis for the discovery of a light Higgs boson in the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) is presented. The associated production channels WH and ZH of a Higgs boson decaying into a photon pair are studied using a full detector simulation. The method of analysis here employed should permit the utilization of real data once they become available in order to optimize the analysis performance and to estimate background rates. Minimizing in this way reliance on simulated data should allow a significant reduction in systematic errors. One year of LHC running at high luminosity (integrated luminosity of 100 fb−1) should allow an observation at 3σ of the Standard Model Higgs boson from the LEP lower limit of 114.4 GeV/c2 up to 146 GeV/c2. Three years of running at high luminosity should allow a 5σ discovery from the LEP lower limit up to 148 GeV/c2. In the context of supersymmetric models, the dominant gluon fusion Higgs boson production process could be strongly suppressed. This light Higgs gluophobic scenario could occur when the mixing in the stop sector is maximal. In such a case, the associated production channels WH and ZH may be recovery channels.

Hard Probe Capabilities of CMS in Heavy Ion Collisions at the LHC

Heavy ion collisions at the Large Hadron Collider (LHC) will produce strongly interacting matter at unprecedented energy densities. At LHC collision energies, new hard probes of the dense initial collision system will become readily available. We present an overview of the capabilities of the Compact Muon Solenoid (CMS) detector to use these probes for a detailed study of QCD phenomenology at the highest energy densities.

Jet Physics in Heavy Ion Collisions with Compact Muon Solenoid detector at the LHC

The status of CMS jet simulations and physics analysis in heavy ion collisions is presented. Jet reconstruction and high-pT particle tracking in the high multiplicity environment of heavy ion collisions at the LHC using the CMS calorimetry and tracking system are described. The Monte Carlo tools used to simulate jet quenching are discussed.