Compact Muon Solenoid Collaboration Research Articles

CMS HGCAL electronics vertical integration system tests

In preparation for the High-Luminosity phase of the CERN Large Hadron Collider, the Compact Muon Solenoid collaboration will replace the existing endcap calorimeters with the High Granularity Calorimeter. Considering both endcaps, this novel sub-detector will have around six million readout channels, pushing approximately 108 Tbit s-1 of usable data between the detector front-end (on-detector) electronics and the back-end (off-detector) electronics. Given the scale and complexity of the endcap calorimeter upgrade project, the electronics testing must be carefully planned. The strategy has been to split the efforts between vertical (start-to-end) and horizontal (parallelisation) test systems wherever possible. An important milestone was the development and operation of a test system that prototypes a complete vertical slice of the future endcap electronics system. For the first time, a version of a test system consisting of the full vertical electronics readout chain was successfully operated in a beam test, where it was used to acquire real physics data.

Machine Learning applications for Data Quality Monitoring and Data Certification within CMS

The Compact Muon Solenoid (CMS) detector is getting ready for datataking in 2022, after a long shutdown period. LHC Run-3 is expected to deliver an ever-increasing amount of data. To ensure that the recorded data has the best quality possible, the CMS Collaboration has dedicated Data Quality Monitoring (DQM) and Data Certification (DC) working groups. These working groups are made of human shifters and experts who carefully watch and investigate histograms generated from different parts of the detector. However, the current workflow is not granular enough and prone to human errors. On the other hand, several techniques in Machine Learning (ML) can be designed to learn from large collections of data and make predictions for the data quality at an unprecedented speed and granularity. Hence, the data certification process can be considered as a perfect problem for ML techniques to tackle. With the help of ML, we can increase the granularity and speed of the DQM workflow and assist the human shifters and experts in detecting anomalies during data-taking. In this presentation, we present preliminary results from incorporating ML to highly granular DQM information for data certification.

H2GCROC: Design and performance of a dedicated very front-end ASIC for SiPM readout of the CMS High Granularity Calorimeter

The HGCROC ASICs are dedicated very front-end electronics designed to read out the High Granularity Calorimeter (HGCAL), which will replace the present end-cap calorimeters of the Large Hadron Collider (LHC) for the Compact Muon Solenoid collaboration (CMS). The H2GCROC ASIC was especially designed to read out the SiPMs coupled to the scintillating tiles of the back hadronic sections, where the radiation constraints are less severe. Inside the chip, the front-end preamplifier is adapted for the SiPM’s higher signal level, expecting pC/MIP rather than fC/MIP ranges. The chip was received end of 2020 and extensively tested in the lab and test beam. This work examines the very front-end design and performance, including its performance with the sensor.

Response of a CMS HGCAL silicon-pad electromagnetic calorimeter prototype to 20–300 GeV positrons

The Compact Muon Solenoid collaboration is designing a new high-granularity endcap calorimeter, HGCAL, to be installed later this decade. As part of this development work, a prototype system was built, with an electromagnetic section consisting of 14 double-sided structures, providing 28 sampling layers. Each sampling layer has an hexagonal module, where a multipad large-area silicon sensor is glued between an electronics circuit board and a metal baseplate. The sensor pads of approximately 1.1 cm2 are wire-bonded to the circuit board and are readout by custom integrated circuits. The prototype was extensively tested with beams at CERN's Super Proton Synchrotron in 2018. Based on the data collected with beams of positrons, with energies ranging from 20 to 300 GeV, measurements of the energy resolution and linearity, the position and angular resolutions, and the shower shapes are presented and compared to a detailed Geant4 simulation.

Performance study of HGCROC-v2: the front-end electronics for the CMS High Granularity Calorimeter

The High Granularity Calorimeter (HGCAL), presently being designed by the Compact Muon Solenoid collaboration (CMS) to replace the existing endcap calorimeters for the High Luminosity phase of the LHC (HL-LHC), will feature unprecedented transverse and longitudinal readout and triggering segmentation for both electromagnetic and hadronic sections. The requirements for the front-end electronics are extremely challenging, including high dynamic range (0–10 pC), low noise (0∼ 200 electrons), high-precision timing information in order to mitigate the pileup effect (25 ps binning) and low power consumption (∼ 15 mW/channel). The front-end electronics will face a harsh radiation environment which will reach 200 Mrad at the end of life. It will work at a controlled temperature of 240 K. HGCROC-v2 is the second prototype of the front-end ASIC. It has 72 channels of the full analog chain: low noise and high gain preamplifier and shapers, and a 10-bit 40 MHz SAR-ADC, which provides the charge measurement over the linear range of the preamplifier. In the saturation range of the preamplifier, a discriminator and TDC provide the charge information from TOT (Time Over Threshold) over 200 ns dynamic range using 50 ps binning. A fast discriminator and TDC provide timing information to 25 ps accuracy. Both charge and timing information are kept in a DRAM memory waiting for a Level 1-trigger decision (L1A). At a bunch crossing rate of 40 MHz, compressed charge data are sent out to participate in the generation of the L1-trigger primitives. We report on the performances of the chip in terms of signal-to-noise ratio, charge and timing, as well as results from radiation qualification with total ionizing dose (TID).

CMS Experience with Adoption of the Community supported DD4hep Toolkit

DD4hep is an open-source software toolkit that provides comprehensive and complete generic detector descriptions for high energy physics (HEP) detectors. The Compact Muon Solenoid collaboration (CMS) has recently evaluated and adopted DD4hep to replace its custom detector description software. CMS has demanding software requirements as a very large, longrunning experiment that must support legacy geometries and study many possible upgraded detector designs of a constantly evolving detector that will be taking data for many years to come. CMS has chosen DD4hep since it is a high-quality, community-supported solution that will benefit from continuing modernization and maintenance. This presentation will discuss the issues of DD4hep adoption, the advantages and disadvantages of the various design choices, performance results, and the integration of the plugin systems from CMS and Gaudi, another open-source software framework. Recommendations about DD4hep based upon the CMS use cases will also be presented.

Improving efficiency of analysis jobs in CMS

Hundreds of physicists analyze data collected by the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider using the CMS Remote Analysis Builder and the CMS global pool to exploit the resources of the Worldwide LHC Computing Grid. Efficient use of such an extensive and expensive resource is crucial. At the same time, the CMS collaboration is committed to minimizing time to insight for every scientist, by pushing for fewer possible access restrictions to the full data sample and supports the free choice of applications to run on the computing resources. Supporting such variety of workflows while preserving efficient resource usage poses special challenges. In this paper we report on three complementary approaches adopted in CMS to improve the scheduling efficiency of user analysis jobs: automatic job splitting, automated run time estimates and automated site selection for jobs.

The CMS high granularity calorimeter for the high luminosity LHC

The CMS (Compact Muon Solenoid) experiment at CERN will undergo significant improvements during the Phase-II Upgrade to cope with a 10-fold increase in integrated luminosity with the HL-LHC (High Luminosity Large Hadron Collider) era. The forward calorimetry faces very high radiation levels and pileup in the detectors. The CMS collaboration is designing a highly granular calorimeter to replace the existing endcap calorimeters (CE). It features unprecedented transverse and longitudinal segmentation for both electromagnetic (CE-E) and hadronic (CE-H) parts. This will facilitate Particle Flow Algorithms (PFAs), where the structure of showers can be measured and used to enhance pileup rejection and particle identification, whilst still achieving good energy resolution. The CE-E and a large fraction of CE-H will use hexagonal silicon sensors produced from 200 mm (8 inch) wafers, with 192 (432) cells of 1 cm 2 (0.5 cm 2 ) size. The rest of the CE-H uses highly-segmented scintillator tiles with on-tile SiPM (Silicon Photomultiplier) readout. An overview of the HGCal (High Granularity Calorimeter) project is presented in this paper with a focus on the silicon sensors. We cover motivation, engineering design, expected performance and the current status of prototypes.

First beam tests of prototype silicon modules for the CMS High Granularity Endcap Calorimeter

The High Luminosity phase of the Large Hadron Collider will deliver 10 times more integrated luminosity than the existing collider, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry. As part of its upgrade program, the Compact Muon Solenoid collaboration is designing a high-granularity calorimeter (HGCAL) to replace the existing endcap calorimeters. It will feature unprecedented transverse and longitudinal readout and triggering segmentation for both electromagnetic and hadronic sections. The electromagnetic section and a large fraction of the hadronic section will be based on hexagonal silicon sensors of 0.5–1 cm2 cell size, with the remainder of the hadronic section being based on highly-segmented scintillators with silicon photomultiplier readout. The intrinsic high-precision timing capabilities of the silicon sensors will add an extra dimension to event reconstruction, especially in terms of pileup rejection. First hexagonal silicon modules, using the existing Skiroc2 front-end ASIC developed for CALICE, have been tested in beams at Fermilab and CERN in 2016. We present results from these tests, in terms of system stability, calibration with minimum-ionizing particles and resolution (energy, position and timing) for electrons, and the comparisons of these quantities with GEANT4-based simulation.

In the company of top quarks

Particle Physics The coupling of elementary particles to the Higgs boson is correlated with their masses. For some particles, it can be measured by observing the decay of the Higgs into those particles. The top quark, however, is too heavy for the Higgs to decay into. Therefore, Sirunyan et al. from the Compact Muon Solenoid Collaboration at the Large Hadron Collider (LHC) looked at the processes in which the Higgs boson is produced in conjunction with the top quark and its antiparticle. By combining the results from the runs at different center-of-mass energies of proton-proton collisions at the LHC, they found that such processes indeed occurred and that the signal strength was consistent with the predictions of the Standard Model of particle physics. Phys. Rev. Lett. 120 , 231801 (2018).

Status of RDMS CMS computing

The Compact Muon Solenoid (CMS) is a high-performance general-purpose detector at the Large Hadron Collider (LHC) at CERN. More than twenty institutes from Russia and Joint Institute for Nuclear Research (JINR) are involved in Russia and Dubna Member States (RDMS) CMS Collaboration. A proper computing grid-infrastructure has been constructed at the RDMS institutes for the participation in the running phase of the CMS experiment. Current status of RDMS CMS computing and plans of its development to the next LHC start are presented.

Bounds on large extra dimensions from the simulation of black hole events at the LHC

If large extra dimensions exist, the Planck scale may be as low as a TeV and microscopic black holes may be produced in high-energy particle collisions at this energy scale. We simulate microscopic black hole formation at the Large Hadron Collider and compare the simulation results with recent experimental data by the Compact Muon Solenoid collaboration. The absence of observed black hole events in the experimental data allows us to set lower bounds on the Planck scale and various parameters related to microscopic black hole formation for a number ($3-6$) of extra dimensions. Our analysis sets lower bounds on the fundamental Planck scale ranging from 0.6 TeV to 4.8 TeV for black holes fully decaying into Standard Model particles and 0.3 TeV to 2.8 TeV for black holes settling down to a remnant, depending on the minimum allowed black hole mass at formation. Formation of black holes with mass less than 5.2 TeV to 6.5 TeV (SM decay) and 2.2 TeV to 3.4 TeV (remnant) is excluded at 95\% C.L. Our analysis shows consistency with and difference from the CMS results.

Searches for Kaluza-Klein graviton excitations and microscopic black holes with the aid of the CMS detector at the LHC

A survey of the results of the Compact Muon Solenoid (CMS) experiment that concern searches for massive Kaluza-Klein graviton excitations and microscopic black holes, quantum black holes, and string balls within models of low-energy multidimensional gravity is presented on behalf of the CMS Collaboration. The analysis in question is performed on the basis of a complete sample of data accumulated for proton-proton collisions at the c.m. energies of 7 and 8 TeV at the Large Hadron Collider (LHC) over the period spanning 2010 and 2012.

Overview of results on heavy flavour and quarkonia from the CMS collaboration

The non-prompt J / ψ from B-meson decays, the prompt J / ψ , the inclusive ψ ′ and the three ϒ states were measured separately using the Compact Muon Solenoid (CMS) experimental apparatus in both pp and heavy-ion collisions at s N N = 2.76 TeV . The results are based on data collected in 2011 which correspond to an integrated luminosity of 150 μ b − 1 of PbPb and 231 nb − 1 of pp collisions. The yields measured in heavy-collisions are compared to those in pp scaled by the number of binary collisions via the nuclear modification factor, R A A . The high- p T prompt J / ψ show a suppression that does not vary with rapidity or p T . The R A A versus centrality calculated separately for ϒ ( 1 S ) and ϒ ( 2 S ) , shows less suppression for the ground state. An upper limit for ϒ ( 3 S ) was also calculated. Combining all the quarkonia states R A A measured by CMS, and considering the binding energy of each state, an ordering of the suppression is observed, which establishes, experimentally, the validity of the sequential melting scenario in heavy-ion collisions. The non-prompt J / ψ R A A dependence with p T and rapidity was measured in fine bins of centrality. These represent the first detailed measurements, in heavy-ion collision, of the b-quark energy loss kinematic dependence.

Tau Reconstruction and Identification at the Compact Muon Solenoid

New Physics beyond the Standard Model could appear at the LHC in final states with tau leptons. The development of efficient and accurate reconstruction and identification algorithms for taus decaying to hadrons is therefore an important item in the physics program of the Compact Muon Solenoid (CMS) experiment. New identification algorithms utilizing information about the known properties of tau hadronic decays have been recently developed and provide considerable performance improvements with respect to algorithms previously used by the CMS collaboration. Details of the strategies for identification of individual tau decay modes are presented in the following, as well as first measurements of the quark and gluon jet mis–tag rate with the first 8.4 nb − 1 of data collected at s = 7 TeV .

Comparing the same-side ridge inp−pangular correlations at 7 TeV to data measured at the BNL Relativistic Heavy Ion Collider

The Compact Muon Solenoid Collaboration (CMS) has recently reported the appearance of a same-side ridge structure in two-particle angular correlations from 7-TeV $p$-$p$ collisions. The ridge in $p$-$p$ collisions at 7 TeV has been compared to a ridge structure in more-central Au-Au collisions at 200 GeV, interpreted by some as evidence for a dense, flowing QCD medium. In this study we make a detailed comparison between 200-GeV $p$-$p$ correlations and the CMS results. We find that 7-TeV minimum-bias jet correlations are remarkably similar to those at 200 GeV, even to the details of the same-side peak geometry. Appearance of a same-side ridge reflects a change in the sign of the azimuth curvature determined by the ratio of azimuth quadrupole-to-dipole amplitudes. Extrapolation of quadrupole systematics from 200 GeV suggests that the same-side ridge at 7 TeV is a manifestation of the quadrupole amplitude enhanced relative to the dipole by the energy increase and applied cuts.

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 cathode strip chamber data acquisition electronics for CMS

Data Acquisition (DAQ) electronics for Cathode Strip Chambers (CSC) [CMS Collaboration, The Muon Project Technical Design Report, CERN/LHCC 97-32, CMS TDR3, 1997] in the Compact Muon Solenoid (CMS) [CMS Collaboration, The Compact Muon Solenoid Technical Proposal, CERN/LHCC 94-38, 1994] experiment at the Large Hadron Collider (LHC) [The LHC study group, The Large Hadron Collider: Conceptual Design, CERN/AC 1995-05, 1995] is described. The CSC DAQ system [B. Bylsma, et al., in: Proceedings of the Topical Workshop on Electronics for Particle Physics, Prague, Czech Republic, CERN-2007-007, 2007, pp. 195–198] includes on-detector and off-detector electronics, encompassing five different types of custom circuit boards designed to handle the high event rate at the LHC. The on-detector electronics includes Cathode Front End Boards (CFEB) [R. Breedon, et al., Nucl. Instr. and Meth. A 471 (2001) 340], which amplify, shape, store, and digitize chamber cathode signals; Anode Front End Boards (AFEB) [T. Ferguson, et al., Nucl. Instr. and Meth. A 539 (2005) 386], which amplify, shape and discriminate chamber anode signals; and Data Acquisition Motherboards (DAQMB), which controls the on-chamber electronics and the readout of the chamber. The off-detector electronics, located in the underground service cavern, includes Detector Dependent Unit (DDU) boards, which perform real time data error checking, electronics reset requests and data concentration; and Data Concentrator Card (DCC) boards, which further compact the data and send it to the CMS DAQ System [CMS Collaboration, The TriDAS Project Technical Design Report, Volume 2: Data Acquisition and High-level Trigger, CERN/LHCC 2002-26, 2002], and serve as an interface to the CMS Trigger Timing Control (TTC) [TTC system 〈http://ttc.web.cern.ch/TTC/intro.html〉] system. Application Specific Integrated Circuits (ASIC) are utilized for analogous signal processing on front end boards. Field Programmable Gate Arrays (FPGA) are utilized on all boards in the system to provide programmability. The DAQ system has been installed and commissioned, and is ready for LHC data taking.

The silicon strip tracker for CMS

Abstract The Compact Muon Solenoid (CMS) is one of the experiments that will be installed at the new Large Hadron Collider in construction at CERN. The Silicon Strip Tracker (SST) constitutes, in conjunction with the pixel system, the inner tracking detector of CMS. It occupies a cylindrical region of 2.4 m diameter and 5.6 m length, instrumented with more than 24,000 micro-strip sensors for a total of about 10 million channels. Its layout and expected performances are described in this paper. The silicon sensors of the SST will operate in a high-radiation environment. The CMS collaboration has carried out an extensive R&D program in order to minimize their susceptibility to radiation damage. A review of this program and the main results that determined the final choices for the sensor technology are given.