The CMS Particle Flow Algorithm

In this thesis, my work in the Compact Muon Solenoid (CMS) experiment on the search for the neutral Minimal Supersymmetric Standard Model (MSSM) Higgs decaying into two muons is presented. The search is performed on the full data collected during the years 2011 and 2012 by CMS in proton-proton collisions at CERN Large Hadron Collider (LHC). The MSSM is explored within the most conservative benchmark scenario, m_h^{max}, and within its modified versions, m_h^{mod +} and m_h^{mod -}. The search is sensitive to MSSM Higgs boson production in association with a b\bar{b} quark pair and to the gluon-gluon fusion process. In the m_h^{max} scenario, the results exclude values of tanB larger than 15 in the m_A range 115-200 GeV, and values of tanB greater than 30 in the m_A range up to 300 GeV. There are no significant differences in the results obtained within the three different scenarios considered. Comparisons with other neutral MSSM Higgs searches are shown.

The Compact Muon Solenoid (CMS) experiment at CERN's Large Hadron Collider (LHC) is scheduled to come on-line in 2007. Fermilab will act as the CMS Tier-1 centre for the US and make experiment data available to more than 400 researchers in the US participating in the CMS experiment. The US CMS Users Facility group, based at Fermilab, has initiated a project to develop a model for optimizing movement of CMS experiment data between CERN and the various tiers of US CMS data centres and to design a WAN emulation facility which will enable controlled testing of unmodified or modified CMS applications and TCP implementations locally under conditions that emulate WAN connectivity. The WAN emulator facility is configurable for latency, jitter, and packet loss. The initial implementation is based on the NISTnet software product. In this paper we will describe the status of this project to date, the results of validation and comparison of performance measurements obtained in emulated and real environment for different applications including multistreams GridFTP. We also will introduce future short term and intermediate term plans, as well as outstanding problems and issues.

The Compact Muon Solenoid (CMS) is a general purpose detector at the Large Hadron Collider (LHC). The LHC luminosity is constantly increased through upgrades of the accel- erator and its injection chain. Two major upgrades will take place in the next years. The rst upgrade involves the LHC injector chain and allows the collider to achieve a luminosity of about 2 10 34 cm-2 s-1 A further upgrade of the LHC foreseen for 2025 will boost its luminosity to 5 10 34 cm-2 s1. As a consequence of the increased luminosity, the detectors need to be upgraded. In particular, the CMS pixel detector will undergo two upgrades in the next years. The rst upgrade (phase I) consists in the substitution of the current pixel detector in winter 2016/2017. The upgraded pixel detector will implement new readout elec- tronics that allow ecient data taking up to a luminosity of 2 10 34 cm-2s-1,twice as much as the LHC design luminosity. The modules that will constitute the upgraded detector are being produced at dierent institutes. Hamburg (University and DESY) is responsible for the production of 350 pixel modules. The second upgrade (phase II) of the pixel detector is foreseen for 2025. The innermost pixel layer of the upgraded detector will accumulate a radiation damage corresponding to an equivalent uence of eq = 2 10 16 cm-2 and a dose of 10 MGy after an integrated luminosity of 3000 fb-1. Several groups are investigating sensor designs and congurations able to withstand such high doses and uences. This work is divided into two parts related to important aspects of the upgrades of the CMS pixel detector. For the phase I upgrade, a setup has been developed to provide an absolute energy calibration of the pixel modules that will constitute the detector. The cali- bration is obtained using monochromatic X-rays. The same setup is used to test the buering capabilities of the modules' readout chip. The maximum rate experienced by the modules produced in Hamburg will be 120 MHz/cm 2 . For this rate the modules' eciency has been measured to be 99%. In view of the module production, the energy calibration procedure has been automated. The modules assigned to the Hamburg production center should be completed by the end of February 2016. For the phase II upgrade, thin silicon sensors with an active thickness of 100 m irradi- ated with protons up to eq = 1 : 3 10 16 cm-2 have been characterized. The charge collection eciency has been measured using pad diodes. Charge multiplication eects have been ob- served for both n- and p-bulk sensors. P-bulk strip sensors with an active thickness of 100 and 200 m have been characterized with a beam test. The signal of these sensors lies be- tween 4000 and 5000 e- after a uence of 1 : 3 10 16 cm-2. The 200 m thick sensors require a higher bias voltage than the 100 m thick sensors to reach this signal height. The threshold necessary to obtain 95% detection eciency is found to be around 2000 e- for the 100 m thick sensors

The Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC) uses Resistive Plate Chambers (RPCs) as a trigger-dedicated muon detector. The RPC subdetector presently consists of 912 chambers, providing a ≈3 ns time resolution for the pseudorapidity region |η| <; 1.6. Up to 18 on-detector Front-End Boards (FEBs) per RPC are responsible for signal processing. Each FEB is configured and monitored through its Inter-Integrated Circuit (I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C) interface to ensure correct and safe detector operation. The resulting ~1.2k I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C lines, serving 3 to 6 FEBs apiece, are accessible through Control Boards (CBs) in token rings. An online control and monitoring system has recently been developed to automatically configure and continuously monitor FEB parameters. A fine-grained software model of hardware and detector components, organized in a dual hierarchical tree structure, facilitates command and data flow. A novel web-based user-interface allows control of and navigation through the system for efficient problem tracing. This paper covers the front-end control and monitoring system for the RPC subdetector; the online software components that allow for flexible configuration and comprehensive monitoring are described.

The Compact Muon Solenoid (CMS) is one of the general purpose experiments at the CERN Large Hadron Collider (LHC). CMS computing relies on different grid infrastructures to provide computational and storage resources. The major grid middleware stacks used for CMS computing are gLite, Open Science Grid (OSG) and ARC (Advanced Resource Connector). Helsinki Institute of Physics (HIP) hosts one of the Tier-2 centers for CMS computing. CMS Tier-2 centers operate software systems for data transfers (PhEDEx), Monte Carlo production (ProdAgent) and data analysis (CRAB). In order to provide the Tier-2 services for CMS, HIP uses tools and components from both ARC and gLite grid middleware stacks. Interoperation between grid systems is a challenging problem and HIP uses two different solutions to provide the needed services. The first solution is based on gLite-ARC grid level interoperability. This allows to use ARC resources in CMS without modifying the CMS application software. The second solution is based on developing specific ARC plugins in CMS software.

The Compact Muon Solenoid (CMS) experiment is operating at the Large Hadron Collider (LHC) with proton–proton collisions at 13-TeV center-of-mass energy and at a bunch spacing of 25 ns. Challenging running conditions for CMS are expected after the High-Luminosity upgrade of the LHC (HL-LHC). We review the CMS ECAL crystal calorimeter upgrade and present results from the first test beam studies. Particular challenges at HL-LHC are the harsh radiation environment, the increasing data rates, and the extreme level of pile-up events, with up to 200 simultaneous proton–proton collisions. Precision timing can be exploited to reduce the effect of the pileup. We report on the timing resolution studies performed with test beams. We discuss the new readout and trigger electronics, which must be upgraded due to the increased trigger and latency requirements at the HL-LHC.

In LHC (Large Hadron Collider) Run 2, the center-of-mass energy for proton-proton collisions is 13 TeV and the instantaneous luminosity has doubled. This has made it more challenging to trigger on interesting events since the number of interactions per crossing (pileup) is significantly larger than in LHC Run 1. The Compact Muon Solenoid (CMS) experiment has installed, commissioned, and is operating the second stage of a two-stage upgrade to the Calorimeter Trigger. This upgrade has improved the trigger algorithms so that the trigger thresholds remain low and physics data is not compromised. The stage-1, which replaced the original CMS Global Calorimeter Trigger, operated successfully in 2015. The completely new stage-2 has replaced the entire calorimeter trigger in 2016 with AMC form-factor boards and optical links operating in a microTCA chassis. It required that updates to the calorimeter back-ends, the source of the trigger primitive data, were also fully installed and operational. The stage-2 system's boards use Xilinx Virtex-7 690T FPGAs and have hundreds of links operating at up to 10 Gbps to maximize data throughput. In addition, a new time-multiplexed architecture was implemented and extensive firmware and software development was necessary. The final commissioning, operation, and performance of the stage-2 calorimeter trigger in 2016 proton collisions are described.

The CMS experiment has greatly benefited from the utilization of the particle-flow (PF) algorithm for the offline reconstruction of data. The Phase II upgrade of the CMS detector for the High Luminosity upgrade of the LHC (HL-LHC) includes the introduction of both tracking and the new high-granularity calorimeters in the Level-1 trigger. The inclusion of tracking in particular offers the possibility of developing a simplified PF algorithm in the Level-1 trigger, as well as the possibility for the use of advanced pileup (PU) mitigation techniques such as Pileup Per Particle Identification (PUPPI). We present the logic of these algorithms, along with their inputs and possible implementation using prototype hardware. We show that these implementations are capable of operating within the budgeted latency requirements of the Level-1 trigger environment. The expected performance and physics implications of such algorithms are shown using Monte Carlo samples with 200 pileup, simulating the harsh conditions of the HL-LHC. We discuss the importance of these advanced techniques in preserving the physics performance in the high-intensity environment.

This thesis presents two research works carried out within the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC): the system validation of the scintillator section of the High Granularity Calorimeter (HGCAL), and a search for a heavy resonance coupling to top quarks and produced in association with top quark pairs in proton–proton collisions at center-of-mass energies of 13 and 13.6 TeV. For the High-Luminosity LHC (HL-LHC) phase, the endcap calorimeters of CMS will be replaced by the HGCAL, a high-precision sampling calorimeter designed to cope with the extreme radiation and pileup conditions expected at the HL-LHC. In regions where radiation levels remain moderate, the hadronic section employs scintillator tiles coupled to silicon photomultipliers (SiPM-on-tile) as active materials. Each HGCAL tilemodule, the basic detector unit of this region, accommodates up to 144 SiPM-on-tile channels read out by dedicated front-end electronics. The performance of several tilemodules was evaluated during test-beam campaigns at the DESY-II facility using 3 GeV electron beams. The measurements serve to validate the response and uniformity of the detector components and to confirm that they meet the design specifications for HL-LHC operation. A search for a new heavy resonance that couples exclusively to top quarks and is produced in association with a top quark pair is presented. The analysis uses proton–proton collision data collected with the CMS detector at center-of-mass energies of 13 TeV (2016–2018) and 13.6 TeV (2022). The search targets the final state with two oppositely charged leptons from the W boson decays of the nonresonant top quarks, and two high-energy jets reconstructing the hadronically decaying resonant top quarks. In this scenario, the two top quarks from the resonance decay are expected to be highly Lorentz-boosted. Their hadronic decays are reconstructed using jets clustered with a variable-radius algorithm and identified with a dedicated top quark tagger based on a boosted decision tree (BDT). Events are selected in a final state containing opposite-sign leptons and b-tagged jets, and the resonance mass is reconstructed from pairs of tagged top jets. The analysis probes resonance masses between 500 GeV and 4 TeV and searches for local excesses in the reconstructed mass spectrum. The results are interpreted in the context of models with vector-like, scalar and pseudoscalar resonances produced in association with top quarks, representing the first such interpretation performed with CMS data.

Exascale science translates to big data. In the case of the Large Hadron Collider (LHC), the data is not only immense, it is also globally distributed. Fermilab is host to the LHC Compact Muon Solenoid (CMS) experiment's US Tier-1 Center, the largest of the LHC Tier-1s. The Laboratory must deal with both scaling and wide-area distribution challenges in processing its CMS data. Fortunately, evolving technologies in the form of 100Gigabit ethernet, multi-core architectures, and GPU processing provide tools to help meet these challenges. Current Fermilab RaD efforts in these areas include optimization of network I/O handling in multi-core systems, modification of middleware to improve application performance in 100GE network environments, and network path reconfiguration and analysis for effective use of high bandwidth networks. This poster will describe the ongoing network-related RaD activities at Fermilab as a mosaic of efforts that combine to facilitate big data processing and movement.

The Compact Muon Solenoid (CMS) detector installed at the CERN Large Hadron Collider (LHC) has an extensive muon system which provides information simultaneously for identification, track reconstruction and triggering of muons. As a consequence of the extreme particle rate and high integrated charge, the essentiality to upgrade the LHC has given rise to the High Luminosity phase of the LHC (HL-LHC) project so that the CMS muon system will be upgraded with superior technological challenges. The CMS GEM collaboration offers a solution to equip the high-eta region of the muon system for Phase 2 (after the year 2017) with large-area triple-layer Gas Electron Multiplier (GEM) detectors, since GEMs have the ability to provide robust and redundant tracking and triggering functions with an excellent spatial resolution of order 100 micron and a high particle rate capability, with a close to 100% detection efficiency. In this contribution, the present status of the triple-GEM project will be reviewed, and the significant achievements from the start of the R&amp;D in 2009 will be emphasized.

The Electromagnetic Calorimeter (ECAL) is one of the particle detectors of the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC). For more than ten years, the CMS ECAL Detector Control System (DCS) and the CMS ECAL Safety Systems (ESS) have supported the experiment operation, contributing to its high availability and safety. The evolution of both systems to fulfil new requirements and constraints, in addition to optimizations towards improving usage and processes automation, led to several changes to their original design. This paper presents the current software/hardware architecture of both CMS ECAL control and safety systems and reviews the major changes applied to both systems during the past years. Furthermore, in view of the CMS Phase-II upgrade of this sub-detector, the corresponding plans for the control and safety systems are also discussed.

The Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC) is undergoing an upgrade program to prepare for the upcoming High-Luminosity era of the LHC. The design of a new timing layer used to measure minimum ionizing particles (MIPs) with a time resolution of (~) 30 ps) and coverage up to pseudo-rapidity |η| = 3.0 is presented. The MIP timing detector (MTD) will be composed of a central barrel region instrumented with LYSO:Ce crystals, and two end-caps instrumented with radiation tolerant low gain avalanche detectors (LGADs). The precision timing information from the MTD will be used to reduce the effects of high pileup on object reconstruction.

The highlight of our last budget period, June 1, 2010, to May 31, 2013, was the discovery of the Higgs boson by the ATLAS and CMS experiments at the CERN Large Hadron Collider (LHC), announced on July 4, 2012, and for which François Englert and Peter Higgs were awarded the 2013 Nobel Prize in Physics on October 8, 2013. The Higgs boson was postulated in 1964 to explain how elementary particles obtain mass and was the missing piece of the Standard Model. However, the Standard Model does not describe everything that we know. There are many unanswered questions, such as how can the Higgs boson have the mass that we have observed, are there more Higgs bosons, why is there more matter than antimatter, and what is the invisible dark matter, which constitutes about 85% of the matter in the universe. Our group played a significant role in the discovery of the Higgs boson and in subsequent analyses. We also carried out searches for new physics, in ways that could help elucidate some of the remaining questions. Our role in the CMS detector focused on the Tracker, a silicon strip outer tracker and pixel inner tracker.

The CERN Large Hadron Collider (LHC) will collide two counter rotating proton beams. The energy stored in each beam is about 350 MJ. If there is a failure in an element of the accelerator, the resulting beam losses could cause damage not only to the accelerator itself, but also to the physics experiments installed. Within the Compact Muon Solenoid experiment (CMS), the use of a Beam Condition Monitor (BCM) is planned to monitor a possible fast increase of the particle flux near the interaction point. The system will flag the onset of adverse beam conditions within the CMS experiment, and, if necessary, input into the beam abort system of the LHC requesting a fast beam dump. Constraints on BCM design from radiation hardness, a minimal material and services budget, and the need for fast signals from sensors with high sensitivity and a large dynamic range, have led to the investigation of synthetic chemical vapor deposited (CVD) diamond for the BCM sensor. In a 5 GeV hadron beam the response of CVD diamonds was tested in fluxes ranging from single minimum ionizing particles (MIPs) to 108 MIPs per cm2, delivered over 40 ns. The signal response, linearity, and stability of both un-irradiated and irradiated sensors were tested over this flux range, and will be presented herein. The results confirm the applicability of CVD diamond for this beam monitoring application