Online data handling and storage at the CMS experiment

During the LHC Long Shutdown 1, the CMS Data Acquisition (DAQ) system underwent a partial redesign to replace obsolete network equipment, use more homogeneous switching technologies, and support new detector back-end electronics. The software and hardware infrastructure to provide input, execute the High Level Trigger (HLT) algorithms and deal with output data transport and storage has also been redesigned to be completely file- based. All the metadata needed for bookkeeping are stored in files as well, in the form of small documents using the JSON encoding. The Storage and Transfer System (STS) is responsible for aggregating these files produced by the HLT, storing them temporarily and transferring them to the T0 facility at CERN for subsequent offline processing. The STS merger service aggregates the output files from the HLT from ~62 sources produced with an aggregate rate of ~2GB/s. An estimated bandwidth of 7GB/s in concurrent read/write mode is needed. Furthermore, the STS has to be able to store several days of continuous running, so an estimated of 250TB of total usable disk space is required. In this article we present the various technological and implementation choices of the three components of the STS: the distributed file system, the merger service and the transfer system.United States. Department of EnergyNational Science Foundation (U.S.

First operational experience with the CMS Run Control System

The Run Control System of the Compact Muon Solenoid (CMS) experiment at CERN's new Large Hadron Collider (LHC) controls the sub-detector and central data acquisition systems and the high-level trigger farm of the experiment. It manages around 10,000 applications that control custom hardware or handle the event building and the high-level trigger processing. The CMS Run Control System is a distributed Java system running on a set of Apache Tomcat servlet containers. Users interact with the system through a web browser. The paper presents the architecture of the CMS Run Control System and deals with operational aspects during the first phase of operation with colliding beams. In particular it focuses on performance, stability, integration with the CMS Detector Control System, integration with LHC status information and tools to guide the shifter.United States. Dept. of EnergyNational Science Foundation (U.S.)European Community. Marie-Curie Research Network

10 Gbps TCP/IP streams from the FPGA for High Energy Physics

The DAQ system of the CMS experiment at CERN collects data from more than 600 custom detector Front-End Drivers (FEDs). During 2013 and 2014 the CMS DAQ system will undergo a major upgrade to address the obsolescence of current hardware and the requirements posed by the upgrade of the LHC accelerator and various detector components. For a loss-less data collection from the FEDs a new FPGA based card implementing the TCP/IP protocol suite over 10Gbps Ethernet has been developed. To limit the TCP hardware implementation complexity the DAQ group developed a simplified and unidirectional but RFC 793 compliant version of the TCP protocol. This allows to use a PC with the standard Linux TCP/IP stack as a receiver. We present the challenges and protocol modifications made to TCP in order to simplify its FPGA implementation. We also describe the interaction between the simplified TCP and Linux TCP/IP stack including the performance measurements.United States. Dept. of EnergyNational Science Foundation (U.S.)Marie Curie International Fellowshi

The new CMS DAQ system for LHC operation after 2014 (DAQ2)

The Data Acquisition system of the Compact Muon Solenoid experiment at CERN assembles events at a rate of 100 kHz, transporting event data at an aggregate throughput of 100 GByte/s. We are presenting the design of the 2nd generation DAQ system, including studies of the event builder based on advanced networking technologies such as 10 and 40 Gbit/s Ethernet and 56 Gbit/s FDR Infiniband and exploitation of multicore CPU architectures. By the time the LHC restarts after the 2013/14 shutdown, the current compute nodes, networking, and storage infrastructure will have reached the end of their lifetime. In order to handle higher LHC luminosities and event pileup, a number of sub-detectors will be upgraded, increase the number of readout channels and replace the off-detector readout electronics with a μTCA implementation. The second generation DAQ system, foreseen for 2014, will need to accommodate the readout of both existing and new off-detector electronics and provide an increased throughput capacity. Advances in storage technology could make it feasible to write the output of the event builder to (RAM or SSD) disks and implement the HLT processing entirely file based.United States. Dept. of EnergyNational Science Foundation (U.S.)Marie Curie International Fellowshi

Search for physics beyond the standard model in events with two leptons, jets, and missing transverse momentum in pp collisions at √s = 8 TeV

A search is presented for physics beyond the standard model in final states with two opposite-sign same-flavor leptons, jets, and missing transverse momentum. The data sample corresponds to an integrated luminosity of 19.4 fb[superscript −1] of proton-proton collisions at √s = 8 TeV collected with the CMS detector at the CERN LHC in 2012. The analysis focuses on searches for a kinematic edge in the invariant mass distribution of the oppositesign same-flavor lepton pair and for final states with an on-shell Z boson. The observations are consistent with expectations from standard model processes and are interpreted in terms of upper limits on the production of supersymmetric particles.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Measurement of the W boson helicity in events with a single reconstructed top quark in pp collisions at √s = 8 TeV

A measurement of the W boson helicity is presented, where the W boson originates from the decay of a top quark produced in pp collisions. The event selection, optimized for reconstructing a single top quark in the final state, requires exactly one isolated lepton (muon or electron) and exactly two jets, one of which is likely to originate from the hadronization of a bottom quark. The analysis is performed using data recorded at a center-of-mass energy of 8 TeV with the CMS detector at the CERN LHC in 2012. The data sample corresponds to an integrated luminosity of 19.7 fb[superscript −1]. The measured helicity fractions are F [subscript L] = 0.298 ± 0.028 (stat) ± 0.032(syst), F [subscript 0] = 0.720 ± 0.039 (stat) ± 0.037(syst), and F [subscript R] = −0.018 ± 0.019 (stat) ± 0.011(syst). These results are used to set limits on the real part of the tWb anomalous couplings, g [subscript L] and g [subscript R]

Search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks using a matrix element method

A search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks is presented. Events with hadronic jets and one or two oppositely charged leptons are selected from a data sample corresponding to an integrated luminosity of 19.5 fb[superscript -1] collected by the CMS experiment at the LHC in pp collisions at a centre-of-mass energy of 8 TeV. In order to separate the signal from the larger t[bar over t] + jets background, this analysis uses a matrix element method that assigns a probability density value to each reconstructed event under signal or background hypotheses. The ratio between the two values is used in a maximum likelihood fit to extract the signal yield. The results are presented in terms of the measured signal strength modifier, μ, relative to the standard model prediction for a Higgs boson mass of 125 GeV. The observed (expected) exclusion limit at a 95 % confidence level is μ < 4.2 (3.3), corresponding to a best fit value [^ over μ] = 1.2[+1.6 over −1.5].United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Search for the production of dark matter in association with top-quark pairs in the single-lepton final state in proton-proton collisions at √s = 8 TeV

A search is presented for particle dark matter produced in association with a pair of top quarks in pp collisions at a centre-of-mass energy of √s = 8 TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 19.7 fb[superscript −1]. This search requires the presence of one lepton, multiple jets, and large missing transverse energy. No excess of events is found above the SM expectation, and upper limits are derived on the production cross section. Interpreting the findings in the context of a scalar contact interaction between fermionic dark matter particles and top quarks, lower limits on the interaction scale are set. These limits are also interpreted in terms of the dark matter-nucleon scattering cross sections for the spin-independent scalar operator and they complement direct searches for dark matter particles in the low mass region.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Search for new physics in events with same-sign dileptons and jets in pp collisions at √s = 8 TeV

A search for new physics is performed based on events with jets and a pair of isolated, same-sign leptons. The results are obtained using a sample of proton-proton collision data collected by the CMS experiment at a centre-of-mass energy of 8 TeV at the LHC, corresponding to an integrated luminosity of 19.5 fb[superscript −1]. In order to be sensitive to a wide variety of possible signals beyond the standard model, multiple search regions defined by the missing transverse energy, the hadronic energy, the number of jets and b-quark jets, and the transverse momenta of the leptons in the events are considered. No excess above the standard model background expectation is observed and constraints are set on a number of models for new physics, as well as on the same-sign top-quark pair and quadruple-top-quark production cross sections. Information on event selection efficiencies is also provided, so that the results can be used to confront an even broader class of new physics models.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio