The LHCb experiment is a specialized experiment for B and D physics at the CERN LHC. The layout of the experiment and the various components are described, with an overview of their performance. ...Global running conditions and performance are also shown. The motivation for the foreseen detector upgrade is presented, together with the proposed new detectors, to be installed during Long Shutdown 2, in 2018.
The LHCb Experiment is a hadronic precision experiment at the LHC accelerator aimed at mainly studying b-physics by profiting from the large b-anti-b-production at LHC. The challenge of high trigger ...efficiency has driven the choice of a readout architecture allowing the main event filtering to be performed by a software trigger with access to all detector information on a processing farm based on commercial multi-core PCs. The readout architecture therefore features only a relatively relaxed hardware trigger with a fixed and short latency accepting events at 1 MHz out of a nominal proton collision rate of 30 MHz, and high bandwidth with event fragment assembly over Gigabit Ethernet. A fast central system performs the entire synchronization, event labelling and control of the readout, as well as event management including destination control, dynamic load balancing of the readout network and the farm, and handling of special events for calibrations and luminosity measurements. The event filter farm processes the events in parallel and reduces the physics event rate to about 2 kHz which are formatted and written to disk before transfer to the offline processing. A spy mechanism allows processing and reconstructing a fraction of the events for online quality checking. In addition a 5 Hz subset of the events are sent as express stream to offline for checking calibrations and software before launching the full offline processing on the main event stream.
LHCb is one of the 4 experiments at the LHC accelerator at CERN. LHCb has approximately 1500 PCs for processing the High Level Trigger (HLT) during physics data acquisition. During periods when data ...acquisition is not required or the resources needed for data acquisition are reduced most of these PCs are idle or very little used. In these periods it is possible to profit from the unused processing capacity to reprocess earlier datasets with the newest applications (code and calibration constants), thus reducing the CPU capacity needed on the Grid. The offline computing environment is based on LHCbDIRAC (Distributed Infrastructure with Remote Agent Control) to process physics data on the Grid. In DIRAC, agents are started on Worker Nodes, pull available jobs from the DIRAC central WMS (Workload Management System) and process them on the available resources. A Control System was developed which is able to launch, control and monitor the agents for the offline data processing on the HLT Farm. It can do so without overwhelming the offline resources (e.g. DBs) and in case of change of the accelerator planning it can easily return the used resources for online purposes. This control system is based on the existing Online System Control infrastructure, the PVSS SCADA and the FSM toolkit.
The production of J/ψ mesons accompanied by open charm, and of pairs of open charm hadrons are observed in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 355 pb−1 ...collected with the LHCb detector. Model independent measurements of absolute cross-sections are given together with ratios to the measured J/ψ and open charm cross-sections. The properties of these events are studied and compared to theoretical predictions.
The production of Upsilon(1S), Upsilon(2S) and Upsilon(3S) mesons in proton-proton collisions at the centre-of-mass energy of sqrt(s)=7 TeV is studied with the LHCb detector. The analysis is based on ...a data sample of 25 pb-1 collected at the Large Hadron Collider. The Upsilon mesons are reconstructed in the decay mode Upsilon -> mu+ mu- and the signal yields are extracted from a fit to the mu+ mu- invariant mass distributions. The differential production cross-sections times dimuon branching fractions are measured as a function of the Upsilon transverse momentum pT and rapidity y, over the range pT < 15 GeV/c and 2.0 < y < 4.5. The cross-sections times branching fractions, integrated over these kinematic ranges, are measured to be sigma(pp -> Upsilon(1S) X) x B(Upsilon(1S)->mu+ mu-) = 2.29 {\pm} 0.01 {\pm} 0.10 -0.37 +0.19 nb, sigma(pp -> Upsilon(2S) X) x B(Upsilon(2S)->mu+ mu-) = 0.562 {\pm} 0.007 {\pm} 0.023 -0.092 +0.048 nb, sigma(pp -> Upsilon(3S) X) x B(Upsilon(3S)->mu+ mu-) = 0.283 {\pm} 0.005 {\pm} 0.012 -0.048 +0.025 nb, where the first uncertainty is statistical, the second systematic and the third is due to the unknown polarisation of the three Upsilon states.
The LHCb measurement of the lifetime ratio of the Λb0 baryon to the B¯0 meson is updated using data corresponding to an integrated luminosity of 3.0 fb−1 collected using 7 and 8 TeV centre-of-mass ...energy pp collisions at the LHC. The decay modes used are Λb0→J/ψpK− and B¯0→J/ψπ+K−, where the π+K− mass is consistent with that of the K¯⁎0(892) meson. The lifetime ratio is determined with unprecedented precision to be 0.974±0.006±0.004, where the first uncertainty is statistical and the second systematic. This result is in agreement with original theoretical predictions based on the heavy quark expansion. Using the current world average of the B¯0 lifetime, the Λb0 lifetime is found to be 1.479±0.009±0.010 ps.
The LHCb Run Control Alessio, F; Barandela, M C; Callot, O ...
Journal of physics. Conference series,
01/2010, Letnik:
219, Številka:
2
Journal Article
Recenzirano
Odprti dostop
LHCb has designed and implemented an integrated Experiment Control System. The Control System uses the same concepts and the same tools to control and monitor all parts of the experiment: the Data ...Acquisition System, the Timing and the Trigger Systems, the High Level Trigger Farm, the Detector Control System, the Experiment's Infrastructure and the interaction with the CERN Technical Services and the Accelerator. LHCb's Run Control, the main interface used by the experiment's operator, provides access in a hierarchical, coherent and homogeneous manner to all areas of the experiment and to all its sub-detectors. It allows for automated (or manual) configuration and control, including error recovery, of the full experiment in its different running modes. Different instances of the same Run Control interface are used by the various sub-detectors for their stand-alone activities: test runs, calibration runs, etc. The architecture and the tools used to build the control system, the guidelines and components provided to the developers, as well as the first experience with the usage of the Run Control will be presented
The differential branching fraction of the decay Λb0→Λμ+μ− is measured as a function of the square of the dimuon invariant mass, q2. A yield of 78±12Λb0→Λμ+μ− decays is observed using data, ...corresponding to an integrated luminosity of 1.0 fb−1, collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. A significant signal is found in the q2 region above the square of the J/ψ mass, while at lower-q2 values upper limits are set on the differential branching fraction. Integrating the differential branching fraction over q2, while excluding the J/ψ and ψ(2S) regions, gives a branching fraction of B(Λb0→Λμ+μ−)=(0.96±0.16(stat)±0.13(syst)±0.21(norm))×10−6, where the uncertainties are statistical, systematic and due to the normalisation mode, Λb0→J/ψΛ, respectively.
The High Level Trigger and Data Acquisition system selects about 2 kHz of events out of the 40 MHz of beam crossings. The selected events are sent to permanent storage for subsequent analysis. In ...order to ensure the quality of the collected data, identify possible malfunctions of the detector and perform calibration and alignment checks, a small fraction of the accepted events is sent to a monitoring farm, which consists of a few tens of general purpose processors. This contribution introduces the architecture of the data stream splitting mechanism from the storage system to the monitoring farm, where the raw data are analyzed by dedicated tasks. It describes the collaborating software components that are all based on the Gaudi event processing framework.
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