Performance and recent developments of the real-time track reconstruction and alignment of the LHCb detector

Conference: EPS 2017, 5-12 July 2017, Venice, Italy

The LHCb detector is a single-arm forward spectrometer, which has been designed for the efficient reconstruction decays of c- and b-hadrons. During the 2013-2015 long shut-down LHCb has introduced a novel real-time detector alignment and calibration strategy for LHC Run II. Data collected at the start of the fill are processed in a few minutes and used to update the alignment, while the calibration constants are evaluated for each run. This procedure permits to obtain the same quality of the processed events in the trigger system as in the offline reconstruction. In addition, the larger timing budget available allows to process the events using the best performing reconstruction in the trigger, which fully includes the particle identification selection criteria. This approach greatly increases the efficiency, in particular for the selection of charm and strange hadron decays. In this talk the basics of the approach are discussed, followed by presentation of the recent developments implemented for the 2017 run of data taking. The topic is discussed in terms of operational performance and reconstruction quality.

The upgrade of the LHCb trigger for Run III

Conference: EPS 2017, 5-12 July 2017, Venice, Italy

The LHCb detector at the LHC is a general purpose detector in the forward region with a focus on reconstructing decays of c- and b-hadrons. For Run III (2021 onwards) of the LHC, LHCb will take data at an instantaneous luminosity of 2 10^{33} cm−2 s−1, five times higher than in Run II (2015-2018). To cope with the harsher data taking conditions, the LHCb collaboration will upgrade the DAQ system and install a purely software based trigger, in addition to various detector upgrades, to process the 30MHz of inelastic collisions delivered by the LHC. A new trigger strategy with real-time reconstruction, alignment and calibration will be employed. We demonstrate how the modified detector infrastructure will be able to face this challenge and discuss the necessary changes to the reconstruction sequence, with particular attention to the performance and execution time budget. We present a novel strategy to distribute and maximise the bandwidth among the different physics channels using a genetic algorithm. This maximises the efficiency for useful physics events.

Novel real-time alignment and calibration of the LHCb Detector in Run2

Conference: CHEP 2016, 10-14 Oct 2016, San Francisco

LHCb has introduced a novel real-time detector alignment and calibration strategy for LHC Run 2. Data collected at the start of the fill are processed in a few minutes and used to update the alignment, while the calibration constants are evaluated for each run. This procedure improves the quality of the online alignment. For example, the vertex locator is retracted and reinserted for stable beam conditions in each fill to be centred on the primary vertex position in the transverse plane. Consequently its position changes on a fill-by-fill basis. Critically, this new real-time alignment and calibration procedure allows identical constants to be used in the online and offline reconstruction, thus improving the correlation between triggered and offline selected events. This offers the opportunity to optimise the event selection in the trigger by applying stronger constraints. The required computing time constraints are met thanks to a new dedicated framework using the multi-core farm infrastructure for the trigger. The motivation for a real-time alignment and calibration of the LHCb detector is discussed from both the operational and physics performance points of view. Specific challenges of this novel configuration are discussed, as well as the working procedures of the framework and its performance.

Machine learning and parallelism in the reconstruction of LHCb and its upgrade

Conference: CHEP 2016, 10-14 Oct 2016, San Francisco

The LHCb detector at the LHC is a general purpose detector in the forward region with a focus on reconstructing decays of c- and b-hadrons. For Run II of the LHC, a new trigger strategy with a real-time reconstruction, alignment and calibration was employed. This was made possible by implementing an offline-like track reconstruction in the high level trigger. However, the ever increasing need for a higher throughput and the move to parallelism in the CPU architectures in the last years necessitated the use of vectorization techniques to achieve the desired speed and a more extensive use of machine learning to veto bad events early on. This document discusses selected improvements in computationally expensive parts of the track reconstruction, like the Kalman filter, as well as an improved approach to get rid of fake tracks using fast machine learning techniques. In the last part, a short overview of the track reconstruction challenges for the upgrade of LHCb, is given: Running a fully software-based trigger, a large gain in speed in the reconstruction has to be achieved to cope with the 40MHz bunch-crossing rate. Two possible approaches for techniques exploiting massive parallelization are discussed.

Novel real-time alignment and calibration of the LHCb Detector in Run2

Conference: 20th Real Time Conference, 5-10 June 2016, Padova, Italy

LHCb has introduced a novel real-time detector alignment and calibration strategy for LHC Run 2. Data collected at the start of the fill are processed in a few minutes and used to update the alignment, while the calibration constants are evaluated for each run. This procedure improves the quality of the online alignment. For example, the vertex locator is retracted and reinserted for stable beam conditions in each fill to be centred on the primary vertex position in the transverse plane. Consequently its position changes on a fill-by-fill basis. Critically, this new real-time alignment and calibration procedure allows identical constants to be used in the online and offline reconstruction, thus improving the correlation between triggered and offline selected events. This offers the opportunity to optimise the event selection in the trigger by applying stronger constraints. The required computing time constraints are met thanks to a new dedicated framework using the multi-core farm infrastructure for the trigger. The motivation for a real-time alignment and calibration of the LHCb detector is discussed from both the operational and physics performance points of view. Specific challenges of this novel configuration are discussed, as well as the working procedures of the framework and its performance.

Additional information:

The LHCb detector consists of subsystems designed to perform track reconstruction and particle identification. The tracking subdetectors are a Vertex Locator around the interaction point, a tracking station with four layers of silicon strip detectors in front of the magnet, and three tracking stations, using either straw-tubes or silicon strip detectors, behind the magnet. This system allows to reconstruct charged particles with a high efficiency (typically > 95% for particles with momentum > 5 GeV) and an excellent momentum resolution (0.5% for particles with momentum < 20 GeV). Two Ring Imaging Cherenkov detectors provide separation between kaons and pions and - in addition to the calorimeters and the muon system - identify particles with a high precision. In Run II of the LHC, a new scheme for the software trigger in LHCb was implemented. It allows splitting the triggering of the event in two stages, giving room to perform the alignment and calibration online after the first stage of the software trigger and using it directly as an input for the second stage of the software trigger. In addition, a larger timing budget is available for both stages, resulting in a more sophisticated track reconstruction which is identical to the one performed offline. To perform the real-time alignment and calibration of the detector a new framework that uses a multi-core farm has been developed. This framework allows the parallelization of the event reconstruction, while the evaluation of the constants is performed on a single node after collecting all the needed information from all the nodes. The procedure is fully automatic and running as soon as enough data are collected. The execution of the alignment tasks is under the control of the LHCb Experiment Control System, and it is implemented as a finite state machine. The data collected at the start of the fill are processed in a few minutes and used to update the alignment, while the calibration constants are evaluated for each run. This procedure improved the quality of the online alignment. This is particularly important for the Vertex Locator, which is retracted and reinserted for stable beam conditions in each fill to be centred on the primary vertex position in the transverse plane and is therefore sensitive to position changes on fill-by-fill basis. Critically, this new real-time alignment and calibration procedure allows identical constants to be used in the online and offline reconstruction, thus improving the correlation between triggered and offline selected events. This offers the opportunity to optimise the event selection in the trigger by applying stronger constraints. The new framework and the alignment and calibration procedure are presented.

VeloStability.pdf Fig. 1 The plot shows the stability of the alignment of the VELO halves during all fills of 2015 data taking. The blue (red) points show the variation of the x (y) translation with respect the previous alignment. TrackerConvergence.png Fig. 2 Convergence of the tracker alignment starting from a misalignment input. Each point shows the change of the alignment parameter outlined in the legend with respect to the previous iteration.

Novel real-time alignment and calibration and track reconstruction for the upgrade at the LHCb detector.

Conference: ACAT 2016, 18-22 January, Valparaiso, Chile

LHCb has introduced a novel real-time detector alignment and calibration strategy for LHC Run 2. Data collected at the start of the fill is processed in a few minutes and used to update the alignment, while the calibration constants are evaluated for each run. This procedure will improve the quality of the online alignment. Critically, this new real-time alignment and calibration procedure allows identical constants to be used in the online and offline reconstruction, thus improving the correlation between triggered and offline selected events. This offers the opportunity to optimise the event selection in the trigger by applying stronger constraints. The required computing time constraints are met thanks to a new dedicated framework using the multi-core farm infrastructure for the trigger. This combined to the improved tracking sequence allows to run in the software trigger the same reconstruction with the same performance as offline. Specific challenges of this novel configuration are discussed, as well as the working procedures of the framework and its performance. A similar scheme is planned to be used in the LHCb upgrade foreseen for 2020. At that time LHCb will run at an instantaneous luminosity of 2x10^33 cm^-2 s^-1 with a fully software based trigger with a read-out of the detector at a rate of 40 MHz. A full new tracking system is being developed: a vertex detector based on silicon pixel sensors, a new silicon micro-strip detector with a high granularity and the scintillating fibre tracker. The new tighter time constraint in the trigger, where only about 13ms are available per event, combined with a higher luminosity by a factor 5 represent a big challenge for the tracking. A new track finding strategy has been considered and new algorithms, partly based on GPUs, and using SIMD instructions are under study. We will present the new strategy and the new fast track reconstruction, including the performance and the highlights of the improvements with respect to the current tracking system of LHCb.

Novel real-time alignment and calibration of the LHCb detector and its performance

Conference: Vienna Conference of Instrumentation 2016, 15-19 February 2016, Vienna, Austria

The LHCb detector is a forward spectrometer at the LHC, designed to perform high precision studies of B and D hadrons. In Run II of the LHC, a new scheme for the software trigger at LHCb allows splitting the triggering of events in two stages, giving room to perform the alignment and calibration in real time. In the novel detector alignment and calibration strategy for Run II, data collected at the start of the fill are processed in a few minutes and used to update the alignment, while the calibration constants are evaluated for each run. This allows identical constants to be used in the online and offline reconstruction, thus improving the correlation between triggered and offline selected events. The required computing time constraints are met thanks to a new dedicated framework using the multi-core farm infrastructure for the trigger. The larger timing budget, available in the trigger, allows to perform the same track reconstruction online and offline. This enables LHCb to achieve the best reconstruction performance already in the trigger, and allows physics analyses to be performed directly on the data produced by the trigger reconstruction. The novel real-time processing strategy at LHCb is discussed from both the technical and operational point of view. The overall performance of the LHCb detector on the data of Run II is presented as well.

Additional information:

The LHCb detector consists of subsystems designed to perform track reconstruction and particle identification. The tracking subdetectors are a Vertex Locator around the interaction point, a tracking station with four layers of silicon strip detectors in front of the magnet, and three tracking stations, using either straw-tubes or silicon strip detectors, behind the magnet. This system allows to reconstruct charged particles with a high efficiency (typically > 95% for particles with momentum > 5 GeV) and an excellent momentum resolution (0.5% for particles with momentum < 20 GeV). Two Ring Imaging Cherenkov detectors provide separation between kaons and pions and - in addition to the calorimeters and the muon system - identify particles with a high precision. In Run II of the LHC, a new scheme for the software trigger in LHCb was implemented. It allows splitting the triggering of the event in two stages, giving room to perform the alignment and calibration online after the first stage of the software trigger and using it directly as an input for the second stage of the software trigger. In addition, a larger timing budget is available for both stages of the software trigger, resulting in a more sophisticated track reconstruction which is identical to the one performed offline. In the novel real-time detector alignment and calibration strategy, data collected at the start of the fill will be processed in a few minutes and used to update the alignment, while the calibration constants will be evaluated for each run. This procedure will improve the quality of the online alignment. For example, the vertex locator is retracted and reinserted for stable beam collisions in each fill to be centred on the primary vertex position in the transverse plane. Consequently its position changes on a fill-by-fill basis. Critically, this new real-time alignment and calibration procedure allows identical constants to be used in the online and offline reconstruction, thus improving the correlation between triggered and offline selected events. This offers the opportunity to optimise the event selection in the trigger by applying stronger constraints. The online calibration facilitates the use of hadronic particle identification using the RICH detectors at the trigger level. The required computing time constraints are met thanks to a new dedicated framework using the multi-core farm infrastructure for the trigger. The motivation for a real-time alignment and calibration of the LHCb detector is discussed from both the operational and physics performance points of view. Specific challenges of this novel configuration are discussed, as well as the working procedures of the framework and its performance. The convergence of the online and offline track reconstruction results in better overall selection efficiencies and reduced systematic uncertainties due to a perfect overlap. We will highlight the developments and improvements in the track reconstruction which were necessary for this unification and give first results from the operation of LHCb in this mode. The overall performances of the LHCb detector on the first data of Run II are presented.

Novel real-time calibration & alignment and tracking performance for LHCb Run II

Conference: DPF 2015,4-8 August 2015, Ann Arbour, USA

The LHCb detector consists of subsystems designed to perform high efficiency track reconstruction (> 95%) with an excellent momentum resolution (0.5% for p< 20 GeV). Two Ring Imaging Cherenkov detectors provide particle identification with a high precision. In Run II of the LHC, a new scheme for the software trigger at LHCb allows splitting the triggering of the event in two stages, giving room to perform the alignment and calibration in real time. In the novel detector alignment and calibration strategy for Run II, data collected at the start of the fill are processed in a few minutes and used to update the alignment, while the calibration constants are evaluated for each run. This allows identical constants to be used in the online and offline reconstruction. The larger timing budget, available in the trigger, results in the convergence of the online and offline track reconstruction. The same performance of the track reconstruction and PID are achieved online and offline. This offers the opportunity to optimise the event selection in the trigger with stronger constraints and including the hadronic PID. It additionally increases selection efficiencies and purity and reduces systematic uncertainties. The novel real-time alignment and calibration strategy at LHCb is discussed from both the operational and physics performance points of view. The development and improvements in the track reconstruction are highlighted. The overall performances of the LHCb detector on the first data of Run II are presented.

Novel real-time calibration & alignment and tracking performance for LHCb Run II

Conference: EPS 2015, 22-29 July 2015, Vienna, Austria

The LHCb detector consists of subsystems designed to perform high efficiency tracking (>95%) with an excellent momentum resolution (0.5% for p<20 GeV). Two Ring Imaging Cherenkov detectors provide precise particle identification. In Run II of the LHC, a new scheme for the LHCb software trigger allows splitting the triggering of the event in two stages, giving room to perform the alignment and calibration in real time. In the novel detector alignment and calibration strategy for Run II, data collected at the start of the fill are processed in a few minutes and used to update the alignment, while the calibration constants are evaluated for each run. This allows identical constants to be used in the online and offline reconstruction. The larger timing budget, available in the trigger, results in the convergence of the online and offline track reconstruction. The same performance of the track reconstruction and PID are achieved online and offline. This offers the opportunity to optimise the event selection in the trigger with stronger constraints and including the hadronic PID. It additionally increases selection efficiencies and purity and reduces systematic uncertainties. The novel real-time alignment and calibration strategy at LHCb is discussed from both the operational and physics performance points of view. The development and improvements in the track reconstruction are highlighted. The overall performances of the LHCb detector on the first data of Run II are presented.

Additional information:

The LHCb detector consists of subsystems designed to perform track reconstruction and particle identification. The tracking subdetectors are a Vertex Locator around the interaction point, a tracking station with four layers of silicon strip detectors in front of the magnet, and three tracking stations, using either straw-tubes or silicon strip detectors, behind the magnet. This system allows to reconstruct charged particles with a high efficiency (typically > 95% for particles with momentum > 5 GeV) and an excellent momentum resolution (0.5% for particles with momentum < 20 GeV). Two Ring Imaging Cherenkov detectors provide separation between kaons and pions and - in addition to the calorimeters and the muon system - identify particles with a high precision. In Run II of the LHC, a new scheme for the software trigger in LHCb was implemented. It allows splitting the triggering of the event in two stages, giving room to perform the alignment and calibration online after the first stage of the software trigger and using it directly as an input for the second stage of the software trigger. In addition, a larger timing budget is available for both stages of the software trigger, resulting in a more sophisticated track reconstruction which is identical to the one performed offline. In the novel real-time detector alignment and calibration strategy, data collected at the start of the fill will be processed in a few minutes and used to update the alignment, while the calibration constants will be evaluated for each run. This procedure will improve the quality of the online alignment. This is particularly important for the Vertex Locator, which is retracted and reinserted for stable beam collisions in each fill to be centred on the primary vertex position in the transverse plane. Therefore, its position changes on a fill-by-fill basis. Critically, this new real-time alignment and calibration procedure allows identical constants to be used in the online and offline reconstruction, thus improving the correlation between triggered and offline selected events. This offers the opportunity to optimise the event selection in the trigger by applying stronger constraints. The online calibration facilitates the use of hadronic particle identification using the RICH detectors at the trigger level. The required computing time constraints are met thanks to a new dedicated framework using the multi-core farm infrastructure for the trigger. The motivation for a real-time alignment and calibration of the LHCb detector is discussed from both the operational and physics performance points of view. Specific challenges of this novel configuration are discussed, as well as the working procedures of the framework and its performance, showing first results of Run II of LHCb. The convergence of the online and offline track reconstruction results in better overall selection efficiencies and reduced systematic uncertainties due to a perfect overlap. We will highlight the developments and improvements in the track reconstruction which were necessary for this unification and give first results from the operation of LHCb in this mode in Run II.

Current and prospective performance of the LHCb tracking system

Conference: VERTEX 2015, 1-5 June, Santa Fe, USA

The LHCb tracking system consists of a Vertex Locator around the interaction point, a tracking station with four layers of silicon strip detectors in front of the magnet, and three tracking stations, using either straw-tubes or silicon strip detectors, behind the magnet. This system allows to reconstruct charged particles with a high efficiency (typically > 95% for particles with momentum > 5 GeV) and an excellent momentum resolution (0.5% for particles with momentum < 20 GeV). The high momentum resolution results in very narrow mass peaks, leading to a very good signal-to-background ratio in such key channels as Bs -> mu mu. Furthermore an optimal decay time resolution is an essential element in the studies of time dependent CP violation. Thanks to the excellent performance of the tracking system, a decay time resolution of ~50 fs is obtained, allowing to resolve the fast B0s oscillation with a mixing frequency of 17.7 ps-1. In this talk, we will give an overview of the track reconstruction in LHCb and review its performance in Run I of the LHC. We will highlight the challenges and improvements of the track reconstruction for the data taking period from 2015 on, discussing efforts to improve the timing in the online reconstruction as well as approaches to unify the online and offline reconstruction. The upgrade of the LHCb experiment will run at an increased instantaneous luminosity of 2x10^33 cm^-2 s^-1 with a fully software based trigger, allowing to read out the detector at a rate of 40MHz. For this purpose, the full tracking system will be newly developed. We will present the performance of the tracking system for the LHCb upgrade, highlighting the improvements with respect to the current tracking system of LHCb, and review the track finding strategy. Special emphasize will be put on the need for fast track reconstruction in the software trigger, also giving examples of the potential use of parallelism in the pattern recognition. Finally, we will give some prospects of the physics performance with the LHCb upgrade for channels relying on excellent tracking capabilities.

Novel real-time alignment and calibration of the LHCb Detector in Run2

Conference: VERTEX 2015, 1-5 June, Santa Fe, USA

LHCb has introduced a novel real-time detector alignment and calibration strategy for LHC Run 2. Data collected at the start of the fill will be processed in a few minutes and used to update the alignment, while the calibration constants will be evaluated for each run. This procedure will improve the quality of the online alignment. For example, the vertex locator is retracted and reinserted for stable beam collisions in each fill to be centred on the primary vertex position in the transverse plane. Consequently its position changes on a fill-by-fill basis. Critically, this new real-time alignment and calibration procedure allows identical constants to be used in the online and offline reconstruction, thus improving the correlation between triggered and offline selected events. This offers the opportunity to optimise the event selection in the trigger by applying stronger constraints. The required computing time constraints are met thanks to a new dedicated framework using the multi-core farm infrastructure for the trigger. The motivation for a real-time alignment and calibration of the LHCb detector is discussed from both the operational and physics performance points of view. Specific challenges of this novel configuration are discussed, as well as the working procedures of the framework and its performance.

Tracking system of the LHCb upgrade

Conference: 13th Pisa Meeting on Advanced Detectors, 24-30 May, Isola d'Elba, Italy

The upgrade of the LHCb experiment will run at an instantaneous luminosity of 2x10^33 cm^-2 s^-1 with a fully software based trigger, allowing to read out the detector at a rate of 40MHz. For this purpose, the full tracking system will be newly developed: the vertex locator (VELO) will be replaced by a pixel-based detector, withstanding the high radiation dose and providing an excellent track reconstruction with an efficiency of above 99% for all charged particles of interest. Upstream of the magnet, a silicon mico-strip detector with a high granularity and an improved acceptance coverage, called the Upstream Tracker (UT), will replace the current silicon strip tracker, and provide a rough momentum estimate. The tracking system downstream of the magnet will be replaced by the Scintillating Fibre tracker (SciFi), which will consist of 12 layers using 2.5m long scintillating fibres read out by silicon photo-multipliers, providing a spatial resolution better than 100 micron and resulting in a total momentum resolution of 0.4% for charged particles with a momentum of 20 GeV. We will present the performance of the tracking system for the LHCb upgrade, highlighting the improvements with respect to the current tracking system of LHCb, and review the track finding strategy. Special emphasize will be put on the need for fast track reconstruction in the software trigger, also giving examples of the potential use of parallelism in the pattern recognition. Finally, we will give some prospects of the physics performance with the LHCb upgrade for channels relying on excellent tracking capabilities.

Performance of the LHCb tracking system in RunI of the LHC

Conference: 13th Pisa Meeting on Advanced Detectors, 24-30 May, Isola d'Elba, Italy

The LHCb tracking system consists of a Vertex Locator around the interaction point, a tracking station with four layers of silicon strip detectors in front of the magnet, and three tracking stations, using either straw-tubes or silicon strip detectors, behind the magnet. This system allows to reconstruct charged particles with a high efficiency (typically > 95% for particles with momentum > 5 GeV) and an excellent momentum resolution (0.5% for particles with momentum < 20 GeV). The high momentum resolution results in very narrow mass peaks, leading to a very good signal-to-background ratio in such key channels as Bs -> mu mu. Furthermore an optimal decay time resolution is an essential element in the studies of time dependent CP violation. Thanks to the excellent performance of the tracking system, a decay time resolution of ~50 fs is obtained, allowing to resolve the fast B0s oscillation with a mixing frequency of 17.7 ps-1. In this talk, we will give an overview of the track reconstruction in LHCb and review its performance in Run I of the LHC. We will highlight the challenges and improvements of the track reconstruction for the data taking period from 2015 on, discussing efforts to improve the timing in the online reconstruction as well as approaches to unify the online and offline reconstruction.

Novel real-time alignment and calibration of the LHCb Detector in Run2

Conference: 13th Pisa Meeting on Advanced Detectors, 24-30 May, Isola d'Elba, Italy

LHCb has introduced a novel real-time detector alignment and calibration strategy for LHC Run 2. Data collected at the start of the fill will be processed in a few minutes and used to update the alignment, while the calibration constants will be evaluated for each run. This procedure will improve the quality of the online alignment. For example, the vertex locator is retracted and reinserted for stable beam collisions in each fill to be centred on the primary vertex position in the transverse plane. Consequently its position changes on a fill-by-fill basis. Critically, this new real-time alignment and calibration procedure allows identical constants to be used in the online and offline reconstruction, thus improving the correlation between triggered and offline selected events. This offers the opportunity to optimise the event selection in the trigger by applying stronger constraints. The online calibration facilitates the use of hadronic particle identification using the RICH detectors at the trigger level. The required computing time constraints are met thanks to a new dedicated framework using the multi-core farm infrastructure for the trigger. The motivation for a real-time alignment and calibration of the LHCb detector is discussed from both the operational and physics performance points of view. Specific challenges of this novel configuration are discussed, as well as the working procedures of the framework and its performance.

Optimization of the LHCb track reconstruction

Conference: CHEP 2015, 13-17 April 2015, Okinawa, Japan

Abstract: The LHCb track reconstruction uses sophisticated pattern recognition algorithms to reconstruct trajectories of charged particles. Their main feature is the use of a Hough-transform like approach to connect track segments from different subdetectors, allowing for having no tracking stations in the magnet of LHCb. While yielding a high efficiency, the track reconstruction is a major contributor to the overall timing budget of the software trigger of LHCb, and will continue to be so in the light of the higher track multiplicity expected from Run II of the LHC. In view of this fact, key parts of the pattern recognition have been revised and redesigned. We will present the main features which were studied. A staged approach strategy for the track reconstruction in the software trigger was investigated: it allows unifying complementary sets of tracks coming from the different stages of the high level trigger, resulting in a more flexible trigger strategy and a better overlap between online and offline reconstructed tracks. Furthermore the use of parallelism was investigated, using SIMD instructions for time-critical parts of the software or - in a later stage - using GPU-driven track reconstruction. In addition a new approach to monitoring was implemented, where quantities important for track reconstruction are monitored on a regular basis, using an automated framework for comparing different figures of merit.

Real-time alignment and calibration of the LHCb Detector in Run2

Conference: CHEP 2015, 13-17 April 2015, Okinawa, Japan

Abstract: Stable, precise spatial alignment and PID calibration are necessary to achieve optimal detector performances. During Run2, LHCb will have a new real-time detector alignment and calibration to reach equivalent performances in the online and offline reconstruction. This offers the opportunity to optimise the event selection by applying stronger constraints as well as hadronic particle identification at the trigger level. The required computing time constraints are met thanks to a new dedicated framework using the multi-core farm infrastructure for the trigger. The motivation for a real-time alignment and calibration of the LHCb detector is discussed from the operative and physics performance point of view. Specific challenges of this configuration are discussed, as well as the designed framework and its performance.

Tracking and Alignment of the LHCb detector

Conference: ICATPP 2013, 23-27 September 2013, Como, Italy

Abstract: The LHCb experiment is designed to study B-decays at the LHC. This purpose is achieved by means of an outstanding track momentum resolution and excellent particle identification. The performance of the detector exceeds expectations, and the physics program of the collaboration is extended to the study of charm decays, QCD and electroweak physics. Both tracking and alignment play a key role for obtaining these results. The tracking efficiency in this high-occupancy environment has been measured during LHC Run I (2010-2012) to be larger than 95% over a wide range of momentum and pseudo-rapidity. The alignment of the detector is based on a Kalman filter fit of the tracks and provides an uncertainty on the momentum scale below 110−4 and a momentum resolution of about 0.4%. These results allowed one to achieve high-precision mass measurements of many charm and B hadrons so far. Starting from Run II of the LHC, the running conditions will continue to push the performance of the detector to its limits. An upgrade of the detector will therefore take place in 2018 to extend its reach. A fast tracking will be a fundamental part of the upgraded detector as well. In light of this, the prospects for the recently proposed upgrade will be discussed.

-- MaurizioMartinelli - 2014-12-16

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