Vertex Locator Research Articles

Performance of the LHCb Vertex Locator

The Vertex Locator (VELO) is a silicon microstrip detector that surrounds the proton-proton interaction region in the LHCb experiment. The performance of the detector duringthe first years of its physics operation is reviewed. The system isoperated in vacuum, uses a bi-phase CO2 cooling system, and thesensors are moved to 7 mm from the LHC beam for physics data taking. The performance and stability of these characteristic features of the detector are described, and details of the material budget are given. The calibration of the timing and the data processing algorithms that are implemented in FPGAs are described.The system performance is fully characterised. The sensors have asignal to noise ratio of approximately 20 and a best hit resolution of4 μm is achieved at the optimal track angle. The typical detectoroccupancy for minimum bias events in standard operating conditions in2011 is around 0.5%, and the detector has less than 1% of faultystrips. The proximity of the detector to the beam means that the innerregions of the n+-on-n sensors have undergone space-charge signinversion due to radiation damage. The VELO performance parametersthat drive the experiment's physics sensitivity are also given. Thetrack finding efficiency of the VELO is typically above 98% and themodules have been aligned to a precision of 1 μm for translations inthe plane transverse to the beam. A primary vertex resolution of 13 μm in thetransverse plane and 71 μm along the beam axis is achieved forvertices with 25 tracks. An impact parameter resolution ofless than 35 μm is achieved for particles with transverse momentumgreater than 1 GeV/c.

Upgrade of the LHCb Vertex Locator

The upgrade of the LHCb experiment, planned for 2018, will transform the entire readout to a trigger-less system operating at 40 MHz. All data reduction algorithms will be executed in a high-level software farm, with access to all event information. This will enable the detector to run at luminosities of 1–2 × 1033/cm2/s and probe physics beyond the Standard Model in the heavy sector with unprecedented precision.The upgraded VELO must be low mass, radiation hard and vacuum compatible. It must be capable of fast pattern recognition and track reconstruction and will be required to drive data to the outside world at speeds of up to 2.5 Tbit/s. This challenge is being met with a new Vertex Locator (VELO) design based on hybrid pixel detectors positioned to within 5 mm of the LHC colliding beams. The sensors have 55 × 55 μm square pixels and the VELOPix ASIC which is being developed for the readout is based on the Timepix/Medipix family of chips. The hottest ASIC will have to cope with pixel hit rates of up to 900 MHz.The material budget will be optimised with the use of evaporative CO2 coolant circulating in microchannels within a thin silicon substrate. Microchannel cooling brings many advantages: very efficient heat transfer with almost no temperature gradients across the module, no CTE mismatch with silicon components, and low material contribution. This is a breakthrough technology being developed for LHCb.LHCb is also focussing effort on the construction of a lightweight foil to separate the primary and secondary LHC vacua, the development of high speed cables and radiation qualification of the module.The 40 MHz readout will also bring significant conceptual changes to the way in which the upgrade trigger is operated. Work is in progress to incorporate momentum and impact parameter information into the trigger at the earliest possible stage, using the fast pattern recognition capabilities of the upgraded detector.The current status of the VELO upgrade will be described together with a presentation of recent beam-test results.

The LHCb VELO: Performance and radiation damage

LHCb is a forward spectrometer experiment dedicated to the search for New Physics in the decays of beauty and charm hadrons produced by the proton–proton interactions at the Large Hadron Collider (LHC) at CERN. The measurement of the flight distance of these hadrons is critical for the physics program. The VErtex LOcator (VELO) is the silicon detector surrounding the LHCb interaction point and provides excellent resolution of charged tracks and vertex positions. The VELO has been run successfully since installation. The sensors have the first sensitive strips at a radius of 8.2mm and are exposed to maximum radiation doses of ~0.6×10141MeVneq/cm2perfb−1 delivered integrated luminosity. The performance of the VELO during the first LHC run is described, together with methods to monitor radiation damage. Results from the radiation damage studies are presented showing interesting features, such as an unexpected charge coupling to the second metal layer routing lines after irradiation. The radiation damage has so far no impact on the track reconstruction performance.

The silicon vertex locator for the LHCb upgrade

The upgrade of the LHCb experiment, planned for 2018, will transform the entire readout to a triggerless system being read out at 40MHz. The upgraded silicon vertex detector (VELO) must be light weight, radiation hard, and compatible with LHC vacuum requirements. It must be capable of fast pattern recognition, fast track reconstruction and high precision vertexing. This challenge is being met with a new VELO design based on hybrid pixel detectors positioned to within 5mm of the LHC colliding beams. The detector will be shielded from the beam by a ~300μm thick aluminium foil. Evaporative CO2 coolant circulating in micro-channels embedded in a thin silicon substrate will be used for cooling.

The LHCb Vertex Locator — performance and radiation damage

LHCb is a dedicated flavour physics experiment at the Large Hadron Collider at CERN. The Vertex Locator (VELO) is an important part of a LHCb tracking system, enabling precision measurement of beauty and charm mesons' flight distance. The VELO consist of a set of silicon micro-strip detectors, arranged in two retractable halves, operating only 7 mm from the interaction region. In these proceedings the VELO performance during the Run 1 is summarised and radiation damage studies are presented.

Radiation damage in the LHCb vertex locator

The LHCb Vertex Locator (VELO) is a silicon strip detector designed toreconstruct charged particle trajectories and vertices produced at the LHCbinteraction region. During the first two years of data collection, the 84 VELOsensors have been exposed to a range of fluences up to a maximum value ofapproximately 45 × 1012 1 MeV neutron equivalent(1 MeV neq). At the operational sensor temperature of approximately−7 °C, the average rate of sensor current increase is18 μA per fb−1, in excellent agreement withpredictions. The silicon effective bandgap has been determined using currentversus temperature scan data after irradiation, with an average value ofEg = 1.16±0.03±0.04 eV obtained. The first observation ofn+-on-n sensor type inversion at the LHC has been made, occurring at a fluenceof around 15 × 1012 of 1 MeV neq. The only n+-on-psensors in use at the LHC have also been studied. With an initial fluence ofapproximately 3 × 1012 1 MeV neq, a decrease in theEffective Depletion Voltage (EDV) of around 25 V is observed. Following this initialdecrease, the EDV increases at a comparable rate to the typeinverted n+-on-n type sensors, with rates of (1.43±0.16) × 10−12 V/ 1 MeV neq and (1.35±0.25) × 10−12 V/ 1 MeV neq measured for n+-on-p andn+-on-n type sensors, respectively. A reduction in the charge collectionefficiency due to an unexpected effect involving the second metal layer readoutlines is observed.

Performance, radiation damage effects and upgrade of the LHCB vertex locator

LHCb is a dedicated experiment to study new physics in the decays of heavy hadrons at the Large Hadron Collider (LHC) at CERN. Heavy hadrons are identified through their flight distance in the Vertex Locator (VELO), the retractable silicon-strip vertex detector surrounding the LHCb interaction point at only 8mm from the beam during normal LHC operation. The VELO consists of a series of silicon micro-strip detectors and operates in an extreme and highly non-uniform radiation environment. The performance of the LHCb VELO during the first three years of LHC physics running and the primary results from radiation damage studies are presented. Plans for an upgraded detector by 2018 with a 40MHz readout are also presented.

Radiation damage on the LHCb-VELO

The LHCb Vertex Locator (VELO) is designed to reconstruct charged particle trajectories and vertices produced at the LHCb interaction region. This is a silicon strip detector system operating at the closest distance from the interaction region among all the currently installed detectors at the CERN LHC. The geometry of the sensors implies that every detector region is exposed to a different dose of radiation depending mainly on the radial distance from the beam line. In the first 2 years of operation they have been exposed to a range of fluences up to a maximum value of about 4.5×1013 1MeVneutron equivalent (neq)cm−2. At the end of 2012 a maximum of about 1.5×1014neq has been reached; data analysis is ongoing. Sensor currents, full depletion voltage and charge collection efficiencies have been studied at various fluences. Observation of type inversion of the n-type silicon sensors has been made (about after 10–15×1012neq). The n-type bulk sensors have been compared with the only p-type bulk detectors installed in the LHC. A reduction in the charge collection efficiency due to charge losses to a second metal layer (used for routing the signal to the readout electronics in LHCb-VELO sensors) has been measured. Possible solutions to this undesirable effect are planned to be studied in the framework of the LHCb-VELO upgrade.

The LHCb VELO upgrade

LHCb is a forward spectrometer experiment dedicated to the study of new physics in the decays of beauty and charm hadrons produced in proton collisions at the Large Hadron Collider (LHC) at CERN.The VErtex LOcator (VELO) is the microstrip silicon detector surrounding the interaction point, providing tracking and vertexing measurements. The upgrade of the LHCb experiment, planned for 2018, will increase the luminosity up to 2×1033cm−2s−1 and will perform the readout as a trigger-less system with an event rate of 40MHz. Extremely non-uniform radiation doses will reach up to 5×10151MeVneq/cm2 in the innermost regions of the VELO sensors, and the output data bandwidth will be increased by a factor of 40. An upgraded detector is under development based in a pixel sensor of the Timepix/Medipix family, with 55×55μm2 pixels. In addition a microstrip solution with finer pitch, higher granularity and thinner than the current detector is being developed in parallel.The current status of the VELO upgrade program will be described together with recent testbeam results.

VeloPix ASIC development for LHCb VELO upgrade

The upgrade of the LHCb experiment, planned for 2018, will transform the readout of the entire experiment to a triggerless system operating at 40MHz. All data reduction algorithms will be run in a high level software farm, and will have access to event information from all subdetectors. This approach will give great power and flexibility in accessing the physics channels of interest in the future, in particular the identification of flavour tagged events with displaced vertices. The data acquisition and front end electronics systems require significant modification to cope with the enormous throughput of data. For the silicon vertex locator (VELO) a dedicated development is underway for a new ASIC, VeloPix, which will be a derivative of the Timepix/Medipix family of chips. The chip will be radiation hard and be able to cope with pixel hit rates of above 500MHz, highly non-uniformly distributed over the 2cm2 chip area. The chip will incorporate local intelligence in the pixels for time-over-threshold measurements, time-stamping and sparse readout. It must in addition be low power, radiation hard, and immune to single event upsets. In order to cope with the datarates and use the pixel area most effectively, an on-chip data compression scheme will integrated. This paper will describe the requirements of the LHCb VELO upgrade, and give an overview of the digital architecture being developed specifically for the readout chip.

LHCb detector status and upgrade

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. 1 General overview The LHCb detector is intended to study beauty and charm physics. At LHC, the production is mainly in the forward and backward directions. Both b particles are going in the same direction, thus a single arm spectrometer allows measuring the interesting b decay together with tracks from the other b decay, for flavour tagging. The overall detector layout is shown in figure 1. The vertex locator measures all tracks near the interaction point, a dipole magnet and tracking stations after are providing accurate momentum measurement, two RICH detectors, calorimeters and a muon system provide full particle identification.

Calibration and Performance Monitoring of the LHCb Vertex Locator

The LHCb experiment is dedicated to searching for New Physics effects in the heavy flavour sector, precise measurements of CP violation and rare heavy meson decays. Precise tracking and vertexing around the interaction point is crucial in achieving these physics goals. The LHCb VELO (VErtex LOcator) silicon micro-strip detector is the highest precision vertex detector at the LHC and is located at only 8.2 mm from the proton beams. The high spatial resolution (down to 4 microns single hit precision) is obtained by a complex chain of processing algorithms to suppress noise and reconstruct clusters. These are implemented in large FPGAs, with over one million parameters that need to be individually optimised. Previously [1], we presented a novel approach that has been developed to optimise the parameters and integrating their determination into the full software framework of the LHCb experiment. Presently we report on the experience gained from regular operation of the calibration and monitoring software with the collision data taken in 2011 by the LHCb experiment. Both the VELO performance and its impact on the physics results will be detailed.

The LHCb VERTEX LOCATOR performance and VERTEX LOCATOR upgrade

LHCb is an experiment dedicated to the study of new physics in the decays of beauty and charm hadrons at the Large Hadron Collider (LHC) at CERN. The Vertex Locator (VELO) is the silicon detector surrounding the LHCb interaction point.The detector operates in a severe and highly non-uniform radiation environment.The small pitch and analogue readout result in a best single hit precision of 4 μm.The upgrade of the LHCb experiment, planned for 2018, will transform the entire readout to a trigger-less system operating at 40 MHz event rate. The vertex detector will have to cope with radiation levels up to 1016 1 MeVneq/cm2, more than an order of magnitude higher than those expected at the current experiment. A solution is under development with a pixel detector, based on the Timepix/Medipix family of chips with 55 x 55 μm pixels. In addition a micro-strip solution is also under development, with finer pitch, higher granularity and lower mass than the current detector. The current status of the VELO will be described together with recent testbeam results.

Radiation damage in the LHCb VELO

LHCb is a dedicated experiment to study new physics in the decays of beauty and charm hadrons at the Large Hadron Collider (LHC) at CERN. The Vertex Locator (VELO) is a silicon micro-strip detector which surrounds the LHCb interaction point and provides μm resolution of charged tracks and vertex positions. The tip of the VELO sensors is predicted to receive a dose of 0.5×1013 1-MeV neq/cm2 per fb of data. The highest fluence of any silicon tracker at the four major LHC experiments. Radiation damage studies have been carried out during the first two years of data taking at LHCb for all 88 sensors of the VELO. Radiation damage has been observed in all sensors, with those sensors in the highest fluence regions showing evidence of type inversion. Radiation induced charge loss due to the second metal layer on the sensors is also observed.

Performance of the LHCb VELO

LHCb is a dedicated experiment to search for new physics in the decays of beauty and charm hadrons at the Large Hadron Collider (LHC) at CERN. Measurement of the flight distance of these hadrons is critical for the physics programme. The Vertex Locator (VELO) is a silicon micro-strip detector which surrounds the LHCb interaction point and provides μm resolution of charged tracks and vertex positions. The VELO has been run successfully for the 2010 and 2011 LHC physics runs. Operational results show a signal-to-noise ratio of approximately 20 and a best hit resolution of 4μm.

Radiation damage in the LHCb VELO

The VErtex LOcator (VELO) is a silicon strip detector designed to reconstruct particle tracks and vertices produced by proton–proton interactions near to the LHCb interaction point. The excellent track resolution and decay vertex separation provided by the VELO are essential to all LHCb analyses. For the integrated luminosity delivered by the LHC up to the end of 2011 the VELO is exposed to higher particle fluences than any other silicon detector of the four major LHC experiments. These proceedings present results from radiation damage studies carried out during the first two years of data taking at the LHC. Radiation damage has been observed in all of the 88 VELO silicon strip sensors, with many sensors showing evidence of type-inversion in the highest fluence regions. Particular attention has been given to the two n+-on-p sensors as this type of sensor is one of the leading candidates for the LHC silicon detector upgrades.

LHCb VELO tracking resolutions

The LHCb detector at the Large Hadron Collider (LHC) at CERN is designed to make precision measurements of mesons and baryons containing b and c quarks. Many analyses performed using data from LHCb examine properties of particles and anti-particles as a function of proper decay time. Precise measurements of production and decay vertices are thus essential. The Vertex Locator (VELO) subdetector of LHCb performs this task. The excellent performance of the VELO with respect to the resolutions it achieves on single hits, impact parameters, and primary vertex positions is presented, with particular attention paid to measurement of impact parameters.

LHCb VErtex LOcator (VELO) upgrade

The VErtex LOcator (VELO) is a vital piece of apparatus providing tracking, triggering and vertexing to the LHCb experiment. Its superb impact parameter resolution and high efficiency enable LHCb to make precision measurements and searches for New Physics in the flavour sector. These proceedings focus on the R&D for the future LHCb VELO detector to be installed in the upgraded LHCb experiment. In order to increase hadronic yields and to be able to run at higher luminosities LHCb plans to upgrade the front end electronics, currently limited by a first level hardware trigger. For the silicon vertex detector this implies a complete rebuild of the modules and electronics, with improved cooling capability to cope with the high voltages and currents expected after significant radiation damage has been accrued. This paper presents the design considerations for the vertex detector upgrade together with the two proposed options for the sensor layout, based on strips or pixels. As part of the R&D programme a pixel based tracking telescope has been developed for use in testbeams, to gain experience with pixel tracking and to evaluate the technologies under consideration. This paper presents results from the last years running of the TimePix telescope and describes the integration of various test devices.

The LHCb VELO (VErtex LOcator) and the LHCb VELO upgrade

LHCb is a forward spectrometer experiment dedicated to the study of new physics in the decays of beauty and charm hadrons produced in proton collisions at the Large Hadron Collider (LHC) at CERN. The VErtex LOcator (VELO) is the silicon detector surrounding the LHCb interaction point. The beauty and charm hadrons are identified through their flight distance in the Vertex Locator (VELO), and hence the detector is critical for both the trigger and the offline physics analyses. The sensors, which have an inner radius of ∼7mm from the beam axis at the edge, and the first sensitive strips at a radius of ∼8.2mm are exposed to maximum radiation doses of ∼0.6×10141MeVneq/cm2 per integrated luminosity of fb−1. The performance of the VELO during the first two years of LHC running is described, together with the methods used to monitor radiation damage. The detector so far shows no significant performance degradation, however many interesting effects have been observed in the sensors, including a coupling of charge to the second metal routing line layer after irradiation. In 2018 the VELO will be upgraded together with the rest of the LHCb detector to a 40MHz readout. The modules together with their front end electronics will be completely replaced with a radiation hard system capable of driving the signals out at the required rates. The current status of the R&D for the LHCb VELO Upgrade is outlined.

Performance of the LHCb Vertex Locator

LHCb is a dedicated flavour physics experiment at the Large Hadron Collider (LHC) at CERN. The Vertex Locator (VELO) is an essential part of the LHCb detector, permitting precision measurements of the production and decay vertices of beauty and charm particles. The VELO consists of a series of silicon micro-strip detectors, arranged in two retractable halves. Positioned only 7 mm from the beam during normal operations, it must withstand very high levels of radiation. The performance of the LHCb VELO during the first year of LHC physics running is presented.