Upgraded Vertex Locator Research Articles

LHCb VELO fast calibration

During the long shutdown 2 of the LHC, the LHCb Experiment was upgraded to a trigger-less system reading out the full detector at 40 MHz bunch crossing rate with all selection algorithms executed in a CPU farm. The upgraded Vertex Locator (VELO) of the LHCb is a hybrid pixel detector read out by the “VeloPix” front-end ASIC with on-chip zero-suppression. This paper describes a novel way of calibrating the VELO detector based on dedicated threshold scan firmware. The firmware is implemented in the control and data acquisition back-end boards of the detector. This threshold scan method has multiple advantages compared with the default one: it is faster as the algorithm was moved from software to firmware, it is more deterministic by minimizing software interruptions and data transfer and it is more precise by reducing noise due to ASIC operation.

The LHCb vertex locator upgrade — the detector calibration overview

The Vertex Locator (VELO) is a silicon tracking detector in the spectrometer of the Large Hadron Collider beauty (LHCb) experiment. LHCb explores and investigates CP violation phenomena in b- and c- hadron decays and is one of the experiments operating on the Large Hadron Collider (LHC) at CERN. After run 1 and run 2 of LHC data taking (2011–2018), the LHCb detectors are being modernized within the LHCb upgrade I program. The upgrade aims to adjust the spectrometer to readout at full LHC 40 MHz frequency, which requires radical changes to the technologies currently used in LHCb. The hardware trigger is removed, and some of the detectors replaced. The VELO changes its tracking technology and silicon strips are replaced by 55 μm pitch silicon pixels. The readout chip for the VELO upgrade is the VeloPix ASIC. The number of readout channels increases to over 40 million, and the hottest ASIC is expected to produce the output data rate of 15 Gbit/s. New conditions challenge the software and the hardware side of the readout system and put special attention on the detector monitoring. This paper presents the upgraded VELO design and outlines the software aspects of the detector calibration in the upgrade I. An overview of the challenges foreseen for the upgrade II is given.

The upgrade I of LHCb VELO—towards an intelligent monitoring platform

The Large Hadron Collider beauty (LHCb) detector is designed to detect decays of b- and c- hadrons for the study of CP violation and rare decays. At the end of the LHC Run 2, many of the LHCb measurements remained statistically dominated. In order to increase the trigger yield for purely hadronic channels, the hardware trigger will be removed, and the detector will be read out at 40 MHz. This, in combination with the five-fold increase in luminosity, requires radical changes to LHCb's electronics, and, in some cases, the replacement of entire sub-detectors with state-of-the-art detector technologies. The Vertex Locator (VELO) surrounding the interaction region is used to reconstruct the collision points (primary vertices) and decay vertices of long-lived particles (secondary vertices). The upgraded VELO will be composed of 52 modules placed along the beam axis divided into two retractable halves. The modules will each be equipped with 4 silicon hybrid pixel tiles, each read out by 3 VeloPix ASICs. The total output data rate anticipated for the whole detector will be around 1.6 Tbit/s. The highest occupancy ASICs will have pixel hit rates of approximately 900 Mhit/s, with the corresponding output data rate of 15 Gbit/s. The LHCb upgrade detector will be the first detector to read out at the full LHC rate of 40 MHz. The VELO upgrade will utilize the latest detector technologies to read out at this rate while maintaining the required radiation-hard profile and minimizing the detector material.

Deep Learning Approach to Track Reconstruction in the upgraded VELO

The LHCb experiment will undergo a major upgrade for LHC Run III, scheduled to start taking data in 2021. In order to exploit the full physics potential of the upgraded detector, LHCb will employ a high level event filter entirely implemented in software. The event filter has to operate in real time at the 40 MHz LHC bunch crossing rate. The LHCb collaboration is currently exploring a variety of new new computing paradigms in order to cope with the challenges posed by the high data taking rates. One contribution to this effort is the application of Machine Learning (ML) techniques to particle track reconstruction. We explore an ML approach to the track reconstruction in the upgraded LHCb Vertex Locator (VELO). The reconstruction algorithm is evaluated with fully simulated Minimum-Bias data that reflects the input to the real time event filter. We have achieved a reasonable track reconstruction efficiency and low ghost rate with our first approach and are currently exploring several methods to further quality of the track reconstruction.

The LHCb Vertex Locator Upgrade

The Large Hadron Collider beauty LHCb detector is a dedicated flavour physics experiment, designed to efficiently detect decays of b- and c-hadrons to perform precise studies of CP violation and rare decays. At the end of Run 2, many of the LHCb measurements will remain statistically dominated. In order to increase the trigger yield for purely hadronic channels, the hardware trigger will be removed, and the full detector will be read out at 40 MHz. This, in combination with the five-fold increase in luminosity necessitates radical changes to LHCb's electronics with entire subdetector replacements required in some cases. The Vertex Locator (VELO) surrounding the interaction region is used to reconstruct the proton-proton collision points (primary vertices) and decay vertices of long-lived particles (secondary vertices). The upgraded VELO will be equipped with silicon hybrid pixel sensors, each read out by VeloPix ASICs. The highest occupancy ASICs will have pixel hit rates of 900 Mhit/s and produce an output data rate of over 15 Gbit/s, with a total rate of 1.6 Tbit/s anticipated for the whole detector. Selected highlights of this challenging and ambitious project are described in this paper.

On-detector Electronics for the LHCb VELO Upgrade

The LHCb Experiment is designed for precision measurements of CP violation and rare decays of beauty and charm hadrons. The experiment will be upgraded to a trigger-less system reading out the full detector at a 40 MHz event rate with all selection algorithms executed in a CPU farm. The upgraded Vertex Locator will be a hybrid pixel detector read out by the VeloPix ASIC with on-chip zero-suppression. The overview of the system and the design of the VELO on-detector electronics that include the front-end hybrid, the opto-conversion and power distribution boards will be summarised. The results from the evaluation of these prototypes and further enhancement techniques will be discussed.

Upgrade of the LHCb VELO detector

The LHCb experiment is a single-arm forward spectrometer optimised for performing heavy-flavour physics analyses, using proton-proton collisions provided by the LHC machine. A major upgrade of the LHCb experiment will take place prior to the start of Run 3 operations in 2021. The upgraded Vertex Locator (VELO) is an essential component of this upgrade. Its main role is to enable high precision track and vertex reconstruction, with data-driven readout to the software trigger at 40 MHz, in the higher-luminosity environment of Run 3. To achieve this goal, significant improvements are planned with respect to the current detector, including a switch from microstrips to pixels, upgraded electronics, and a new cooling system. I will briefly motiviate the need for an upgrade, describe the main aspects of the VELO upgrade design, and show highlights of recent sensor characterisation studies using the CERN SPS test beam.

LHCb VELO upgrade

The upgrade of the LHCb experiment, scheduled for LHC Run-III, scheduled to start in 2021, will transform the experiment to a trigger-less system reading out the full detector at 40MHz event rate. All data reduction algorithms will be executed in a high-level software farm enabling the detector to run at luminosities of 2×1033cm−2s−1.The Vertex Locator (VELO) is the silicon vertex detector surrounding the interaction region. The current detector will be replaced with a hybrid pixel system equipped with electronics capable of reading out at 40MHz. The upgraded VELO will provide fast pattern recognition and track reconstruction to the software trigger. The silicon pixel sensors have 55×55μm2 pitch, and are read out by the VeloPix ASIC, from the Timepix/Medipix family. The hottest region will have pixel hit rates of 900Mhits/s yielding a total data rate of more than 3Tbit/s for the upgraded VELO. The detector modules are located in a separate vacuum, separated from the beam vacuum by a thin custom made foil. The foil will be manufactured through milling and possibly thinned further by chemical etching.The material budget will be minimised by the use of evaporative CO2 coolant circulating in microchannels within 400μm thick silicon substrates. The current status of the VELO upgrade is described and latest results from operation of irradiated sensor assemblies are presented.

The LHCb VELO upgrade

The upgrade of the LHCb experiment, planned for 2019, will transform the experiment to a trigger-less system reading out the full detector at 40MHz event rate. All data reduction algorithms will be executed in a high-level software farm. The upgraded detector will run at luminosities of 2×1033cm−2s−1 and probe physics beyond the Standard Model in the heavy flavour sector with unprecedented precision. The Vertex Locator (VELO) is the silicon vertex detector surrounding the interaction region. The current detector will be replaced with a hybrid pixel system equipped with electronics capable of reading out at 40MHz. The detector comprises silicon pixel sensors with 55×55μm2 pitch, read out by the VeloPix ASIC, based on the TimePix/MediPix family. The hottest region will have pixel hit rates of 900Mhits/s yielding a total data rate more than 3Tbit/s for the upgraded VELO. The detector modules are located in a separate vacuum, separated from the beam vacuum by a thin custom made foil. The detector halves are retracted when the beams are injected and closed at stable beams, positioning the first sensitive pixel at 5.1mm from the beams. The material budget will be minimised by the use of evaporative CO2 coolant circulating in microchannels within 400μm thick silicon substrates.

The upgrade of the LHCb Vertex Locator

The LHCb experiment is set for a significant upgrade, which will be ready for Run 3 of the LHC in 2020. This upgrade will allow LHCb to run at a significantly higher instantaneous luminosity and collect an integrated luminosity of 50fb−1 by the end of Run 4. In this process the Vertex Locator (VELO) detector will be upgraded to a pixel-based silicon detector. The upgraded VELO will improve upon the current detector by being closer to the beams and having lower material modules with microchannel cooling and a thinner RF-foil. Simulations have shown that it will maintain its excellent performance, even after the radiation damage caused by collecting an integrated luminosity of 50fb−1.