Real-time highly-parallel tracking processing with FPGA at LHCb Fantechi, R.; Baldini, W.; Bassi, G. ...
2023 IEEE Nuclear Science Symposium, Medical Imaging Conference and International Symposium on Room-Temperature Semiconductor Detectors (NSS MIC RTSD),
2023-Nov.-4
Conference Proceeding
For the future high luminosity LHC runs, it is expected to reconstruct events more complex than the actual ones. in view of this need, the LHCb Collaboration has established a testbed for ...heterogeneous computing equipment to develop solutions for real-time event reconstruction integrated with the LHCb DAQ infrastructure. The most advanced one is a highly-parallelized tracking processor, based on the "Artificial Retina", which uses a set of FPGA, to which the data are distributed using a custom optical mesh with high speed links. The aim at the testbed is to implement a demonstrator for the tracking of pixel detectors, able to manage the data of a sector of a detector. The scalability to a full size processor will be discussed, as well as the DAQ integration issues for a system running on real data.
The muon detector of LHCb, which comprises 1368 multi-wire-proportional-chambers (MWPC) for a total area of 435 m2, is the largest instrument of its kind exposed to such a high-radiation environment. ...In nine years of operation, from 2010 until 2018, we did not observe appreciable signs of ageing of the detector in terms of reduced performance. However, during such a long period, many chamber gas gaps suffered from HV trips. Most of the trips were due to Malter-like effects, characterised by the appearance of local self-sustained high currents, presumably originating from impurities induced during chamber production. Very effective, though long, recovery procedures were implemented with a HV training of the gaps in situ while taking data. The training allowed most of the affected chambers to be returned to their full functionality and the muon detector efficiency to be kept close to 100%. The possibility of making the recovery faster and even more effective by adding a small percentage of oxygen in the gas mixture has been studied and successfully tested.
A method is described which allows to deduce the dead-time of the front-end electronics of the LHCb muon detector from a series of measurements performed at different luminosities at a bunch-crossing ...rate of 20 MHz. The measured values of the dead-time range from 70 ns to 100 ns. These results allow to estimate the performance of the muon detector at the future bunch-crossing rate of 40 MHz and at higher luminosity.
With its ∼1650m2 of MWPCs, the muon detector of LHCb is one of the largest instrument of this kind worldwide, and one of the most irradiated. Currently we run at the relatively low instantaneous ...luminosity of 4⋅1032cm−2s−1, nevertheless the most irradiated MWPCs already integrated ∼0.7 C/cm of accumulated charge per wire. The statistics of gas gaps affected by high voltage trips in the proportional chambers is presented for the whole period of operation. Most of the problematic chambers were successfully recovered in situ during data taking, under the nominal LHC beam conditions, by means of a long-term HV training (with the working gas mixture). The appearing of self-sustained currents in one of the MWPC gaps and the effectiveness of the recovery procedures put in place, indicate that the large majority of the trips are due to Malter effect. The method has proven to be very effective, allowing to keep the muon detector efficiency very close 100%, as it was initially designed. In parallel, a test has been performed of a systematic addition of a small amount of oxygen to the nominal gas mixture: results of this test will be discussed.
The LHCb experiment is currently taking data with a completely renewed DAQ system, capable for the first time of performing a full real-time reconstruction of all collision events occurring at LHC ...point 8. The Collaboration is now pursuing a further upgrade (“LHCb Upgrade-II”), to enable the experiment to retain the same capability at luminosities an order of magnitude larger than the maximum planned for the current Run3. To this purpose, a vigorous R&D program is ongoing to boost the real-time processing capability of LHCb, needed to cope both with the luminosity increase and the adoption of correspondingly more granular and complex detectors. New heterogeneous computing solutions are being explored, with the aim of moving reconstruction and data reduction to the earliest possible stages of processing. In this talk, we describe the results obtained from a realistic demonstrator for a high-throughput reconstruction of tracking detectors, operating parasitically on real LHCb data from Run3 in a purposely-built testbed facility. This demonstrator is based on a extremely parallel, “Artificial Retina” architecture, implemented in commercial, PCIe-hosted FPGA cards interconnected by fast optical links, and encompasses a sizeable fraction of the LHCb VELO pixel detector. The implications of the results in view of potential applications in HEP are discussed.
The first observation of the Lambda(0)(b) -> D-s(-) p decay is presented using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of root s = 13TeV, ...corresponding to a total integrated luminosity of 6 fb(-1). Using the Lambda(0)(b) -> Lambda(+pi-)(c) decay as the normalisation mode, the branching fraction of the Lambda(0)(b) -> D-s(-) p decay is measured to be B (Lambda(0)(b) -> D-s(-) p) = (12.6 +/- 0.5 +/- 0.3 +/- 1.2) x 10(-6), where the first uncertainty is statistical, the second systematic and the third due to uncertainties in the branching fractions of the Lambda(0)(b) -> Lambda(+pi-)(c), D-s(-) -> K-K+pi(-) and Lambda(+)(c) -> pK(-)pi(+) decays.
The prompt production of Λ$_{c}^{+}$ baryons is studied in proton-lead collisions collected with the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of 1.58 ...nb$^{−1}$ recorded at a nucleon-nucleon centre-of-mass energy of $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV. Measurements of the differential cross-section and the forwardbackward production ratio are reported for Λ$_{c}^{+}$ baryons with transverse momenta in the range 2 < p$_{T}$ < 10 GeV/c and rapidities in the ranges 1.5 < y$^{∗}$ < 4.0 and −4.5 < y$^{∗}$ < −2.5 in the nucleon-nucleon centre-of-mass system. The ratio of cross-sections of Λ$_{c}^{+}$ baryons and D$^{0}$ mesons is also reported. The results are compared with next-to-leading order calculations that use nuclear parton distribution functions.
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