13th Pisa Meeting on Advanced Detectors

24 May 2015, 08:00 → 30 May 2015, 18:00 Europe/Zurich

Isola D'Elba (La Biodola)

This agenda item is meant for uploading the abstracts submitted to 13th Pisa Meeting on Advanced Detectors, to be held in La Biodola, Isola d'Elba, Italy 24-30 May 2015. Each contribution's owner is responsible to update the status of his/her contribution: draft, submitted, approved presentation, approved poster. This is also the location where to upload presentations (drafts and final) and papers (for review and final). Please create a contribution in the selected category, using the description field for the abstract. The "material" should be used to indicate the status of the proposal, adding a link to the appropriate web page on the 13th Pisa Meeting on Advanced Detectors web site. http://www.pi.infn.it/pm/2015/

Sunday 24 May

08:00 → 18:00 Detector

Conveners: Dr Alessandro Cardini (INFN Cagliari, Italy), Dr Antonis Papanestis (STFC - Rutherford Appleton Lab. (GB)), Kurt Rinnert (University of Liverpool (GB)), Mark Tobin (Ecole Polytechnique Federale de Lausanne (CH)), Niels Tuning (Nikhef), Pascal Perret (Univ. Blaise Pascal Clermont-Fe. II (FR))

08:00 Calorimeter: First years of running for the LHCb calorimeter system and preparation for run 2

The LHCb experiment is dedicated to precision measurements of CP violation and rare decays of B hadrons at the Large Hadron Collider (LHC) at CERN (Geneva). It comprises a calorimeter system composed of four subdetectors: a Scintillating Pad Detector (SPD) and a Pre-Shower detector (PS) in front of an electromagnetic calorimeter (ECAL) which is followed by a hadron calorimeter (HCAL). They are used to select transverse energy hadron, electron and photon candidates for the first trigger level and they provides the identification of electrons, photons and hadrons as well as the measurement of their energies and positions. The calorimeter has been pre-calibrated before its installation in the pit. The calibration techniques have been tested with data taken in 2010 and used regularly during run 1. For run 2, new calibration methods have been devised to follow and correct online the calorimeter detector response. The design and construction characteristics of the LHCb calorimeter will be recalled. Strategies for monitoring and calibration during data taking will be detailed in all aspects. Scintillating fibres, plastics and photomultipliers suffer from ageing due to radiation damage or high currents. Different methods which are used to calibrate the detectors and to recover the initial performances will be presented. The performances achieved will be illustrated in selected channels of interest for B physics.

08:20 LHCb Upgrade: Scintillating Fibre Tracker

The LHCb detector will be upgraded during 2018/19 in order to collect data from proton-proton collisions at the LHC at higher instantaneous luminosities and to read out the data at 40\,MHz using a trigger-less read-out system. All front-end electronics will be replaced and several sub-detectors must be redesigned to cope with the higher occupancy. The current tracking detectors downstream of the LHCb dipole magnet will be replaced by the Scintillating Fibre (SciFi) Tracker. The SciFi Tracker will be constructed using 2.5\,m long scintillating fibres and read out by Silicon Photomultipliers (SiPM) located outside the acceptance. The fibres have a diameter of 0.25\,mm, are wound into ribbons with 5 or 6 staggered layers of fibres, and will cover a total active area of around 360\,m$^2$. State-of-the-art multi-channel SiPM arrays are being developed to read out the fibres. A custom ASIC, the PACIFIC, will be used to digitise the signals from the SiPMs and additional front-end electronics based on FPGAs will be used to reconstruct hit positions. There are a number of challenges involved in the construction of this detector: the radiation hardness of the fibres and the SiPMs; the mechanical precision required while building large active detector components; and the cooling required to mitigate the effects of radiation damage. The evolution of the design since the Technical Design Report in 2014 and the latest R\&D results, including test beam data, will be presented.

Speaker: Mark Tobin (Ecole Polytechnique Federale de Lausanne (CH))

08:40 Performance, radiation resistance, and expectations of the Outer Tracker straw tube detector for the LHCb Experiment

The LHCb experiment is a single arm spectrometer, designed to study CP violation in B-decays at the LHC. It is crucial to accurately and efficiently detect the charged decay particles, in the high-density particle environment of the LHC. For this, the Outer Tracker (OT) was constructed, consisting of 54,000 straw tubes, covering in total an area of 360 m2 of double layers. The detector operated in 2011/2012 under large particle rates, up to 100 kHz/cm per straw in the region closest to the beam. The performance of the OT detector during Run-I of the LHC has been studied in detail, in terms of efficiency, resolution and noise rate. Particular attention is devoted to the radiation hardness of this sensitive gaseous detector, that has shown to suffer from gain loss after mild irradiation in laboratory conditions. During the shutdown period of the LHC, extensive studies have been performed on subtle spatial alignment effects, and real-time calibration procedures have been prepared for run-II. In addition, expectations of the OT during run-II in 2015 will be shown. The increased center-of-mass energy of 13 TeV will result in larger particle densities, which is further enhanced by out-of-time hits due to the reduced bunch spacing of 25ns in run-II.

09:00 LHCb upgrade: the VELO detector

The upgrade of the LHCb experiment, planned for 2018, will transform the experiment to a trigger-less system reading out the full detector at 40 MHz event rate. All data reduction algorithms will be executed in a high-level software farm with access to the complete event information. This will enable the detector to run at luminosities of 2 x 10^33 /cm^2/s 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 40 MHz, designed to withstand the irradiation expected at an integrated luminosity of 50 fb-1 and beyond. The upgraded VELO will form an integral part of the software trigger, and must provide fast pattern recognition and track reconstruction while maintaining the exceptional resolution of the current detector. The detector will be composed of silicon pixel sensors with 55x55 um^2 pitch, read out by the VeloPix ASIC which is being developed based on the TimePix/MediPix family. The hottest region will have pixel hit rates of 900 Mhits/s yielding a total data rate more than 3 Tbit/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 detector halves are retracted when the beams are injected and closed at stable beams, positioning the first sensitive pixel at 5.1 mm from the beams. The high data rates require development of low-mass, high-speed, flexible electrical serial links bringing the data out of the vacuum where electrical-to-optical conversion is performed. The material budget will be minimised by the use of evaporative CO_2 coolant circulating in microchannels within 400 um thick silicon substrates. 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. 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 test results, including operation of irradiated sensor and ASIC assemblies in testbeam and lab environments.

09:20 The upgraded LHCb RICH detector: status and perspectives

The LHCb experiment is designed to perform high-precision measurements of CP violation and search for New Physics using the enormous flux of beauty and charmed hadrons produced at the Large Hadron Collider (LHC). The two RICH detectors installed in LHCb have performed successfully during the 2010-2012 data taking period. The data from these detectors were essential to most of the physics results published by LHCb. In order to extend its potential for discovery and study of new phenomena it is planned to upgrade the LHCb experiment in 2018 with a 40MHz readout and a much more flexible software-based triggering system. This would increase the readout rate and occupancies for the RICH detectors. The RICH detector will require new photon detectors and modifications of the optics of the upstream RICH detector. Tests of the complete opto-electronic chain have been performed during testbeam sessions in autumn 2014. The status and perspectives of the RICH upgrade project will be presented.

Speaker: Roberta Cardinale (Universita e INFN Genova (IT))

09:40 LHCb VELO: Performance and Radiation Damage in Run 1 and Preparation for Run 2

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 VELO comprises 42 modules made of two n+-on-n 300 um thick half-disc silicon sensors with R-measuring and phi-measuring micro-strips. In order to allow retracting the detector, the VELO is installed as two movable halves containing 21 modules each. The detectors are operated in a secondary vacuum and are cooled by a bi-phase CO2 cooling system. During data taking in LHC Run 1 the LHCb VELO has operated with an extremely high efficiency and excellent performance. The track finding efficiency is typically greater than 98%. An impact parameter resolution of less than 35 um is achieved for particles with transverse momentum greater than 1 GeV/c. An overview of all important peformance parameters will be given. The VELO sensors have received a large and non-uniform radiation dose of up to 1.2 x 10^14 1 MeV neutron equivalent / cm^2 over the first LHC run. Type-inversion has been observed in regions close to the interaction point. Results of various radiation damage analyses will be presented. The preparations for LHC Run 2 are well under way and the VELO has already recoreded tracks from injection line tests. The current status and plans for new operational procedures addressing the non-uniform radiation damage will be discussed.

Monday 25 May

08:00 → 18:00 Electronics

Tuesday 26 May

08:00 → 19:00 Trigger

08:00 The LHCb Turbo stream

The LHCb experiment will record an unprecedented dataset of beauty and charm hadron decays during Run II of the LHC, set to take place between 2015 and 2018. A key computing challenge is to store and process this data, which limits the maximum output rate of the LHCb trigger. So far, LHCb has written out a few kHz of events containing the full raw sub-detector data, which are passed through a full offline event reconstruction before being considered for physics analysis. Charm physics in particular is limited by trigger output rate constraints. A new streaming strategy includes the possibility to perform the physics analysis with candidates reconstructed in the trigger, thus bypassing the offline reconstruction. In the "turbo stream" the trigger will write out a compact summary of "physics" objects containing all information necessary for analyses, and this will allow an increased output rate and thus higher average efficiencies and smaller selection biases. This idea will be commissioned and developed during 2015 with a selection of physics analyses. It is anticipated that the turbo stream will be adopted by an increasing number of analyses during the remainder of LHC Run-II (2015-2018) and ultimately in Run-III (starting in 2020) with the upgraded LHCb detector.

08:20 General Trigger + Upgrade

The current LHCb trigger system consists of a hardware level, which reduces the LHC inelastic collision rate of 30 MHz to 1 MHz, at which the entire detector is read out. In a second level, implemented in a farm of 20k parallel-processing CPUs, the event rate is reduced to about 5 kHz. We review the performance of the LHCb trigger system, focusing on the High Level Trigger, during Run I of the LHC. Special attention is given to the use of multivariate analyses in the Hight Level Trigger and their importance in controlling the output rate. We demonstrate that despite its excellent performance to date, the major bottleneck in LHCb's trigger efficiencies for hadronic heavy flavour decays is the hardware trigger. The LHCb experiment plans a major upgrade of the detector and DAQ system in the LHC shutdown of 2018. In this upgrade, a purely software based trigger system is being developed, which will have to process the full 30 MHz of inelastic collisions delivered by the LHC. We demonstrate that the planned architecture will be able to meet this challenge, particularly in the context of running stability and long term reproducibility of the trigger decisions. We discuss the use of disk space in the trigger farm to buffer events while performing run-by-run detector calibrations, and the way this real time calibration and subsequent full event reconstruction will allow LHCb to deploy offline quality multivariate selections from the earliest stages of the trigger system. We discuss the cost-effectiveness of such a software-based approach with respect to alternatives relying on custom electronics. We discuss the particular importance of multivariate selections in the context of a signal-dominated production environment, and report the expected efficiencies and signal yields per unit luminosity in several key physics benchmarks the LHCb upgrade.

Wednesday 27 May

08:00 → 18:00 Computing

Thursday 28 May

08:00 → 18:00 DAQ

08:00 The 40 MHz trigger-less DAQ system for the LHCb upgrade

The LHCb experiment will undergo a major upgrade during the second long shutdown (2018 - 2019), aiming to let LHCb collect an order of magnitude more data with respect to run 1 and run 2. The maximum readout rate of 1 MHz is the main bottleneck of the present LHCb trigger. The upgraded detector foresees apart from major detector upgrades, a full readout into the DAQ, running at the LHC bunch crossing frequency, using an entirely software based trigger. A high-throughput PCIe Generation 3 based read-out board has been designed to read out the detector at 40MHz. The readout boards will allow a cost-effective implementation of the DAQ by means of high-speed PC network. The network-based DAQ system reads data fragments, performs the event building, and transport data to the High-Level software trigger at an estimated aggregate rate of ~32 Tbit/s. Possibile technologies candidates for high speed network under study are Infiniband and Gigabit Ethernet. Different architecture for the DAQ can be implemented, such as push, pull and traffic shaping with barrel-shifter. In order the explore and find the best implementation we are performing tests on different platforms and technologies. The event builder evaluator is flexible, to be used on small size test beds and HPC scale facilities, and allows to explore different network protocols. The architecture of DAQ system and up to date performance results will be presented.

Friday 29 May

08:00 → 18:00 Calibration and Tracking

Conveners: Michel De Cian (Ruprecht-Karls-Universitaet Heidelberg (DE)), Silvia Borghi (University of Manchester (GB))

08:00 Poster: Novel real-time alignment and calibration of the LHCb Detector in Run2

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.

Speakers: Mark Tobin (Ecole Polytechnique Federale de Lausanne (CH)), Zhirui Xu (Ecole Polytechnique Federale de Lausanne (CH))

Slides poster_FDFP2015_Alignment_v2.pdf poster_FDFP2015_Alignment_v3.pdf

08:20 Poster: Performance of the LHCb tracking system in RunI of the LHC

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.

Speaker: Adam Davis (University of Cincinnati (US))

Slides

• RunITracking_Final.pdf
• RunITracking.pdf
• RunITracking_v2.pdf
• SlidesAdamDavisRunITrackingLHCb.pdf

08:40 Poster: Tracking system of the LHCb upgrade

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.

Speaker: Tomasz Szumlak (AGH University of Science and Technology (PL))