The ATLAS ITk strip local support structures Diez, Sergio
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
September 2024, Volume:
1066
Journal Article
Peer reviewed
Open access
A new silicon tracker for the ATLAS detector is envisioned during the Phase-II upgrade of the Large Hadron Collider experiment (LHC), the so-called High Luminosity LHC (HL-LHC). The new Inner Tracker ...(ITk) consists of a silicon pixel inner tracker and a silicon microstrips outer tracker. This paper focuses on the strips ITk detector, and, in particular, on the high precision, low-mass, high thermo-mechanical performance structures supporting the silicon microstrip modules, so-called “staves” for the barrel region and “petals” for the end-cap regions. A detailed description of these structures is provided, along with the manufacturing procedures employed. This paper covers also the Quality Control (QC) program during pre-production phase, evaluating the mechanical, electrical and thermal performance of twenty support structures of each type, and the validation for their production phase.
The new ATLAS Inner Tracker (ITk) will replace the current tracking detector of the ATLAS detector to cope with the challenging conditions for the Phase-II upgrade of the Large Hadron Collider ...experiment (LHC), the so-called High Luminosity LHC (HL-LHC). The new tracking detector is an all-silicon detector consisting of a pixel inner tracker and a silicon microstrips outer tracker, differentiated again in a central barrel section around the interaction point and two end-cap sections covering the forward regions. This contribution focuses on the currently developed full system tests for the ITk strips detector, being the testbed for testing and evaluating the performance of several close-to-final detector components before production. These will also serve in the future for training and testing purposes of the detector during operation. The barrel system test is conducted in SR1 at CERN and will consist of 8 staves - mechanical core structures loaded with rectangular short (∼2.5cm) and long (∼5cm) strip sensor modules. In a similar fashion, the system test for the end-caps is developed at DESY in Hamburg/Germany loaded with up to 12 petals — again a core structure loaded with trapezoidal shaped sensors of various lengths and strip pitches including the readout and power electronics. The staves and petals are mechanically held in place within a support structure and connected to the electrical, optical and cooling services as realistic as possible as in the latter detector integration. As such it is possible to validate the detector design, verify the detector DAQ and perform tests with the services, e.g. concerning the dual-phase CO2 cooling. This contribution gives an overview of the developed system tests for the ITk strip detector, summarizes the current status of the two sites, and shows a selection of performance measurements conducted in the last months.
Jets are an important tool to study the hot, dense matter produced in Pb+Pb collisions at the LHC. Jet rates have been found to be reduced by approximately a factor of two, in the most central events ...and over a wide kinematic range. In order to understand precisely how the jets are modified, it is important to measure how the jet momentum is carried by its fragmentation products. In this proceedings, we present the status of fragmentation function measurements at 5.02 TeV for p+Pb and Pb+Pb collisions as well as measurement for Pb+Pb and pp collisions at 2.76 TeV.
The High Luminosity upgrade of Large Hadron Collider (HL-LHC) will increase the LHC luminosity and with it the density of particles on the detector by an order of magnitude. For protecting the inner ...silicon detectors of the ATLAS experiment and for monitoring the delivered luminosity, a radiation hard beam monitor was developed based on polycrystalline Chemical Vapor Deposition (pCVD) diamond detectors and a new dedicated rad-hard front-end ASIC. Due to the large range of particle flux through the detector, flexibility is very important. To satisfy the requirements imposed by the HL-LHC, our solution is based on segmenting diamond sensors into devices of varying size and reading them out with new multichannel readout ASICs divided into two independent parts — each of them serving one of the tasks of the system. This paper describes the system design including detectors, electronics, mechanics and services and presents preliminary results from the most recent detectors fabricated, using our prototype ASIC with data from beam tests at CERN.
Measurements of both the inclusive and differential production cross sections of a top-quark–antiquark pair in association with a Z boson ($t\bar{t}Z$) are presented. The measurements are performed ...by targeting final states with three or four isolated leptons (electrons or muons) and are based on $\sqrt{s}$=13 TeV proton–proton collision data with an integrated luminosity of 139 fb-1, recorded from 2015 to 2018 with the ATLAS detector at the CERN Large Hadron Collider. The inclusive cross section is measured to be σ$t\bar{t}Z$ =0.99 ± 0.05 (stat.) ± 0.08 (syst.) pb, in agreement with the most precise theoretical predictions. The differential measurements are presented as a function of a number of kinematic variables which probe the kinematics of the $t\bar{t}Z$ system. Both absolute and normalised differential cross-section measurements are performed at particle and parton levels for specific fiducial volumes and are compared with theoretical predictions at different levels of precision, based on a χ2/ndf and p value computation. Overall, good agreement is observed between the unfolded data and the predictions.
Measurements of both the inclusive and differential production cross sections of a top-quark–antiquark pair in association with a Z boson ($t\bar{t}Z$) are presented. The measurements are performed ...by targeting final states with three or four isolated leptons (electrons or muons) and are based on $\sqrt{s}$=13 TeV proton–proton collision data with an integrated luminosity of 139 fb-1, recorded from 2015 to 2018 with the ATLAS detector at the CERN Large Hadron Collider. The inclusive cross section is measured to be σ$t\bar{t}Z$ =0.99 ± 0.05 (stat.) ± 0.08 (syst.) pb, in agreement with the most precise theoretical predictions. The differential measurements are presented as a function of a number of kinematic variables which probe the kinematics of the $t\bar{t}Z$ system. Both absolute and normalised differential cross-section measurements are performed at particle and parton levels for specific fiducial volumes and are compared with theoretical predictions at different levels of precision, based on a χ2/ndf and p value computation. Overall, good agreement is observed between the unfolded data and the predictions.
The large increase of pileup is one of the main experimental challenges for the HL-LHC physics program. A powerful new way to address this challenge is to exploit the time spread of the interactions ...to distinguish between collisions occurring very close in space but well separated in time. A High-Granularity Timing Detector, based on low gain avalanche detector technology, is proposed for the ATLAS Phase-II upgrade. Covering the pseudorapidity region between 2.4 and 4.0, with a timing resolution of 30 ps for minimum-ionizing particles, this device will significantly improve the performance in the forward region. High-precision timing greatly improves the track-to-vertex association, leading to a performance similar to that in the central region for the reconstruction of both jets and leptons, as well as for the tagging of heavy-flavor jets. These improvements in object reconstruction performance translate into important sensitivity gains and enhance the reach of the HL-LHC physics program. In addition, the High-Granularity Timing Detector offers unique capabilities for the online and offline luminosity determination.
•During the HL-LHC program high pileup impacts the reconstruction of physics objects.•A forward timing detector can improve the performance of the ATLAS detector.•LGAD sensors of size 1.3 × 1.3 mm2 can reach a timing resolution of 30 ps.•Forward highly granular detector can be used to measure the luminosity.
The ATLAS muon spectrometer consists of an efficient muon trigger system and precision muon tracking chambers providing high momentum resolution up to the TeV scale. Yet, in the regions between the ...inner barrel and endcap of the muon spectrometer the trigger selectivity is limited. Furthermore, at the future High-Luminosity LHC the efficiency of the resistive plate trigger chambers (RPCs) will decrease due to ageing effects. Therefore, additional RPCs will be installed at the ends of the inner barrel layer of the muon spectrometer in the current long shutdown for the Phase-1 upgrade of the LHC in 2019 and 2020. In order to free space for them, the current Muon Drift Tube (MDT) chambers will be replaced by small-diameter Muon Drift Tube (sMDT) chambers with 15 instead of 30 mm tube diameter, which will be integrated with thin-gap RPCs. Due to their higher background rate capability, the new sMDT chambers are also suitable precision muon tracking detectors at future hadron colliders. An overview of the design and production of the new ATLAS sMDT chambers, their performance and their mechanical integration with the RPCs is given. The construction of these new chambers also serves as a pilot project for the replacement of half of the barrel inner layer in the Phase-2 upgrade of the ATLAS detector.
In the long shutdown for the Phase-1 upgrade of the Large Hadron Collider (LHC) in 2019–2020, 16 new integrated muon tracking and trigger chambers will be installed at the ends of the toroid magnet ...coils in the small azimuthal sectors of the inner barrel layer (BIS) of the ATLAS muon spectrometer in order to improve the trigger selectivity and fake trigger suppression in the transition region 1.0<|η|<1.3 between the barrel part and the endcaps. The new muon detectors consist of a small-diameter muon drift tube (sMDT) precision tracking chamber with 15 mm tube diameter and a pair of thin-gap RPC chambers with 1 mm gas gap width. The new integrated chamber modules (labeled BIS 78) are currently under construction and will replace the present BIS 7 and 8 MDT tracking chambers with 30 mm diameter drift tubes. The project is the pilot phase for the complete replacement of the small barrel inner layer MDT chambers with the new integrated tracking and trigger detectors in the ATLAS Phase-2 upgrade in 2024–2026 in order to increase the barrel first-level muon trigger coverage and efficiency at the high luminosities at HL-LHC. The sMDT chambers have been chosen to make room for the new trigger chambers and because of their eight times higher rate capability than MDT chambers. The new thin-gap RPC chambers have about 15 times lower avalanche charges and correspondingly increased lifetime and rate capability at HL-LHC and will be operated in coincidence with the endcap trigger chambers. They consist of a triplet of gas gaps which has to be very thin as well and which is supported by a light-weight aluminum structure which is interleaved with the sMDT chamber supports.
Small diameter muon drift-tube (sMDT) chambers with 15 mm tube diameter provide excellent spatial resolution like the MDT chambers with 30 mm tube diameter used in the ATLAS muon spectrometer so far, ...but can be operated at ten times higher background rates and allow for the instrumentation of regions where MDT chambers do not fit in. In April 2014 two such chambers (called BME) have been installed at the bottom of the barrel middle layer of the muon spectrometer, followed in January 2016 by another 12 sMDT chambers (called BMG) inserted in the detector feet in the barrel middle layer. They are since then operational in ATLAS, increasing the acceptance for precision muon momentum measurement in all three chamber layers. An unprecedently high sense wire positioning accuracy of 5μm (rms) has been achieved. In the next long LHC shutdown 2019–2020, 16 new sMDT chambers (called BIS 78) will be installed in the barrel inner layer in the transition region to the endcaps in order to make room for the installation of new RPC muon trigger chambers which will reduce the accidental trigger rate in this region as required for operation at the high-luminosity upgrade of the LHC (HL-LHC). This is a pilot project for the complete replacement of the MDT chambers in the small azimuthal sectors of the barrel inner layer (called BIS 1-6) by integrated sMDT-RPC detectors in the long shutdown 2024–2026 for the upgrade to HL-LHC.
•Small-diameter muon drift tube (sMDT) chambers used for ATLAS muon system upgrades.•sMDTs with 1/2 the tube diameter have 10 x higher rate capability than the present ATLAS MDT chambers.•A record sense wire positioning accuracy of better than 5 μm has been achieved for sMDT chambers.•14 sMDT chambers are in operation, 16 more under construction for installation in 2019/20.•96 sMDT chambers will replace the MDT chambers in the barrel muon detector inner layer for HL-LHC.
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