LHC Upgrade Research Articles

The ATLAS ITk strip detector system for the Phase-II LHC upgrade

ATLAS is currently preparing for the HL-LHC upgrade, with an all-silicon Inner Tracker (ITk) that will replace the current Inner Detector. The ITk will feature a pixel detector surrounded by a strip detector, with the strip system consisting of four Barrel layers and six endcap disks. After completion of final design reviews in key areas, such as Sensors, Modules, Front-End electronics and ASICs, a large scale prototyping program has been completed successfully. We present an overview of the Strip System, and highlight the final design choices of sensors, modules and ASICs. We will summarise results achieved during prototyping and the current status of production and pre-production on various detector components, with an emphasis on QA and QC procedures.

First results on the final readout chip for the High-Luminosity LHC upgrade of the CMS Inner Tracker

The CMS Readout Chip (CROC) is a 65nm CMOS hybrid pixel readout chip for the High-Luminosity LHC upgrade of the CMS Inner Tracker. The chip has been developed by the CERN RD53 Collaboration in order to withstand radiation doses up to 10MGy and hit rates up to 3GHzcm−2 on the innermost tracking layer. Moreover, it must handle an increased sensor granularity (pixel size of 2500µm2) with respect to current detectors and operate at detection thresholds as low as 1000e. Twenty wafers of the prototype chip (CROCv1) have been produced in 2021. The CROCv1 characterisation and verification campaign has, overall, demonstrated the radiation resistance of the chip and its performance. The production version of the chip (CROCv2) was submitted in October 2023 and the engineering run wafers have been received in January 2024. In this contribution, the first results from CROCv2 wafer-level testing of more than 1900 chips from the engineering run will be outlined.

Field Quality Analysis of the Separation-Recombination Dipole MBRD for the High-Luminosity Upgrade of LHC

Field Quality Analysis of the Separation-Recombination Dipole MBRD for the High-Luminosity Upgrade of LHC

Cold Mass Assembly of First Full-Scale Prototype of Beam Separation Dipole Magnet for the High-Luminosity LHC Upgrade

Cold Mass Assembly of First Full-Scale Prototype of Beam Separation Dipole Magnet for the High-Luminosity LHC Upgrade

Longevity study of a triple-GEM chamber for the HL-LHC upgrade

As part of the high-luminosity LHC (HL-LHC) upgrade, the CMS muon spectrometer will extend its coverage in the very forward region with triple-GEM detectors. These detectors will cope with a harsh environment with expected background fluxes up to 150 kHz/cm (Sauli, 2016) [2]. At the end of HL-LHC operation, the total accumulated charge at the hottest point is expected to reach 7.9 C/cm (Sauli, 2016) [2]. This accumulated charge is unprecedented for a GEM detector.A full-size triple-GEM chamber was built using the design planned for the most forward CMS muon station using GEM foils produced at CERN. While operated with a gas mixture of Ar/CO2 (70/30)%, the chamber was irradiated with photons from a silver-target X-ray source over 1.5 years to reach an accumulated charge of 8 C/cm2. Before and after irradiation the chamber was validated using the standard quality control procedures; gas gain and energy resolution were measured. During irradiation the gain was monitored weekly. The irradiation was interrupted only for the certification measurements. A non-irradiated sector was monitored for comparison. Temperature and pressure in the lab were continuously measured to derive correction factors to calibrate the gas gain. No degradation in gas gain was observed when reaching 8 C/cm2. Irradiated and non-irradiated chamber components were inspected for potential impacts from irradiation.

Radiation hardness and quality validation of the on-detector electronics for the CMS Drift Tubes upgrade

In view of the High Luminosity LHC upgrade, the so-called Phase 2 upgrade, the electronics of the Drift Tubes (DT) subdetector of CMS will undergo a complete innovation. The requirements in terms of trigger rate will exceed the capabilities of the present electronics. Thus, all the on-detector electronics together with the associated back-end need to be replaced. Phase-2 on-detector electronics for DT consist of about 800 FPGAs (Field Programmable Gate Array) based boards called OBDT (On-detector Board for Drift Tubes). These boards are sub-divided in two different categories: 600 OBDT ϕ and 200 OBDT θ, targeting respectively the readout of DT wires parallel and normal to the LHC beams. Each OBDT ϕ is able to time-digitize 240 channels with sub-nanosecond resolution and upstream to the back end using multiple high-speed optical links running at 10.24 Gb/s. The choice of components known to have good resistance to radiation was a requirement in the design of the OBDT. The main component, the FPGA, is a flash-based PolarFire from Microsemi, already qualified in different facilities for radiation hardness tests. As a validation step, a campaign of radiation tests was carried out at the INFN-TIFPA Protontherapy Centre in Trento, Italy, using proton beams. The behavior of an OBDT ϕ board was evaluated during radiation exposure with a total dose much higher than expected to be integrated during 10 years of HL-LHC, which is 0.5 Gy.

ALICE upgrades during the LHC Long Shutdown 2

A Large Ion Collider Experiment (ALICE) has been conceived and constructed as a heavy-ion experiment at the LHC. During LHC Runs 1 and 2, it has produced a wide range of physics results using all collision systems available at the LHC. In order to best exploit new physics opportunities opening up with the upgraded LHC and new detector technologies, the experiment has undergone a major upgrade during the LHC Long Shutdown 2 (2019–2022). This comprises the move to continuous readout, the complete overhaul of core detectors, as well as a new online event processing farm with a redesigned online-offline software framework. These improvements will allow to record Pb-Pb collisions at rates up to 50 kHz, while ensuring sensitivity for signals without a triggerable signature.

Testing and characterisation of the prototype readout chip for the High-LuminosityLHC upgrade of the CMS Inner Tracker

This contribution describes the characterisation and validation campaign of the prototype of the CMS Readout Chip (CROC), a 65 nm CMOS pixel readout ASIC for the CMS Inner Tracker upgrade for High Luminosity LHC. This validation campaign includes tests with single-chip and multi-chip modules, irradiation campaigns, test beams and wafer-level tests. The main results obtained in the testing of the CROC prototype will be outlined. Key improvements and fixes that have been implemented in the final version of the chip before the October 2023 submission will be described.

Chips for calibration of the ATLAS Liquid Argon calorimeter

The LHC upgrade requires redoing the liquid Argon (LAr) calibration system which should provide a 16-bit range signal with 1‰ accuracy while being radiation tolerant. The fundamental operating principle remains unchanged: a precise current is stored in an inductor, and upon switching off the current, a pulse is generated for injection into the readout electronics. This is achieved by two chips: the first one, in CMOS 130 nm, provides the 16-bit DAC as well as the calibration management system; the second one, in XFAB 180 nm, embeds switches to generate the pulses. A description of both chips and measurement results will be presented.

CMS iRPC FEB development and validation

In view of the High Luminosity upgrade of the CERN LHC, the forward CMS Muon spectrometer will be extended with two new stations of improved Resistive Plate Chambers (iRPC) covering the pseudorapidity range from 1.8 to 2.4. Compared to the present RPC system, the gap thickness is reduced to lower the avalanche charge, and an innovative 2D strip readout geometry is proposed. These improvements will allow iRPC detector to cope with higher background rates. A new Front-End-Board (FEB) is designed to readout iRPC signals with a threshold as low as 30fC and an integrated Time Digital Converter with a resolution of 30ps. In addition, the communication bandwidth is significantly increased by using optical fibers. The history, final design, certification, and calibration of this FEB are presented.

Weak Scale Supersymmetry Emergent from the String Landscape.

Superstring flux compactifications can stabilize all moduli while leading to an enormous number of vacua solutions, each leading to different 4-d laws of physics. While the string landscape provides at present the only plausible explanation for the size of the cosmological constant, it may also predict the form of weak scale supersymmetry which is expected to emerge. Rather general arguments suggest a power-law draw to large soft terms, but these are subject to an anthropic selection of a not-too-large value for the weak scale. The combined selection allows one to compute relative probabilities for the emergence of supersymmetric models from the landscape. Models with weak scale naturalness appear most likely to emerge since they have the largest parameter space on the landscape. For finetuned models such as high-scale SUSY or split SUSY, the required weak scale finetuning shrinks their parameter space to tiny volumes, making them much less likely to appear compared to natural models. Probability distributions for sparticle and Higgs masses from natural models show a preference for Higgs mass mh∼125 GeV, with sparticles typically beyond the present LHC limits, in accord with data. From these considerations, we briefly describe how natural SUSY is expected to be revealed at future LHC upgrades. This article is a contribution to the Special Edition of the journal Entropy, honoring Paul Frampton on his 80th birthday.

The readout panels for the BI-RPC project for ATLAS Phase-II upgrade

To take full advantage from the LHC upgrade to high luminosity in 2029, the ATLAS community has approved an intensive detector upgrade program that includes the construction of an additional trigger layer positioned close to the BI MDT chambers of the muon spectrometer. These chambers are RPC with thin gas gap, thin High Pressure Laminate electrodes coated with graphite on one side, and only use strips orthogonal to the beam-axis to reconstruct the eta and phi coordinates of the detector point where an ionizing particle passes. A detailed description of the construction and validation of these strip panels in China and Italy assembly sites, is presented here.

The CMS Inner Tracker DAQ system for the High Luminosity upgrade of LHC: From single-chip testing, to large-scale assembly qualification

The CMS Inner Tracker DAQ system for the High Luminosity upgrade of LHC: From single-chip testing, to large-scale assembly qualification

LHC low-beta quadrupole magnets: cryogenic refrigeration capacity and improved controls for luminosity optimization

The LHC low-β quadrupole magnets, also known as “Inner Triplets”, are the final focusing magnets located on each side of LHC interaction points. The current LHC Inner triplets are NbTi superconducting magnets operated in superfluid helium at 1.9 K and use a bayonet heat exchanger to extract the heat deposited by the secondary particles coming from the proton collisions. The dynamic heat loads in Inner Triplet are consequently proportional to the LHC luminosity and due to the recent upgrades of LHC and its injectors, the cryogenic capacity limit can be reached around ATLAS and CMS experiments where the luminosity can go slightly beyond the LHC ultimate luminosity. First, this paper summarizes the history of the Inner Triplet cryogenics with the different tests performed in the past to assess their cooling capacity. Then, the different techniques implemented in the cryogenic control system to handle the luminosity transients are detailed and finally, a new control interaction between the cryogenic system and the LHC luminosity server is detailed to optimize online the LHC luminosity.

Deployment of ML in Changing Environments

The High-Luminosity LHC upgrade of the CMS experiment will utilise a large number of Machine Learning (ML) based algorithms in its hardware-based trigger. These ML algorithms will facilitate the selection of potentially interesting events for storage and offline analysis. Strict latency and resource requirements limit the size and complexity of these models due to their use in a high-speed trigger setting and deployment on FPGA hardware. It is envisaged that these ML models will be trained on large, carefully tuned, Monte Carlo datasets and subsequently deployed in a real-world detector environment. Not only is there a potentially large difference between the MC training data and real-world conditions but these detector conditions could change over time leading to a shift in model output which could degrade trigger performance. The studies presented explore different techniques to reduce the impact of this effect, using the CMS track finding and vertex trigger algorithms as a test case. The studies compare a baseline retraining and redeployment of the model and episodic training of a model as new data arrives in a continual learning context. The results show that a continually learning algorithm outperforms a simple retrained model when degradation in detector performance is applied to the training data and is a viable option for maintaining performance in an evolving environment such as the High-Luminosity LHC.

Overview of high energy physics and prospective dark matter detections at HL-LHC and CEPC

This paper first takes an overview of the current development of high-energy physics, including an introduction to the fundamental particles and forces described by the standard model, physics beyond the standard model like super-symmetry and matter-antimatter asymmetry, and current high-energy physics experiments such as ATLAS and CMS at the large hadron collider. Then we focus on the prospective dark matter detections at the high-luminosity large hadron collider (HL-LHC) and circular electron-positron collider (CEPC), especially the upgrades of the current LHC and different working modes of the CEPC. Finally, the paper discusses the prospects of dark matter detection and possibly dark matter candidates.

Analysis of the Mechanical Performance of the 4.2-m-Long MQXFA Magnets for the Hi-Lumi LHC Upgrade

Under the U.S. High Luminosity LHC Accelerator Upgrade Project (HL-LHC AUP), the 150 mm bore, high-field Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn low-β MQXFA quadrupole magnets are being fabricated, assembled and tested, in the context of the CERN Hi-Luminosity LHC (HL-LHC) upgrade. These magnets have 4.2 m magnetic length and 4.56 m long iron yoke. To date, eight MQXFA magnets have been tested. One of the magnets additionally underwent a successful endurance test with 40 triggered quenches, and two magnets did not perform as expected. This work summarizes for the first time the available strain gauge data from eight identical Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn MQXFA tested magnets, focusing on the endurance test, and on a possible cause of underperformance of the two magnets that did not pass the vertical test. We applied methods to prevent this from happening in future MQXFA magnets, which shown to be effective for last two tested magnets.

The Challenges and Solutions of Meeting the Assembly Specifications for the 4.5 m Long MQXFA Magnets for the Hi-Luminosity LHC

The U.S. High-Luminosity LHC Accelerator Upgrade Project (HL-LHC AUP) has, in the recent years, developed assembly specifications for the 4.5 m long MQXFA magnets, which are 150 mm aperture high-field Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn low-β quadrupole magnets that are being built for the CERN Hi-Luminosity LHC (HL-LHC) upgrade. While the specifications were based on lessons learned from the LHC Accelerator Research Program (LARP) effort and the MQXFS and MQXFA prototype magnets, the experience gained from having both MQXFA07 and MQXFA08 magnets not meeting performance specifications during cold testing actually catalyzed a better understanding of the impact of the target assembly specifications and a subsequent refinement of the same. This paper summarizes a body of assembly data from the Pre-Series (MQXFA03-MQXFA07) and Series magnets (MQXFA08-MQXFA11) that have been built to date, and discusses the processes employed to successfully face the challenge of ensuring that the assembly specifications are met for the duration of the project.

First Prototype of the Long Orbit Nested Corrector for HL-LHC

2.5-m-long nested orbit correctors (so-called MCBXFA) are necessary for the upgrade of LHC, in the framework of HL-LHC project. These magnets provide 2.1 T in vertical and horizontal direction and they share the same cross-section of their shorter version MCBXFB, for which two prototypes and the first two series magnets have been manufactured and tested. In this paper we first present the specific aspects of MCBXFA magnet design: (i) field quality in the different powering scenarios, and (ii) mechanical analysis, with special attention to torque under combined operation. We then overview the manufacturing techniques, which are very similar to those used for MCBXFB, pointing out some difficulties that have arisen during the coil vacuum impregnation. The components of the prototype magnet are being produced by CIEMAT and the magnet will be assembled at CERN facilities.

The New Small Wheel electronics

The increase in luminosity, and consequent higher backgrounds, of the LHC upgrades require improved rejection of fake tracks in the forward region of the ATLAS Muon Spectrometer. The New Small Wheel upgrade of the Muon Spectrometer aims to reduce the large background of fake triggers from track segments that don't originate from the interaction point. The New Small Wheel employs two detector technologies, the resistive strip Micromegas detectors and the “small” Thin Gap Chambers, with a total of 2.45 million electrodes to be sensed. The two technologies require the design of a complex electronics system given that it consists of two different detector technologies and is required to provide both precision readout and a fast trigger. It will operate in a high background radiation region up to about 20 kHz/cm2 at the expected HL-LHC luminosity of ℒ = 7.5 × 1034 cm-2 s-1. The architecture of the system is strongly defined by the GBTx data aggregation ASIC, the newly-introduced FELIX data router and the software based data handler of the ATLAS detector. The electronics complex of this new detector was designed and developed in the last ten years and consists of multiple radiation tolerant Application Specific Integrated Circuits, multiple front-end boards, dense boards with FPGA's and purpose-built Trigger Processor boards within the ATCA standard. The New Small Wheel has been installed in 2021 and is undergoing integration within ATLAS for LHC Run 3. It should operate through the end of Run 4 (December 2032). In this manuscript, the overall design of the New Small Wheel electronics is presented.