High Luminosity Phase Of LHC Research Articles

New RPC gas mixtures for sustainable operation in the CMS experiment

The current operation of the Resistive Plate Chamber (RPC) system within the CMS experiment involves approximately 95% tetrafluoroethane (C2H2F4, TFE). However, in response to climate change concerns, the European Union has instituted a ban on TFE owing to its elevated Global Warming Potential (GWP), resulting in an associated increase in market prices. In this framework, shared endeavors within the RPC EcoGas@GIF++ Collaboration, have been dedicated to investigating novel ecological gaseous mixtures based on tetrafluoropropene (C3H2F4, HFO-1234ze) to ensure the sustainable functionality of RPCs. This presentation will delve into the performance outcomes derived from improved RPC gas gaps operating on HFO/CO2-based mixtures as ecologically viable alternatives, particularly in anticipation of the High Luminosity LHC phase (HL-LHC). Additionally, the utilization of TFE/CO2 mixtures will be explored as a pragmatic strategy to swiftly alleviate gas-related operational costs.

On novel front-end electronics for the ATLAS BI RPC upgrade at HL-LHC developed in SiGe BiCMOS technology with a high-resolution rad-hard Time-To-Digital converter embedded

The High Luminosity phase of LHC will require a huge improvement on the ATLAS detector in terms of performance, being the entire apparatus operated in much harsher conditions. The BI project is one of the ATLAS Phase-2 approved upgrades, ensuring the demands coming from the physics for the next 20 years. In this framework, a novel dedicated Front-End electronics has been developed, which exploits a BJT-based preamplifier, a fast discriminator and a high resolution (¡ 100 ps) Time-To-Digital converter in SiGe BiCMOS technology, to vastly enhance the detector rate capability. This front-end electronics is integrated for the first time within the detector Faraday cage, largely reducing the effects of spurious noise and allowing a minimum effective charge threshold on the induced signal of 1-2 fC. The integration of the front-end electronics directly within the detector Faraday cage is also permitted by the low power consumption of 15 mW/ch. The RPC coupled with this novel front-end electronics represents a new generation of large area timing detectors, granting a record time resolution of 350 ps on a single gas gap of 1 mm with 1.2 mm electrodes thickness and operated with the ATLAS standard gas mixture. The effect of the extremely low threshold has also an impact on the gas mixture, enabling the usage of eco-friendly gas mixtures which would not be usable elsewise. The latest performance of this newly developed front-end electronics along with the results achieved with RPC detector coupled with it will be shown.

ATLAS ITk Pixel Outer Endcap CO[formula omitted] cooling system prototypes

In preparation for the high-luminosity LHC phase, the ATLAS detector will be upgraded with a new silicon inner tracker, the ITk, relying on a cooling system based on carbon dioxide (CO2) evaporative properties.In order to test the key aspects of the cooling, prototypes of the cooling system for the different ITk Outer Endcap layers is built in Milan and tested at the CERN CO2 BabyDEMO cooling plant. The facility is able to provide a CO2 flow of 150 g/s with a temperature as low as -45 °C. The presentation illustrates the mechanical construction of the prototype and the use of 3D-printed titanium parts. The thermal load of the detector (up to 3 kW on the Layer 4 half-shell during normal operation) is also simulated. The sizing of the capillary present in the system, required to reach the design pressure drop of 8 bar and to trigger the CO2 evaporation, is also be discussed. The pressure and temperature sensors installed in the prototype and the data acquisition is described. The measurements performed at the BabyDEMO cooling plant, both at the nominal ATLAS operating condition and in more extreme scenarios, will be described. The systems are proved to be stable under all the conditions tested, and the total pressure drops are consistent with the requirements of the system specification.

3D silicon pixel sensors for the CMS experiment tracker upgrade

The upgrade program of the CMS experiment (CMS Collaboration, 2024) in view of the LHC High Luminosity phase (HL–LHC) includes a replacement of the silicon pixel tracker. This is necessary to guarantee the same tracking performance of the current detector under harsher operating conditions, including higher radiation fluences and hit rates. The first layer of the central (barrel) detector will be located at radial distance of 3 cm from the interaction point where the radiation fluence after 7 years of operation will be 1.9×1016neq/cm2. Following an extensive R&D program, comprising both laboratory and test beam measurements, 3D sensors will be employed in this layer due to their higher radiation tolerance and lower power consumption after irradiation. Test beam measurements after irradiation up to 1.6×1016neq/cm2 showed a hit detection efficiency larger than 96% at normal incidence with less than 2% masked pixels, for applied bias voltages between 100 V and 130 V.

Investigating the M1 radiative decay behaviors and the magnetic moments of the predicted triple-charm molecular-type pentaquarks

In this work, we systematically study the electromagnetic properties including the M1 radiative decay widths and the magnetic moments of the isoscalar ΞccD(*), ΞccD1, and ΞccD2* triple-charm molecular-type pentaquark candidates, where we adopt the constituent quark model and consider both the S−D wave mixing effect and the coupled channel effect. Our numerical results suggest that the M1 radiative decay widths and the magnetic moments of the isoscalar ΞccD(*), ΞccD1, and ΞccD2* triple-charm molecular-type pentaquark candidates can reflect their inner structures, and the study of the electromagnetic properties is an important step to construct the family of the triple-charm molecular-type pentaquarks. With the accumulation of the experimental data during the high-luminosity phase of LHC, we expect that the present work combined with the corresponding mass spectrum information can encourage the experimental colleagues at LHCb to focus on the isoscalar ΞccD(*), ΞccD1, and ΞccD2* triple-charm molecular-type pentaquark candidates. Published by the American Physical Society 2024

Test and performance of the LiTE-DTU ASIC for the HL-LHC upgrade of the CMS ECAL barrel

A data conversion and compression ASIC, named LiTE-DTU, has been developed for the upgrade of the CMS electromagnetic calorimeter (ECAL) for the High-Luminosity phase of LHC. The ASIC integrates two 12-bit 160 MS/s ADCs, a data processing unit for gain selection and data compression, and a 1.28 Gb/s serializer.The ASIC has been extensively tested in laboratory and in beam tests showing excellent yield and performance. The radiation tolerance has been verified with dedicated test campaigns for both total ionizing dose and single event effects. Results from these tests, showing the design readiness for mass production, will be presented.

Heavy vector-like quarks decaying to exotic scalars: a case study with triplets

We investigate the pair production of a vector-like quark triplet with hypercharge 5/3 decaying into top quark and a complex scalar triplet with hypercharge 1 at the LHC. This novel scenario, featuring particles with exotic charges — two quarks with charge 8/3 and 5/3 and a scalar with charge 2 — serves as a unique window to models based on the framework of partial compositeness, where these particles naturally emerge as bound states around the TeV scale. Leveraging on the LHC data we establish exclusion limits on the masses of the vector-like quark and the scalar triplet. Subsequently, we design an analysis strategy aimed at improving sensitivity in the region which is still allowed. Our analysis focuses on two specific regions in the parameter space: the first entails a large mass gap between the vector-like quarks and the scalars, so that the vector-like quarks can decay into the scalars; the second involves a small mass gap, such that this decay is forbidden. To simplify the parameter space, both vector-like quarks and scalars are assumed to be degenerate or almost degenerate within the triplets, such that chain decays between fermions and scalars are suppressed. As a result, we found that final states characterized by a same-sign lepton pair, multiple jets, and high net transverse momentum (i.e. effective mass) will play a pivotal role to unveil this model and, more in general, models characterised by multiple vector-like quarks around the same mass scale during the high luminosity LHC phase.

Upgrade of ATLAS hadronic Tile Calorimeter for the High Luminosity LHC

The Tile Calorimeter (TileCal) is the hadronic calorimeter covering the central region of the ATLAS experiment. The High-Luminosity phase of LHC, delivering five times the LHC nominal instantaneous luminosity, is expected to start in 2029. TileCal will require new electronics to meet the requirements of a 1 MHz trigger, higher ambient radiation, and to ensure better performance under high pile-up conditions. Both the on- and off-detector TileCal electronics will be replaced during the shutdown of 2026–2028. Approximately 10% of the PMTs, those reading out the most exposed cells, will be replaced. PMT signals from every TileCal cell will be digitized and sent directly to the back-end electronics, where the signals are reconstructed, stored, and sent to the first level of trigger at a rate of 40 MHz. This will provide better precision of the calorimeter signals used by the trigger system and will allow the development of more complex trigger algorithms. The modular front-end electronics feature radiation-tolerant components and redundant design to minimise single points of failure. The timing, control and communication interface with the off-detector electronics is implemented with modern Field Programmable Gate Arrays (FPGAs) and high speed fiber optic links running up to 9.6 Gb/s. The TileCal upgrade program has included extensive R&D and test beam studies. A Demonstrator module equipped with the new electronics but with reverse compatibility with the existing readout system was inserted in ATLAS in 2019 for testing in actual detector conditions. The status of the various components and the results of test-beam campaigns with the electronics prototypes will be discussed.

Latest results of Longevity studies on the present CMS RPC system for HL-LHC phase

The present Compact Muon Solenoid Resistive Plate Chambers system has been worked efficiently during Run I and Run II of data taking period (Shah et al., 2020) [1]. In the coming years of operation with the High Luminosity LHC (HL-LHC), the expected rate and integrated charge are expected to be about 600 Hz/cm2 and 840 mC/cm2, respectively (including a safety factor of three). Therefore, the HL-LHC phase will be a challenge for the RPC system since the expected operating conditions are much harsher than those for which the detectors have been designed, and could introduce non-recoverable aging effects which can alter the detector properties. A longevity test has been started at the CERN Gamma Irradiation Facility to estimate the impact of HL-LHC conditions on the RPC detector performance in order to determine whether the RPC system will survive the harsher background conditions expected at HL-LHC. The latest results of the irradiation test will be presented.

The Fast Simulation Chain in The ATLAS Experiment

The physics program in the ATLAS experiment at the Large Hadron Collider has achieved high-quality and competitive physics results since its inception, based on large and accurate datasets of simulated Monte Carlo events. Generating these billions of Monte Carlo using the Geant4 framework requires significant computing resources. As such the ATLAS CPU is limited and taking into account the expected increase of the average number of proton-proton collisions during the high luminosity LHC phase, a very fast detector simulation is critical when high accuracy is not needed. In order to solve this problem and to meet the challenge of simulated sample statistics requirements, fast alternatives approaches have been developed by ATLAS to replace the algorithms currently used in the standard MC production chain. This document provides a description of the Fast simulation chain tools and also presents the latest physics performance studies: Fast tracking detector simulation, Fast digitization and Pile-up simulation.

The HL-LHC Upgrade of the ATLAS hadronic Tile Calorimeter

The High-Luminosity phase of LHC, scheduled to begin in late 2027, will deliver up to ten times the LHC nominal instantaneous luminosity to the experiments. To ensure sound performance under the higher pile-up and radiation conditions, the ATLAS hadronic Tile Calorimeter (TileCal) will replace both the on- and off- detector electronics systems during the LHC long shutdown 3 (2025-2027). The upgraded front-end system will continuously digitize and read out shaped photomultiplier tube (PMT) signals from every TileCal cell at a rate of 40 MHz, transmitting them over high-speed fiber links to the new back-end electronics to be stored in latency pipelines and digitally summed to produce improved trigger tower data for the Level-1 trigger. The front-end electronics are based on radiation-qualified commercial components, and use extensive redundancy to minimize single point failures. The Tile upgrade program has undergone extensive R&D and beam tests, and a “demonstrator” module was installed on ATLAS in 2019 for integration and testing in the actual detector environment.

Upgrade of ATLAS hadronic Tile Calorimeter for the High-Luminosity LHC

The Tile Calorimeter (TileCal) is a sampling hadronic calorimeter covering the central region of the ATLAS experiment, with steel as absorber and plastic scintillators as active medium. The High-Luminosity phase of LHC, delivering an instantaneous luminosity up to 7.5×1034 cm−2 s−1, is expected to begin in 2029. TileCal will require new electronics to meet the requirements of a 1 MHz trigger (calorimeter output rate), higher ambient radiation, and to ensure better performance under high pile-up conditions. Both the on- and off-detector TileCal electronics will be replaced during the shutdown of 2026–2028. The TileCal upgrade program has included extensive R&D and test beam studies. A Demonstrator module with reverse compatibility with the existing system was inserted in ATLAS in August 2019 for testing in actual detector conditions. The ongoing developments for on- and off-detector systems, together with expected performance characteristics and recent results of test-beam campaigns with the electronics prototypes will be discussed.

Sensitivity of anomalous quartic gauge couplings via Zγγ production at future hadron-hadron colliders

Triple gauge boson production provides a promising opportunity to probe the anomalous quartic gauge couplings in understanding the details of electroweak symmetry breaking at future hadron-hadron collider facilities with increasing center of mass energy and luminosity. In this paper, we investigate the sensitivities of dimension-8 anomalous couplings related to the ZZγγ and Zγγγ quartic vertices, defined in the effective field theory framework, via pp→Zγγ signal process with Z-boson decaying to charged leptons at the high luminosity phase of LHC (HL-LHC) and future facilities, namely the High Energy LHC (HE-LHC) and Future Circular hadron-hadron collider (FCC-hh). We analyzed the signal and relevant backgrounds via a cut based method with Monte Carlo event sampling where the detector responses of three hadron collider facilities, the center-of-mass energies of 14, 27 and 100 TeV with integrated luminosities of 3, 15 and 30ab−1 are considered for the HL-LHC, HE-LHC and FCC-hh, respectively. The reconstructed 4-body invariant mass of l+l−γγ system is used to constrain the anomalous quartic gauge coupling parameters under the hypothesis of absence of anomalies in triple gauge couplings. Our results indicate that the sensitivity on anomalous quartic couplings fT8/Λ4 and fT9/Λ4 (fT0/Λ4, fT1/Λ4 and fT2/Λ4) at 95% C.L. for FCC-hh with Lint=30ab−1 without systematic errors is two (one) order better than the current experimental limits. Considering a realistic systematic uncertainty such as 10% from possible experimental sources, the sensitivity of all anomalous quartic couplings gets worsen by about 1.2%, 1.7% and 1.5% compared to those without systematic uncertainty for HL-LHC, HE-LHC and FCC-hh, respectively.

Test of low-dropout voltage regulators with neutrons and protons

The Muon System of the ATLAS experiment at the CERN LHC will be upgraded for the high-luminosity phase of LHC to cope with higher rates and higher radiation levels. Most of the Muon-System on-detector electronics will be replaced. Commercial low-dropout voltage regulators have been considered as a robust, low-noise and economic solution to power distribution. These components should be selected based on their capability to comply to radiation requirements. We tested 7 different types of CMOS LDOs, monitoring online the output voltage of 10 samples of each type. Irradiations were performed in the Radial Channel 1 of the RSV TAPIRO fast neutron reactor at ENEA Casaccia (Rome), to test resistance to non-ionizing energy loss, and at the PIF 200 MeV proton beam at PSI (Villigen), to test for total ionizing dose and single event effects. The experimental setup and the results are presented and discussed in this paper.

CP violation at ATLAS in effective field theory

CP violation beyond the Standard Model (SM) is a crucial missing piece for explaining the observed matter-antimatter symmetry in the Universe. Recently, the ATLAS experiment at the Large Hadron Collider has performed an analysis of electroweak $Zjj$ production, thereby excluding the SM locally at 95\% confidence level in the measurement of CP-sensitive observables. We take the excess' interpretation in terms of anomalous gauge-Higgs interactions at face value and discuss further steps that are required to scrutinize its origin. In particular, we discuss the relevance of multi-boson production using adapted angular observables to show how they can be used to directly tension the reported $Zjj$ excess in a more comprehensive analysis. To connect the excess to a concrete UV scenario for which the underlying assumptions of the $Zjj$ analysis are valid, we identify vector-like leptons as a candidate theory consistent with the observed CP-odd Wilson coefficient hierarchy observed by ATLAS. We perform a complete one-loop matching calculation to motivate further model-specific and correlated new physics searches. In parallel, we provide estimates of the sensitivity reach of the LHC's high luminosity phase for this particular scenario of CP-violation in light of electroweak precision and Run-2 Higgs data. These provide strong constraints on the model's CP-even low-energy phenomenology, but also inform the size of the CP-odd SM deformation indirectly via our model hypothesis.

Radiation hardness of the low gain avalanche diodes developed by NDL and IHEP in China

This paper studies the radiation hardness of low gain avalanche detector (LGAD) developed by the Novel Device Laboratory (NDL) in Beijing and the Institute of High Energy Physics (IHEP) of Chinese Academy of Sciences, in the context of an upgrade project of the ATLAS detector for the high luminosity phase of LHC. NDL LGAD sensors with different layouts, epitaxial resistivity and doping profile were irradiated up to 1.02 × 1015 neq/cm2 by 70 MeV protons at Cyclotron and Radioisotope Center (CYRIC). The timing resolution of NDL LGAD sensors reached 50 ps and the collected charge reached 3 - 4 fC after irradiation.

Lepton flavor violation and dilepton tails at the LHC

Starting from a general effective Lagrangian for lepton flavor violation (LFV) in quark-lepton transitions, we derive constraints on the effective coefficients from the high-mass tails of the dilepton processes pp rightarrow ell _k ell _l (with kne l). The current (projected) limits derived in this paper from LHC data with 36~mathrm {fb}^{-1} (3~mathrm {ab}^{-1}) can be applied to generic new physics scenarios, including the ones with scalar, vector and tensor effective operators. For purely left-handed operators, we explicitly compare these LHC constraints with the ones derived from flavor-physics observables, illustrating the complementarity of these different probes. While flavor physics is typically more constraining for quark-flavor violating operators, we find that LHC provides the most stringent limits on several flavor-conserving ones. Furthermore, we show that dilepton tails offer the best probes for charm-quark transitions at current luminosities and that they provide competitive limits for tauonic brightarrow d transitions at the high-luminosity LHC phase. As a by-product, we also provide general numerical expressions for several low-energy LFV processes, such as the semi-leptonic decays Krightarrow pi ell ^{pm }_k ell ^{{mp }}_l, Brightarrow pi ell ^{pm }_k ell ^{{mp }}_l and Brightarrow K^{(*)} ell ^{pm }_k ell ^{{mp }}_l.

Performance of a Front End prototype ASIC for picosecond precision time measurements with LGAD sensors

For the High-Luminosity phase of LHC, the ATLAS experiment is proposing the addition of a High Granularity Timing Detector (HGTD) in the forward region, to mitigate the effects of the increased pile-up. The chosen detection technology is Low Gain Avalanche Detector (LGAD) silicon sensors that can provide an excellent timing resolution below 50 ps. The front-end read-out ASIC must exploit the large signal derivative and small noise provided by the sensor, while keeping low power consumption. This paper presents the results on the first prototype of a front-end ASIC, named ALTIROC0, which contains the analog stages (preamplifier and discriminator) of the read-out chip. The ASIC was characterised both alone and as part of a module with a 2×2 LGAD array of 1.1×1.1 mm2 pads bump-bonded to it. The various contributions of the electronics to the time resolution were investigated in test-bench measurements with a calibration setup. Both when the ASIC is alone or with a bump-bonded sensor, the jitter of the ASIC is better than 20 ps for an injected charge of 10 fC . The time walk effect, which arises from the different preamplifier response for various injected charges, can be corrected up to 10 ps using a Time Over Threshold measurement. The combined performance of the ASIC and the LGAD sensor, which was measured during a beam test campaign in October 2018 with pions of 120 GeV energy at the CERN SPS, is around 40 ps for all measured modules. All tested modules show good efficiency and time resolution uniformity.

Learning representations of irregular particle-detector geometry with distance-weighted graph networks

We explore the use of graph networks to deal with irregular-geometry detectors in the context of particle reconstruction. Thanks to their representation-learning capabilities, graph networks can exploit the full detector granularity, while natively managing the event sparsity and arbitrarily complex detector geometries. We introduce two distance-weighted graph network architectures, dubbed GarNet and GravNet layers, and apply them to a typical particle reconstruction task. The performance of the new architectures is evaluated on a data set of simulated particle interactions on a toy model of a highly granular calorimeter, loosely inspired by the endcap calorimeter to be installed in the CMS detector for the High-Luminosity LHC phase. We study the clustering of energy depositions, which is the basis for calorimetric particle reconstruction, and provide a quantitative comparison to alternative approaches. The proposed algorithms provide an interesting alternative to existing methods, offering equally performing or less resource-demanding solutions with less underlying assumptions on the detector geometry and, consequently, the possibility to generalize to other detectors.

Upgrade of the ATLAS Tile Calorimeter for the High Luminosity LHC

The Tile Calorimeter (TileCal) is the hadronic calorimeter covering the central region of the ATLAS experiment. TileCal is a sampling calorimeter with steel as absorber and scintillators as active medium. The scintillators are read-out by wavelength shifting fibers coupled to photomultiplier tubes (PMTs). The analogue signals from the PMTs are amplified, shaped, digitized by sampling the signal every 25 ns and stored on detector until a trigger decision is received. The High-Luminosity phase of LHC (HL-LHC) expected to begin data taking in 2026 requires readout electronics suitable for a 1 MHz trigger rate, higher ambient radiation, and for better performance under high pileup. Both the on- and off-detector TileCal electronics will be replaced during the shutdown of 2024-2025. PMT signals from every TileCal cell will be digitized and sent directly to the back-end electronics, where the signals are reconstructed, stored, and sent to the first trigger level at a rate of 40 MHz. This will provide better precision of the calorimeter signals used by the trigger system and will allow the development of more complex trigger algorithms. Changes to the electronics will also enhance the data integrity and reliability of the system. Three front-end board options were built and investigated both in laboratory and in several beam test campaigns. The final version has been chosen after evaluating the results. A hybrid Demonstrator for the new readout architecture and compatible with the present system has been developed, adopting the new chosen front-end option. The Demonstrator is undergoing extensive testing and is planned for future insertion in ATLAS.