High Luminosity Phase Research Articles

Phenomenology of electroweak portal dark showers: high energy direct probes and low energy complementarity

We investigate the phenomenology of a dark QCD sector interacting with the Standard Model (SM) via the electroweak (EW) portals. The portal interactions allow SM bosons, such as Z and h, or additional bosons that mix with them, to decay into dark quarks, producing dark showers. The light dark mesons are expected to be long-lived particles (LLPs), as their decays back to the SM states through the EW-portal interactions typically have macroscopic decay lengths. We focus on dark shower events initiated by various bosons at the Large Hadron Collider (LHC). The most prominent signal is the displaced decay of GeV-scale dark pions as LLPs. Current limits on dark shower signals at LHC detectors are recast from public data to provide simplified limits insensitive to UV physics details. Future limits in the high-luminosity phase and proposed auxiliary detectors are also projected. Additionally, we study the flavor-changing neutral current (FCNC) B decays into dark pions, obtaining both current and projected constraints at the LHC and other facilities. These constraints can be combined for specific models, which are illustrated in two EW-portal benchmarks: one with the heavy doublet fermion mediation and another with the Z′ mediator including a mass mixing. The collider reach shows significant potential to probe the parameter space unconstrained by EW precision tests, highlighting the necessity of dedicated LLP search strategies and facilities.

Hard processes in multi-TeV ion collisions

Motivated by the ion-collision program at the Large Hadron Collider, plans for its high-luminosity upgrade, and ongoing discussions for multi-TeV future hadron colliders, we systematically investigate hard-scattering, Standard Model processes in many-TeV ion-ion collisions. We focus on the symmetric beam configurations Pb208−Pb208, Xe131−Xe131, C12−C12, and pp, and we catalog total and fiducial cross sections for dozens of processes, ranging from associated-Higgs and multiboson production to associated-top pair production, at next-to-leading order in QCD for nucleon-nucleon collision energies from sNN=1 to 100 TeV. We report the residual scale uncertainties at this order as well as the uncertainties originating from fits of nuclear parton densities. We also discuss the propagation of nuclear dynamics (as encoded in nuclear parton densities) into parton luminosities and ultimately into predictions for cross sections. Finally, we report on the emergence of trends and the reliability of extrapolating cross sections across different nuclei. For Pb-Pb collisions at a hypothetical Future Circular Collider with sNN=39 TeV, O(108) weak bosons, O(105) diboson pairs, O(104) WH and ZH pairs, O(103) triboson events, O(105) high-pT photons events, and O(107) tt¯ pairs can be produced with L=33 nb−1 of data. At sNN=5.52 TeV, one can expect O(10–106) single, multiboson, and top events per 1 nb−1. Decay rates and experimental selection/acceptance rates will impact final event yields and merit further study; as an illustrative example, we focus on select diboson and triboson channels in lead-lead collisions and discuss their observability at the high-luminosity phase of the Large Hadron Collider and the Future Circulate Collider. Published by the American Physical Society 2025

Optimization of LYSO crystals and SiPM parameters for the CMS MIP timing detector

For the High-Luminosity (HL-LHC) phase, the upgrade of the Compact Muon Solenoid (CMS) experiment at CERN will include a novel MIP Timing Detector (MTD).The central part of MTD, the barrel timing layer (BTL), is designed to provide a measurement of the time of arrival of charged particles with a precision of 30 ps at the beginning of HL-LHC, progressively degrading to 60 ps while operating in an extremely harsh radiation environment for over a decade.In this paper we present a comparative analysis of the time resolution of BTL module prototypes made of LYSO:Ce crystal bars read out by silicon photo-multipliers (SiPMs).The timing performance measured in beam test campaigns is presented for prototypes with different construction and operation parameters, such as different SiPM cell sizes (15, 20, 25 and 30 μm), SiPM manufacturers and crystal bar thicknesses. The evolution of time resolution as a function of the irradiation level has been studied using non-irradiated SiPMs as well as SiPMs exposed up to 2 × 1014 neq/cm2 fluence.The key parameters defining the module time resolution such as SiPM characteristics (gain, photon detection efficiency, radiation induced dark count rate) and crystal properties (light output and dimensions) are discussed.These results have informed the final choice of the MTD barrel sensor configuration and offer a unique starting point for the design of future large-area scintillator-based timing detectors in either low or high radiation environments.

An integrated flux-symmetric spectrometer-magnet system for the SND@LHC experiment upgrade

The proposed upgrade of the SND@LHC experiment for the High Luminosity phase of the LHC (HL-LHC) will strongly benefit from the presence of a magnetized region, allowing for muon momentum and charge measurement. In this paper we describe an iron core magnet system that is partly integrated with the calorimeter and that is designed to respect the strict constraints from the available space in the experimental cavern, power consumption, and field requirements. Semi-analytical tools are introduced to explore the parameter space, in order to define the primary design options. A full 3-D analysis is then performed in order to validate the optimal choice, and to propose a conceptual design, including sizing of the components, detector performances and stray fields. Several technical options are also discussed, anticipating the design phase.

Content delivery network solutions for the CMS experiment: The evolution towards HL-LHC

The Large Hadron Collider at CERN in Geneva is poised for a transformative upgrade, preparing to enhance both its accelerator and particle detectors. This strategic initiative is driven by the tenfold increase in proton-proton collisions anticipated for the forthcoming high-luminosity phase scheduled to start by 2029. The vital role played by the underlying computational infrastructure, the World-Wide LHC Computing Grid, in processing the data generated during these collisions underlines the need for its expansion and adaptation to meet the demands of the new accelerator phase. The provision of these computational resources by the worldwide community remains essential, all within a constant budgetary framework. While technological advancements offer some relief for the expected increase, numerous research and development projects are underway. Their aim is to bring future resources to manageable levels and provide cost-effective solutions to effectively handle the expanding volume of generated data. In the quest for optimized data access and resource utilization, the LHC community is actively investigating Content Delivery Network (CDN) techniques. These techniques serve as a mechanism for the cost-effective deployment of lightweight storage systems that support both, traditional and opportunistic compute resources. Furthermore, they aim to enhance the performance of executing tasks by facilitating the efficient reading of input data via caching content near the end user. A comprehensive study is presented to assess the benefits of implementing data cache solutions for the Compact Muon Solenoid (CMS) experiment. This in-depth examination serves as a use-case study specifically conducted for the Spanish compute facilities, playing a crucial role in supporting CMS activities. Data access patterns and popularity studies suggest that user analysis tasks benefit the most from CDN techniques. Consequently, a data cache has been introduced in the region to acquire a deeper understanding of these effects. In this paper, the details of the implementation of a data cache system in the PIC Tier-1 compute facility are presented. It includes insights into the developed monitoring tools and discusses the positive impact on CPU usage for analysis tasks executed in the region. The study is augmented by simulations of data caches, with the objective of discerning the most optimal requirements in both size and network connectivity for a data cache serving the Spanish region. Additionally, the study delves into the cost benefits associated with deploying such a solution in a production environment. Furthermore, it investigates the potential impact of incorporating this solution into other regions of the CMS computing infrastructure.

Bosonic multi-Higgs correlations beyond leading order

The production of multiple Higgs bosons at the LHC and beyond is a strong test of the mechanism of electroweak symmetry breaking. Taking inspiration from recent experimental efforts to move toward limits on triple-Higgs production at the Large Hadron Collider, we consider generic bosonic deviations of HH and HHH production from the Standard Model in the guise of Higgs effective field theory (HEFT). Including one-loop radiative corrections within the HEFT and going up to O(p4) in the momentum expansion, we provide a detailed motivation of the parameter range that the LHC (and future hadron colliders) can explore, through accessing nonstandard coupling modifications and momentum dependencies that probe Higgs boson nonlinearities. In particular, we find that radiative corrections can enhance the sensitivity to Higgs self-coupling modifiers and HEFT-specific momentum dependencies can vastly increase triple-Higgs production, thus providing further motivation to consider these processes during the LHC’s high-luminosity phase. Published by the American Physical Society 2024

Testing the CKM unitarity at high energy via the W+W− production at the LHC and future colliders

We propose a novel test to assess the unitarity of the Cabibbo-Kobayashi-Maskawa matrix, VCKM, at present and future collider experiments. Our strategy makes use of the W+W− production cross section to directly probe the VCKM†VCKM product, which regulates the high-energy behavior of the observable. The violation of unitarity is signaled by an anomalous behavior of the cross section that grows quadratically with the W+W− invariant mass with respect to the Standard Model prediction. By using the recent ATLAS measurements of the W+W− cross section we are able to constrain the maximal unitarity violation allowed by current data, producing a bound complementary to the results of flavor physics experiments. Forecasts for the high luminosity phase of the LHC and for the future 100 TeV hadron collider are also discussed.

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.

R&D of a timing measurement ASIC for possible HL-LHC upgrade

The Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) at CERN will undergo a major upgrade for the High Luminosity phase of the LHC (HL-LHC), which is expected to start in 2029 [1]. In addition to improving the detector rate capabilities and performance at increased higher luminosity, precision timing measurements are added to mitigate pile-up effects. The timing detector currently under construction covers pseudo-rapidity up to η=3[2] . A possible pathway for further improvements is the extension of timing capabilities to cover the full tracker acceptance up to η=4. Low Gain Avalanche Detectors (LGAD) pixels have been shown to be a suitable candidate for replacing a part of the pixel detector end-caps during a future Long Shutdown or Year-End Technical Stop of the LHC. Here, we present preliminary results of our design efforts towards a readout Application-specific integrated circuit (ASIC) capable of operating with LGAD pixel sensors [3]. The first results of the modeling of a part of the ASIC are demonstrated.

Search for a leptophobic doubly charged Higgs in same-sign four-lepton and six-lepton signatures in a left-right symmetric model

We investigate the possibility of multi-lepton (four and six) signatures, including an exotic signature of same-sign four-lepton (SS4L) as signals of pair production of a doubly charged Higgs in the minimal left-right symmetric model, extended with two doublet scalars. The right-handed neutrino masses are generated in this model through a dimension-5 lepton-number violating operator allowing the triplet scalar interactions with leptons to become negligibly small. This leads to interesting six-lepton and SS4L signatures that can be observed at the high-luminosity phase of the Large Hadron Collider (HL-LHC) with almost no background for doubly charged Higgs with mass below 500 GeV.

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.

Dispelling the L\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{\\mathcal {L}} $$\\end{document} myth for the High-Luminosity LHC

Extrapolations of sensitivity to new interactions and standard model parameters critically inform the programme at the Large Hadron Collider (LHC) and potential future collider cases. To this end, statistical considerations based on inclusive quantities and established analysis strategies typically give rise to a sensitivity scaling with the square root of the luminosity, L\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{\\mathcal {L}}$$\\end{document}. This suggests only a mild sensitivity improvement for LHC’s high-luminosity phase, compared to the collected data up to the year 2025. We discuss representative analyses in top quark, Higgs boson and electroweak gauge boson phenomenology and provide clear evidence that the assumption that the sensitivity in searches and measurement scales only with L\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{\\mathcal {L}}$$\\end{document} at the High-Luminosity LHC is overly conservative at best, and unrealistic in practice. As kinematic coverage enables more targeted search strategies with sufficient statistical sensitivity, employing a multitude of features in data dispels the scaling based on more inclusive selections.

Ultrafast jet classification at the HL-LHC

Three machine learning models are used to perform jet origin classification. These models are optimized for deployment on a field-programmable gate array device. In this context, we demonstrate how latency and resource consumption scale with the input size and choice of algorithm. Moreover, the models proposed here are designed to work on the type of data and under the foreseen conditions at the CERN large hadron collider during its high-luminosity phase. Through quantization-aware training and efficient synthetization for a specific field programmable gate array, we show that O(100) ns inference of complex architectures such as Deep Sets and Interaction Networks is feasible at a relatively low computational resource cost.

A Lightweight Algorithm to Model Radiation Damage Effects in Monte Carlo Events for High-Luminosity Large Hadron Collider Experiments.

Radiation damage significantly impacts the performance of silicon tracking detectors in Large Hadron Collider (LHC) experiments such as ATLAS and CMS, with signal reduction being the most critical effect; adjusting sensor bias voltage and detection thresholds can help mitigate these effects, generating simulated data that accurately mirror the performance evolution with the accumulation of luminosity, hence fluence, is crucial. The ATLAS and CMS collaborations have developed and implemented algorithms to correct simulated Monte Carlo (MC) events for radiation damage effects, achieving impressive agreement between collision data and simulated events. In preparation for the high-luminosity phase (HL-LHC), the demand for a faster ATLAS MC production algorithm becomes imperative due to escalating collision, events, tracks, and particle hit rates, imposing stringent constraints on available computing resources. This article outlines the philosophy behind the new algorithm, its implementation strategy, and the essential components involved. The results from closure tests indicate that the events simulated using the new algorithm agree with fully simulated events at the level of few %. The first tests on computing performance show that the new algorithm is as fast as it is when no radiation damage corrections are applied.

Overview of the ATLAS High-Granularity Timing Detector: project status and results

The increase of the particle flux (pile-up) at the high-luminosity phase of the Large Hadron Collider (LHC) with an instantaneous luminosity up to L ≈ 7.5 × 1034 cm-2 s-1 will have a severe impact on the ATLAS detector reconstruction and trigger performance. A High Granularity Timing Detector (HGTD) will be installed in the forward region for pile-up mitigation and luminosity measurement. This detector, based on Low Gain Avalanche Detectors and custom ASICs, will provide a time resolution of 30 ps per track at the beginning of HL-LHC and 50 ps at the end. This proceeding paper will summarise the overall specifications of the HGTD as well as the project status.

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

High-rate tests on resistive plate chambers operated with eco-friendly gas mixtures

Results obtained by the RPC ECOgas@GIF++ Collaboration, using Resistive Plate Chambers operated with new, eco-friendly gas mixtures, based on tetrafluoropropene and carbon dioxide, are shown and discussed in this paper. Tests aimed to assess the performance of this kind of detectors in high-irradiation conditions, analogous to the ones foreseen for the coming years at the Large Hadron Collider experiments, were performed, and demonstrate a performance basically similar to the one obtained with the gas mixtures currently in use, based on tetrafluoroethane, which is being progressively phased out for its possible contribution to the greenhouse effect. Long term aging tests are also being carried out, with the goal to demonstrate the possibility of using these eco-friendly gas mixtures during the whole High Luminosity phase of the Large Hadron Collider.

Design validation of the CMS Phase-2 Triple-GEM detectors

The High-Luminosity LHC will deliverproton-proton collisions at 5.0–7.5 times the nominal LHC luminosity, with anexpected number of 140–200 pp-interactions per bunch crossing. To maintain the performance of muon triggering and reconstruction underhigh background, the forward part of the Muon spectrometer of the CMSexperiment will be upgraded with Gas Electron Multipliers (GEM) and improvedResistive Plate Chambers detectors. Particularly challenging isthe extension of the pseudorapidity of the muon system up to |η| < 2.8with a 6-layer station, named ME0, that will be installed behind the newhigh granularity calorimeter and that will see particle rates up to150 kHz/cm2 and integrate a dose of 250 krad by the end of the High Luminosity phase of the LHC.In this contribution we will present the major design changes of the Triple-GEMdetectors to adapt them for the harsh radiation environment and the highparticle rate. We shall summarize the performance of prototype Triple-GEMdetectors measured with X-rays and gamma at theCERN GIF++ irradiation facility.

Investigation of flow patterns in two-phase carbon dioxide in horizontal and vertical pipes

Modern particle detectors crucially depend on efficient cooling systems. Two-phase carbon dioxide (CO2) is a suitable solution as a cooling agent. This publication presents the observations and results of investigations of horizontal and vertical flow of two-phase CO_2 at a temperature of T = -15 °C and a pressure of approximately 23 bar. Heat fluxes between 98.5 kW/m2 and 200 kW/m2 were applied to the CO2, covering the range expected to occur in the future ATLAS Pixel detector being built for the high-luminosity phase of the Large Hadron Collider. Flow speeds ranged from 11.8 m/s to 28.1 m/s. Dedicated sensors measured the temperature and the pressure before and after heating the CO2. Two-phase flow patterns occuring in the pipe after heating the CO2 were recorded with a high-speed camera. Stratified, wavy and slug flow are found to be the predominant patterns for horizontal flow, while upward vertical flow is mainly found to be slug or churn. Based on the recorded images the void fraction of the CO2 after heating is determined and compared for the different setups. The results are summarised in a flow-pattern map. A clear distinction between vertical and horizontal flow is found, with horizontal flow exhibiting a significantly higher void fraction than vertical flow. Based on the pressure measurements, the pressure drop after heating the CO2 is measured and the corresponding Euler number is computed. While the pressure drop increases with the heat flux for horizontal flow, the pressure drop reduces with the heat flux in the case of upward vertical flow.

Hunting muonic forces at emulsion detectors

Only two types of Standard Model particles are able to propagate the 480meters separating the ATLAS interaction point and FASER: neutrinos and muons. Furthermore, muons are copiously produced in proton collisions. We propose to use FASERν as a muon fixed target experiment in order to search for new bosonic degrees of freedom coupled predominantly to muons. These muon force carriers are particularly interesting in light of the recent measurement of the muon anomalous magnetic moment. Using a novel analysis technique, we show that even in the current LHC run, FASERν could potentially probe previously unexplored parts of the parameter space. In the high-luminosity phase of the LHC, we find that the improved sensitivity of FASERν2 will probe unexplored parameter space and may be competitive with dedicated search proposals. Published by the American Physical Society 2024