LHC Experiments Research Articles

FTS Service Evolution and LHC Run-3 Operations

FTS Service Evolution and LHC Run-3 Operations

Evolving the LHCOPN and LHCONE networks to support HL-LHC computing requirements

Evolving the LHCOPN and LHCONE networks to support HL-LHC computing requirements

P4flow: A software-defined networking approach with programmable switches for accounting and forwarding IPv6 packets with user-defined flow label tags

A comprehensive analysis of the HEP (High Energy Physics) experiment traffic across LHCONE (Large Hadron Collider Open Network Environment) and other networks, is essential for immediate network optimisation (for example by the NOTED project) and highly desirable for long-term network planning. Such an analysis requires two steps: tagging of network packets to indicate the type and owner of the traffic being carried and then processing of the tagged packets. The RNTWG (Research Network Technical Working Group) has defined a specification to identify the experiment and the application that originates a given network flow, named scitags (Scientific Network Tags) that is applied to the flow label field of the IPv6 header. We report here on the second step: processing of packets tagged according to this specification. We developed P4flow as a software-defined networking approach by using P4 (Programming Protocol-Independent Packet Processors), a language for programming the data plane of network devices to accounting and process IPv6 packets with a scitags-based stamp in the flow label field, to understand the network utilisation and the applications used by the WLCG (Worldwide Large Hadron Collider Computing Grid) sites. With P4flow, and exploiting the control plane capabilities provided by RARE/FreeRtr (an Open Source Network Operating System developed by the GÉANT community), we cannot only generate statistics concerning the traffic per experiment and application but can also, using an Intel Tofino P4-programmable ASIC Ethernet Switch, decide how to forward traffic matching defined flow labels. This latter capability is particularly interesting as we prepare for a future where LHC experiments will be sharing network links with other major science collaborations such as SKA and ITER.

Support for experiments at INFN-T1

Support for experiments at INFN-T1

Data Centre Refurbishment with the aim of Energy Saving and Achieving Carbon Net Zero

Queen Mary University of London (QMUL) as part of the refurbishment of one of its’s data centres will install water to water heat pumps to use the heat produced by the computing servers to provide heat for the university via a district heating system. This will reduce the use of high carbon intensity natural gas heating boilers, replacing them with electricity which has a lower carbon intensity due to the contribution from wind, solar, hydroelectric, nuclear and biomass sources of power sources. The QMUL GridPP cluster today provides 15PB of storage and over 20K jobs slots mainly devoted to the ATLAS experiment. The data centre that houses the QMUL GridPP cluster, was originally commissioned in 2004. By 2020 it was in significant need of refurbishment. The original design had a maximum power capacity of 200KW, no hot/cold aisle containment, down flow air conditioning units using refrigerant cooling and no raised floor or ceiling plenum. The main requirements of the refurbishment are: To significantly improve the energy efficiency and reduce the carbon usage of the University; Improve the availability and reliability of the power and cooling; Increase the capacity of the facility to provide for future expansion; Provide a long term home for the GridPP cluster to support the computing needs of the LHC and other new large science experiments (SKA/LSST) into the next decade. After taking into account the future requirements and likely funding allocation, floor space in the data centre and the space available to house the cooling equipment the following design was chosen: A total power capacity of 390KW with redundant feeds to each rack; 39 racks with an average of 10KW of power per rack (flexible up to 20KW); An enclosed hot aisle design with in row cooling units using water cooling; water to water heat pumps connected to the universities district heating system An overview of the project, it’s status and expected benefits in power and carbon saving are presented.

The integration of heterogeneous resources in the CMS Submission Infrastructure for the LHC Run 3 and beyond

The integration of heterogeneous resources in the CMS Submission Infrastructure for the LHC Run 3 and beyond

HPC resources for CMS offline computing: An integration and scalability challenge for the Submission Infrastructure

HPC resources for CMS offline computing: An integration and scalability challenge for the Submission Infrastructure

DCache integration with CERN Tape Archive

The ever-increasing amount of data that is produced by modern scientific facilities like EuXFEL or LHC puts high pressure on the data management infrastructure at the laboratories. This includes poorly shareable resources of archival storage, typically, tape libraries. To achieve maximal efficiency of the available tape resources, a deep integration between hardware and software components is required. The CERN Tape Archive (CTA) is an open-source storage management system developed by CERN to manage LHC experiment data on tape. Although today CTA’s primary target is CERN Tier-0, the data management group at DESY considers the CTA as a main alternative to commercial HSM systems. dCache has an extensible tape interface that allows connectivity to almost any tape system. Together with the CERN Tape Archive developers, the storage team at DESY is working on seamless integration of CTA into dCache.

Heavy flavor machine learning algorithms for fast data processing in sPHENIX

The sPHENIX experiment at RHIC utilizes the first new heavy ion detector since the switch on of the LHC experiments. It’s optimized for precision jet and heavy flavor physics measurements, and recorded its first collisions in spring 2023. sPHENIX uses a tracking system with streaming readout and barrel calorimetry to reconstruct the collision topology. Event plane detectors, minimum bias detectors and zero-degree calorimeters are used to characterize the event. The streaming readout detectors are capable of recording 10% of the minimum bias rate, in addition to triggered events, in p+p collisions which will enable unabated, precision b-hadron and heavy flavor jet measurements at RHIC. An AI-assisted hardware trigger demonstrator is under development to sample the remaining 90% of minimum-bias p+p collisions with an aim for further deployment at the EIC.

Extending Rucio with modern cloud storage support

Rucio is a software framework designed to facilitate scientific collaborations in efficiently organising, managing, and accessing extensive volumes of data through customizable policies. The framework enables data distribution across globally distributed locations and heterogeneous data centres, integrating various storage and network technologies into a unified federated entity. Rucio offers advanced features like distributed data recovery and adaptive replication, and it exhibits high scalability, modularity, and extensibility. Originally developed to meet the requirements of the high-energy physics experiment ATLAS, Rucio has been continuously expanded to support LHC experiments and diverse scientific communities. Recent R&D projects within these communities have evaluated the integration of both private and commercially-provided cloud storage systems, leading to the development of additional functionalities for seamless integration within Rucio. Furthermore, the underlying systems, FTS and GFAL/Davix, have been extended to cater to specific use cases. This contribution focuses on the technical aspects of this work, particularly the challenges encountered in building a generic interface for self-hosted cloud storage, such as MinIO or CEPH S3 Gateway, and established providers like Google Cloud Storage and Amazon Simple Storage Service. Additionally, the integration of decentralised clouds like SEAL is explored. Key aspects, including authentication and authorisation, direct and remote access, throughput and cost estimation, are highlighted, along with shared experiences in daily operations.

EOS software evolution enabling LHC Run 3

EOS software evolution enabling LHC Run 3

An Object Condensation Pipeline for Charged Particle Tracking at the High Luminosity LHC

Recent work has demonstrated that graph neural networks (GNNs) trained for charged particle tracking can match the performance of traditional algorithms while improving scalability to prepare for the High Luminosity LHC experiment. Most approaches are based on the edge classification (EC) paradigm, wherein tracker hits are connected by edges, and a GNN is trained to prune edges, resulting in a collection of connected components representing tracks. These connected components are usually collected by a clustering algorithm and the resulting hit clusters are passed to downstream modules that may assess track quality or fit track parameters. In this work, we consider an alternative approach based on object condensation (OC), a multi-objective learning framework designed to cluster points belonging to an arbitrary number of objects, in this context tracks, and regress the properties of each object. We demonstrate that OC shows very promising results when applied to the pixel detector of the trackML dataset and can, in some cases, recover tracks that are not reconstructable when relying on the output of an EC alone. The results have been obtained with a modular and extensible open-source implementation that allows us to efficiently train and evaluate the performance of various OC architectures and related approaches.

The “green” use of fluorocarbons in Cherenkov detectors and silicon tracker cooling systems: challenges and opportunities in an unfolding era of alternatives

Saturated fluorocarbons (SFCs) of form CnF(2n+2) are chosen for their optical properties as Cherenkov radiators, with C4F10 and CF4 currently used at CERN in the COMPASS and LHCb ring imaging Cherenkov detectors. Their non-conductivity, non-flammability and radiation-resistance also make SFCs ideal coolants: C6F14 liquid cooling is used in all LHC experiments, while C3F8 is used for the evaporative cooling of TOTEM and the ATLAS silicon tracker. These fluids, however, have high global warming potentials (5000–10000*GWPCO2), and represented around 36% of CERN’s CO2-equivalent emissions in 2018. There is thus an impetus to reduce their use, losses in purification and wastage through leaks, through improved monitoring and closed circulation system design. Newer spur-oxygenated fluoro-ketones, for example from the 3 M NOVEC® range, with CnF2nO structures, can offer similar performance to SFCs with but with very low, or zero GWP. Although these fluids do not yet exist in large quantities over the full CnF2 “matrix” the radiation tolerance and thermal performance of NOVEC 649 (C6F12O) was sufficiently promising for it to be chosen as a C6F14 replacement for cooling silicon photomultipliers. Additionally, subject to optical testing, NOVEC 5110 (C5F10O) could (if blended with nitrogen) replace both C4F10 and CF4 in Cherenkov detectors. Lighter molecules (for example C2F4O, with similar thermodynamics to C2F6)—if and when available in industrial quantities—might allow lower temperature operation than evaporative CO2 in future silicon trackers operated at very high luminosity. Ultrasonic gas mixture analysis is very sensitive to concentration changes of a heavy vapour in a light carrier, and is used—in the only such fluorocarbon coolant leak monitoring system operating at LHC—for real-time monitoring of C3F8 coolant leaks from the ATLAS pixel and SCT silicon trackers into their nitrogen-flushed environmental volumes. A typical C3F8 sensitivity of better than 10−5 is achieved. Advanced new ultrasonic algorithms allow measurement of the concentrations of a pair of gases of particular interest on top of a varying known baseline of other gases. The technique is thus of considerable value in leak monitoring and could be used to blend fluoro-ketones with nitrogen or argon to reduce the GWP “load” of large volume atmospheric pressure gas Cherenkov radiators without the recourse to higher-pressure noble gas approaches. This paper outlines an approach to GWP reduction with fluoro-ketone fluids and the blending of heritage SFCs or fluoro-ketones with lighter gases using ultrasonic monitoring and control. Possible avenues for the use of fluoro-ketones in liquid phase and evaporative cooling of silicon trackers are discussed.

Moments of multiplicity distributions for KNO scaling study using the ATLAS results

The normalised order-q moments of primarily charged-particle multiplicity distributions are studied for KNO scaling investigation in pp collisions as deduced from the results of the ATLAS at the LHC. The normalised moments for the LHC and low-energy experiments are compared for the kinematic region with an absolute pseudorapidity less than 2.5. The normalised moments show a increases linearly with centre-of-mass energies, and therefore the KNO scaling is violated for the full-scaled multiplicity region. The normalised moments for scaled multiplicity greater than one average multiplicity are constant for the highest centre-of-mass energies, and therefore the KNO scaling is concluded to hold.

Exploring SMEFT operators in the tHq production at the LHC

We study the top-quark production along with a Higgs boson and a jet (tHq) at the LHC experiment within the framework of the Standard Model Effective Field Theory (SMEFT). A strategy is developed to constrain the Wilson Coefficients (WC) corresponding to the associated SMEFT operators using the latest LHC measurements. The best-fit values of these WCs are presented. Finally, we demonstrate the feasibility of finding the effects of these operators on various kinematical observables of the tHq process at the LHC. We find that for a set of best-fitted values of the considered WCs, the excess of signal over the backgrounds can be achieved with a reasonable significance at the center of mass energy s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV and for integrated luminosity options L\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{L} $$\\end{document} =300 fb−1 and 3000 fb−1.

Studies on RPC detectors operated with environmentally friendly gas mixtures in LHC-like conditions

Resistive Plate Chambers (RPC) are gasesous detectors employed at CERN LHC experiments thanks to their trigger performance, timing capabilities and contained production costs. High Pressure Laminate RPCs are operated with a three-component gas mixture, made of 90–95% of C_2H_2F_4, around 5% of i-C_4H_{10} and 0.3% of SF_6. Due to the presence of leaks at detector level and to the greenhouse characteristics of C_2H_2F_4 and SF_6, RPCs in ATLAS and CMS were accounting for about 87% of CO_2 equivalent emissions during LHC Run 2. To address this, several alternative gases were studied, including R-1234ze as a possible substitute for R-134a. Furthermore, the addition of some amount of CO_2 into the RPCs gas mixture was explored as a possible short-to-medium term solution to lower the total greenhouse gas emissions and reduce the usage of C_2H_2F_4. A dedicated data taking campaign was performed at the Gamma Irradiation Facility at CERN, where RPCs detectors performance were studied with muon beam and gamma background. The detectors were operated with the addition of 30% and 40% and 50% of CO_2 to the standard gas mixture, together with an increased fraction of SF_6. Two different amounts of i-C4H10 were also evaluated to assess compatibility with the CMS and ATLAS requirements. Results from these beam tests with the above-mentioned gas mixtures are reported in this work.

Search for heavy Majorana neutrinos in the τ final state at proton-electron colliders

We utilize the lepton number violation signal process p e− → τ+jjj to search for heavy Majorana neutrinos at future proton-electron colliders. The LHeC (FCC-eh) is considered to run with an electron beam energy of 60 GeV, a proton beam energy of 7 (50) TeV and an integrated luminosity of 1 (3) ab−1, and the electron beam is considered to be unpolarized. We apply detector configurations and simulate signal and related standard model background events for both hadronic τh and leptonic τℓ final states, ℓ being a muon. After preselection, multivariate analyses are performed to reject the background. The strategy to reconstruct the heavy neutrino mass is developed and distributions of reconstructed mass are presented. Discovery sensitivities on parameter |VτN|2|VeN|2/(|VτN|2 + |VeN|2) for the heavy neutrino mass between 10 and 3000 GeV are predicted. At the 2-σ significance, the best discovery sensitivity is ∼ 1.2 × 10−5 (5.0 × 10−6) at the LHeC (FCC-eh) when mN ∼ 100 GeV for the hadronic τh final state. Sensitivities for the leptonic τℓ final state are found to be similar to those for the hadronic τh final state for most of the parameter space investigated. We also derive the limits on mixing parameters from electroweak precision data (EWPD) and DELPHI experiment. Assuming |VτN|2 = |VeN|2 = |VℓN|2, sensitivity bounds from the LHeC and FCC-eh experiments are found to be stronger than those from EWPD when mN ≲ 900 GeV, and also stronger than those from DELPHI when mN ≳ 70 GeV. Constraints are also interpreted and compared in the |VτN|2 vs. |VeN|2 plane. Compared with current limits from EWPD, DELPHI, and LHC experiments, future pe experiments can probe large additional regions in the parameter space formed by |VτN|2 and |VeN|2, and thus significantly enhance the discovery potential for a large portion of the |VτN|2 vs. |VeN|2 plane.

Exclusive Photo-production of J/Ψ and Ψ(2s) as a tool to explore the transition to high and saturated gluon densities at the LHC.


 
 
 We study the energy dependence of the cross-section for exclusive photo-production of vector mesons J/Ψ and Ψ(2s) and search for signs for the onset of non-linear QCD dynamics in this observable. Our study is based on two dipole models: the Golec-Biernat, Wuesthoff Model (GBW) and the Bartels, Golec-Biernat, Kowal- ski Model (BGK). We find that differences between linear and non-linear implementations of these models are relatively small in the kinematic region probed by both HERA and LHC experiments if the energy dependence of the photo-production cross-section is being considered. We however find that the ratio of both cross-sections grows with energy in the presence of non-linear effects, while it remains approximately constant in the linearized case. The ratio of photo-production cross-sections might therefore provide a suitable tool to characterize the size of non-linear QCD effects at current collider energies.
 
 

Discovering New Science in the Noise from LHC Experiments

Steven Schramm and his team of researchers in the DISCOVERHEP project are searching for evidence of new physics in previously ignored ‘noise’ data of Large Hadron Collider experiments.

The Higgs condensate as a quantum liquid: A critical comparison with observations

The triviality of four-dimensional scalar quantum field theories poses challenging problems to the usually adopted perturbative implementation of the Higgs mechanism. In the first part of the paper, we compare the triviality scenario and the renormalized two-loop perturbation theory to precise and extensive results from nonperturbative numerical simulations of the real scalar field theory on the lattice. The proposal of triviality and spontaneous symmetry breaking turns out to be in good agreement with numerical simulations, while the renormalized perturbative approach seems to suffer significant deviations from the numerical simulation results. In the second part of the paper, we try to illustrate how the triviality of four-dimensional scalar field theory leads, nevertheless, to the spontaneous symmetry breaking in the scalar sector of the Standard Model. We show how triviality allows us to develop a physical picture of the Higgs mechanism in the Standard Model. We suggest that the Higgs condensate behaves like a relativistic quantum liquid leading to the prevision of two Higgs bosons. The light Higgs boson resembles closely the new LHC narrow resonance at 125 GeV. The heavy Higgs boson is a rather broad resonance with mass of about 730 GeV. We critically compare our proposal to the complete LHC Run 2 data collected by the ATLAS and CMS Collaborations. We do not find convincingly evidences of the heavy Higgs boson in the ATLAS datasets. On the other hand, the CMS full Run 2 data display evidences of a heavy Higgs boson in the main decay modes [Formula: see text], while in the preliminary Run 2 data there are hints of the decays [Formula: see text] in the golden channel. We also critically discuss plausible reasons for the discrepancies between the two LHC experiments.