Large Hadron Collider Collisions Research Articles

The FASER detector

FASER, the ForwArd Search ExpeRiment, is an experiment dedicated to searching for light, extremely weakly-interacting particles at CERN's Large Hadron Collider (LHC). Such particles may be produced in the very forward direction of the LHC's high-energy collisions and then decay to visible particles inside the FASER detector, which is placed 480 m downstream of the ATLAS interaction point, aligned with the beam collisions axis. FASER also includes a sub-detector, FASERν, designed to detect neutrinos produced in the LHC collisions and to study their properties. In this paper, each component of the FASER detector is described in detail, as well as the installation of the experiment system and its commissioning using cosmic-rays collected in September 2021 and during the LHC pilot beam test carried out in October 2021. FASER has successfully started taking LHC collision data in 2022, and will run throughout LHC Run 3.

Commissioning of the ALICE readout software for LHC Run 3

ALICE (A Large Ion Collider Experiment) is a heavy-ion detector studying the physics of strongly interacting matter and the quarkgluon plasma at the CERN LHC (Large Hadron Collider). During the second long shut-down of the LHC, the ALICE detector was upgraded to cope with an interaction rate of 50 kHz in Pb-Pb collisions, producing in the online computing system (O2) a sustained input throughput of 3.5 TB/s. In the past years, the O2/FLP project built the new data-acquisition system capable of handling this load. It consists of 200 readout nodes, collecting the data transferred from over 8000 detector links to PCs memory by dedicated PCI boards. The readout software manages the hardware and software memory buffers used for DMA and inter-process communication. It initiates the data flow, performs on-the-fly consistency checks, formats the data, reports performance, and finally pushes the data to the local processing pipeline. The output is then sent by the data distribution software over 100Gb/s links to a dedicated event processing farm. The readout software modular design allowed to address the manifold needs faced during the prototyping, installation and commissioning phases, which proved essential from the lab tests to physics production, like file replay and recording, or online multi-threaded LZ4 compression. We will describe the hardware and software implementation of the O2 readout system, and review the challenges met during the commissioning and first months of operation with LHC collisions in 2022.

Spatio-Temporal Anomaly Detection with Graph Networks for Data Quality Monitoring of the Hadron Calorimeter.

The Compact Muon Solenoid (CMS) experiment is a general-purpose detector for high-energy collision at the Large Hadron Collider (LHC) at CERN. It employs an online data quality monitoring (DQM) system to promptly spot and diagnose particle data acquisition problems to avoid data quality loss. In this study, we present a semi-supervised spatio-temporal anomaly detection (AD) monitoring system for the physics particle reading channels of the Hadron Calorimeter (HCAL) of the CMS using three-dimensional digi-occupancy map data of the DQM. We propose the GraphSTAD system, which employs convolutional and graph neural networks to learn local spatial characteristics induced by particles traversing the detector and the global behavior owing to shared backend circuit connections and housing boxes of the channels, respectively. Recurrent neural networks capture the temporal evolution of the extracted spatial features. We validate the accuracy of the proposed AD system in capturing diverse channel fault types using the LHC collision data sets. The GraphSTAD system achieves production-level accuracy and is being integrated into the CMS core production system for real-time monitoring of the HCAL. We provide a quantitative performance comparison with alternative benchmark models to demonstrate the promising leverage of the presented system.

The DAQ and clock distribution system of CMS MIP Timing Detector

The Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) is undergoing an extensive Phase-II upgrade program to cope with the challenging conditions of the High-Luminosity LHC (HL-LHC). A new timing detector is designed to measure minimum ionizing particles (MIPs) with a time resolution of 30–60 ps during the entire HL-LHC phase. A common data acquisition (DAQ) system will collect data from readout chips, reconstruct timing information, and send data to the event builder. The MIP timing detector (MTD) DAQ system is built around the state-of-the-art ATCA-form-factor Serenity board with two high-speed FPGAs. The precision clock is synchronized to the LHC collision rate of 40 MHz and is received at the subsystem and transmitted to the detector via high-speed data links. The detector system with a full-readout chain has been tested using prototypes of the DAQ, on-detector electronics, and sensors, showing that the system can successfully achieve timing resolution below 30 ps.

Distinguishing signatures of scalar leptoquarks at hadron and muon colliders

While the hunt for new states beyond the standard model (SM) goes on for various well motivated theories, the leptoquarks are among the most appealing scenarios at recent times due to a series of tensions observed in B-meson decays. We consider SU(2) singlet and triplet scalar leptoquarks separately, which contribute to charged and neutral current B-meson decays. Focusing on the single production of these two scalar leptoquarks, we perform a PYTHIA-based simulation considering all the dominant SM backgrounds at the current and future setups of the Large Hadron Collider (LHC). The mono-b-jet + not !!{p_T} finalstate gives the strongest signal for the singlet leptoquark at the 30 TeV LHC or Future Circular Collider (FCC), with a possibility of 5sigma signal significance with gtrsim 1000 fb^{-1} of integrated luminosity, for the chosen benchmark scenarios. The finalstate consisting of a c-jet and two tau -jets provides highest reach for the singlet leptoquark, probing an {mathcal {O}}(10^{-1}) value of the Yukawa-type couplings for up to 3.0 TeV leptoquark mass. For the triplet leptoquark, topology is the most optimistic signature at the LHC, probing leptoquark couplings to fermions at {mathcal {O}}(10^{-1}) value for the leptoquark mass range up to 4.0 TeV. The invariant mass edge distribution is found to be instrumental in determination of the leptoquark mass scale at the LHC. We also perform the analysis at the proposed multi-TeV muon collider, where an {mathcal {O}}(10^{-1}) leptoquark Yukawa coupling can be probed for a 5.0 TeV leptoquark mass.

Operational Experience and Evolution of the ATLAS Tile Hadronic Calorimeter Read-Out Drivers

TileCal is the central hadronic calorimeter of the ATLAS experiment at the Large Hadron Collider (LHC). It is a sampling detector where scintillating tiles are embedded in steel absorber plates. The tiles are grouped forming cells, which are read-out on both sides by photomultiplier tubes (PMTs). The PMT digital samples are transmitted to the Read-Out Drivers (ROD) located in the back-end system for the events accepted by the Level 1 trigger system. The ROD is the core element of the back-end electronics and it represents the interface between the front-end electronics and the ATLAS overall Data AcQuisition (DAQ) system. It is responsible for energy and time reconstruction, trigger and data synchronization, busy handling, data integrity checking and lossless data compression. The TileCal ROD is a standard 9U VME board equipped with DSP based Processing Units mezzanine cards. A total of 32 ROD modules are required to read-out the entire TileCal detector. Each ROD module has to process the data from up to 360 PMTs in real time in less than 10 microseconds. The commissioning of the RODs was completed in 2008 before the first LHC collisions. Since then, several hardware and firmware updates have been implemented to accommodate the RODs to the evolving ATLAS Trigger and DAQ conditions adjusted to follow the LHC parameters. The initial ROD system, the different updates implemented and the operational experience during the LHC Run 1 and Run 2 are presented.

CutLang as an analysis description language for introducing students to analyses in particle physics

The fifth edition of the ‘Computing Applications in Particle Physics’ school was held on 3–7 February 2020, at İstanbul University, Turkey. This particular edition focused on the processing of simulated data from the large hadron collider collisions using an analysis description language and its runtime interpreter called CutLang. 24 undergraduate and 6 graduate students were initiated to collider data analysis during the school. After 3 days of lectures and exercises, the students were grouped into teams of 3 or 4 and each team was assigned an analysis publication from ATLAS or CMS experiments. After 1.5 days of independent study, each team was able to reproduce the assigned analysis using CutLang.

Probing tqZ anomalous couplings in the trilepton signal at the HL-LHC, HE-LHC, and FCC-hh * *Supported by the Foundation of the Henan Institute of Science and Technology (2016ZD01), part by the NExT Institute and the STFC CG (ST/L000296/1)

We investigate the prospect of discovering the Flavour Changing Neutral Current (FCNC) couplings via two production processes yielding trilepton signals: top quark pair production with one top quark decaying to the Z boson and one light jet and the anomalous single top quark plus Z boson production process . We study these channels at various successors of the Large Hadron Collider (LHC), i.e., the approved High-Luminosity LHC (HL-LHC) as well as the proposed High-Energy LHC (HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh). We perform a full simulation for the signals and the relevant Standard Model (SM) backgrounds and obtain limits on the Branching Ratios (BRs) of , eventually yielding a trilepton final state through the decay modes and . The upper limits on these FCNC BRs at 95% Confidence Level (CL) are obtained at the HL-LHC with TeV and 3 ab−1, at the HE-LHC with TeV and 15 ab−1, and at the FCC-hh with TeV and 30 ab−1.

Performance of the ATLAS Resistive Plate Chamber detector and Level-1 muon barrel trigger at √s = 13 TeV

The ATLAS experiment at the Large Hadron Collider (LHC) utilises a trigger system consisting of a first level (Level-1) trigger based on custom hardware and a higher level trigger based on computer farms. The Level-1 muon trigger system selects muon candidates with six thresholds of transverse momentum and associates them with correct LHC bunch crossings. The Level-1 muon barrel trigger uses Resistive Plate Chamber (RPC) detectors to form trigger decisions in the region of |η | < 1.05. The RPC detectors are arranged in three concentric double layers, for a total of 3700 gas volumes, with a total surface of more than 4000 square meters, operating in a toroidal magnetic field. The performance of the RPC detector system and of the Level-1 muon barrel trigger during the 2018 data-taking period is discussed in this contribution. 60.8 fb−1 out of 62.2 fb−1 of data recorded by the ATLAS detector at LHC are used. Measurements of the RPC detector response and time resolution, obtained using muon candidates produced in LHC collisions, are presented. Trigger performance and efficiency are measured with muons originating from the decay of Z bosons. Finally, studies of the RPC detector response at different high voltage and threshold settings are shown, as a preview of the expected detector performance after the High Luminosity LHC upgrade.

Exclusive and diffractive gamma gamma production in PbPb collisions at the LHC, HE-LHC and FCC

In this paper we present a detailed analysis of the contribution of the Light-by-Light (LbL), Durham and double diffractive processes for the diphoton production in ultraperipheral PbPb collisions at the Large Hadron Collider (LHC), High-Energy LHC (HE-LHC) and Future Circular Collider (FCC). The acceptance of the central and forward LHC detectors is taken into account and predictions for the invariant mass, rapidity, transverse momentum and acoplanarity distributions are presented. Our results indicate that the contribution of the Durham process is negligible and that the double diffractive process can be strongly suppressed by the exclusivity cuts, which will allow to perform a precise analysis of the LbL scattering, as well the search of beyond Standard Model physics in this final state.

Particle Production in XeXe Collisions at the LHC within the Integrated Hydrokinetic Model

The paper is devoted to the theoretical study of particle production in the Large Hadron Collider (LHC) Xe+Xe collisions at the energy s N N = 5 . 44 TeV. The description of common bulk observables, such as mean charged particle multiplicity, particle number ratios, and p T spectra, is obtained within the integrated hydrokinetic model, and the simulation results are compared to the corresponding experimental points. The comparison shows that the model is able to adequately describe the measured data for the considered collision type, similarly as for the cases of Pb+Pb LHC collisions and top Relativistic Heavy Ion Collider (RHIC) energy Au+Au collisions, analyzed in our previous works.

Search for the t \u2192 ch decay at hadron colliders

We study the observability for the flavor-changing decay of a top quark t → ch at the Large Hadron Collider (LHC) and future hadron colliders, namely, High-Luminosity LHC (HL-LHC), High-Energy LHC (HE-LHC) and Future Circular hadron-hadron Collider (FCC-hh). Two scenarios in which the Higgs boson could decay: into a quark bottom pair (bb-channel) and two photons (γγ-channel) are analyzed. A Monte Carlo analysis of the signal and the Standard Model (SM) background is computed. Center-of-mass energies of sqrt{s}=14,27 and 100 TeV and integrated luminosities from 0.3 to 30 ab−1 are explored. The theoretical framework adopted in this work is the Type-III Two-Higgs Doublet Model (THDM-III) for which, constraints on the parameter space from the Higgs boson coupling modifiers κi are presented and used in order to evaluate the branching ratio of the t → ch decay and the left( ppto toverline{t}, tto chright) production cross section. We find that with the integrated luminosity achieved at the LHC, the t → ch decay is out of the reach of detection. More promising results emerge for the HL-LHC, HE-LHC and FCC-hh in which potential discoveries could be claimed.

Improved Monte Carlo Glauber predictions at present and future nuclear colliders

We present the results of an improved Monte Carlo Glauber (MCG) model of relevance for collisions involving nuclei at center-of-mass energies of the BNL Relativistic Heavy Ion Collider ($\sqrt{{s}_{\mathit{NN}}}=0.2$ TeV), CERN Large Hadron Collider (LHC) ($\sqrt{{s}_{\mathit{NN}}}=2.76--8.8\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$), and proposed future hadron colliders ($\sqrt{{s}_{\mathit{NN}}}\ensuremath{\approx}10--63$ TeV). The inelastic $pp$ cross sections as a function of $\sqrt{{s}_{\mathit{NN}}}$ are obtained from a precise data-driven parametrization that exploits the many available measurements at LHC collision energies. We describe the nuclear density of a lead nucleus with two separated two-parameter Fermi distributions for protons and neutrons to account for their different densities close to the nuclear periphery. Furthermore, we model the nucleon degrees of freedom inside the nucleus through a lattice with a minimum nodal separation, combined with a ``recentering and reweighting'' procedure, that overcomes some limitations of previous MCG approaches. The nuclear overlap function, number of participant nucleons and binary nucleon-nucleon collisions, participant eccentricity and triangularity, overlap area, and average path length are presented in intervals of percentile centrality for lead-lead (PbPb) and proton-lead ($p\mathrm{Pb}$) collisions at all collision energies. We demonstrate for collisions at $\sqrt{{s}_{\mathit{NN}}}=5.02\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$ that the central values of the Glauber quantities change by up to 7% in a few bins of reaction centrality, due to the improvements implemented, though typically they remain within the previously assigned systematic uncertainties, while their new associated uncertainties are generally smaller (mostly below 5%) at all centralities than for earlier calculations. Tables for all quantities versus centrality at present and foreseen collision energies involving Pb nuclei, as well as for collisions of XeXe at $\sqrt{{s}_{\mathit{NN}}}=5.44\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$, and AuAu and CuCu at $\sqrt{{s}_{\mathit{NN}}}=0.2\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$, are provided. The source code for the improved Monte Carlo Glauber model is made publicly available.

Review of hydrodynamic tunneling issues in high power particle accelerators

Abstract Full impact of one Large Hadron Collider (LHC) 7 TeV proton beam on solid targets made of different materials including copper and carbon, was simulated using an energy deposition code, FLUKA and a two-dimensional hydrodynamic code, BIG2, iteratively. These studies showed that the penetration depth of the entire beam comprised of 2808 proton bunches significantly increases due to a phenomenon named hydrodynamic tunneling of the protons and the shower. For example, the static range of a single 7 TeV proton and its shower is about 1 m in solid copper, but the full LHC beam will penetrate up to about 35 m in the target, if the hydrodynamic effects were included. Due to the potential implications of this result on the machine protection considerations, it was decided to have an experimental verification of the hydrodynamic tunneling effect. For this purpose, experiments were carried out at the CERN HiRadMat (High Radiation to Materials) facility in which extended solid copper cylindrical targets were irradiated with the 440 GeV proton beam generated by the Super Proton Synchrotron (SPS). Simulations of beam-target heating considering the same beam parameters that were used in the experiments, were also performed. These experiments not only confirmed the existence of the hydrodynamic tunneling, but the experimental measurements showed very good agreement with the experimental results as well. This provided confidence in the work on LHC related beam-matter heating simulations. Currently, a design study is being carried out by the international community (with CERN taking the leading role) for a post LHC collider named, the Future Circular Collider (FCC) which will accelerate two counter rotating proton beams up to a particle energy of 50 TeV. Simulations of the full impact of one FCC beam comprised of 10,600 proton bunches with a solid copper target have also been done. These simulations have shown that although the static range of a single 50 TeV proton and its shower in solid copper is around 1.8 m, the entire beam will penetrate up to about 350 m in the target. Feasibility studies of developing a water beam dump for the FCC have also been carried out. A review of this work and its implications on machine protection system are presented in this paper.

Large Scale Software Building with CMake in ATLAS

The offline software of the ATLAS experiment at the Large Hadron Collider (LHC) serves as the platform for detector data reconstruction, simulation and analysis. It is also used in the detector’s trigger system to select LHC collision events during data taking. The ATLAS offline software consists of several million lines of C++ and Python code organized in a modular design of more than 2000 specialized packages. Because of different workflows, many stable numbered releases are in parallel production use. To accommodate specific workflow requests, software patches with modified libraries are distributed on top of existing software releases on a daily basis. The different ATLAS software applications also require a flexible build system that strongly supports unit and integration tests. Within the last year this build system was migrated to CMake.A CMake configuration has been developed that allows one to easily set up and build the above mentioned software packages. This also makes it possible to develop and test new and modified packages on top of existing releases. The system also allows one to detect and execute partial rebuilds of the release based on single package changes. The build system makes use of CPack for building RPM packages out of the software releases, and CTest for running unit and integration tests.We report on the migration and integration of the ATLAS software to CMake and show working examples of this large scale project in production.

Prospects for identification the direct and indirect effects of extra spatial dimensions at the Large Hadron Collider

The existence of massive graviton states, that may be produced as real and virtual particles in high-energy proton collisions, is predicted by the modern developments of Kaluza–Klein models with extra spatial dimensions. The direct and indirect signatures of large and warped extra spatial dimensions may be revealed by analyzing the specific characteristics of dilepton and diphoton final states formed in proton–proton collisions at the Large Hadron Collider (LHC). Virtual effects in the Kaluza–Klein models with large extra spatial dimensions can be discovered by the specic behavior of the dilpton and diphoton invariant-mass distributions, and their identication (in case of discovery) can be performed by the analysis of their angular distributions with integrated center-edge asymmetry. Assuming the nominal values of the LHC collision energy (14 TeV) and luminosity (100 fb–1), for the models with large extra spatial dimensions we find that the sensitivity to the cutoff parameter M S will extend up to 8.5 and 7.6 TeV for their discovery and identification, respectively. For the Randall–Sundrum model with a warped extra dimension, the LHC experiments will be sensitive to the graviton resonance with mass up to 4.4 and 3.1 TeV for its discovery and identification, respectively.

Z–Z' mixing effects in W boson pair production processes at hadron and lepton high-energy colliders

Potential possibilities to detect the effects of Z–Z' mixing in the W-pair production process in proton-proton and electron–positron collisions at the Large Hadron Collider (LHC) and International Linear Collider (ILC) have been studied. It has been established that the processes of W boson pair production are very sensitive to the angle of Z–Z' mixing and their measurements in current and future experiments will make it possible to improve modern restrictions on the angle of Z–Z' mixing in the models with extended gauge sector. At a nominal energy of 14 TeV and an integral luminosity of 100 fb–1, the LHC collider can offer much more precise information on the parameter of Z–Z' mixing and the mass M2 than can be obtained using the ILC leptonic collider (0.5 TeV).

Natural NMSSM with a light Singlet Higgs and Singlino LSP

Supersymmetry (SUSY) is an attractive extension of the Standard Model (SM) of particle physics which solves the SM hierarchy problem. Motivated by the theoretical $\mu$-term problem of the Minimal Supersymmetric Model (MSSM), the Next-to MSSM (NMSSM) can also account for experimental deviations from the SM like the anomalous muon magnetic moment and the dark matter relic density. Natural SUSY, motivated by naturalness considerations, exhibits small fine tuning and a characteristic phenomenology with light higgsinos, stops and gluinos. We describe a scan in NMSSM parameter space motivated by Natural SUSY and guided by the phenomenology of an NMSSM with a slightly broken Peccei-Quinn symmetry and a lightly coupled singlet. We identify a scenario which survives experimental constraints with a light singlet Higgs and a singlino lightest SUSY particle. We then discuss how the scenario is not presently excluded by searches at the Large Hadron Collider (LHC) and which channels are promising for discovery at the LHC and International Linear Collider.

LHC – perspectives at the energy frontier

After a design and construction phase that lasted more than two decades, the Large Hadron Collider (LHC) started its first run in 2010 and after just over two years, the discovery of the Higgs boson at the LHC was announced. In the future the LHC collision energy will be increased by nearly a factor of two, and the dataset will be increased by more than a factor of 100. These improvements dramatically increase the potential for finding new physics at the weak scale via either precision measurements or direct searches or both. The LHC is in a unique position to directly explore the weak energy scale and shed light on some of the biggest puzzles in nature, e.g. the origin of Dark Matter or the hierarchy problem.

Analysis of 440 GeV proton beam–matter interaction experiments at the High Radiation Materials test facility at CERN

In a previous paper [Schmidt et al., Phys. Plasmas 21, 080701 (2014)], we presented the first results on beam–matter interaction experiments that were carried out at the High Radiation Materials test facility at CERN. In these experiments, extended cylindrical targets of solid copper were irradiated with beam of 440 GeV protons delivered by the Super Proton Synchrotron (SPS). The beam comprised of a large number of high intensity proton bunches, each bunch having a length of 0.5 ns with a 50 ns gap between two neighboring bunches, while the length of this entire bunch train was about 7 μs. These experiments established the existence of the hydrodynamic tunneling phenomenon the first time. Detailed numerical simulations of these experiments were also carried out which were reported in detail in another paper [Tahir et al., Phys. Rev. E 90, 063112 (2014)]. Excellent agreement was found between the experimental measurements and the simulation results that validate our previous simulations done using the Large Hadron Collider (LHC) beam of 7 TeV protons [Tahir et al., Phys. Rev. Spec. Top.--Accel. Beams 15, 051003 (2012)]. According to these simulations, the range of the full LHC proton beam and the hadronic shower can be increased by more than an order of magnitude due to the hydrodynamic tunneling, compared to that of a single proton. This effect is of considerable importance for the design of machine protection system for hadron accelerators such as SPS, LHC, and Future Circular Collider. Recently, using metal cutting technology, the targets used in these experiments have been dissected into finer pieces for visual and microscopic inspection in order to establish the precise penetration depth of the protons and the corresponding hadronic shower. This, we believe will be helpful in studying the very important phenomenon of hydrodynamic tunneling in a more quantitative manner. The details of this experimental work together with a comparison with the numerical simulations are presented in this paper.