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In cultural heritage conservation, it is increasingly common to rely on non-destructive imaging methods based on the absorption or scattering of photons ($X$ or $\gamma$ rays) or neutrons. However, physical and practical issues limit these techniques: their penetration depth may be insufficient for large and dense objects, they require transporting the objects of interest to dedicated laboratories, artificial radiation is hazardous and may induce activation in the material under study. Muons are elementary particles abundantly and freely produced in cosmic-ray interactions in the atmosphere. Their absorption and scattering in matter are characteristically dependent on the density and elemental composition of the material that they traverse, which offers the possibility of exploiting them for sub-surface remote imaging. This novel technique, nicknamed "muography", has been applied in use cases ranging from geophysics to archaeology to nuclear safety, but it has been so far under-explored for a vast category of cultural heritage objects that are relatively large (from decimeters to human size) and dense (stone, metals). The development of portable muon detectors makes muography particularly competitive in cases where the items to be analysed are not transportable, or set up in a confined environment. This document reviews the relevant literature, presents some exemplary use cases, and critically assesses the strengths and weaknesses of muography in this context., Comment: Submitted to a special issue of iScience about "Cosmic-Ray Muography and Applications"

The MUon RAdiography of VESuvius (MURAVES) project aims at the study of Mt. Vesuvius, an active and hazardous volcano near Naples, Italy, with the use of muons freely and abundantly produced by cosmic rays. In particular, the MURAVES experiment intends to perform muographic imaging of the internal structure of the summit of Mt. Vesuvius. The challenging measurement of the rock density distribution in its summit by muography, in conjunction with data from other geophysical techniques, can help model possible eruption dynamics. The MURAVES apparatus consists of an array of three independent and identical muon trackers, with a total sensitive area of 3 square meters. In each tracker, a sequence of 4 XY tracking planes made of plastic scintillators is complemented by a 60 cm thick lead wall inserted between the two downstream planes to improve rejection of background from low energy muons. The apparatus is currently acquiring data. This paper presents preliminary results from the analysis of the first data samples acquired with trackers pointing towards Mt. Vesuvius, including the first relative measurement of the density projection of two flanks of the volcano at three different altitudes; we also present the workflow of the simulation chain of the MURAVES experiment and its ongoing developments.

Muography is finding applications in various domains such as volcanology, archaeology, civil engineering, industry, mining, and nuclear waste surveys. To simplify transportation and installation in remote locations after laboratory testing, a fully portable and autonomous muon telescope based on Resistive Plate Chambers (RPCs) is being developed. Two glass-RPC prototypes have been created, sharing the same design goals but with different detector parameters, and comparative studies are ongoing. Drawing from prototype experience, a double-gap RPC with advanced features and improved spatial resolution is constructed. Resistive electrodes are produced manually, and a new data acquisition board is currently undergoing calibration. The results on prototype performance, readout board comparisons and the technical progress on the double-gap RPC are presented.

Muography is a non-invasive imaging technique that exploits cosmic-ray muons to probe various targets by analyzing the absorption or scattering of muons. The method is particularly useful for applications ranging from geophysical exploration to security screening, including the identification of nuclear materials. This study leverages both Monte Carlo simulations and the Point of Closest Approach (PoCA) algorithm for image reconstruction to specifically explore the distortions caused by magnetic fields in scattering muography images. In the PoCA algorithm, it is assumed that all scattering of a muon during its travel in material occurs at a single point, known as the PoCA point. Each PoCA point is characterized by a scattering angle, whose distribution provides insights into the density and elemental composition of the target material. However, magnetic fields can influence muon trajectories according to Lorentz law, affecting the estimated positions of the PoCA points and the calculated scattering angles. This introduces challenges in applications such as border security control systems. Moreover, the presence of magnetic fields can lead to what we term "magnetic jamming", where the resulting muography image is distorted or misleading. This effect further complicates the accurate identification and interpretation of target materials. Our findings underline the necessity to account for magnetic field distortions when utilizing scattering muography in practical scenarios.

In this article we examine recent developments in the research area concerning the creation of end-to-end models for the complete optimization of measuring instruments. The models we consider rely on differentiable programming methods and on the specification of a software pipeline including all factors impacting performance -- from the data-generating processes to their reconstruction and the extraction of inference on the parameters of interest of a measuring instrument -- along with the careful specification of a utility function well aligned with the end goals of the experiment. Building on previous studies originated within the MODE Collaboration, we focus specifically on applications involving instruments for particle physics experimentation, as well as industrial and medical applications that share the detection of radiation as their data-generating mechanism., Comment: 70 pages, 17 figures. To be submitted to journal

We describe a software package, TomOpt, developed to optimise the geometrical layout and specifications of detectors designed for tomography by scattering of cosmic-ray muons. The software exploits differentiable programming for the modeling of muon interactions with detectors and scanned volumes, the inference of volume properties, and the optimisation cycle performing the loss minimisation. In doing so, we provide the first demonstration of end-to-end-differentiable and inference-aware optimisation of particle physics instruments. We study the performance of the software on a relevant benchmark scenario and discuss its potential applications. Our code is available on Github., Comment: V3: Updated to published version; 29 pages content + appendix + refs

Non-destructive subsurface imaging methods based on the absorption or scattering of photons or neutrons are becoming increasingly popular in cultural asset conservation. However, these techniques are limited by physical and practical issues: their penetration depth may be insufficient for large items, and they usually necessitate transferring the objects of interest to specialised laboratories. The latter issue is recently being addressed by the development of portable sources, but artificial radiation can be harmful and is thus subjected to strict regulation. Muons are elementary particles that are abundantly and freely created in the atmosphere by cosmic-ray interactions. Their absorption and scattering in matter are respectively dependent on the density and elemental composition of the substance they traverse, suggesting that they could be used for subsurface remote imaging. This novel technique, dubbed "muography", has been used in applications ranging from geophysics to archaeology, but has remained largely unexplored for a wide range of cultural heritage objects that are small by muography standards but whose size and density are too large for conventional imaging methods. This document outlines the general arguments and some early simulation studies that aim at exploring the low-size limit of muography and its relevance for cultural heritage preservation.

We have proposed a novel application for cosmic-ray muography, called Magic-$\mu$, which is short for Magnetic field Imaging by Cosmic-ray Muons. The general goal of Magic-$\mu$ is to detect the presence of a magnetic field or magnetic flux density whose three-dimensional distribution is unknown. Depending on the application, Magic-$\mu$ can have three detection modes. The first is "magnetic field imaging," which is detecting the presence of a magnetic field in specific voxels within a region of space. The other two modes, transmission and deflection, aim not only to detect the presence but also to measure the flux density of the magnetic field. We have performed a feasibility study using the PHITS Monte Carlo simulation code, for strong and weak magnetic fields. In this paper, we first give an overview of the concept and basic principles of magnetic field muography. Then, the results of the feasibility study on magnetic field imaging for a strong magnetic field (more than 500 mT) are presented.

Motivated by the expectation that new physics may manifest itself in the form of very heavy new particles, most of the operation time of the LHC is devoted to $pp$ collisions at the highest achievable energies and collision rates. The large collision rates imply tight trigger requirements that include high thresholds on the final-state particles' transverse momenta $p_{T}$ and an intrinsic background in the form of particle pileup produced by different collisions occurring during the same bunch crossing. This strategy is potentially sub-optimal for several well-motivated new physics models where new particles are not particularly heavy and can escape the online selection criteria of the multi-purpose LHC experiments due to their light mass and small coupling. A solution may be offered by complementary datasets that are routinely collected by the LHC experiments. These include heavy ion collisions, low-pileup runs for precision physics, and the so-called 'parking' and 'scouting' datasets. While some of them are motivated by other physics goals, they all have the usage of mild $p_{T}$ thresholds at the trigger-level in common. In this study, we assess the relative merits of these datasets for a representative model whose particular clean signature features long-lived resonances yielding displaced dimuon vertices. We compare the reach across those datasets for a simple analysis, simulating LHC data in Run 2 and Run 3 conditions with the Delphes simulation. We show that the scouting and parking datasets, which afford low-$p_{T}$ trigger thresholds by only using partial detector information and delaying the event reconstruction, respectively, have a reach comparable to the standard $pp$ dataset with conventional thresholds. We also show that heavy ion and low-pileup datasets are far less competitive for this signature., Comment: v2: version accepted by JHEP. 23 pages with tables and figures

The scattering angle due to the target volume can be split into two interior angles in the tomographic setups based on the muon scattering, and we call this property as the triangular correlation where the sum of these two interior angles is equal to the scattering angle. In this study, we apply this triangular correlation for a multi-block material configuration that consist of concrete, stainless steel, and uranium. By changing the order of this material set, we employ the GEANT4 simulations and we show that the triangular correlation is valid in the multi-block material setups, thereby providing the possibility of supportive information for the coarse prediction of the material order in such configurations., Comment: 3 figures, 1 table. arXiv admin note: substantial text overlap with arXiv:2112.00376

Muography (or muon radiography) is an imaging technique that relies on the use of cosmogenic muons as a free and safe radiation source. It can be applied in various fields such as archaeology, civil engineering, geology, nuclear reactor monitoring, nuclear waste characterization, underground surveys, etc. In such applications, sometimes deploying muon detectors is challenging due to logistics, e.g. in a narrow underground tunnel or mine. Therefore, we are developing muon detectors whose design goals include portability, robustness, autonomy, versatility, and safety. Our portable muon detectors (or ``muoscopes'') are based on Resistive Plate Chambers (RPC), planar detectors that use ionization in a thin gas gap to detect cosmic muons. Prototype RPCs of active area $16 \times 16~cm^2$ and $28 \times 28~cm^2$ were built in our laboratories at Louvain-la-Neuve (UCLouvain) and Ghent (UGent) to test and compare various design options. Benefiting from the experience gained in building and operating these prototypes, we are proceeding towards the development of improved prototypes with more advanced technical layout and readiness. In this paper we provide the status of our performance studies, including the cross-validation of the two types of prototypes in a joint data taking, and an outline of the direction ahead.

Recent applications of cosmic-ray muons require accurate modeling of their flux at low-energy. However, no measurement has been reported below 400 MeV. Therefore, we developed a full-absorption muon energy spectrometer to obtain energy differential flux below 400 MeV. Because our main detector can measure muon energies below 75 MeV, an energy degradation method is adopted (using 5- and 20-cm thick lead blocks) to shift the sensitive energy range. Three measurements were performed (in the normal mode and the two energy degrading modes) for 10 and 11 days each. The measurement results were compared with an analytical cosmic-ray model, PARMA (the particle and heavy ion transport code system-based analytical radiation model in the atmosphere) and we found that the model can precisely predict the lower energy part of the flux., Comment: 8 pages, 15 figures

In muon scattering tomography, the investigated materials are discriminated according to the scattering angle that mainly depends on the atomic number, the density, and the thickness of the medium at a given energy value. The scattering angles at different initial energies also provide the opportunity to classify the incoming muons into a number of energy groups. In this study, by employing the GEANT4 code, we show that the deflection angle exponentially decays as a function of energy, and the numerical values for the current configuration are below the detector accuracy except the initial energy bins owing to the low-Z, low density, and low thickness of the current plastic scintillators. This implies the necessity of additional components that provoke the muon scattering. Therefore, we introduce stainless steel surfaces into the top and bottom sections in order to amplify the deflection angle as well as to reduce the uncertainty, thereby improving the detector performance.

The full optimization of the design and operation of instruments whose functioning relies on the interaction of radiation with matter is a super-human task, given the large dimensionality of the space of possible choices for geometry, detection technology, materials, data-acquisition, and information-extraction techniques, and the interdependence of the related parameters. On the other hand, massive potential gains in performance over standard, "experience-driven" layouts are in principle within our reach if an objective function fully aligned with the final goals of the instrument is maximized by means of a systematic search of the configuration space. The stochastic nature of the involved quantum processes make the modeling of these systems an intractable problem from a classical statistics point of view, yet the construction of a fully differentiable pipeline and the use of deep learning techniques may allow the simultaneous optimization of all design parameters. In this document we lay down our plans for the design of a modular and versatile modeling tool for the end-to-end optimization of complex instruments for particle physics experiments as well as industrial and medical applications that share the detection of radiation as their basic ingredient. We consider a selected set of use cases to highlight the specific needs of different applications., Comment: 109 pages, 32 figures. To be submitted to Reviews in Physics

Opportunities for searches for phenomena beyond the Standard Model (BSM) using heavy-ions beams at high energies are outlined. Different BSM searches proposed in the last years in collisions of heavy ions, mostly at the Large Hadron Collider, are summarized. A few concrete selected cases are reviewed including searches for axion-like particles, anomalous $\tau$ electromagnetic moments, magnetic monopoles, and dark photons. Expectations for the achievable sensitivities of these searches in the coming years are given. Studies of CP violation in hot and dense QCD matter and connections to ultrahigh-energy cosmic rays physics are also mentioned., Comment: 26 pages, 5 figures. White paper of the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021)

In this study, we exhibit a number elementary strategies that might be at disposal in diverse computational applications in the GEANT4 simulations with the purpose of hemispherical particle sources. To further detail, we initially generate random points on a spherical surface for a sphere of a practical radius by employing Gaussian distributions for the three components of the Cartesian coordinates, thereby obtaining a generating surface for the initial positions of the corresponding particles. Since we do not require the half bottom part of the produced spherical surface for our tomographic applications, we take the absolute value of the vertical component in the Cartesian coordinates by leading to a half-spherical shell, which is traditionally called a hemisphere. Last but not least, we direct the generated particles into the target material to be irradiated by favoring a selective momentum direction that is based on the vector construction between the random point on the hemispherical surface and the origin of the target material, hereby optimizing the particle loss through the source biasing. In the end, we incorporate our strategy by using G4ParticleGun in the GEANT4 code. Furthermore, we also exhibit a second scheme that is based on the coordinate transformation from the spherical coordinates to the Cartesian coordinates, thereby reducing the number of random number generators. While we plan to exert our strategy in the computational practices for muon scattering tomography, this source scheme might find its straightforward applications in different neighboring fields including but not limited to atmospheric sciences, space engineering, and astrophysics where a 3D particle source is a necessity for the modeling goals., Comment: 3 figures

So far, most of the developments in muography (or cosmic-ray muon radiography) have been based on either the scattering or the absorption of cosmic-ray muons produced by the nuclear interactions between primary cosmic-rays and the nuclei of the Earth's atmosphere. Applications of muography are increasing in various disciplines. A new use of this technique to measure a magnetic field has recently been proposed by our group. This new application takes advantage of the electric charge of cosmic-ray muons, which causes them to change their trajectory due to the Lorentz force generated by a magnetic field. In this study, we present a feasibility study of the proposed technique by simulating a simple dipole magnet using the three-dimensional finite element solution package AMaze, together with the PHITS Monte Carlo simulation tools. The distribution of magnetic field flux densities around the magnet was calculated in AMaze and entered into the PHITS code. Positive and negative cosmic-ray muons were generated based on the PHITS-based analytical radiation model (PARMA). A comparison of the count rate maps of the detected muons on two position-sensitive scintillator detectors for the magnetic field ON and OFF was studied using PHITS. The simulation results show the effect of the magnet on the count rate maps and are promising for the newly proposed application of cosmic-ray muons, the imaging of a magnetic field.

In this study, by attempting to resolve the angular complication during the particle generation for the muon tomography applications in the GEANT4 simulations, we exhibit an unconventional methodology that is hinged on the direction limitation via the vectorial construction from the generation location to the restriction area rather than using a certain angular distribution or interval. In other words, we favor a momentum direction that is determined by a vector constructed between an initial point randomly chosen on a generative point/plane and a latter point arbitrarily selected on a restrictive plane of the same dimensions with the basal cross section of the volume-of-interest (VOI). On account of setting out such a generation scheme, we optimize the particle loss by keeping an angular disparity that is directly dependent on the VOI geometry as well as the vertical position of the restrictive plane for a tomographic system of a finite size. We demonstrate our strategy for a set of target materials including aluminum, copper, iron, lead, and uranium with a dimension of 40$\times$10$\times$40 $\rm cm^{3}$ over three restrictive planes of different positions by using a discrete energy spectrum between 0.1 and 8 GeV and we compute the scattering angle, the number of absorption, and the particle loss. Upon our simulation outcomes, we show that the particle generation by means of restrictive planes is an effective strategy that is flexible towards a variety of computational objectives in the GEANT4 simulations., Comment: 7 pages, 2 figures, 9 tables, ACAT 2021

The average deflection angle of the tracked muons in the muon scattering tomography exponentially declines in function of the initial kinetic energy, the angular dependence of which provides an opportunity to set out a binary relation between the initial kinetic energy and the average deflection angle, thereby leading to a coarse energy prediction founded on the mean deflection angle in the case of experimental incapabilities or limitations. In this study, we address the problem of the muon energy classification for a tomographic system consisting of 0.4-cm plastic scintillators manufactured from polyvinyl toluene and we explore a four-group structure besides a ternary partitioning between 0.25 and 8 GeV. In the first instance, we determine the deflection angles by tracking the hit locations in the detector layers on the sub-divided uniform energy intervals through the GEANT4 simulations. In the latter step, we express two misclassification probabilities where the first approach assumes a symmetrical linear propagation bounded by one standard deviation in one dimension, whereas the second procedure employs a positively defined modified Gaussian distribution that governs the overlapping area in two dimensions. In the final stage, we compare qualitatively and quantitatively the adjacent energy groups by using the computed misclassification probabilities. In the absence of any further data manipulation, we explicitly show that the misclassification probabilities increase when the number of energy groups augments. Furthermore, we also conclude that it is feasible to benefit from the mean deflection angle to roughly estimate the muon energies up to four energy groups by taking the misclassification probabilities into consideration, while the classification viability significantly diminishes when the partition number exceeds four on the basis of standard deviation., Comment: 8 pages, 6 figures, 2 tables, RAP21

The angular deviation commonly represented by the scattering angle generally serves to provide the characteristic discrimination in the muon scattering tomography. The regular procedure to determine the scattering angle comprises the collection of exactly four hit locations in four detector layers among which two top detector layers are utilized to construct the first vector, whereas the second vector is built by using two bottom detector layers. Although this procedure acts to classify the target volumes in the tomographic systems based on the muon scattering, the scattering angle obtained through the usual methodology founded on four detector layers is dubious for not yielding any information about the position of target volume. Nonetheless, the same set of four detector layers also imparts the possibility of splitting the scattering angle into two separate angles by creating a triangular correlation in such a way that the scattering angle is referred to an exterior angle, whereas the separate angles are considered the interior opposite angles that are not neighboring this exterior angle. In this study, we first show that a combination of three detector layers out of four fulfills the calculation of the interior opposite angles. Then, by employing the GEANT4 simulations over our tomographic configuration composed of three plastic scintillators in either section, we demonstrate that the interior opposite angles differ towards the vertical spatial variation, while the exterior angle approximately remains constant, thereby implying a beneficial feature to be used for the image reconstruction purposes., Comment: 5 pages, 3 figures, 1 table, International Workshop on Cosmic-Ray Muography (Muography2021)

In the tomographic configurations based on the muon scattering, the angular variation with respect to the kinetic energy indirectly brings forth the ability to coarsely predict the kinetic energy by using the deflection angle owing to the detector layers. Nevertheless, the angular deviation due to the detector components is expected to be minuscule in addition to a relatively high uncertainty in the case of the plastic scintillators. In the present study, we contrast our current tomographic prototype, which consists of the detector layers manufactured from polyvinyl toluene besides a detector accuracy of 1 mrad, with an alternative hodoscope scheme containing stainless steel layers by aiming to investigate the three-group energy structure. Initially, we determine the average deflection angles together with the corresponding standard deviations for our present setup as well as for the alternative scheme by means of the GEANT4 simulations. In the second place, we express a brace of misclassification probabilities founded on the standard deviations where the first procedure assumes a linear finite approximation, whereas the latter approach rests on a positively defined modified Gaussian distribution. Upon our simulation results, we demonstrate that the introduced stainless steel layers in the proposed hodoscope setup do not only serve to augment the average deflection angles, but they also diminish the misclassification probabilities, therewith reducing the classification uncertainty apart from an improved detection performance., Comment: 8 pages, 4 figures, 2 tables, 22nd International Workshop on Radiation Imaging Detectors (iWoRiD2021)

In this study, we employ the Monte Carlo simulations by using the GEANT4 code to demonstrate the capability of muon tomography based on the dual-parameter analysis in the examination of the nuclear waste barrels. Our current hodoscope setup consists of three top and three bottom plastic scintillators made of polyvinyl toluene with the thickness of 0.4 cm, and the composite target material is a cylindrical nuclear waste drum with the height of 96 cm and the radius of 29.6 cm where the outermost layer is stainless steel with the lateral thickness of 3.2 cm and the filling material is ordinary concrete that encapsulates the nuclear materials of dimensions 20$\times$20$\times$20 cm$^{3}$. By simulating with a narrow planar muon beam of 1$\times$1 cm$^{2}$ over the uniform energy interval between 0.1 and 8 GeV, we determine the variation of the average scattering angle together with the standard deviation by utilizing a 0.5-GeV bin length, the counts of the scattering angle by using a 1-mrad step, and the number of the absorption events for the five prevalent nuclear materials starting from cobalt and ending in plutonium. Via the duo-parametric analysis that is founded on the scattering angle as well as the absorption in the present study, we show that the presence of the nuclear materials in the waste barrels is numerically visible in comparison with the concrete-filled waste drum without any nuclear material, and the muon tomography is capable of distinguishing these nuclear materials by coupling the information about the scattering angle and the number of absorption in the cases where one of these two parameters yields strong similarity for certain nuclear materials., Comment: 9 pages, 5 figures, 3 tables

Between the years 2015 and 2019, members of the Horizon 2020-funded Innovative Training Network named "AMVA4NewPhysics" studied the customization and application of advanced multivariate analysis methods and statistical learning tools to high-energy physics problems, as well as developed entirely new ones. Many of those methods were successfully used to improve the sensitivity of data analyses performed by the ATLAS and CMS experiments at the CERN Large Hadron Collider; several others, still in the testing phase, promise to further improve the precision of measurements of fundamental physics parameters and the reach of searches for new phenomena. In this paper, the most relevant new tools, among those studied and developed, are presented along with the evaluation of their performances., Comment: 101 pages, 21 figures, submitted to Elsevier. [v2]: Updated to published version (in 'Reviews in Physics')

Imaging methods based on the absorption or scattering of atmospheric muons, collectively named under the neologism "muography", exploit the abundant natural flux of muons produced from cosmic-ray interactions in the atmosphere. Recent years have seen a steep rise in the development of muography methods in a variety of innovative multidisciplinary approaches to study the interior of natural or man-made structures, establishing synergies between usually disconnected academic disciplines such as particle physics, geology, and archaeology. Muography also bears promise of immediate societal impact through geotechnical investigations, nuclear waste surveys, homeland security, and natural hazard monitoring. Our aim is to provide an introduction to this vibrant research area, starting from the physical principles at the basis of the methods and reviewing several recent developments in the application of muography methods to specific use cases, without any pretence of exhaustiveness. We then describe the main detector technologies and imaging methods, including their combination with conventional techniques from other disciplines, where appropriate. Finally, we discuss critically some outstanding issues that affect a broad variety of applications, and the current state of the art in addressing them., Comment: Submitted to Reviews in Physics

We show that heavy ion collisions at the LHC provide a promising environment to search for signatures with displaced vertices in well-motivated New Physics scenarios. Compared to proton collisions, they offer several advantages, i) the number of parton level interactions per collision is larger, ii) there is no pile-up, iii) the lower instantaneous luminosity compared to proton collisions allows to operate the LHC experiments with very loose triggers, and iv) there are new production mechanisms that are absent in proton collisions. In the present work we focus on the third point and show that the modification of the triggers alone can increase the number of observable events by orders of magnitude if the long lived particles are predominantly produced with low transverse momentum. Our results show that collisions of ions lighter than lead are well-motivated from the viewpoint of searches for New Physics. We illustrate this for the example of heavy neutrinos in the Neutrino Minimal Standard Model., Comment: 18 pages, 9 figures, 2 tables; published version

Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments --- as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER --- to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the High-Luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity "dark showers", highlighting opportunities for expanding the LHC reach for these signals.

This document summarises proposed searches for new physics accessible in the heavy-ion mode at the CERN Large Hadron Collider (LHC), both through hadronic and ultraperipheral $\gamma\gamma$ interactions, and that have a competitive or, even, unique discovery potential compared to standard proton-proton collision studies. Illustrative examples include searches for new particles -- such as axion-like pseudoscalars, radions, magnetic monopoles, new long-lived particles, dark photons, and sexaquarks as dark matter candidates -- as well as new interactions, such as non-linear or non-commutative QED extensions. We argue that such interesting possibilities constitute a well-justified scientific motivation, complementing standard quark-gluon-plasma physics studies, to continue running with ions at the LHC after the Run-4, i.e. beyond 2030, including light and intermediate-mass ion species, accumulating nucleon-nucleon integrated luminosities in the accessible fb$^{-1}$ range per month., Comment: 20 pages, 6 figures. Minor updates to match the final version published as JPG 47 (2020) 060501. (A slightly reduced version of this document was submitted as input to the update of the European Particle Physics Strategy EPPS-2019)

We show that heavy ion collisions at the LHC provide a promising environment to search for new long lived particles in well-motivated New Physics scenarios. One advantage lies in the possibility to operate the main detectors with looser triggers, which can increase the number of observable events by orders of magnitude if the long lived particles are produced with low transverse momentum. In addition, the absence of pileup in heavy ion collisions can avoid systematic nuisances that will be present in future proton runs, such as the problem of vertex mis-identification. Finally, there are new production mechanisms that are absent or inefficient in proton collisions. We show that the looser triggers alone can make searches in heavy ion data competitive with proton data for the specific example of heavy neutrinos in the Neutrino Minimal Standard Model, produced in the decay of B mesons. Our results suggest that collisions of ions lighter than lead, which are currently under discussion in the heavy ion community, are well-motivated from the viewpoint of searches for New Physics., Comment: Version accepted by Physical Review Letters for publication as a Letter. 6 pages, 3 figures

Single top quark production cross sections at hadron colliders are traditionally used to extract the modulus of the $V_{tb}$ element of the Cabibbo-Kobayashi-Maskawa matrix under the following assumption: $|V_{tb}| \gg |V_{td}|, |V_{ts}|$. For the first time, direct limits on $|V_{td}|$ and $|V_{ts}|$ are obtained using experimental data without the assumption of the unitarity of the CKM matrix. Limits on the $|V_{td}|$, $|V_{ts}|$ and $|V_{tb}|$ are extracted from differential measurements of single top quark cross sections in $t$-channel as a function of the rapidity and transverse momentum of the top quark and the light jet recoiling against the top quark. We have shown that the pseudorapidity of the forward jet in the single top production is one of the most powerful observables for discriminating between the $|V_{td}|$ and $|V_{tb}|$ events. We perform a global fit of top quark related CKM elements to experimental data from the LHC Runs I and II and Tevatron. Experimental data include inclusive and differential single top cross sections in $t$-channel, inclusive tW production cross section, and top quark branching ratio to b quark and W boson. We present bounds on $|V_{tb}|$, $|V_{ts}|$ and $|V_{td}|$ using current data and project the results for future LHC data sets corresponding to luminosities of 300 and 3000 \fb.

We report on the first steps in the development of a small-size muon telescope based on glass Resistive Plate Chambers with small active area ($16\times 16~{\rm cm}^2$). The long-term goal of this project is to focus on applications of muography where the telescope may have to be operated underground and/or inside small rooms, and in challenging logistic situations. Driving principles in our design are therefore compact size, light weight, gas tightness, and robustness. The first data-taking experiences have been encouraging, and we elaborate on the lessons learnt and future directions for development., Comment: Proceedings of the "Cosmic-Ray Muography" meeting of the Royal Society, 14-15 May 2018 at the Kavli Royal Society Centre, Chicheley Hall, Newport Pagnell (UK)

At the time of the 10th International Workshop on Top Quark Physics (TOP2017), top quark physics is a very dynamic research area. Thanks to the unprecedentedly fast accumulation of high-energy data at the LHC during the ongoing Run~2, statistical starvation is a matter of the past for most of the traditional top-quark analyses, that are now experiencing the luxury of having to worry about how to punch through the "Systematics Wall" and maximize the utility of their data. New processes involving top quarks are being studied for the first time, and the good old pair-production processes are being explored in unusual settings, such as collisions involving heavy ions, or "reference data" collected by the LHC at relatively low centre-of-mass energy. The TOP2017 conference featured 37 talks delivered by experimental physicists, including seven in the "Young Scientists Forum" where young colleagues were given the opportunity to elaborate more deeply than usual on their own work. As it is impossible to do justice to all the experimental results presented at this conference while staying within a reasonable length, this document contains a very biased selection, mostly based on the personal taste of the author., Comment: Proceedings of the 10th International Workshop on Top Quark Physics, Braga, Portugal, September 17-22, 2017

This paper provides a review of the experimental studies of processes with a single top quark at the Tevatron proton-antiproton collider and the LHC proton-proton collider. Single top-quark production in the t-channel process has been measured at both colliders. The s-channel process has been observed at the Tevatron, and its rate has been also measured at the center-of-mass energy of 8 TeV at the LHC in spite of the comparatively harsher background contamination. LHC data also brought the observation of the associated production of a single top quark with a W boson as well as with a Z boson. The Cabibbo-Kobayashi-Maskawa matrix element |Vtb| is extracted from the single-top-quark production cross sections, and t-channel events are used to measure several properties of the top quark and set constraints on models of physics beyond the Standard Model. Rare final states with a single top quark are searched for, as enhancements in their production rates, if observed, would be clear signs of new physics., Comment: 44 pages, accepted by to Review of Modern Physics

This paper summarises a few selected topics discussed during Working Group 5 of the Deep Inelastic Scattering 2017 conference, Physics with Heavy Flavours, related to the study of charm, bottom, and top quark physics. While the programme of this Working Group was structured by thematic areas, this conference was the occasion for intense cross-pollination between traditionally disjoint research lines. The four LHC experiments all contribute to heavy-flavour physics, with some degree of overlap in most areas, while experiments at other accelerators provide vital input in complimentary kinematic regions. Theorists now have the possibility to take inputs from more sources, and experimentalists focus on measurements that maximise utility. The interplay of LHC heavy quark cross-section measurements with DIS expertise is greatly improving PDF precision, leading to much improved models that, amongst other things, better inform the prospects for future colliders., Comment: 14 pages, 11 figures, to appear in the proceedings of 25th International Workshop on Deep Inelastic Scattering and Related Topics (DIS 2017), 3-7 April 2017, University of Birmingham, UK

This paper is an experimental review of the study of processes with a single top quark at the LHC. The pioneering times are over, and this is now a sector of "precision physics" at colliders. Angular distributions of the decay products of singly-produced top quarks are unique tests of the electroweak interaction. Searches for rare final states of the form t+X (where X=$\gamma$, Z, H) are very sensitive to new physics, and will enter with Run II in a very interesting zone of the parameter space of some theories. The relative sign of the Yukawa coupling of the top quark with respect to the Higgs coupling to gauge bosons will be conclusively measured very soon in the tHq final state., Comment: Invited review paper, to be published on Reviews in Physics

In new-physics processes that produce b or c jets, a measurement of the initial b or c-quark polarization could provide crucial information about the structure of the new physics. In the heavy-quark limit, the b and c-quark polarizations are preserved in the lightest baryons they hadronize into, Lambda_b and Lambda_c, respectively. We revisit the prediction for the polarization retention after the hadronization process and extend it to the case of transverse polarization. We show how ATLAS and CMS can measure the b-quark polarization using semileptonic Lambda_b decays, and the c-quark polarization using Lambda_c+ -> p K- pi+ decays. For calibrating both measurements we suggest to use ttbar samples in which these polarizations can be measured with precision of order 10% using 100/fb of data in Run 2 of the LHC. Measurements of the transverse polarization in QCD events at ATLAS, CMS and LHCb are motivated as well. The proposed measurements give access to nonperturbative QCD parameters relevant to the dynamics of the hadronization process., Comment: 47 pages, 5 figures; v2: minor improvements, published version

This paper presents a personal point of view on the prospects open for top quark physics analyses at the LHC with 10 fb$^{-1}$ of pp collisions at 7 TeV. We discuss the main directions for improvement for the analyses presented at TOP2011 when moving to a regime where systematic uncertainties are the limiting factors, and suggest some new studies that become possible for the first time thanks to the larger statistics., Comment: 7 pages, 2 figures, presented at TOP2011: 4th International Workshop on Top Quark Physics, Sant Feliu de Guixols, Spain, September 25 - 30, 2011