Modern Particle Research Articles

Deep Learning Study of an Electromagnetic Calorimeter

The accurate and precise extraction of information from a modern particle detector, such as an electromagnetic calorimeter, may be complicated and challenging. In order to overcome the difficulties, we process the simulated detector outputs using the deep-learning methodology. Our algorithmic approach makes use of a known network architecture, which has been modified to fit the problems at hand. The results are of high quality (biases of order 1 to 2%) and, moreover, indicate that most of the information may be derived from only a fraction of the detector. We conclude that such an analysis helps us understand the essential mechanism of the detector and should be performed as part of its design procedure.

Kant's approach to understanding space from the perspective of modern natural science

The logical-historical subtext of Kant's definition of space and time as pure forms of sensory knowledge is investigated. The author analyzes the thinker's revision of the concept of a priori, his assertion of the existence of a priori synthetic judgments that serve as the basis for the formulation of the problem of the possibility of a priori forms of sensuality. In the center of the consideration is Kant's correlation of the categories of substance and form, matter and form, spatial incongruence as justifications of transcendental aesthetics. Special emphasis is placed on the differentiation, even the opposition of the categories of matter and form, substance and form by the thinker. The main method is hermeneutical reinterpretation of Kant's legacy from the standpoint of achievements and problems of modern cosmology. The main conclusions of this study are: 1) The formulation of the problem of the human dimension of our Universe in Kant's philosophy, which echoes the anthropic principle widely discussed in physics and testifies to the enduring projective significance of the philosopher's creativity.2) In this regard, it is permissible to attribute a priori forms of sensuality to the innate features of the human body. The three-dimensionality of the form of human sensory perception in the models of eleven-dimensional space-time discussed in modern science determines the very fact of the possibility of its existence. 3) In Kantian philosophy, the question is not raised how the form is attached to the essence. The development of modern elementary particle physics and cosmology in geometrodynamic content has come close to this priority issue.

Inverse problems, real-time dynamics and lattice simulations

The determination of real-time dynamics of strongly coupled quantum fields is a central goal of modern nuclear and particle physics, which requires insight into quantum field theory beyond the weak-coupling approximation. While lattice QCD has provided vital insights into the non-perturbative static properties of quarks and gluons it hides their real-time dynamics behind an ill-posed inverse problem. In this proceeding I will discuss developments in tackling the inverse problem on the lattice and touch upon progress in the direct simualtion of real-time dynamics.

Evidence for Non-Baryonic Dark Matter

There exists an infinite number of quarks u(∞) and anti-quarks at an infinite sub-layer level. These particles are considered as the ultimate building blocks of the universe, since they are structure-less and absolutely stable. These particles are also regarded as the non-baryonic dark matter, since the baryon number is zero and the Rp-parity is -1. It is emphasized that supersymmetric particle, neutralino has also the Rp-parity of -1 and well known good cold dark matter candidate. In modern particle physics, all ordinary particles have the Rp-parity of +1, while both the ultimate quark u(∞) and neutralino have the Rp-parity of -1. This means that these particles can only be created or annihilated in pairs in reactions of ordinary particles. From electron-positron annihilation experiments at high energies, it is shown that the prediction value from the ultimate quark u(∞) is in good agreement with many ring-storage collider experiments.

Challenging problems of particle physics and astrophysics. The preface

The preface to the special issue of IJMPD “Challenging Problems of Particle physics and Astrophysics” briefly reviews some new ideas in the development of modern Astrophysics, Cosmology, Particle and Astroparticle physics inspired by discussions at the Fifth International Conference on Particle Physics and Astrophysics (ICPPA2020).

First Proof-of-Concept Prototype of an Additive Manufactured Radio Frequency Quadrupole

Continuous developments in additive manufacturing (AM) technology are opening up opportunities in novel machining, and improving design alternatives for modern particle accelerator components. One of the most critical, complex, and delicate accelerator elements to manufacture and assemble is the radio frequency quadrupole (RFQ) linear accelerator, which is used as an injector for all large modern proton and ion accelerator systems. For this reason, the RFQ has been selected by a wide European collaboration participating in the AM developments of the I.FAST (Innovation Fostering in Accelerator Science and Technology) Horizon 2020 project. The RFQ is as an excellent candidate to show how sophisticated pure copper accelerator components can be manufactured by AM and how their functionalities can be boosted by this evolving technology. To show the feasibility of the AM process, a prototype RFQ section has been designed, corresponding to one-quarter of a 750 MHz 4-vane RFQ, which was optimised for production with state-of-the-art laser powder bed fusion (L-PBF) technology, and then manufactured in pure copper. To the best of the authors’ knowledge, this is the first RFQ section manufactured in the world by AM. Subsequently, geometrical precision and surface roughness of the prototype were measured. The results obtained are encouraging and confirm the feasibility of AM manufactured high-tech accelerator components. It has been also confirmed that the RFQ geometry, particularly the critical electrode modulation and the complex cooling channels, can be successfully realised thanks to the opportunities provided by the AM technology. Further prototypes will aim to improve surface roughness and to test vacuum properties. In parallel, laboratory measurements will start to test and improve the voltage holding properties of AM manufactured electrode samples.

Grain boundary segregation and carbide precipitation in heat treated niobium superconducting radio frequency cavities

A fundamental understanding of superconducting radio frequency Nb cavity processing is necessary to achieve the desired improvement in their performance, which is needed for further upgrades of modern particle accelerators. To recognize the physical processes behind the losses in the accelerator modules, it is required to address not only the observed improvements but also the degradation occurring after different surface treatments. Here, we report on microscopic and spectroscopic studies of several cutouts from an extremely well performing cavity, which showed a systematic degradation after modified surface treatments and annealing conditions. Our results suggest that an abundance of low-angle grain boundaries surrounding the small sized grains can be related to the local superconductivity breakdown at high accelerating field gradients. Losses due to grain boundary segregated carbides are discussed to being most dominant and to leading to an anomalous Q-degradation of the whole cavity starting at low fields.

Magnetic field sensors for detection of trapped flux in superconducting radio frequency cavities.

Superconducting radio frequency (SRF) cavities are fundamental building blocks of modern particle accelerators. They operate at liquid helium temperatures (2-4 K) to achieve very high quality factors (1010-1011). Trapping of magnetic flux within the superconductor is a significant contribution to the residual RF losses, which limit the achievable quality factor. Suitable diagnostic tools are in high demand to understand the mechanisms of flux trapping in technical superconductors, and the fundamental components of such diagnostic tools are magnetic field sensors. We have studied the performance of commercially available Hall probes, anisotropic magnetoresistive sensors, and flux-gate magnetometers with respect to their sensitivity and capability to detect localized, low magnetic flux amplitudes, of the order of a few tens of magnetic flux quantum at liquid helium temperatures. Although Hall probes have the lowest magnetic field sensitivity (∼96 nV/μT at 2K), their physical dimensions are such that they have the ability to detect the lowest number of trapped vortices among the three types of sensors. Hall probes and anisotropic magnetoresistive sensors have been selected to be used in a setup to map regions of trapped flux on the surface of a single-cell SRF cavity.

First observation of quasi–monochromatic optical Cherenkov radiation in a dispersive medium (quartz)

The present article summarizes the results of a study of optical Cherenkov radiation (ChR) spectral properties both theoretically and experimentally. This type of radiation has a continuous spectral distribution which allows to use it in different fields of physics as for charged particle identification or generation of intense THz radiation. By exploiting the frequency dependency of the target permittivity it is possible to observe quasi–monochromatic radiation. A theoretical model based on a surface current approach is presented which allows to predict angular and spectral properties of ChR. In order to test the model predictions, an experiment was carried out using 855 MeV electrons and a 0.2 mm thick quartz target as radiator which could be rotated with respect to the beam axis. Quasi–monochromatic ChR was observed with a spectrometer placed at a fix observation angle, and tilting the radiator crystal offered the possibility to tune the radiation wavelength. The monochromatization effect is attributed to the frequency dependency of the quartz permittivity, and taking into account the refraction law for emitted ChR crossing the boundary between radiator target and vacuum it is possible to deduce a dispersion relation which connects ChR wavelength and outgoing photon angle - or in an alternative way ChR wavelength and target tilt angle for fixed observation angle. The dispersion relation is clearly confirmed in the experiment, and the model predictions show a satisfactory agreement with the measurements. Exploiting the ChR monochromatization mechanism might offer versatile tools which can find applications for example in beam diagnostics at modern particle accelerators.

Conformal transformation with multiple scalar fields and geometric property of field space with Einstein-like solutions

Multiple scalar fields appear in vast modern particle physics and gravity models. When they couple to gravity non-minimally, conformal transformation is utilized to bring the theory into Einstein frame. However, the kinetic terms of scalar fields are usually not canonical, which makes analytic treatment difficult. Here we investigate under what conditions the theories can be transformed to the quasi-canonical form, in which case the effective metric tensor in field space is conformally flat. We solve the relevant nonlinear partial differential equations for arbitrary number of scalar fields and present several solutions that may be useful for future phenomenological model building, including the $\sigma$-model with a particular non-minimal coupling. We also find conformal flatness can always be achieved in some modified gravity theories, for example, Starobinsky model.

Next-to-Next-to-Leading Order Event Generation for Top-Quark Pair Production.

The production of top-quark pairs in hadronic collisions is among the most important reactions in modern particle physics phenomenology and constitutes an instrumental avenue to study the properties of the heaviest quark observed in nature. The analysis of this process at the Large Hadron Collider relies heavily on MonteCarlo simulations of the final state events, whose accuracy is challenged by the outstanding precision of experimental measurements. In this Letter we present the first matched computation of top-quark pair production at next-to-next-to-leading order in QCD with all-order radiative corrections as implemented via parton-shower simulations. Besides its intrinsic relevance for LHC phenomenology, this work also establishes an important step towards the simulation of other hadronic processes with color charges in the final state.

How to discover QCD Instantons at the LHC

The Standard Model of particle physics predicts the existence of quantum tunnelling processes across topological inequivalent vacua, commonly known as Instantons. In Quantum Chromodynamics, these Instantons play a fundamental role in explaining much of the theory long-distance behaviour. However, they have not yet been observed experimentally. Their direct observation would mark a breakthrough in modern particle physics, shedding light on our fundamental understanding of the non perturbative dynamics in the Standard Model. Recently, new calculations for QCD Instanton processes in proton–proton collisions became public, suggesting sizeable cross sections as well as possible experimental signatures at the LHC. In this work, we explore possible analysis strategies for the LHC experiments to discover small-size QCD Instanton induced processes. Moreover, we derive a first limit on the Instanton production cross section using published data of Minimum Bias processes at sqrt{s}=13 TeV at the LHC.

Electromagnetic effects of equatorially misaligned RF cavities

One of the most challenging problems in modern particle accelerator systems is the manufacture of RF cavities within the desired tolerance limits. In this study experimental and computational investigations to quantify the effects of transversal half-cell misalignments on the fundamental accelerator cavity parameters and beam dynamics are presented. Equivalent circuit components of an equatorially misaligned single-cell aluminum elliptical cavity are obtained from the measured data and are employed to calculate longitudinal impedance and modal wake function. Critical coupling and bead-pull measurements are performed at the TM010-like mode frequency, 2.45 GHz for the quality factor and shunt impedance of the high-β cavity. We report equivalent circuit analysis for higher-order modes and variations of the equivalent circuit components with respect to considered misalignment errors for the MICE experiment's muon cooling cavity. It is shown that using the equivalent circuit model decreases the computational load significantly for the wake field simulations of resonator cavities. Good agreement between simulations and measurements in terms of accelerating cavity parameters and impedances is illustrated.

Getting High: High Fidelity Simulation of High Granularity Calorimeters with High Speed

Accurate simulation of physical processes is crucial for the success of modern particle physics. However, simulating the development and interaction of particle showers with calorimeter detectors is a time consuming process and drives the computing needs of large experiments at the LHC and future colliders. Recently, generative machine learning models based on deep neural networks have shown promise in speeding up this task by several orders of magnitude. We investigate the use of a new architecture—the Bounded Information Bottleneck Autoencoder—for modelling electromagnetic showers in the central region of the Silicon-Tungsten calorimeter of the proposed International Large Detector. Combined with a novel second post-processing network, this approach achieves an accurate simulation of differential distributions including for the first time the shape of the minimum-ionizing-particle peak compared to a full Geant4 simulation for a high-granularity calorimeter with 27k simulated channels. The results are validated by comparing to established architectures. Our results further strengthen the case of using generative networks for fast simulation and demonstrate that physically relevant differential distributions can be described with high accuracy.

Symmetry fundamentalism in quantum mechanics

Modern particle physics suggests an intriguing vision of physical reality: we are to imagine the symmetries of the world as fundamental, whereas the material constituents of the world (such as particles and fields) are ontologically derivative of them. This paper develops a novel ontology for non-relativistic quantum mechanics which gives precise metaphysical content to this vision.

Direct evidence of microstructure dependence of magnetic flux trapping in niobium

Elemental type-II superconducting niobium is the material of choice for superconducting radiofrequency cavities used in modern particle accelerators, light sources, detectors, sensors, and quantum computing architecture. An essential challenge to increasing energy efficiency in rf applications is the power dissipation due to residual magnetic field that is trapped during the cool down process due to incomplete magnetic field expulsion. New SRF cavity processing recipes that use surface doping techniques have significantly increased their cryogenic efficiency. However, the performance of SRF Nb accelerators still shows vulnerability to a trapped magnetic field. In this manuscript, we report the observation of a direct link between flux trapping and incomplete flux expulsion with spatial variations in microstructure within the niobium. Fine-grain recrystallized microstructure with an average grain size of 10–50 µm leads to flux trapping even with a lack of dislocation structures in grain interiors. Larger grain sizes beyond 100–400 µm do not lead to preferential flux trapping, as observed directly by magneto-optical imaging. While local magnetic flux variations imaged by magneto-optics provide clarity on a microstructure level, bulk variations are also indicated by variations in pinning force curves with sequential heat treatment studies. The key results indicate that complete control of the niobium microstructure will help produce higher performance superconducting resonators with reduced rf losses1 related to the magnetic flux trapping.

Modern Machine Learning and Particle Physics

Over the past five years, modern machine learning has been quietly revolutionizing particle physics. Old methodology is being outdated and entirely new ways of thinking about data are becoming commonplace. This article will review some aspects of the natural synergy between modern machine learning and particle physics, focusing on applications at the Large Hadron Collider (LHC). A sampling of examples is given, from signal/background discrimination tasks using supervised learning to direct data-driven approaches. Some comments on persistent challenges and possible future directions for the field are included at the end.

A surrogate-based approach to nonlinear, non-Gaussian joint state-parameter data assimilation

<p style='text-indent:20px;'>Many recent advances in sequential assimilation of data into nonlinear high-dimensional models are modifications to particle filters which employ efficient searches of a high-dimensional state space. In this work, we present a complementary strategy that combines statistical emulators and particle filters. The emulators are used to learn and offer a computationally cheap approximation to the forward dynamic mapping. This emulator-particle filter (Emu-PF) approach requires a modest number of forward-model runs, but yields well-resolved posterior distributions even in non-Gaussian cases. We explore several modifications to the Emu-PF that utilize mechanisms for dimension reduction to efficiently fit the statistical emulator, and present a series of simulation experiments on an atypical Lorenz-96 system to demonstrate their performance. We conclude with a discussion on how the Emu-PF can be paired with modern particle filtering algorithms.</p>

Noble liquid calorimetry at the LHC and prospects of its application in future collider experiments

Calorimetry is an important measurement technique in experimental particle physics. Although calorimeters based on liquefied noble gases were first proposed 50 years ago, they continue to play an important role in modern particle physics and have substantially contributed to the discovery of the Higgs boson at the Large Hadron Collider (LHC) at CERN in 2012.

Measurement of single-spin asymmetry for charged pions in the SPASCHARM experiment at U70 accelerator

The SPASCHARM experiment at U70 aims an exploration of a fundamental problem in modern particle physics, the role of spin in strong interactions. At present, the first physics data have been accumulated at a negative 28 GeV beam, interacting with a frozen polarized proton target. The SPASCHARM wide-aperture spectrometer can detect both charged and neutral particles in the large solid angle with 2π azimuthal coverage in the fragmentation region of beam-particles. It covers the kinematic region of non-perturbative quantum chromodynamics (QCD), where the theoretical predictions are difficult and unreliable due to the full strength quark confinement at low and medium momentum transfers. In this report, the current status of the experiment is presented. The algorithm for reconstructing charged tracks is discussed along with its results on real data and the comparison with the Monte Carlo (MC) simulations. Based on a real track reconstruction, the statistical errors for the measurements of single-spin asymmetries in inclusive charged pion production are estimated. The data analysis is in progress.