High Energy Physics Research Research Articles

Mount Aragats as a stable electron accelerator for atmospheric high-energy physics research

Observation of the numerous thunderstorm ground enhancements (TGEs), i.e., enhanced fluxes of electrons, gamma rays, and neutrons detected by particle detectors located on the Earth's surface and related to the strong thunderstorms above it, helped to establish a new scientific topic---high-energy physics in the atmosphere. Relativistic runaway electron avalanches (RREAs) are believed to be a central engine initiating high-energy processes in thunderstorm atmospheres. RREAs observed on Mount Aragats in Armenia during the strongest thunderstorms and simultaneous measurements of TGE electron and gamma-ray energy spectra proved that RREAs are a robust and realistic mechanism for electron acceleration. TGE research facilitates investigations of the long-standing lightning initiation problem. For the last 5 years we were experimenting with the ``beams'' of ``electron accelerators'' operating in the thunderclouds above the Aragats research station. Thunderstorms are very frequent above Aragats, peaking in May--June, and almost all of them are accompanied with enhanced particle fluxes. The station is located on a plateau at an altitude 3200 asl near a large lake. Numerous particle detectors and field meters are located in three experimental halls as well as outdoors; the facilities are operated all year round. All relevant information is being gathered, including data on particle fluxes, fields, lightning occurrences, and meteorological conditions. By the example of the huge thunderstorm that took place at Mount Aragats on August 28, 2015, we show that simultaneous detection of all the relevant data allowed us to reveal the temporal pattern of the storm development and to investigate the atmospheric discharges and particle fluxes.

Core–shell diodes for particle detectors

High performance particle detectors are needed for fundamental research in high energy physics in the exploration of the Higgs boson, dark matter, anti-matter, gravitational waves and proof of the standard model, which will extend the understanding of our Universe. Future particle detectors should have ultrahigh radiation hardness, low power consumption, high spatial resolution and fast signal response. Unfortunately, some of these properties are counter-influencing for the conventional silicon drift detectors (SDDs), so that they cannot be optimized simultaneously. In this paper, the main issues of conventional SDDs have been analyzed, and a novel core–shell detector design based on micro- and nano-structures etched into Si-wafers is proposed. It is expected to simultaneously reach ultrahigh radiation hardness, low power consumption, fast signal response and high spatial resolution down to the sub-micrometer range, which will probably meet the requirements for the most powerful particle accelerators in the near future. A prototype core–shell detector was fabricated using modern silicon nanotechnology and the functionality was tested using electron-beam-induced current measurements. Such a high performance detector will open many new applications in extreme radiation environments such as high energy physics, astrophysics, high resolution (bio-) imaging and crystallography, which will push these fields beyond their current boundaries.

Intrusion Prevention and Detection in Grid Computing - The ALICE Case

Grids allow users flexible on-demand usage of computing resources through remote communication networks. A remarkable example of a Grid in High Energy Physics (HEP) research is used in the ALICE experiment at European Organization for Nuclear Research CERN. Physicists can submit jobs used to process the huge amount of particle collision data produced by the Large Hadron Collider (LHC). Grids face complex security challenges. They are interesting targets for attackers seeking for huge computational resources. Since users can execute arbitrary code in the worker nodes on the Grid sites, special care should be put in this environment. Automatic tools to harden and monitor this scenario are required. Currently, there is no integrated solution for such requirement. This paper describes a new security framework to allow execution of job payloads in a sandboxed context. It also allows process behavior monitoring to detect intrusions, even when new attack methods or zero day vulnerabilities are exploited, by a Machine Learning approach. We plan to implement the proposed framework as a software prototype that will be tested as a component of the ALICE Grid middleware.

Dynamic Resource Allocation with the arcControlTower

Distributed computing resources available for high-energy physics research are becoming less dedicated to one type of workflow and researchers workloads are increasingly exploiting modern computing technologies such as parallelism. The current pilot job management model used by many experiments relies on static dedicated resources and cannot easily adapt to these changes. The model used for ATLAS in Nordic countries and some other places enables a flexible job management system based on dynamic resources allocation. Rather than a fixed set of resources managed centrally, the model allows resources to be requested on the fly. The ARC Computing Element (ARC-CE) and ARC Control Tower (aCT) are the key components of the model. The aCT requests jobs from the ATLAS job management system (PanDA) and submits a fully-formed job description to ARC-CEs. ARC-CE can then dynamically request the required resources from the underlying batch system. In this paper we describe the architecture of the model and the experience of running many millions of ATLAS jobs on it.

Internal targets at storage rings

Internal targets play an important role in nuclear and high energy physics research. After many decades of development, these targets have become very common and highly complex devices. Different types of polarized and unpolarized targets, such as atomic beam, gaseous-, liquid- and solid-state targets, are used in various experiments at storage rings all over the world. The choice and usage of devices (both current and those in development) for internal experiments are strongly dependent on the many parameters of stored beams (e.g. dimensions, lifetime, cooling availability and polarization) and design parameters of the target (areal density, dimensions of the interaction point, target cooling, the gas load to the target chamber and time structure of the target). All these parameters are tightly coupled and must be considered together. The different internal targets are presented in this paper.

Progress with High-Field Superconducting Magnets for High-Energy Colliders

One of the possible next steps for high-energy physics research relies on a high-energy hadron or muon collider. The energy of a circular collider is limited by the strength of bending dipoles, and its maximum luminosity is determined by the strength of final focus quadrupoles. For this reason, the high-energy physics and accelerator communities have shown much interest in higher-field and higher-gradient superconducting accelerator magnets. The maximum field of NbTi magnets used in all present high-energy machines, including the LHC, is limited to ∼10 T at 1.9 K. Fields above 10 T became possible with the use of Nb3Sn superconductors. Nb3Sn accelerator magnets can provide operating fields up to ∼15 T and can significantly increase the coil temperature margin. Accelerator magnets with operating fields above 15 T require high-temperature superconductors. This review discusses the status and main results of Nb3Sn accelerator magnet research and development and work toward 20-T magnets.

A beam of hope for heavy ion radiotherapy: Promising clinical results and better designs are adding new momentum to the push for more proton and carbon ion radiotherapy centers.

A beam of hope for heavy ion radiotherapy: Promising clinical results and better designs are adding new momentum to the push for more proton and carbon ion radiotherapy centers.

First Considerations on Beam Optics and Lattice Design for the Future Electron-Positron Collider FCC-ee

Following the recommendations of the European Strategy Group for High Energy Physics, CERN launched the Future Circular Collider Study (FCC) to investigate the feasibility of a new large circular collider for high energy physics research. This paper presents the constraints on the design of the lattice and optics of the lepton collider version of FCC, that has to be optimised for four different beam energies and parameter sets. Special emphasis is put on the need for a highly flexible magnet lattice in order to achieve the required beam emittances for the four energies and on the layout of the interaction region that will have to combine an advanced mini-beta concept, an effective beam separation scheme and a local chromaticity control to optimise the momentum acceptance and dynamic aperture of the ring. INTRODUCTION The lepton collider part of the FCC study is based on racetrack geometry with a circumference of about 100 km and foresees the design of an electron-positron collider, running at four different centre-of-mass energies to allow precision measurements at the Z resonance, at the energy with maximum Higgs production rate, as well as above the WW and t-tbar thresholds [1]. For each energy the beam parameters depend crucially on the synchrotron light emission and the lattice has to be optimised to provide the emittance target values that are summarised together with the general beam parameters in the parameter list of Table 1. The general layout of the machine is shown in Figure 1. Figure 1: Geometry of the FCC storage ring. MAIN PARAMETRES The general parameters [2] have been optimised for each beam energy and are determined by the overall synchrotron radiation load that can be accepted in the design. In general, for all operation energies the same global synchrotron radiation limit of Pγ =50 MW has been assumed, leading e.g. to a considerable higher number of stored bunches at the lowest operation energy and to a large variation of beam emittances over the complete energy range of the machine. Table 1: FCC-ee Parameters at Four Different Beam Energies

Evaluation of electropolished stainless steel electrodes for use in DC high voltage photoelectron guns

DC high voltage photoelectron guns are used to produce polarized electron beams for accelerator-based nuclear and high-energy physics research. Low-level field emission (∼nA) from the cathode electrode degrades the vacuum within the photogun and reduces the photoelectron yield of the delicate GaAs-based photocathode used to produce the electron beams. High-level field emission (>μA) can cause significant damage the photogun. To minimize field emission, stainless steel electrodes are typically diamond-paste polished, a labor-intensive process often yielding field emission performance with a high degree of variability, sample to sample. As an alternative approach and as comparative study, the performance of electrodes electropolished by conventional commercially available methods is presented. Our observations indicate the electropolished electrodes exhibited less field emission upon the initial application of high voltage, but showed less improvement with gas conditioning compared to the diamond-paste polished electrodes. In contrast, the diamond-paste polished electrodes responded favorably to gas conditioning, and ultimately reached higher voltages and field strengths without field emission, compared to electrodes that were only electropolished. The best performing electrode was one that was both diamond-paste polished and electropolished, reaching a field strength of 18.7 MV/m while generating less than 100 pA of field emission. The authors speculate that the combined processes were the most effective at reducing both large and small scale topography. However, surface science evaluation indicates topography cannot be the only relevant parameter when it comes to predicting field emission performance.

Look to the clouds and beyond

Research in high-energy physics produces masses of data, demanding extensive computational resources. The scientists responsible for managing these resources are now turning to cloud and high-performance computing.

History of the bubble chamber and related active- and internal-target nuclear tracking detectors

Donald Glaser, 1960 Nobel laureate in Physics, recently passed away (2013), as have many of his colleagues who were involved with the early development of bubble chambers at the University of Michigan. In this paper I will review those early years and the subsequent wide-spread application of active-target (AT) bubble chambers that dominated high-energy physics (HEP) research for over thirty years. Some of the related, but more modern nuclear tracking detectors being used in HEP, neutrino astrophysics and dark-matter searches also will be discussed.

The Jeffreys–Lindley paradox and discovery criteria in high energy physics

The Jeffreys-Lindley paradox displays how the use of a p-value (or number of standard deviations z) in a frequentist hypothesis test can lead to an inference that is radically different from that of a Bayesian hypothesis test in the form advocated by Harold Jeffreys in the 1930s and common today. The setting is the test of a well-specified null hypothesis (such as the Standard Model of elementary particle physics, possibly with "nuisance parameters") versus a composite alternative (such as the Standard Model plus a new force of nature of unknown strength). The p-value, as well as the ratio of the likelihood under the null hypothesis to the maximized likelihood under the alternative, can strongly disfavor the null hypothesis, while the Bayesian posterior probability for the null hypothesis can be arbitrarily large. The academic statistics literature contains many impassioned comments on this paradox, yet there is no consensus either on its relevance to scientific communication or on its correct resolution. The paradox is quite relevant to frontier research in high energy physics. This paper is an attempt to explain the situation to both physicists and statisticians, in the hope that further progress can be made.

A phenomenological cost model for high energy particle accelerators

Accelerator-based facilities have enabled forefront research in high-energy physics for more than half a century. The accelerator technology of colliders has progressed immensely, while beam energy, luminosity, facility size, and cost have grown by several orders of magnitude. Themethod of colliding beams has not fully exhausted its potential but has slowed down considerably in its progress. In this paper we derive a simple scaling model for the cost of large accelerators and colliding beam facilities based on costs of 17 big facilities which have been either built or carefully estimated. Although this approach cannot replace an actual cost estimate based on an engineering design, this parameterization is to indicate a somewhat realistic cost range for consideration of what future frontier accelerator facilities might be fiscally realizable.

Scholarly literature and the press: scientific impact and social perception of physics computing

The broad coverage of the search for the Higgs boson in the mainstream media is a relative novelty for high energy physics (HEP) research, whose achievements have traditionally been limited to scholarly literature. This paper illustrates the results of a scientometric analysis of HEP computing in scientific literature, institutional media and the press, and a comparative overview of similar metrics concerning representative particle physics measurements. The picture emerging from these scientometric data documents the relationship between the scientific impact and the social perception of HEP physics research versus that of HEP computing. The results of this analysis suggest that improved communication of the scientific and social role of HEP computing via press releases from the major HEP laboratories would be beneficial to the high energy physics community.

Practical Design of Emittance Dominated Linear Beams for RF Amplifiers

As the frequency of linear beam RF amplifiers increases, the effect of electron beam emittance starts to play a more important role in the design of real world devices. Accurate analytic models and quantitative predictive capability are of particular value when determining the operating parameter regime of a new device or when performing tradeoffs based on specific design criteria. Several considerations relating to emittance effects in the RF amplifiers are presented, and are seen to play a role for thermionic devices operating at millimeter wave frequencies and above, and for field emitter devices as low as microwave frequencies. Existing theory originally derived for particle beams in high-energy physics research is applied specifically to methods and the parameter regimes found in RF amplifier development. Practical enhancements to some expressions allow for accurate prediction of beam behavior without the need for time consuming numerical analysis and optimization. In this vein, beam emittance effects on RF defocusing in the high power energy extraction sections of RF circuits are also analyzed. The general formulation developed here has been validated with numerical optics simulations across a wide range of beam properties typical of those found in devices operating from the microwave to terahertz frequency regimes.

Enclaves of anarchy: Preprint sharing, 1940‐1990

ABSTRACTThe purpose of this paper is to provide a timeline of the gradual organization of preprint sharing of traditional research articles and its consolidation as the preferred means of connection among scientists engaged at the forefront of increasingly narrower sub‐specialties that emerged after World War II. At mid‐century, the flood of research that scientific journals faced created a burden on the traditional system of publication. The social dynamics involved in the production of high energy physics research, in particular, proved to be the main arena of scientific communication that contributed to the advent of preprint exchange as an alternate system of publication during the 20th century. Increasing sophistication of information and communication technology relative to cost and convenience of use were factors that ultimately led to the online deployment of arχiv in 1991. The history of preprint sharing in scientific publishing is a relatively unexplored area of study, and subserves the larger need to understand the immediate circumstances surrounding the move to digital publication by scientific journals. In particular, the challenge presented by preprint sharing to the formal system of peer review that print journals have traditionally offered was an over‐riding concern throughout the course of the changes described here.

CERN and the high energy frontier

This paper presents the particle physics programme at CERN at the high-energy frontier. Starting from the key open questions in particle physics and the large-scale science facilities existing at CERN, concentrating on the Large Hadron Collider(LHC), this paper goes on to present future possibilities for global projects in high energy physics. The paper presents options for future colliders, all being within the framework of the recently updated European Strategy for Particle Physics, and all of which have a unique value to add to experimental particle physics. The paper concludes by outlining key messages for the way forward for high-energy physics research.

High-quality multi-GeV electron bunches via cyclotron autoresonance

Autoresonance laser acceleration of electrons is theoretically investigated using circularly polarized focused Gaussian pulses. Many-particle simulations demonstrate feasibility of creating over 10-GeV electron bunches of ultra-high quality (relative energy spread of order 10^-4), suitable for fundamental high-energy particle physics research. The laser peak intensities and axial magnetic field strengths required are up to about 10^18 W/cm^2 (peak power ~10 PW) and 60 T, respectively. Gains exceeding 100 GeV are shown to be possible when weakly focused pulses from a 200-PW laser facility are used.

Symmetry breaking, subgroup embeddings, and the Weyl group

We present a systematic approach to finding Higgs vacuum expectation values, which break a symmetry G to differently embedded isomorphic copies of a subgroup $H \subset G$ . We give an explicit formula for recovering each point in the vacuum manifold of a Higgs field which breaks G -> H. In particular we systematically identify the vacuum manifold G/H with linear combinations of the vacuum expectation values breaking G -> H_1 -> ... -> H_l. We focus on the most applicable case for current work on grand unified theories in extra dimensional models and low-energy effective theories for quantum chromodynamics. Here the subgroup, H, stabilizes the highest weight of the fundamental representation leading to a simple expression for each element of the vacuum manifold; especially for an adjoint Higgs field. These results are illustrated explicitly for adjoint Higgs fields and clearly linked to the mathematical formalism of Weyl groups. We use the final section to explicitly demonstrate how our work contributes to two contemporary high-energy physics research areas.

Three-dimensional Čerenkov tomography of energy deposition from ionizing radiation beams.

Since its discovery during the 1930s the Čerenkov effect (light emission from charged particles traveling faster than the local speed of light in a dielectric medium) has been paramount in the development of high-energy physics research. The ability of the emitted light to describe a charged particle's trajectory, energy, velocity, and mass has allowed scientists to study subatomic particles, detect neutrinos, and explore the properties of interstellar matter. However, to our knowledge, all applications of the process to date have focused on the identification of particles themselves, rather than their effect upon the surroundings through which they travel. Here we explore a novel application of the Čerenkov effect for the recovery of the spatial distribution of ionizing radiation energy deposition in a medium and apply it to the issue of dose determination in medical physics. By capturing multiple projection images of the Čerenkov light induced by a medical linear accelerator x-ray photon beam, we demonstrate the successful three-dimensional tomographic reconstruction of the imparted dose distribution.