We report on a direct search for sub-GeV dark photons (A^{'}), which might be produced in the reaction e^{-}Z→e^{-}ZA^{'} via kinetic mixing with photons by 100 GeV electrons incident on an active ...target in the NA64 experiment at the CERN SPS. The dark photons would decay invisibly into dark matter particles resulting in events with large missing energy. No evidence for such decays was found with 2.75×10^{9} electrons on target. We set new limits on the γ-A^{'} mixing strength and exclude the invisible A^{'} with a mass ≲100 MeV as an explanation of the muon g_{μ}-2 anomaly.
Studies in many areas of particle and astroparticle physics require a good knowledge of hadron spectra produced at small angles to the primary particle direction, e.g. in the TeV energy range at the ...LHC. The present work is dedicated to development of a particle identification technique based on the transition radiation produced by highly relativistic particles. Dedicated experimental studies were carried out and simulation models were developed to reproduce experimental data obtained with different prototypes. On the basis of these studies, the possibility of making detectors able to provide hadron composition measurement with high accuracy and identify particles with high efficiency in the forward experiments at the LHC was demonstrated. Two concepts of large scale TRDs are proposed: the straw TRD and the GaAs/straw TRD. They allow the reconstruction of hadron spectra with accuracy about or below 1% and to identify particles with high efficiency in individual events. As an example, suppression of the combinatorial background was demonstrated for the D0→K−π+ and D̄0→K+π− decays.
Sparse matrix-vector multiplication is a critical building block for numerical algorithms in a wide range of scientific and engineering applications. However, its performance is far below the peak ...values of existing computing systems. To enhance the performance, more efficient methods for storing sparse matrices are required. The paper introduces an extension of the Compressed Sparse Row format, namely the Successive Row Incremental Compressed Sparse Row format. This format is based on the Row Incremental modification of the Compressed Sparse Row format proposed earlier and aims to reduce the memory consumption required for storing the column indices of nonzero matrix elements. The new format stores incremental offsets of each subsequent column index relative to the previous one. The efficiency and applicability of the modification are evaluated for matrix-vector multiplication using a subset of matrices from the SuiteSparse Matrix Collection. The speedup by factors 1.28 and 1.16 is achieved for matrix-vector multiplication using single and double precision floating point numbers, respectively. The effect of indices compression optimization for the original Compressed Sparse Row format and its modifications is evaluated for solving systems of linear algebraic equations. The obtained results demonstrate that the use of reduced indices data types can be beneficial even for the original data storage format, but the proposed modifications can significantly increase the calculation performance. The corresponding linear solver performance gain results in a calculation time decrease of about 15% and 10%, but the single precision linear solver suffers from the residual deviation issue. The use of a mixed precision iterative refinement procedure allows alleviating this issue and ensures single precision calculation speedup while maintaining the accuracy of double precision calculations.
Abstract
The problem of hygroscopic expansion of FR4 based large-size PCBs is discussed using the example of Micromegas detector. The readout electrodes of the detector located on the anode printed ...circuit board assumed to have precise dimensions. During the production and delivery process, the readout PCB is exposed to different temperature and humidity conditions. As a result, the PCB size differs from the nominal one at the moment of assembly of the detector. The problem appears to be relevant for any other large-size gaseous detectors with the readout structure based on FR4.
The swelling of two test PCB samples during water absorption is studied. The size of the samples is 650× 500× 0.5 mm
3
. Both samples have copper strips on one side. The second side is naked on sample 1 and fully covered with a copper layer on sample 2.
The elongation of the samples from dry conditions to 50% RH is measured. The influence of the copper layers on the absorption rate and the value of equilibrium elongation is discussed. It is shown that elongation of sample 1 follows the Fick's law while the absorption process in sample 2 is more complicated. The coefficient of linear hygroscopic expansion of sample 1 is measured and discussed.
The results of the study of a large-size, multilayer Micromegas detector with X-ray source Cd-109 are discussed. The detector consists of 4 layers, each of them is a Micromegas detector with ...resistive anode and strip-based read-out structure. The gas volume of the chamber is split to 4 parts interconnected in 6 points. Results of the measurements of the gas gain curves and the 1st Townsend coefficient as well as the E_amp/E_drift characteristics are presented and discussed. The detector presented a non-negligible gas leak, affecting the reported results. The influence of the leak on operation of the module is estimated.
Distributed computing environments execute great amount of various computing jobs that can fail or break for some reason. The analysis of the error messages describing the reasons of failures has ...become one of the most crucial parts of the existing monitoring systems. This analysis is complicated by the presence of a large number of messages, especially in the case of the retrospective analysis. ClusterLogs framework was developed as a modular and flexible tool for the clustering of error messages of computing jobs in distributed computing infrastructures. The general purpose of this tool is to simplify the error messages analysis by grouping together messages that share similar failure reasons and textual patterns. Proposed clustering method includes a set of sequential data processing stages and provides various clustering options: deterministic similarity-based clustering and unsupervised multiple machine learning methods with preliminary vectorization of error messages using the word embedding technique. The performance tests had revealed the most time consuming stages. In this paper we describe the parallelilzing method for these stages and demonstrate how it has allowed the increased performance of the whole clustering pipeline. The performance tests were executed on the HPC system Polus.
The possibility of designing a distributed fibre-optic sensor, allowing one to measure cryogenic temperatures (to liquid nitrogen boiling point), is experimentally demonstrated. The principle of ...operation of the sensor is based on measuring the intensity of boson peaks of Raman scattering in a fibre material, which are spaced by 1 to 3 THz from the probe frequency. The measurements are performed using a single-mode telecommunication fibre with a 15-μm-thick polyimide coating. The probe wavelength is 1.55 μm, the sensor spatial resolution is 4 m, and the averaging time is 60 s. Experiments are carried out in the temperature range of 75.6 - 79.6 K, with a temperature resolution of 0.5 K.
To improve accuracy of light attenuation measurements in optical fibres, especially in short ones, tens and hundreds of metres in length, we propose rejecting a conventional reflectometric approach ...based on Rayleigh scattering intensity measurements. To this end, we propose for the first time the use of boson peaks in Raman scattering, which, on the one hand, produce no interference effects and no related noise in reflectograms, and, on the other, lie within the C-band. Even at a fibre length as short as 50 m, the attenuation measurement error does not exceed 0.002 dB km−1. We demonstrate the possibility of compensating for the temperature variation of boson peak intensity by concurrently obtaining a reflectogram for the anti-Stokes line of the fundamental Raman band.
X-ray transition radiation detectors (TRDs) are used for particle identification in both high energy physics and astroparticle physics. In most of the detectors, emission of the X-ray transition ...radiation (TR) starts at Lorentz factors above γ∼500 and reaches saturation at γ∼2÷3⋅103. However, many experiments require particle identification up to γ∼105, which is very difficult to achieve with conventional detectors. Semiconductor pixel detectors offer a unique opportunity for precise simultaneous measurements of spectral and angular parameters of TR photons. Test beam studies of the energy and the angular distributions of TR photons emitted by electrons and muons of different momenta crossing several types of radiators were performed at the CERN SPS with a 480 μm thick silicon detector bonded to a Timepix3 chip. High resolution images of the energy−angle phase space of the TR produced by different radiators were obtained and compared with MC simulations. The characteristic interference patterns are in agreement with the theoretical models with an unprecedented level of details. The studies presented in this paper also show that simultaneous measurements of both the energy and the emission angles of the TR X-rays could be used to enhance the particle identification performances of TRDs.
Cardiovascular diseases and diabetes mellitus, debuting as arterial hypertension (AH) syndrome and prediabetes, are common types of chronic non-communicable processes, that are the leading cause of ...death in the world. The main treatment method for above mentioned disorders, according to the current guidelines, is pharmacotherapy. However, it is possible to effectively apply non-pharmacological correction methods, aimed at the probable etiological factor and inversive mechanism involved in AH maintenance, in the early stages when no permanent changes are maintaining a high level of blood hypertension (BH) and glycemia. Frequently, this mechanism is hypoxia in the vertebral arteries system due to cervical spine osteochondrosis.
To evaluate the therapeutic effect of non-pharmacological methods of restoring brainstem blood supply in patients with AH and prediabetes.
The number of patients equal 125 (57 men and 68 women, mean age 63.3±11.5 and 65.4±11.8 y.o., respectively) with prediabetes and 1st degree of AH without target organs damage, among whom 102 patients with prehypertension or 1st degree of hypertension and 24 ones with 2nd degree of hypertension, were examined. The original method of manually restoring brainstem blood supply developed in the Shishonin's Clinic was applied to all patients. The control group included patients with the same disorder, who did not receive manipulations. Blood pressure (BP) measurement, ultrasound and triplex ultrasonography of vertebral arteries, biochemical blood test, and estimation of glycemia and glycated hemoglobin were performed.
All patients of the study group had decreased levels of systolic BP (by 23.8±10.7 mm Hg for men and 32.8±11.9 mm Hg for women), an increase of flow velocity in vertebral arteries (by 20.6±7.5 and 21.5±7.2 cm/s, respectively), a decrease of glycated hemoglobin concentration (by 0.32±0.51 and 0.34±0.41%, respectively). In the comparison group, there were no patients with improvement in these indicators.
The effectiveness of the author's manual method of cervical spine osteochondrosis correction in the reduction of BP and glycemia levels in the early stages of the disease is shown.
PDF
