Physics

The paper describes a method of the charged particle identification, developed for the \mbox{CMD-3} detector, installed at the VEPP-2000 e + e − collider. The method is based on the application of the boosted decision trees classifiers, trained for the optimal separation of electrons, muons, pions and kaons in the momentum range from 100 to 1200 MeV/c . The input variables for the classifiers are linear combinations of the energy depositions of charged particles in 12 layers of the liquid xenon calorimeter of the \mbox{CMD-3}. The event samples for training of the classifiers are taken from the simulation. Various issues of the detector response tuning in simulation and calibration of the calorimeter strip channels are considered. Application of the method is illustrated by the examples of separation of the e + e − (γ) and π + π − (γ) final states and of selection of the K + K − final state at high energies.

Principles of the precision cleaning dedicated to ultra-high vacuum applications are reviewed together with the techniques for the evaluation of surface cleanliness. Methods to verify the effectiveness of cleaning procedures are addressed. Examples are presented to illustrate the influence of packaging and storage on the recontamination of the surface after cleaning. Finally, the effect of contamination on some relevant surface properties, such as secondary electron emission and wettability, is presented. This article is an updated and shortened version of the one previously published for the CAS school on the vacuum of accelerators 2006.

Liquid Argon Time Projection Chambers (LArTPCs) are a class of detectors that produce high resolution images of charged particles within their sensitive volume. In these images, the clustering of distinct particles into superstructures is of central importance to the current and future neutrino physics program. Electromagnetic (EM) activity typically exhibits spatially detached fragments of varying morphology and orientation that are challenging to efficiently assemble using traditional algorithms. Similarly, particles that are spatially removed from each other in the detector may originate from a common interaction. Graph Neural Networks (GNNs) were developed in recent years to find correlations between objects embedded in an arbitrary space. The Graph Particle Aggregator (GrapPA) first leverages GNNs to predict the adjacency matrix of EM shower fragments and to identify the origin of showers, i.e. primary fragments. On the PILArNet public LArTPC simulation dataset, the algorithm achieves achieves a shower clustering accuracy characterized by a mean adjusted Rand index (ARI) of 97.8 % and a primary identification accuracy of 99.8 %. It yields a relative shower energy resolution of (4.1+1.4/ E(GeV) − − − − − − − √ )% and a shower direction resolution of (2.1/ E(GeV) − − − − − − − √ ) ∘ . The optimized algorithm is then applied to the related task of clustering particle instances into interactions and yields a mean ARI of 99.2 % for an interaction density of ∼O(1) m −3 .

The MEG experiment at the Paul Scherrer Institut (PSI) represents the state of the art in the search for the charged Lepton Flavour Violating (cLFV) μ + → e + γ decay. With the phase 1, MEG set the new world best upper limit on the BR( μ + → e + γ)<4.2× 10 −13 (90% C.L.). With the phase 2, MEG II, the experiment aims at reaching a sensitivity enhancement of about one order of magnitude compared to the previous MEG result. The new Cylindrical Drift CHamber (CDCH) is a key detector for MEG II. CDCH is a low-mass single volume detector with high granularity: 9 layers of 192 drift cells, few mm wide, defined by ∼12000 wires in a stereo configuration for longitudinal hit localization. The filling gas mixture is Helium:Isobutane (90:10). The total radiation length is 1.5× 10 −3 X 0 , thus minimizing the Multiple Coulomb Scattering (MCS) contribution and allowing for a single-hit resolution <120 μ m and an angular and momentum resolutions of 6 mrad and 90 keV/c respectively. This article presents the CDCH commissioning activities at PSI after the wiring phase at INFN Lecce and the assembly phase at INFN Pisa. The endcaps preparation, HV tests and conditioning of the chamber are described, aiming at reaching the final stable working point. The integration into the MEG II experimental apparatus is described, in view of the first data taking with cosmic rays and μ + beam during the 2018 and 2019 engineering runs. The first gas gain results are also shown. A full engineering run with all the upgraded detectors and the complete DAQ electronics is expected to start in 2020, followed by three years of physics data taking.

The upgrade of the Inner Tracking System (ITS) of ALICE (A Large Ion Collider Experiment) will extend measurements of heavy-flavour hadrons and low-mass dileptons to a lower transverse momentum than currently achieved and increase the readout capabilities to incorporate the full interaction. Furthermore, the tracking efficiency will be improved at low transverse momentum. To achieve this, the new ALICE ITS is comprised of seven layers of a custom Monolithic Active Pixel Sensor design known as ALPIDE, with a spatial resolution of 5μm . The use of the ALPIDE-based detector design will reduce the material budget to 0.35% X 0 per layer for the innermost three layers, and to 1.0% X 0 per layer for the outermost four layers, compared to 1.14% X 0 per layer in the previous ITS. The construction effort in numerous sites around the world has resulted in a fully assembled and connected detector, which is currently undergoing on surface commissioning before its installation in the ALICE cavern. This contribution discusses the design and the current status of the commissioning of the new ITS detector, including the methods used to characterise the detector and the results obtained so far.

In the paper, a comparison is described of the microwave power standard based on thermoelectric sensors against an analogous standard based on bolometric sensors. Measurements have been carried out with the classical twin-type microcalorimeter, fitted with N-connector test ports suitable for the frequency band 0.05 - 18 GHz. An appropriate measurand definition is given for being suitable to both standard types. A system accuracy assessment is performed applying the Gaussian error propagation through the mathematical models that interpret the microcalorimeter response in each case. The results highlight advantages and weaknesses of each power standard type.

Since Key Comparison CCT-K2, only few comparisons on realizations of cryogenic fixed points have been carried out, be they bilateral (three, of which one still pending) or multilateral (two trilateral). Since a forthcoming general follow-up is unlikely, any bilateral comparison, not only key comparisons, is most welcome to provide evidence of the continuing thermometric capabilities of the laboratories involved in the realization of the ITS-90. Not too long after the creation in 2018 of the Joint Research Laboratory for Fluid Metrology Evangelista Torricelli between LNE-CNAM and INRIM, the two laboratories agreed to perform a bilateral comparison at all the cryogenic fixed points of the scale between 13 K and 273 K, including the two hydrogen vapour-pressure temperatures required for the full platinum resistance thermometer range 3.3.1 of the ITS-90. The results are reported here and show a substantial agreement, within the combined uncertainties.

The DArk Matter Particle Explorer (DAMPE) is a satellite-borne detector for high-energy cosmic rays and γ -rays. To fully understand the detector performance and obtain reliable physical results, extensive simulations of the detector are necessary. The simulations are particularly important for the data analysis of cosmic ray nuclei, which relies closely on the hadronic and nuclear interactions of particles in the detector material. Widely adopted simulation softwares include the GEANT4 and FLUKA, both of which have been implemented for the DAMPE simulation tool. Here we describe the simulation tool of DAMPE and compare the results of proton shower properties in the calorimeter from the two simulation softwares. Such a comparison gives an estimate of the most significant uncertainties of our proton spectral analysis.

The aim of this study is to estimate the intrinsic efficiency and energy resolution of different types of solid-state gamma-ray detectors in order to generate a precise dual-energy x-ray beam from the conventional x-ray tube using external x-ray filters. The x-ray spectrum of a clinical x-ray tube was experimentally measured using a high purity Germanium detector (HPGe) and the obtained spectrum validated by Monte Carlo (MC) simulations. The obtained x-ray spectrum from the experiment was employed to assess the energy resolution and detection efficiency of different inorganic scintillators and semiconductor-based solid-state detectors, namely HPGe, BGO, NaI, and LYSO, using MC simulations. The best performing detector was employed to experimentally create and measure a dual-energy x-ray spectrum through applying attenuating filters to the original x-ray beam. The simulation results indicated a 9.16% energy resolution for the HPGe detector wherein the FWHM of the energy resolution for the HPGe detector was about 1/3rd of the other inorganic detectors. The x-ray spectra estimated from the various source energies exhibited a good agreement between experimental and simulation results with a maximum difference of 6%. Owing to the high-energy discrimination power of the HPGe detector, a dual-energy x-ray spectrum was created and measured from the original x-ray spectrum using 0.5 and 4.5 mm Aluminum external filters, which involves 70 and 140 keV energy peaks with 8% overlap. The experimental measurements and MC simulations of the HPGe detector exhibited close agreement in high-energy resolution estimation of the x-ray spectrum. Given the accurate measurement of the x-ray spectrum with the HPGe detector, a dual-energy x-ray spectrum was generated with minimal energy overlap using external x-ray filters.

The next generation of Far-infrared and X-ray space observatories will require detector arrays with thousands of transition edge sensor (TES) pixel. It is extremely important to have a tool that is able to characterize all the pixels and that can give a clear picture of the performance of the devices. In particular, we refer to those aspects that can affect the global energy resolution of the array: logarithmic resistance sensitivity with respect to temperature and current ( α and β parameters, respectively), uniformity of the TESs and the correct understanding of the detector thermal model. Complex impedance measurement of a TES is the only technique that can give all this information at once, but it has been established only for a single pixel under DC bias. We have developed a complex impedance measurement method for TESs that are AC biased since we are using a MHz frequency domain multiplexing (FDM) system to readout an array. We perform a complete set of AC impedance measurements for different X-ray TES microcalorimeters based on superconducting TiAu bilayers with or without normal metal Au bar structures. We discuss the statistical analysis of the residual between impedance data and fitting model to determine the proper calorimeter thermal model for our detectors. Extracted parameters are used to improve our understanding of the differences and capabilities among the detectors and additionally the quality of the array. Moreover, we use the results to compare the calculated noise spectra with the measured data.