Frascati Scienza

International audience

Astrophysical observations provide compelling evidence for gravitationally interacting dark matter in the universe that cannot be explained by the standard model of particle physics. The extraordinary amount of data from the CERN LHC presents a unique opportunity to shed light on the nature of dark matter at unprecedented collision energies. This Report comprehensively reviews the most recent searches with the CMS experiment for particles and interactions belonging to a dark sector and for dark-sector mediators. Models with invisible massive particles are probed by searches for signatures of missing transverse momentum recoiling against visible standard model particles. Searches for mediators are also conducted via fully visible final states. The results of these searches are compared with those obtained from direct-detection experiments. Searches for alternative scenarios predicting more complex dark sectors with multiple new particles and new forces are also presented. Many of these models include long-lived particles, which could manifest themselves with striking unconventional signatures with relatively small amounts of background. Searches for such particles are discussed and their impact on dark-sector scenarios is evaluated. Many results and interpretations have been newly obtained for this Report.

The solid-state power amplifiers (SSPAs) have been chosen for the ion cyclotron resonance heating (ICRH) system of the Divertor Tokamak Test (DTT) facility due to the lack of suitable grid tubes and the advances in solid-state technology. Two transmitters, each delivering 1.2 MW over 60–90MHz for 50 s/h, are being procured, and an update about their development is given in this article. Each transmitter includes 128 radio frequency (RF) modules of 11 kW, based on robust design from broadcasting and using laterally diffused metal–oxide–semiconductors (LDMOS) transistors. A central control system optimizes drain voltages provided by over 600 commercial power supplies. A multistage combination strategy enables wide bandwidth operation, overcoming the limitations of cavity resonators. The first RF module has been recently characterized in factory in terms of RF, electrical, and thermal parameters, passing all tests and marking the start of series production. This article addresses the progress in DTT transmitter development, focusing on the experimental characterization of the RF module prototype.

A heuristic i.e. empirical approach to the problem of prime number gaps of many kinds and types, different degrees and orders, treated as simple raw experimental data from the statistical viewpoint is presented. The aim of the article is to show a picture of the actual situation of prime number gaps in order to describe and to try to understand the structure itself of prime gaps of various kinds and orders as well as of primes themselves. The data base comprises the finite sequences of prime number gaps up to the value Pn of the prime counter n = 5∙107 that is P5E7 = P(5∙107) = 982,451,653 all of them available in the net. The statistical distributions of prime gaps are best-fitted by the pseudo-Voigt fit function, a convolution of the Lorentz and the Gauss differential distribution functions, or by the so-called E-exp or exp-exp differential distribution function or by a log-linear histogram according to the kind of gaps examined, either δiPn (higher order gaps) or ΔkPm = Pm – Pm–k (delta-lags) with i and k ≥ 2 or the simple linear differences δ1Pm = Δ1Pm = ΔPm= Pm – Pm–1 respectively. One of the unexpected results of the investigation is the appearance of inner structures at high values of nΔ, the number of the intervals of the distributions, suggesting the presence of groups or clusters strictly linked to the nature of prime numbers themselves in which the same phenomenology is present.

The Copernicus Sentinel-2 Global Reference Image (GRI) was originally designed with the main goal of being used by the Ground Segment Level-1 processor to geometrically refine the Sentinel-2 data. The usage of the GRI has enabled a real improvement of the Sentinel-2 data geometric performance. Indeed, both absolute geolocation and relative (multi-temporal) performances have significantly improved and meet the requirements.It is expected that the use of the GRI could be then beneficial to other missions than Sentinel-2. In this framework and driven by user’s needs, ESA decided to freely give access to the scientific community to the entire GRI. Moreover, in order to facilitate the use of the GRI, a set of Level-1C images and a database of Ground Control Points (Level-1B and Level-1C geometries) have been derived from the Level-1B Sentinel-2 GRI. This paper recalls the characteristics of this Calibration/Validation GRI databases as well as the validations performed.

We report an investigation of X-ray induced desorption of neutrals, cations and anions from CO ice. The desorption of neutral CO, by far the most abundant, is quantified and discussed within the context of its application to astrochemistry. The desorption of many different cations, including large cations up to the mass limit of the spectrometer, is observed. In contrast, the only desorbing anions detected are O- and C-. The desorption mechanisms of all these species are discussed with the aid of their photodesorption spectrum. The evolution of the X-ray absorption spectrum shows significant chemical modifications of the ice upon irradiation, which along with the desorption of large cations gives a new insight into X-ray induced photochemistry in CO ice.

In order to optimize the performance of devices based on porphyrin thin films it is of great importance to gain a physical understanding of the various factors which affect their charge transport and light-harvesting properties. In this work, we have employed a multi-technique approach to study vacuum deposited zinc octaethyl porphyrin (ZnOEP) thin films with different degrees of long-range order as model systems. An asymmetrical stretching of the skeletal carbon atoms of the porphyrin conformer has been observed and attributed to ordered molecular stacking and intermolecular interactions. For ordered films, a detailed fitting analysis of the X-ray absorption near edge structure (XANES) using the MXAN code establishes a symmetry reduction in the molecular conformer involving the skeletal carbon atoms of the porphyrin ring; this highlights the consequences of increased π-π stacking of ZnOEP molecules adopting the triclinic structure. The observed asymmetrical stretching of the π conjugation network of the porphyrin structure can have significant implications for charge transport and light harvesting, significantly influencing the performance of porphyrin based devices.

Current bearing wire compensators were successfully used in the 2005-2006 run of the DA{\Phi}NE collider to mitigate the detrimental effects of parasitic beam-beam interactions. A marked improvement of the positron beam lifetime was observed in machine operation with the KLOE detector. In view of the possible application of wire beam-beam compensators for the High Luminosity LHC upgrade, we revisit the DA{\Phi}NE experiments. We use an improved model of the accelerator with the goal to validate the modern simulation tools and provide valuable input for the LHC upgrade project.

Multi-walled nanotube (MWNT) functionalisation was investigated by surface-enhanced Raman spectroscopy (SERS). The MWNTs were deposited as dilute dispersions on SERS-active substrates. We used nano-structured gold surfaces with various morphologies for our measurements. The surface enhancement effect was used to amplify the Raman signal from functional molecules bound to the nanotube walls. The recorded spectral features allowed for discrimination between the differently functionalised MWNTs. Although the present study is limited to a few examples, our measurements indicate the higher specificity obtained by the SERS approach and its possible use for a systematic study of functionalisation effects on MWNT structures.