Multiplicity and pseudorapidity (η) density (dNch/dη) distributions of charged hadrons provide key information towards understanding the particle production mechanisms and initial conditions of ...high-energy heavy-ion collisions. However, detector constraints limit the η-range across which charged particle measurements can be carried out. Extrapolating the measured distributions to large η-range by parameterizing measured distributions and by using calculations from event generators, we characterize the production of charged particles over the full kinematic range. In the present study, we use three different ansätze to obtain quantitative descriptions of the shape of pseudorapidity distributions of charged hadrons produced in pp, p-A, and A-A collisions for beam energies (sNN) ranging from a few GeV to a few TeV corresponding to RHIC and LHC energies. We study the limiting fragmentation behavior in these collisions and report evidence for participant-scaling violations in high-energy collisions at the TeV scale. We additionally examine measured pseudorapidity distributions to constrain models describing initial conditions of particle production. We predict the centrality dependence of charged particle multiplicity distributions at FAIR and NICA energies and give an estimation of charged particle multiplicity at η = 0 for the proposed HE-LHC and FCC energies.
We present the first estimates of isothermal compressibility (kT) of hadronic matter formed in relativistic nuclear collisions (sNN=7.7 GeV to 2.76 TeV) using experimentally observed quantities. kT ...is related to the fluctuation in particle multiplicity, temperature, and volume of the system formed in the collisions. Multiplicity fluctuations are obtained from the event-by-event distributions of charged particle multiplicities in narrow centrality bins. The dynamical components of the fluctuations are extracted by removing the contributions to the fluctuations from the number of participating nucleons. From the available experimental data, a constant value of kT has been observed as a function of collision energy. The results are compared with calculations from UrQMD, AMPT, and EPOS event generators, and estimations of kT are made for Pb–Pb collisions at the CERN Large Hadron Collider. A hadron resonance gas (HRG) model has been used to calculate kT as a function of collision energy. Our results show a decrease in kT at low collision energies to sNN∼20 GeV, beyond which the kT values remain almost constant.
The longitudinal asymmetry arises in relativistic heavy ion collisions due to fluctuation in the number of participating nucleons. This asymmetry causes a shift in the center of mass rapidity of the ...participant zone. The rapidity shift as well as the longitudinal asymmetry have been found to be significant at the top LHC energy for collisions of identical nuclei. We study the longitudinal asymmetry and its effect on charged particle rapidity distribution and anisotropic flow parameters at relatively lower RHIC energies using a model calculation. The rapidity shift is found to be more pronounced for peripheral collisions, smaller systems and also for lower beam energies due to longitudinal asymmetry. A detailed study has been done by associating the average rapidity shift to a polynomial relation where the coefficients of this polynomial characterize the effect of the asymmetry. We show that the rapidity shift may affect observables significantly at RHIC energies.
Radar sounders (RSs) are low-frequency instruments that profile the shallow subsurface of planetary targets to obtain valuable scientific information. The prediction of the RS performance and the ...interpretation of the target properties from the RS data are challenging due to the complex electromagnetic interaction among many acquisition variables. Simulation of RS data can address this issue by modeling the complex interaction and producing simulated radargrams representing the acquisition scenario. In this article, we present an approach to generate databases of geoelectrical models and simulated radargrams corresponding to combinations of: 1) target geoelectrical hypotheses; 2) RS parameters; and 3) acquisition geometry configurations. The proposed approach exploits this database for: 1) predicting the detection performance and sensitivity of the RS and 2) understanding the interpretability of the underlying hypotheses. In order to identify hypothesis combinations that can be unambiguously inverted from the radargrams, we analyze the similarity between pairs of geoelectrical models and between the simulated radargrams, and the statistical distance between radargram features. The approach is demonstrated for the case of Radar for Icy Moons Exploration (RIME), using three selected targets on the Jovian moon Ganymede, with three different simulation techniques. The results are very promising and reveal the effectiveness of the proposed approach in extracting valuable information regarding: 1) the target detection performance of RIME; 2) the sensitivity to the dielectric contrast; 3) the separability of radargram features; and 4) the identification of hypothesis combinations producing significantly different radar response, and thus invertible.
Simulation of radar sounder (RS) data is important for understanding the radar response of subsurface features to facilitate the interpretation of the real data. Conventional electromagnetic ...simulators require the definition of complex geoelectrical models of the investigated targets. They also involve time-complex solutions of Maxwell's equations for computing the received electric field, which leads to very high computation time. Furthermore, the simulated radargrams are often not realistic as it is very difficult to model all the variables involved in the data acquisition. In this paper, we propose a novel simulation approach that exploits the data available from existing RSs in geologically analogous terrains, to produce realistic simulations of the investigated RS target. This simulation strategy is based on minimizing the difference between the analog and the investigated acquisition scenarios. This is done by applying a series of corrections, which depend on the relation between the radargram characteristics and the physical variables describing the acquisition process. The aim is to produce radargrams that resemble the investigated scenario in terms of the echo magnitude, bandwidth, range resolution, and along-track resolution. Experimental results present three case studies for different possibilities of the analog and the investigated scenarios. The validation of the simulated radargrams with actual data demonstrates the effectiveness of the proposed approach. Finally, we also present a real application of this approach for the simulation of Radar for Icy Moon Exploration (RIME) radargrams for a combination of instrument and target parameters, using the SHAllow RADar (SHARAD) radargram acquired over the geological analog of a selected RIME target.
This work is aimed at showing the present capabilities and future potentialities of an imaging radar system that can be mounted onboard flexible aerial platforms, such as helicopters or small ...airplanes, and may operate in the UHF and VHF frequency bands as Sounder and as Synthetic Aperture Radar (SAR). More specifically, the Sounder operates at 165 MHz, whereas the SAR may operate either at 450 MHz or at 860 MHz. In the work, we present the first results relevant to a set of Sounder and SAR data collected by the radar during a helicopter-borne campaign conducted in 2018 over a desert area in Erfoud, Morocco, just after the conclusion of a system upgrading procedure. In particular, a first analysis of the focusing capabilities of the Sounder mode and of the polarimetric and interferometric capabilities of the SAR mode is conducted. The overall system, originally developed by CO.RI.S.T.A. according to a ASI funding set up in 2010, has been upgraded in the frame of a contract signed in 2015 between ASI and different private and public Italian Research Institutes and Universities, namely CO.RI.S.T.A., IREA-CNR, Politecnico di Milano and University of Trento.
Radar sounders (RSs) are gaining importance in planetary missions thanks to their unique capability of providing direct measurements of subsurface (SS) structures. To support their design and data ...interpretation, several electromagnetic (e.m.) simulation techniques have been developed with enhanced capabilities for emulating the RS acquisition process. However, the raw simulated radargrams obtained from e.m. simulators are difficult to interpret and analyze without a focusing operation, which results in an underestimation of the RS detection performance. While frequency methods for range and azimuth compression of real RS data are well-established, their use on simulated data is not addressed in the literature and requires major modifications. This article presents a novel method that implements azimuth compression using unfocused and focused processing on simulated raw data. The proposed method is based on an adaptation of the range-Doppler algorithm to the case of raw data generated by a coherent RS simulator. The method is demonstrated in three case studies to show the similarity between simulated and real data processing: 1) simple geometries; 2) a simulated SHAllow RADar (SHARAD) radargram compared with the real data product; and 3) a real application scenario for supporting the design of a new RS instrument. The results indicate higher fidelity of the focused simulated data with the real data product and the target structure, confirming the usefulness of the proposed approach in obtaining realistic processing of simulated radargrams.
The exploration of Venus is increasingly gaining importance in the planetary science community. Recently, EnVision has been selected as the European Space Agency's fifth Medium-class mission with a ...launch targeted in 2030. The subsurface radar sounder (SRS) instrument on board EnVision aims at profiling the shallow crust of Venus. The current phase of development of SRS focuses on a detailed performance analysis based on 3D simulations of the expected subsurface scenarios. This requires inputs on the composition, roughness, location and geometry of the geological features. However, the high uncertainty in the current knowledge of Venus due to the lack of high-quality data implies that several hypotheses exist for these inputs. The goal of this paper is to identify these hypotheses from the perspective of the scientific objectives of subsurface exploration of Venus' shallow crust. In this context, we identify geological features (a.k.a. targets) that are likely to be associated with subsurface dielectric interfaces. For each target, we review the literature for information on the simulation inputs, analogs of the targets (with possible detection by past radar sounders on other planetary bodies), expected subsurface models representing different hypotheses and the potential role of SRS data in resolving the ambiguities. The material presented here will be critical to support future activities on detailed performance assessment and radar sounder simulations. We also present a map of the potential targets for subsurface sounding, which can support operations planning of SRS.
•Definition and analysis of the science objectives of the Subsurface Radar Sounder onboard ESA's EnVision mission.•Identification of subsurface targets and review of their properties.•Analysis of target properties such as dimension, composition, location and geological analogs.•A map of SRS regions of interest is defined and provided.
The first estimation of the isothermal compressibility (
k
T
) of matter is presented for a wide range of collision energies from
√s
NN
= 7.7 GeV to 2.76 TeV.
k
T
is estimated with the help of ...event-byevent charged particle multiplicity fluctuations from experiment. Dynamical fluctuations are extracted by removing the statistical fluctuations obtained from the participant model.
k
T
is also estimated from event generators AMPT, UrQMD, EPOS and a hadron resonance gas model. The values of isothermal compressibility are estimated for the Large Hadron Collider (LHC) energies with the help of the event generators.
The Radar for Icy Moon Exploration (RIME) on-board the JUICE mission will look for dielectric and mechanical interfaces below the icy crust of the Galilean moon Ganymede. Previous missions suggest ...that the surface of Ganymede is covered by two types of terrains, namely the dark terrain and bright terrain. The bright terrain covers two-thirds of the surface, and presents two main morphologies, i.e. the grooved and smooth bright terrains. For understanding the geological history of Ganymede, a still-open question regards the sequence and styles of processes that formed these morphologies. While in the literature different formation hypotheses are highly debated, direct evidence of these can be proven by subsurface probing, for which RIME will offer a unique opportunity. In this work, we aim to understand whether RIME can actually detect and differentiate between the different hypotheses. To this purpose, we perform 3D simulations of RIME radargrams, following a progressive insertion approach which allows to simplify the data interpretability. We focus on the bright terrain morphologies and analyze in detail the RIME detectability of geological components that can support the formation hypotheses of the grooved and smooth bright terrains. The results suggest that RIME can possibly detect the subsurface interfaces associated with the geological components, and differentiate between their radar responses. We also provide a key to interpretation of the RIME data over these targets, and link the radar responses to the formation hypotheses debated in the literature.
•Science objectives of RIME (Radar for Icy Moon Exploration) on the JUICE mission.•Study of the RIME capability to detect subsurface features on Ganymede.•Analysis of the formation hypothesis of grooved and smooth bright terrains.•Development of 3D simulations of Ganymede RIME radargrams.•Identification and discussion of key elements for the interpretation of RIME data.
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