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Light Antinuclei from the Laboratory to the Cosmos
No full textThe antiproton was experimentally discovered at the Bevatron, Berkeley, in 1955, earning Segré and Chamberlain the 1959 Nobel Prize in Physics. After that, light antinuclei, bound states of antiprotons and antineutrons, have been observed in high-energy interactions in the laboratory from antideuteron to antihelium-4 [1]. In nature, antinuclei are extremely rare objects to be found. The search for antinuclei in space has received considerable attention in recent years, following the suggestion that cosmic antinuclei might be produced in the annihilation or decay of dark matter (DM) particles [2]. Alternatively, “secondary” antinuclei could be produced in ordinary high-energy interactions of primary cosmic rays with the interstellar matter in our galaxy. A precise assessment of the background constituted by secondary antinuclei is pivotal for these searches and for the interpretation of the results. The spectrum of antiprotons observed in cosmic rays is consistent with the hypothesis of secondary production. No evidence of primary antiprotons, antihelium, and antideuterons has been found in the cosmic radiation so far. It is clear that the study of the formation of composite antimatter objects cannot but rely on samples of antimatter produced in the laboratory. Comprehensive measurements of different nuclear (and hypernuclear1) species are necessary to meaningfully constrain formation models and require large data samples to be inspected, as the production of nuclear clusters becomes rarer with increasing mass number. Additional fundamental constraints to the production models are obtained from systematic studies of different particle sources, from proton–proton (pp) to heavy-ion collisions, where the size of the system can be experimentally controlled based on the number of particles (multiplicity) produced in the collision
Exotic particles and nuclei
Full text linkLight nuclei, antinuclei and hypernuclei constitute a laboratory to study the mechanisms of formation of bound states in proton-proton and nucleus-nucleus collisions over a broad range of collision energies, providing insights into the nuclear structure as well as into the strong interaction. In this contribution, a selection of the experimental results and latest developments presented at the Quark Matter 2023 conference is reviewed
Testing production scenarios for (anti-)(hyper-)nuclei and exotica at energies available at the CERN Large Hadron Collider
Full text linkWe present a detailed comparison of coalescence and thermal-statistical models for the production of (anti-) (hyper-)nuclei in high-energy collisions. For the first time, such a study is carried out as a function of the size of the object relative to the size of the particle emitting source. Our study reveals large differences between the two scenarios for the production of objects with extended wave functions. While both models give similar predictions and show similar agreement with experimental data for (anti-)deuterons and (anti-)He3 nuclei, they largely differ in their description of (anti-)hypertriton production. We propose to address experimentally the comparison of the production models by measuring the coalescence parameter systematically for different (anti-)(hyper-)nuclei in different collision systems and differentially in multiplicity. Such measurements are feasible with the current and upgraded Large Hadron Collider experiments. Our findings highlight the unique potential of ultrarelativistic heavy-ion collisions as a laboratory to clarify the internal structure of exotic QCD objects and can serve as a basis for more refined calculations in the future
Testing production scenarios for (anti-)(hyper-)nuclei with multiplicity-dependent measurements at the Lhc∗
Full text linkThe production of light anti- and hyper-nuclei provides unique observables to characterise the system created in high-energy proton–proton (pp), proton–nucleus (pA) and nucleus–nucleus (AA) collisions. In particular, nuclei and hyper-nuclei are special objects with respect to non-composite hadrons (such as pions, kaons, protons, etc.), because their size is comparable to a fraction or the whole system created in the collision. Their formation is typically described within the framework of coalescence and thermal-statistical production models. In order to distinguish between the two production scenarios, we propose to measure the coalescence parameter BA for different anti- and hyper-nuclei (that differ by mass, size and internal wave function) as a function of the size of the particle emitting source. The latter can be controlled by performing systematic measurements of light anti- and hyper-nuclei in different collision systems (pp, pA, AA) and as a function of the multiplicity of particles created in the collision. While it is often argued that the coalescence and the thermal model approach give very similar predictions for the production of light nuclei in heavy-ion collisions, our study shows that large differences can be expected for hyper-nuclei with extended wave functions, as the hyper-triton. We compare the model predictions with data from the ALICE experiment and we discuss perspectives for future measurements with the upgraded detectors during the High-Luminosity LHC phase in the next decade
Runs test for assessing volatility forecastability in financial time series
No full textIn this work we refine a nonparametric methodology firstly applied in Christoffersen and Diebold [Review of
Economics and Statistics 82 (2000) 12] for assessing volatility forecastability in financial time series based on discretization
and on the use of runs tests. Empirical results are provided for SP500 and MIB30 indexes that lead naturally
to a discretized one-period Markov chain. The results are confirmed with other persistence measures and their robustness
is studied via numerical simulatio
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