Research

11 pages, 426 KiB

Open AccessArticle

Testing the Paradigm of Nuclear Many-Body Theory

by Omar Benhar

Particles 2023, 6(2), 611-621; https://doi.org/10.3390/particles6020035 - 31 May 2023

Cited by 5 | Viewed by 1028

Nuclear many-body theory is based on the tenet that nuclear systems can be accurately described as collections of point-like particles. This picture, while providing a remarkably accurate explanation of a wealth of measured properties of atomic nuclei, is bound to break down in [...] Read more.

Nuclear many-body theory is based on the tenet that nuclear systems can be accurately described as collections of point-like particles. This picture, while providing a remarkably accurate explanation of a wealth of measured properties of atomic nuclei, is bound to break down in the high-density regime, in which degrees of freedom other than protons and neutrons are expected to come into play. Valuable information on the validity of the description of dense nuclear matter in terms of nucleons, needed to firmly establish its limit of applicability, can be obtained from electron–nucleus scattering data at large momentum transfer and low energy transfer. The emergence of y-scaling in this kinematic region, unambiguously showing that the beam particles couple to high-momentum nucleons belonging to strongly correlated pairs, indicates that at densities as large as five times nuclear density—typical of the neutron star interior—nuclear matter largely behaves as a collection of nucleons. Full article

(This article belongs to the Special Issue 2022 Feature Papers by Particles’ Editorial Board Members)

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15 pages, 911 KiB

Open AccessArticle

Long-Lived Particles Anomaly Detection with Parametrized Quantum Circuits

by Simone Bordoni, Denis Stanev, Tommaso Santantonio and Stefano Giagu

Particles 2023, 6(1), 297-311; https://doi.org/10.3390/particles6010016 - 13 Feb 2023

Cited by 3 | Viewed by 1956

Abstract

We investigate the possibility to apply quantum machine learning techniques for data analysis, with particular regard to an interesting use-case in high-energy physics. We propose an anomaly detection algorithm based on a parametrized quantum circuit. This algorithm was trained on a classical computer [...] Read more.

We investigate the possibility to apply quantum machine learning techniques for data analysis, with particular regard to an interesting use-case in high-energy physics. We propose an anomaly detection algorithm based on a parametrized quantum circuit. This algorithm was trained on a classical computer and tested with simulations as well as on real quantum hardware. Tests on NISQ devices were performed with IBM quantum computers. For the execution on quantum hardware, specific hardware-driven adaptations were devised and implemented. The quantum anomaly detection algorithm was able to detect simple anomalies such as different characters in handwritten digits as well as more complex structures such as anomalous patterns in the particle detectors produced by the decay products of long-lived particles produced at a collider experiment. For the high-energy physics application, the performance was estimated in simulation only, as the quantum circuit was not simple enough to be executed on the available quantum hardware platform. This work demonstrates that it is possible to perform anomaly detection with quantum algorithms; however, as an amplitude encoding of classical data is required for the task, due to the noise level in the available quantum hardware platform, the current implementation cannot outperform classic anomaly detection algorithms based on deep neural networks. Full article

(This article belongs to the Special Issue 2022 Feature Papers by Particles’ Editorial Board Members)

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26 pages, 835 KiB

Open AccessArticle

Parametrizations of Collinear and k_T-Dependent Parton Densities in Proton

by Nizami A. Abdulov, Anatoly V. Kotikov and Artem Lipatov

Particles 2022, 5(4), 535-560; https://doi.org/10.3390/particles5040039 - 28 Nov 2022

Cited by 4 | Viewed by 2033

Abstract

A new type of parametrization for parton distribution functions in the proton, based on their

Q^{2}

-evolution at large and small x values, is constructed. In our analysis, the valence and nonsinglet parts obey the Gross–Llewellyn–Smith and Gottfried sum rules, respectively. For [...] Read more.

A new type of parametrization for parton distribution functions in the proton, based on their

Q^{2}

-evolution at large and small x values, is constructed. In our analysis, the valence and nonsinglet parts obey the Gross–Llewellyn–Smith and Gottfried sum rules, respectively. For the singlet quark and gluon densities, momentum conservation is taken into account. Then, using the Kimber–Martin–Ryskin prescription, we extend the consideration to Transverse Momentum Dependent (TMD, or unintegrated) gluon and quark distributions in the proton, which currently plays an important role in a the number of phenomenological applications. The analytical expressions for the latter, valid for both low and large x, are derived for the first time. Full article

(This article belongs to the Special Issue 2022 Feature Papers by Particles’ Editorial Board Members)

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9 pages, 381 KiB

Open AccessArticle

Electromagnetic Response in an Expanding Quark–Gluon Plasma

by Igor A. Shovkovy

Particles 2022, 5(4), 442-450; https://doi.org/10.3390/particles5040034 - 22 Oct 2022

Cited by 8 | Viewed by 1241

Abstract

The validity of conventional Ohm’s law is tested in the context of a rapidly evolving quark–gluon plasma produced in heavy-ion collisions. Here, we discuss the electromagnetic response using an analytical solution in kinetic theory. As conjectured previously, after switching on an electric field [...] Read more.

The validity of conventional Ohm’s law is tested in the context of a rapidly evolving quark–gluon plasma produced in heavy-ion collisions. Here, we discuss the electromagnetic response using an analytical solution in kinetic theory. As conjectured previously, after switching on an electric field in a nonexpanding plasma, the time-dependent current is given by

J (t) = (1 - e^{- t / τ_{0}}) σ_{0} E

, where

τ_{0}

is the transport relaxation time and

σ_{0}

is the steady-state electrical conductivity. Such an incomplete electromagnetic response reduces the efficiency of the magnetic flux trapping in the quark–gluon plasma, and may prevent the observation of the chiral magnetic effect. Here, we extend the study to the case of a rapidly expanding plasma. We find that the decreasing temperature and the increasing transport relaxation time have opposite effects on the electromagnetic response. While the former suppresses the time-dependent conductivity, the latter enhances it. Full article

(This article belongs to the Special Issue 2022 Feature Papers by Particles’ Editorial Board Members)

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17 pages, 2779 KiB

Open AccessArticle

Original e⁻ Capture Cross Sections for Hot Stellar Interior Energies

by Panagiota Giannaka, Theocharis Kosmas and Hiroyasu Ejiri

Particles 2022, 5(3), 390-406; https://doi.org/10.3390/particles5030031 - 12 Sep 2022

Cited by 2 | Viewed by 1584

Abstract

The nuclear electron capture reaction possesses a prominent position among other weak interaction processes occurring in explosive nucleosynthesis, especially at the late stages of evolution of massive stars. In this work, we perform exclusive calculations of absolute

e^{-}

-capture cross sections using [...] Read more.

The nuclear electron capture reaction possesses a prominent position among other weak interaction processes occurring in explosive nucleosynthesis, especially at the late stages of evolution of massive stars. In this work, we perform exclusive calculations of absolute

e^{-}

-capture cross sections using the proton–neutron (pn) quasi-particle random phase approximation. Thus, the results of this study can be used as predictions for experiments operating under the same conditions and in exploring the role of the

e^{-}

-capture process in the stellar environment at the pre-supernova and supernova phase of a massive star. The main goal of our study is to provide detailed state-by-state calculations of original cross sections for the

e^{-}

-capture on a set of isotopes around the iron group nuclei (

^{28}

Si,

^{32}

S,

^{48}

Ti,

^{56}

Fe,

^{66}

Zn and

^{90}

Zr) that play a significant role in pre-supernova as well as in the core–collapse supernova phase in the energy range

0 \leq E \leq 50

MeV. Full article

(This article belongs to the Special Issue 2022 Feature Papers by Particles’ Editorial Board Members)

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13 pages, 1683 KiB

Open AccessArticle

Electron Capture on Nuclei in Stellar Environment

by Panagiota Giannaka and Theocharis Kosmas

Particles 2022, 5(3), 377-389; https://doi.org/10.3390/particles5030030 - 12 Sep 2022

Cited by 1 | Viewed by 1650

Abstract

The stellar electron capture on nuclei is an essential, semi-leptonic process that is especially significant in the central environment of core-collapse supernovae and in the explosive stellar nucleosynthesis. In this article, on the basis of the original (absolute) electron-capture cross-sections under laboratory conditions [...] Read more.

The stellar electron capture on nuclei is an essential, semi-leptonic process that is especially significant in the central environment of core-collapse supernovae and in the explosive stellar nucleosynthesis. In this article, on the basis of the original (absolute) electron-capture cross-sections under laboratory conditions that we computed in our previous work for a set of medium-weight nuclear isotopes, we extend this study and evaluate folded

e^{-}

-capture rates in the stellar environment. With this aim, we assume that the parent nuclei and the projectile electrons interact when they are in the deep stellar interior during the late stages of the evolution of massive stars. Under these conditions (high matter densities and high temperatures of the pre-supernova and core-collapse supernova phases), we choose two categories of nuclei; the first includes the

^{48} T i

and

^{56} F e

isotopes that have

A < 65

and belong to the iron group of nuclei, and the second includes the heavier and more neutron-rich isotopes

^{66} Z n

and

^{90} Z r

(with

A > 65

). In the former, the electron capture takes place mostly during the pre-supernova stage, while the latter occurs during the core-collapse supernova phase. A comparison with previous calculations, which were obtained by using various microscopic nuclear models employed for single-charge exchange nuclear reactions, is also included. Full article

(This article belongs to the Special Issue 2022 Feature Papers by Particles’ Editorial Board Members)

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20 pages, 1110 KiB

Open AccessArticle

Colliding and Fixed Target Mode in a Single Experiment—A Novel Approach to Study the Matter under New Extreme Conditions

by Oleksandr V. Vitiuk, Valery M. Pugatch, Kyrill A. Bugaev, Nazar S. Yakovenko, Pavlo P. Panasiuk, Elizaveta S. Zherebtsova, Vasyl M. Dobishuk, Sergiy B. Chernyshenko, Borys E. Grinyuk, Violetta Sagun and Oleksii Ivanytskyi

Particles 2022, 5(3), 245-264; https://doi.org/10.3390/particles5030022 - 18 Jul 2022

Viewed by 1946

Abstract

Here, we propose a novel approach to experimentally and theoretically study the properties of QCD matter under new extreme conditions, namely having an initial temperature over 300 MeV and baryonic charge density over three times the values of the normal nuclear density. According [...] Read more.

Here, we propose a novel approach to experimentally and theoretically study the properties of QCD matter under new extreme conditions, namely having an initial temperature over 300 MeV and baryonic charge density over three times the values of the normal nuclear density. According to contemporary theoretical knowledge, such conditions were not accessible during the early Universe evolution and are not accessible now in the known astrophysical phenomena. To achieve these new extreme conditions, we proposed performing high-luminosity experiments at LHC or other colliders by means of scattering the two colliding beams at the nuclei of a solid target that is fixed at their interaction region. Under plausible assumptions, we estimate the reaction rate for the p+C+p and Pb+Pb+Pb reactions and discuss the energy deposition into the target and possible types of fixed targets for such reactions. To simulate the triple nuclear collisions, we employed the well-known UrQMD 3.4 model for the beam center-of-mass collision energies

\sqrt{s_{N N}}

= 2.76 TeV. As a result of our modeling, we found that, in the most central and simultaneous triple nuclear collisions, the initial baryonic charge density is approximately three times higher than the one achieved in the ordinary binary nuclear collisions at this energy. Full article

(This article belongs to the Special Issue 2022 Feature Papers by Particles’ Editorial Board Members)

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10 pages, 382 KiB

Open AccessArticle

Defining the Underlying-Event Activity in the Presence of Heavy-Flavour Processes in Proton-Proton Collisions at LHC Energies

by László Gyulai, Szende Sándor and Róbert Vértesi

Particles 2022, 5(3), 235-244; https://doi.org/10.3390/particles5030021 - 07 Jul 2022

Viewed by 1554

Abstract

We present a systematic analysis of heavy-flavour production in the underlying event in connection to a leading hard process in pp collisions at

\sqrt{s} = 13

TeV, using the PYTHIA 8 Monte Carlo event generator. We compare results from events selected by triggering [...] Read more.

We present a systematic analysis of heavy-flavour production in the underlying event in connection to a leading hard process in pp collisions at

\sqrt{s} = 13

TeV, using the PYTHIA 8 Monte Carlo event generator. We compare results from events selected by triggering on the leading hadron, as well as those triggered with reconstructed jets. We show that the kinematics of heavy-flavour fragmentation complicates the characterisation of the underlying event, and the usual method which uses the leading charged final-state hadron as a trigger may wash away the connection between the leading process and the heavy-flavour particle created in association with that. Events triggered with light or heavy-flavour jets, however, retain this connection and bring more direct information on the underlying heavy-flavour production process, but may also import unwanted sensitivity to gluon radiation. The methods outlined in the current work provide means to verify model calculations for light and heavy-flavour production in the jet and the underlying event in great details. Full article

(This article belongs to the Special Issue 2022 Feature Papers by Particles’ Editorial Board Members)

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15 pages, 768 KiB

Open AccessArticle

Coupled-Channel Analysis of the Process γγ→π⁰π⁰

by Yury S. Surovtsev, Petr Bydžovský, Thomas Gutsche, Robert Kamiński, Valery E. Lyubovitskij and Miroslav Nagy

Particles 2022, 5(3), 210-224; https://doi.org/10.3390/particles5030019 - 30 Jun 2022

Viewed by 1390

Abstract

We study the process

γ γ \to π^{0} π^{0}

involving the principal mechanisms, the structure of its cross section and the role of individual isoscalar-tensor resonances in the saturation of its energy spectrum. Full article

(This article belongs to the Special Issue 2022 Feature Papers by Particles’ Editorial Board Members)

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