Search

We provide an update on our semi-classical transport approach for quarkonium production in high-energy heavy-ion collisions, focusing on J / ψ and ψ (2 S) mesons in 5.02 TeV Pb-Pb collisions at the Large Hadron Collider (LHC) at both forward and mid-rapidity. In particular, we employ the most recent charm-production cross sections reported in pp collisions, which are pivotal for the magnitude of the regeneration contribution, and their modifications due to cold-nuclear-matter (CNM) effects. Multi-differential observables are calculated in terms of nuclear modification factors as a function of centrality, transverse momentum, and rapidity, including the contributions from feeddown from bottom hadron decays. For our predictions for ψ (2 S) production, the mechanism of sequential regeneration relative to the more strongly bound J / ψ meson plays an important role in interpreting recent ALICE data. [ABSTRACT FROM AUTHOR]

The Schwinger confinement mechanism stipulates that a massless fermion and a massless antifermion are confined as a massive boson when they interact in the Abelian QED interaction in (1+1)D.If we approximate light quarks as massless and apply the Schwinger confinement mechanism to quarks, we can infer that a light quark and a light antiquark interacting in the Abelian QED interaction are confined as a QED meson in (1+1)D. Similarly, a light quark and a light antiquark interacting in the QCD interaction in the quasi-Abelian approximation will be confined as a QCD meson in (1+1)D. The QED and QCD mesons in (1+1)D can represent physical mesons in (3+1)D when the flux tube radius is properly taken into account. Such a theory leads to a reasonable description of the masses of π 0 , η , and η ′ , and its extrapolation to the unknown QED sector yields an isoscalar QED meson at about 17 MeV and an isovector QED meson at about 38 MeV. The observations of the anomalous soft photons, the hypothetical X17 particle, and the hypothetical E38 particle bear promising evidence for the possible existence of the QED mesons. Pending further confirmation, they hold important implications on the properties on the quarks and their interactions. [ABSTRACT FROM AUTHOR]

Flavour changing neutral current (FCNC) processes are described by loop diagrams in the Standard Model (SM), while in 331 models, based on the gauge group SU (3) C × SU (3) L × U (1) X , they are dominated by tree-level exchanges of a new heavy neutral gauge boson Z ′ . By exploiting this feature, observables related to FCNC decays of K, B d and B s mesons can be considered in several variants of 331 models. The variants are distinguished by the value of a parameter β that plays a key role in this framework. Imposing constraints on the Δ F = 2 observables, we select possible ranges for the mass of the Z ′ boson in correspondence to the values β = ± k / 3 , with k = 1 , 2 . The results are used to determine the impact of 331 models on b → s processes and on the correlations among them, in the light of new experimental data recently released. [ABSTRACT FROM AUTHOR]

The rho meson has long been successfully identified with a dynamical gauge boson of Hidden Local Symmetry (HLS) H local in the non-linear sigma model G / H gauge equivalent to the model having the symmetry G global × H local , with G = [ S U (2) L × S U (2) R ] ≃ O (4) , H = S U (2) V ≃ O (3) . However, under a hitherto unproven assumption that its kinetic term is dynamically generated, together with an ad hoc choice of the auxiliary field parameter " a = 2 ", we prove this assumption, thereby solving the long-standing mystery. The rho meson kinetic term is generated simply by the large N limit of the Grassmannian model G / H = O (N) / [ O (N − 3) × O (3) ] gauge equivalent to O (N) global × [ O (N − 3) × O (3) ] local , extrapolated to N = 4 , O (4) global × O (3) local , with all the phenomenologically successful " a = 2 results", i.e., ρ -universality, KSRF relation, and the Vector Meson Dominance, realized independently of the parameter "a". This in turn establishes validity of the large N dynamics at the quantitative level directly by the experiments. The relevant cutoff reads Λ ≃ 4 π F π for N = 4 , which is regarded as a matching scale of the HLS as a "magnetic dual" to QCD. Skyrmion is stabilized by such a dynamically generated rho meson without recourse to the underlying QCD, a further signal of the duality. The unbroken phase with a massless rho meson may be realized as a novel chiral-restored hadronic phase in the hot/dense QCD. [ABSTRACT FROM AUTHOR]

We establish a statistical two-body fractal (STF) model to study the spectrum of J / ψ . J / ψ serves as a reliable probe in heavy-ion collisions. The distribution of J / ψ in hadron gas is influenced by flow, quantum and strong interaction effects. Previous models have predominantly focused on one or two of these effects while neglecting the others, resulting in the inclusion of unconsidered effects in the fitted parameters. Here, we study the issue from a new point of view by analyzing the fact that all three effects induce a self-similarity structure, involving a J / ψ - π two-meson state and a J / ψ , π two-quark state, respectively. We introduce modification factor q T B S and q 2 into the probability and entropy of charmonium. q T B S denotes the modification of self-similarity on J / ψ , q 2 denotes that of self-similarity and strong interaction between c and c ¯ on quarks. By solving the probability and entropy equations, we derive the values of q T B S and q 2 at various collision energies and centralities. Substituting the value of q T B S into distribution function, we successfully obtain the transverse momentum spectrum of low- p T   J / ψ , which demonstrates good agreement with experimental data. The STF model can be employed to investigate other mesons and resonance states. [ABSTRACT FROM AUTHOR]

A formalism for the experimental analysis of mesons produced by a beam of linearly polarized photons is presented. This formalism introduces a more general use of the reflectivity operator. The goal is to recognize resonances in cross-sections, their associated quantum numbers, and production mechanisms by performing partial wave analysis of multiple-meson final states. [ABSTRACT FROM AUTHOR]

Lepton flavor universality exists in the Standard Model, and hence any observation of the violation of this universality will be a hint for new physics. Recent experimental searches for processes violating this symmetry have attracted much attention among theorists and experimentalists alike. In recent years, such hints have been observed in flavor changing neutral current weak processes such as b → s l l and charged current weak processes such as b → c l ν processes by collider experiments like Belle, Belle II, BaBar, LHCb, ATLAS, and CMS collaborations, where b , s , c are the bottom, strange, and charm quarks, respectively, and l , ν stand for lepton and the corresponding lepton neutrino, respectively. This article is a review of some of the interesting anomalies observed in the B-sector and includes decays of B s mesons. [ABSTRACT FROM AUTHOR]

In this paper, we present two machine learning algorithms to identify D mesons produced in a colour singlet state from radiative W boson decays at the LHC. The combined network algorithm is able to identify D mesons via its hadronic decays with an efficiency of 47% while suppressing a background of quark and gluon jets by a factor of 100. Using the developed algorithm, we perform a prospective study for the measurement of B (W → D s γ) . [ABSTRACT FROM AUTHOR]

For investigating the relationship between the surface corona discharge of a DC wire and other influencing factors, a hybrid numerical model based on a fluid-chemical reaction was proposed to simulate the discharge process at the tip defect of the wire. Under different defect geometries and gas pressures achieved via simulation, the microscopic process of the reaction and movement of electrons and heavy particles during a positive corona discharge was studied, and characteristic parameters such as corona inception voltage and discharge current were analyzed. Furthermore, through the corona cage test, for a specific electrode configuration, corona inception voltages under different pressures were compared and verified, which showed that the model was reasonable. The results showed that the maximum electron density of the streamer head was about 1 × 1020 m−3, the rise time of the pulse current was about 10 ns, and the decay time was about 300–500 ns. The corona inception voltage decreased with an increase in the tip height and decreases in the tip curvature radius, conductor radius, and background air pressure; the amplitude of the pulse current increased with increases in the wire radius and curvature radius of the defect tip and decreases in tip height and background air pressure. The experimental results are consistent with the simulation results, which verifies the reasonability of the model. [ABSTRACT FROM AUTHOR]

Heavy and light quarks produced in high- p T partonic collisions radiate differently. Heavy quarks regenerate their color field, stripped-off in the hard reaction, much faster than the light ones and radiate a significantly smaller fraction of the initial quark energy. This peculiar feature of heavy-quark jets leads to a specific shape of the fragmentation functions observed in e + e − annihilation. Differently from light flavors, the heavy quark fragmentation function strongly peaks at large fractional momentum z, i.e., the produced heavy–light mesons, B or D, carry the main fraction of the jet momentum. This is a clear evidence of the dead-cone effect, and of a short production time of a heavy–light mesons. Contrary to propagation of a small q q ¯ dipole, which survives in the medium due to color transparency, a heavy–light Q q ¯ dipole promptly expands to a large size. Such a big dipole has no chance to remain intact in a dense medium produced in relativistic heavy ion collisions. On the other hand, a breakup of such a dipole does not affect much the production rate of Q q ¯ mesons, differently from the case of light q q ¯ meson production. [ABSTRACT FROM AUTHOR]

This paper was written in memory of Joao da Providência who passed away in November 2021. It is a pursuit of works developed recently by Joao, Steven and inspired by our many years of discussions. Neutron stars are described within the quark–meson coupling Bogoliubov (QMC Bogoliubov) nuclear model which includes u, d and s quarks. The model is improved by including the ω - b 3 mixing term so that constraints imposed by ab-initio chiral effective field theory pure neutron matter calculations are satisfied. The effects of the symmetry energy slope on the structure and properties of neutron stars are investigated. In particular, the effect on the radius, on the particle fractions, and on the onset of the nuclear direct Urca processes is discussed. It is shown that the improved model is in accordance with GW170817 observations, and that the constrained symmetry energy does not allow for nucleonic direct Urca processes inside neutron stars. Within the present model, no hyperons nucleate inside neutron stars. [ABSTRACT FROM AUTHOR]

We reconsider the semileptonic decays of B → D 1 (′) l ν ¯ l . The previous theoretical calculations predict a significantly smaller rate for the semileptonic decay of B to D 1 ′ (J l = 1 2) compared with that to the D 1 (J l = 3 2) , which is not consistent with the current experimental data. This conflict is known as the so-called ' 1 2 vs. 3 2 puzzle'. In this work, we propose a simple scheme to fix this problem, where we suppose the strong eigenstates D 1 (′) that do not coincide with the eigenstate of the weak interaction, since no experimental results show that the weak and the strong interactions have to share the same eigenstates. Within the framework of this tentative scheme, meson B first weakly decays to the weak eigenstates D α (β) and then the latter are detected as the D 1 (′) by the strong decay products D * π . We predict that there exist two new particles D α (β) with J P = 1 + , which were not previously identified. The good performance of the new scheme in describing the experimental data may hint at new symmetry in the weak decays of B q to 1 + heavy–light mesons. To test the scheme proposed here, we suggest an experiment to detect the difference in the invariant mass spectra of D 1 that is reconstructed from the B weak decay and from the strong decay products. [ABSTRACT FROM AUTHOR]

In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field ( σ ¯ 3 = f K ± − f K 0 ) and the third generator of the matrix of the explicit symmetry breaking [ h 3 = m a 0 2 f K ± − f K 0 ] are estimated in terms of the decay constants of the neutral ( f K 0 ) and charged Kaon ( f K ± ) and the mass of a 0 meson. Both quantities σ ¯ 3 and h 3 are then evaluated, at finite baryon ( μ B ), isospin chemical potential ( μ I ), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the ( T − μ I ) phase diagram In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field ( σ ¯ 3 = f K ± − f K 0 ) and the third generator of the matrix of the explicit symmetry breaking [ h 3 = m a 0 2 f K ± − f K 0 ] are estimated in terms of the decay constants of the neutral ( f K 0 ) and charged Kaon ( f K ± ) and the mass of a 0 meson. Both quantities σ ¯ 3 and h 3 are then evaluated, at finite baryon ( μ B ), isospin chemical potential ( μ I ), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the ( T − μ I ) phase diagram. The in-medium modifications of pseudoscalars ( J p c = 0 − + ), scalars ( J p c = 0 + + ), vectors ( J p c = 1 − − ), and axial-vectors ( J p c = 1 + + ) meson states are then analyzed in thermal and dense medium. We conclude that the QCD phase diagram ( T − μ I ) is qualitatively similar to the ( T − μ B ) phase diagram. We also conclude that both temperature and isospin chemical potential enhance the in-medium modifications of the meson states a 0 , σ , η ′ , π , f 0 , κ , η , K, ρ , ω , κ * , ϕ , a 1 , f 1 , K * , and f 1 * . Regarding their chemical potential, at high temperatures the various meson states likely dissolve into colored partonic phase. In this limit, the meson masses form a universal bundle. Thus, we conclude that the increase in the chemical potential similar to temperature derives the colorless confined meson states into the colored deconfined parton phase. [ABSTRACT FROM AUTHOR]

As known, the realistic, exponential, fall-off of the rate of production of light mesons in the chromo-electric field of a quark–antiquark string, as a function of the meson mass, can be obtained from the Schwinger-formula Gaussian fall-off within a phenomenological approach which assumes a certain distribution of the string tension. This approach gets a clear meaning in the London limit of the dual superconductor, where the logarithmic increase of the chromo-electric field towards the core of the string leads precisely to the change of the Gaussian fall-off to the exponential one, thus allowing for an identification of the phenomenological distribution of the string tension. In this paper, we demonstrate that, for this distribution of the string tension, the distribution of large-size Yang–Mills instantons, which are interacting with the confining monopole background, becomes O (1 / ρ 3) , where ρ is the size of an instanton. Since such a distribution of large-size instantons is known to yield confinement, we conclude that, in the London limit of the dual-superconductor vacuum, instantons can form a confining medium, and we evaluate their contribution to the total string tension. [ABSTRACT FROM AUTHOR]

In this paper, we review our findings concerning fractal entropy of microscopic configurations corresponding to the production of K S 0 mesons in AuAu collisions in the z-scaling approach. The entropy is expressed via structural and fragmentation fractal dimensions, and model parameter c AuAu is interpreted as a specific heat of produced medium. These parameters are related to the respective momentum fractions of the colliding nuclei, the momentum fractions of the scattered constituents that fragment into the produced hadrons, and the multiplicity density of negative particles in the central interaction region. The dependence of the entropy on the collision energy over the range of 7.7–200 GeV for most central and most peripheral events is studied as a function of the transverse momentum of the produced K S 0 mesons. A non-trivial dependence of the entropy on the collision energy with decreasing transverse momentum is found. This reflects the irregularity of the behavior of the specific heat, c AuAu , and can point to a manifestation of phase transition in nuclear matter. [ABSTRACT FROM AUTHOR]

In this study, we calculate the pressure of the interacting pion gas using the Beth–Uhlenbeck approach to the relativistic virial expansion with Breit–Wigner phase shifts for the σ - and ϱ -meson resonances. The repulsive phase shift δ 0 2 is taken from the quark interchange model of Barnes and Swanson, which is in very good agreement with the experimental data. In this work we show that the cancellation of the attractive (I = 0) and repulsive (I = 2) isospin channel contributions to the scalar π π interaction in the low-energy region that is known for the vacuum phase shifts also takes place at a finite temperature. This happens despite the strong medium dependence of these phase shifts that enters our model by the temperature dependence of the σ -meson and constituent quark masses, because for these masses the relation M σ (T) ≈ 2 m q (T) holds and the scattering length approximation is valid as long as the strong decay channel σ → π π is open. Exploiting the Nambu–Jona-Lasinio model for describing the dynamical breaking of chiral symmetry in the vacuum and its restoration at a finite temperature, we justify with our approach that the σ -meson should be absent from the hadron resonance gas description at low temperatures because the above cancellation holds. However, since this cancellation breaks down in the vicinity of the hadronization transition, where due to chiral symmetry restoration the decay channel σ → π π closes and the σ -meson becomes a good resonance, the latter should be included into the statistical model description of chemical freeze-out in heavy-ion collisions. [ABSTRACT FROM AUTHOR]

Understanding the strong interaction dynamics that govern the emergence of hadron mass (EHM) represents a challenging open problem in the Standard Model. In this paper we describe new opportunities for gaining insight into EHM from results on nucleon resonance ( N * ) electroexcitation amplitudes (i.e., γ v p N * electrocouplings) in the mass range up to 1.8 GeV for virtual photon four-momentum squared (i.e., photon virtualities Q 2 ) up to 7.5 GeV 2 available from exclusive meson electroproduction data acquired during the 6-GeV era of experiments at Jefferson Laboratory (JLab). These results, combined with achievements in the use of continuum Schwinger function methods (CSMs), offer new opportunities for charting the momentum dependence of the dressed quark mass from results on the Q 2 -evolution of the γ v p N * electrocouplings. This mass function is one of the three pillars of EHM and its behavior expresses influences of the other two, viz. the running gluon mass and momentum-dependent effective charge. A successful description of the Δ (1232) 3 / 2 + and N (1440) 1 / 2 + electrocouplings has been achieved using CSMs with, in both cases, common momentum-dependent mass functions for the dressed quarks, for the gluons, and the same momentum-dependent strong coupling. The properties of these functions have been inferred from nonperturbative studies of QCD and confirmed, e.g., in the description of nucleon and pion elastic electromagnetic form factors. Parameter-free CSM predictions for the electrocouplings of the Δ (1600) 3 / 2 + became available in 2019. The experimental results obtained in the first half of 2022 have confirmed the CSM predictions. We also discuss prospects for these studies during the 12-GeV era at JLab using the CLAS12 detector, with experiments that are currently in progress, and canvass the physics motivation for continued studies in this area with a possible increase of the JLab electron beam energy up to 22 GeV. Such an upgrade would finally enable mapping of the dressed quark mass over the full range of distances (i.e., quark momenta) where the dominant part of hadron mass and N * structure emerge in the transition from the strongly coupled to perturbative QCD regimes. [ABSTRACT FROM AUTHOR]

ALICE-3 is being designed as a next-generation heavy-ion experiment to be operated at the high-luminosity Large Hadron Collider. With luminosities higher by a factor of fifty, ALICE-3 will be able to study5 properties of quark–gluon matter with probes and precision which were previously unavailable due to small cross sections, high background levels, and insufficient detector sensitivity. In particular, the properties of hot and dense QCD matter will be studied by measuring production cross sections, flow coefficients, azimuthal angular correlations and nuclear modification factors for open-charm hadrons. In this contribution, we present the results of feasibility studies for the measurement of ground and excited states of open-charm mesons in decay channels D0 → K− + π+ + π0, D*(2007)0 → D0 + γ and D*(2010)± → D0 + π± in pp, p-Pb and Pb-Pb collisions at LHC energies using the ALICE-3 experimental setup. We formulate the main requirements for the selection of particles and their combinations to ensure reliable signal extraction in a wide transverse momentum range and estimate the minimum size of the required data samples. The results obtained are also compared to previous findings for the open-charm measurements in different decay channels. [ABSTRACT FROM AUTHOR]

We review recent studies of vortical motion and the resulting polarization of Λ hyperons in heavy-ion collisions at NICA energies, in particular, within the model of three-fluid dynamics (3FD). This includes predictions of the global Λ polarization and ring structures that appear in Au+Au collisions. The global Λ polarization in Au+Au collisions is calculated, including its rapidity and centrality dependence. The contributions of the thermal vorticity and meson-field term (proposed by Csernai, Kapusta, and Welle) to the global polarization are considered. The results are compared with data from recent STAR and HADES experiments. It is predicted that the polarization maximum is reached at s N N ≈ 3 GeV if the measurements are performed with the same acceptance. It is demonstrated that a pair of vortex rings are formed, one at forward rapidities and another at backward rapidities, in ultra-central Au+Au collisions at s N N > 4 GeV. The vortex rings carry information about the early stage of the collision, in particular, the stopping of baryons. It is shown that these rings can be detected by measuring the ring observable R Λ , even in the midrapidity region at s N N = 5–20 GeV. At forward/backward rapidities, the R Λ signal is expected to be stronger. The possibility of observing the vortex-ring signal against the background of non-collective transverse polarization is discussed. [ABSTRACT FROM AUTHOR]

This paper review the modelling efforts regarding Generalised Parton Distributions (GPDs) using continuum techniques relying on Dyson–Schwinger and Bethe–Salpeter equations. The definition and main properties of the GPDs are first recalled. Then, we detail the strategies developed in the last decade in the meson sector, highlighting that observables connected to the pion GPDs may be measured at future colliders. We also highlight the challenges one will face when targeting baryons in the future. [ABSTRACT FROM AUTHOR]

Laser-induced nuclear reactions in ultra-dense hydrogen H(0) (review in Physica Scripta 2019) create mesons (kaons and pions). These mesons decay mainly to muons. The muons created are useful (patented source) for the muon-induced fusion process. The sign of the muons from the source depends on the initial baryons used. With D(0) (ultra-dense deuterium) the source produces mainly positive muons and with p(0) (ultra-dense protium) the source produces mainly negative muons. Negative muons are required for muon-induced fusion. This charge asymmetry was reported earlier, and has now been confirmed by experiments with a coil current transformer as the beam detector. The current coil detector would give no signal from the muons if charge symmetry existed. The charge asymmetry could indicate unknown processes, for example, caused by the different annihilation processes in D(0) and p(0). The conclusions of a new analysis of the results are presented here. Using D(0) in the muon source, the asymmetry is likely due to the capture of µ- in D atoms and D2 molecules. This leads to emission of excess µ+ from D(0). With p(0) in the muon source, the capture rate of µ- is lower than in D(0). The emitted number of µ+ will be decreased by the reaction between µ+ and the surrounding abundant electrons, forming neutral muonium particles. This effect decreases the amount of emitted µ+ for both p(0) and D(0), and it is proposed to be the main reason for a larger fraction of emitted µ- in the case of p(0). Thus, there is no dominant emission of negative muons which would violate charge conservation. [ABSTRACT FROM AUTHOR]

In this work, we interpret the newly observed η 1 (1855) resonance with exotic J P C = 1 − + quantum numbers in the I = 0 sector, reported by the BESIII Collaboration, as a dynamically generated state from the interaction between the lightest pseudoscalar mesons and axial-vector mesons. The interaction is derived from the lowest order chiral Lagrangian from which the Weinberg–Tomozawa term is obtained, describing the transition amplitudes among the relevant channels, which are then unitarized using the Bethe–Salpeter equation, according to the chiral unitary approach. We evaluate the η 1 (1855) decays into the η η ′ and K K ¯ * π channels and find that the latter has a larger branching fraction. We also investigate its SU(3) partners, and according to our findings, the π 1 (1400) and π 1 (1600) structures may correspond to dynamically generated states, with the former one coupled mostly to the b 1 π component and the latter one coupled to the K 1 (1270) K ¯ channel. In particular, our result for the ratio Γ (π 1 (1600) → f 1 (1285) π) / Γ (π 1 (1600) → η ′ π) is consistent with the measured value, which supports our interpretation for the higher π 1 state. We also report two poles with a mass about 1.7 GeV in the I = 1 / 2 sector, which may be responsible for the K * (1680) . We suggest searching for two additional η 1 exotic mesons with masses around 1.4 and 1.7 GeV. In particular, the predicted η 1 (1700) is expected to have a width around 0.1 GeV and can decay easily into K K ¯ π π . [ABSTRACT FROM AUTHOR]

The temperature dependence of the QCD string-breaking distance is evaluated in terms of the string tension and the rate of production of light mesons in the chromo-electric field of a flux tube. As a function of the meson mass, the mentioned rate can be falling off either as a Gaussian, as suggested by the Schwinger formula, or as an exponential, which is the case in the London limit of the dual superconductor. We find an excellent agreement of the so-evaluated temperature dependence of the string-breaking distance with the respective lattice data, for the case of the meson-production rate corresponding to the London limit. [ABSTRACT FROM AUTHOR]

Laser-induced nuclear reactions in ultra-dense hydrogen H(0) produce mesons with both relatively low kinetic energy and with high kinetic energy. The kaons have up to 100 MeV of kinetic energy, thus a velocity of 0.55 c. Each laser pulse of >0.1 J of energy and length of 5 ns produces 1013 mesons. The operation of the meson generator is here demonstrated by measuring all decay times for mesons in the ns range after induction by a pulsed laser. These decay times are the unique fingerprints of the mesons, and they also produce the kinetic energy of the mesons created from their time-dilated decay. The charged pion decay time at rest from this generator is measured to be 25.92 ± 0.04 ns (standard fit error), in reasonable agreement with the tabulated results of 26.033 ns. A similar accuracy is found for the other mesons as for the charged kaons, with 96 MeV of kinetic energy, at 14.81 ± 0.05 ns. The same general behaviour is found with both deuterium and normal hydrogen forming the ultra-dense phase H(0) on the laser target. This meson generator gives intense meson showers useful for many types of particle physics experiments at a small fraction of the cost of using particle accelerators. A particle accelerator would need an energy of at least 1021 eV to produce a similar shower of 1013 mesons. Thus, the described generator is among the most intense meson sources that exist. Other important applications include nuclear energy generation and particle (pion) radiation for cancer treatment. [ABSTRACT FROM AUTHOR]

We study the process γ γ → 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. [ABSTRACT FROM AUTHOR]

In the framework of a multi-source thermal model at the partonic level, we have analyzed transverse momentum spectra of hadrons measured by the ALICE Collaboration in proton–proton ( p p or p–p) collisions at the center-of-mass energy of s = 7 and 13 TeV, proton–lead (p–Pb) collisions at s N N = 5.02 TeV, and lead–lead (Pb–Pb) collisions at s N N = 2.76 TeV. For mesons (baryons), the contributions of two (three) constituent quarks are considered, in which each quark contributes to hadron transverse momentum to obey the revised phenomenological Tsallis transverse momentum distribution for Maxwell–Boltzmann particles (the TP-like function, in short) with isotropic random azimuthal angles. Three main parameters, namely, the revised index a 0 , effective temperature T, and entropy-related index n, are obtained, showing the same tendency for both small and large systems with respect to the centrality (or multiplicity) of events, the rest mass of hadrons, and the constituent mass of quarks. [ABSTRACT FROM AUTHOR]

The paper proposes to study the onset of color transparency in hard exclusive reactions in the backward regime. Guided by the encouraging Jefferson Laboratory (JLab) results on backward π and ω electroproduction data at moderate virtuality Q 2 , which may be interpreted as the signal of an early scaling regime, where the scattering amplitude factorizes in a hard coefficient function convoluted with nucleon to meson transition distribution amplitudes, the study shows that investigations of these channels on nuclear targets opens a new opportunity to test the appearance of nuclear color transparency for a fast-moving nucleon. [ABSTRACT FROM AUTHOR]

The color transparency (CT) of a hadron, propagating with reduced absorption in a nucleus, is a fundamental property of QCD (quantum chromodynamics) reflecting its internal structure and effective size when it is produced at high transverse momentum, Q. CT has been confirmed in many experiments, such as semi-exclusive hard electroproduction, e A → e ′ π X , for mesons produced at Q 2 > 3 GeV 2 . However, a recent JLab (Jefferson Laboratory) measurement for a proton electroproduced in carbon e C → e ′ p X , where X stands for the inclusive sum of all produced final states, fails to observe CT at Q 2 up to 14.2 GeV 2 . In this paper, the onset of CT is determined by comparing the Q 2 -dependence of the hadronic cross sections for the initial formation of a small color-singlet configuration using the generalized parton distributions from holographic light-front QCD. A critical dependence on the hadron's twist, τ , the number of hadron constituents, is found for the onset of CT, with no significant effects from the nuclear medium. This effect can explain the absence of proton CT in the present kinematic range of the JLab experiment. The proton is predicted to have a "two-stage" color transparency with the onset of CT differing for the spin-conserving (twist-3, τ = 3 ) Dirac form factor with a higher onset in Q 2 for the spin-flip Pauli (twist-4) form factor. In contrast, the neutron is predicted to have a "one-stage" color transparency with the onset at higher Q 2 because of the dominance of its Pauli form factor. The model also predicts a strong dependence at low energies on the flavor of the quark current coupling to the hadron. [ABSTRACT FROM AUTHOR]

We describe the mapping at high density of topological structure of baryonic matter to a nuclear effective field theory that implements hidden symmetries emergent from strong nuclear correlations. The theory constructed is found to be consistent with no conflicts with the presently available observations in both normal nuclear matter and compact-star matter. The hidden symmetries involved are "local flavor symmetry" of the vector mesons identified to be (Seiberg-)dual to the gluons of QCD and hidden "quantum scale symmetry" with an IR fixed point with a "genuine dilaton (GD)" characterized by non-vanishing pion and dilaton decay constants. Both the skyrmion topology for N f ≥ 2 baryons and the fractional quantum Hall (FQH) droplet topology for N f = 1 baryons are unified in the "homogeneous/hidden" Wess–Zumino term in the hidden local symmetry (HLS) Lagrangian. The possible indispensable role of the FQH droplets in going beyond the density regime of compact stars approaching scale-chiral restoration is explored by moving toward the limit where both the dilaton and the pion go massless. [ABSTRACT FROM AUTHOR]

We calculated the shear viscosity of hot and dense nuclear matter produced in a symmetric system of central gold–gold collisions at energies of BES RHIC, FAIR and NICA. For calculations of the collisions, the transport model UrQMD was employed. The shear viscosity was obtained within the Green–Kubo formalism. The hadron resonance gas model was used to determine temperature and chemical potentials of baryon charge and strangeness out of microscopic model calculations. In contrast to our previous works, we determined the partial viscosity of the main hadron species, such as nucleons, pions, kaons and Lambdas, via the nucleon–nucleon, pion–pion and so forth, correlators. A decrease in the beam energy from E l a b = 40 to 10 AGeV leads a to rise in baryon shear viscosity accompanied by a drop in the shear viscosity of mesons. The ratio of total shear viscosity to entropy density also decreases. [ABSTRACT FROM AUTHOR]

In this work, we present the results of a component-level analysis with Monte Carlo simulations, which aid the interpretation of recent ALICE results of the azimutal correlation distribution of prompt D mesons with charged hadrons in pp and p–Pb collisions at s NN = 5.02 TeV. Parton-level contributions and fragmentation properties are evaluated. Charm and beauty contributions are compared in order to identify the observables that serve as sensitive probes of the production and hadronisation of heavy quarks. [ABSTRACT FROM AUTHOR]

Some of the outstanding questions of particle physics today concern the neutrino sector, in particular whether there are more neutrinos than those already known and whether they are Dirac or Majorana particles. There are different ways to explore these issues. In this article we describe neutrino-mediated decays of charged pseudoscalar mesons such as π±, K± and B±, in scenarios where extra neutrinos are heavy and can be on their mass shell. We discuss semileptonic and leptonic decays of such kinds. We investigate possible ways of using these decays in order to distinguish between the Dirac and Majorana character of neutrinos. Further, we argue that there are significant possibilities of detecting CP violation in such decays when there are at least two almost degenerate Majorana neutrinos involved. This latter type of scenario fits well into the known neutrino minimal standard model (νMSM) which could simultaneously explain the Dark Matter and Baryon Asymmetry of the Universe. [ABSTRACT FROM AUTHOR]

We discuss the sensitivity of the high-scale supersymmetry (SUSY) at 10-1000 TeV in B0, Bs, K0 and D meson systems together with the neutron electric dipole moment (EDM) and the mercury EDM. In order to estimate the contribution of the squark flavor mixing to these flavor changing neutral currents (FCNCs), we calculate the squark mass spectrum, which is consistent with the recent Higgs discovery. The SUSY contribution in ϵK could be large, around 40% in the region of the SUSY scale 10-100 TeV. The neutron EDM and the mercury EDM are also sensitive to the SUSY contribution induced by the gluino-squark interaction. The predicted EDMs are roughly proportional to ∣ϵSUSYK∣. If the SUSY contribution is the level of O(10%) for ϵK, the neutron EDM is expected to be discovered in the region of 10-28-10-26 ecm. The mercury EDM also gives a strong constraint for the gluino-squark interaction. The SUSY contribution of ΔMD is also discussed. [ABSTRACT FROM AUTHOR]

Some of the outstanding questions of particle physics today concern the neutrino sector, in particular whether there are more neutrinos than those already known and whether they are Dirac or Majorana particles. There are different ways to explore these issues. In this article we describe neutrino-mediated decays of charged pseudoscalar mesons such as π±, K± and B±, in scenarios where extra neutrinos are heavy and can be on their mass shell. We discuss semileptonic and leptonic decays of such kinds. We investigate possible ways of using these decays in order to distinguish between the Dirac and Majorana character of neutrinos. Further, we argue that there are significant possibilities of detecting CP violation in such decays when there are at least two almost degenerate Majorana neutrinos involved. This latter type of scenario fits well into the known neutrino minimal standard model (νMSM) which could simultaneously explain the Dark Matter and Baryon Asymmetry of the Universe. [ABSTRACT FROM AUTHOR]

The U (3) × U (3) chiral symmetric NJL model describing pseudoscalar, vector, and axial-vector mesons in both the ground state and first radially excited states is shortly presented in this review. In this model, it is possible to describe a large number of low-energy interactions of mesons, τ lepton decays into mesons, and processes of meson production in electron–positron annihilations in satisfactory agreement with the experiments. In describing a number of processes, it turned out to be necessary to take into account the interactions of mesons in the final state. [ABSTRACT FROM AUTHOR]

The LHCb experiment has been able to collect the largest sample ever produced of charm-hadron decays, performing a number of measurements of observables related to C P violation in the charm sector. In this document, the most recent results from LHCb on the search of direct C P violation in D 0 → K s 0 K s 0 , D (s) + → h + π 0 and D (s) + → h + η decays are summarised, in addition to the most precise measurement of time-dependent C P asymmetry in D 0 → h + h − decays and the first observation of mass difference between neutral charm-meson eigenstates. [ABSTRACT FROM AUTHOR]

We present a chiral K ¯ N interaction model that has been developed and optimized in order to account for the experimental data of inelastic K ¯ N reaction channels that open at higher energies. In particular, we study the effect of the higher partial waves, which originate directly from the chiral Lagrangian, as they could supersede the role of high-spin resonances employed in earlier phenomenological models to describe meson-baryon cross sections in the 2 GeV region. We present a detailed derivation of the partial wave amplitudes that emerge from the chiral SU(3) meson-baryon Lagrangian up to the d-waves and next-to-leading order in the chiral expansion. We implement a nonperturbative unitarization in coupled channels and optimize the model parameters to a large pool of experimental data in the relevant energy range where these new contributions are expected to be important. The obtained results are encouraging. They indicate the ability of the chiral higher partial waves to extend the description of the scattering data to higher energies and to account for structures in the reaction cross-sections that cannot be accommodated by theoretical models limited to the s-waves. [ABSTRACT FROM AUTHOR]

The charmonium-like exotic states Y (4230) and the less known Y (4320) , produced in e + e − collisions, are sources of positive parity exotic hadrons in association with photons or pseudoscalar mesons. We analyze the radiative and pion decay channels in the compact tetraquark scheme, with a method that proves to work equally well in the most studied D ∗ → γ / π + D decays. The decay of the vector Y into a pion and a Z c state requires a flip of charge conjugation and isospin that is described appropriately in the formalism used. Rates are found to depend on the fifth power of pion momentum, which would make the final states π Z c (4020) strongly suppressed with respect to π Z c (3900) . The agreement with BES III data would be improved considering the π Z c (4020) events to be fed by the tail of the Y (4320) resonance under the Y (4230) . These results should renovate the interest in further clarifying the emerging experimental picture in this mass region. [ABSTRACT FROM AUTHOR]

We present a quantum algorithm for simulation of quantum field theory in the light-front formulation and demonstrate how existing quantum devices can be used to study the structure of bound states in relativistic nuclear physics. Specifically, we apply the Variational Quantum Eigensolver algorithm to find the ground state of the light-front Hamiltonian obtained within the Basis Light-Front Quantization (BLFQ) framework. The BLFQ formulation of quantum field theory allows one to readily import techniques developed for digital quantum simulation of quantum chemistry. This provides a method that can be scaled up to simulation of full, relativistic quantum field theories in the quantum advantage regime. As an illustration, we calculate the mass, mass radius, decay constant, electromagnetic form factor, and charge radius of the pion on the IBM Vigo chip. This is the first time that the light-front approach to quantum field theory has been used to enable simulation of a real physical system on a quantum computer. [ABSTRACT FROM AUTHOR]

Heavy hadron spectroscopy was well understood within the naive quark model until the end of the past century. However, in 2003, the X (3872) was discovered, with puzzling properties difficult to understand in the simple naive quark model picture. This state made clear that excited states of heavy mesons should be coupled to two-meson states in order to understand not only the masses but, in some cases, unexpected decay properties. In this work, we will give an overview of a way in which the naive quark model can be complemented with the coupling to two hadron thresholds. This program has been already applied to the heavy meson spectrum with the chiral quark model, and we show some examples where thresholds are of special relevance. [ABSTRACT FROM AUTHOR]

The neutral kaon system is a very peculiar system that offers unique possibilities to perform precise tests of the CPT symmetry. The entanglement of neutral kaon pairs that are produced at a ϕ -factory opens up new ways and scenarios in order to test this fundamental discrete symmetry. In this paper, the results of the most recent and significant CPT tests are reviewed. Experiments have set stringent limits on the CPT-violating parameters of different phenomenological models, some of them associated to possible decoherence mechanisms or Lorentz symmetry violation which might be justified in a quantum gravity framework. The present results show no violation of CPT symmetry, while their accuracy in some cases reaches the interesting level at which–in the most optimistic scenarios–quantum gravity effects might show up. [ABSTRACT FROM AUTHOR]

We analyze the structure of excited states of new heavy hadrons in the scenario with hadronic dark matter. Fine mass-splitting in a doublet of new mesons stipulates the existence of charged metastable heavy mesons. We describe the structure of new meson excited states in the framework of the heavy quark effective theory. Phenomenological consequences of fine and hyperfine splitting are considered in the hadronic dark matter scenario and beyond. [ABSTRACT FROM AUTHOR]

The rank-3 antisymmetric tensors which are the magnetic monopoles of SU(N) Yang–Mills gauge theory dynamics, unlike their counterparts in Maxwell's U(1) electrodynamics, are non-vanishing, and do permit a net flux of Yang–Mills analogs to the magnetic field through closed spatial surfaces. When electric source currents of the same Yang–Mills dynamics are inverted and their fermions inserted into these Yang–Mills monopoles to create a system, this system in its unperturbed state contains exactly three fermions due to the monopole rank-3 and its three additive field strength gradient terms in covariant form. So to ensure that every fermion in this system occupies an exclusive quantum state, the Exclusion Principle is used to place each of the three fermions into the fundamental representation of the simple gauge group with an SU(3) symmetry. After the symmetry of the monopole is broken to make this system indivisible, the gauge bosons inside the monopole become massless, the SU(3) color symmetry of the fermions becomes exact, and a propagator is established for each fermion. The monopoles then have the same antisymmetric color singlet wavefunction as a baryon, and the field quanta of the magnetic fields fluxing through the monopole surface have the same symmetric color singlet wavefunction as a meson. Consequently, we are able to identify these fermions with colored quarks, the gauge bosons with gluons, the magnetic monopoles with baryons, and the fluxing entities with mesons, while establishing that the quarks and gluons remain confined and identifying the symmetry breaking with hadronization. Analytic tools developed along the way are then used to fill the Yang–Mills mass gap. [ABSTRACT FROM AUTHOR]

The two-pole structure refers to the fact that particular single states in the spectrum as listed in the PDG tables are often two states. The story began with the Λ (1405) , when in 2001, using unitarized chiral perturbation theory, it was observed that there are two poles in the complex plane, one close to the K ¯ p and the other close to the π Σ threshold. This was later understood combining the SU(3) limit and group-theoretical arguments. Different unitarization approaches that all lead to the two-pole structure have been considered in the mean time, showing some spread in the pole positions. This fact is now part of the PDG book, although it is not yet listed in the summary tables. Here, I discuss the open ends and critically review approaches that cannot deal with this issue. In the meson sector, some excited charm mesons are good candidates for such a two-pole structure. Next, I consider in detail the D 0 * (2300) , which is another candidate for this scenario. Combining lattice QCD with chiral unitary approaches in the finite volume, the precise data of the Hadron Spectrum Collaboration for coupled-channel D π , D η , D s K ¯ scattering in the isospin I = 1 / 2 channel indeed reveal its two-pole structure. Further states in the heavy meson sector with I = 1 / 2 exhibiting this phenomenon are predicted, especially in the beauty meson sector. I also discuss the relation of these two-pole structures and the possible molecular nature of the states under consideration. [ABSTRACT FROM AUTHOR]

We analyze the low-energy Lagrangian of hadronic dark matter interaction with nucleons and leptons. The analysis was fulfilled within the framework of the effective meson-exchange model, which is based on dynamic realization of SU(3)-symmetry. Using this Lagrangian, we calculate the cross-section of low-energy scattering of nucleons on hadronic dark matter particles. Effective vertex of W-boson interaction with new hadrons is constructed and the cross-section of lepton scattering on dark matter particles is calculated. [ABSTRACT FROM AUTHOR]

We explore the phase diagram and the modification of mesonic observables in a hot and dense medium using the (2 + 1) Polyakov-Nambu-Jona-Lasinio model. We present the phase diagram in the ( T , μ B) -plane, with its isentropic trajectories, paying special attention to the chiral critical end point (CEP). Chiral and deconfinement transitions are examined. The modifications of mesonic observables in the medium are explored as a tool to analyze the effective restoration of chiral symmetry for different regions of the phase diagram. It is shown that the meson masses, namely that of the kaons, change abruptly near the CEP, which can be relevant for its experimental search. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the departure from equilibrium in two specific types of thermal plasmas. The first type deals with the plasma produced during the atmospheric entry of a spatial vehicle in the upper layers of an atmosphere, specifically the one of Mars. The second type concerns the plasma produced during the laser-matter interaction above the breakdown threshold on a metallic sample. We successively describe the situation and give the way along which modeling tools are elaborated by avoiding any assumption on the thermochemical equilibrium. The key of the approach is to consider the excited states of the different species as independent species. Therefore, they obey to conservation equations involving collisional-radiative contributions related to the other excited states. These contributions are in part due to the influence of electrons and heavy particles having a different translation temperature. This 'state-to-state' approach then enables the verification of the excitation equilibrium by analyzing Boltzmann plots. This approach leads finally to a thorough analysis of the progressive coupling until the equilibrium asymptotically observed. [ABSTRACT FROM AUTHOR]