Search

In this note we study the tensor and vector exchange contributions to the elastic reactions involving the pseudoscalars mesons π + π - , K + K - and D + D - . In the case of the tensor-exchange contributions we assume that an intermediate tensor f 2 (1270) is dynamically generated from the interaction of two virtual ρ mesons, with the use of a pole approximation. The calculation of the two-loop amplitude is facilitated since the triangle loops can be factorized and computed separately. The results show very small contributions coming from the tensor-exchange mechanisms when compared with those from the vector-exchange processes. We compare our results for π π and K K ¯ scattering with those obtained in other works where the f 2 (1270) is considered as an ordinary q q ¯ meson. Our picture provides a smaller contribution but of similar order of magnitude for pion scattering and stabilizes the results in the case of K K ¯ , allowing us to make estimates for D D ¯ scattering. [ABSTRACT FROM AUTHOR]

There are two stages in the process of low-temperature nuclear fusion. The first stage corresponds to the bringing together of nuclei due to attraction to the negative charge in the internuclear space. This charge is formed by massive electron pairs located in a circular orbit. According to hadronic mechanics, the attraction of electrons (with opposite spins) is ensured by contact interaction. The second stage corresponds to the exchange of nuclei by pions, which begins when the nuclei approach each other to a distance equal to the strong interaction radius Rs, To estimate the maximum value of Rs*, the concepts of hadron mechanics about the πn0 - meson as a bound electron - positron (e- e 1+ pair are used. The main attention is paid to the visual interpretation of the electromagnetic interaction (e- e+) - pairs with nuclei, promoting the attraction of nuclei. [ABSTRACT FROM AUTHOR]

We present a symmetry-preserving scheme to derive the pion and kaon generalized parton distributions (GPDs) in Euclidean space. The key to maintaining crucial symmetries under this approach is the treatment of the scattering amplitude, such that it contains both the traditional leading-order piece and the scalar/vector pole contributions automatically, the latter being necessary to ensure the soft-pion theorem. The GPD is extracted analytically via the uniqueness and definition of the Mellin moments and we find that it naturally matches the double distribution representation; consequently, the polynomiality condition and sum rules are satisfied. The present scheme thus paves the way for the extraction of the GPD in Euclidean space using the Dyson-Schwinger equation framework or similar continuum approaches. [ABSTRACT FROM AUTHOR]

A unified set of predictions for pion and kaon elastic electromagnetic and gravitational form factors is obtained using a symmetry-preserving truncation of each relevant quantum field equation. A key part of the study is a description of salient aspects of the dressed graviton + quark vertices. The calculations reveal that each meson's mass radius is smaller than its charge radius, matching available empirical inferences; and meson core pressures are commensurate with those in neutron stars. The analysis described herein paves the way for a direct calculation of nucleon gravitational form factors. [ABSTRACT FROM AUTHOR]

In light of the contribution of the states with isospin in the difference of the amplitudes of the processes and being very small, the dispersion sum rules for the difference between the dipole polarizabilities of the charged and neutral pions are analyzed as a function of the meson's parameters. Using the value of the chiral theory of perturbations for , is found for the meson parameter within the region MeV, MeV, keV. Estimated optimum value of decay width yields keV. [ABSTRACT FROM AUTHOR]

The invariant differential cross sections of inclusive and mesons were measured at midrapidity in pp collisions at TeV and in p–Pb collisions at TeV in a wide transverse momentum () range with the ALICE experiment. The unprecedented large range up to 200 GeV/ for mesons was achieved by combining various analysis techniques as well as triggers involving the Electromagnetic Calorimeter (EMCal) and the Photon Spectrometer (PHOS). A method to reconstruct properly merged clusters of high neutral pions, originally developed for EMCal, was implemented in PHOS and its results are discussed for the first time in this paper. The obtained cross sections provide strong constraints on parton distributions and fragmentation functions for light mesons, and can be used to further improve the theoretical descriptions of hadron production. The first multiplicity study of light-neutral meson production in pp collisions at TeV shows modification of light-neutral meson yields. The nuclear modification factors, recently measured in p–Pb collisions at TeV for high , are consistent with unity, providing no evidences of parton energy loss in small colliding systems. [ABSTRACT FROM AUTHOR]

We study the properties of pseudoscalar mesons, pion, kaon, η and η ′ , and compute the γ ∗ γ → π 0 , η , η ′ transition form factor in the framework of the Schwinger–Dyson equations and Bethe–Salpeter equations, using a momentum independent contact interaction. The contact interaction is capable to describe the observable properties, but produces a transition form factor whose evolution for large Q 2 disagrees with experiment and perturbative QCD. Invited contribution to a Special Issue of Few Body Systems: "Emergence and Structure of Baryons—Selected Contributions from the International Conference Baryons 2022" [ABSTRACT FROM AUTHOR]

We calculated transitions of the higher radial excited charmonia ψ (n S) (n = 3 , 4 , 5) to the orbital excited charmonium h c (1 P) with emission of one pion or eta meson. In calculations, the intermediate S- and P-wave charmed meson loops were considered in terms of the nonrelativistic effective field theory. The results indicate that the transitions of interest are dominated by the loops involving the s l P = (1 / 2) + charmed mesons, whereas the s l P = (1 / 2) - charmed meson loops are of minor contributions. The partial decay widths of ψ (n S) → h c π 0 are of the order of 0.01–1 keV. For the case of ψ (n S) → h c η , the partial decay widths are from 0.1 to 100 keV, implying the branching ratios from 10 - 5 to 10 - 3 . Moreover, the partial decay widths for ψ (n S) → h c η are found to decrease as the η - η ′ mixing angle increases. It is hoped that the present calculated results would be observed in the future experiments. [ABSTRACT FROM AUTHOR]

Multi-particle states with additional pions are expected to result in a difficult-to-control excited-state contamination in lattice simulations. We show that heavy meson chiral perturbation theory can be employed to estimate the contamination due to two-particle B π states in various B-meson observables, like the B-meson decay constant and the B ∗ B π coupling. We work in the static limit and to next-to-leading order in the chiral expansion, i.e. including O (p). The B π states are found to typically lead to an overestimation of the observables at the few percent level. We determine two of the LECs from B → π form factor computations of the KEK group (Colquhoun et al. in Phys. Rev. D 106:054502, 2022) and discuss ways to determine the others. In particular, one LEC which is associated with smeared interpolating fields seems to be easily accessible and thus opens up a way to systematically study the effect of smearing on excited-state effects. [ABSTRACT FROM AUTHOR]

We present a method to compute the responses of meson screening masses to the chemical potential by Taylor expanding the correlator using lattice QCD simulation. We start by comparing the free theory lattice results with the analytical expression. Then, using symmetry arguments, we obtain an expression for the correlator in a series of the chemical potential at finite temperature. Using this, we obtain the lowest order correction to the screening mass at a finite chemical potential for temperatures around 2.5 GeV. Our lattice analysis is limited to isoscalar chemical potential for the pseudoscalar channel. The calculations were performed using (2+1)-flavors of the Highly Improved Staggered Quark (HISQ/tree) action, with the ratio of the strange quark mass to the light quark mass ms/mℓ = 20 corresponding to pion masses of 160 MeV. [ABSTRACT FROM AUTHOR]

We study the pion electromagnetic form factor in the modulus squared dispersion relation, and do the model independent extraction of the chiral mass embedded in the sub-leading twist light-cone distribution amplitude. The motivation of this work is the recent measurement of timelike form factor in the resonant regions, which makes up the piece lacking solid QCD-based calculation. With the perturbative QCD calculation up to next-to-leading-order of strong coupling and twist four level of meson distribution amplitudes, we obtain the chiral mass of pion meson as m 0 π (1 GeV) = 1. 31 - 0.30 + 0.27 GeV . Due to the chiral enhancement contribution from the sub-leading twist distribution amplitudes in the perturbative QCD calculation, we can not extract the lowest Gegenbauer moments of pion from the study of electromagnetic form factor. This problem could be settled down with the foresee Belle-II and BESIII measurement of the transition form factor especially in the large momentum transfers regions. [ABSTRACT FROM AUTHOR]

The simple analytic structure of meson scattering amplitudes in the large-Nc limit, combined with positivity of the spectral density, provides precise predictions on low-energy observables. Building upon previous studies, we explore the allowed regions of chiral Lagrangian parameters and meson couplings to pions. We reveal a structure of kinks at all orders in the chiral expansion and develop analytical tools to show that kinks always correspond to amplitudes with a single light pole. We build (scalar- and vector-less) deformations of the Lovelace-Shapiro and Coon UV-complete amplitudes, and show that they lie close to the boundaries. Moreover, constraints from crossing-symmetry imply that meson couplings to pions become smaller as their spin increases, providing an explanation for the success of Vector Meson Dominance and holographic QCD. We study how these conclusions depend on assumptions about the high-energy behavior of amplitudes. Finally, we emphasize the complementarity between our results and Lattice computations in the exploration of large-Nc QCD. [ABSTRACT FROM AUTHOR]

We study the interactions of systems of two and three nondegenerate mesons composed of pions and kaons at maximal isospin using lattice QCD, specifically π+K+, π+π+K+ and K+K+π+. Utilizing the stochastic LapH method, we determine the spectrum of these systems on two CLS Nf = 2 + 1 ensembles with pion masses of 200 MeV and 340 MeV, and include many levels in different momentum frames. We constrain the K matrices describing two- and three-particle interactions by fitting the spectrum to the results predicted by the finite-volume formalism, including up to p waves. This requires also results for the π+π+ and K+K+ spectrum, which have been obtained previously on the same configurations. We explore different fitting strategies, comparing fits to energy shifts with fits to energies boosted to the rest frame, and also comparing simultaneous global fits to all relevant two- and three-particle channels to those where we first fit two-particle channels and then add in the three-particle information. We provide the first determination of the three-particle K matrix in π+π+K+ and K+K+π+ systems, finding statistically significant nonzero results in most cases. We include s and p waves in the K matrix for π+K+ scattering, finding evidence for an attractive p-wave scattering length. We compare our results to Chiral Perturbation Theory, including an investigation of the impact of discretization errors, for which we provide the leading order predictions obtained using Wilson Chiral Perturbation Theory. [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]

We apply the nuclear model with explicit mesons to photoproduction of neutral pions off protons at the threshold. In this model the nucleons do not interact with each other via a potential but rather emit and absorb mesons that are treated explicitly on equal footing with the nucleons. We calculate the total cross section of the reaction for energies close to threshold and compare the calculations with available experimental data. We show that the model is able to reproduce the experimental data and determine the range of the parameters where the model is compatible with the experiment. [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]

The vector U‐bosons, or so‐called "dark photons," are one of the possible candidates for the dark matter mediators. They are supposed to interact with the standard matter via a "vector portal" due to the U(1)−U(1)′$$ U(1)-U{(1)}^{\prime } $$ symmetry group mixing which might make them visible in particle and heavy‐ion experiments. While there is no confirmed observation of dark photons, the detailed analysis of different experimental data allows us to estimate the upper limit for the kinetic mixing parameter ϵ2$$ {\epsilon}^2 $$ depending on the mass MU$$ {M}_U $$ of U‐bosons which is also unknown. We have introduced a procedure to define theoretical constraints on the upper limit of ϵ2MU$$ {\epsilon}^2\left({M}_U\right) $$ from heavy‐ion (as well as p + p and p+A$$ p+A $$) dilepton data. Our analysis is based on the microscopic Parton‐Hadron‐String Dynamics transport approach where we incorporated the decay of hypothetical U‐bosons to dileptons, U→e+e−$$ U\to {e}^{+}{e}^{-} $$, where the U‐bosons themselves are produced by the Dalitz decay of pions π0→γU$$ {\pi}^0\to \gamma U $$, η‐mesons η→γU$$ \eta \to \gamma U $$, and Delta resonances Δ→NU$$ \Delta \to NU $$. The extension of our procedure to other dark matter candidates is foreseen. [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 influence of leptophilic dark matter interactions on decays of muons and ground state mesons in existing experiments. We consider a secluded dark sector exclusively interacting with leptons via either a (leptophilic) scalar or vector mediator. These interactions will therefore influence leptonic decays and deform the energy spectra. We first study the Michel decay of muons, μ + → e + ν e ν ¯ μ , which allow us to constrain the parameter space reasonably well. Secondly, the rare π ± , K ± , D ± and D s ± decays to e ν will be considered. Scalar mediators would remove the Standard Model helicity suppression, so that strong constraints can be derived. The resulting bounds on the couplings of the light mediators to electrons and muons still turn out to be somewhat weaker than those from searches at low-energy e + e - colliders and the magnetic moment of the muon, respectively. Finally, we show that kaon and pion decays basically exclude a "Co-SIMP" scenario where a scalar dark matter particle has a dimension-5 coupling to electrons. [ABSTRACT FROM AUTHOR]

Using a symmetry-preserving truncation of the quantum field equations describing hadron properties, parameter-free predictions are delivered for pion and kaon elastic electromagnetic form factors, F P = π , K , thereby unifying them with kindred results for nucleon elastic electromagnetic form factors. Regarding positive-charge states, the analysis stresses that the presence of scaling violations in QCD entails that Q 2 F P (Q 2) should exhibit a single maximum on Q 2 > 0. Locating such a maximum is both necessary and sufficient to establish the existence of scaling violations. The study predicts that, for charged π , K mesons, the Q 2 F P (Q 2) maximum lies in the neighbourhood Q 2 ≃ 5 GeV2. Foreseeable experiments will test these predictions and, providing their Q 2 reach meets expectations, potentially also provide details on the momentum dependence of meson form factor scaling violation. [ABSTRACT FROM AUTHOR]

The temperature behavior of the pion width in the hadronic phase is investigated in the framework of the Nambu–Jona–Lasinio (NJL) model. The contribution to the width from the pion–pion collision is considered with a scalar sigma-meson as an intermediate state. It is shown that the pion width significantly broadens at T > 0. 1 GeV. Using the two-step iteration method, suggested by Kadanoff and Baym, the pion spectral function in a hot pion gas is calculated at different temperatures. [ABSTRACT FROM AUTHOR]

A method for reconstructing spectra of short-range charged particles in experimental investigations of stopped-pion absorption by nuclei is described. This approach is based on the use of a monitor system, which consists of two Si detectors, and a "live" target, which is also a Si detector. By simultaneously analyzing data from the monitor detectors and the live target, it is possible to determine the depth at which a pion stops inside the target. It is shown that the use of the presented "aiming" method with targets ∼0.1 g/cm2 thick makes it possible to correctly reconstruct the energy spectra of 3He and 4He isotopes in the energy range of 16−35 MeV. [ABSTRACT FROM AUTHOR]

We compute the hadronic light-by-light scattering contribution to the muon g - 2 from the charm quark using lattice QCD. The calculation is performed on ensembles generated with dynamical (u, d, s) quarks at the SU(3) f symmetric point with degenerate pion and kaon masses of around 415 MeV. It includes the connected charm contribution, as well as the leading disconnected Wick contraction, involving the correlation between a charm and a light-quark loop. Cutoff effects turn out to be sizeable, which leads us to use lighter-than-physical charm masses, to employ a broad range of lattice spacings reaching down to 0.039 fm and to perform a combined charm-mass and continuum extrapolation. We use the η c meson to define the physical charm-mass point and obtain a final value of a μ HLbL , c = (2.8 ± 0.5) × 10 - 11 , whose uncertainty is dominated by the systematics of the extrapolation. Our result is consistent with the estimate based on a simple charm-quark loop, whilst being free of any perturbative scheme dependence on the charm mass. The mixed charm–light disconnected contraction contributes a small negative amount to the final value. [ABSTRACT FROM AUTHOR]

The inclusive spectra of pions and kaons produced in BeBe collisions as functions of their transverse momentum p T at mid-rapidity are calculated within the approach, which is based on the assumption of the similarity of inclusive spectra of hadrons produced in AA collisions at their small transverse momenta in the mid-rapidity region. The essence of the modification of the self-similarity approach consists in the inclusion of a quark-gluon dynamics in hadron production in nucleon–nucleon interaction at mid-rapidity. We focus mainly on the ratio of cross-sections of K ± to π ± mesons produced in BeBe collisions as a function of s . A fast rise of this ratio, when the initial energy increases starting from the kaon production threshold up to s ≃ 20–30 GeV, is revealed together with its very slow increase up to LHC energies. The energy dependence of this ratio is due to the conservation laws of four-momenta and quantum numbers of the initial and produced hadrons and the Regge asymptotic behavior of the total and inelastic cross-sections of nucleon–nucleon collisions at large initial energies The satisfactory description of NA61/SHINE data on these ratios is demonstrated. Some predictions for RHIC and LHC on the K + / π + and K - / π - yield ratios as functions of s in BeBe collisions as functions of s are presented. The similarity of these observables to the ones for pp collisions at mid-rapidity and in the wide range of initial energies is illustrated. [ABSTRACT FROM AUTHOR]

The Nambuâ€"Jonaâ€"Lasinio model is considered with flavor-dependent coupling constants G i j ( ψ ÂŻ λ i ψ) ( ψ ÂŻ λ j ψ) + ( ψ ÂŻ i Îł 5 λ i ψ) ( ψ ÂŻ i Îł 5 λ j ψ) for i , j = 0 , 1 … N f 2 âˆ' 1 , and N f = 3. A self-consistent calculation of quark effective masses and coupling constants is performed, making the strange quark effective mass vary considerably. Quantum mechanical mixings between up, down and strange constituent quarks yield a strangeness content (s-content) of the light u and d quark constituent and of the pion. Different types of estimates for the strangeness contribution for the pion mass are provided. Mixing-type interactions, G i ≠j , induce light meson mixings, and estimates for the Ď€ 0 âˆ' η and η âˆ' η ′ mixings are provided. The η âˆ' Ď€ 0 mixing is argued to be an indication of the s-content of the pion. [ABSTRACT FROM AUTHOR]

We have identified the decay modes of the D s + → π + K ∗ + K ∗ - , π + K ∗ 0 K ¯ ∗ 0 reactions producing a pion and two vector mesons. The posterior vector–vector interaction generates two resonances that we associate to the f 0 (1710) and the a 0 (1710) recently claimed, and they decay to the observed K + K - or K S 0 K S 0 pair, leading to the reactions D s + → π + K + K - , π + K S 0 K S 0 . The results depend on two parameters related to external and internal emission. We determine a narrow region of the parameters consistent with the large N c limit within uncertainties which gives rise to decay widths in agreement with experiment. With this scenario we make predictions for the branching ratio of the a 0 (1710) contribution to the D s + → π 0 K + K S 0 reaction, finding values within the range of (1.3 ± 0.4) × 10 - 3 . Comparison of these predictions with coming experimental results on that latter reaction will be most useful to deepen our understanding on the nature of these two resonances. [ABSTRACT FROM AUTHOR]

[Display omitted] In a recent measurement LHCb reported pronounced structures in the J / ψ J / ψ spectrum. One of the various possible explanations of those is that they emerge from non-perturbative interactions of vector charmonia. It is thus important to understand whether it is possible to form a bound state of two charmonia interacting through the exchange of gluons, which hadronise into two pions at the longest distance. In this paper, we demonstrate that, given our current understanding of hadron-hadron interactions, the exchange of correlated light mesons (pions and kaons) is able to provide sizeable attraction to the di- J / ψ system, and it is possible for two J / ψ mesons to form a bound state. As a side result we find from an analysis of the data for the ψ (2 S) → J / ψ π π transition including both π π and K K ¯ final state interactions an improved value for the ψ (2 S) → J / ψ transition chromo-electric polarisability: | α ψ (2 S) J / ψ | = (1.8 ± 0.1) GeV - 3 , where the uncertainty also includes the one induced by the final state interactions. [ABSTRACT FROM AUTHOR]

Theoretical models of the neutrino-induced meson production reaction are reviewed. The formulation of various approaches to the neutrino reactions in the resonance region is briefly discussed. The total cross-section, the distribution of charged lepton and pion are examined using the dynamical coupled channel (DCC) model. Possible test of the models of axial vector current in the resonance region is discussed. [ABSTRACT FROM AUTHOR]

We study the problem of π production in heavy-ion collisions in the context of the isospin-dependent Boltzmann–Uehling–Uhlenbeck transport model. We generated nucleon densities using two different models, the Skyrme–Hartree–Fock (SHF) model and the configuration interaction shell model (SM). Indeed, inter-nucleon correlations are explicitly taken into account in SM, while they are averaged in the SHF model. As an application of our theoretical frameworks, we calculated the π − and π + yields in collisions of nuclei with A = 30–40 nucleons. We used different harmonic oscillator lengths b HO to generate the harmonic oscillator basis for SM in order to study both theoretical and experimental cases. It is found that the SM framework with b HO = 2.5 fm and SHF can be distinguished by the yield of π mesons, in this case the density distribution calculated by the SM produces more π in the collision. In comparison, SM with b HO = 2.0 fm is distinguished from SHF by the double π −/ π + ratios with different large impact parameters, from which one can find that the double π −/ π + ratios of SM change smoother and are less than those of SHF. [ABSTRACT FROM AUTHOR]

Two-particle Azimuthal correlations are measured with the ALICE apparatus in pp collisions at s = 13 TeV to explore strangeness- and multiplicity-related effects in the fragmentation of jets and the transition regime between bulk and hard production, probed with the condition that a strange meson ( K S 0 ) or baryon (Λ ) with transverse momentum p T > 3 GeV/ c is produced. Azimuthal correlations between kaons or Λ hyperons with other hadrons are presented at midrapidity for a broad range of the trigger ( 3 < p T trigg < 20 GeV/ c ) and associated particle p T (1 GeV/ c < p T assoc < p T trigg ), for minimum-bias events and as a function of the event multiplicity. The near- and away-side peak yields are compared for the case of either K S 0 or Λ ( Λ ¯ ) being the trigger particle with that of inclusive hadrons (a sample dominated by pions). In addition, the measurements are compared with predictions from PYTHIA 8 and EPOS LHC event generators. [ABSTRACT FROM AUTHOR]

Pions make up a large part of the hadronic environment typical of accelerator mixed fields. Characterizing device cross sections against pions is usually disregarded in favor of tests with protons, whose single-event latch-up (SEL) cross section is, nonetheless, experimentally found to be lower than that of pions for all energies below 250 MeV. While Monte Carlo simulations are capable of reproducing such behavior, the reason for the observed pion cross-section enhancement can only be explained by a deeper analysis of the underlying mechanisms dominating proton–silicon and pion–silicon reactions. The mechanisms dominating the SEL response are found to vary with the energy under consideration. While a higher pion nuclear reaction rate, that is, probability of interaction, can explain the observed latch-up cross-section enhancement at energies >100 MeV, it is the volume-equivalent linear energy transfer (LETEQ) of the secondary ions that keeps the pion latch-up response high at lower energies. The higher LETEQ of secondary ions from pion–silicon interactions is caused by the pion absorption mechanism, which is highly exothermic. In spite of the observed higher cross section for pions, the high-energy hadron approximation is found to still provide reliable estimations of the latch-up response of a device in mixed fields. [ABSTRACT FROM AUTHOR]

Following the recent measurement of several hadron yields by NA61/SHINE collaboration, the unified set of yields of particles produced in proton–proton collisions at = 17.3 GeV (laboratory beam momentum 158 GeV/c) is evaluated, combining the results of the NA49 and NA61/SHINE collaborations at the CERN SPS. With the statistical hadronization code Thermal-Fist we confirm the unacceptably high value of χ2, both in the canonical and grand canonical—strangeness canonical approach, and the common volume for all the hadrons. The use of the energy-dependent width of the Breit–Wigner parametrization for the mass distributions of unstable particles improves the quality of the description of particle yields only slightly. We confirm the observation that exclusion of the ϕ meson yield makes the fit result more reasonable. The complete experimental data set of particle yields can be also reasonably fitted if the canonical volumes of hadrons without and with open strangeness are allowed to vary independently. The canonical volume of strangeness was found to be larger than that for non-strange hadrons. The femtoscopy measurements with kaon pairs and pion pairs at 27.4, 63 and 900 GeV are not precise enough to confirm or reject this observation. The model with the best-fit parameters allows to predict the yields of several not yet measured particles emitted from p + p at = 17.3 GeV. [ABSTRACT FROM AUTHOR]

A description of a procedure for selecting events during the absorption of stopped pions in thin targets is presented. This approach is based on the use of two monitor Si-detectors and a "live" target, which is also an Si-detector, as the last layers of the moderator. Setting the thresholds on monitor detectors and analyzing signals from a "live" target allow one to select pions with a residual range corresponding to the target thickness and reliably exclude the background from stops in the monitor system. It is shown that this method provides an efficiency of identifying stopped π–-mesons of 90%. [ABSTRACT FROM AUTHOR]

The questions of how the bulk of the Universe's visible mass emerges and how it is manifest in the existence and properties of hadrons are profound, and probe the heart of strongly interacting matter. Paradoxically, the lightest pseudoscalar mesons appear to be key to a further understanding of the emergent mass and structure mechanisms. These mesons, namely, the pion and kaon, are the Nambu–Goldstone boson modes of quantum chromodynamics (QCD). Unravelling their partonic structure and the interplay between emergent and Higgs-boson mass mechanisms is a common goal of three interdependent approaches—continuum QCD phenomenology, lattice-regularised QCD, and the global analysis of parton distributions—linked to experimental measurements of hadron structure. Experimentally, the anticipated electron–ion collider will enable a revolution in our ability to study pion and kaon structures, accessed by scattering from the 'meson cloud' of the proton through the Sullivan process. With the goal of enabling a suite of measurements that can address these questions, we examine key reactions that identify the critical detector-system requirements needed to map tagged pion and kaon cross-sections over a wide range of kinematics. The excellent prospects for extracting pion structural, functional, and form-factor data are outlined, and similar prospects for kaon structures are discussed in the context of a worldwide programme. The successful completion of the programme outlined herein will deliver deep, far-reaching insights into the emergence of pions and kaons, their properties, and their role as QCD's Goldstone boson modes. [ABSTRACT FROM AUTHOR]

We propose a simple classical electrodynamics model in which a Lorentz pseudoscalar field and a Dirac field are present in the general Lagrangian of the system. The model is constructed by allowing explicit violation of chiral symmetry. This approach is intended to predict possible electromagnetic decays of the neutral pion in effective terms. [ABSTRACT FROM AUTHOR]