Narrow Results

Scale factor matrices relating mesonic fields in chiral Lagrangians and quark-level operators of QCD sum-rules are shown to be constrained by chiral symmetry, resulting in universal scale factors for each chiral nonet. Built upon this interplay between chiral Lagrangians and QCD sum-rules, the scale factors relating the $a_0$ isotriplet scalar mesons to their underlying composite quark fields were recently determined. It is shown that the same technique when applied to $K_0^{\ast }$ isodoublet scalars reproduces the same scale factors, confirming the universality property and further validating this connection between chiral Lagrangians and QCD sum-rules, which can have nontrivial impacts on our understanding of the low-energy QCD, in general, and the physics of scalar mesons in particular.

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.

I give a short description of some recent developments in hadron spin physics focussing on the concept of Generalized Parton Distributions and the role of lattice-QCD-calculations.

Unlike some models whose relevance to Nature is still a big question mark, Quantum Chromodynamics (QCD) will stay with us forever. QCD, born in 1973, is a very rich theory supposed to describe the widest range of strong interaction phenomena: from nuclear physics to Regge behavior at large E, from color confinement to quark–gluon matter at high densities/temperatures (neutron stars); the vast horizons of the hadronic world: chiral dynamics, glueballs, exotics, light and heavy quarkonia and mixtures thereof, exclusive and inclusive phenomena, interplay between strong forces and weak interactions, etc. Efforts aimed at solving the underlying theory, QCD, continue. In a remarkable entanglement, theoretical constructions of the 1970's and 1990's combine with today's ideas based on holographic description and strong–weak coupling duality, to provide new insights and a deeper understanding.

Excitation of the nucleon at low Q² and energies up to several GeV reveals clearly measurable structures that indicate the existance of resonances. A major goal of experiments carried out at the accelerator facility ELSA in Bonn/Germany is to explore this resonance structure, which gives valuable input to models describing the QCD structure of the nucleon. Resonance contributions for nuclear reaction channels, such as single pion, two pion and eta production from the experiments can be given using the Bonn-Gatchina partial wave analysis¹. The talk at the conference MESON 2008 in Krakow gave an overview of results from experiments at ELSA and plans for the near future.

The physics program of the Crystal Ball spectrometer at MAMI-C began in early 2007. Experiments utilize the upgraded electron accelerator that provides high intensity beams of circularly and linearly polarized real photons with maximum energy of 1.5 GeV. The highly segmented nearly 4π acceptance detection system consists of the Crystal Ball, particle identification detector and versatile endcap TAPS. A wide range of physics topics is under study including the production and decay of η, ω, and η' mesons, the investigation of coherent meson photoproduction on nuclei, measurements of polarization and double polarization observables in meson photoproduction on proton and neutron. The current status of the experiment and some preliminary results are reported.

The KLOE detector at the DA$\mathrm{\Phi }$NE $\varphi$-factory has been operating in two periods from 2001–2006 and from 2014–2018 collecting a large sample of $\varphi$-meson decays. This allowed to perform precision measurements and studies of fundamental symmetries, and searches of New Physics phenomena. In this overview, the results of KLOE and KLOE-2 Collaborations are presented. The most recent results from the KLOE experiment are discussed, covering: the measurement of the running fine-structure constant ${\alpha }_{\mathrm{\text{em}}}$, the Dalitz plot measurement of $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$, the search of a $U$ boson, tests of discrete symmetries and quantum decoherence.

In this paper, the mass spectra of mesons with one or two heavy quarks and their diquarks partners are estimated within a nonrelativistic framework by solving Schrödinger equation with an effective potential inspired by a symmetry preserving Poincaré covariant vector–vector contact interaction model of quantum chromodynamics. Matrix Numerov method is implemented for this purpose. In our survey of mesons with heavy quarks, we fix the model parameter to the masses of groundstates and then extend our calculations for radial excitations and diquarks. The potential model used in this work gives results which are in good agreement with experimental data and other theoretical calculations.

We study the applications of nonextensive Tsallis statistics to high energy and hadron physics. These applications include studies of $pp$ collisions, equation of state of QCD, as well as Bose–Einstein condensation. We also analyze the connections of Tsallis statistics with thermofractals, and address some of the conceptual aspects of the fractal approach, which are expressed in terms of the renormalization group equation and the self-energy corrections to the parton mass. We associate these well-known concepts with the origins of the fractal structure in the quantum field theory.

Dyson–Schwinger equations furnish a Poincaré covariant framework within which to study hadrons. A particular feature is the existence of a nonperturbative, symmetry preserving truncation that enables the proof of exact results. The gap equation reveals that dynamical chiral symmetry breaking is tied to the long-range behavior of the strong interaction, which is thereby constrained by observables, and the pion is precisely understood, and seen to exist simultaneously as a Goldstone mode and a bound state of strongly dressed quarks. The systematic error associated with the simplest truncation has been quantified, and it underpins a one-parameter model efficacious in describing an extensive body of mesonic phenomena. Incipient applications to baryons have brought successes and encountered challenges familiar from early studies of mesons, and promise a covariant field theory upon which to base an understanding of contemporary large momentum transfer data.

We sketch the basic ideas of the lattice regularization in Quantum Field Theory, the corresponding Monte Carlo simulations, and applications to Quantum Chromodynamics (QCD). This approach enables the numerical measurement of observables at the non-perturbative level. We comment on selected results, with a focus on hadron masses and the link to Chiral Perturbation Theory. At last, we address two outstanding issues: topological freezing and the sign problem.

The study of average characteristics of ${\pi }^{-}$-mesons in Helium–Carbon and Carbon–Carbon interactions at 4.2A GeV/c is presented. The average values of multiplicity, momentum and transverse momentum of ${\pi }^{-}$-mesons are analyzed as a function of the number of identified protons in an event. The latter is used to fix the centrality of collisions. The results are compared with Cascade model and modified Fritiof model. Some deviations of experimental data are observed than the models, which could be connected to collective interaction of inner nucleus nucleons.

Recent results of the BESIII experiment are presented, including the first observation of the M1 transition ψ(3686) → γη_c(2S), the measurement of J/ψ → 3γ, η_c decays into baryon anti-baryon pairs, the discovery of Z_c(3900), and the study of .

The most recent results from the KLOE experiment are presented, covering: the measurement of the running fine-structure constant ${\alpha }_{em}$, the Dalitz plot measurement of $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$, the search of a U boson, tests of discrete symmetries and quantum coherence. The KLOE-2 Collaboration will take data until mid 2018 aiming to collect 5 fb¹ increasing the data set, in order to produce new precision measurements and continue studies of fundamental symmetries and New Physics.

The ANDA experiment at the new FAIR facility at Darmstadt (Germany) will investigate antiproton collisions on proton and nuclear targets in the charm quark mass regime. The wide-range physics program requires a universal detector concept, combining state-of-the-art and novel techniques in particle measurements and data readout. This paper gives an overview of the detector setup and summarizes the status, in particular of the charged particle tracking detectors in the ANDA spectrometer.

As of the year 2018 the Facility for Antiproton and Ion Research (FAIR) will offer access to exotic ion beams and beams of antiproton of unprecedented luminosity. The facility currently under construction in Darmstadt, Germany, adjacent to the existing accelerator at the GSI Helmholtz Centre for Heavy-Ion Research, will serve several collaborations and fields simultaneously: atomic, hadron, nuclear, and plasma physics.