The ELSA electron accelerator at Bonn university, Germany, has a long record of contributions to hadron physics with electromagnetic probes, electrons up to 3.2 GeV beam energy and photons from bremsstrahlung conversion including polarization degrees of freedom. In particular, the experiments (currently the BGO-OD setup and CB- ELSA/TAPS) allow to measure across the baryon spectrum. An...
Nowadays, experimentally observed states that are often assigned to the light meson or charmonium sector might indicate an exotic nature. Such exotic particles include e.g. glueballs, hybrids, and tetraquarks. Not only do these states pose a theoretical challenge, but experimentally it is often difficult to distinguish exotic and non-exotic matter and to characterise their nature. In such...
In this contribution, I will present a brief review of the recent results that demonstrate that the study of particle production by photon - induced interactions at the Large Hadron Collider (LHC) can be used to improve our understanding about exotic systems as, e.g., tetraquarks and pentaquarks. In addition, prospects to investigate these particles in the future electron-ion collider (EIC)...
Hadronic final state interactions (FSI) play a major role in hadronic decays. They can generate new mechanisms for CP violation in $B\to 3h$ decays at low and high mass regions. We explained LHCb observation for CP violation in $D\to 2h$ as a FSI mechanism, contrary to QCD-based approaches that claim new physics. It is also needed to explain unexpected large branching fractions of some rare...
The COMPASS experiment has collected the largest data set of diffractively produced excitations using beams of pions and kaons at 190 GeV energy. The search for resonances and new phenomena among light hadrons has been carried out for decades by partial wave analyses. The large amount of data available and the availability of large computing power have allowed the development of new...
The last 20 years are being highlighted by theoretical and experimental endeavours towards understanding all possible hadronic structures allowed by QCD. Since the discovery of the exotic meson $X(3872)$ by the Belle Collaboration, a handful amount of other exotic hadrons with unexpected properties appeared in particle accelerations around the world. As for their elusive structure, one of the...
In this talk I discuss the formation of molecular resonances of three-hadrons. We solve Faddeev equations for three-meson systems or that of two-meson and one baryon. We find a special characteristics of the dynamics in such systems, which is a cancellation of the different amplitudes of three-body forces. I will show the results of some of our recent studies.
The production of fully - heavy tetraquark states in proton-proton ($pp$) and proton - nucleus ($pA$) collisions at the center-of-mass energies of the Large Hadron Collider (LHC) and at the Future Circular Collider (FCC) is investigated considering that these states are produced through the double parton scattering mechanism. We estimate the cross sections for the $T_{4c}$, $T_{4b}$ and...
In this work we show how to evaluate the $X(3872)$ to $\psi(2S)$ yield ratio $(NX/N \psi(2S))$ in $PbPb$ collisions, taking into account the interactions of the $\psi(2S)$ and $X(3872)$ states with light mesons in the hadron gas formed at the late stages of these collisions. We employ an effective Lagrangian approach to estimate the thermally-averaged cross sections for the production and...
Author: Bernhard Ketzer
The unambiguous detection of exotic non-qqbar states and their identification in terms of quark and gluonic degrees of freedom is one of the most ambitious goals of hadron spectroscopy. In the charm- and bottom-quark regime, many of the new $X, Y, Z$ states are believed to be of exotic nature, but until now the internal structure of almost all of them is still a matter...
In this talk I will make a short summary of the history of dibaryons, i.e. resonant states containing six quarks. Dibaryons are looked at sceptically (apart from the deuteron) because of the many states that have been predicted by theory and claimed in experiments that did not survive more careful investigations. I will give one example of an almost discovery and present a relatively recent...
Magnetic fields of a large intensity can be generated in peripheral high-energy heavy-ion collisions. Although the intensity drops down fast and, moreover, it is not clear whether the fields last long enough to induce a magnetization during the quark-gluon plasma phase, most of the models and simulations predict a significant intensity that lasts up to proper times of order 1 fm after the...
We estimate for the first time the bound-state energies and the corresponding coordinate space radial wave functions of $B_c$-nucleus systems using a momentum space calculation. We compare the bound-state energies obtained with and without the Coulomb potential, and discuss the interference effect of the strong (nuclear) potential in the Coulomb interaction.
Currently, the effect of strong magnetic fields on the QCD phase diagram in the ($T \times e B$) plane is well-established, thanks to extensive research using effective QCD models and lattice simulations. However, the situation is different when it comes to incorporating electric fields. Electric fields make the QCD action complex, making standard lattice simulations impractical. To tackle...
Recently, the quark anomalous magnetic moment (AMM) has been applied in the context of the two-flavor Nambu--Jona-Lasinio model to explore different aspects of the magnetized phase diagram of quantum chromodynamics. By means of the Schwinger ansatz, the quark AMM has been considered a new parameter, chosen to reproduce the proton and neutron magnetic moments. Then, in the mean field...
The LHCb experiment, focused on studying heavy-flavor hadrons, provides crucial insights into the quark binding mechanisms within hadrons and makes valuable contributions to understanding the non-perturbative regime of QCD. In this presentation, we highlight the latest results from LHCb on exotic hadron spectroscopy, with a particular focus on the diffractive production of these states.
In meson-photon collisions resonances may be formed, such as the $\rho(770)$ or $a_2(1320)$ for pions, and $K^*(892)$ when kaons collide with photons. For low collision energies, chiral dynamics governs the process, eventually leading to final states with additional mesons that do not come from resanace decays. The production of an additional pi0 is determined by the chiral anomaly, and its...
The GlueX Collaboration, based at Jefferson Lab, has collected a unique set of photon-proton collision data using linearly polarized photons in the 8-12 GeV energy range. This data set permits a study of the production dynamics of resonances and searches for new states, including hybrid mesons. I will present recent results on the production of established light mesons and the $J / \psi$ as...
In this talk, we explore the light-front wave functions of heavy quarkonia, , and mesons by deriving their leading Fock state components from the projections of Bethe-Salpeter wave functions onto the light front. We focus on computing the leading-twist time-reversal even transverse momentum distributions and parton distribution functions for these mesons.
In this seminar I will analyze the structure of the pion obtained from a dynamical model based on the solution of the Bethe-Salpeter equation in Minkowski space. The components of the Bethe-Salpeter amplitude are written in terms of the Nakanishi integral representation. The interaction kernel has massive quark and gluon propagators and an extended quark-gluon vertex. Within this model, we...
In recent times, the amount of data collected from high-energy experiments has increased continuously. In order to match this amount of data, significantly more Monte Carlo data is required as well. These simulations often take a long time and occupy a lot of computing power. For complex simulation steps, such as the simulation of electromagnetic calorimeters, neural networks can offer...
We study the nonabelian dipole problem in the context of a simple semiclassical approach which incorporates some essential features of the infrared sector of Yang-Mills theories in the Landau gauge, in particular, the fact that the running coupling remains of moderate size at infrared scales and gluons acquire a mass while ghosts remain massless. We obtain a simple flux-tube solution in a...
Over recent decades, the continuous increase of experimental data in high-energy physics applications has led to significant demand in computational resources. In particular, the time-consuming coupled channel analyses, which sometimes require fits with several hundred free parameters extending over several weeks, are an area where such optimization is of great value. To address this issue, we...
A careful study of the low-lying flavor-singlet meson spectrum using lattice QCD can help to better understand the nature of the current glueball candidates. We use light meson, charmonium, glueball and two-pion operators to map this spectrum and quantify the mixing between the different states. We increase the overlap with physical states by using highly improved mesonic and gluonic...
In this seminar we discuss how the heavy ion collisions (HICs) appear as a promising scenario to investigate the properties of the non-conventional hadronic states. In the sequence we present some of our contributions on this topic, focusing on how to distinguish the intrinsic nature of these exotic states from the relevant observables, such as their multiplicities and femtoscopic correlation...
We search for a $B$ decay mode where one can find a peak for a $D \bar{D}$ bound state predicted in effective theories and in Lattice QCD calculations, which has also been claimed from some reactions that show an accumulated strength in $D \bar{D}$ production at threshold. We find a good candidate in the $B^{+} \rightarrow K^{+} \eta \eta$ reaction, by looking at the $\eta \eta$ mass...
The Yang-Mills theory is revisited from the point of view of classical configurations starting from wave modes. This reveals a kind of classical solutions which reconstruct effective Klein-Gordon excitations, along with a new mass generation mechanism. The effective Klein-Gordon equation gives rise to a set of equations of motion whose solutions may exhibit a confined behavior. Furthermore,...
The spin-1 particles is an admirable two quarks bound state system to understand electromagnetic properties from hadronic states. These systems are generally relativistic, and therefore need an approach using quantum field theory. In the present work, we will use both the quantum field theory at the instant form, as well, quantum field theory on the light-front~(LFQFT). In general, it is used...
We present a partial-wave analysis of $\tau^{-} \rightarrow \pi^{-} \pi^{-} \pi^{+} \nu_\tau$ decays using the world's largest sample of these decays from the Belle experiment at KEK, Japan; and we discuss challenges of this analysis. We give preliminary results on light-meson resonances appearing in the $\pi^{-} \pi^{-} \pi^{+}$system, including $a_1(1420)$, and in the $\pi^{-}...
By considering a quark-antiquark interaction mediated by one (non perturbative) gluon exchange, standard techniques are applied to derive effective interactions between meson fields, that are arranged in $U\left(N_f\right)$ flavor multiplets, and constituent quark currents. A large quark mass (and / or gluon effective mass) expansion of the quark determinant leads to a wide variety of...
We summarize recent results for exotic mesons, i.e. glueballs and four-quark states, using functional methods. We explain the generation and present results for the spectrum of glueballs in pure Yang-Mills theory and discuss prospects for full QCD results. We furthermore discuss the spectrum and the internal structure of open flavour four-quark states in the charm and bottom energy region.
In this talk, we present recent results on the transversely-projected three- and four-gluon vertices. Our approach is based on the one-loop dressed Schwinger-Dyson equations derived from the nPI effective action. The key hypothesis in both cases is the planar degeneracy property of these vertices, which becomes apparent when the Bose symmetry of the vertices are properly exploited. The planar...
In this work we present a calculation of exotic charmonium production in ultra-peripheral collisions, in which the exotic state is explicitly treated as a meson molecule. Our formalism is general but we focus on the lightest possible exotic charmonium state: a $D^+D^−$ molecular bound state. It was proposed some time ago and it has been the object of experimental searches. Here we study the...
I will review the application of few-body methods to explore the structure of light hadrons in Minkowski space. The description of the nucleon is based on the solution of the Bethe-Salpeter equation in Minkowski space built with phenomenological kernels. In particular, it will be presented a quantitative exploration of the proton properties obtained by solving the projected...
In recent years, significant efforts have been developed to formulate and solve the Bethe-Salpeter and Dyson-Schwinger equations (DSE) directly in Minkowski space, in contrast to the usual procedure of formulation in the Euclidean space and subsequent extension to Minkowski space, which is the approach used in lattice gauge theories. In this talk, the solution for the Dyson-Schwinger equation...
There is a great interest in magnetized hadronic matter due to the intense magnetic fields reported by experiments in heavy-ion collisions and also present in compact stars. We review some results obtained with modified NJL models, like condensates, meson masses, magnetization and other thermodynamic quantities.
In this work we study the influence of proton and lead structures in charmed mesons production. We investigate the role of the spatial distribution of partons in the proton and in the nuclei by assuming that the proton has an Y shape. In this configuration, quarks are more at the surface, and gluons in the inner part of the proton. Going from peripheral to more central, and then to...
The study of exotic hadrons and their properties has recently experienced a colossal boom. The development in this area is so tremendous that studying exotic hadrons has become one of the main, and more prolific, research lines at experimental facilities like BES and LHC. There is an intrinsic challenge when studying these particles as they belong to the non-perturbative region of QCD. The use...
In this work, we study the quark-gluon vertex in the context of unquenched QCD with two degenerate light dynamical quarks in the Landau gauge. We determine the eight form factors of the transversely projected quark-gluon vertex in general kinematics by solving its Schwinger-Dyson equation, derived from the 3PI effective action formalism. For the analysis, we employ as input the lattice data...
