Proceedings Series


Vol. 10 (2017), No. 4, pp. 931 – 1208

International Meeting Excited QCD 2017

Sintra, Lisbon, Portugal; May 7–13, 2017

Heavy and Heavy–Light Mesons and the Lorentz Structure of the Quark–Antiquark Interaction

abstract

We solve a Minkowski-space integral equation, derived in the Covariant Spectator Theory, for quark–antiquark bound states describing heavy and heavy–light mesons. The equation’s kernel contains a one-gluon exchange interaction and a covariant generalization of a linear confining potential with a mixed scalar, pseudoscalar, and vector Lorentz structure, characterized by a continuous mixing parameter. We investigate to what extent the Lorentz structure of the confining kernel can be determined by fitting the mixing parameter to the meson spectrum.


\(\rho \)-Meson Form Factors in the Point Form

abstract

We present a calculation of the electromagnetic form factors of the \(\rho ^+\) meson. Our formalism is based on the point form of relativistic quantum mechanics. Electron–\(\rho \)-meson scattering is formulated as a coupled-channel problem for a Bakamjian–Thomas mass operator such that the dynamics of the exchanged photon is taken explicitly into account. The \(\rho \)-meson current is extracted from on-shell matrix elements of the optical potential of the scattering process. As a consequence of the violation of cluster separability in the Bakamjian–Thomas framework, our current includes additional, unphysical contributions, which can be separated from the physical ones uniquely. Our results for the form factors are in a good agreement with other approaches.


Spin 1 Low-lying Meson Spectra and the Subtle Link to the Spin 0 Mesons

abstract

An NJL-type three-flavor quark model with a complete set of explicit chiral symmetry breaking terms is extended to include vector and axial–vector effective interaction terms. The bosonized Lagrangian is written up to quadratic order in the bosonic fields and the role of the new interactions is analyzed in detail. The model’s parameters are fitted to yield reasonable values to the four low-lying spin 0 and spin 1 meson nonets’ masses.


From the Gribov Ambiguity to Confining Effective Models

abstract

We briefly review a confining quark model that aims at the extension of the refined Gribov–Zwanziger framework to the matter sector. Interactions are encoded in a non-local quark propagator that displays dynamical chiral symmetry breaking in the infrared, while reproducing the perturbative expectations in the deep ultraviolet limit.


Holographic Picture of Heavy Vector Mesons in a Finite Density Plasma

abstract

We present the results of a holographic model for heavy vector mesons inside a plasma at finite temperature and density. The spectral function shows a nice description of the dissociation of the mesons in the medium, corresponding to the decrease in the height of the peaks as the temperature and (or) the density increase. We consider the case of bottomonium states at finite temperature and also the case of charmonium dissociation at zero temperature but finite chemical potential.


The Topological Susceptibility via the Gribov Horizon?

abstract

We analyze the SU(2) and SU(3) topological susceptibility \(\chi ^4\), in a BRST invariant fashion, using Padé approximation and the Refined Gribov–Zwanziger gluon propagator.


Decays of Light Mesons Triggered by Chiral Chemical Potential

abstract

Light meson (\(\pi ,\ \sigma ,\ a_0\)) properties in the environment with chiral imbalance are analyzed with the help of meson effective Lagrangian associated with QCD. New spatial parity violating decays of scalar mesons arise as a result of mixing of \(\pi \) and \(a_0\) mesons under the influence of chiral charge density. The pion electromagnetic form factor gets an unusual parity-odd contribution. Pion effective masses depend on their velocities and may vanish in flight. The possible determination of chiral chemical potential in heavy-ion collisions based on the above-mentioned phenomena is discussed.


The Quark Propagator in the Complex Domain: A Status Report

abstract

In these proceedings, I review the status of an ongoing project that aims at solving the quark propagator Dyson–Schwinger equation in the complex domain. The novel aspect of the approach is that the non-analyticities arising throughout the iteration of the equation are to be taken into account in an appropriate way through dynamic contour deformation. Because of the complexity of the approach, these studies are undertaken in a heavily truncated scenario that serves as a toy model for the development of the numerical techniques that are required to treat the system in a mathematically sound way.


Matter–Antimatter Coexistence Method for Finite Density QCD

abstract

We propose a “matter–antimatter coexistence method” for the finite-density lattice QCD, aiming at a possible solution of the sign problem. In this method, we consider matter and antimatter systems on two parallel \({\bf R}^4\)-sheets in five-dimensional Euclidean space-time. For the matter system \(M\) with a chemical potential \(\mu \in {\bf C}\) on a \({\bf R}^4\)-sheet, we also prepare the antimatter system \(\bar M\) with \(-\mu ^*\) on the other \({\bf R}^4\)-sheet shifted in the fifth direction. In the lattice QCD formalism, we introduce a correlation term between the gauge variables \(U_\nu \equiv e^{iagA_\nu }\) in \(M\) and \(\tilde U_\nu \equiv e^{iag \tilde A_\nu }\) in \(\bar M\), such as \(S_\lambda \equiv \sum _{x,\nu } 2\lambda \{N_{\rm c}-{\rm Re~tr} [U_\nu (x) \tilde U_\nu ^\dagger (x)]\} \simeq \sum _x \frac {1}{2}\lambda a^2 \{A_\nu ^a(x)-\tilde A_\nu ^a(x)\}^2\) with a real parameter \(\lambda \). In the limit of \(\lambda \rightarrow \infty \), a strong constraint \(\tilde U_\nu (x)=U_\nu (x)\) is realized, and the total fermionic determinant is real and non-negative. In the limit of \(\lambda \rightarrow 0\), this system goes to two separated ordinary QCD systems with the chemical potential of \(\mu \) and \(-\mu ^*\). On a finite-volume lattice, if one takes a large enough value of \(\lambda \), \(\tilde U_\nu (x) \simeq U_\nu (x)\) is realized and there occurs a phase cancellation approximately between two fermionic determinants in \(M\) and \(\bar M\), which is expected to suppress the sign problem and to make the lattice calculation possible. For the obtained gauge configurations of the coexistence system, matter-side quantities are evaluated through their measurement only for the matter part \(M\). By the calculations with gradually decreasing \(\lambda \) and their extrapolation to \(\lambda =0\), physical quantities in finite density QCD are expected to be estimated.


Lattice Landau Gauge Gluon Propagator at Finite Temperature: Non-zero Matsubara Frequencies and Spectral Densities

abstract

The lattice Landau gauge gluon propagator at finite temperature is computed including the non-zero Matsubara frequencies. Furthermore, the Källén–Lehmann representation is inverted and the corresponding spectral density evaluated using a Tikhonov regularisation together with the Morozov discrepancy principle. Implications for gluon confinement are discussed.


Center Vortices, Topological Charge and Chiral Symmetry Breaking

abstract

I review important aspects of the interplay between center vortices and topological charge, leading to chiral symmetry breaking.


The Quark Propagators of QCD and QCD-like Theories

abstract

We investigate the phase structures of theories which differ from QCD only in the gauge group and can be simulated on the lattice at non-vanishing chemical potential \(\mu \). These theories can thus serve as a testing ground for functional methods at non-vanishing density. We determine the chiral and confinement/deconfinement transitions at \(\mu =0\) for the three gauge groups SU(3), SU(2) and G\(_2\) for two-quark flavors and extend the study of the chiral transition to non-zero \(\mu \). We locate the critical point where the chiral crossover becomes a real phase transition. Within the employed truncation, we find that all three theories behave qualitatively very similarly.


Strong Decays of Excited Vector Mesons

abstract

We study two nonets of excited vector mesons, predominantly corresponding to radially excited vector mesons with quantum numbers \(n^{2S+1}L_{J}\) \(=2^3S_1\) and to orbitally excited vector mesons with quantum numbers \(n^{2S+1}L_{J}=1^3D_1\). We evaluate two types of decays of these mesons: into two pseudoscalar mesons and into a pseudoscalar and a ground-state vector meson. We compare the results with experimental data taken from PDG. We also make predictions for the strange–antistrange state in the \(1^3D_1\) nonet denoted as \(\phi (1930)\), which has not yet been discovered.


Heavy Glueballs: Status and Large-\(N_{\rm c}\) Widths Estimate

abstract

Glueballs, an old and firm prediction of various QCD approaches (lattice QCD, bag models, AdS/QCD, effective models, etc.), have not yet been experimentally confirmed. While for glueballs below \(2.6\) GeV some candidates exist, the situation for heavy glueballs (above \(2.6\) GeV) is cloudy. Here, after a brief review of scalar, tensor, and pseudoscalar glueballs, we present predictions for the decays of a putative pseudotensor glueball with a lattice predicted mass of \(3.04\) GeV and a putative vector glueball with a lattice predicted mass of \(3.81\) GeV. Moreover, we discuss in general the width of heavy glueballs by using large-\(N_{\rm c}\) arguments: we obtain a rough estimate according to which the width of a glueball (such as the vector one) is about \(10\) MeV. Such a width would be narrow enough to enable measurement at the future PANDA experiment.


The \(f_0(1790)\) and \(a_0(1950)\) Resonances as Excited \(\bar {q}q\) States in the Extended Linear Sigma Model

abstract

A decade ago, the BES Collaboration reported the discovery of a new scalar isosinglet resonance denoted as \(f_0(1790)\). The finding was subsequently confirmed by the LHCb. Recently, the existence of the corresponding isotriplet state — the \(a_0(1950)\) resonance — has been claimed by the BaBar Collaboration. We investigate whether these resonances can be described as excited \(\bar {q}q\) states. To this end, a comprehensive Lagrangian containing ground-state \(\bar {q}q\) mesons as well as their first excitations is constructed in accordance with symmetries of the strong interaction. Both \(f_0(1790)\) and \(a_0(1950)\) emerge as compatible with \(\bar {q}q\) excitations; however, tension appears to arise between the simultaneous interpretation of \(f_0(1790)\)/\(a_0(1950)\) and pseudoscalar mesons \(\eta (1295)\), \(\pi (1300)\), \(\eta (1440)\) and \(K(1460)\) as excited \(\bar {q}q\) states.


Analytic Approach to \(\pi K\) Scattering and Strange Resonances

abstract

We review our analysis of \(\pi K\) scattering using forward dispersion relations. The method yields a set of simple parameterizations that are compatible with forward dispersion relations up to 1.6 GeV while still describing the data. Once the partial waves are obtained, we calculate the poles in the complex plane by means of the Padé approximants, thus avoiding a particular model for the pole parameterization. The resonances calculated below 1.8 GeV are the much debated scalar \(\kappa \)-meson, nowadays known as \(K_0^*(800)\), the \(K_0^*(1430)\) scalar, the \(K^*(892)\) and \(K_1^*(1410)\) vectors, the spin-two \(K_2^*(1430)\) as well as the spin-three \(K^*_3(1780)\).


Study of LHCb Pentaquarks with CLAS12

abstract

The experimental study of the \(J/\psi \) photoproduction near threshold is an attractive subject for studying the nucleon gluonic form-factor and, as has been shown recently, is a direct way to produce and study hidden-charm pentaquark states claimed by the LHCb, \(P_c(4380)\) and \(P_c(4450)\). The CLAS12 experiment in Hall B at Jefferson Laboratory has developed a program to measure near-threshold \(J/\psi \) photoproduction using the low-\(Q^2\) electroproduction technique. Given the foreseen resolution in the invariant mass of the \(p\)–\(J/\psi \) system and the expected production rate for the pentaquark states, the experiment will be able to unambiguously confirm the existence of these states, measure the corresponding line-shape, and determine their quantum numbers.


Formation and Deformation of the \(\psi (3770)\)

abstract

The form of resonance line-shapes unveils information about its non-perturbative properties and formation mechanisms. Here, we study the non-Breit–Wigner energy distribution of the resonance \(\psi (3770)\) using an unitarized effective Lagrangian approach that includes the effect of the nearby threshold \(D^{+}D^{-}\). Two poles are found in the second Riemann sheet near the resonance amplitude. We discuss the setting of the free parameters and possible effects contributing to the signal.


General Unquenching Properties of Two-meson Scattering and Production Amplitudes

abstract

Besides the unitarity and symmetry requirements for a multi-resonance scattering amplitude, several other natural conditions can easily exclude unrealistic proposals. In particular, the behaviour of singularities under the variation of model parameters yields important information. We discuss how resonance poles should move in the complex-energy plane when coupling constants and masses are varied, how resonances above threshold can turn into bound states below threshold, and how the light-quark spectrum can be turned into the spectrum of heavy quarks, with one and the same analytic expression for the scattering amplitude. Moreover, it is shown that perturbative approximations usually do not satisfy these natural conditions.


Unquenching and Unitarising Mesons in Quark Models and on the Lattice

abstract

Mesons with masses below their lowest OZI-allowed strong-decay thresholds have very small widths. Thus, it is usually believed that they can be safely treated as pure quark–antiquark bound states in spectroscopy models. However, unitarised and coupled-channel models from decades ago already indicated that this may not be the case, owing to significant virtual meson-loop contributions. Recent unquenched lattice calculations that include two-meson interpolators besides the usual \(q\bar {q}\) ones confirm the latter conclusion, in particular for the enigmatic narrow \(D_{s0}^\star (2317)\), \(D_{s1}(2460)\), and \(X(3872)\) states. Here, we briefly review several predictions of some old and new quark models that go beyond the static description of mesons, also in comparison with up-to-date lattice results.


Production of \(f_0(500)\), \(f_0(980)\) and \(a_0(980)\) in the \(\chi _{c1} \to \eta \pi ^+ \pi ^-\) and \(\eta _c \to \eta \pi ^+ \pi ^-\) Decay

abstract

Using the chiral unitary approach in coupled channels and SU(3) symmetry, we describe the production of \(f_0(500)\), \(f_0(980)\) and \(a_0(980)\) in the \(\chi _{c1} \to \eta \pi ^+ \pi ^-\) reaction, recently performed by the BESIII Collaboration. A very strong peak for the \(a_0(980)\) can be seen in the \(\eta \pi \) invariant mass, while clear signals for the \(f_0(500)\) and \(f_0(980)\) appear in the one of \(\pi ^+\pi ^-\). Next, we make predictions for the analogous decay \(\eta _c \to \eta \pi ^+ \pi ^-\), which could also be measured experimentally. We discuss the differences of these reactions which are interesting to test the picture where these scalar mesons are dynamically generated from the interaction of pairs of pseudoscalars.


Thermodynamically Consistent Formulation of Quasiparticle Viscous Hydrodynamics

abstract

A novel formulation of the second-order relativistic viscous fluid dynamics based on the effective Boltzmann equation for quasi-particles with medium-dependent masses is briefly reviewed. The evolution equations for the shear and bulk dissipative corrections, and the corresponding transport coefficients are presented. Resulting approach allows for thermodynamically-consistent incorporation of the lattice QCD equation of state in the fluid dynamical framework.


Excited Hadrons and Quark–Hadron Duality

abstract

We review how Quark–Hadron Duality (QHD) for (\(u,d\)) flavors at high energies and in the scaling regime suggests a radial and angular behaviour of mesonic and baryonic resonance masses of the Regge form \(M^2_{nJ} = \mu ^2 n + \beta ^2 J + M_0^2 \). The radial mass dependence is asymptotically consistent with a common two-body dynamics for mesons and baryons in terms of the quark–anti-quark (\(q \bar q\,)\) and quark–diquark (\(qD\)) degrees of freedom, respectively. This formula is validated phenomenologically within an uncertainty determined by half the width of the resonances, \(\Delta M_{nJ}^2 \sim {\mit \Gamma }_{nJ} M_{nJ}\). With this error prescription, we find from the non-strange PDG hadrons different radial slopes \(\mu ^2_{\bar qq}=1.34(4)~{\rm GeV}^2\) and \(\mu ^2_{qD}=0.75(3)~{\rm GeV}^2\), but similar angular slopes \(\beta _{\bar q q}^2 \sim \beta _{ q D}^2 \sim 1.15~{\rm GeV}^2\).


Features of the QCD Phase Diagram from Small, Noisy, Fluctuating Systems

abstract

Current heavy-ion collision experiments might lead to the discovery of a first-order chiral symmetry breaking phase-transition line, ending in a second-order critical point. Nevertheless, the extraction of information about the equilibrium thermodynamic properties of baryonic matter from the highly dynamic, small, noisy and fluctuating environment formed in such collisions is an extremely challenging task. We address some of the limitations present in the experimental search for the QCD critical point.


Transverse Momentum Fluctuations and Correlations

abstract

We study fluctuations and correlations of the average transverse momentum of particles emitted in heavy-ion collisions. Fluctuations of the average transverse momentum are related to event-by-event fluctuations of the size and entropy of the initial source. Hydrodynamic calculations using a Glauber model with quark degrees of freedom reproduce the data. We study correlations of the average transverse momentum in different rapidity bins. We propose a definition of the observable that can be directly related to correlations of the collective flow variables.


Scale Invariant Resummed Thermal Perturbative Expansions

abstract

We illustrate how our recently developed renormalization group optimized perturbation (RGOPT) efficiently resums perturbative expansions in thermal field theories. The residual renormalization scale dependence of optimized thermodynamical quantities is drastically improved as compared to either standard perturbative expansions, or related methods such as the screened perturbation or (resummed) hard-thermal-loop perturbation. Our approach is illustrated briefly for the nonlinear sigma model, as a toy model for thermal QCD. Finally, preliminary applications of RGOPT to hard thermal loop resummation for the QCD pressure are sketched.


Phase Diagram and Isentropic Curves from the Vector Meson Extended Polyakov Quark Meson Model

abstract

In the framework of the \(N_{\rm f} = 2+1\) flavor (axial)vector meson extended Polyakov quark meson model, we investigate the QCD phase diagram at finite temperature and density. We use a \(\chi ^2\) minimization procedure to parameterize the model based on tree-level decay widths and vacuum scalar and pseudoscalar curvature masses which incorporate the contribution of the constituent quarks. Using a hybrid approximation (mesons at tree level, fermions at one-loop level) for the grand potential, we determine the phase boundary both on the \(\mu _{\rm B}\)–\(T\) and \(\rho \)–\(T\) planes. We also determine the location of the critical end point of the phase diagram. Moreover, by calculating the pressure and other thermodynamical quantities derived from it, we determine a set of isentropic curves in the crossover region. We show that the curves behave very similarly as their counterparts obtained from the lattice in the crossover regime.


all authors

E. Oset, W.-H. Liang, M. Bayar, R.P. Pavao, J. Nieves, Z.S. Xie

\({\mit \Lambda }_b\) and \({\mit \Xi }_b\) Weak Decays Into \({\mit \Lambda }_c^*\) and \({\mit \Xi }_c^*\) and Dynamics of \({\mit \Lambda }_c^*\) and \({\mit \Xi }_c^*\)

abstract

We report on work done for the decay rates of \({\mit \Lambda }_b \to \pi ^- {\mit \Lambda }_c(2595)\) \(({\mit \Lambda }_c(2625))\) from the perspective that the \({\mit \Lambda }_c(2595)\) and \({\mit \Lambda }_c(2625)\) are dynamically generated resonances from the \(DN\), \(D^* N\) interaction and coupled channels. We also evaluate the semileptonic decays going to these resonances, \({\mit \Lambda }_b \to \bar \nu _l l {\mit \Lambda }_c(2595) ({\mit \Lambda }_c(2625))\), and a good agreement is found with experiment. The exercise is also done for the \({\mit \Xi }_b^- \rightarrow \pi ^- (D_s^-) \ {\mit \Xi }_c^0 (2790)\) \(({\mit \Xi }_c^0 (2815))\) and \({\mit \Xi }_b^- \rightarrow \bar {\nu }_l l \ {\mit \Xi }_c^0 (2790) ({\mit \Xi }_c^0 (2815))\), making predictions for the rates of these decays.


Polarized Drell–Yan Measurements at COMPASS

abstract

COMPASS is a fixed-target experiment operating on north area of SPS (M2 beamline) at CERN. An important part of the physics programme of the experiment is the exploration of the transverse spin structure of the nucleon via measurements of spin-(in)dependent azimuthal asymmetries in the semi-inclusive DIS and, recently, also in Drell–Yan processes. Drell–Yan measurements with a 190 GeV/\(c\) \(\pi ^-\) beam impinging on a transversely polarized NH\(_3\) target started in the year 2015 (18 weeks data taking) and will be continued in 2018. The measurement of the Sivers and other azimuthal asymmetries in polarized SIDIS and Drell–Yan performed by COMPASS provides a unique possibility to test (pseudo-)universal features of transverse momentum-dependent parton distribution functions, predicted in QCD. In this review, results of the first ever measurements of the polarized Drell–Yan reaction performed by COMPASS are presented.


all authors

K. Piscicchia, M. Cargnelli, C. Curceanu, R. Del Grande, L. Fabbietti, C. Guaraldo, J. Marton, P. Moskal, A. Scordo, M. Silarski, D. Sirghi, M. Skurzok, I. Tucakovic, O. Vazquez Doce, S. Wycech, E. Widmann, J. Zmeskal

Low-energy Antikaon–Nucleon Absorption Studies by AMADEUS

abstract

The AMADEUS experiment investigates the low-energy kaon–nuclei hadronic interaction at the DA\(\Phi \)NE collider at LNF-INFN. In particular, the study of hyperon resonances formation, following \(K^-\)-induced reactions in light nuclear targets, will be presented. The 0 step of the experiment consisted in the reanalysis of the 2004/2005 KLOE data, exploiting \(K^-\) absorptions in H, \({}^4\)He, \({}^9\)Be and \({}^{12}\)C, leading to the first invariant mass spectroscopic study with very low momentum (about 100 MeV) in-flight \(K^-\) captures. With AMADEUS step 1, a dedicated pure carbon target was implemented in the central region of the KLOE detector, providing a high statistic sample of pure at-rest \(K\) nuclear interaction. The results obtained in the analyses of the hyperon–pion correlated events, searching for the resonant shapes of Y* states, will be described.


Azimuthal Correlations and Mixed Higher Order Flow Harmonics from CMS at the LHC

abstract

Two-particle correlations measurements of \(v_{n}\) (\(n=2\)–4) in 8.16 TeV \(p\)Pb collisions, and event-by-event correlations of different \(v_{n}\) are measured using symmetric cumulants in 13 TeV \(pp\), 5.02 and 8.16 TeV \(p\)Pb and 5.02 TeV PbPb collisions at the LHC. These new results give important insights to the origin of collectivity observed in small collision systems. Additionally, using the scalar product method and the method of two-particle correlations, the mixed higher order flow harmonics and extracted nonlinear response coefficients of charged particles are measured for the first time as a function of \(p_{\rm T}\) and centrality in 2.76 and 5.02 TeV PbPb collisions. The obtained results are compared with different theoretical predictions.


Relativistic Hydrodynamics of Particles with Spin 1/2

abstract

A new hydrodynamic framework for particles with spin 1/2, based solely on the conservation laws for charge, energy, momentum and angular momentum, is discussed.


Thermal Entropy of a Quark–Antiquark Pair from a Dynamical Holographic EMD Model

abstract

Lattice QCD indicates a large amount of entropy associated with a quark–antiquark (\(q \bar {q}\)) pair near the deconfinement temperature. The entropy shows a sharp peak near the transition temperature and increases with the interquark distance. We use the gauge/gravity duality to reproduce these lattice results holographically. We consider a phenomenological bottom–up Einstein–Maxwell-dilaton (EMD) gravity model and analytically construct the gravity solutions, whose dual boundary theory satisfies the properties of confined/deconfined phases. We study the entropy of the \(q\bar {q}\) pair and find that our holographic model qualitatively reproduces the corresponding lattice results. We further provide holographic results for the \(q\bar {q}\) entropy with chemical potential.


Recent QCD-related Results from Kaon Physics at CERN (NA48/2 and NA62)

abstract

The NA48/2 experiment presents a preliminary result of \(K^\pm _{l}\) decays form factors measurement based on the \(4.28 \times 10^6\) \(K^\pm _{e3}\) and \(2.91 \times 10^6\) \(K^\pm _{\mu 3}\) selected decays collected in 2004. The result is competetive with other measurements in \(K^\pm _{\mu 3}\) mode and has a smallest uncertainty for \(K^\pm _{e3}\), that leads to the most precise combined \(K^\pm _{l3}\) result and allows to reduce the form factor uncertainty of \(|V_{\rm US}|\). The NA62 experiment collected a large sample of charged kaon decays with a highly efficient trigger for decays into electrons in 2007. A final result of a new measurement of the electromagnetic transition form factor slope of the neutral pion in the time-like momentum region from the \(1.11 \times 10^6\) fully reconstructed \(\pi ^{0}\) Dalitz decays is presented in the second part of this article.


Hadronic Vacuum Polarization in \(e^{+}e^{-}\to \mu ^{+}\mu ^{-}\) Process Below 3 GeV

abstract

The interference effect between leptonic radiative corrections and hadronic polarization functions is calculated via optical theorem for \(\mu \)-pair productions. It is achieved by using the data for dominant channels of the production cross section \(\sigma _{\rm h}(e^+e^-\rightarrow \) hadrons). The result is compared with the KLOE experiment for \(\mu ^{-}\mu ^{+}\) production at \(\phi \)-meson energy for which we take into account specific experimental conditions. Moreover, running fine structure coupling is compared with the KLOE2 experiment for radiative return \(\mu ^{-}\mu ^{+}\) production at \(\omega /\rho \)-meson energy.


A Collisional Model for Scalar Mesons Below 1 GeV

abstract

A collisional model for hadron resonances appearing in hadron collisions is proposed. The given approach leads to a simple explanation of the scalar sector below 1 GeV with correct predictions for masses and dominant decay modes.


Mixture of Quark and Gluon Fluids Described in Terms of Anisotropic Hydrodynamics

abstract

A system of equations of anisotropic hydrodynamics that describes a mixture of quark and gluon fluids is studied. The equations are based on the zeroth, first, and second moments of the RTA kinetic equations. Tests of this formulation are performed by comparing the results of anisotropic hydorodynamics with the exact solutions of the Boltzmann equations for a mixture of fluids in the Bjorken flow limit. One finds a very good agreement between the hydrodynamic and kinetic theory results.


Charmonium Spectral Functions in \(\bar p A\) Collision

abstract

We study the in-medium propagation of low-lying charmonium states: \(J/{\mit \Psi }\), \({\mit \Psi }\)(3686), and \({\mit \Psi }\)(3770) in a \(\bar p\,\)Au 10 GeV collision. This energy regime will be available for the PANDA experiment. The time evolution of the spectral functions of the charmonium states is studied with a BUU-type transport model. We observe a substantial effect of the medium in the dilepton spectrum.


Recent Results from NA61/SHINE

abstract

NA61/SHINE at the CERN SPS is a fixed-target experiment pursuing a rich physics program including measurements for heavy ion, neutrino and cosmic ray physics. The main goal of the strong interactions program is to study the properties of the onset of deconfinement and to search for the signatures of the critical point. In this contribution, the latest NA61/SHINE results on particle spectra as well as on fluctuations and correlations from \(p\)+\(p\), Be+Be, and Ar+Sc energy scans will be presented. The NA61 measurements will be compared with world data and with model predictions.


Jets and Charged Hadrons in Heavy-ion Collisions with the ATLAS Detector

abstract

Ultrarelativistic heavy-ion collisions at the LHC produce the quark–gluon plasma. Jets are a useful probe to study this state of matter since they are produced at the early stages of the collisions and are expected to be modified as propagating through the medium. One observable is the energy loss lowering the jet yields at a given transverse momentum. Other observables are the modification of the dijet momentum balance and the modification of fragmentation functions. A phenomenon strictly correlated to the jet energy loss is the modification of the charged-hadron momentum spectrum. The large new Pb+Pb data sample collected by ATLAS in Run 2 allows for precision measurements of these observables in a wide transverse momentum range and in different centrality and rapidity intervals.


Magnetized QCD Phase Diagram

abstract

Using the (2+1)-flavor Nambu–Jona-Lasinio (NJL) model with the Polyakov loop, we determine the structure of the QCD phase diagram in an external magnetic field. Beyond the usual NJL model with constant couplings, we also consider a variant with a magnetic field-dependent scalar coupling, which reproduces the Inverse Magnetic Catalysis (IMC) at zero chemical potential. We conclude that the IMC affects the location of the Critical End Point, and found indications that, for high enough magnetic fields, the chiral phase transition at zero chemical potential might change from an analytic to a first-order phase transition.


Hollowness in \(pp\) Scattering at the LHC

abstract

We examine how the effect of hollowness in \(pp\) scattering at the LHC (minimum of the inelasticity profile at zero impact parameter) depends on modeling of the phase of the elastic scattering amplitude as a function of the momentum transfer. We study the cases of the constant phase, the Bailly, and the so-called standard parameterizations. It is found that the 2D hollowness holds in the first two cases, whereas the 3D hollowness is a robust effect, holding for all explored cases.


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