Proceedings Series

Vol. 9 (2016), No. 3, pp. 355 - 658

International Meeting Excited QCD

full authors' list

O. Oliveira, A. Kızılersü, P.J. Silva, J.-I. Skullerud, A. Sternbeck, A.G. Williams

Lattice Landau Gauge Quark Propagator and the Quark–Gluon Vertex

Acta Phys. Pol. B Proc. Suppl. 9, 363 (2016)

page 363 •


We report preliminary results of our ongoing lattice computation of the Landau gauge quark propagator and the soft gluon limit of the quark–gluon vertex with 2 flavors of dynamical \(\mathcal {O} (a)\) improved Wilson fermions.

In-medium \(\eta \rightarrow 3\pi \) Decay Width and Chiral Restoration in Nuclear Medium

Acta Phys. Pol. B Proc. Suppl. 9, 369 (2016)

page 369 •


We investigate the effect of nuclear medium on \(\eta \rightarrow 3\pi \) decay using linear sigma model with a particular attention to the role of the \(\sigma \) meson. We find that the decay width is enhanced in the nuclear medium in association with the softening of the \(\sigma \) meson. The in-medium \(\eta \rightarrow 3\pi \) decay width can be a possible probe for the chiral restoration in the nuclear medium.

Leading and Sub-leading Flows at the LHC from the CMS

Acta Phys. Pol. B Proc. Suppl. 9, 377 (2016)

page 377 •


The initial state fluctuations of the colliding heavy-ion nuclei play a major role in understanding the anisotropic flow of final state particles. Furthermore, an important signature of these fluctuations is the flow (event-plane) angle dependence from \(p_{\rm T}\) that induces a measurable effect of factorization breaking in a pure relativistic hydrodynamic picture. Here, the effect of factorization breaking is described using a new method based on principal component analysis (PCA) and two-particle correlations. The method exposes leading and sub-leading mode, the leading corresponding to the standard elliptic and triangular flow and the sub-leading representing a new variable that is a direct response to initial state fluctuations. In this study, first measurements of the subflow are presented, as a function of transverse momentum in PbPb collisions at \(\sqrt {s_{NN}}= 2.76\) TeV and high-multiplicity \(p\)Pb collisions at \(\sqrt {s_{NN}}= 5.02\) TeV with CMS data.

Thermalization and Hydrodynamization in the Color-flux-tube Model

Acta Phys. Pol. B Proc. Suppl. 9, 383 (2016)

page 383 •


The study of transverse-momentum spectra of quarks and gluons produced by the color electric flux tube decaying through the Schwinger tunneling mechanism is reviewed. The hints for a fast hydrodynamization in the ultra-relativistic heavy-ion collisions are found.

A Non-perturbative Study of the Correlation Functions of Three-dimensional Yang–Mills Theory

Acta Phys. Pol. B Proc. Suppl. 9, 389 (2016)

page 389 •


Yang–Mills theory is studied in three dimensions using the equations of motion of the \(1\)PI and \(3\)PI effective actions. The employed self-contained truncation includes the propagators, the three-point functions and the four-gluon vertex dynamically. In the gluon propagator, also two-loop diagrams are taken into account. The higher gluonic correlation functions show sizable deviations from the tree-level only at low momenta. Also the couplings derived from the vertices agree well down to a few GeV. In addition, different methods to subtract spurious divergences are explored.

Saturation and Geometrical Scaling in Small Systems

Acta Phys. Pol. B Proc. Suppl. 9, 395 (2016)

page 395 •


Saturation and geometrical scaling (GS) of gluon distributions are a consequence of the non-linear evolution equations of QCD. We argue that in \(pp\), GS holds for the inelastic cross section rather than for the multiplicity distributions. We also discuss possible fluctuations of the proton saturation scale in \(pA\) collisions at the LHC.

Heavy Quark Entropy Shift: From the Hadron Resonance Gas to Power Corrections

Acta Phys. Pol. B Proc. Suppl. 9, 401 (2016)

page 401 •


A heavy quark placed in the medium modifies its specific heat. Using a renormalization group argument, we show a low-energy theorem in terms of the defect in the trace of the energy-momentum tensor which allows the unambiguous determination of the corresponding entropy shift after imposing the third principle of thermodynamics for degenerate states. We show how recent lattice QCD data can be understood in the confined phase in terms of a singly-heavy hadronic spectrum and above the phase transition through power corrections which are analysed by means of a dimension-2 gluon condensate of the dimensionally reduced theory.

Description of EM Structure of Nonet of Pseudoscalar Mesons by Unitary and Analytic Model Leads to More Accurate Muon \(g-2\) Anomaly and QED \(\alpha (M^2_Z)\) Evaluation

Acta Phys. Pol. B Proc. Suppl. 9, 407 (2016)

page 407 •


It is demonstrated that the description of electromagnetic structure of pseudoscalar meson nonet by the sophistical Unitary and Analytic (U&A) model leads to a more precise evaluation of muon \(g-2\) anomaly and QED \(\alpha (M^2_Z)\).

Light Quark Mass Differences in the \(\pi ^0\)–\(\eta \)–\(\eta '\) System

Acta Phys. Pol. B Proc. Suppl. 9, 413 (2016)

page 413 •


A generalized 3 flavor Nambu–Jona-Lasinio Lagrangian, including the explicit chiral symmetry breaking interactions which contribute at the same order in the large \(1/N_{\rm c}\) counting as the U\(_{\rm A}(1)\) ’t Hooft flavor determinant, is considered to obtain the mixing angles in the \(\pi ^0\)–\(\eta \)–\(\eta '\) system and related current quark mass ratios in close agreement with phenomenological values. At the same time, an accurate ordering and magnitude of the splitting of states in the low-lying pseudoscalar nonet is obtained.

full authors' list

C. Morningstar, J. Bulava, B. Fahy, J. Fallica, A. Hanlon, B. Hörz, K. Juge, C.H. Wong

Lattice QCD Study of Excited Hadron Resonances

Acta Phys. Pol. B Proc. Suppl. 9, 421 (2016)

page 421 •


The spectrum of excited hadron resonances in QCD is studied using Monte Carlo path integration techniques formulated on a large \(32^3\times 256\) anisotropic space-time lattice. A large number of probe interpolating operators are used, and calculation of temporal correlations is accomplished using a stochastic method of treating the low-lying modes of quark propagation that exploits Laplacian Heaviside quark-field smearing. Plans to use an effective Hamiltonian to interpret the finite-volume energies and determine the masses and widths of the resonances are outlined. The construction of tetraquark operators is discussed.

Twisted Mass Wilson \(\chi \)-PT Versus Lattice Data: a Case Study

Acta Phys. Pol. B Proc. Suppl. 9, 427 (2016)

page 427 •


We compare lattice data obtained from a dynamical simulation with twisted mass fermions to the analytical predictions of Twisted Mass Wilson \(\chi \)-PT and extract an estimate for the chiral condensate and the LEC \(W_8\).

QCD Results in the Forward Region (LHCb)

Acta Phys. Pol. B Proc. Suppl. 9, 433 (2016)

page 433 •


LHCb, while conceived initially for \(b\)-physics, also functions as a general purpose forward detector, covering the pseudo-rapidity range from 2.0 to 5.0. A wide variety of forward QCD measurements have been performed, including jet production measurements, soft inclusive particle distributions and correlations, and central exclusive production. A selection of these results will be presented, highlighting the scope of the LHCb physics programme.

full authors' list

G. Aarts, C. Allton, D. De Boni, S. Hands, B. Jäger, C. Praki, J.-I. Skullerud

Finite Temperature Lattice QCD — Baryons in the Quark–Gluon Plasma

Acta Phys. Pol. B Proc. Suppl. 9, 441 (2016)

page 441 •


Baryonic correlation functions provide an ideal tool to study parity doubling and chiral symmetry using lattice simulations. We present a study using \(2+1\) flavours of anisotropic Wilson clover fermions on the FASTSUM ensembles and find clear evidence that parity doubling emerges in the quark–gluon plasma. This result is confirmed on the level of spectral functions, which are obtained using a MEM reconstruction. We further highlight the importance of Gaussian smearing in this study.

Flux Tubes at Finite Temperature

Acta Phys. Pol. B Proc. Suppl. 9, 447 (2016)

page 447 •


In this work, we show the flux tubes of the quark–antiquark and quark–quark at finite temperature for SU(3) lattice QCD. The chromomagnetic and chromoelectric fields are calculated above and below the phase transition.

Calculation of Regge Trajectories of Strange Resonances and Identification of the \(K_0^*(800)\) as a Non-ordinary Meson

Acta Phys. Pol. B Proc. Suppl. 9, 453 (2016)

page 453 •


We review how the Regge trajectory of an elastic resonance can be obtained just from its pole position and coupling, using a dispersive formalism. This allows us to deal correctly with the finite widths of resonances in Regge trajectories. In this way, we can calculate the Regge trajectories for the \(K^*(892)\), \(K_1(1400)\) and \(K^*_0(1430)\), obtaining ordinary linear Regge trajectories, expected for \(q \bar q\) resonances. In contrast, for the \(K^*_0(800)\) meson, the resulting Regge trajectory is non-linear and with much smaller slope, strongly supporting its non-ordinary nature.

Forward Dispersion Relations for \(\pi K\) Scattering and the \(K^*_0(800)\) Resonance

Acta Phys. Pol. B Proc. Suppl. 9, 459 (2016)

page 459 •


We review the recent analysis of \(\pi K\) scattering data in terms of forward dispersion relations, and also present the parameters of the strange resonances. This work consists of fits to the data that are constrained to satisfy analyticity requirements. The method yields a set of simple and consistent parameterizations that are compatible with forward dispersion relations up to 1.6 GeV while still describing the data. We also obtain the pole parameters of the \(K^*_0(800)\) and the \(K^*(892)\) resonances.

A Covariant Nonlocal Lagrangian for the Description of the Scalar Kaonic Sector

Acta Phys. Pol. B Proc. Suppl. 9, 467 (2016)

page 467 •


Mesons are extended objects, hence their interaction can be described by utilizing form factors. At the Lagrangian level, one can use nonlocal interaction terms. Here, we describe two possible nonlocal Lagrangians leading to a 3D form factor: the first one is simple but does not fulfill covariance (if one insists on a 3D cutoff), the second extension is more involved but guarantees covariance. Such form factors are useful when calculating mesonic loops. As an important example, we discuss the scalar kaonic sector, \(I(J^{P})=\frac {1}{2}(0^{+})\). The Lagrangian contains a single scalar kaon (the well-establish state \(K_{0}^{\ast }(1430)\)), but through loops \(K_{0}^{\ast }(800)\) emerges as a dynamically generated companion pole (which disappears in the large-\(N_{\rm c}\) limit).

Status and Perspectives with Exotic States at LHCb

Acta Phys. Pol. B Proc. Suppl. 9, 473 (2016)

page 473 •


The analysis of the full LHC Run 1 data set of proton–proton collision events collected with the LHCb detector, corresponding to an integrated luminosity of 3.0 fb\(^{-1}\), is yielding several improved results on exotic hadron candidates, such as \(X(3872)\) and \(Z(4430)^+\), as well as the first observation of two new states compatible with the pentaquark hypothesis. Run 2 data allow LHCb to further sharpen the experimental picture, opening up the possibility to observe new states. The measurements of the properties of these exotic states and the Run 2 prospects will be presented, including the determination of their quantum numbers, with model-dependent and independent methods.

Initial State Correlations and the Ridge

Acta Phys. Pol. B Proc. Suppl. 9, 479 (2016)

page 479 •


We point out that Bose enhancement in a hadronic wave function generically leads to correlations between produced particles. We show explicitly, by calculating the projectile density matrix in the Color Glass Condensate approach to high-energy hadronic collisions, that the Bose enhancement of gluons in the projectile leads to azimuthal collimation of long range rapidity correlations of the produced particles, the so-called ridge correlations.

Final Combined Deep Inelastic Scattering Cross Sections at HERA

Acta Phys. Pol. B Proc. Suppl. 9, 485 (2016)

page 485 •


The combination is presented of all inclusive deep inelastic scattering cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current \(ep\) scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV, and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb\(^{-1}\) and span six orders of magnitude in negative four-momentum-transfer squared, \(Q^2\), and Bjorken \(x\). The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. Additionally, the inclusion of jet-production cross sections made a simultaneous and precise determination of parton distributions and the strong coupling constant possible. Brief highlights of the results are presented.

Recent Heavy-ion Results from the LHC and Future Perspectives

Acta Phys. Pol. B Proc. Suppl. 9, 491 (2016)

page 491 •


Strongly interacting matter at high densities and temperatures can be created in high-energy collisions of heavy atomic nuclei. Since 2010, the Large Hadron Collider at CERN provides proton–proton, proton–lead and lead–lead collisions at an unprecedented energy to study the so-called quark–gluon plasma (QGP) state. Several experimental probes have been proposed to determine the properties of the QGP. In this contribution, a selection of recent results from the heavy-ion programme at RHIC and the LHC are reviewed and discussed.

Kinetic Properties of the Gribov–Zwanziger Plasma

Acta Phys. Pol. B Proc. Suppl. 9, 497 (2016)

page 497 •


The idea of the Gribov–Zwanziger plasma is introduced and used to calculate the bulk and shear viscosities of the system of gluons at high temperature.

From the Density-of-states Method to Finite Density Quantum Field Theory

Acta Phys. Pol. B Proc. Suppl. 9, 503 (2016)

page 503 •


During the last 40 years, Monte Carlo calculations based upon Importance Sampling have matured into the most widely employed method for determining first principle results in QCD. Nevertheless, Importance Sampling leads to spectacular failures in situations in which certain rare configurations play a non-secondary role as it is the case for Yang–Mills theories near a first order phase transition or quantum field theories at finite matter density when studied with the re-weighting method. The density-of-states method in its Linear Logarithmic Relaxation (LLR) formulation has the potential to solve such overlap or sign problems by means of an exponential error suppression. We here introduce the LLR approach and its generalisation to complex action systems. Applications include U(1), SU(2) and SU(3) gauge theories as well as the \(Z_3\) spin model at finite densities and heavy-dense QCD.

QCD with Chiral Chemical Potential: Models Versus Lattice

Acta Phys. Pol. B Proc. Suppl. 9, 515 (2016)

page 515 •


An emergence of local spatial parity breaking (LPB) in central heavy-ion collisions (HIC) at high energies is discussed. The QCD phenomenology of LPB in the fireball is induced by a difference between the number densities of right- and left-handed chiral fermions which is triggered by a chiral (axial) chemical potential. For the description of peculiarities of LPB, a number of QCD-inspired models are considered and confronted to certain lattice results. In particular, from the meson effective Lagrangian, it is found that the lightest states may become massless and some scalars turn out to be stable. In experimental studies, the asymmetry in production of longitudinal and transverse polarized states of \(\rho \) and \(\omega \) mesons for different values of the invariant mass can serve as a characteristic indication of local spatial parity breaking which can be derived from an abnormal yield of dilepton pairs in the PHENIX, STAR and ALICE collaborations.

Magnetic Properties in the Inhomogeneous Chiral Phase

Acta Phys. Pol. B Proc. Suppl. 9, 523 (2016)

page 523 •


We investigate the magnetic properties of quark matter in the inhomogeneous chiral phase, where both scalar and pseudoscalar condensates spatially modulate. The energy spectrum of the lowest Landau level becomes asymmetric about zero in the external magnetic field, and gives rise to the remarkably magnetic properties: quark matter has a spontaneous magnetization, while the magnetic susceptibility does not diverge on the critical point.

full authors' list

E. Oset, H.-X. Chen, A. Feijoo, L.-S. Geng, W.-H. Liang, D.-M. Li, J.-X. Lu, V.K. Magas, J. Nieves, A. Ramos, L. Roca, E. Wang, J.-J. Xie

Reactions Looking for Hidden Charm Pentaquarks With or Without Strangeness

Acta Phys. Pol. B Proc. Suppl. 9, 529 (2016)

page 529 •


Results for five reactions, \({\mit \Lambda }_b \to J/\psi K^- p\), \({\mit \Lambda }_b \to J/\psi \eta {\mit \Lambda }\), \({\mit \Lambda }_b \to J/\psi \pi ^- p\), \({\mit \Lambda }_{b}\rightarrow J/\psi K^{0}{\mit \Lambda }\) and \({\mit \Xi }^-_b \to J/\psi K^- {\mit \Lambda }\) are presented on predictions made for molecular states of hidden charm, with or without strangeness, evaluating invariant mass distributions for \(J/\psi p\) or \(J/\psi {\mit \Lambda }\). We show that in all of these reactions, one finds peaks where the pentaquark states show up.

Photoproduction of Kaons

Acta Phys. Pol. B Proc. Suppl. 9, 537 (2016)

page 537 •


A new isobar model for photoproduction of \(K{\mit \Lambda }\) on the proton was constructed utilizing the data from CLAS, LEPS, and GRAAL collaborations. In the model, nucleon and hyperon resonances with spin 3/2 and 5/2 in the intermediate state are included using a consistent formalism in which only the physical degrees of freedom contribute to the invariant amplitude. These higher-spin resonances were shown to play an important role in data description. The model describes well the data in the third resonance region in full range of kaon angles. Results of the model are also compared with the hybrid Regge-plus-resonance model constructed recently. Predictions of the models in the very-forward-angle region, important for calculations of the hypernucleus cross sections, are also briefly discussed.

Numerical Study of the Baryon Spectrum and Chiral Symmetry Restoration

Acta Phys. Pol. B Proc. Suppl. 9, 543 (2016)

page 543 •


We study light baryons using a simple relativistic but non-covariant Coulomb Gauge QCD-inspired model. A variational basis is employed to compute the energies and wave functions of the baryon states, for different values of angular momentum and parity. Results are obtained for both the \(N\) and the \({\mit \Delta }\) excitations. A special look is given to the high angular momentum states going up to \(J = 13/2\). In this limit, we test the effect of chiral symmetry restoration on the baryonic spectrum.

Searches for Supersymmetry and Exotic Phenomena with the ATLAS Detector

Acta Phys. Pol. B Proc. Suppl. 9, 551 (2016)

page 551 •


Weak-scale supersymmetry is one of the best motivated and studied extensions of the Standard Model and it is explored, together with other new physics scenarios, exploiting the recent increase in the center-of-mass energy of proton–proton collisions at the Large Hadron Collider. This paper summarizes the searches performed with the ATLAS detector in the first Run 2 data using 3.2 fb\(^{-1}\) at 13 TeV.

Studies of the SM Higgs Boson and Searches for BSM Higgs Bosons with the ATLAS Detector

Acta Phys. Pol. B Proc. Suppl. 9, 561 (2016)

page 561 •


The ATLAS Collaboration has searched for the Standard Model Higgs boson in the first LHC Run 2 data using 3.2 fb\(^{-1}\) at 13 TeV. Results are presented in terms of central values and limits on the total cross section in the four-lepton and \(\gamma \gamma \) channels. Several “Beyond Standard Model” theories predict the existence of additional heavy Higgs particles or di-Higgs resonances. Searches are conducted using the \(\gamma \gamma \), \(ZZ\), \(WW\) and fermionic decay channels, and cover a large range of masses for the hypothetical resonances.

Light-by-light Scattering in Ultraperipheral Heavy-ion Collisions at the LHC

Acta Phys. Pol. B Proc. Suppl. 9, 567 (2016)

page 567 •


We present cross sections for diphoton production in (semi)exclusive PbPb collisions, relevant for the LHC. The calculation is based on equivalent photon approximation in the impact parameter space. The cross sections for elementary elastic scattering \(\gamma \gamma \to \gamma \gamma \) subprocess are calculated including two mechanisms: box diagrams with leptons and quarks in the loops and a mechanism based on vector-meson dominance (VDM-Regge) model with virtual intermediate vector-like excitations of the photons. We get measureable cross sections in PbPb collisions. We present many interesting differential distributions which could be measured by the ALICE, CMS or ATLAS collaborations at the LHC. We study whether a separation of box and VDM-Regge contributions is possible. We find that the cross section for elastic \(\gamma \gamma \) scattering could be measured in the heavy-ion collisions for subprocess energies smaller than \(W_{\gamma \gamma } \approx 15\)–20 GeV.

Description of Hadronic Effects in Weak Decays of Beauty Mesons Using Covariant Quark Model

Acta Phys. Pol. B Proc. Suppl. 9, 575 (2016)

page 575 •


Description of rare \(B\)-meson decays in the Standard Model requires an appropriate description of hadronic effects. Covariant quark model with infrared confinement represents a suitable framework for doing it. In this text, we briefly describe the model and its application to the \(B \to K^\ast \mu \mu \) and \(B_s \to \phi \mu \mu \) decays, including numerical results.

Modeling Two-boson Mass Distributions, \(E\)(38 MeV) and \(Z\)(57.5 GeV)

Acta Phys. Pol. B Proc. Suppl. 9, 583 (2016)

page 583 •


Besides general features of the Resonance Spectrum Expansion for two-boson mass distributions, experimental results are discussed. Furthermore, \(E\)(38 MeV) and \(Z\)(57.5 GeV) are highlighted.

Thermodynamics of the Vector Meson Extended Linear Sigma Model

Acta Phys. Pol. B Proc. Suppl. 9, 589 (2016)

page 589 •


We use a \(\chi ^2\) minimization procedure to parameterize the Polyakov loop and (axial-)vector meson extended \(N_{\rm f}=2+1\) flavor linear sigma model (L\(\sigma \)M) based on tree-level decay widths and vacuum scalar and pseudoscalar curvature masses which includes the contribution of the constituent quarks. Using a quark improved Polyakov loop potential and a simple approximation for the grand potential, we determine and compare with lattice results the pressure and thermodynamical observables derived from it. We also determine the location of the critical end point of the \(\mu _B\)–\(T\) phase diagram.

Soft-wall Modelling of Meson Spectra

Acta Phys. Pol. B Proc. Suppl. 9, 597 (2016)

page 597 •


The holographic methods inspired by the gauge/gravity correspondence from string theory have been actively applied to the hadron spectroscopy in the last eleven years. Within the phenomenological bottom–up approach, the linear Regge-like trajectories for light mesons are naturally reproduced in the so-called “soft-wall” holographic models. I will give a very short review of the underlying ideas and technical aspects related to the meson spectroscopy. A generalization of soft-wall description of Regge trajectories to arbitrary intercept is proposed. The problem of incorporation of the chiral symmetry breaking is discussed.

A Real-time Lattice Simulation of the Thermalization of a Gluon Plasma: First Results

Acta Phys. Pol. B Proc. Suppl. 9, 603 (2016)

page 603 •


To achieve an understanding of the thermalization of a quark–gluon plasma, starting from QCD without using model assumptions, is a formidable task. We study the early stage dynamics of a relativistic heavy-ion collision in the framework of real-time simulations of the classical Yang–Mills theory in a static box with the color glass condensate as an initial condition. Our study generalizes a previous one by Fukushima and Gelis from SU\((2)\) to the realistic case of SU\((3)\). We calculate the chromo-electric and chromo-magnetic energy densities as well as the ratio of longitudinal and transverse pressure as a function of time as probes for thermalization. Our preliminary results on coarse lattices show the occurrence of Weibel instabilities prior to thermalization.

Unitary Multi-channel \(\pi \pi \) Scattering Amplitudes of \(f_2\) and \(\rho _3\) Mesons

Acta Phys. Pol. B Proc. Suppl. 9, 609 (2016)

page 609 •


In a unitary multi-channel approach, precise determination of \(\pi \pi \) scattering amplitudes for \(D\) and \(F\) waves has been presented. These scattering amplitudes are in the \(I^{G}J^{PC}=0^{+}2^{++}\) sector of the processes of \(\pi \pi \rightarrow \pi \pi \), \(4\pi \), \(K \bar K\) and \(\eta \eta \), likewise in the \(I^{G}J^{PC}=1^{+}3^{--}\) sector of the processes of \(\pi \pi \rightarrow \pi \pi \), \(4\pi \), \(\omega \pi \) and \(K \bar K\). The amplitudes were refined and re-fitted to the dispersion relations up to 1.1 GeV, and to the experimental data in the effective two pion mass from the threshold to 2.7 GeV and 1.9 GeV for \(D\) and \(F\) waves, respectively. Unsuitable behaviour of phase shift near threshold has been optimized for both waves.

Large-\(N\) Pion Scattering, Finite-temperature Effects and the Relationship of the \(f_{0}(500)\) with Chiral Symmetry Restoration

Acta Phys. Pol. B Proc. Suppl. 9, 615 (2016)

page 615 •


In this work, we review how the mass and the width of the \(f_{0}(500)\) pole behave in a regime where temperature is below the critical chiral transition value. This is attained by considering a large-\(N\) \(O(N+1)/O(N)\) invariant Nonlinear Sigma Model (NLSM) such that we can study the dynamical generation of an \(f_{0}(500)\) resonance. Introducing thermal effects via the imaginary time formalism allows us to study the behavior of the pole and relate it to chiral restoration.

Complex Langevin in Lattice QCD: Dynamic Stabilisation and the Phase Diagram

Acta Phys. Pol. B Proc. Suppl. 9, 621 (2016)

page 621 •


Complex Langevin simulations provide an alternative to sample path integrals with complex weights and, therefore, are suited to determine the phase diagram of QCD from first principles. We use our proposed method of Dynamic Stabilisation (DS) to ensure improved convergence to the right limit and present new systematic tests of this technique. We also show results on QCD in the limit of heavy quarks and an analysis of DS compared to known results from reweighting.

Attempt to Determine Mass Differences \(m_{K_{\rm L}}-m_{K_{\rm S}}\) and \(m_{K_2}-m_{K_1}\) from CPLEAR Data on Semi-leptonic Decay of \(K^0\) and \(\bar K^0\)

Acta Phys. Pol. B Proc. Suppl. 9, 627 (2016)

page 627 •


It is demonstrated that the theoretical formula for asymmetry, which has been used to determine mass difference \(m_{K_{\rm L}}-m_{K_{\rm S}}\) by its comparison with the CPLEAR Collaboration data, is incorrect. If one considers the \(K^0\leftrightarrow \bar K^0\) oscillations through \(K_{\rm L}\) and \(K_{\rm S}\) mesons to be defined in order to take into account CP violation in \(K\)-meson physics, the correct theoretical formula for asymmetry is calculated and by its comparison with the CPLEAR data, slightly different value for \(m_{K_{\rm L}}-m_{K_{\rm S}}\) is expected to be found. If \(K^0\leftrightarrow \bar K^0\) oscillations through \(K_2\) and \(K_1\) mesons, which reflect CP conservation in \(K\)-meson physics, are calculated, formally the identical theoretical formula for asymmetry is found with that used by the CPLEAR Collaboration, however, it depends on \(m_{K_2}-m_{K_1}\) mass difference and also on the \({\mit \Gamma }_{K_2}\) and \({\mit \Gamma }_{K_1}\) decay widths as unknown parameters. We expect that by a comparison of the latter with the CPLEAR Collaboration data, one can, in principle, find mass difference \(m_{K_2}-m_{K_1}\) and also the decay widths of \(K_2\), \(K_1\) mesons for the first time.

Computing the Topological Susceptibility from Fixed Topology QCD Simulations

Acta Phys. Pol. B Proc. Suppl. 9, 635 (2016)

page 635 •


The topological susceptibility is an important quantity in QCD, which can be computed using lattice methods. However, at a fine lattice spacing, or when using high-quality chirally symmetric quarks, typical simulation algorithms tend to get stuck in a single topological sector. In such cases, the computation of the topological susceptibility is not straightforward. Here, we explore two methods to extract the topological susceptibility from lattice QCD simulations restricted to a single topological sector. The first method is based on the correlation function of the topological charge density, while the second method relies on measuring the topological charge within spacetime subvolumes. Numerical results for two-flavor QCD obtained by using both methods are presented.

Heavy–Light Mesons in Minkowski Space

Acta Phys. Pol. B Proc. Suppl. 9, 641 (2016)

page 641 •


Following up on earlier work on the \(q\bar {q}\)-bound-state problem using a covariant, chiral-symmetric formalism based upon the Covariant Spectator Theory, we study the heavy–light case for both pseudoscalar and vector mesons. Derived directly in Minkowski space, our approach approximates the full Bethe–Salpeter-equation, taking into account, effectively, the contributions of both ladder and crossed ladder diagrams in the kernel. Results for several mass spectra using a relativistic covariant generalization of a Cornell plus a constant potential to model the interquark interaction are given and discussed.

Chiral-symmetry Breaking and Pion Structure in the Covariant Spectator Theory

Acta Phys. Pol. B Proc. Suppl. 9, 647 (2016)

page 647 •


We introduce a covariant approach in Minkowski space for the description of quarks and mesons that exhibits both chiral-symmetry breaking and confinement. In a simple model for the interquark interaction, the quark mass function is obtained and used in the calculation of the pion form factor. We study the effects of the mass function and the different quark pole contributions on the pion form factor.

Unquenching the Meson Spectrum: A Model Study of Exited \(\rho \) Resonances

Acta Phys. Pol. B Proc. Suppl. 9, 653 (2016)

page 653 •


Quark models taking into account the dynamical effects of hadronic decay often produce very different predictions for mass shifts in the hadron spectrum. The consequences for meson spectroscopy can be dramatic and completely obscure the underlying confining force. Recent unquenched lattice calculations of mesonic resonances that also include meson–meson interpolators provide a touchstone for such models, despite the present limitations in applicability. On the experimental side, the \(\rho (770)\) meson and its several observed radial recurrences are a fertile testing ground for both quark models and lattice computations. Here, we apply a unitarised quark model that has been successful in the description of many enigmatic mesons to these vector \(\rho \) resonances and the corresponding \(P\)-wave \(\pi \pi \) phase shifts. This work is in progress, with encouraging preliminary results.


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