Quark mass function from a OGE-type interaction in Minkowski space

• Elmar Biernat (Instituto Superior Tecnico, Universidade de Lisboa)

I present the first results for the quark mass function in Minkowski space in both the spacelike and timelike regions calculated from the same quark-antiquark interaction kernel used in the latest meson calculations within the Covariant Spectator Theory. This kernel consists of a Lorentz vector effective one-gluon-exchange-type interaction, a vector constant, and a mixed scalar-pseudoscalar covariant linear confining interaction that does not contribute to the mass function. Our results are obtained in a general linear covariant gauge, their gauge dependence is analyzed and the Yennie gauge is identified as the appropriate gauge to be used in our calculations. Our results are compared in the spacelike region to the existing lattice QCD data and we find good agreement.

Signs of universal vector-meson coupling constants $f_\rho$, $f_\omega$, $f_\Phi$ with photon

• Stanislav Dubnicka (Institute of Physics)

Universal coupling constants $f_\rho$, $f_\omega$, $f_\Phi$ are determing the lepton decay widths of vector mesons in a quadratic form, therefore in their numerical evaluation from experimental values of $\Gamma(V\to e^+e^-)$ one does not know their signs. It is demonstrated strong dependence of the signs of $f_\rho$, $f_omega$, f_{\rho} on the $\omega-\Phi$ mixing forms. However, by application of the $\omega-\Phi$ mixing directly to electromagnetic currents of $\omega$ and $\Phi$ vector mesons and by a comparison of obtained results with Kroll-Lee_Zumino electromagnetic current to be identified with a linear combination of renormalized $\rho^0$, $\omega$ and $\Phi$ fields, signs of all coupling constants $f_{\rho}, $f_{\omega}$ and $f_{Phi}$ are specified.

New approach in knowledge of $a_{mu}^{(LO)had} values to the muon $g-2$ anomaly

• Adubni Dubnickova (Comenius University (SK))

Recently Pavia-Padova-Parma-Frascati group of theoretitions has suggested novel approach to determine the leading order of hadronic contribution $a_{\mu}^{(LO)had}$ to the muon $g-2$ anomaly, consisting in a measurement of the running QED fine structure constant by Bhaba $\mu e\to \mu e$ scattering at CERN and an extraction of $\delta\alpha_{had}^5(s)$ from the latter, to be crucial in determination of $a_{\mu}^{(LO)had}$. It is demonstrated how by one elaborated Unitary and Analytic model of electromagnetic structure of hadrons can be predicted $\delta\alpha_{had}^5(s)$ before measurements carried out at CERN.

Deconfinement temperature in AdS/QCD from the spectrum of scalar glueballs

• Sergey Afonin (Saint Petersburg State University)

We scrutinize various hologrphic estimations of the deconfinement temperature within the bottom-up AdS/QCD models. A special emphasis is put on the recent idea of isospectral potentials in the holographic approach. It is demonstrated that different models from an isospectral family (i.e., the models leading to identical predictions for the spectrum of hadrons with fixed quantum numbers) result in different predictions for the deconfinement temperature. This difference is found to be quite small in the scalar glueball channel but very large in the vector meson channel which is often used for fixing parameters of holographic models. The observed stability in the former case clearly favors the choice of the glueball channel for thermodynamic predictions in AdS/QCD models, with the scalar glueball trajectory being taken from lattice simulations and used as a basic input in improved versions of the Soft Wall holographic model.

Parton-pseudo distribution functions from Lattice QCD

• Savvas Zafeiropoulos (Universität Heidelberg)

The light-cone definition of Parton Distribution Functions (PDFs) does not allow for a direct ab initio determination employing methods of Lattice QCD simulations that naturally take place in Euclidean spacetime. In this presentation we focus on pseudo-PDFs where the starting point is the equal time hadronic matrix element with the quark and anti-quark fields separated by a finite distance. We focus on Ioffe-time distributions, which are functions of the Ioffe-time ν, and can be understood as the Fourier transforms of parton distribution functions with respect to the momentum fraction variable x. We present lattice results for the case of the nucleon and we also perform a comparison with the pertinent phenomenological determinations.

Strange resonances from analyticity and dispersion relations

• Jose R. Pelaez

I will review recent work on the determination of strange resonance parameters from meson-meson scattering data, using dispersion relations and other techniques based on analytic properties of amplitudes. Although I will discuss resonances below 1.7 GeV, I will pay particular attention to the lightest strange resonance K*(800) or kappa meson and the dispersive determination of its existence and its pole paramters as well as its possible non-ordinary nature.

Determination of the lightest hybrid meson candidate

• Arkaitz Rodas Bilbao (Universidad Complutense de Madrid)

In this talk I will review the recent analyses and other activities carried out by the JPAC collaboration. In particular, the recent phenomenological analysis of the COMPASS data on $\eta^{(')} \pi$ partial waves. We fit the data using a coupled-channel amplitude based on first principles, determining in a robust way the pole position of the hybrid meson candidate $\pi_1(1600)$, as well as the ordinary mesons $a_2(1320)$ and the $a'_2(1700)$.

Mesonic bound states in a nearly-conformal gauge theory

• Madeleine Adrien (University of Graz)

The matter content of a QCD-like gauge theory is tuned such that one is close to the conformal window, but still in the confining and chiral-symmetry-breaking regime. Properties of the respective mesonic-type bound states are discussed. Preliminary results towards an investigation of the spectrum of such a theory are presented.​

Dramatic Implications of Unitarity for Meson Spectroscopy

• George Rupp (CeFEMA/IST)

The most fundamental cornerstone of the PDG tables is the uniqueness of $S$-matrix pole positions of unstable particles, as a consequence of quantum-field-theory principles. Therefore, the unitarity property of the $S$-matrix should ideally be respected in whatever description of mesonic resonances in experiment, on the lattice, and in quark models. Unfortunately, simple Breit-Wigner parametrisations continue to be widely used in data analyses of mesonic processes, while lattice and model calculations are often still done by ignoring strong decay with its inevitable dynamical effects. All such approaches manifestly violate unitarity. On the other hand, most mesonic resonances are nowadays not generated in elastic scattering but instead in production processes, like electron-positron annihilation or multiparticle decays of much heavier mesons. In such processes, an extended unitarity relation holds between the production amplitude and the T-matrix for the scattering of two mesons from the resonance's decay. This relation is most naturally obeyed by writing the production amplitude as a purely kinematic, non-resonant lead term plus a term proportional to a sum over T-matrix elements. The lead term is a consequence of the vertex of the initial meson coupling to two lighter mesons, which is followed by rescattering through the T-matrix. Because of the non-pointlike nature of this vertex, dominated by $^{3\!}P_0$ quark-antiquark creation, it will give rise to an enhancement in the production cross section starting at the two-meson threshold. This may be mistaken for a true resonance or otherwise distort any true resonance in its vicinity. The implications of the above for modern meson spectroscopy will be briefly discussed on the basis of several model examples.

Resonance effects in bound states interaction kernels

• Ángel Miramontes (University of Graz)

We present results on the study of decay-channel effects in the properties of hadrons using covariant Bethe-Salpeter equations (BSEs). The main goal will be to develop BSE kernels that contain explicit decay mechanisms. This will be first explored in the meson sector where, for example, a kernel suitable to study the rho meson should contain a virtual 𝜌 → 𝜋+𝜋 decay mechanism. This will be tackled by including explicit pion degrees of freedom in addition to quarks and gluons.

The road to solving the Gribov problem of the center vortex model in quantum chromo dynamics.

• Rudolf Golubich (Technische Universität Wien)

Capable of explaining confinement, chiral symmetry breaking and the topological charge of the QCD vacuum, the centre vortex model still suffers from Gribov problems: Direct maximal centre gauge and centre projection can lead to an underestimation of the string tension in smooth configurations. Concrete improvements of the vortex detection procedures will be presented and a possible solution of the Gribov problem will be discussed.

T-dependence of the axion mass when the U_A(1) and chiral symmetry breaking are tied

• Dubravko Klabucar (Physics department, PMF, University of Zagreb)

Up to the scale of the spontaneous breaking of Peccei-Quinn symmetry, the axion mass M_a is determined by the QCD topological susceptibility χ(T) at all temperatures T. Using an approach tying the U_A(1) and chiral symmetry breaking, we calculate χ(T) for an effective Dyson-Schwinger model of nonperturbative QCD and obtain a good agreement with lattice results for χ(T), and thus also for M_a(T), for T as high as twice the chiral restoration temperature. The axion mass follows the dictate of the QCD topological susceptibility from vanishing T over the chiral phase transition to hight T where the chiral and U_A(1) symmetries are restored. Our prediction is additionally supported by the fact that our topological susceptibility yields the T-dependence of the U_A(1) anomaly-influenced masses of η' and η mesons which is consistent with experimental evidence.

Nuclei using topological solitons: Skyrmions and rho mesons

• Carlos Naya (INFN)

The Skyrme model is a low energy effective field theory of strong interactions where nuclei and baryons appear as topological solitons, more concretely as collective excitations of pionic degrees of freedom. Proposed by Tony Skyrme in the sixties, his ideas received further support when it was discovered that in the limit of the large number of colours of QCD, an effective theory of mesons arises. In the last years, there has been a revival of Skyrme's ideas and new related models have been proposed to overcome two of the main drawbacks of the theory, namely, the too large binding energies and the lack of cluster structures. The aim of this talk is to successfully address both issues at the same time, something that has not been done before, by extending the standard Skyrme model with the inclusion of the rho meson, via dimensional deconstruction of pure Yang-Mills theory in one higher dimension.

What does the yield of light nuclei tell us about relativistic heavy ion reactions

• Thomas Cohen (University of Maryland)

The yield of hadrons and light nuclei are described remarkable well by a very simple statistical hadronization model. The assumptions underlying this model are that below a certain temperature the system is well described by an equilibrated gas of hadrons that are sufficiently weakly interacting that their density is given by the density of noninteracting particle of the appropriate mass and that all of the species including the light nuclei chemically freeze out at the same temperature. At the LHC this temperature is approximately 155 MeV. This talk uses the light nuclei as a probe of the assumptions underlying the model. There is very strong evidence that the behavior of the light nuclei is incompatible with these assumptions.

Photoproduction of resonances from compact and spatially extended sources

• Lukasz Bibrzycki (Pedagogical University of Cracow)

Understanding the mechanisms of resonance photoproduction is essential for both fundamental and practical reasons. On the one hand the structure of resonances is directly related to basic properties of QCD like the confinement. On the other hand reliable models are badly needed to describe the wealth of the resonance photoproduction data to be expected in near future from JLab, ELSA, MAMI, and SPring-8 experiments. Of particular interest is the photoproduction of $\pi^+\pi^-$ pairs on the proton as for a time being this is the only reaction where the photoproduction of scalar $f_0$ resonances has been observed. We propose a uniform approach which enabled us to simultaneously describe the photoproduction of resonances in low partial waves $S$, $P$ and $D$ [1]. In our approach the photoproduction amplitude consists of two modes, the long range mode - dominated by one pion exchange and the short range mode which collectively includes contributions related to singularities located far away from the physical region. To describe the long rage mode we have combined the Deck model with SAID parametrisation of the $\pi p$ scattering amplitude. Such approach makes the description of the long range mode essentially parameter free. The short range mode, which includes eg. the exchange of heavier mesons and quark/gluon processes can be parametrized in terms of smooth functions. In this respect we have chosen the 1-st order polynomials in $\pi\pi$ invariant mass. The coefficients of these polynomials were then fitted to experimental mass distributions. This way we have obtained a very good description of $\pi^+\pi^-$ mass distributions for $S$, $P$ and $D$ partial waves, consistent with the fact that they are dominated by resonances $f_0(980)$, $\rho(770)$ and $f_2(1270)$, respectively. Moreover, we have found that strengths of the short range components for the $P$ and $D$ waves are much larger than for the $S$ wave. This is equivalent to saying that $\rho(770)$ and $f_2(1270)$ resonances are photoproduced from the compact source while the $f_0(980)$ from the diffuse source. This in turn is in accord with the expectation that $\rho(770)$ and $f_2(1270)$ are conventional $q\bar{q}$ states while the $f_0(980)$ is a more loosely bound four quark state. **References** [1] Ł. Bibrzycki, P. Bydžovský, R. Kamiński, A.P. Szczepaniak, Phys. Lett. B 789, 287-291 (2019), doi.org/10.1016/j.physletb.2018.12.045

X(3872) as a virtual companion pole

• Francesco Giacosa (Kielce University)

We study the state X(3872) as a companion state of a regular axial-vector charm-anticharm state, which is dressed by D-D* mesonic loops. As a consequence, in addition to a quite broad quark-antiquark state predicted by the quark model, a very narrow peak at the D-D* threshold -identified with X(3872) -emerges quite naturally. Moreover, the quarkonium core can explain the prompt production of this state. Quite interestingly, our approach can explain the magnitude of the isospin-suppressed decay into a j/Psi and a rho meson. Radiative decays are also studied. In conclusion, a consistent picture of the different and quite conflicting features of this enigmatic states can be explained in a simple quantum field theoretical framework.

New NA48/2 results on rare kaon decays

• Sergey Shkarovskiy (Joint Institute for Nuclear Research (RU))

NA48/2 results related to ChPT testing are presented. A most precise measurement of the charged kaon semileptonic form factors has been obtained from 4.4 million Ke3 and 2.3 million Kmu3 events collected in 2004. In addition, the branching ratio of the K+- -> pi+- pi0 e+ e- decay, never observed so far, has been obtained from a sample of about 4900 candidates. with less than 5% background. The branching ratio in the full kinematic region is (4.24 +- 0.14)x10^-6, in agreement with ChPT predictions.

$K^+\rightarrow\pi^+\nu\bar\nu$ decay and NP searches at NA62

• Silvia Martellotti (INFN e Laboratori Nazionali di Frascati (IT))

The decay $K^+\rightarrow\pi^+\nu\bar\nu$ has a very precisely predicted branching ratio (BR) of less than $10^{-10}$ and is one of the best candidates to reveal indirect effects of new physics at high mass scales. The NA62 experiment at CERN SPS is designed to measure $BR(K^+\rightarrow\pi^+\nu\bar\nu)$ with in-flight decays, a novel technique for this channel. NA62 took its first physics data in 2016, reaching sensitivity to the decay at the Standard Model BR. The experiment collected 10 times more statistics in 2017 and a similar amount of data is expected from the 2018 run. The result on $K^+\rightarrow\pi^+\nu\bar\nu$ from the full 2016 data set will be presented and prospects for future improvements will be discussed. Fixed target experiments are a useful tool in the search for very weakly coupled particles in the MeV–GeV range, which are of interest, e.g. as potential dark-matter mediators. Due to the high beam energy and hermetic detector coverage, NA62 also has the opportunity to directly search for a multitude of long-lived beyond-Standard-Model particles, such as dark photons, dark scalars, axion-like particles, and heavy neutral leptons. The status of these searches will be reviewed together with prospects for future data taking at NA62.

Doubly heavy tetraquarks

• Michal Praszalowicz (Jagiellonian University, Krakow)

With the discovery of doubly charmed Xi baryon a somewhat forgotten issue of tetraquarks containing two heavy and two light (anti) quarks aroused theorist's interest. We will discuss different approaches that have been used to estimate binding energy of such objects including a model where the light sector is treated as a soliton. We will show that this model has very different large Nc limit from other approaches and speculate that this might be a reason for stronger binding in the soliton case.

Overview of the Higgs boson measurements with the ATLAS detector

• Valerio Dao (CERN)

Overview of the Higgs boson measurements with the ATLAS detector

Physics prospects at HL-LHC

• Predrag Milenovic (University of Belgrade (RS))

Physics prospects at HL-LHC

New extended interpolating operators for hadron correlation functions

• Mauro Papinutto ("Sapienza" Universita` di Roma)

New extended interpolating operators made of quenched three dimensional fermions are introduced in the context of lattice QCD. The mass of the 3D fermions can be tuned in a controlled way to find a better overlap of the extended operators with the states of interest. The extended operators have good renormalisation properties and are easy to control when taking the continuum limit. Moreover the short distance behaviour of the two point functions built from these operators is greatly improved with respect to Jacobi smeared sources and point sources. A numerical comparison with point sources and Jacobi smeared sources on dynamical 2 + 1 flavour configurations is presented.

Heavy ion and fixed target results at LHCb

• Michael Schmelling (Max-Planck-Gesellschaft (DE))

Heavy ion and fixed target results at LHCb

Recent results on hard processes in p+Pb, Pb+Pb, and photon-photon collisions from the ATLAS Experiment at the LHC

• Radim Slovak (Charles University (CZ))

Recent results on hard processes in p+Pb, Pb+Pb, and photon-photon collisions from the ATLAS Experiment at the LHC

Recent hard probe measurements with STAR at RHIC

• Jana Bielcikova (Acad. of Sciences of the Czech Rep. (CZ))

Studies of hot and dense QCD matter created in high energy heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) revealed that the matter resembles properties of strongly coupled liquid with very low viscosity. High statistics data and major upgrades of the STAR experiment opened recently a new era of tomography of the QCD matter at RHIC using hard probes. In particular, the Heavy Flavor Tracker enables precision measurements of open heavy flavor hadrons and the Muon Telescope Detector greatly improves quarkonium measurements. Studies in the heavy flavor sector are corroborated by measurements of jet properties that provide further insights into the partonic energy loss in the QCD matter. In this talk, an overview of recent results on open heavy flavor hadron, quarkonium and jet production in Au+Au collisions at the top RHIC collision energy of 200 GeV per nucleon pair measured with the STAR experiment will be presented.

Study of Central Exclusive Production in proton-proton collisions with ALICE at LHC

• Paul Alois Buhler (Stefan Meyer Institute for Subatomic Physics (SMI), Austrian Academy of Sciences (AT))

Central Exclusive Production (CEP) in hadron-hadron collisions is a diffractive process in which the scattered hadrons remain intact, but exchange sufficient energy to produce a state X at central rapidity. As predicted by Regge theory the diffractive cross section at LHC energies is dominated by the Double Pomeron (DP) exchange. Due to the nature of the DP interaction it can be expected that states coupling preferentially to gluons, like glueballs and hybrids, are produced. The CEP events are characterized by large rapidity gaps. Using a combination of subdetectors of ALICE this specific event topology can be exploited to extract a clean sample of CEP events. The centrally produced X eventually decay into hadrons which are detected and identified with the central-barrel trackers of ALICE. In this talk we will further motivate these studies, discuss the experimental techniques applied, and present latest results of the two-pion and two-kaon invariant mass spectra observed in the selected CEP event sample, based on data taken during 2017 and 2018 at a center-of-mass energy of 13 TeV.

Heavy quarks in the quark-gluon plasma from lattice QCD

• Jon-Ivar Skullerud (National University of Ireland Maynooth)

We present recent results for correlators and spectral functions of mesons containing charm and beauty quarks below and above the deconfinement crossover. The results are obtained using anisotropic lattice QCD with 2+1 dynamical quark flavours. The high-temperature results are benchmarked against reconstructed correlators determined from the zero-temperature correlator, allowing us to disentangle temperature effects from the effects of the reduced range of the temporal correlator. In the open-charm sector, we find significant thermal modifications already below the deconfinement crossover, and no sign of any surviving bound states above T_c. For S-wave quarkonium, our results suggest that these states survive well into the QGP phase.

Initial deformation of a QGP droplet from collisions with polarized deuterons

• Wojciech Broniowski (IFJ PAN)

We propose to study ultra-relativistic collisions of polarized deuterons with heavy nuclei. Hydrodynamic expansion of the deformed initial source yields azimuthal asymmetry in the hadron emission with respect to the polarization axis. This provides an unequivocal way to probe experimentally the shape-flow transmutation mechanism responsible for the observed collectivity in small systems. [based on Phys.Rev.Lett. 121 (2018) 202301]

Lattice study of "rate" observables in Quark-Gluon Plasma: viscosities and sphaleron rate

• Andrey Kotov

Non-perturbative lattice computations, carried out in Euclidean space, are very powerful for determination of static observables. Numerical lattice methods can be also used for studying "rate" observables, which determine the rate of various processes in Quark-Gluon Plasma. The calculations are based on the Kubo relations, which relate these observables and the correlators of the corresponding operators. In this report we discuss non-perturbative lattice measurements of such quantities as shear and bulk viscosities, which describe the evolution of stress-energy tensor, and sphaleron rate, which gives the rate of topology-changing transitions in QGP. To invert Kubo relations we apply the state-of-art lattice methods. We discuss the final results and compare them with ones obtained by other methods.

Lattice study of deconfinement in two-color dense quark matter

• Nikita Astrakhantsev

In this work we studied the two-color QCD at finite density and low temperature within lattice simulation. The aim was to study of the interaction within a static quark-antiquark pair in two-color dense quark matter. To this end we performed measured the Polyakov loop correlation functions and calculated the color averaged, color singlet and color triplet grand potentials. Having determined the renormalized grand potentials, we calculated the renormalized grand potential of a single quark/antiquark, average Polyakov loop, string tension and the Debye mass. In addition we calculated the quark number induced by a static quark antiquark pair and its specific energy. The observed confinement/deconfinement transition at finite density manifests itself in an increasing value of the Polyakov loop. Contrary to the finite temperature confinement/deconfinement transition, the finite density transition does not show a region of rapid rise of the Polyakov loop. For this reason we conclude that the observed transition from confinement to deconfinement at finite density is smooth. Moreover, we observe string breaking at large chemical potentials, which we believe is also a manifestation of the confinement/deconfinement transition.

Density of State method for complex action systems

• Olmo Francesconi (Swansea University & LPMMC Grenoble)

While importance sampling Monte Carlo algorithms have proved to be a crucial tool for numerical studies in modern physics, they fail when we take into consideration complex action systems. The density of states approach provides a way to simulate such systems and reduce the sign problem that afflicts them to a 1-dimensional oscillatory integral. In this talk, I will review the density of states approach as well as the Linear Logarithmic Relaxation algorithm and present some recent development concerning the bias control of the latter. The results of a benchmark study on the relativistic Bose gas will be presented as well.

Inhomogeneous phases in the 1+1 dimensional Gross-Neveu model at finite numbers of fermion flavors

• Laurin Pannullo (Goethe University)

We study the phase diagram of the 1+1 dimensional Gross-Neveu model at finite numbers of fermion flavors using lattice field theory. Particular focus is put on simulations at small temperature and large chemical potential. First results are presented, which indicate the existence of an inhomogeneous phase.

Measurements of correlated hadron production with the ATLAS detector

• David Anthony Milstead (Stockholm University (SE))

Measurements of correlated hadron production with the ATLAS detector

Nonperturbative propagators and vertices from Dyson-Schwinger equations

• Markus Huber (University of Graz)

Correlation functions of quantum chromodynamics can be used to calculate bound states or investigate the phase diagram. I will report on the present state of determining the correlation functions of pure QCD from Dyson-Schwinger equations. Various investigations, like calculations beyond primitively divergent correlations functions or of two-loop diagrams, hint at favorable convergence properties of the system.

Light scalar and first steps towards heavy axialvector tetraquarks in the BSE/DSE framework

• Paul C. Wallbott

During the last years numerous new states in the charmonium spectrum around threshold have been found. However, they still lack satisfactory explanation. Prominent examples are the XYZ states. In some cases the properties suggest at a minimum four quarks; the so-called tetraquarks. To describe these bound states of the strong force, mainly lattice QCD and potential models have thus far been used. We develop an approach that allows for the calculation of four quark states with continuum QCD methods, namely the BSEs and DSEs. In recent years it has already successfully been applied to the full meson and baryon sector, as well as light scalar tetraquarks. We present a new method for solving the tetraquark BSE and show its application to light scalars as well as first results in the heavy axialvector (charmonium) sector.

Two- and Three-Body Resonances in the Finite Volume

• Michael Döring (The George Washington University)

Unitarity dictates the on-shell condition of multi-particle systems. It is therefore the tool to determine the leading finite-volume effects needed for the extrapolation of lattice QCD results. Together with unitary extensions of Chiral Perturbation Theory, one may attempt to extrapolate to the physical point. After a short summary on recent extrapolations in the two-body resonance sector (sigma, rho), a new, relativistic method for the extrapolation of three-particle systems is presented, based on a three-body unitary isobar expansion. Existing data from the NPLQCD collaboration on a system of three interacting pions is analyzed and, for the first time, excited levels for a physical three-body system are predicted.

Chiral perturbation theory in the environment with chiral imbalance

• Aleksandr Andrianov (Saint Petersburg State University)

Chiral imbalance in quark medium is imprinted into the hadron matter after hadronization. It is a consequence of quark/hadron continuity. For low momenta it modifies a chiral lagrangian reappearing as a chiral chemical vector, namely a constant axial vector field. It modifies the pion spectral properties: its decays, its formfactors and polarizability. This modification of ChPT will be elucidated in details beung a good phenomenological basis for discovery of local parity breaking in heavy ion collisions.

Two-body correlations in ultra-relativistic nuclear collisions within a generic string model with wounded quarks

• Martin Rohrmoser (Jan Kochanowski University Kielce)

While string models describe initial state radiation in ultra-relativistic nuclear collisions suitably well, they mainly differ among each other in the presumed end-point positions of the strings in spatial rapidity. We present a generic model where wounded quarks are amended with strings whose both end-point positions fluctuate and analyze semi-analytically various scenarios of string-end-point fluctuations. In particular we constrain the different cases to experimental data on rapidity spectra from collisions at $\sqrt{s_{\rm NN}}=200$ GeV, and explore their respective two-body correlations. We find that the popular measures used to quantify the longitudinal fluctuations are limited with upper and lower bounds and assume close values for the most likely models of the end-point distributions, which may explain why various approaches yield here very similar results.