Proceedings Series


Vol. 2 (2009), No. 2, pp. 187 – 466

International Meeting Excited QCD

Zakopane, Poland; February 8-14, 2009

Energy Losses in a Hot Plasma

abstract

The energy loss of a fast charged particle crossing a hot plasma is reviewed.


LHC Heavy Quark Perspectives

abstract

After a short presentation of the motivations for measuring heavy flavors in heavy ion collisions at the LHC, the three LHC experiments ALICE, CMS and ATLAS are detailed. Then some selected physics channels are discussed.


\(S\)-Wave Interactions Between Charmed Mesons and Goldstone Bosons from Chiral Dynamics

abstract

We study the interaction between the charmed mesons and the Goldstone bosons using unitarized chiral perturbation theory. In this scheme the \(D_{s0}^*(2317)\) is dynamically generated in the \((S,I)=(1,0)\) channel, and its isospin violating decay width is calculated including both the strong and electromagnetic contributions. Furthermore, the \(S\)-wave scattering lengths for charmed mesons scattering off Goldstone bosons, as well as their quark mass dependences, are investigated. We suggest two different ways to identify the nature of the \(D_{s0}^*(2317)\).


Light Scalar Mesons: Comments on Their Behavior in the \(1/N_c\) Expansion Near \(N_c=3\) Versus the \(N_c\rightarrow \infty \) Limit

abstract

We briefly review how light meson resonances are described within one and two-loop Unitarized Chiral Perturbation Theory amplitudes and how, close to \(N_c=3\), light vectors follow the \(N_c\) behavior of \(q\bar q\) mesons whereas light scalars do not. This supports the hypothesis that the lightest scalar is not predominantly a \(q\bar q\) meson, although a subdominant \(q\bar q\) component is suggested around 1 GeV at somewhat larger \(N_c\). In contrast, when \(N_c\) is very far from 3, like in the \(N_c\rightarrow \infty \) limit, we explain again in detail why unitarization is not, a priori, reliable nor robust and why this limit should not be used to drag any conclusions about the dominant nature of physical light scalar mesons.


Comparative Analysis of Large \(N_c\) QCD and Quark Model Approaches to Baryons

abstract

We show that a remarkable compatibility exists between the results of a potential model with constituent quarks and the \(1/N_c\) expansion mass formula for strange and nonstrange baryon resonances. Such compatibility brings support to the basic assumptions of relativistic quark models and sheds light on the physical content of the model-independent large \(N_c\) mass formula. Good agreement between both approaches is also found for heavy baryons, made of one heavy and two light quarks, in the ground state band.


Baby Steps Beyond Rainbow–Ladder

abstract

We discuss the impact of including corrections beyond single gluon exchange in light mesons within the nonperturbative framework of Dyson–Schwinger equations (DSE) and Bethe–Salpeter equations (BSE). We do this by considering unquenching effects in the form of hadronic resonance contributions, notably pion exchange, and by the inclusion of the dominant gluon self-interactions to the quark–gluon vertex. Thus we make steps towards an ab initio description of light mesons by functional methods.


Influence of Vector Mesons on the \(f_0(600)\) Decay Width in a Linear Sigma Model with Global Chiral Invariance

abstract

We consider a globally invariant chiral Lagrangian that contains vector and axial-vector mesons. We compute the \(f_0(600) \rightarrow \pi \pi \) decay width and \(\pi \pi \) scattering lengths and compare width the corresponding results in which the (axial-)vector degrees of freedom decouple. We show that the role of vector mesons has a great impact on both quantities.


Resummation in Fractional APT: How Many Loops Do We Need to Take into Account?

abstract

We give a short introduction to the Analytic Perturbation Theory (APT) [D.V. Shirkov, I.L. Solovtsov, JINR Rapid Commun. 2, 5 (1996); Phys. Rev. Lett. 79, 1209 (1997); Theor. Math. Phys. 150, 132 (2007)] and its generalization to fractional powers — FAPT [A.P. Bakulev, S.V. Mikhailov, N.G. Stefanis, Phys. Rev. D72, 074014 (2005), 119908(E); 75, 056005 (2007); 77, 079901(E) (2008) and A.P. Bakulev, A.I. Karanikas, N.G. Stefanis, Phys. Rev. D72, 074015 (2005)]. We describe how to treat heavy-quark thresholds in FAPT and then show how to resume perturbative series in both the one-loop APT and FAPT. As an application we consider FAPT description of the Higgs boson decay \(H^0\to b\bar {b}\).


Search for Exotics in \(\overline {\mathrm {P}}\)ANDA

abstract

At GSI is in preparation a new international research facility, called FAIR. A key feature of this new facility will be the delivery of an intense, high-quality secondary beam of antiprotons at the High Energy Storage Ring (HESR) on which the \(\overline {{\rm P}}\)ANDA experiment will be installed. In this paper, the rich spectroscopy program on exotic hadrons of \(\overline {{\rm P}}\)ANDA, is presented.


Glueballs and Statistical Mechanics of the Gluon Plasma

abstract

Describing the gluon plasma as an ideal gas of transverse gluons with a temperature-dependent mass \(m(T)\) allows to reproduce its equation of state, computed in pure glue lattice QCD. Dealing with \(m(T)\) demands to build a thermodynamically consistent framework. We propose a general way to obtain such a formalism and apply it to the gluon plasma. Then we argue that the peculiar behavior of \(m(T)\) near the critical temperature \(T_{\rm c}\) is due to color interactions between the gluons. Using an effective glueball model with a lattice QCD-derived screened color interaction, we show that those interactions are strong enough to bind the lightest glueballs up to 1.13 \(T_{\rm c}\). Moreover, the thermodynamical properties of the gluon plasma can be understood by describing it as a mixture of an ideal gas of free gluons and glueballs, with a temperature-dependent glueball abundance.


The Physics of Glueballs

abstract

I present a model for glueballs with two and three constituent gluons. I show that, even if spin-1 gluons seem to reproduce properly the lattice QCD spectrum for \(C=+\) states, the extension for \(C=-\) cannot match with the lattice results. Resorting to the helicity formalism, we show how transverse gluons fit in better agreement the lattice QCD spectrum. We then conclude that even if gluons gain an effective mass, they remain transverse particles.


Lattice QCD and Three-Body Exotic Systems in the Static Limit

abstract

The static potentials for quark–antiquark–gluon and 3-gluon systems are computed with lattice QCD methods. For the quark–antiquark–gluon hybrid meson the static potential is obtained for different values of the angle between the quark–gluon and antiquark–gluon segments. The simulations support the formation of an adjoint string for small angles, while for large angles, the adjoint string is replaced by two fundamental strings connecting the gluon and the quarks. For the 3-gluon glueball, we discuss the corresponding Wilson loops and show that the gluons are connected by fundamental strings when the gluons are far apart.


Unquenching and Requenching the Quark Model

abstract

Theoretical issues with incorporating virtual quark effects in the constituent quark model are discussed. A formalism for integrating out virtual meson channels is described.


Anthropic Constraints on Fermion Masses

abstract

We summarize the results of previous research on the constraints imposed on quark masses by the anthropically-motivated requirement that there exist stable nuclei with the right charge to form complex molecules. We also mention an upper bound on the mass of the lightest lepton, derived from the requirement that such nuclei be stable against electron capture.


Pion Form Factor in the QCD Sum-Rule Approach with Nonlocal Condensates

abstract

We present results of a calculation of the electromagnetic pion form factor within the framework of QCD Sum Rules with nonlocal condensates, using a perturbative spectral density which includes \(O(\alpha _{\rm s})\) contributions.


The Four-Gluon Vertex and the Running Coupling in Landau Gauge Yang–Mills Theory

abstract

We summarise results for the running coupling from the four-gluon vertex in Landau gauge, SU(\(N_c\)) Yang–Mills theory as given by a combination of dressing functions of the vertex and the gluon propagator. These functions have been determined numerically from the corresponding set of Dyson–Schwinger equations. In the infrared we obtain a nontrivial infrared fixed point which is three orders of magnitude smaller than the corresponding one in the coupling of the ghost-gluon vertex.


Exploring Excited Hadrons in Lattice QCD

abstract

Progress in extracting the spectrum of excited hadron resonances in lattice QCD Monte Carlo calculations is reviewed and the key issues and challenges in such computations are outlined. The importance of multi-hadron states as simulations with lighter pion masses are done is discussed, and the need for all-to-all quark propagators is emphasized.


Baryon Spectroscopy at ELSA

abstract

The CsI(Tl) Crystal Barrel calorimeter at ELSA, University of Bonn, Germany, is the ideal instrument to study various multi-photon final states over the full dynamical range. For the data presented at this workshop, the Two-Armed Photon Spectrometer (TAPS) was placed in the forward direction, serving as a fast trigger and increasing the overall angular coverage to essentially the full \(4\pi \) solid angle. Differential cross-sections for the reactions \(\gamma p\to p\eta \) and \(\gamma p\to p\eta \,'\) have been determined and are discussed here as an example of recent results. The \(\eta \) meson has been studied in its two neutral decay modes (\(\eta \to 3\pi ^0 \to 6\gamma \) and \(\eta \to 2\gamma \)) for incoming photon energies in the range of \(E_{\gamma } = 850\)–2550 MeV. The \(\eta \,'\) meson has been identified in its neutral decay mode into \(2\pi ^0\eta \to 6\gamma \) for a photon energy range of \(E_{\gamma } = 1500\)–2550 MeV. Both the \(\eta \) and \(\eta \,'\) photoproduction data cover the full angular range (\(-1 \lt {\rm cos}\,\theta ^{\rm \,c.m.}_{\rm meson}\lt 1\)).


Excited Baryons as Experimental Probes of the Quark Mass

abstract

We observe that excited hadrons provide an opportunity to probe from experiment the power-law running of the quark mass in the mid infrared, while the condition \(m(k)\lt k\) remains valid. A relatively clean analysis is possible for the maximum spin excitations of the \({\mit \Delta }\) baryons accessible at current experimental facilities such as ELSA and Jlab.


About the Origin of the Mass of the Nucleon in a Linear Sigma Model

abstract

Beyond the contribution of the chiral condensate to the nucleon mass, in the so-called mirror assignment a chirally invariant mass term \(\sim m_{0}\) is possible. In the present work it is discussed on light of recent results which is the role of both terms in generating the nucleon mass. Also, the origin of \(m_{0}\) in terms of tetraquark and gluon condensates is briefly discussed.


QCD’s Partner Needed for Mass Spectra and Parton Structure Functions

abstract

As in the case of the hydrogen atom, bound-state wave functions are needed to generate hadronic spectra. For this purpose, in 1971, Feynman and his students wrote down a Lorentz-invariant harmonic oscillator equation. This differential equation has one set of solutions satisfying the Lorentz-covariant boundary condition. This covariant set generates Lorentz-invariant mass spectra with their degeneracies. Furthermore, the Lorentz-covariant wave functions allow us to calculate the valence parton distribution by Lorentz-boosting the quark-model wave function from the hadronic rest frame. However, this boosted wave function does not give an accurate parton distribution. The wave function needs QCD corrections to make a contact with the real world. Likewise, QCD needs the wave function as a starting point for calculating the parton structure function.


Nuclear DVCS Within the High Energy QCD Color Dipole Formalism

abstract

In this contribution, we present a study of the coherent and incoherent nuclear DVCS process, \(\gamma ^* A \rightarrow \gamma \,X\), in the small-\(x\) regime within the color dipole formalism. Predictions for the nuclear DVCS cross-section at photon level in the collider kinematics are presented.


Precision Measurements of Radiative Charged Kaon Decays at NA48/2

abstract

This paper presents results obtained by the NA48/2 experiment at CERN SPS. Data samples of \(1.24\times 10^5\ K^\pm \to \pi ^\pm \pi ^0 \gamma \), \(7146\,K^\pm \to \pi ^\pm e^+ e^-\), \(1164\,K^\pm \to \pi ^\pm \gamma \gamma \) and \(120\,K^\pm \to \pi ^\pm e^+e^- \gamma \) decays (this last one observed for the first time) have been collected with small background, allowing precise measurements of branching fractions and other characteristics of these rare kaon decays.


Hyperon Resonances in Radiative Kaon Capture

abstract

We use crossing symmetry to extend our Regge model for electromagnetic kaon production from the proton to the case of radiative kaon capture. Our model is based on the exchange of the \(K(494)\) and \(K^*(892)\) Regge trajectories in the \(t\)-channel. We use the parameters fitted to describe the \(p(\gamma ,K^+)Y\) reaction to make predictions for the \(p(K^-,\gamma )Y\) process. The differential crosss-sections of the latter for kaon momenta of 520 and 750 MeV/\(c\) show a satisfactory agreement with data from the Crystal Ball Collaboration.


Steiner-Tree Confinement and Tetraquarks

abstract

The linear confinement in quarkonium is generalised as a minimal tree, with interesting geometrical properties. This model binds tetraquarks more easily than the additive model used in earlier investigations.


all authors

R. Sahoo, T.K. Nayak, J. Alam, S. Kabana, B.K. Nandi, D.P. Mahapatra

\(\phi \) Meson As a Probe of QCD Equation of State

abstract

In this work, we extract the QCD Equation of State (EoS) using experimental results of the \(\phi \) meson produced in nuclear collisions at AGS, SPS and RHIC energies. The data are confronted to simple thermodynamic expectations and lattice results. The experimental data indicate a first order phase transition, with a mixed phase stretching energy density between \(\sim 1\) and 3.2 GeV/fm\(^3\).


Holographic QCD with Matter

abstract

In this brief note, we will discuss the quark density dependence of the deconfinement phase transition using the probe approximation, in which only the low density regime is valid. When considering the first correction of the quark density, the deconfinement temperature decreases as the quark density increases like the lattice QCD result.


Timelike Compton Scattering at LHC

abstract

Exclusive photoproduction of dileptons, \(\gamma N\to \ell ^+ \ell ^- N\), is and will be measured in ultraperipheral collisions at hadron colliders. We demonstrate that the timelike deeply virtual Compton scattering (TCS) mechanism \(\gamma q \to \ell ^+ \ell ^- q\), where the lepton pair comes from the subprocess \(\gamma q \to \gamma ^* q\), dominates in some accessible kinematical regions, thus opening a new way to study generalized parton distributions in the nucleon at small skewedness.


Search for the \(\eta \)-Mesic Helium at COSY

abstract

We review status and perspectives of the search of the \(\eta \)-mesic helium at the cooler synchrotron COSY.


Tests of Chiral Perturbation Theory with \(K_{e4}\) Decays at NA48/2

abstract

The experiment NA48/2 at CERN SPS performed high precision measurement of the form factors of \(K^\pm \rightarrow \pi ^+\pi ^-e^\pm \nu \) decays and \(s\)-wave \(\pi \pi \) scattering lengths \(a_0\) and \(a_2\) for isospin 0 and 2, respectively. The preliminary result on the full available statistics of more than 1 million \(K^{+-}_{e4}\) decays achieves a precision similar to the theoretical one and provides excellent test of Chiral Perturbation Theory.


Once and Twice Subtracted Dispersion Relations in the Analysis of \(\pi \pi \) Amplitudes

abstract

Once and twice subtracted crossing symmetric dispersion relations applied to \(\pi \pi \to \pi \pi \) scattering data are analyzed and compared. Both sets of dispersion relations can be used to test the \(\pi \pi \) amplitudes in low partial waves up to about 1 GeV. We show how once subtracted dispersion relations can provide stronger constraints for \(\pi \pi \) amplitudes than twice subtracted ones in the 400 to 1100 MeV range, given the same experimental input.


Hadronic Interactions of \(K^-\) in Light Nuclei: The AMADEUS Experiment and KLOE Data Analysis

abstract

The AMADEUS experiment will perform for the first time full-acceptance studies of hadronic interactions of \(K^-\) in light nuclei, with a complete experimental program for the case of the deeply bound kaonic nuclear states. The possible formation of a kaonic cluster could provide information concerning the modification of the kaon mass and of the \(\bar {K}N\) interaction in the nuclear medium A preliminary study of this kind of hadronic interaction is being done by the AMADEUS Collaboration by analyzing the KLOE data.


The Phase Transition in Chiral Fluid Dynamics

abstract

We present a chiral fluid dynamic model that allows for the dynamic study of the QCD phase transition and of the critical point. The non-equilibrium propagation of the chiral fields influences the fluid dynamic evolution of the quark fluid. This leads to inhomogeneities of the energy density in a discontinuous phase transition. When passing through a critical point the correlation length grows. This could be the basis for signatures of the critical point in heavy ion collisions.


Testing the Predicted Dynamically Generated Hidden Charm Scalar \(X\) State Through the Radiative Decay of the \(\psi (3770)\) and the \(D\bar D\) Invariant Mass Spectrum

abstract

In this talk we present our model to generate resonances dynamically from the interaction of two mesons in coupled channels. Our phenomenological model describes many of the experimentally known scalar and axial charmed resonances and it also predicts a hidden charm scalar state with mass close to the \(D\bar D\) threshold. We investigate the possibility to observe this resonance through the radiative decay of the \(\psi (3770)\) and we also perform a calculation of the mass spectrum of \(D\bar D\) in the reaction \(e^+e^-\rightarrow J/\psi D\bar D\), assuming that the \(D\bar D\) pair originates from this scalar resonance.


Charm at FAIR

abstract

Charmed mesons in hot and dense matter are studied within a self-consistent coupled-channel approach for the experimental conditions of density and temperature expected at the CBM experiment at FAIR/GSI. The \(D\) meson spectral function broadens with increasing density with an extended tail towards lower energies due to \({\mit \Lambda }_c(2593) N^{-1}\) and \({\mit \Sigma }_c(2800) N^{-1}\) excitations. The in-medium \(\bar D\) meson mass increases with density. We also discuss the consequences for the renormalized properties in nuclear matter of the charm scalar \(D_{s0}(2317)\) and \(D(2400)\), and the predicted hidden charm \(X(3700)\) resonances at FAIR energies.


KLOE Results on Light Meson Spectroscopy

abstract

An important part of the program of the KLOE experiment has been dedicated to the study of the \(\phi \) radiative decays into scalar (\(f_0(980)\) and \(a_0(980)\)) and pseudoscalar (\(\eta \) and \(\eta ^{\prime }\)) mesons.


The Nature of the \(X(2175)\)

abstract

We study the puzzling vector meson \(X(2175)\) in a multichannel generalisation of the Resonance Spectrum Expansion model. Besides the usual \(P\)-wave pseudoscalar–pseudoscalar, pseudoscalar–vector, and vector–vector channels that couple to mesons with vector quantum numbers, we also include the important \(S\)-wave vector–scalar, pseudoscalar–axial-vector and vector–axial-vector channels, including the observed \(\phi (1020)\,f_0(980)\) decay mode. The strong coupling to nearby \(S\)-wave channels originate dynamically generated poles, two of which come out close to the energy region of the \(X(2175)\), viz. at \((2.037-i0.170)\) GeV and \((2.382-i0.20)\) GeV. Further improvements are proposed.


Light and Not So Light Scalar Mesons

abstract

A multichannel description of the light scalar mesons in the framework of the Resonance Spectrum Expansion is generalised by including vector–vector and scalar–scalar channels, besides the usual pseudoscalar–pseudoscalar channels. Experimental data for the isoscalar, isodoublet and isovector cases are fitted up to energies well above 1 GeV. The resulting pole positions of the light and intermediate scalar mesons are compared to the listed resonances. Possible further improvements are discussed.


Confinement of Electrons in QED2+1 and Quarks in QCD3+1 in Temporal Euclidean Space

abstract

Without any analytical assumption we solve the ladder QED2+1 in Minkowski space. Further, we transform Greens functions to the Temporal Euclidean space, wherein we show that in the special case of ladder QED2+1 the solution is fully equivalent to the Minkowski one. QCD quark gap equation is solved in the framework of Temporal Euclidean space as well. In both models, the obtained complex fermion propagators exhibits confinement, since it does not satisfies Khallen–Lehmann representation.


Application of Chiral Quarks to High-Energy Processes and Lattice QCD

abstract

Results of the chiral quark models for the soft matrix elements involving pions and photons, relevant for high-energy processes, are reviewed. We discuss quantities related to the generalized parton distributions of the pion: the parton distribution functions, the parton distribution amplitudes, and the generalized form factors. The model predictions are compared to the data or lattice simulations, with good agreement. The QCD evolution from the low quark model scale up to the experimental scales is a crucial ingredient of the approach.


Low-\(x\) QCD at the LHC with the ALICE Detector

abstract

We give a brief review of the physics of gluon saturation and non-linear QCD evolution at small value of the Bjorken-\(x\) variable. We discuss the ALICE capability for low-\(x\) studies at the LHC. In particular, we concentrate on the heavy quark production in the CGC framework and its observation with the ALICE Muon Spectrometer.


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