INTERNATIONAL WORKSHOP ON CHIRAL SYMMETRY IN HADRONS AND NUCLEI
1322(2010); http://dx.doi.org/10.1063/1.3541982View Description Hide Description
The NA60 experiment at the CERN SPS has studied muon-pair production in 158A GeV In-In collisions. The unprecedented precision of the data has allowed to isolate a strong excess of pairs above the known sources in the whole invariant mass region 0.2<M<2.6 GeV. The (mostly) Planck-like shape of the mass spectra, exponential spectra, zero polarization and the general agreement with thermal-model results allow for a consistent interpretation of the excess dimuons as thermal radiation from a randomized system. For M<1 GeV, the process dominates. The associated space-time averaged ρ spectral function shows a nearly diverging width in approaching chiral symmetry restoration, but essentially no shift in mass. Some in-medium effects are also seen for the ω, but not for the φ. For M>1 GeV, the average temperature associated with the mass spectrum is about 200 MeV, considerably above implying a transition to dominantly partonic emission sources in this region. The transition itself is mirrored by a large jump-like drop in the inverse slope of the transverse mass spectra around 1 GeV.
1322(2010); http://dx.doi.org/10.1063/1.3541971View Description Hide Description
We introduce the concept of viscosity (both shear and bulk) in the context of hadron physics and in particular the meson gas, highlighting the current theoretical efforts to connect possible measurements of the viscosities to underlying physics such as a phase transition or the trace anomaly.
1322(2010); http://dx.doi.org/10.1063/1.3541981View Description Hide Description
The long-standing “Kaonic-helium puzzle”, i.e., the discrepancy between the measured and calculated 2p-level strong-interaction shift of kaonic helium 4, has been solved by the KEK E570 experiment; the measured 2p-level shift was thus agreeing with a majority of the theoretical calculations. The smallness of the kaonic helium-4 2p-level shift has recently been confirmed by the SIDDHARTA collaboration at DAΦNE. Both of these experiments used silicon drift X-ray detectors (SDDs), and have used elaborate in-situ calibration methods. In order to further study the low-energy kaon-nucleus interaction, the J-PARC E17 experiment will soon measure the kaonic helium-3 2p-level shift to high precision. I also briefly discuss the status of kaonic hydrogen x-ray spectroscopy. I also discuss recent experimental efforts to search for kaon-nucleus deeply-bound systems.
1322(2010); http://dx.doi.org/10.1063/1.3542008View Description Hide Description
We discuss the relevance of the scalar modes appearing in chiral theories with spontaneous symmetry breaking such as the NJL model for nuclear matter studies. We show that it depends on the relative role of chiral symmetry breaking and confinement in the nucleon mass origin. It is only in the case of a mixed origin that nuclear matter can be stable and reach saturation. We describe models of nucleon structure where this balance is achieved. We show how chiral constarints and confinement modify the QCD sum rules for the mass evolution in nuclear matter.
1322(2010); http://dx.doi.org/10.1063/1.3542028View Description Hide Description
We review recent results on properties of the meson gas relevant for Heavy Ion Collision and Nuclear Matter experiments, within the framework of chiral lagrangians. In particular, we describe the temperature and density evolution of the σ and ρ poles and its connection with chiral symmetry restoration, as well as the chemical nonequilibrated phase and transport coefficients.
1322(2010); http://dx.doi.org/10.1063/1.3542032View Description Hide Description
Medium modifications of the electromagnetic spectral function in hadronic and quark-gluon matter are reviewed. A strong broadening of the ρ meson, which dominates the spectral function in the low-mass regime, is quantitatively consistent with dilepton excess spectra measured in photoproduction off cold nuclei (CLAS/JLab) and in fixed-target ultrarelativistic heavy-ion collisions (NA45,NA60/CERN-SPS). The large excess observed by PHENIX at RHIC remains unexplained to date, but is most likely not due to emission from the Quark-Gluon Plasma. Connections to thermal lattice QCD promise progress in the search for chiral symmetry restoration.
1322(2010); http://dx.doi.org/10.1063/1.3542033View Description Hide Description
I will review our present understanding of in-medium changes of the properties of hadrons. Results of calculations for cold (nuclear matter) and for hot (heavy-ion collisions) strongly interacting matter will be discussed. The focus will be on hadrons made out of light quarks, in particular vector mesons and their interrelation to baryonic resonances.
1322(2010); http://dx.doi.org/10.1063/1.3542034View Description Hide Description
Hadron properties in strongly interacting matter provide a link between experimental observables and Quantum Chromodynamics (QCD) in the strong coupling regime. According to QCD sum rules changes in chiral and higher order condensates, which may partially be associated with a restoration of chiral symmetry in the nuclear medium, lead to significant modifications in the low-energy spectrum of hadrons. Reactions with elementary probes and heavy-ion collisions have been used to extract experimental information on in-medium properties of hadrons, in particular on the light vector mesons ρ, ω, and φ. Almost all experiments report a softening of the spectral functions in the nuclear medium. The increase in width depends on the density and temperature of the hadronic environment. No evidence for mass shifts is found in the majority of experiments. Remaining inconsistencies among experimental results call for further measurements.
1322(2010); http://dx.doi.org/10.1063/1.3542035View Description Hide Description
The pion plays an important role in a nucleus. Until now, its effect was treated in terms of the Brueckner theory in nuclear matter through the G-matrix effective interaction. The difficulty of handling the pion exchange interaction in a finite nucleus is through the strong tensor interaction due to the pion exchange. The tensor optimized shell model (TOSM) together with the unitary correlation operator method (UCOM) was demonstrated to provide a quantitative account of tensor correlation in a finite nucleus. We discuss in this paper the recently developed relativistic chiral mean field model for finite nuclei by taking the concept of TOSM and UCOM.
1322(2010); http://dx.doi.org/10.1063/1.3542036View Description Hide Description
We summarize the work of ref.  where a theoretical study of the properties of the axial-vector resonance in a cold nuclear medium is carried out. We start from a vacuum model for the resonance where it is generated dynamically from the interactions of a pseudoscalar and vector meson (ρπ and KK̄*) in a coupled channel chiral unitary approach. The medium effects are implemented through the modification of the ρ and π propagators at finite nuclear density from well established microscopic many-body calculations. The resulting in-medium exhibits significant broadening with increasing density as reflected in the ρπ scattering amplitude. The possible relation of our results with partial restoration of chiral symmetry in nuclear matter is discussed in terms of in-medium Weinberg sum rules.
1322(2010); http://dx.doi.org/10.1063/1.3542037View Description Hide Description
The self-consistent Green’s function method within the ladder approximation provides a microscopic description of correlated nuclear systems which properly treats the nucleon-nucleon correlations induced by the short-range and tensor components present in any realistic interaction. These correlations produce a sizable depletion of low momenta below the Fermi surface as well as the occupation of high momenta in the nuclear ground state. A few representative results for nuclear matter are presented to illustrate the present progress in the application of this method to nuclear systems.
1322(2010); http://dx.doi.org/10.1063/1.3541969View Description Hide Description
We have investigated the in-medium modifications of ω mesons in photoproduction experiments using the Crystal Barrel(CB)/TAPS detector system at the ELSA accelerator facility in Bonn. The ω-mesons were reconstructed using the channel. In a first analysis of the data set on a Nb target, published by Trnka et al. [Phys. Rev. Lett. 94(2005) 192303], evidence for an in-medium mass shift of the ω-meson was deduced from the observed ω line shape. The extracted signal shape was, however, found to be sensitive to the background subtraction. For this reason a re-analysis of the same data set was initiated with the goal to reduce the background and to deduce the shape and the absolute magnitude of the background directly from the data. Here we present recent results from this re-analysis. The omega signal resulting after background subtraction has been compared to different scenarios of GiBUU transport model calculations for the full incident photon energy range (900–2200 MeV) and near the production threshold (900–1300 MeV).
1322(2010); http://dx.doi.org/10.1063/1.3541970View Description Hide Description
The Dielectron Spectrometer HADES installed at GSI Darmstadt recently provided new intriguing results on production of electron pairs and strangeness from elementary and nucleus-nucleus collisions. The obtained data call for further systematic investigations of heavier systems and/or at higher energies.
For this purpose, the HADES spectrometer has been upgraded with a high-granularity RPC time-of-flight wall. In addition, a completely new detector read-out and data-acquisition system has been implemented which will greatly improve our data-taking rates.
We describe the current status of the HADES spectrometer and our plans for experiments on heavy system collisions at energies up to 10 A GeV on the upcoming FAIR facility.
1322(2010); http://dx.doi.org/10.1063/1.3541972View Description Hide Description
We report on the recent developments of a new effective field theory for nuclear matter [1, 2, 3]. We present first the nuclear matter chiral power counting that takes into account both short- and long-range inter-nucleon interactions. It also identifies non-perturbative strings of diagrams, related to the iteration of nucleon-nucleon interactions, which have to be re-summed. The methods of unitary chiral perturbation theory has been shown to be a useful tool in order to perform those resummations. Results up to next-to-leading order for the ground state energy per particle of nuclear matter, the in-medium chiral quark condensate and pion self-energy are discussed.
1322(2010); http://dx.doi.org/10.1063/1.3541973View Description Hide Description
Algebraic realization of chiral symmetry and its implications are studied. Hadrons are classified by linear representations with mixing when chiral symmetry is spontaneously broken. The axial vector coupling constant is then determined by representation mixing. Phenomenological test for measuring of a nucleon resonance is discussed.
1322(2010); http://dx.doi.org/10.1063/1.3541974View Description Hide Description
The importance is stressed of formulating a scattering theory that incorporates both unitarity in a multi-channel space and analyticity and in addition is consist with low energy theorems. Two very different possible approaches to come to such a model are presented, one based on solving an integral equation and one following a simpler algebraic approach. The latter is based on an extension of the K-matrix formalism into the complex momentum plane.
1322(2010); http://dx.doi.org/10.1063/1.3541975View Description Hide Description
The KLOE experiment has collected at the peak of the φ resonance at the collider DAΦNE in Frascati and KLOE-2 is expected to start data taking at the upgraded DAΦNE φ-factory late 2010, with the aim to collect at the φ peak and it is under discussion the collection of between 1 and 2.5 GeV. KLOE data have been used to investigate the properties of the light scalar mesons and light pseudoscalar mesons η, η′, using φ radiative decays. Gamma-gamma interactions allow to investigate also the meson, observing the reaction into a direct search of the into decay is performed with data taken at a center of mass of 1 GeV, where φ decays are suppressed. We present ongoing analysis and final results already published with the full KLOE statistics and the scientific program of KLOE-2 collaboration on hadron physics.
1322(2010); http://dx.doi.org/10.1063/1.3541976View Description Hide Description
The WASA detector facility is an internal experiment at the COoler SYnchrotron COSY in Jülich, Germany. The COSY accelerator provides proton and deuteron beams with momenta up to 3.7 GeV/c giving access to hadron physics including the strange quark sector. The WASA-at-COSY physics program focuses on light meson decays where rare decays are used to scrutinize symmetries and symmetry breaking. The structure of hadrons is probed with transition form factors and hadron spectroscopy while hadron dynamics is studied via reaction dynamics and few body reactions. Goals and status are reported with special emphasis on the meson Dalitz decays.