Search

A new transversely polarised frozen spin target has been developed at MAMI which will be used in conjunction with the photon tagger and the Crystal Ball detector. The new target permits a major new programme of accurate measurement of polarisation observables in meson photoproduction. This contribution presents some of the preliminary analysis from experimental data taken near the threshold and in the region of the Δ(1232) resonance. Observables will be obtained for the pπ0 and pπ+ final states. [ABSTRACT FROM AUTHOR]

[lowercase_phi_synonym] meson photoproduction is discussed as a part of a combined analysis of meson production reactions. Particular emphasis is given to analyze the recent photoproduction data from the LEPS Collaboration, where a bump structure at √s ≈ 2.15 GeV has been observed. [ABSTRACT FROM AUTHOR]

A new generation of complete experiments in pseudoscalar meson photo-production is being pursued at several laboratories. While new data are emerging, there is some confusion regarding definitions of asymmetries and the conventions used in partial wave analyses (PWA). We present expressions for constructing asymmetries as coordinate-system independent ratios of cross sections, along with the names used for these ratios by different PWA groups. [ABSTRACT FROM AUTHOR]

We study the stability of resonance poles in πN P11 partial wave, particularly the Roper resonance, by varying parameters significantly within the EBAC dynamical coupled-channels model, keeping a good fit to the empirical amplitude. We find that two Roper poles are stable against the variation. However, for higher energies, the number of poles can change depending on how the parameters fitted within error bars. We also developed a model with a bare nucleon which forms the physical nucleon by being dressed by the meson-cloud. We still find a good stability of the Roper poles. [ABSTRACT FROM AUTHOR]

Problems in the construction of amplitudes from meson photoproduction data are examined. Methods are applied to pion and kaon photoproduction data with the goal of minimal model bias. [ABSTRACT FROM AUTHOR]

Amplitude and partial wave anlaysis for pion, eta or kaon photoproduction are discussed in the context of 'complete experiments'. It is shown that the model-independent helicity amplitudes obtained from 8 polarization observables including beam, target and recoil polarization can not be used to determine underlying resonance parameters. However, a truncated partial wave analysis, which theoretically requires only 5 observables will be possible with minimal model input. [ABSTRACT FROM AUTHOR]

An overview of current theoretical approaches to generate meson-baryon reaction amplitudes is given. [ABSTRACT FROM AUTHOR]

The experimental focus of the ELSA facility at the University of Bonn and recent achievements in the instrumentation are outlined. Selected results on unpolarized cross sections for meson and N* production and single and double polarization observables to study the nucleon excitation spectrum are briefly addressed. [ABSTRACT FROM AUTHOR]

A Large Ion Collider Experiment (ALICE) is one of the four experiments at the Large Hadron Collider (LHC), and it is dedicated to the study of ultra-relativistic heavy-ion collisions, with the goal of investigating the properties of the high-density state of QCD matter produced in such events. The first Pb-Pb collisions at a centre of mass energy of [formula] TeV per nucleon pair were delivered by LHC in November 2010. In Pb-Pb collisions heavy quarks are regarded as sensitive probes of the interaction dynamics between the parton and the medium produced in such collisions as they are produced on a very short time scale in the initial hard scattering processes and they follow all the evolution of the medium. At the energies available at the LHC charm is produced with large cross section and therefore it is possible to measure its production with good statistical precision. The study of open charm hadrons such as D+, D0, D*+, Ds and Λc in heavy ion collision is of particular interest because it can provide significant insight on the properties of the medium. Proton-proton collision data, that are being recorded at an energy of [formula] TeV since March 2010 provide an essential reference for these studies and allow to test perturbative QCD calculations in an unexplored energy domain. In this paper the analysis of D-meson production, carried out through a study of the hadronic decay channels in Pb-Pb collisions, will be presented in detail. The results for the reconstruction of D0, D+, D*+, and Ds hadrons at central rapidity will be shown along with the first results for the measurement of the D0 and D+ nuclear modification factor and prospects for azimuthal anisotropy studies. [ABSTRACT FROM AUTHOR]

The production of resonances in pp collisions at 7 TeV using their hadronic decay was measured by the ALICE experiment at LHC. In particular, transverse momentum spectra dN/dydpT at midrapidity |y|<0.5 for K*(892)°, [lowercase_phi_synonym](1020) and |y|<0.8 for Σ(1385)± are presented and compared to model prediction. Different levels of agreement are obtained for mesons spectra, while baryonic spectrum is always underestimated. The [lowercase_phi_synonym](1020) spectra in the rapidity range (2.5

The properties of hadrons, such as their masses and widths, are predicted to be modified in dense and/or hot nuclear matter. Particular attention has been given to the modifications of vector-meson properties in ordinary nuclear matter where chiral symmetry is predicted to be partially restored due to a change in the quark condensate. Different models predict relatively large measurable changes in the mass and/or the width of these mesons. The e+e- decay channel of these mesons has negligible final-state interactions (FSI), providing an ideal tool to study their possible in-medium modifications Due to its short lifetime, the ρ meson has a substantial probability of decaying in the nucleus and its study has been previously reported. Due to their long lifetimes, the ω and ϕ mesons are ideal candidates for the study of possible modifications of the in-medium meson-nucleon interaction through their absorption inside the nucleus. These mesons have been photo-produced in several targets ranging from deuterium to lead. Nuclear transparencies ratios have been derived for different decay channels. These ratios indicate larger in-medium widths compared with what have been reported in other reaction channels. The absorption of the ω meson is stronger than that reported by the CBELSATAPS experiment. These results are compared to recent theoretical models. [ABSTRACT FROM AUTHOR]

Eta-meson photoproduction from proton near threshould is studied by using Effective Lagrangian Approach (ELA). While the resonance S11 (1535) is the dominant channel, contributions from Born terms and Vector meson (t-channel) are also included. The charactistics of amplitudes are analyzed for different channels and different couplings, and these features are used to extract information on the strength of pseudo-scalar (PS) and pseudo-vector (PV) couplings. It is found that there exists an approximate equivalence between the PS and PV couplings for S11 resonance. [ABSTRACT FROM AUTHOR]

Jefferson Lab's experiment E04-005, the largest integrated luminosity real photon CLAS experiment to date, provided a large sample of leptonic data; allowing for studies of the ρ-ω interference in the dileptonic decay channel, as well as charge radius and comparative branching ratio studies of the η and η′ through the Dalitz decay channel. An experimental study of the ρ-ω provides valuable input for theoretical models and calculations in addition to establishing a comparative basis for medium modification studies of vector mesons off of heavier targets. The total statistics collected for the η dalitz exceed the world's published statistics by an order of magnitude, while the η′ Daltiz decay is observed and measured for the first time. [ABSTRACT FROM AUTHOR]

We present several predictions for the single spin asymmetry for the π, K, and η-meson productions at RHIC kinematics using the twist-3 quark-gluon correlation functions determined from our analysis of RHIC data. After discussing the PT-dependence of AN, we give predictions for AN for pions and kaons at S = 500 GeV and AN for the η-meson at S = 200 GeV. [ABSTRACT FROM AUTHOR]

Studying the possible breaking of various parton model symmetries by the parton distribution functions of the nucleon can provide important information for the non-perturbative structure of hadrons and the strong interaction. We review theoretical calculations for the breaking of flavor symmetry, quark-antiquark symmetry and charge symmetry in the unpolarized and polarized nucleons using the meson cloud model. We report an estimation for the total distribution of strange and antistrange quarks in the nucleon by combining theoretical calculations of SU(3) flavor symmetry breaking with light antiquark distributions obtained from global analysis of available experimental data. [ABSTRACT FROM AUTHOR]

We study the single spin asymmetries for the D-meson production, Drell-Yan lepton-pair production and the direct-photon production in the pp collision induced by the twist-3 three-gluon correlation functions in the transversely polarized nucleon. We present a corresponding polarized cross section formula in the leading-order with respect to the QCD coupling and a model calculation for the asymmetries, illustrating the sensitivity to the form of the correlation functions. [ABSTRACT FROM AUTHOR]

Neutrino reactions recorded by the MINOS Near Detector in exposures totalling 2.8×1020 protons-on-target were searched for single, highly-forward π0 mesons produced by coherent neutral current interactions νμ+A→νμ+A+π0. Events having topologies consistent with single electromagnetic showers were isolated. Contributions from neutrino-induced backgrounds are determined using a data-driven fit of Monte Carlo distributions over sideband regions. The fit is used to project the background levels into signal regions. An excess of events above the best-fit background is observed for shower topologies of few GeV energies and at very forward angles. The partial cross section for NC(π0) coherent scattering yielding Evis(π0)>1.0 GeV averaged over incident neutrino energies 2.4<=Eν<=9.0 GeV is (31.6±10.5)×10-40 cm2/nucleus. Total cross sections for coherent scattering from nuclei of average nucleon number Aeff = 48 and for iron (A = 56) nuclei are estimated for = 4.9 GeV. [ABSTRACT FROM AUTHOR]

Nuclear medium effects in the weak structure functions F2(x,Q2) and F3(x,Q2) have been studied for deep inelastic neutrino/antineutrino reactions in iron nucleus by taking into account Fermi motion, binding, pion and rho meson cloud contributions, target mass correction, shadowing and anti-shadowing corrections. The calculations have been performed in a local density approximation using relativistic nuclear spectral functions which include nucleon correlations. Using these structure functions we have obtained the ratio RF2,F3A(x,Q2) = 2F2,3A(x,Q2)AF2,3D(x,Q2), the differential scattering cross section 1Ed2σdxdy and the total scattering cross section σ. The results of our numerical calculations in 56Fe are compared with the experimental results of NuTeV and CDHSW collaborations. [ABSTRACT FROM AUTHOR]

I explain the Sato-Lee (SL) model and its extension to the neutrino-induced pion production off the nucleon. Then I discuss applications of the SL model to incoherent and coherent pion productions in the neutrino-nucleus scattering. I mention a further extension of this approach with a dynamical coupled-channels model developed in Excited Baryon Analysis Center of JLab. [ABSTRACT FROM AUTHOR]

Coherent π0-photoproduction on the deuteron including polarization effects in the energy region from π-threshold up to 1 GeV is studied using an enhanced elementary pion photo-production operator on the free nucleon and a realistic NN potential model for the deuteron wave function. Results for double polarization observables are predicted for which the sensitivity to various models for the elementary pion photoproduction amplitude is investigated. We find considerable dependence of the results on the elementary amplitude. In addition, results for differential cross section are predicted and compared with the experimental data from TAPS and a satisfactory agreement was found. [ABSTRACT FROM AUTHOR]

In this opening talk at MENU2010 we outline some of the key achievements in the field over the past few years as well as some of its major challenges and opportunities. [ABSTRACT FROM AUTHOR]

The study of hyperon resonances has entered a new era of precision with advent of high-statistics photoproduction data from the CLAS detector at Jefferson Lab. These data have multi-particle final states, allowing clean identification of exclusive reactions associated with strange mesons and baryons. Examples of physics results are: evidence for isospin interference in the decay of the Λ(1405) resonance; a strong suggestion of meson cloud effects in the structure of the Σ(1385) resonance; data from K* photoproduction that will test the existence of the purported K0(800) meson. Properties of other hyperon resonances will also be studied in the near future. [ABSTRACT FROM AUTHOR]

The new experiment GlueX is currently being constructed at Jefferson Lab. The experiment was designed to search for hybrid mesons with exotic-quantum-numbers using a beam of linearly polarized photons incident on a liquid hydrogen target. We will discuss the discovery potential of the GlueX experiment and briefly overview its physics program. [ABSTRACT FROM AUTHOR]

The Nambu-Jona-Lasinio (NJL)-jet model provides a sound framework for calculating the fragmentation functions in an effective chiral quark theory, where the momentum and isospin sum rules are satisfied without the introduction of ad hoc parameters. The most recent version of the model includes the fragmentation of the light and strange quarks to pions, kaons, nucleons, and antinucleons; where the effects of the production of secondary pions and kaons from the vector mesons ρ, K* and [lowercase_phi_synonym] are also calculated. The results for the model fragmentation function exhibit a qualitative agreement with the empirical parameterizations. The results also allow to test, within the model assumptions, several assumption in parametrizations of the unfavored fragmentation functions used in empirical fits to the experimental data. [ABSTRACT FROM AUTHOR]

Recently there have been considerable interests in studying hadronic states beyond the usual two and three quark configurations. With the renewed experimental interests in σ(600) and the inability of quark model to incorporate too many light scalar mesons, it is quite appropriate to study hadronic states with four quark configurations. Moreover, some of the newly observed charmed hadrons may well be described by four quark configurations. Lattice QCD is perhaps the most desirable tool to adjudicate the theoretical controversy of the scalar mesons and to interpret the structures of the newly observed charmed states. Here we briefly reviewed the lattice studies of four-quark hadrons. [ABSTRACT FROM AUTHOR]

The Nucleon-Nucleon One Meson Exchange Potential, its wave functions and related Meson Exchange Currents are analyzed for point-like nucleons. The leading Nc contributions generate a local and energy independent potential which presents 1/r3 singularities, requiring renormalization. We show how invoking suitable boundary conditions, neutron-proton phase shifts and deuteron properties become largely insensitive to the nucleon substructure and to the vector mesons. Actually, reasonable agreement with low energy data for realistic values of the coupling constants (e.g. SU(3) values) is found. The analysis along similar lines for the Meson Exchange Currents suggests that this renormalization scheme implies tremendous simplifications while complying with exact gauge invariance at any stage of the calculation. [ABSTRACT FROM AUTHOR]

Reaction η→e+e-γ is used to investigate the transition form factor of η meson with WASA detector at COSY. Where the η meson is produced in pp collision at 1.4 GeV. We present the analysis techniques and preliminary results of η Dalitz decays. [ABSTRACT FROM AUTHOR]

A covariant spectator quark model is applied to estimate the valence quark contributions to the F1*(Q2) and F2*(Q2) transition form factors for the γN→P11(1440) reaction. The Roper resonance, P11(1440), is assumed to be the first radial excitation of the nucleon. The model requires no extra parameters except for those already fixed by the previous studies for the nucleon. The results are consistent with the experimental data in the high Q2 region, and those from the lattice QCD. Finally the model is also applied to estimate the meson cloud contributions from the CLAS and MAID analysis. [ABSTRACT FROM AUTHOR]

The η meson can be bound to atomic nuclei. Experimental search is discussed in the form of final state interaction for the reactions dp→3Heη and dd→4Heη. For the latter case tensor polarized deuterons were used in order to extract the s-wave strength. For both reactions complex scattering lengths are deduced: In a two-nucleon transfer reaction under quasi-free conditions, p27Al→3HeX, was investigated. The system X can be the bound 25Mgxη at rest. When a possible decay of an intermediate N*(1535) is required, a highly significant bump shows up in the missing mass spectrum. The data give for a bound state a binding energy of 13.3±1.6 MeV and a width of σ = 4.4±1.3 MeV. [ABSTRACT FROM AUTHOR]

To investigate the interaction of η-meson with the nucleons, its production, near the kinematical threshold, in proton-proton collisions has been studied with the WASA detector at COSY storage ring in Juelich, Germany. The data has been taken at beam energy 1400 MeV (corresponding to excess energy (Q = 57 MeV). The η-meson was detected via its 3π0 decay in nearly 4π detector and two protons were measured in forward direction. The determination of four vectors of both protons and the η-meson in the final state allowed to derive complete kinematical information of the ppη-system. The analysis resulted in 9×106 events of η→3π0 giving total production cross-section (8.87±0.03stat±2.57sys)μb. The angular distribution of η-meson in the center of mass frame is anisotropic and squared invariant mass distributions for proton-proton and proton-η shows deviation from pure phase space. [ABSTRACT FROM AUTHOR]

The recent breakthroughs in the technology of polarised targets have enabled a new generation of meson photo-production experiments to be carried out. A measurement of a full set of polarisation observables off both polarised proton and neutron targets and in a large number of meson-production channels has come within sight. Such a measurement would very significantly reduce model-dependence in the analysis of the data and thus has the potential to resolve long-standing issues, such as the 'missing resonance' problem, and shed new light on the nucleon excitation spectrum. This has formed the motivation for the recent N* experimental programme of CLAS. [ABSTRACT FROM AUTHOR]

Elastic πN scattering and the reaction π+p→K+Σ+ are described simultaneously in a unitary coupled-channels approach which respects analyticity. SU(3) flavor symmetry is used to relate the t- and u- channel exchanges that drive the meson-baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. The pole structure of the amplitudes is extracted from the analytic continuation. [ABSTRACT FROM AUTHOR]

We analyze meson-baryon scattering lengths in the framework of covariant baryon chiral perturbation theory at leading one-loop order. We compute the complete set of matching relations between the dimension-two low-energy constants in the two- and three-flavor formulations of the theory. We derive new two-flavor low-energy theorems for pion-hyperon scattering that can be tested in lattice simulations. [ABSTRACT FROM AUTHOR]

Meson-baryon scattering and photon-nucleon reactions are described in a coupled-channel approach for energies below 2 GeV. Poles and residues of the reaction amplitudes are obtained by analytical continuation. The dependence of the resonance poles on the pion mass is investigated. [ABSTRACT FROM AUTHOR]

We present the current status of a combined and simultaneous analysis of meson production reactions based on a dynamical coupled-channels (DCC) model, which is conducted at Excited Baryon Analysis Center (EBAC) of Jefferson Lab. [ABSTRACT FROM AUTHOR]

We present preliminary results of the exclusive electroproduction of ρ+ on the proton at CLAS. We discuss the interpretation of the cross sections in terms of t-channel Reggeon exchanges and in terms of Generalized Parton Distributions (GPDs) formalism. [ABSTRACT FROM AUTHOR]

The latest results on B hadron spectroscopy from the DO\ experiment at the Tevatron are presented. The mass measuremen of the Bc- meson in the Bc-→J/ψπ- decay channel, the observation of excited Bs mesons, the first direct observation of the Ξb- baryon, and the first observation of the Ωb- baryon. [ABSTRACT FROM AUTHOR]

We study the dependence of the ππ scattering phase shifts on the light quark mass in both standard and unitarized SU(2) Chiral Perturbation Theory (ChPT) to one and two loops. We then use unitarized SU(3) ChPT to study the elastic f0(600), κ(800), ρ(770) and K*(892) resonances. The quark masses are varied up to values of interest for lattice studies. We find a very soft dependence on the light quark mass of the ππ phase shifts at one loop and lightly stronger at two loops and a good agreement with lattice results. The SU(3) analysis shows that the properties of the ρ(770) and K*(892) depend smoothly on the quark mass whereas the scalar resonances present a non-analyticity at high quark masses. We also confirm the lattice assumption of quark mass independence of the vector two-meson coupling that, however, is violated for scalars. [ABSTRACT FROM AUTHOR]

In this paper we present the preliminary results on the measurement of the branching ratio of a rare decay η→π0γγ with the WASA Detector at COSY. We have used a sample of 107 η mesons produced at the COSY ring using the pd→3Heη reaction close to threshold. We detail the intricate extraction of the signal, which has about 360±70 (stat) η→π0γγ events, from the overwhelming background channels for example η→3π0, pd→3He 3π0 and pd→3He 2π0. [ABSTRACT FROM AUTHOR]

We demonstrate the equivalence of the light-front, equal-time and covariant formulations in meson-baryon interactions. In particular, we discuss the self-energy Σ of a nucleon dressed by pion loops with the pseudovector πNN coupling. It is shown that the leading nonanalytic behavior of Σ is equivalent whichever formulations are used for the derivation. [ABSTRACT FROM AUTHOR]

In the usual holographic approach to QCD, the meson spectrum is generated due to a non-trivial 5-dimensional background. We propose an alternative 5-dimensional scenario in which the spectrum emerges due to the coupling to a scalar field whose condensation is supposed to be dual to the formation of a gluon condensate and mimics the scale anomaly in QCD. The spectrum of model has a finite number of discrete states plus continuum and reveals a Regge-like behavior in the strong coupling regime. [ABSTRACT FROM AUTHOR]

The paper gives an overview of strangeness-production experiments at the Cooler Synchrotron COSY. Results on kaon-pair and [lowercase_phi_synonym] meson production in pp, pd and dd collisions, hyperon-production experiments and Λp final-state interaction studies are presented. [ABSTRACT FROM AUTHOR]

The KLOE experiment has collected 2.5 fb-1 of e+e- collisions at the [lowercase_phi_synonym] peak and about 250 pb-1 in the center of mass energy 1 GeV. Data taken on peak are used to study properties of light scalar and pseudoscalar mesons, produced through [lowercase_phi_synonym] radiative decays. Off-peak data are used to perform preliminary analyses of the reactions e+e- → e+e-π0π0 and e+e- → e+e-η. All these studies will be extended with the coming KLOE-2 run. [ABSTRACT FROM AUTHOR]

We provide a brief review of the main existing theoretical efforts to extract and interpret the properties of baryon resonances from the experimental data for hadro-, photo- and electro-production of mesons on the nucleon. The focus is set on the dynamical coupled-channels models. An effort is made to highlight the relevant aspects of the different approaches, within the space limitations of these proceedings. [ABSTRACT FROM AUTHOR]

We overview a holographic QCD based on the D4-D8 string theory model, with emphasis on baryons and nucleon-meson interactions thereof. Baryons are realized as holographic images of Skyrmions, but with much qualitative changes. This allows us to derive, without adjustable parameters, couplings of baryons to the entire tower of spin one mesons and also to pseudoscalar mesons. We find some surprisingly good match against empirical values for nucleons, in particular. Tensor couplings to all axial-vectors and iso-singlet vectors all vanish, while, for ρ mesons, tensor couplings are found to be dominant. We close with various cautionary comments and speculations. [ABSTRACT FROM AUTHOR]

The N* programme at CLAS in Jefferson Lab is dedicated to the study of the spectrum of baryon resonances and the search for missing resonances. Recent developments in polarized beams and targets at CLAS have made it possible to measure many of the single and double polarization observables which are necessary to disentangle the contributing processes. In particular, CLAS is well on the way to making the first complete measurement on pseudoscalar meson production. The current status of the N* program is presented together with preliminary results from recently completed experiments. A brief overview of the hadron spectroscopy capabilities of the upgraded CLAS12 detector is also be presented, with emphasis on the plans for a tagged, quasi real photon beam. [ABSTRACT FROM AUTHOR]

The role of the tensor meson K2*(1430) exchange is investigated in the kaon photoproduction within the Regge framework. Inclusion of the K2* exchange with the meson-baryon coupling constants chosen from the SU(3) symmetry reproduces the cross sections in good agreement with the experimental data. This shows the importance of the tensor meson exchange in the present process. [ABSTRACT FROM AUTHOR]

We study whether the nonmonotonic behavior found in the differential cross section of the φ-meson photoproduction near threshold can be described by a resonance. The resonant contribution is evaluated by using an effective Lagrangian approach. We find that, with the assumption of a JP = 3/2- resonance with mass of 2.10±0.03 GeV and width of 0.465±0.141 GeV, LEPS data can indeed be well described. The ratio of the helicity amplitudes A1/2/A3/2 calculated from the re-22 sulting coupling constants differs in sign from that of the known D13(2080). We further find that the addition of this postulated resonance can substantially improve the agreement between the existing theoretical predictions and the recent ω photoproduction data if a large value of the OZI evading parameter xOZI = 12 is assumed for the resonance. [ABSTRACT FROM AUTHOR]

During the last few years, a series of experiments has been done at the ELSA accelerator in Bonn with the Crystal Barrel/TAPS setup and at the MAMI accelerator in Mainz with the Crystal Ball/TAPS setup. Photoproduction of light mesons off the deuteron and 3He-nuclei has been studied in detail. We will report some of the most interesting results. A completely unexpected finding, is the pronounced structure in the excitation function of the γn → nη reaction around 1 GeV, which has no counterpart for the proton. Recent measurements at GRAAL, Sendai, ELSA [1] and MAMI estimate it's width below 50 MeV, which would be extremely narrow for a nucleon resonance at this excitation energy. In the experiment with the 3He target, special attention was given to the threshold behavior of the γHe3 reactions in view of possible indications for the formation of (quasi-)bound η-nucleus states, so-called η-mesic nuclei. A very strong threshold enhancement of coherent η-photoproduction off 3He was found. In a new experiment, this reaction was measured with much better statistical accuracy compared to an earlier experiment at MAMI-B using the TAPS detector [2]. [ABSTRACT FROM AUTHOR]

We develop a practical method to analyze the mixing structure of hadrons consisting of two components of quark composite and hadronic composite by taking the a1(1260) meson as an example. We also make reference to the large Nc procedure and its limitation for the classification of such a mixed state. [ABSTRACT FROM AUTHOR]