The pp-> pp eta reaction was investigated at excess energies of 15 MeV and 72 MeV using the azimuthally symmetric WASA detector and a polarized proton beam of the Cooler Synchrotron COSY. The aim of the studies is the determination of partial wave contributions to the production process of the eta meson in nucleon-nucleon collisions. Here we present preliminary results of the extraction of the position of the interaction region with respect to the WASA detector and preliminary results on the degree of polarization of the COSY proton beam used in the experiment.
We report on the status of the search for eta-mesic nuclei and the studies of the interaction of the eta meson with nucleons. Recently we have completed the analysis of the new WASA-at-COSY data on the production of the eta meson with polarized proton beam. New results on the analyzing power for the pp->ppeta reaction with more than an order of magnitude improved precision shed a new light on the production mechanism of the eta meson in nucleon-nucleon collisions. Also, the latest results of the search for eta-mesic nuclei are discussed.
We report on the exclusive production of omega and eta mesons in p+p reactions at 3.5 GeV beam kinetic energy. Production cross sections, angular distributions and Dalitz plots of both mesons were determined. Moreover, the relative contribution of the N(1535) resonance in eta production at this energy was evaluated. We conclude that eta mesons produced via N(1535) exihibit an isotropic angular distribution, whereas those produced directly show a strong anisotropic distribition. omega mesons show a slightly anisotropic angular distribition.
Photoproduction of eta-mesons off 3He has been studied at the MAMI accelerator using the Crystal Ball/TAPS detector setup. The total cross section for the coherent eta-photoproduction was measured with improved statistical quality. Both, the total and differential cross sections show evidence for dominant final state interaction. Additionally, the photoproduction of eta- mesons off quasi-free protons and neutrons was studied. The preliminary cross section on the neutron confirms the narrow bump-like structure at W \simeq 1.7 GeV, which was already seen in different experiments on the deuterium…
We shortly discuss results on the isospin dependence of the eta-prime production cross section in nucleon-nucleon collisions, results of comparative analysis of the invariant mass distributions for the pp-->pp eta-prime and pp-->pp eta reactions, and we present the value of the total width of the eta-prime meson as derived directly from the mass distribution measured with the mass resolution of 0.3 MeV/c^2.
Intensive quest for the eta and eta' bound states is currently ongoing at both theoretical and experimental levels e.g. at COSY, ELSA, GSI, JINR, JPARC, LPI, and MAMI. These studies were already supported by data provided by the COSY-11 collaboration including determination of the total width of the eta' meson. In addition, the first rough estimation of the eta'-N interaction from the excitation function of the cross section for the pp-->pp eta' reaction was also performed. Recent precise measurement in this field from the COSY-11 experiment allows to summarize results on the eta' meson produc…
We shortly discuss results on the isospin dependence of the eta-prime production cross section in nucleon-nucleon collisions, results of comparative analysis of the invariant mass distributions for the pp-->pp eta-prime and pp-->pp eta reactions, and we present the value of the total width of the eta-prime meson as derived directly from the mass distribution measured with the mass resolution of 0.3~MeV/c^2.
Polarized $p+p$ collisions provide insight into the structure of the nucleon. $A_N$ of eta mesons at forward rapidities are of particular interest, as asymmetries of other mesons observed both by PHENIX and other experiments show significant deviation from zero in the forward region. Several mechanisms have been proposed that attempt to explain these non-zero asymmetries, and a comparison of different probes may further constrain these models. Therefore, measurements of $A_N$ with inclusive eta mesons at forward rapidities are an important tool toward understanding the underlying mechanism. Us…
The upper limit of the total cross section for quasi-free pn -> pn eta-prime reaction has been determined in the excess energy range near the kinematic threshold. The measurement has been carried out at the COSY-11 detection setup using a proton beam and a deuteron cluster target. The identification of the eta-prime meson has been performed using the missing mass technique. The energy dependence of the upper limit of the cross section is extracted with a fixed proton beam momentum of p_beam}=3.35GeV/c and exploiting the Fermi momenta of nucleons inside the deuteron. The data cover a range of c…
Data on the photoproduction of omega mesons on nuclei have been re-analyzed in search for in-medium modifications. The data were taken with the Crystal Barrel(CB)/TAPS detector system at the ELSA accelerator facility in Bonn. The extracted omega line shape was found to be sensitive to the background subtraction. In experiments at the tagged photon facility of the Mainz MAMI accelerator photoproduction of mesons from light nuclear targets (deuteron and 3He) has been studied. The experiments used the combined Crystal Ball/TAPS setup in Mainz. Measurements of eta- and pi0-photoproduction off a li…
Based on recent COSY-11 results of measurements of total cross sections for the quasi-free pn-->pn eta reaction we determine the isospin I=0 component of the total cross section for the NN-->NN eta reaction down to the threshold. We show that the energy dependence of the total cross section ratios {σ_{I=0}(pn-->pn eta)}/{σ(pp-->pp eta)} and σ_{I=0}(pn-->pn eta)}/{σ(pn-->d eta)} can be described using the Faldt and Wilkin analitical parametrization of the nucleon-nucleon final state interaction.
Taking advantage of both the low-emittance proton-beam of the Cooler Synchrotron COSY and the high momentum precision of the COSY-11 detector system, the mass distribution of the eta' meson was measured with a resolution of 0.33 MeV/c^2 (FWHM), improving the experimental mass resolution by almost an order of magnitude with respect to previous results. Based on the sample of more than 2300 reconstructed pp --> pp eta' events the total width of the eta' meson was determined to be 0.226 +- 0.017(stat.) +- 0.014(syst.) MeV/c^2.
We present results on the isospin dependence of the eta-prime production cross section in nucleon-nucleon collisions, as well as the results of comparative analysis of the invariant mass distributions for the pp-->pp eta-prime and pp-->pp eta reactions in the context of the proton-eta and proton-eta-prime interaction. Additionally, the value of the total width of the eta-prime is reported as derived directly from the measurement of the mass distribution and an explanation of the experimental technique used in order to achieve a precision about an order of magnitude better then former experimen…
Hadronic interaction of eta and eta-prime mesons with nucleons
由于它们的短寿命，味中性介子不能用作自由次级束或靶，因此通过直接散射实验研究它们与核子的相互作用是不可能的。然而，这种相互作用可以通过它对能量依赖性的影响--以及对产生这些介子的反应的截面的相空间分布的影响--来获得。在p p--> p p eta反应的情况下，实验确定的接近产生阈值的微分截面的分布不能仅通过考虑S波质子-质子和质子-η相互作用来描述。在这里，我们表明，在COSY-11设施确定的角分布揭示了一些证据的P波混合物中的质子-质子子系统已经在一个过剩的能量低至Q = 15.5兆电子伏。我们还提出，人们可以估计的相对强度的η-核子和η-素数核子相互作用的比较的η和η-素数的产生产额。
The aim of this work was to determine the total width of the eta-prime meson. The investigated meson was produced via the pp->ppeta-prime reaction in the collisions of beam protons from COSY synchrotron with protons from a hydrogen cluster target. The COSY-11 detector was used for the measurement of the four-momentum vectors of outgoing protons. The mass of unregistered meson was determined via the missing mass technique, while the total width was directly derived from the mass distributions established at five different beam momenta. Parallel monitoring of the crucial parameters (e.g. size an…
Neutral pions and eta mesons as probes of the expanding hadronic fireball in nucleus-nucleus collisions at SIS
中性介子和η介子的生产轻，中等质量，和重核碰撞在0.8 A GeV和2.0 A GeV之间的光束能量的框架内进行了讨论，假设在强子化学和热冻结平衡，分别。从相对粒子产额的温度为56-90 MeV和重子化学势为780-675 MeV的化学冻结。中性π介子和η介子的中快度谱与得到的温度是一致的，如果，此外，测量的碰撞区的横向膨胀被考虑在内。与AGS和SPS数据的类似分析结果相反，推导出的冻结参数远低于强子气体和夸克-胶子等离子体之间的相边界。
The azimuthally symmetric WASA detector and the polarised proton beam of COSY, enable investigations of energy and angular dependence of the beam analysing power in the pp --> ppeta reaction. The aim of the studies is the determination of the partial wave contributions via interference terms which are inaccessible from spin averaged observables. The partial wave decomposition is mandatory for the understanding of the reaction dynamics and for the determination of the eta-proton interaction, independently of the theoretical paradigm used.
The p + 6Li --> eta + 7Be reaction has been investigated with an emphasis on the eta meson and 7Be interaction in the final state. Considering the 6Li and 7Be nuclei to be alpha-d and alpha-3He clusters respectively, the reaction is modelled to proceed via the p + d [alpha] --> 3He [α] + eta reaction with the alpha remaining a spectator. The eta meson interacts with 7Be via multiple scatterings on the 3He and alpha clusters inside 7Be. The individual eta-3He and eta-alpha scatterings are evaluated using few body equations for the eta-3N and eta-4N systems with a coupled channel eta-N interacti…
We review the present understanding of etaprime and eta meson physics and these mesons as a probe of gluon dynamics in low-energy QCD. Recent highlights include the production mechanism of eta and etaprime mesons in proton-nucleon collisions from threshold to high-energy, the etaprime effective mass shift in the nuclear medium, searches for possible eta and etaprime bound states in nuclei as well as precision measurements of eta decays as a probe of light-quark masses. We discuss recent experimental data, theoretical interpretation of the different measurements and the open questions and chall…
New experimental data are presented on the energy dependence of the total cross sections for the np -> d eta and quasi-two-body pp -> pp eta reactions, where the final diproton is detected at very low excitation energy. Differential cross sections of pp -> pp eta away from threshold show the influence of higher partial waves and a partial wave decomposition is attempted.
The role played by subthreshold meson-baryon dynamics is demonstrated in kaonic-atom, Kbar-nuclear and eta-nuclear bound-state calculations within in-medium models of Kbar-N and eta-N interactions. New analyses of kaonic atom data reveal appreciable multi-nucleon contributions. Calculations of eta-nuclear bound states show, in particular, that the eta-N scattering length is not a useful indicator of whether or not eta mesons bind in nuclei nor of the widths anticipated for such states.
Invariant cross sections for neutral pions and eta mesons in pp collisions at sqrt(s) = 0.9, 2.76, and 7 TeV were measured by the ALICE detector at the Large Hadron Collider. Next-to-leading order (NLO) perturbative QCD calculations describe the pi0 and eta spectra at 0.9 TeV, but overestimate the measured cross sections at 2.76 TeV and 7 TeV. The measured eta/pi0 ratio is consistent with mT scaling at 2.76 TeV. At 7 TeV indications for a violation of mT scaling were found.
We shed light upon the eta' mass in nuclear matter in the context of partial restoration of chiral symmetry, pointing out that the U_{A}(1) anomaly effects causes the eta'-eta mass difference necessarily through the chiral symmetry breaking. As a consequence, it is expected that the eta' mass is reduced by order of 100 MeV in nuclear matter where partial restoration of chiral symmetry takes place. The discussion given here is based on Ref. [1].
Using a relativistic transport model ART1.0, we explore effects of nuclear symmetry energy on eta meson production and its rare decay to the dark U-boson in heavy-ion reactions from 0.2 to 10 GeV/nucleon available at several current and future facilities. The yield of eta mesons at sub-threshold energies is found to be very sensitive to the density dependence of nuclear symmetry energy. Above a beam energy of about 5 GeV/nucleon in Au+Au reactions, the sensitivity to symmetry energy disappears. Using the branching ratio of the rare eta decay (eta->gamma U) available in the literature, we estim…
We discuss the role of QCD symmetries in understanding the eta and etaprime mesons in nuclear media. Recent results on the etaprime mass in nuclei from the CBELSA/TAPS collaboration are very similar to the prediction of the Quark Meson Coupling model.
