W. Krzemien, J. Smyrski, A. Budzanowski, E. Czerwinski, R. Czyzykiewicz, D. Gil, D. Grzonka, L. Jarczyk, B. Kamys, A. Khoukaz, P. Klaja, P. Moskal, W. Oelert, J. Przerwa, J. Ritman, T. Sefzick, M. Siemaszko, M. Silarski, A. Taeschner, M. Wolke, P. Wuestner, J. Zdebik, M. J. Zielinski, W. Zipper
We have measured excitation function for dp -> ppp_pi- reaction near the eta production threshold. We observe an enhancement of the counting rate above the threshold which can originate from the production of the eta meson in the reaction dp -> 3He eta and its subsequent absorption on neutron in the 3He nucleus leading to creation of the p_pi- pair.
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继续探索
We review status and perspectives of the search of the eta-mesic helium at the cooler synchrotron COSY.
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…
In November 2010, the search for the 4He-η bound state was per formed with high statistics and high acceptance with the WASA-at-COSY facility using a ramped beam technique. The signature of eta - mesic nuclei is searched for in the measured excitation functions for the two reaction channels: dd ->3He n pi0 and dd ->3He p pi- near the eta production threshold. This report includes the description of the experimental method and the status of the data analysis.
We describe a new high precision measurement of the production cross-section for the eta' meson in proton-proton collisions for five beam momenta at low access energy region Q conducted at the COSY-11 detection system together with an updated results of all other previous measurements of cross-section for (pp-->pp eta') at COSY-11.
In this report one of the methods used for the luminosity determination for the experiment performed by WASA Collaboration to search for 3He-eta mesic nuclei is presented. The method is based on the analysis of pd -> 3He eta process.
Using COSY-11 apparatus for the precise studies of the natural width of the eta prime meson
给出了测量eta素介子总宽度的初步结果和动机。
A search for the 4He-eta bound state via exclusive measurement of the excitation function for the dd->3Heppi- reaction, was performed at the Cooler Synchrotron COSY-Juelich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 GeV/c to 2.400 GeV/c crossing the kinematic threshold for the eta production in the dd -> 4He-eta reaction at 2.336 GeV/c. The corresponding excess energy in the 4He-eta system varied from -51.4 MeV to 22 MeV. The shape of the excitation function for the dd -> 3Heppi- was examined. No signal of the 4He-eta bound sta…
Summary of studies of the eta meson production with polarized proton beam at COSY-11
本文报道了COSY-11对p（pol）p -> ppeta反应的分析能力的测量结果，并在介子交换模型的框架下对测量结果进行了解释。
We conduct a search for the 4He-eta bound state with the WASA-at-COSY facility via the measurement of the excitation function for the reaction dd->3Heppi-. In first experiment performed in June 2008, we used COSY deuteron beam with a slowly ramped beam momentum corresponding to a variation of the excess energy for the 4He-eta system from -51.4 MeV to 22 MeV. Here we report on the status of the measurement and the data evaluation.
The eta-mesic nuclei in which the eta meson is bound with nucleus via strong interaction was postulated about 25 years ago, however till now no experiment confirmed empirically its existence. The discovery of this new kind of an exotic nuclear matter would be very important for better understanding of the eta meson structure and its interaction with nucleons. The search for eta-mesic helium is carried out with high statistic and high acceptance with the WASA-at-COSY detection setup and the Cooler Synchrotron COSY. The search is conducted via the measurement of the excitation function for the c…
We describe the experimental method and consecutive steps of the analysis of the pp-->pp eta prime reaction measured by means of the COSY-11 detection setup. The conducted investigation aim at the determination of the total width of the eta prime meson directly from its mass distribution. The preliminary results show that the statistical error is in the order of ~10 keV.
We search for an evidence of eta-mesic He with the WASA detector. Two dedicated experiments were performed at the Cooler Synchrotron COSY-Juelich. The experimental method is based on the measurement of the excitation functions for the two reaction channels: dd->3Heppi- and dd->3Henpi0, where the outgoing N-pi pairs originate from the conversion of the eta meson on a nucleon inside the He nucleus.In this contribution, the experimental method is shortly described and the current status of the analysis is presented.
We performed a search for 4He-eta bound state with high statistics and high acceptance with the WASA-at-COSY facility using a ramped beam technique. The signature of eta-mesic nuclei is searched for in dd -> 3Henpi0 and dd -> 3Heppi- reactions by the measurement of the excitation functions in the vicinity of the η production threshold. This paper presents the experimental method and the preliminary results of the data analysis for dd -> 3Henpi0 process.
We conduct a search for the 4He-eta bound state with WASA-at-COSY facility, via a measurement of the excitation functions for the dd->3Heppi- reaction, where the outgoing p-pi- pairs originate from the conversion of the eta meson on a nucleon inside the He nucleus. Determination of the profile of the excitation curve below the threshold of the dd->4He-eta reaction will allow to establish the binding energy and the width of the He-eta bound state. In June, 2008 first measurements of the excitation functions for the dd->3Heppi- reaction were performed. In the experiment we used a slowly ramped C…
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.
Measurement of the Eta Production in Proton Proton Collisions with the COSY Time of Flight Spectrometer
利用飞行时间谱仪在Juelich冷却器同步加速器COSY的外靶上，在15和41 MeV的过量能量下测量了反应pp -> pp eta。大约25000事件被测量的过剩能量为15 MeV和约8000为41 MeV。两个质子的过程pp eta检测接受度接近100%，并通过缺失质量技术重建eta。对于这两个多余的能量的角分布被发现是近各向同性。在不变的质量分布强烈偏离纯相空间分布。
Measurement of the eta->3pi0 Dalitz Plot Distribution with the WASA Detector at COSY
在COSY的WASA实验的第一次生产运行中，在质子束动能为1.4 GeV的质子-质子相互作用中测量了η衰变为三个中性π介子。使用1.2e5完全重建的事件研究了三个π介子的Dalitz图，二次斜率参数α被确定为-0.027+/-0.008（stat）+/-0.005（syst）。这一结果与以前的测量结果一致，进一步证实了π介子-π介子末态相互作用的重要性。
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.
At the turn of October and November 2008, the WASA-at-COSY collaboration performed an experiment to collect data on the eta meson decays in pd-->3He eta reactions. This report presents results of a study of the eta-->e+e-g conversion decay. The desired feature of this decay is that the final state e+e- pairs come from the conversion of a virtual gamma quantum and, therefore, they constitute a rich source of knowledge about the electromagnetic structure of decaying meson. This is a very important characteristic when it comes to study of a short-lived neutral particle like the eta meson, because…
In June 2008 we performed a search for the 4He-eta bound state by measuring the excitation function of the dd to 3He p pi- reaction near the eta production threshold using the WASA-at-COSY detector. During the experimental run the momentum of the deuteron beam was varied continuously within each acceleration cycle from 2.185 GeV/c to 2.400 GeV/c, crossing the kinematic threshold for the eta production in the dd to 4He eta reaction at 2.336 GeV/c. The preliminary excitation function indicates no structure in the angular range close to the 180 degree where the signal is expected. The preliminary…
The eta-mesic nuclei in which the eta meson is bound with nucleus via strong interaction was postulated already in 1986, however till now no experiment confirmed empirically its existence. The discovery of this new kind of an exotic nuclear matter would be very important for better understanding of the eta meson structure and its interaction with nucleons. The search for eta-mesic helium is carried out with high statistic and high acceptance with the WASA-at-COSY detection setup in the Forschungszentrum Julich. The search is conducted via the measurement of the excitation function for the chos…
The existence of eta-mesic nuclei in which the eta meson is bound in a nucleus by means of the strong interaction was postulated already in 1986, albeit not yet confirmed it by experiment. The discovery of this new kind of an exotic nuclear matter would be very important as it might allow for a better understanding of the eta meson structure and its interaction with nucleons. The search for eta-mesic helium 4He-eta is carried out with high statistics and high acceptance with the WASA detector, installed at the cooler synchrotron COSY of the Research Center Juelich. The search is conducted via …
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…
Study of the 3He-eta system in d-p collisions at COSY-11
我们目前的初步结果，从dp -> 3 He X（X= π 0，eta）测量近eta生产阈值。这些数据是在COSY内部氘核束散射到质子靶上的缓慢斜坡过程中获取的。用COSY-11探测装置记录3 He喷射物。正在进行的数据分析应提供高精度数据的dp --> 3 He eta总和微分截面的过剩能量的范围从阈值高达9兆电子伏。反应dp -> 3 He π 0的初始激发函数没有显示出任何可能源于3 He-η束缚态衰变的结构。本文还给出了dp -> 3 He X通道的阈激发曲线。与SATURNE的相应结果相反，我们在eta阈值附近没有看到尖点。
We performed a search for the 4He-eta bound state via exclusive measurement of the excitation function for the dd->3Heppi- reaction, where the outgoing p-pi- pair originates from the conversion of the eta meson on a neutron inside the 4He nucleus. The measurements were performed at the Cooler Synchrotron COSY-Juelich with the WASA-at-COSY detection system.The internal deuteron beam of COSY was scattered on a pellet-type deuteron target. The data were taken during a slow acceleration of the beam from 2.185 GeV/c to 2.400 GeV/c crossing the kinematical threshold for the eta production in the dd-…
The measurement of the quasi-free production of the eta prime meson has been carried out at the COSY-11 detection setup using a proton beam and a deuteron cluster target. The energy dependence of the cross section is extracted using a fixed proton beam momentum of p_beam=3.35 GeV/c and exploiting the Fermi momenta of nucleons inside deuterons. The data cover a range of centre-of-mass excess energies from 0 to 24 MeV. Due to the low statistics at the present stage only upper limits for the cross sections could be extracted. In this article we focus on the functioning and efficiency determinatio…
Heavy Meson Production at COSY - 11
COSY-11合作测量了过剩能量范围Q = 1.5 MeV至Q = 23.6 MeV和Q = 0.5 MeV至Q = 5.4 MeV的pp --> pp eta-prime和pp --> pp eta反应的总截面。在pp --> pp eta反应的总光度为73 nb^（-1）和pp --> pp eta-prime反应的总光度为1360 nb^（-1）的条件下进行了测量。最近的结果进行了介绍和讨论。
Feasibility study of the quasi-free creation of the eta-prime meson in the reaction pn --> pn eta-prime
本文讨论了用COSY-11内靶装置研究pn -> pn η-素数反应的可行性。评估是基于假设的准自由反应束质子，循环在冷却器同步COSY，中子从一个无窗的氘核簇目标。
Since the eta meson is a short-lived neutral particle, it is not possible to investigate its structure via classical methods of particle scattering. To learn about its quark wave function, one studies those decay processes of this meson in which a pair of photons is produced, where at least one of them is virtual. The virtual photons have a non-zero mass and convert into lepton-antilepton pairs. Therefore, information about the quarks' spatial distribution inside the meson can be extracted from the lepton-antilepton invariant mass distributions by comparing the empirical results with QED predi…
We search for an evidence of eta-mesic 4He with the WASA-at-COSY detector. Two dedicated experiments were performed at the Cooler Synchrotron COSY-Juelich. The experimental method is based on the measurement of the excitation functions for the two reaction channels: dd-->3Heppi- and dd-->3Henpi0, where the outgoing N-pi pairs originate from the conversion of the eta meson on a nucleon inside the He nucleus. In this contribution, the experimental method is shortly described and preliminary excitation functions from the 2010 data are presented.
A value for the mass of the eta meson has been determined at the COSY-ANKE facility through the measurement of a set of deuteron laboratory beam momenta and associated 3He center-of-mass momenta in the d+p -> 3He+X reaction. The eta was then identified by the missing-mass peak and the production threshold determined. The individual beam momenta were fixed with a relative precision of 3 x 10^-5 for values around 3 GeV/c by using a polarized deuteron beam and inducing an artificial depolarizing spin resonance, which occurs at a well-defined frequency. The final-state momenta in the two-body d+p …
Taking advantage of both the high mass resolution of the COSY-11 detector and the high energy resolution of the low-emittance proton-beam of the Cooler Synchrotron COSY we determine the excitation function for the pp --> pp eta' reaction close-to-threshold. Combining these data with previous results we extract the scattering length for the eta'-proton potential in free space to be Re(a_{p eta'}) = 0+-0.43 fm and Im(a_{p eta'}) = 0.37(+0.40)(-0.16) fm.
We present a comparison of the two-body invariant mass distributions for the pp -> ppeta and pp -> ppeta-prime reactions, both measured at a nominal excess energy value of Q = 15.5 MeV. For the pp -> ppeta reaction, in addition, the differential cross sections were extracted for an excess energy of Q = 10 MeV. The comparison of the results for the eta and eta-prime meson production rather excludes the hypothesis that the enhancement observed in the invariant mass distributions is due to the interaction of the meson and the proton.
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.
Analysing power A(y) in the reaction p(pol.)p --> pp eta near threshold
在COSY同步加速器COSY的内部设施COSY-11上对反应p（pol）p -> pp eta在生产阈值附近的分析能力进行了第一次测量。
An exclusive measurement of the excitation function for the dd->3Heppi- reaction was performed at the Cooler Synchrotron COSY-Juelich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 GeV/c to 2.400 GeV/c crossing the kinematic threshold for the eta meson production in the dd->4He-eta reaction at 2.336 GeV/c. The corresponding excess energy with respect to the 4He-eta system varied from -51.4MeV to 22MeV. The integrated luminosity in the experiment was determined using the dd->3Hen reaction. The shape of the excitation function for th…
Wasa at Cosy
广角簇射装置（WASA）已从储存环CELSIUS（TSL，乌普萨拉，瑞典）转移到冷却器同步加速器COSY（FZ Juelich，德国）。在本报告中，报告了WASAatCOSY项目的现状和规划。主要的物理方面是η介子和η '介子的稀有衰变以及氘-氘相互作用中的同位旋破坏。
Near-Threshold eta Meson Production in Proton-Proton Collisions
利用COSY-11内部实验装置在低温同步加速器COSY上测量了质子-质子相互作用过程中近反应阈的η介子产生。总截面确定为8个不同的过剩能量范围从0.5 MeV至5.4 MeV。总截面的能量依赖性很好地描述了由FSI因子加权的质子-质子和质子-η对的可用相空间体积。
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.
The eta-mesic nuclei in which the η meson is bound with nucleus via strong interaction was postulated already in 1986, however till now no experiment confirmed empirically its existence. The discovery of this new kind of an exotic nuclear matter would be very important for better understanding of the η meson structure and its interaction with nucleons. The search for η-mesic helium is carried out with high statistic and high acceptance with the WASA-at-COSY detection setup in the Research Center Juelich. The search is conducted via the measurement of the excitation function for the chosen deca…
Multimeson production in pp interactions as a background for eta and eta' decays
pp相互作用中多介子的产生是COSY计划用WASA探测器进行的η、ω和η '介子产生实验及其衰变研究的重要背景。有关反应的可用信息进行了总结，并强调需要努力描述的过程。
Proton-proton and proton-eta invariant mass distributions and the total cross section for the pp to pp eta reaction have been determined near the threshold at an excess energy of Q=10 MeV. The experiment has been conducted using the COSY-11 detector setup and the cooler synchrotron COSY. The determined invariant mass spectra reveal significant enhancements in the region of low proton-proton relative momenta, similarly as observed previously at higher excess energies of Q=15.5 MeV and Q= 40MeV.
The upper limit of the total cross section for the pn --> pn eta' reaction has been determined near the kinematical threshold in the excess energy range from 0 to 24 MeV. The measurement was performed using the COSY-11 detector setup, a deuteron cluster target, and the proton beam of COSY with a momentum of 3.35 GeV/c. The energy dependence of the upper limit of the cross section was extracted exploiting the Fermi momenta of nucleons inside the deuteron. Comparison of the determined upper limit of the ratio R_eta' = sigma(pn --> pn eta') / sigma(pp --> pp eta') with the corresponding ratio for…
We present recent results on the search for the U boson based on the data collected by means of the WASA detector and the Cooler Synchrotron COSY.
Total and Differential Cross Sections for the pp-->pp eta-prime Reaction Near Threshold
利用COSY-11内束流装置，在Q = 26.5，32.5和46.6MeV的过剩能量下，研究了pp → pp η-prime反应中η-prime介子的产生。给出了最高Q值的总截面和一个角分布。近阈值数据的激发函数可以用纯s波相空间分布来描述，其中包括质子-质子末态相互作用和库仑效应。所得到的η素介子的角分布也与纯s波的产生相一致。
Energy Dependence of the Near-Threshold Total Cross-Section for the pp --> pp eta' Reaction
在Q = 1.53 MeV ~ Q = 23.64 MeV的过剩能范围内，测量了pp → pp eta'反应的总截面。实验是在COSY-11装置上用COSY同步加速器的随机冷却质子束和氢团簇靶进行的。所确定的总截面的能量依赖性削弱了eta'介子与质子之间S波排斥相互作用的假设。新的数据与基于仅由质子-质子终态相互作用（FSI）修改的相空间分布的预测吻合得很好。
The search for 4He-eta bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the dd->3He n pi0 and dd->3He p pi- processes. The beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd->4He eta reaction ranging from Q=-70 MeV to Q=30 MeV. The luminosity was determined based on the dd->3He n reaction and quasi-free proton-proton scattering via dd->pp n_spectator n_spectator reactions. The excitation functions determined independently for the measured reactions do not reveal a s…
Experimental study of the eta-meson interaction with two-nucleons
利用COSY-11探测系统，利用冷同步加速器COSY的随机冷却质子束流和氢团簇靶，对Q = 15.5MeV的pp → pp eta反应进行了高统计测量。该实验基于两个出射质子的四动量测定。这允许识别pp --> pp eta事件，并导出完整的eta-p-p系统的运动学信息，从而允许随后的eta-p相互作用的研究。观测到的质子-质子系统的不变质量的光谱强烈偏离相空间分布，揭示了出射粒子之间的终态相互作用或主要生产机制的非平凡特征的影响。
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…
Eta physics at threshold
在CELSIUS、COSY和SATURNE同步加速器上研究了基本核子-核子碰撞中η和η素介子的产生。总截面的大小和能量依赖性以及相空间的占据分布可作为研究产生过程和介子与核子相互作用机制的观测量。通过pp --> pp eta（eta-prime）反应产生eta和eta-prime介子的精确数据，可以确定eta和eta-prime介子产生的一般特征，并揭示上述观测值对核子-核子-介子终态相互作用的敏感性。特殊的产生性质，例如在eta产生的情况下，导致S_11核子同量异位素激发的主要交换过程的确定，必须通过与其他可观测量的对抗来确定。简要介绍了这项调查的现状，重点是COSY-11合作的结果。从产生机制和介子-核子相互作用的角度解释了现有的数据。
Quasi-free production of the eta and eta-prime mesons in nucleon-nucleon collisions
本文讨论了近阈区介子准自由产生的一些问题。本文简要介绍了WASA/PROMICE协作组用于提取中子靶产生η的激发函数的一种数据分析方法。讨论了在COSY与WASA进行类似研究的可行性。
Measurement of the dp -->3He eta reaction near threshold
在~ 3 He质心动量从17.1 MeV/c到87.5 MeV/c的范围内，测量了dp ->~ 3 He eta反应的总截面和微分截面.这些数据是在COSY-11设施探测3 He喷射物的质子靶上散射的COSY内部氘束缓慢上升期间采集的。前后不对称的微分截面明显偏离为零的质心动量高于50 MeV/c，表明存在较高的分波在最终状态。低于50 MeV/c质心动量，将终态增强因子与总截面数据拟合，得到3 He eta散射长度a =| 2.9 +/- 0.6| + i（3.2 +/-0.4）fm。
Study of the production mechanism of the eta meson in proton-proton collisions by means of analysing power measurements
本文所研究的p（pol）p -> pp eta反应的分析功率测量结果被用来确定核子-核子碰撞中产生eta介子的反应机制。测量已在接近阈值的能量区域中，在p（束）=2.010和2.085 GeV/c，对应于Q = 10和36 MeV的过剩能量，分别在束动量。实验是通过冷却器同步加速器和储存环COSY以及集群射流靶来实现的。为了登记反应产物，使用了COSY-11设施。用丢失质量法鉴别了η介子。分析功率的角依赖性与迄今所确定的核子-核子碰撞中$η$介子产生的总截面的同位旋依赖性的结果结合起来，揭示了一个统计上有意义的指示，即核子对S_{11}共振的激发，是η介子产生的中间过程，主要是由于碰撞核子之间π介子的交换。在这两个过剩能量的分析功率的确定值是一致的零，这意味着η介子主要是产生在s波在这两个过剩能量。
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.
We report on the experimental search for the bound state of an $η$ meson and $^{3}\hspace{-0.03cm}\mbox{He}$ nucleus performed using the WASA-at-COSY detector setup. In order to search for the $η$-mesic nucleus decay, the $pd\rightarrow$ $^{3}\hspace{-0.03cm}\mbox{He} 2γ$ and $pd\rightarrow$ $^{3}\hspace{-0.03cm}\mbox{He} 6γ$ channels have been analysed. These reactions manifest the direct decay of $η$ meson bound in $^{3}\hspace{-0.03cm}\mbox{He}$ nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained exci…
The proton-proton and proton-eta' invariant mass distributions have been determined for the pp -> ppeta' reaction at an excess energy of Q = 16.4 MeV. The measurement was carried out using the COSY-11 detector setup and the proton beam of the cooler synchrotron COSY. The shapes of the determined invariant mass distributions are similar to those of the pp -> ppeta reaction and reveal an enhancement for large relative proton-proton momenta. This result, together with the fact that the proton-eta interaction is much stronger that the proton-eta' interaction, excludes the hypothesis that the obser…
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.
Near threshold production of the pseudoscalar mesons at the COSY-11 facility
我们总结了COSY-11合作组对质子-质子相互作用中近阈赝标介子产生的激发函数的测量结果。在介子-核子和超子-核子相互作用的背景下讨论了结果。我们得出结论，$η$ -质子相互作用明显强于η '-质子相互作用。同样，我们发现超子λ与核子的相互作用比超子σ强得多，并且（K-）-质子的相互作用比（K+）-质子的强得多。
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.
Near threshold eta meson production in the d+d->alpha+eta reaction
利用COSY-Juelich的ANKE装置研究了d+d->alpha+eta反应在阈值附近的情况。在两个过剩能量Q=2.6 MeV和7.7 MeV下测量了总截面和微分截面，并在Q=-2.6 MeV下进行了亚阈值测量以研究物理背景。虽然在较低的能量下与各向同性一致，但角分布在较高的能量下显示出明显的各向异性，表明存在较高的分波。分解成部分振幅的选项和它们的后果，用于确定的s-波的η-α散射长度进行了讨论。
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