Search

The installation of the WASA detector at the cooler synchrotron COSY opened the possibility to search for η-mesic helium with high statistics and high acceptance. A search for the 4He—η bound state is conducted via an exclusive measurement of the excitation function for the dd→3Hepπ- reaction varying continuously the beam momentum around the threshold for the dd→4Heη reaction. Ramping of the beam momentum and taking advantage of the large acceptance of the WASA detector allows to minimize systematical uncertainities. [ABSTRACT FROM AUTHOR]

A method for the calculation of the luminosity for the proton-nucleus collisions based on the quasi-free proton-proton scattering is presented. As an example of application the integrated luminosity for the scattering of protons off the deuteron target is determined for the experiment of the quasi-free pn→pnη reaction performed by means of the COSY-11 facility. [ABSTRACT FROM AUTHOR]

Based on the high statistics data from the pp→ppX reaction measured by the COSY-11 collaboration [1] we have derived a two-proton correlation function for the production of the ppη and pp+pions systems. The measured correlation function normalized to the value simulated for a point-like source was compared with a theoretical prediction in order to estimate the size of the reaction volume. [ABSTRACT FROM AUTHOR]

Measurements of the pp→ppK+K- reaction, performed with the experiment COSY-11 at the Cooler Synchrotron COSY, reveal a significant discrepancy between obtained excitation function and theoretical expectations neglecting interactions of kaons. Thus, the observed enhancement of the data above the predictions may be plausibly assigned to the influence of K+K- or Kp interaction. This may manifest itself even stronger in the distributions of the differential cross-sections. Therefore, in order to deepen our knowledge about the low energy dynamics of the ppKK system we investigate population of events for the pp→ppK+K- reaction as a function of the invariant masses of two particle subsystems. In particular generalizations of the Dalitz plot for the four particles proposed by Chodrow and Goldhaber will be presented. [ABSTRACT FROM AUTHOR]

We briefly describe the present knowledge about the mechanism of the η meson production in the collisions of nucleons. We stress the role of the spin degrees of freedom and discuss a possibility of investigations of the spin observables for the pvector p→ppη reaction using the WASA-at-COSY apparatus and the vertically polarized proton beam of COSY. [ABSTRACT FROM AUTHOR]

Measurements of the pp→ppK+K- reaction, performed with the experiment COSY-11 at the Cooler Synchrotron COSY, reveal a significant discrepancy between obtained excitation function and theoretical expectations neglecting interactions of kaons. Thus, the observed enhancement of the data above the predictions may be plausibly assigned to the influence of K+K- or Kp interaction. This may manifest itself even stronger in the distributions of the differential cross-sections. Therefore, in order to deepen our knowledge about the low energy dynamics of the ppKK system we investigate population of events for the pp→ppK+K- reaction as a function of the invariant masses of two particle subsystems. In particular generalizations of the Dalitz plot for the four particles proposed by Chodrow and Goldhaber will be presented. [ABSTRACT FROM AUTHOR]

The COSY-11 experimental setup is an internal facility installed at the COoler SYnchrotron COSY in Jülich. It allows to investigate meson production in free and quasi-free nucleon-nucleon collisions, eg. pp → pp meson and pd → pspnp meson reactions. Drift chambers and scintillators permit to measure outgoing protons, separated in the magnetic field of the COSY-11 dipole. Neutrons are registered in the neutron modular detector installed downstream from the target. Recently, the experimental setup has been extended with spectator detector, deuteron drift chamber and polarization monitoring system, and since then meson production can be investigated also as a function of spin and isospin of colliding nucleons. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

According to the quark model, the masses of η and η′ mesons should be almost equal. However, the empirical values of these masses differ by more than a factor of two. Similarly, though they have almost the same quark-antiquark content, the total cross section for the creation of these mesons close to the kinematical thresholds in the pp → ppX reaction differs significantly. Using the COSY-11 detection setup we intend to determine whether this difference will also be so significant in the case of the production of these mesons in the proton-neutron scattering. Additionally, the comparison of the pp → ppη′ and pn → pnη′ total cross sections will allow to learn about the production of the η′ meson in the channels of isospin I = 0 and I = 1 and to investigate aspects of the gluonium component of the η′ meson. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Based on the experience from the production of light antihyperon-hyperon (ΛΛ, ΣΣ) pairs at LEAR (experiment PS185) it is suggested to continue the investigations towards the heavier antihyperon-hyperon pairs [cap_xi][cap_xi] and ΩΩ in view of: 1. the production dynamics of the heavier antihyperon-hyperon out of the pp annihilation 2. a comparison of the “(3 s) (3 s)”- quark system ΩΩ to the 3 (ss) = 3 [lowercase_phi_synonym] meson production, where both systems the ΩΩ and the 3 [lowercase_phi_synonym] have similar masses (3.345 and 3.057, respectively) and identical valence quark content. A systematic study of the antihyperon-hyperon production with increasing strangeness content is interesting for the following reasons: The ΩΩ production is the creation of two spin 3/2 objects out of the two spin 1/2 pp particles. Results of the PS185 experiments prove a clear dominance of the spin triplet ss dissociation. In the Ω(Ω) the three s-quarks (three s-quarks) are aligned to spin 3/2 each. If the three ss pairs are now all in spin triplet configurations when created out of the gluonic interaction they should have spin parity quantum number as 3- as long as ΩΩ is created with relative L = 0 angular momentum. The comparison of the ΩΩ baryon pair to the [lowercase_phi_synonym][lowercase_phi_synonym][lowercase_phi_synonym] three meson production (where the three ss quark pairs might not but can be produced without relative correlation) would provide a unique determination of the intermediate matter state. Measurements of excitation functions and polarization transfers should be used to examine these gluon rich pp → ΩΩ and pp → [lowercase_phi_synonym][lowercase_phi_synonym][lowercase_phi_synonym] reaction channels. Such experiments should be performed at the PANDA detector at the FAIR facility of the GSI. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

A comparison of the close-to-threshold total cross sections for the η′ meson production in both the pp→ppη′ and pn→pnη′ reactions should provide insight into the flavour-singlet (perhaps also into gluonium) content of the η′ meson and the relevance of quark-gluon or hadronic degrees of freedom in the creation process. The excitation function for the reaction pp→ppη′ has been already established. At present, experimental investigations of the quasi-free pn→pnX reactions are carried out at the COSY-11 facility using a beam of stochastically cooled protons and the deuteron cluster target. A method of measurement and preliminary results from the test experiments of the pn→pnη reaction are presented in this report. [ABSTRACT FROM AUTHOR]

Measurements of the near threshold Λ and Σ0 production via the pp→pK+Λ/Σ0 reaction at COSY-11 have shown that the Λ/Σ0 cross section ratio exceeds the value at high excess energies (Q ≥ 300 MeV) by an order of magnitude. For a better understanding additional data have been taken between 13 MeV and 60 MeV excess energy. Within the first 20 MeV excess energy a strong decrease of the cross section ratio is observed, with a less steep decrease in the higher excess energy range. A description of the data with a parametrisation including p-Y final state interactions suggests a much smaller p-Σ0 FSI compared to the p-Λ system. [ABSTRACT FROM AUTHOR]

Polarisation observables constitute a powerful tool for establishing the production mechanism of the η meson and for infering the presence of higher partial waves in the final system. Measurements of the proton analysing power for the p→p→ppη reaction have been performed by the COSY-11 group at three different excess energies: Q=10, 37 and 40 MeV. Data at Q=40 MeV indicate that the η meson is probably produced in partial waves higher than s wave. [ABSTRACT FROM AUTHOR]

The near threshold total cross section and angular distributions of K[sup +]K[sup -] pair production via the reaction pp → ppK[sup +]K[sup -] have been studied at an excess energy of Q - 17 MeV using the COSY-11 facility at the cooler synchrotron COSY. The obtained cross section as well as an upper limit at an excess energy of Q = 3 MeV represent the first measurements on the K[sup +]K[sup -] production in the region of small excess energies where production via the channel pp → ppφ → ppK[sup +]K[sup -] is energetically forbidden. [ABSTRACT FROM AUTHOR]

The COSY-11 collaboration has measured the total cross section for the pp→ppη[sup ′] and pp→ppη reactions in the excess energy range from Q=1.5 MeV to Q=23.6 MeV and from Q=0.5 MeV to Q=5.4 MeV, respectively. Measurements have been performed with the total luminosity of 73 nb-1 for the pp→ppη reaction and 1360 nb-1 for the pp→ppη[sup ′] one. Recent results are presented and discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Close-to-threshold data on the elementary kaon and antikaon production channels in the proton-proton interaction have been taken using the COSY-11 installation at the cooler synchrotron COSY Ju¨lich. The experimental technique applied at the internal COSY-11 facility—designed for meson production studies at small excess energies—is outlined. The threshold excitation functions for the kaon-hyperon production via the reactions pp→pK[sup +]Λ and pp→pK[sup +]Σ[sup 0] are presented. The magnitude of the production amplitudes is compared at equal excess energies and physical implications of the observed Σ[sup 0] suppression in the threshold region are discussed. In addition, within a Dalitz plot analysis the spin-averaged S-wave scattering parameters could be extracted for the Λ-p channel. With the possibility of detecting all final state particles the elementary antikaon production in the reaction pp→ppK[sup +]K[sup -] has been investigated. Results on the exclusive total cross section fix the scale of the strangeness dissociation into two kaons. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Measurements on the η meson production in proton-deuteron collisions have been performed using the COSY-11 facility at COSY (Jülich). Here we present preliminary results on total and differential cross sections for the pd→3He η reaction at five excess energies between Q = 5.1 and Q = 40.6 MeV. The obtained angular distributions for the emitted η mesons in the center of mass system expose a transition from an almost isotropic emission to a highly anisotropic distribution. The extracted total cross sections support a strong η-3He final state interaction and will be compared with model predictions. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]