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Register a new userDynamics of the near threshold eta meson production in proton-proton interaction
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We present the results of measurements of the analysing power for the p(pol)p --> pp eta reaction at the excess energies of Q=10 and 36 MeV, and interpret these results within the framework of the meson exchange models. The determined values of the analysing power at both excess energies are consistent with zero implying that the eta meson is produced predominantly in s-wave.
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Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high degree of the polarized proton beam of COSY, the reaction pp{to} pp{eta} has been measured close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined with the precision improved by more than one order of magnitude with respect to previous results allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q = 15 MeV signaling s wave production with no evidence for higher partial waves. At Q = 72 MeV the data reveals strong interference of P s and P p partial waves and cancellation of (P p) and Ss*Sd contributions. These results rule out the presently available theoretical predictions for the production mechanism of the {eta} meson.
The near threshold total cross section and angular distributions of K+K- pair production via the reaction pp --> ppK+K- 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+K- production in the region of small excess energies where production via the channel pp --> pp Phi --> ppK+K- is energetically forbidden. The possible influence of a resonant production via intermediate scalar states f0(980) and a0(980) is discussed.
We describe a novel technique for comparing total cross sections for the reactions pp --> pp pi(0), pp --> pp eta, and pp --> pp eta close to threshold. The initial and final state proton-proton interactions are factored out of the total cross section, and the dependence of this reduced cross section on the volume of phase space is discussed. Different models of the proton-proton interaction are compared. We argue that the scattering length of the S-wave eta-proton interaction is of the order of 0.1 fm.
The $pp to pp eta^{prime}$ (958) reaction has been measured at COSY using the internal beam and the COSY-11 facility. The total cross sections at the four different excess energies mbox{$ Q = ~1.5 ~MeV, ~1.7 ~MeV, ~2.9 ~MeV,$ and $ ~4.1 MeV$} have been evaluated to be mbox{$ sigma = 2.5 pm 0.5~nb$, $~~~ 2.9 pm 1.1~nb$, $~~~ 12.7 pm 3.2~nb$, ~ and $~~~ 25.2 pm 3.6 ~nb $}, respectively. In this region of excess energy the $eta^{prime}$ (958) cross sections are much lower compared to those of the $pi ^0$ and $eta$ production.
Photoproduction of $phi$-meson on protons was studied by means of linearly polarized photons at forward angles in the low-energy region from threshold to $E_{gamma}$= 2.37 GeV. The differential cross sections at $t = -|t|_{min}$ do not increase smoothly as $E_{gamma}$ increases, but show a local maximum at around 2.0 GeV. The angular distributions demonstrate that $phi$-mesons are photo-produced predominantly by helicity-conserving processes, and the local maximum is not likely due to unnatural-parity processes.
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