The proton–proton elastic differential cross section at very small four momentum transfer squared has been measured at three different incident proton momenta in the range of 2.5 to 3.2 GeV/c by ...detecting the recoil proton at polar angles close to 90∘. The measurement was performed at COSY with the KOALA detector covering the Coulomb–nuclear interference region. The total cross section σtot, which has been determined precisely, is consistent with previous measurements. The values of the slope parameter B and the relative real amplitude ratio ρ determined in this experiment alleviate the lack of data in the relevant energy region. These precise data on ρ might be an important check for a new dispersion analysis.
We report on the experimental search for the bound state of an η meson and He3 nucleus performed using the WASA-at-COSY detector setup. In order to search for the η-mesic nucleus decay, the pd→3He2γ ...and pd→3He6γ channels have been analysed. These reactions manifest the direct decay of the η meson bound in a He3 nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to a 3He-η nucleus width Γ above 20 MeV and binding energy Bs between 0 and 15 MeV. However, the determined cross sections are consistent with zero in the range of the systematic uncertainty. Therefore, as final result we estimate only the upper limit for the cross section of the η-mesic He3 nucleus formation followed by the η meson decay which varies between 2 nb and 15 nb depending on possible bound state parameters.
Stopped antiproton annihilation can initiate an effcient chain of reactions to produce Ξ hyperons in recoil free kinematics, suitable for further investigations of Ξ
N
interactions. Four delayed ...decays and presence of eight charged particles in the final state provide a clean reaction signature and allow for usage of a non-magnetic detection system. With the low energy phase space cooled antiproton beam from ELENA at the CERN AD or future FLAIR facility the realisation of this experiment would become possible. In this article the foreseen detector setup and the experimental program will be presented.
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The
Λ
polarization, the analyzing power, and the
Λ
spin transfer coefficient of the reaction
pp
→
pK
+
Λ
were measured at beam momenta of 2.70GeV/c and 2.95GeV/c corresponding to excess energies of ...122MeV and 204MeV. While the analyzing power and the spin transfer coefficient do not change significantly with the excess energy, the
Λ
polarization varies strongly and changes its sign. As this is the first measurement of polarization observables below an excess energy of 200MeV, the change of the sign of the
Λ
polarization was not observed before. The high statistics of the data (
≈
200 k events for each momentum) enables detailed studies of the dependence of the
Λ
polarization and the analyzing power on the center-of-mass momentum of the particles. The results of the spin transfer coefficient are in qualitative agreement with the DISTO experiment. The
Λ
polarization data of 2.95GeV/c are only conform with the DISTO experiment, while both the 2.70GeV/c and 2.95GeV/c data differ strongly from all previous measurements, whether exclusive or inclusive.
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