The differential and total cross sections for kaon pair production in the pp → ppK + K − reaction have been measured at three beam energies of 2.65, 2.70, and 2.83 GeV using the ANKE magnetic spectrometer at the COSY-Jülich accelerator. These near-threshold data are separated into pairs arising from the decay of the φ-meson and the remainder. For the non-φ selection, the ratio of the differential cross sections in terms of the K − p and K + p invariant masses is strongly peaked towards low masses. This effect can be described quantitatively by using a simple ansatz for the K − p final state interaction, where it is seen that the data are sensitive to the magnitude of an effective K − p scattering length. When allowance is made for a small number of φ events where the K − rescatters from the proton, the φ region is equally well described at all three energies. A very similar phenomenon is discovered in the ratio of the cross sections as functions of the K − pp and K + pp invariant masses and the identical final state interaction model is also very successful here. The world data on the energy dependence of the non-φ total cross section is also reproduced, except possibly for the results closest to threshold.
A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune-defined as the number of spin precessions per turn-is given by ν s ¼ γG (γ is the Lorentz factor, G the gyromagnetic anomaly). At 970 MeV=c, the deuteron spins coherently precess at a frequency of ≈120 kHz in the Cooler Synchrotron COSY. The spin tune is deduced from the up-down asymmetry of deuteron-carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the PRL 115, 094801 (2015) P H Y S I C A L
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.