Cross sections of the pp→K+Σ+n reaction close to threshold

The legacy of the hadron physics programme at COSY

“…If it is only the K + that is detected it is not possible to distinguish true Σ production from Λ production where there is a cusp at the ΣN thresholds. For example, the HIRES collaboration measured pp → K + X at θ K = 0 • and found a big jump at M X ≈ M Σ + M N [14]. How much of this was due to Σ production -impossible to tell in an inclusive measurement.…”

Study of the Λp interaction close to the and thresholds

“…However, these experiments although having rather large acceptances suffer from insufficient resolution to study a peak in the threshold region. These unfavorable boundary conditions were overcome with sufficient high resolution by Siebert et al [11] employing the SPES4 spectrometer at Saclay and, more recently, even more by the HIRES experiment [12,35] making use of the Big Karl spectrometer [36] at the COoler SYnchrotron COSY Jülich. The disadvantage of the experiments from Refs.…”

“…The disadvantage of the experiments from Refs. [11,12,32,35] is that they are inclusive. This means that above the ΣN threshold also the Σ 0 p and Σ + n channels contribute to the experimental cross section.…”

“…[11] and [12]. In these experiments the four momentum of the kaon was measured and the missing mass of the Y N system was deduced.…”

“…Experimental information about the reaction 4, in the region of the ΣN threshold, has become available much more recently and clear evidence for the presence of an enhancement at that threshold is only emerging right now. Here we perform an analysis of data from the inclusive measurements of the reaction pp → K + X performed at Saclay [11] and in Jülich [12], respectively, and attempt to extract the enhancement and its position from those experiments too. This sort of analysis suffers from lacking precise pp exclusive data to rely on.…”