p femtoscopy in collisions of Ar+KCl at 1.76A GeV

Results on Ap femtoscopy are reported at the lowest energy so far. At a beam energy of 1.76A GeV, the reaction Ar + KCl was studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS 18/GSI. A high-statistics and high-purity A sample was collected, allowing for the investigation of Ap correlations at low relative momenta. The experimental correlation function is compared to corresponding model calculations allowing the determination of the space-time extent of the Ap emission source. The Ap source radius is found to be slightly smaller than the pp correlation radius for a similar collision system. The present Ap radius is significantly smaller than that found for Au + Au/Pb + Pb collisions in the AGS, SPS, and RHIC energy domains but larger than that observed for electroproduction from He. Taking into account all available data, we find the Ap source radius to increase almost linearly with the number of participants to the power of one-third.