Studying the onset of deconfinement at NA61/SHINE

The study of particle production in high-energy collisions of heavy ions offers a unique opportunity to explore the phase transition of strongly interacting matter. The NA61/SHINE experiment, a fixed-target setup located in the CERN SPS North Area, plays a crucial role in this investigation. To perform a two-dimensional scan of the phase diagram of strongly interacting matter, the experiment varies both the beam momentum (ranging from 13 to 150/158 GeV/c per nucleon) and the size of the colliding ions (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La, Pb+Pb). This article presents a study of the properties of the onset of deconfinement by measuring the K+/pi+ ratio, which is proportional to the strangeness to entropy ratio of the produced system. New results from central Pb+Pb collisions at 30A GeV/c, focusing on the spectra of charged kaons and pions, confirm the presence of the horn structure in the energy dependence of the K+/pi+ ratio, consistent with earlier observations by NA49 and STAR, which could be interpreted as a hint of the onset of deconfinement at middle SPS energies.