Heavy-ion physics at the CERN SPS H2: NA35, NA49 and NA61/SHINE (with personal recollections)

Abstract

This review presents a unified account of the NA35, NA49, and NA61/SHINE experiments, which together form a continuous programme of heavy-ion studies conducted at the H2 beamline of the CERN North Area using the SPS accelerator. The programme, spanning about 40 years, was driven by the search for a high-density state of strongly interacting matter - the quark--gluon plasma (QGP) - and the transitions leading to it. The review focuses on this primary line of research. The highlights of the programme include the observation of the first signal of QGP creation at the top SPS energy in S+S collisions by NA35, evidence for the onset of deconfinement at low SPS energies by NA49, and the establishment by NA61/SHINE of the diagram of high-energy nuclear collisions, featuring transitions between hadron-, string-, and QGP-dominated regimes. This predominantly scientific review is complemented by brief personal recollections related to the discussed topics.

Figures (11)

• Figure 1: The top view of the NA35 experimental setup Sandoval:170613; see text for details.
• Figure 2: An iconic image of a central S+Au collision at 158$A$ GeV/$c$ recorded by the NA35 streamer chamber.
• Figure 3: The ratio of the mean multiplicities of strange hadrons within the experimental acceptance to the total negative hadron multiplicity in S+S collisions at 200$A$ GeV/$c$ is shown for peripheral, intermediate, and central collisions. The two leftmost points represent the corresponding results for p+p and $p$+S interactions. The predictions of the simple superposition model, Fritiof, are independent of the $h^-$ mean multiplicity. The figure is taken from Ref. NA35:1990teq.
• Figure 4: Top: Top view of the NA49 experimental setup as originally proposed by NA35 Panagiotou:295042. Bottom: The setup constructed by the NA49 Collaboration NA49:1999myq. For further details, see the references above and the text.
• Figure 5: Left: Energy dependence of the $\langle K^+ \rangle / \langle \pi^+ \rangle$ ratio measured in central Pb+Pb and Au+Au collisions (full symbols), compared to the corresponding results from p+p($\bar{p}$) reactions (open circles). Right: Energy dependence of relative strangeness production as measured by the $E_S$ ratio in central Pb+Pb and Au+Au collisions (full symbols), compared to results from p+p($\bar{p}$) reactions (open circles). The curves in the figures represent predictions from various models. The plots and caption are taken from Ref. NA49:2007stj, where details and references are provided.