Recent searches at the CERN SPS for evidence of the critical point of strongly interacting matter are discussed. Experimental results on theroretically expected signatures, such as event-to-event fluctuations of the particle multiplicity and the aver
age transverse momentum as well as intermittency in particle production are presented.
Collisions of lead nuclei have been studied at the CERN SPS since 1994. A review is presented of the evidence for the production of deconfined matter, the location of the energy of the onset of deconfinement and the search for the critical point of stronly interacting matter
New measurements by the NA49 experiment of the centrality dependence of event-by-event fluctuations of the particle yield ratios (K$^{+}$+K$^{-}$)/($pi^{+}+pi^{-}$), (p+$bar{text p}$)/($pi^{+}+pi^{-}$), and (K$^{+}$+K$^{-}$)/(p+$bar{text p}$) are pre
sented for Pb+Pb collisions at 158$A$ GeV. The absolute values of the dynamical fluctuations of these ratios, quantified by the measure $sigma_{text{dyn}}$, increase by about a factor of two from central to semi-peripheral collisions. Multiplicity scaling scenarios are tested and found to apply for both the centrality and the previously published energy dependence of the (K$^{+}$+K$^{-}$)/($pi^{+}+pi^{-}$) and (p+$bar{text p}$)/($pi^{+}+pi^{-}$) ratio fluctuations. A description of the centrality and energy dependence of (K$^{+}$+K$^{-}$)/(p+$bar{text p}$) ratio fluctuations by a common scaling prescription is not possible since there is a sign change in the energy dependence.
Production of the $K^{ast}(892)^0$ and $bar{K}^{ast}(892)^0$ resonances was studied via their $K^+ pi^-$ and $K^- pi^+$ decay modes in central Pb+Pb, Si+Si, C+C and inelastic p+p collisions at 158agev ($sqrt{s_{NN}}$ = 17.3 GeV) with the NA49 detecto
r at the CERN SPS. Transverse momentum and rapidity distributions were measured and total yields were estimated. The yield of $K^{ast}$ exceeds that of $bar{K}^{ast}$ by about a factor of two in nucleus-nucleus reactions. The total yield ratios $< K^{ast} >/< K^+ >$ and $< bar{K}^{ast} >/< K^->$ are strongly suppressed in central Pb+Pb compared to p+p, C+C and Si+Si collisions in agreement with the expected attenuation of these short-lived resonance states in the hadronic phase of the expanding fireball. The UrQMD model, although incorporating such a scenario, does not provide a quantitative description of the experimental results. The statistical hadron gas model assuming the same freeze-out parameters for stable hadrons and resonances overestimates the $< K^{ast} >/< K >$ ratios in central Pb+Pb collisions by about a factor of 2.5.
