Event-by-event fluctuations of particle ratios in central Pb+Pb collisions at 20-158 A GeV

Recent results of the NA49 energy scan programme show a sharp maximum of the ratio of K+ to pi(+) yields in central Pb+Pb collisions at beam energies of 20-30 A GeV. This observation has been interpreted as an indication of a phase transition at low SPS energies. We present results on event-by-event fluctuations of the kaon to pion and proton to pion ratios at beam energies close to this maximum. A significant increase of the fluctuation signal of the kaon to pion ratio with deceasing beam energy is observed.