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Measurements of the forward and the transverse energy in 158 GeV per nucleon Pb + Pb collisions are presented.A total transverse energy of about 1 TeV is created in central collisions. An energy density of about 3 GeV/fm is estimated for near head-on collisions. Only statistical fluctuations are seen in the ratio of electromagnetic to hadronic transverse energy. PACS numbers: 25.75.+r, 12.38.Mh Collisions of heavy nuclei at high energies serve as a unique tool for studying strongly interacting matter under conditions of extreme density and temperature. The recent acceleration of Pb ions in the CERN SPS to an energy of 158 GeV per projectile nucleon has extended this field of study to a new domain where bulk nuclear matter is excited to such high energy densities that it might undergo a phase transition into a deconfined and/or chirally restored state, as predicted by lattice QCD calculations [1]. If equilibrium is achieved, global observables such as transverse energy production can be related to thermodynamic variables, such as energy and entropy density, commonly used to characterize these collisions. The systematic comparison of such quantities for various collision systems may elucidate the dynamical mechanisms involved and identify observables and conditions under which to search for signals of a possible phase transition. One such observable is the relative production rate of electromagnetic to hadronic energy, which rejects the relative abundance of neutral to charged pions. In a chiral phase transition, transient domains of disoriented chirality may be formed and if sufficiently large would lead to large fluctuations in the ratio of charged to neutral pions [2]. In this Letter we present and discuss the first data on transverse energy production in Pb + Pb collisions, and also make comparison to previously published S + Au and S + S data [3]. We estimate that the energy density in head-on Pb + Pb collisions at this energy reaches about 3 GeV/fm, thus surpassing the critical energy density predicted by lattice QCD [1].However, no unusual physics is observed in the ratio of electromagnetic to hadronic transverse energy.The NA49 experiment is designed to perform inclusive as well as single event measurements of a variety of observables for 2osPb induced reactions at 158 GeV/nucleon 3814 0031-9007/95/75(21)/3814(4)$06. 00

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