Simultaneous multiplicity and forward energy characterization of particle spectra in Au+Au collisions at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>1</mml:mn><mml:mn>1</mml:mn><mml:mo>.</mml:mo><mml:mn>6</mml:mn><mml:mi>A</mml:mi></mml:math>GeV/<b><i>c</i></b>

In this paper Au+Au collisions at $11.6A$ $\mathrm{GeV}/c$ are characterized by two global observables: the energy measured near zero degrees ${(E}_{\mathrm{ZCAL}})$ and the total event multiplicity. Particle spectra are measured for different event classes that are defined in a two-dimensional grid of both global observables. For moderately central events $(\ensuremath{\sigma}/{\ensuremath{\sigma}}_{\mathrm{int}}&lt;12%)$ the proton $dN/dy$ distributions do not depend on ${E}_{\mathrm{ZCAL}}$ but only on the event multiplicity. In contrast the shape of the proton transverse spectra shows little dependence on the event multiplicity. The change in the proton $dN/dy$ distributions suggests that different conditions are formed in the collision for different event classes. These event classes are studied for signals of new physics by measuring pion and kaon spectra and yields. In the event classes doubly selected on ${E}_{\mathrm{ZCAL}}$ and multiplicity there is no indication of any unusual pion or kaon yields, spectra, or $K/\ensuremath{\pi}$ ratio even in the events with extreme multiplicity.