  We present new, exact, finite solutions of relativistic hydrodynamics for
longitudinally expanding fireballs for arbitrary constant value of the speed of
sound. These new solutions generalize earlier, longitudinally finite, exact
solutions, from an unrealistic to a reasonable equation of state, characterized
by a temperature independent (average) value of the speed of sound. Observables
like the rapidity density and the pseudorapidity density are evaluated
analytically, resulting in simple and easy to fit formulae that can be matched
to the high energy proton-proton and heavy ion collision data at RHIC and LHC.
In the longitudinally boost-invariant limit, these new solutions approach the
Hwa-Bjorken solution and the corresponding rapidity distributions approach a
rapidity plateaux.
