We show that fluctuations of the fireball shape in the longitudinal direction generate nontrivial rapidity correlations that depend not only on the rapidity difference, y_{ 1} - y_{ 2}, but also on the rapidity sum, y_{ 1} + y_{ 2}. This is explicitly demonstrated in a simple wounded nucleon model, and the general case is also discussed. We show how to extract different components of the fluctuating fireball shape from the measured two-particle rapidity correlation function. The experimental possibility of studying the longitudinal initial conditions in heavy-ion and proton-proton collisions is emphasized.
Categories: nucl-th hep-ph nucl-ex
