NET proton and negatively-charged hadron spectra from the NA49 experiment

摘要

The collision of heavy nuclei at ultrarelativistic energies provides an opportunity to study a highly excited system with an energy density of several GeV/fm~3 in a volume about the size of the ion. Quantum Chromodynamics (QCD) predicts that hadronic matter at a sufficiently high energy density will be transformed into a state of deconfined quarks and gluons called the quark-gluon plasma (QGP). In a nucleus-nucleus collision, a portion of the initial longitudinal energy that is carried by the beam and target baryons is transformed to other degrees of freedom. namely produced particles and transverse momentum. The rapidity shift of the baryons. or "stopping", is estimated by the final state rapidity distribution of the net protons (p-p_. The final state negatively-charged hadrons (h~-) consisting of pi~-, K~-, and p are all created by the collision and are a measure of the total particle production are roughly equal. While these measurements alone cannot show that a phase transition to a QCP has occured, they characterize the basic features of the collisions.