Diagnostics with two-particle correlations

We have used data from an exact hydro dynamical model and we showed for the first time that differential Hanbury-Brown-Twiss (DHBT) interferometry can measure the rotation in a heavy-ion collision. The measurements would be sensitive to the rotation as well as the shape and radial velocity. It has been shown that the size of the system is measured differently if the detector is placed at different positions. A perfectly cylindrical symmetric system will be measured as an asymmetric object if rotation is taken into account, which would not be the case if the rotation is not present. Recently the rotation of the matter in heavy ion collisions was confirmed by experimental Lambda polarization measurements at the Beam Energy Scan programme of the RHIC at Brookhaven National Laboratory. This verifies our predictions, and increases the importance of our results.

The two particle correlation method is used to determine the space-time size of the system emitting the observed particles, thus providing valuable information on the exploding and expanding system at the freeze out stage of a heavy ion collision. This me thod is based on the Hanbury Brown and Twiss (HBT) method, originally used for the determination of the size of distant stars. A detailed two particle correlation study of flow rotation was not performed up to now. This became actual now in heavy ion the ory as at higher beam energies, where the initial angular momentum of the participant system is increasing in peripheral reactions, the system may rotate causing a significant and detectable effect. We have earlier presented a Differential Hanbury Brown and Twiss (DHBT) method, which can sensitively determine the strength (vorticity or circulation) of rotating flow and the direction of rotation in relativistic heavy ion collisions. Since the HBT method has worked from detecting size of stars and down to particles, and with the study of flow rotation, the objective is to study two-particle diagnostic tools for heavy ion reactions and for other possible applications.