Study Of Using Event-plane-rotating To Get System Shape Anisotropy

High energy heavy-ion collision experiments have produced huge amounts ofexperimental data which include freeze-out particles’ types, energies and momentums.How to detect the status of initial moment and the dynamic mechanisms of thesecollisions has became the focus of physicists’ attention. One of the starting points ofthese backtracking processes should be the shape of system detected by HBTinterferometry. Then the shapes’ anisotropy will become the basis and an important partof the treatment of the experimental data produced by heavy-ion collisions.This article is a study of shape’s anisotropy of particle emission source produced inhigh energy heavy-ion collisions, where the shape of the particle emission source is thevariation of the HBT radii’s squares with azimuth of two particles’ average momentum.For the event-plane-alignment method’s inadequacies, this article proposes anevent-plane-rotation method. Using of this new approach can randomize a single event’sazimuth difference of event-planes, and as the pretreatment process ofevent-plane-alignment method, event-plane-rotation is applied to the analysis ofobtaining the system shape anisotropy.After proposing the event-plane-rotation method, this article has prepared ablast-wave parametric statistic model for verifying the necessity and suitability of thismethod. By convenience of adjusting the azimuth of event-planes of this model, it hassimulated two scenarios, namely the rotation method’s objective having been reached ornot reached. In these two cases only the event-plane-alignment method was used to treatdata. Results show that while the objective of the rotation method hasn’t been reached,detected n order’s system shape anisotropy is not pure, it will contain other orders’component. While the objective of the rotation method has been reached, alignmentmethod could detect the system shape anisotropy preset in the model exactly. In order toverify the suitability of the rotation method, it was used to treat a single event producedby Monte Carlo to change some event-plane to a predetermined angle. The results showthat the event-plane was changed to the predetermined angle plane accurately, and therewere no effect to the other orders’ event-plane angle and values of transverse flow. Thisarticle adjusted the azimuth of event-plane of the blast-wave parametric statistic modelto the direction of collision parameter, and combined these two methods to analysis these data. The results show that, except for a small deviation of phases, anisotropywith cosine curve preset is detected successfully. This is a good illustration of thesuitability of rotation method. So the rotation method becomes a pretreatment process ofthe alignment method. This paper will also use event-plane-rotation method to treat2500noncentering200GeV Au+Au events simulated by AMPT model with stringmelting. The second order’s system shape anisotropy of these events are increasing,decreasing and increasing firstly and then decreasing with the azimuth by directions ofout, side and outside. The first, third and fourth orders’ system shape anisotropy of theseevents are very little.Event plane rotation method effectively complements the event plane alignmentmethod, and is very effective in obtaining system shape anisotropy.