STAR   Computing  Simulation  
  Maintained by Maxim Potekhin

Current Situation

The current situation concerning the hadronic interaction simulation within our GEANT framework is as follows:
  • Prior analyses done by the spectra group used a GHEISHA-based GEANT simulation. While analyzing the spectra of charged hadrons, a feature a.k.a. "bump" was discovered in both the experimental data and in the Monte Carlo sample, roughly in the vicinity of Pt=2.0-2.5 GeV. Some fraction of the particles contributing to this part of the spectrum could be then traced to antinucleons as their parents, in the simulations studies.

    This is often referred to as "annihilation" peak, however this might not be the right way to term it as we aren't observing photons or their conversion in the final state, and are rather dealing with charged hadrons as products of interactions of pbars and nbars propagating in the detector. When looking at plots of hadronic cross sections in GEANT, it becomes clear that "annihilation" is not considered to be a distinct process in either package.

  • There was an indication that the magnitude of this "bump" was somewhat larger in the GHEISHA-based simulation as compared to the data.
  • In the summer of year 2002, the GALOR hadronic interactions package was put to use in the STAR simulation runs. This was based on two facts:
    1. at that time, there were a problem with the GSTAR/STAF executable and GHEISHA simply didn't work -- which since have been fixed
    2. There had been reports (see some links below) that GALOR may indeed be a better tool -- with the proviso that this would of course depend on the application.
  • When running with GALOR, the aforementioned feature in the Pt spectrum disappears.

All of this has bearing on the systemtic error estimates made for the spectra, and thus very important. We must therefore make a decision about which package to use. This page was created in order to facilitate the ongoing discussion.

GCALOR related Pages

Last updated by Maxim Potekhin on 5/09/2003