Charged Particle Spectra for Au+Al Fixed Target √s = 2.98GeV

As many have seen, during the lowest energies of the BES, the STAR detector recorded millions of beam collisions with the beampipe (Au+Al). The following begins some analysis on the data Au+Al at a center of mass energy 2.98 GeV, recorded during the 7.7GeV AuAu beam runs.

Analyzing this data allows the STAR collaboration to make measurements at energies below the current capabilities of the accelerator, probing energies where Au beams are not stable enough to record colliding beam data. With these measurements, we can have data points above and below the proposed critical point and thus ensure any fluctuations seen are indeed fluctuations.

Vy versus Vx (Primary vertex position), Log Z, both axes in cm.

Choose vertices by vertex position, removing the beam spot ( Vr > 2cm) and to ensure the collisions are with Al and not Be, set 75cm < |Vz| <100cm.

Z-Vertex distribution. What's going on at Vz between 75 and 100cm? Y-axis is counts, x-axis is Z-vertex position in cm.

More studies to come on attempting to define the collisions at Vz between 75 and 100cm.

              Fig A                                                                            Fig B                                                                         Fig C

The fraction of hits (figure A) to qualify as a good track follows the usual distribution (comparing to AuAu 200GeV). This leads to the usual cut of fraction of hits > 0.5 .  The current "equivalent" of a refMult distribution (figure B) is looking at the total multiplicity of primary tracks in a given event, following the restriction of the fraction of hits. Again, something weird is happening with this distribution as Au+Al multiplicity looks like it should drop to zero around 60 tracks. What kind of collision is occurring to give the primary track multiplicity > 100? And the last plot is the "refmult equivalent" given that the events with greater than 80 tracks are removed.

     Here we have dE/dx plotted against total momentum for positive particles. You can see the pions, protons, deuterons, tritons and helions (only a few). The fuzz between the pions and protons constitute the (100?) kaons and electrons. Below is the same plot for negative particles.

Well, I wonder what these particles are.... pions again. And maybe 3 anti-protons... and 1 K-minus.

Still having issues reading text files to create root Ntuples, but a comparison of E895 spectra to this analysis spectra will come shortly.