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About the Author

William (aka Bill) Christie is a Physicist at BNL, and is the Operations Coordinator for the STAR Detector. In this role he is responsible for all aspects of the maintenance, setup, and operation of the STAR Detector system. Bill has also served as the STAR Run Coordinator for runs 2 through 8.

STAR has a successful dAu Physics Run

By W.B. Christie

The STAR Collaboration / Experiment had a very successful FY08 deuteron on gold (dAu) Physics run. In addition to accumulating a physics data set that we’re confident will produce exciting and significant physics results, we successfully installed, integrated, and took data with three new detector systems.

The STAR physics goals for the dAu run required that we accumulate what can be categorized as three types of events. These three categories are a minimum bias data set, a rare triggers data set, and a Forward Meson Spectrometer (FMS) data set.

For the events in the min-bias data set we read out the full compliment of STAR detectors. This includes what we refer to as Fast readout detectors (e.g. Barrel Electromagnetic Calorimeter (BEMC), Endcap EMC, FMS, and trigger detectors (Zero Degree Calorimeters (ZDCs), Beam Beam Counters (BBCs), etc.)) as well as the Slow readout detectors (Time Projection Chamber (TPC), Forward TPC, etc.). The STAR goal for this min-bias data set was to accumulate a minimum of 30 million events (Mevts) which have collision vertices along the RHIC beamline within +- 50 cm of the center of STAR. Figure 1 shows the running sum of the min-bias events which satisfy this criteria. Our final total for the dAu run is ~ 46 Mevts, which significantly exceeds our minimum goal.

Figure 1. Running total of min-bias events collected.

The STAR rare triggers data set is for the STAR high Pt and Heavy Flavor physics programs. The triggers used for this data set included four cascading BEMC High Tower threshold triggers, a single EEMC High Tower trigger, and a higher level (L2) Upsilon trigger. The events for all of these triggers included the readout of the full complement (i.e. both Fast and Slow) of the STAR detector subsystems. The physics goal for this data set was to sample at least 30 inverse nano barns (nb-1) of luminosity with this set of rare triggers. Figure 2 shows the running sum of the sampled luminosity for the rare trigger data set. Our final tally for the dAu run is ~ 36 nb-1, fully achieving our goal for the run.

Figure 2. Running sum of sampled luminosity for rare event triggers.

The third category of data set that STAR was after was for the FMS program. This data set will allow STAR to look for evidence of gluon saturation in the nucleons of the Au nucleus (aka Colored Glass Condensate or CGC), by studying the correlations, as a function of Pt and X_F, of forward scattered partons and their away side (in phi) partner parton. In the FMS, which is a large array of Lead-glass cells covering pseudorapidites from 2.5 to 4 on the side of STAR in the direction that the deuteron beam travels, the forward scattered parton energy is measured via leading pi zeroes, and/or clustered Electromagnetic energy. The away side partner parton is measured using the rest of the STAR sub systems, as well as the FMS. To maximize the sampled luminosity used for the FMS program we took FMS triggered and min-bias events reading out the STAR Fast readout detectors when the slow detectors were busy reading out a previous event, as well as FMS triggered events that included the full STAR readout (i.e. fast and slow readout subsystems). Our original goal at the start of the dAu run was to sample 60 nb-1 of luminosity with the FMS trigger. Due to the time necessary to fully commission and calibrate this large (~ 1300 cell) new calorimeter we didn’t get started on the FMS triggered component of this data set until early in January. As shown in Figure 2, we achieved a data set with ~ 48 nb-1 of sampled luminosity. This fully meets a modified goal that we went to during the run (30 nb-1) and we anticipate this data set to lead to exciting physics results.

Figure 3. Sampled luminosity for the FMS triggered data set. The blue points include some data taken prior to the final calibration of the FMS. The red points are the luminosity sampled with the final online calibration of the FMS.

Finally, STAR installed, commissioned, and took physics data with three new detector systems during the dAu run. The FMS, already discussed above, is a large array (~ 1300 cells) of lead-glass cells, read out with a new electronics system that combines fast digitizers with the first level of trigger logic. This device was fully installed, debugged, commissioned, calibrated, and included in the trigger for the dAu run.

Another new system for STAR in the dAu run was a partial installation of the new “DAQ1000” readout electronics for the STAR TPC. One complete sector (out of a total of 24) of the TPC was outfitted with the new DAQ1000 FEE boards, readout boards, and back end DAQ system for the dAu run. This system was operational from the start of the dAu physics run, was fully integrated into the STAR system, and was included in the TPC readout for the physics data sets.

Finally, five trays (out of a total of 120) of the final design Time of Flight (TOF), along with the TOF start detectors (Vertex Position Detectors (VPD)), and the final readout electronics all the way to DAQ, were installed for the FY08 physics run. The debugging and commissioning of the TOF system continued through much of the dAu run, and was integrated into the readout for the Physics data sets towards the end of the run.

In summary, the RHIC collider did an exceptional job and delivered an integrated luminosity that was very close to the upper bounds of their pre-run estimates. Through the dedicated efforts of members of the STAR collaboration we had a very successful dAu physics run and look forward to the exciting physics results that will come from the accumulated data.