Future Plans for ZDC as a Local Polarimeter

    At the Spin PWG meeting on 17 July 2008, there were three options discussed for using the ZDC as a local polarimeter:

(1) Dedicated runs – take ZDC polarimeter data during dedicated runs and analyze the data offline (perhaps what PHENIX does);

(2) Separate data trigger – take ZDC polarimeter data using a separate trigger or data stream dedicated to this purpose; and

(3) Scalers for ZDC – include ZDC data on scalers, similar to BBC data. 

Option (3) would require the most lead time for implementation, compared to options (1) and (2).  It was decided at that time to have further discussions on these options.

   On 22 July 2008, a phone meeting was held between collaborators at ANL and Valparaiso University to further discuss future plans to use the ZDC as a polarimeter, especially for Run 9.  The three options listed above were discussed at some length.  It was thought that option (3), using scalers, may be premature at this point.  It is hard to justify the amount of work necessary to include the ZDC data in scalers, when the data set used for analysis was very limited in amount and of poor quality.  In the longer term, this option may be the best, once the analyzing power and detectors are shown to work at higher energies.

   Options (1) and (2) seem to be better choices for this next run.  Option (1) may be the easiest to implement, but there were some questions about turn-around time for obtaining the polarization.  Option (2) would require a separate trigger and perhaps separate data path to select good ZDC events.  Perhaps some sort of level 2 trigger and Panitkin plot could be developed, the latter giving a visual indication online that everything is working properly.  

   In future runs, there are several tests that need to be made with the ZDCs.  The beam needs to contain all spin states and the spin rotators need to be cycled on/off to verify that the ZDCs can detect these polarization changes. It is also important to compare results with the BBCs.  Verification of the results at 200 GeV would be useful, and data from 500 GeV is needed for a proof of using the ZDCs as a local polarimeter.

   In addition, further tests need to be made with the offline analysis.  For example, the number of bins and slats used to calculate the asymmetry as a function of the phi-angle may need to be optimized which may be different from the current method. This scheme would impact option (3). 

   The VU group, along with individuals at ANL, is planning to develop the software needed for a polarization measurement using the ZDCs, and implementing it into the trigger for the upcoming run.