[Halld-pid] Minutes, GlueX Start Counter Meeting, Mar. 10 '11

[Mark M. Ito]

Find the minutes at 
http://www.jlab.org/Hall-D/software/wiki/index.php/GlueX_Start_Counter_Meeting%2C_March_10%2C_2011#Minutes 
and below as text.

   ==

GlueX Start Counter Meeting, March 10, 2011
Minutes

    Present:
      * FIU: Werner Boeglin, Lei Guo
      * JLab: Mark Ito (chair), Sasha Somov


Start Counter News

      * The new scintillators have been shipped to Plastic Craft[?].
      * Werner and Eric have looked at a new fast shaping amplifier. It
        looks good so far. They will start on a series of measurements
        tomorrow to see if it helps with time resolution.
      * FIU is interested in pursuing the same detection/read-out scheme
        that Richard Jones is exploring for the tagger microscope. The idea
        is to use four independent single-cell 3x3 mm SiPM's rather than
        the 16-cell array being used for the BCAL. Because of higher
        capacitance in the array, rise-times are much longer that those
        expected for single cell devices. The signals out of the individual
        pre-amps would be summed and the summed signal discriminated
        [amplified/shaped first?]. If the rise-time can be preserved
        through this process, better time resolution should result.
      * Sascha will be ordering several of the single-cell devices for
        testing this idea to supply both the microscope and start counter
        investigations. There was some detailed discussion of surface mount
        vs. ceramic types and 25 micron vs. 50 micron technology. The price
        seems to be in the neighborhood of $200 per device.
      * The current goal for timing resolution is about 350 ps[?]. The
        results from SiPM's with the prototype counters are in the range
        500-600 ps thus far[?]. Mark asked if we could live with a device
        with poorer resolution than this goal and rely on other detector
        elements to provide enough time discrimination to pick out the
        correct RF bucket. Others thought that having the good resolution
        was important and we should not give up the idea of the start
        counter independently determining the beam-on-target time.
      * [Added in press.] Mark discussed this issue with Elton after the
        meeting and he mentioned that CLAS has been able to use its start
        counter to determine the beam time in just this way and this
        capability was important in the reconstruction.
      * FIU also plans to pursue the option of using fine-mesh PMT's for
        the readout. Recall that this requires some sort of light guide so
        that the tubes can be in a region of sufficiently low magnetic
        field (a meter or so of light guide).


MOU Status

    Mark will review and accept the changes that Werner sent last month and
    distribute it more widely within the Hall D group for comment.

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