[Halld-pid] Minutes, Start Counter Meeting, Mon. Dec. 20 '10

[Mark M. Ito]

Find the minutes at 
http://www.jlab.org/Hall-D/software/wiki/index.php/GlueX_Start_Counter_Meeting%2C_December_20%2C_2010#Minutes 
and below as text.

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GlueX Start Counter Meeting, December 20, 2010
Minutes

      * FIU: Werner Boeglin, Lei Guo
      * JLab: Mark Ito, Sascha Somov


Wrapping material

    Paul Eugenio has sent some ESR sheets sent to FIU. They have not been
    received yet.

Counter Fabrication

    Lei has had futher contact with the company that is fabricating light
    guides for the CLAS12 central TOF.
      * They can do bending for no extra charge.
      * They estimate a failure rate of 3 out of 8.
      * The cost should be a few hundred dollars per counter.
      * One possibility is to buy scintillator in sheets and have the
        company do the cutting, bending, and polishing.
      * Practice for the company with plexiglass seems the likely next
        step.


Neutrons and SiPM damage rates

    Sasha reviewed the damage estimates on [23]his wiki page.
      * The damage rate is comparable to that of the downstream end of the
        BCAL.
      * Polyethylene shielding helps. This was studied for the tagger and
        reduced the damage rate by about a factor of 7.
           + The support structure itself could be made out of shielding
             material.
      * The start counter is a timing application, not an energy
        measurement. That should increase its tolerance to dark current.


Further Tests

      * Werner wants to look at new scintillator bars with new SiPM. So far
        the timing resolution has been dominated by light output.
      * Sascha reported that Richard Jones simulated discriminator response
        in the microscope with a SiPM with elevated dark rate. He found
        that the timing resolution was OK with a factor of 50 increase in
        dark rate. For the microscope he expects 300 pe's total.
      * Werner suggested that we can change dark current with temperature
        in order to test timing response.
           + We need to ask Carl Zorn how hot does it have to be.
      * Sascha quoted a start counter rate of 12 kHz, versus 1 MHz for the
        microscope.
      * Werner has a 4x4 array: Hamamatsu F10943.
           + Sascha suggested we ask Carl for another one.
      * Werner is changing his set-up to do light output measurements to
        accommodate the SiPM as main detector.
      * The new scintillators he plans to use are:
           + 2 mm and 3 mm thick, 12 mm and 15 mm wide
           + The 15 mm wide counters could be used for a 30 element design.
           + Since he observed light output reduced by edges, a wider wider
             counter has less edge area fractionally.
      * The plan is to focus on the SiPM solution, using the same one as
        for the BCAL.


Other Items

      * Werner mentioned the possibility of funding the project through an
        MRI.
      * The light guide design is non-trivial. Although there is a rough
        match in cross sectional area between the scintillator and SiPM,
        the aspect ratios are pretty different.

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References

   23. http://www.jlab.org/Hall-D/software/wiki/index.php/Comparison_of_radiation_damage_between_FLUKA_and_Geant

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