[Lad_hallc] Runplan final draft

[Florian Hauenstein]

Hi Larry

here are some answers on the questions which we didn't fully addressed during the RC meeting:


  1.
 item 2.1: what is the difference between setting PS6=0 (accept all, no prescale) and other triggers ps = 1?  What prescale factor does ps=1 correspond to?

ps=1 corresponds to only record every second event for this trigger. The general formula is
trigger rate = input-rate / (2^{psvalue - 1} + 1)
ps =-1 means that the trigger is disabled

  1.
item 2.4: can we take enough data at some of the settings (especially 5) to measure the H(e, e’) cross section?  It is always good to be able to normalize the spectrometers.

discussed at the meeting, we take more data to do this

  1.  p6: GEM optics
     *
is there an advantage to inserting the sieve for the GEM foil optics run?  It will kill our event rate.  We will already know the HMS optics so we will know the electron angles.
as discussed don't need sieve here
     *
Where is the GEM located at this run?  Forward or back?  Can it see the protons?
at final position, we can not see elastic protons
     *
what trigger will we use?  The SHMS trigger should be ps = -1
this is correct and we missed it to add here. we will add trigger setting
     *
should we check the reference bar timing at this time?  should it be on?
reference bar timing will be moved before GEM optics as also Axel pointed out
  2.
item 2.5: where is the reference bar placed?  Where is the GEM at this time?  If both are forward, we can do this during the GEM optics check by changing the target from multi-foil to LH2.

Reference bar is at ~42-45 degrees where the elastics are. GEM is in final position e.g. 90-157 deg

  1.  item 2.7:
     *
should we set the ps so that ps2 = 0 and ps4 = 0? Then we can take single arm data from both HMS and SHMS (luminosity scan).  Item 2.6 specified ps1 = ps2 = 0.
  2.
thanks for catching this. It is a typo and needs to be corrected to ps2 and ps4
     *
is the raster on or off?
  3.
technically can be both at our currents according to my last chat with Dave Meekings about it. I thought to run without raster if we can.
  4.  item 3.1 (and similarly for 3.2 and 3.5)
     *
Do we run raster off when beam current is 1 uA or less?
I would prefer this so acceptance and beam pos is more or less the same throughout the production running and one less system to worry about.
     *
how do we set ps1 and ps3?  1% or 10% each?
Probably at least 1% or maybe lower. We will see with beam.
     *   #7:  I assume it is "<= 2 kHz”             yes will be fixed
     *
what determines the maximum luminosity that we can run at?  This specifies trigger rates less than 1 kHz in each arm.  Why should we change the prescalers to achieve this rate, rather than the beam current?
technically we should first consider to reduce the beam current. 2kHz is roughlt the limit of the DAQ. The physics event rate is of the order of 100s Hz so we should be below 1kHz easily. Any large trigger rate might be coming from accidentals or background readctions. I mostly consider to set prescales for other triggers (ps1 and ps3)based on rates.
     *
#11: how long should the dummy run be?
To be seen when data comes in. I would say a percentage of the charge collected. And we also should discuss later if we dummy and/or empty target
  5.
item 4.1: we are using the carbon multi foil for optics calibration for the GEMs and HMS/SHMS.  Do we use this target for LAD at all?  These are 55 mg/cm^2 target foils.  There would be significant material (>500 mg/cm^2) for the LAD bar at 90 degrees and the two bars on either side of it.
I considered this target to look for coincidence photons (and possibly charged particles) in the LAD bars during commissioning. But this would be parasitic at this point.
  6.  there is no item 8

- Larry

On Mar 19, 2025, at 10:32 AM, Florian Hauenstein <hauenst at jlab.org> wrote:

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Dear all,

please find attached the final draft  from Dien, Holly and me of the run plan.
The amount of production running in each setting is not fully set in stone since it depends on the observed statistics.
Please let us know your comments as soon as possible.

Best,
Florian
<LAD_Runplan-5.pdf>_______________________________________________
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Lawrence B. Weinstein
University Professor and Eminent Scholar
Physics Dept
Old Dominion University
Norfolk, VA 23529
weinstein at odu.edu
http://www.lions.odu.edu/~lweinste/
757 683 5803








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