August 13, 2014 Calibration

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GlueX Calibration Meeting
Wednesday, August 13, 2014
11:00 am, EDT
JLab: CEBAF Center, F326

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Agenda

  1. Announcements
  2. Commissioning Planning
  3. Simulations
  4. Online Monitoring
  5. AOT

Slides

Talks can be deposited in the directory /group/halld/www/halldweb1/html/talks/2014-3Q on the JLab CUE. This directory is accessible from the web at https://halldweb1.jlab.org/talks/2014-3Q/ .

Minutes

Attending: Sean (NU); Simon, Lubomir, Mark I., Beni, Manuel, Mike S., Eugene, Elton, Mark D. (JLab); Curtis (CMU); Justin (MIT); Volker, Paul, Sasha, Aristeidis (FSU)

We started by discussing the requirements for the Fall running for each subdetector. Note that the Fall 2014 Commissioning Plan contains the official list of items such as radiators and targets.

CDC

  • Curtis was out of town so there is no new information beyond what already exists at the CDC commissioning page. For initial calibrations, tracks from any events are sufficient.

FDC

  • The first step should be to align the beam with the FDC HV off, so that we are sure that the beam is well inside the "low mass" region of the FDC. One difficult step will be to check the FDC/Start Counter relative alignment. We have a limited ability to move the collimator around.
  • Next, take data with the magnetic field off for FDC alignment. At least 3M events are needed. These are expected to come from the commissioning target and the plastic target attached to the end of the vacuum beam pipe upstream from the magnet.
    • Running with an additional cross-shaped target would be beneficial. Eugene said that this target would have to be placed inside the commissioning target assembly, as there is currently no other place to mount another target upstream. The beam profile monitor could be used as an additional target.
    • Eugene pointed out that we may have to run the solenoid at a very low current instead of zero current. We will need to know how this affects the alignment procedure.
    • Running with a non-standard gas mixture (90/10 Ar/CO2) could be done if the schedule allows.
  • At least 3M tracks are needed with the magnet on to determine resolutions and Lorentz deflection effects.

There was some additional discussion of the properties of the commissioning target

  • The hydrogen target is 2% radiation lengths (R.L.) thick, while a 2 mm plastic target is 0.5^ RL thick
  • More relevant to photoproduction is the difference in the densities (0.1 g/cm^2 versus 1 g/cm^2?)
  • Also, with the plastic target, only ~1/6 of the nuclear recoils will be "clean" protons.
  • Overall, the 2 mm plastic target has very roughly 1/10 of the rate of the hydrogen target?

FCAL

  • The conditions for FCAL are loose - anything that produces pi0's that can be used for calibrations is fine.
  • The total number of events needed should be determined, but from previous experiences it should be a few million.
  • The effect of EM backgrounds and trigger thresholds needs to be studied.
  • Currently, folks at IU are studying exclusive omega photoproduction events as a source of pi0's. Curtis pointed out that the overall gamma p -> pi+ pi- pi0 cross section is an order of magnitude larger. This shouldn't be a problem since the charged tracks are (presumably) being used to reduce the background and we don't need to fix to a narrow resonance. Inclusive pi0's might be useful after an initial calibration as well.

BCAL

  • pi0 and eta decays into two photons will be used. Their angular distributions need to be studied in detail, but the pi0's tend to illuminate the downstream end of the detector, while the eta's have a more uniform distribution. Decays that have one shower in the FCAL and one in the BCAL will be especially useful.
  • Eugene pointed out that once the CDC is calibrated, charged tracks that enter the BCAL could be used as well.

TOF

Start Counter

Trigger

  • Probably a version of the "standard GlueX trigger" will be used (i.e. primarily FCAL and BCAL energy sums).
  • At least one day will be needed for trigger commissioning.
  • The BCAL and FCAL energy trigger thresholds will need to be studied.
  • Beni suggested that it might be useful to take some data where the full waveforms are written out to disk. This data would be very disk intensive, but could be useful for other detector and trigger studies.

Action Items

  • Update desired event counts (all)
  • Update photoproduction event rate calculations
  • How will a low solenoid current affect FDC alignment?
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