Difference between revisions of "Start Counter Calibration Procedures"

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== '''Warning''' ==
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Some of the procedures described here will commit calibration constants to a database that is used by the entire collaboration. Extreme  care must be taken to not inadvertently write to the database. When writing to the database, this should be discussed and coordinated with experts.
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== Introduction ==
 
== Introduction ==
  

Revision as of 12:43, 9 November 2022

Warning

Some of the procedures described here will commit calibration constants to a database that is used by the entire collaboration. Extreme care must be taken to not inadvertently write to the database. When writing to the database, this should be discussed and coordinated with experts.

Introduction

This page describes the calibration procedures for the Start Counter. If you are not familiar with the concepts of time-walk effect and propagation time in scintillators, you should read Chapter 4: Start Counter Calibration in Eric Pooser's dissertation[1].

The procedure employs three plugins, which are used to analyze raw data files (evio):

  • 1) Start Counter Time Walk Corrections Plugin (st_tw_corr_auto)
  • 2) Start Counter Propagation Time Corrections Plugin (ST_Propagation_Time)
  • 3) Start Counter Time Resolution Plugin (ST_Tresolution)

These plugins provide histogram files, which subsequently are analyzed with root macros. You can find and inspect these plugins and their associated root macros on GitHub or in your local installation at $HALLD_RECON_HOME/src/plugins/Calibration. A summary of how to run each code and the expected outcomes of the macros will be shown in details below

ST Time Walk Plugin "st_tw_corr_auto"

The signals from the start counter's silicone photomultipliers (SciPMs) are split into to branches. One is processed by leading edge discriminators; the discriminator output, which is subject to the pulse height dependent time-walk is fed into F1TDCs. The second branch is fed into the FADC250, which record pulse height as well as timing. The FADC time can serve as a reference time to extract the time-walk corrections for the F1TDCs.

This plugin must run in two passes. In the first pass the parameter USE_TIMEWALK_CORRECTION = 0.Therefore this plugin will generate a ROOT file from an EVIO data file that contains histograms of the time difference (self timing) versus pedestal-subtracted pulse peak amplitude for all 30 start counter sectors. A separate ROOT macro (st_tw_fits.C) will analyze and fit these histograms and provide a table for the CCDB. After uploading the constants into the CCDB, the plugin must run the second pass where USE_TIMEWALK_CORRECTION = 1. The Walk corrected times will be calculated during this pass. The ST self timing resolution is calculated using the macro st_tw_resols.C. In this macro verification plots for each sector is also created.

Plugin Files:

   JEventProcessor_st_tw_corr_auto.cc
   JEventProcessor_st_tw_corr_auto.h

Macros Files:

   st_tw_fits.C
   st_tw_resols.C

To run the plugin, use the following command:

hd_root -PPLUGINS=st_tw_corr_auto /path/to/datafile

To run the first pass macro , use the command :

.x st_tw_fits.C("hd_root.root")

The file st_timewalks.txt will be created with the needed constants for the walk corrections. To upload these constants into the CCDB use the command:

Add timewalk_parms_v2 st_timewalks.txt

After running the plugin for the second time, run the macro st_tw_resols.C using the command

.x st_tw_resols.C("hd_root.root")

Examples of the excpected plots can be found here ST_tw_corr

ST_Propagation_Time

This plugin must run after we have the walk corrected times from the ST and TOF. The first pass of this plugin will generate a ROOT file from an EVIO data file that contains histograms of the ST propagation time versus Z coordinate of the ST hit location for all 30 start counter sectors. A separate ROOT macro (st_prop_time_v1.C) will analyze and fit these histograms and provide a table for the CCDB through an output text file named (st_prop_time_constants.txt). In order to add these constants to the CCDB use the Command :

Add  propagation_time_corr st_prop_time_constants.txt

To check that these constants work fine run the plugin in the second pass using the command:

hd_root -PPLUGINS=st_tw_corr_auto /path/to/datafile 

Then run the macro st_prop_time_corr_v1.C using the command:

.x st_prop_time_corr_v1.C("hd_root.root")

When the corrected times are calculated use the ST_Tresolution plugin to calculate the ST time resolution.

ST_Tresolution

This plugin must run after the ST propagation time constants are uploaded in the CCDB. This plugin will generate a ROOT file from an EVIO data file that contains histograms of the ST corrected time for each paddle versus Z coordinate of the ST hit location. To run the plugin use the hd_root command mentioned in section 1 of this page. To run the macro use the command :

.x st_time_resolution.C("hd_root.root")

The output of this macro will be 30 canvas of the two dimensional histograms mentioned above in addition to Y projection of these histograms. The time resolution will be ploted in another canvas. Examples of these histograms can be found in the following link ST Propagation Time Correction and Time resolution


References

  1. Pooser, Eric J., "The GlueX Start Counter & Beam Asymmetry \Sigma in Single \pi ^{{0}} Photoproduction" (2016). FIU Electronic Theses and Dissertations. 2450. https://digitalcommons.fiu.edu/etd/2450