BCAL Costhe Efficiency

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Description of Method

We use the isotropy of the decay of pi0->gamma gamma to determine relative photon reconstruction efficiencies. PI0 mesons are spineless particles and, therefore, their decay is isotropic in their rest frame. In addition, the photons are massless, so the energy distribution of the photons in the lab is directly related to the angular distribution in the pi0 rest frame. This fact allows us to infer relative inefficiencies in the photon detection/reconstruction efficiency from non-uniformities of the energy distribution in the lab. A description of the method and the results of the using this method for the 2017 data can be found in GlueX-doc-4002.

Analysis Procedure

Steps to run DSelector to determine the photon reconstruction efficiencies using the Costhe Eff method. The scripts used for the analysis can be found on GitHub hd_utilities. Below we reproduce information from the README file.

The is a preliminary setup for Data and MC is a little different:

  • Data setup:
    1. For the data, one starts with the output trees of the event filter specifying for the reaction 1_14__7_8_9_14 (g p -> pi0 pi+ pi- p). The are generated as part of the GlueX analysis launches. The files are found for example in /cache/halld/RunPeriod-2017-01/analysis/ver27/tree_pi0pippim__B4/merged/tree*.root.
  • MC setup:
    1. Events are generated with the output of g p -> pi0 pi+ pi- p and simulated using HDGeant4.
      • For FCAL, use g p -> omega p events with a Bslope = 6 GeV2. Examples of the output can be found at /cache/halld/gluex_simulations/REQUESTED_MC/gen_omega_3pi_efficiency_2017_01_20200525020622pm/hddm/dana_rest_gen_amp_*.hddm
      • For BCAL, FCAL/BCAL, use g p -> pi0 pi+ pi- p, where M(pi0pi+pi-) peaks at about 1.2 GeV with a wide distribution, and B = 2.5 GeV-2. Examples can be found at /cache/halld/gluex_simulations/REQUESTED_MC/2017/gen_amp__3piHighMass_t2.5__G4_20190501054440pm/hddm/*.hddm
    2. The REST (.hddm) files must be processed with the reaction filter to produce root trees. This is accomplished with the following command:
      • > hd_root ${indir}dana_rest_gen_amp_${run}.hddm --config=jana.config, where ${indir} is the residing directory and ${run} is the run_file identifier.
  • Processing:
    1. The data and/or the MC root trees are processed using the DSelector as follows:
      • > root -b -q tree_pi0pippim__B4.root 'call_DSelector.C("DSelector_pi0pippim__B4_ver21.C+")'
      • Save the output root histograms to the desired ${outdir} direcgtory
      • > cp DSelector_pi0pippim__B4.root ${outdir}/DSelector_pi0pippim__B4_gen_amp_${run}.root
    2. Edit the script plot_compare2DEff.C to point to the appropriate data and MC root files to obtain comparison plots of data and MC.
      • > root -l
      • > .x plot_compare2DEff.C

Data Studies