- production type: production_pp500_2022
 
 - data stream: st_fwd

 - event generation: before (include) day 360, use daq files then by BFC process to get the analysis result; after (include) day 361, use MuDst files to analyze.

 - trigger: all the FCS trigger (not apply any FCS trigger filter)

 - photon candidate: FCS cluster

 - vertex z: ??? (not sure how the source of vertex z)

 - cluster z: offset_z + z * cos(a) - x * sin(a) - vertex_z; where a is the detector angle, x,z are the tower position in local frame.

 - cluster four-vector: (E,x,y,z), mass is 0

 - event selection: same as previous study
    1. gain : 5.3 MeV/ch (default)
    2. TOF mult < 20 (before day 360, starting day 361 will skip this cut)
    3. each cluster energy > 1 GeV
    4. energy asymmetry for cluster pair < 0.7
    5. keep the only best cluster pair with highest energy

 - Invariant mass plot position: https://www.star.bnl.gov/protected/spin/liangxl/run22pp500/2021/$day   (for runs in 2022, will use https://www.star.bnl.gov/protected/spin/liangxl/run22pp500/2022/$day)