Golden run analysis

Statistics

Run 134908, 10 Mevents, each event contains cluster with E>1.5GeV

Cluster selection

1. Misalignment from Rongrong applied
2. Pi0 calibration coefficients not applied
3. Non-linearity correction applied (recalculated on the present dataset)
4. Number of cells in cluster: no cuts
5. Cluster pt threshold: 0.5 GeV/c
6. Clusters with the leading cell closer that 1 cell to the SM edge and to warm cells were removed.

Non-linearity correction

The behaviour of the non-linearity correction has been changed in comparison with the with the run triggered by minimum bias trigger (see https://twiki.cern.ch/twiki/bin/view/ALICE/EMCALnonlinCorr). The behavior of the pi0 mass wih decay photons hitting different SM is different in comparison with that one with photons in the same SM. The application of the "plateau" non-linearity correction following the parameterization f(E)=p0+p1*exp(-p2*(E/2_{pi0})) gives a giant fall in low enegy region (in all SM), giant rise (two photons in one SM), fall and shift (two photons in different SM), please see the figures below.

Symmetric Pi0 decays after the "plateau" non-linearity applied

Symmetric Pi0 decays, two photons in the same SM, after the "plateau" non-linearity applied

Symmetric Pi0 decays, two photons hitting the different SM, after the "plateau" non-linearity applied

Only pairs SM0-SM1, SM1-SM3, SM2-SM3, SM0-SM2 were taken. The other combinations have no pi0 peak.

Discussion

• The run triggered by the EMCAL L0 trigger seems to not very suitable for non-linerity correction caclulation, maybe due to the bias spectrum of low-energy clusters.
• The behavior of the pi0 mass with two photons in one SM and two photons in different pairs of SM was also studied on the run triggered by minimum bias trigger data, see https://twiki.cern.ch/twiki/bin/view/Sandbox/MisalignmentInfluence.
• The difference between pi0 mass in single supermodule and in different supermodules might be a sign ethier of a wrong misalignment or wrong calculation of a coordinate correction for inclined photons.