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Pi0 and Direct photon cross section in Pythia

Updated on Tue, 2010-02-16 15:32. Originally created by jgma on 2010-02-16 15:31.

Direct photon and Pi0 cross section seems to the very different in different Pythia versions. Here shown is the invariant differential cross section for Pi0 and direct photon in Pythia 6.222 and 6.410.

For the simulation, the following selections are made:

3.4 < eta < 4.0

 

Fig. 1. Direct photon cross section. The total cross section is 11.09 ub in both Pythia 6.222 and 6.410, but the shape of the differential cross section is different, with 6.410 being much harder.

 

Fig. 2. Pi0 differential cross section from Pythia and STAR measurement. The STAR data is taken from 2003 paper Phys. Rev. Lett. 92 (2004) 171801. Same as for direct photons, the Pi0 spectrum has become much harder in Pythia 6.410 than in 6.222. When compare to STAR measurement, Pythia 6.222 gives a pretty good description of the measurement in the measured energy region.

 

 

 

 

Here is the mean pt (GeV/c) and mean eta for the data points in the above figure:

E (GeV) 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 75-80
STAR             1.5 1.7 1.9 2.1 2.2          
Pythia 6.222 0.14 0.35 0.58 0.79 1.00 1.21 1.43 1.66 1.90 2.10 2.29 2.51 2.70 3.08    
Pythia 6.410 0.15 0.36 0.59 0.81 1.02 1.24 1.46 1.68 1.88 1.08 2.27 2.48 2.67 2.88 3.02 3.26

 

 

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