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Update grid files for ZZ production, to use default setting of 'ncall1'

Hang Yin requested to merge yinh_powheg into master

Recently, we tested these newly generated POWHEG-BOX ZZ grid files, as described Merge Request (!4 (merged)), by generating ZZ events in full phase space. And we found the lepton eta distributions generated used these grid files are unexpected, as ZZ_Muon_Eta_Old.pdf

So we make serval more tests to figure out why eta distributions are so weird. Eventually, we found the parameter 'ncall1' caused this problem. In the PowhegProduction.cpp, the

ncall1 10000

is used, while in the default powheg.input in ZZ package of POWHEG-BOX,

ncall1 40000

is used.

After increase ncall1, the lepton eta problem is fixed, as shown in this figure. ZZ_Muon_Eta_New.pdf

Therefore, these grid files of ZZ productions are updated to fix the problem. We also checked this option for other production, such as Z-> mumu, Z->ee, H->ZZ, there is no impact on these channels.

Edited by Hang Yin

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