There is a bug in 2012 MC generated with BcVegPy:
The bug has been reported to the simulation group [JIRA task] and a fix has been developed. Since the bug was due to a statistical fluctuation in the 8 TeV grade files, it only affects 2012 MC, not any other year.
I also reported it in the B2OC meeting and the B2OC summary of LHCb week.
I produced 50M generator level Bc events without any cuts before and after the fix. Taking the ratio of the two gives weights that can be used to correct the buggy MC. The weights as a function of the Bc production spectrum (pT, eta) or (pT, y) are available in my public area:
/afs/cern.ch/user/a/atully/public/BcVegPy_weights/BcVegPy_weights_2012.root
Inside this root file are a few histograms:
The weights in (pT, eta) look like this: https://twiki.cern.ch/twiki/pub/Main/BcVegPyWeights/BcVegPy_weights_eta_2012.pdf
To evaluate the weights, the MC truth values of pT(Bc) (in MeV/c) and eta(Bc) or y(Bc) should be used as the x and y coordinates. The z value of the corresponding bin is the weight. These weights can be used for any Bc decay mode since they are based on the properties of the Bc.
When I evaluated the weights on my Bc->DD MC, the mean was ~0.9. This is slightly counterintuitive behaviour:
-- AlisonTully - 2019-08-06
I | Attachment | History | Action | Size | Date | Who | Comment |
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BcVegPy_weights_eta_2012.pdf | r1 | manage | 22.8 K | 2019-08-06 - 11:03 | AlisonTully | ||
Bc_ETA_2012.pdf | r1 | manage | 20.4 K | 2019-08-06 - 10:55 | AlisonTully |