LHCb Specific Pythia8 Tuning

Here we'll document the process of creating new LHCb specific tunes for GAUSS based on the PYTHIA8 event generator. Please, feel free to contribute and correct the information resumed on this page.

GAUSS Configuration

Through-out this campaign events will be generated using the Gauss system relying mainly on PYTHIA8 event generator to produce the events. As LHCb was designed to study physics of b-hadrons the decays of such hadrons is performed by EvtGen which we'll use in its default configuration.

The final state radiation (FSR) is traditionally simulated in LHCb using PHOTOS. However the FSR mechanism implemented in PYTHIA8 was found to have an anomalous behaviour (see slide 15-21) when used together with PHOTOS. Therefore, at least when optimizing parameters in the weak decay sector it is recommended to use either PYTHIA8 without PHOTOS applied or have the PYTHIA8 FSR model turned off. For PYTHIA8 the FSR switches are documented on the Master Switches -- the PartonLevel:FSR* switches. The use of PHOTOS with PYTHIA8 FSR models turned off may be seen in various event type definitions in the DecFiles package (e.g. look at $DECFILESROOT/options/Zgammamumu=PHOTOS.py).

Tips in using Professor/RIVET

As reminder, a better understanding of the effect of a generator optimization using the Professor/RIVET can be obtained by generating MC statistics with the optimized set of steering parameter values for the considered event generator and processing the events with a set of RIVET analysis modules (not necessarily the same that was used in the tuning) to which one can always add the standard or extended set of MC_* generic plug-ins available in the library. For the complete list and minimal details about these plug-ins issue:

$ rivet --list-analyses | grep MC_


-- AlexGrecu - 25 Sep 2014

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Topic revision: r4 - 2016-10-05 - AlexGrecu
 
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