Protos LHEF interface for ATLAS

NEW TAG: ProtosLHEF_i-00-00-02 (

ProtosLHEF_i is a new interface implemented in Athena to convert Protos raw-output files to the standard LHEF format files, which then can be directly matched with different parton shower generators.

This interface was presented in detail in a MC generator meeting (see the slides here).


Protos is a LO generator for some new physics processes involving the top quark. The program and documentation can be downloaded from the author website. Some 'quick-start' information can be found in this Twiki Page.

Protos generates weighted events in a raw-output text format. It also includes an unweighting tool which generates two output files:

  • protos.dat: Stores the generator parameters and theoretical values from the process.
  • Stores the unweighted events information of the decay products from the process.

In principle, these files can be interfaced to a parton shower generator, but the specific output format requires a specific interface for each generator. For now, ATLAS MC productions have only been using the Protos_i interface, which allows the matching with the Pythia6 generator. However, if the Protos raw-output format could be converted in the LHEF standard format (LHEF documentation here), the matching with any Parton Shower generator that accepts LHEF inputs could be achieved. This was the main motivation for implementing the ProtosLHEF_i package.

ProtosLHEF_i package

The goal is to read Protos raw-output files (protos.dat and and create one standard LHEF file from them. Then, this LHEF file can be directly read by any Parton Shower generator that accepts LHEF inputs.

Actually, this new Protos LHEF interface (namely ProtosLHEF_i) is based on the existing code from the old Pythia6 interface (namely Protos_i), since it already read Protos raw-output files and stored the information in LHEF commonblocks which were processed by Pythia6.

Package setup

The package is available in the repositories:

Once the Athena version is set up as usual (see more on this here), the package can be checked out and compiled:

cmt co -r ProtosLHEF_i-00-00-01 Generators/ProtosLHEF_i

cd Generators/ProtosLHEF_i/cmt

cmt config


Hopefully with no errors.

Standalone usage

In Generators/ProtosLHEF_i/share you can find:

  • test sample protos.dat
  • test sample

Once Athena is set up and the package compiled, one can run a standalone test by:

cd Generators/ProtosLHEF_i/share

And this will generate the LHEF format file called events.lhe.

ATLAS generation usage

This package can be used to directly interface Protos raw-ouput files to different Parton Shower generators in the ATLAS generation chain.

In the directory Generators/ProtosLHEF_i/share, one can find the file This file must be included in the global generation job options, before the Parton Shower generator (Pythia6, Pythia8, Herwig...) job options are included, which must be the corresponding for that PS generator to read LHEF inputs.

  • Note that one should not use evgenConfig.generators = ["Protos"], since this refers to the old Pythia6 interface.

So, the generation command line will look something like: ecmEnergy='8000' runNumber=% firstEvent='1' randomSeed='1' jobConfig='MC12JobOptions/' outputEVNTFile='EVNT._000001.pool.root' inputGeneratorFile='group.phys.gener.protos22.%.TXT.mc12_v1._00001.tar.gz'

where the inputGeneratorFile includes Protos raw-output format files and jobConfig are the job options that must include

This will generate the outputEVNTFile of pool.root format events and (as an intermediate file) the LHEF format file events.lhe.

You can find more details on the presentation slides here.

Validation with Pythia6

For this validation, see section 3 of these presentation slides here.

Matching with Pythia8 and Herwig

For this matching, see section 4 of these presentation slides here.

Discussion & open issues

Things to be discussed and investigated:

  • The official ATLAS Protos+Pythia6 MC12 production has null lepton (and light quark) masses for many events, while the new Protos LHEF interface has the corresponding masses for all. (See slide 27 of this presentation here).

  • For the matching with Fortran Herwig(Jimmy), there are important discrepancies in the pseudorapity variable for all objects.

  • There is an Athena error when trying to use this interface with Herwipp, which doesn't look like a Herwigpp problem, since it doesn't reach to create even the LHEF file. (But why only for Herwigpp?)

-- PatriciaFernandez - 24 Jul 2014

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Topic revision: r4 - 2015-03-25 - PatriciaFernandez
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