Les Houches

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===== Large pT in POWHEG =====

The issue is a significant hardening of the pT-spectrum after showering in POWHEG+Pythia8 for certain observables, even for non-zero values of the POWHEG damping factor (specific examples are gg->HH, see [[http://arxiv.org/abs/arXiv:1703.09252|arXiv:1703.09252]], or gg->H, see [[http://arxiv.org/abs/arXiv:1510.08850|arXiv:1510.08850]]).

Here are a few questions/topics that arose in the discussion:

   * Can one identify classes of observables where the effect is more prominent than in others?
   * Is the effect specific to Pythia8, or is it observed also with Pythia6?
     Here are example plots {{2017:working_groups:sm:nlo_swr_hdamp_pthh_full_py6.pdf| hdamp=250}},{{2017:working_groups:sm:nlo_swr_pthh_full_py6.pdf| hdamp=infty}} from gg to HH which suggest that the effect is more pronounced with Pythia8 than with Pythia6. The plots are also in version 2 (journal version) of [[http://arxiv.org/abs/arXiv:1703.09252|arXiv:1703.09252]].

   * Is the effect specific to POWHEG?
   * In [[http://arxiv.org/abs/arXiv:1510.08850|arXiv:1510.08850]], it was proposed to restrict the shower scale in the remnant events: is this legitimate for all observables?

Les Houches

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