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-- LauraReina - 2015-12-16

Standard setup for the comparison of tTH simulations at NLO QCD + Parton Shower

This is the setup we propose for the comparison of tTH production in NLO QCD+Parton Shower simulations.

General assumptions

For the comparison among existing NLO QCD+PS tools we will consider only the case of a scalar and will include only NLO QCD corrections. EW corrections will be discussed in the section on signal and are included in the tables that give fixed-order results obtained scanning over MH for various center of mass energy.

We propose to compare results from:

  • Sherpa2.1.1+Openloops1.2.2
  • MG5_aMC@NLO 2.3.2+Pythia8.2.1.0
  • Powheg+Pythia8.2.1.0
  • Powhel+Pythia8.2.1.0
The last two simulations should give very similar results by default, since they are both based on Powheg, but they have never been compared, so we think it will be useful to. Upom agreement, we would probably quote only one set of results as coming from the interface with Powheg-Box.

Simulation setup

All the input parameters will be chosen in compliance with the official Higgs HXSWG note https://cds.cern.ch/record/2047636/files/LHCHXSWG-INT-2015-006.pdf

In particular we suggest to

  • consider sqrt(s)=13 GeV;
  • use MH=125 GeV and mt=172.5 GeV (see recommendation);
  • use NLO PDF4LHC15;
  • is the MC setup: no hadronization, no UE;
  • consider either fixed (mt+MH/2) or dynamical (geometric mean of transverse mass of H,t,T) renormalization/factorization scale (the difference is minimal, so let's agree on either on eor the other): estimate the uncertainty varying independently by a factor of 2 about teh central value;
  • estimate the dependence on other simulator-dependent scales (PS, hdamp, etc.) that needs to be considered in the comparison;
  • first: do not include top/Higgs decays and compare distributions for: pT(H), eta(H), pT(t), eta(t), pT(tTH);
  • second: include top and H(bB) decays, requiring 4 b jets+2 leptons+missing ET (defined according to well-defined cuts that we will spell out), and compare distributions for: pT(hardest b), pT(next-to-hardest b), pT(hardest lepton), phi(l+,l-) (azimuthal angle between hardest l+ and l-), studying effects of spin correlation in this last case.
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Topic revision: r1 - 2015-12-17 - LauraReina
 
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