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Accurate predictions for the differential signal cross sections in the SM in gluon-gluon fusion (NNLO in the EFT, top-quark mass effects at NLO, NLO+PS, merged and matched samples), especially as a function of the Higgs trilinear coupling.
HH subgroup meeting, 20th October 2014
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Q == Question
A == Answer
C == Comment
Action
Introduction: Roberto Salerno
List of topics the HH subgroup plans to cover and approximate deadlines
Q: What about VBF HH?
A: Part of our charge is to deploy a program to compute differential cross sections in VBF.
1. speaker: Michel Spira
"Theoretical Aspects of Higgs Pair Production @ LHC”
Q (Sally Dawson): How to choose scales? Dynamic vs Fixed scale?
A (Michael Spira): It needs to be discussed in detail. The dynamic (Q^2-dependent) scale should be chosen, depending on the subject of study. In the case of di-Higgs production m_HH, in case of HH+jets something like m_HH+pT.
Q: How about bbWW being hopeless? Isn’t it premature, why dismiss it now?
A (Michael Spira): It was “provocative” in the talk. We need an analysis from the experimental side
C: fully leptonic channels (completely hopeless) and semi leptonic (could be promising).
C: Remember that investigation of semi-leptonics has been doing using MVA (not done in other channels).
C: 6ab-1 is extremely conservative, one can explore other final states (example VBF) and boost the discovery
C (Leandro Nisati): The positive interference is a strong reason to put qq->ttHH in the list of interesting channels.
Action: the discussion of the the possible final state signatures at the LHC will be the main topic of one of the next HH subgroup meeting.
2. speaker: Eleni Vryonidou
"HH production : NLO+PS and top-quark mass effects in gg fusion”
Q: How to estimate the uncertainty between the two approaches at NLO, yours and Spira’s (HPAIR)?
A: It should be about 10%
Q: Why full NLO correction are only 2%?
A: it’s not 2% on the exact result (we don’t have it) but there is a large cancellation between triangle and box.
Q: What about the error associated with the usage of Effective Field Theory?
A: It is not quoted here but it is of the order of 10% and that is what we see from different calculations from different groups.
Q (Michael Spira): In your scheme threshold cancellations are not exact
A: True, but this is not where the bulk of the x-section sits
Then Michael made a suggestion that corrections to the box and triangle are different and 10% uncertainty of the MG5 framework can be inferred from MSSM case with additional heavy scalar. (not sure if I got this one right).
3. Jonathan Grigo
"Top quark mass effects (NLO) and matching coefficient (NNLO) for Higgs boson pair production"
C: We have for the corrections from top mass effect +10% / -10% from 2 different groups,
this is an indication of the uncertainties is +/- 10%.
We need to compare the 2 calculations and understand where the different signs come from.
Suggestions:
*) apply the procedure for single Higgs production of 500 - 600 GeV (~ to the triangle in the HH) and see if it works
*) check for the real correction only.
Action: to be discussed. Personal note: it will be great if the two groups will arrive with the suggested checks at the next HH subgroup meeting in mid-November.
4. Javier Mazzitelli
“Higgs Boson Pair Production at NNLO in the EFT”
Q: soft-virtual approximation works better? Is it true? We need to be careful with the statement is not better.
A: The quality of the approximation should decrease with the collider energy
A: soft-virtual approximation works better for HH than for H;
A: disagree because mass effects are larger in HH
A: (Daniel de Florian): in Mellin space this is not true
Q: 90% C.L. MSTW08 sets —> other results use 68%
A: Only 1 pdf is used here at the end we will following the recommendation of the LHCPDF group
Q: Uncertainty coming from the use of the EFT is not included. Can you guess it?
A: It could be about 10% as in the NLO case.
5. Andreas Papaefstathiou
"Higgs boson pair production: The road ahead"
Discussion: Magdalena Slawinska
Action: Check the central scale with different code
C (Daniel de Florian): it can absorb part of the resummation if we change the scale (like in the single Higgs case). First we need the resummation.
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