HH Subgroup Meeting

40/R-B10 (CERN)



Show room on map
Christoph Englert (Heidelberg University) , Magdalena Slawinska (NIKHEF (NL)) , Maxime Gouzevitch (Universite Claude Bernard-Lyon I (FR)) , Roberto Salerno (Ecole Polytechnique (FR)) , Sally Dawson (BNL)

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

Q == Question
A == Answer
C == Comment

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.
*) 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.


There are minutes attached to this event. Show them.
    • 2:30 PM 2:50 PM
      Introduction 20m
      Speakers: Christoph Englert (Heidelberg University) , Magdalena Slawinska (NIKHEF (NL)) , Maxime Gouzevitch (Universite Claude Bernard-Lyon I (FR)) , Dr Roberto Salerno (Ecole Polytechnique (FR)) , Sally Dawson (BNL)
    • 2:50 PM 3:10 PM
      Theoretical Aspects of Higgs Pair Production at LHC 20m
      Speaker: Michael Spira (Paul Scherrer Institut (CH))
    • 3:10 PM 3:30 PM
      HH production : NLO+PS and top-quark mass effects in gg fusion 20m
      Speakers: Eleni Vryonidou (Universite catholique de Louvain) , Fabio Maltoni (Universite Catholique de Louvain (UCL) (BE)) , Marco Zaro (LPTHE Jussieu, Paris)
    • 3:30 PM 3:50 PM
      Top quark mass effects (NLO) and matching coefficient (NNLO) for Higgs boson pair production 20m
      Speakers: Jonathan Grigo , Kirill Melnikov , Matthias Steinhauser (KIT)
    • 3:50 PM 4:10 PM
      HH production at NNLO in the EFT 20m
      Speakers: Daniel De Florian , Javier Mazzitelli
    • 4:10 PM 4:30 PM
      Higgs boson pair production: The road ahead 20m
      Speakers: Andreas Papaefstathiou (U) , Philipp Maierhöfer
    • 4:30 PM 4:50 PM
      Discussion 20m
      Speaker: ALL