ttH/tH Higgs Associated Production Process

Goals of the group

The ttH/tH subgroup mandate is as follows:

• Based on a review of the current status and ongoing plans of ttH and tH experimental analyses and all relevant theory predictions we will:
  • Identify and characterize state-of-the art theoretical predictions+tools for signals and backgrounds in all relevant ttH and tH searches.
  • Identify all important theory related sources of uncertainties and prioritize them according to their impact on experimental analyses and the likelihood of theory improvements in the near future.

• In this context we will:
  • Give more emphasis to precision theory predictions/simulations for ttH/tH backgrounds.
  • Address nontrivial aspects of theory uncertainties that play an important role in the ATLAS/CMS analyses (e.g. signal and background shape uncertainties).
  • Try to involve more key experts (experimentalists and theorists) in the ttH/tH subgroup.
  • Foster communication between ATLAS and CMS, as well as between the experiments and theorists working on issues of interest to the experiments.

Group Contacts

• Maria Moreno Llacer (CERN) - ATLAS
• Joshuha Thomas-Wilsker (IHEP, Beijing) - CMS
• Stefano Pozzorini (Zurich Univ.) - Theory
• Laura Reina (Florida State Univ.) - Theory

• Mail to Conveners

ttH/tH Mailing List

Public meetings and general announcements regarding the ttH/tH subgroup will be communicated through the mailing list of WG1. Anybody who is interested in following or contributing to the ttH activities is invited to subscribe to the lhc-higgs-xsbr-tth mailing list using this link (search for "lhc-higgs-xsbr-tth") or by contacting the conveners.

Meeting Plans for the ttH/tH subgroup (Oct 2014-Present)

Practical information

• Meetings will be announced to the mailing list above.
• A link to the WG1 Indico page can be found here: Higgs XS&BR WG Indico Page

Date	Time (CERN)	Title	Indico/Vidyo	Summary
Oct 20, 2014	17:00-18:30	Signal modeling in ttH	Indico	meeting summary
Nov 3, 2014	16:30-18:00	Backgrounds and uncertainties in experimental ttH, H-->bb searches	Indico	meeting summary
Nov 10, 2014	16:30-18:00	Theory perspectives on tt+jets and tt+HF production	Indico	meeting summary
Nov 24, 2014	16:30-18:00	Backgrounds and uncertainties in ttH, H-->gamma gamma	Indico	meeting summary
Dec 1, 2014	16:30-18:00	Backgrounds and uncertainties in ttH, H-->multileptons	Indico	meeting summary
Jan 12, 2015	16:30-18:00	ttH Combination: Systematics and correlations	Indico	meeting summary
Jan 26, 2015	16:30-18:00	Signal modeling in tHq	Indico
Feb 2, 2015	16:30-18:00	Backgrounds and uncertainties in tHq	Indico
June 9, 2015	16:30-18:00	Theory update	Indico
Dec 10, 2015	16:30-17:30	Coordination of ttbb simulations	Indico
May 31, 2016	16:30-18:30	Coordination of ttbb simulations	Indico
Feb 6, 2017	17:00-18:30	Common meeting on tt+b-jet backgrounds to ttH(bb)	Indico
July 6, 2017	17:00-18:30	Common meeting on tt+b-jet backgrounds to ttH(bb)	Indico
Nov 6, 2017	17:00-18:30	Common meeting on tt+b-jet backgrounds to ttH(bb)	Indico
Feb 12, 2018	16:30-18:00	Informal meeting with tt+b jets Monte Carlo's authors	Indico
Mar 5, 2018	16:30-18:00	Informal meeting with tt+b jets Monte Carlo's authors	Indico
Mar 19, 2018	16:30-18:00	Informal meeting with tt+b jets Monte Carlo's authors	Indico
Apr 16, 2018	16:30-18:00	Informal meeting with tt+b jets Monte Carlo's authors	Indico
Oct 22, 2018	14:30-16:00	Common meeting on tt+b-jet backgrounds to ttH(bb)	Indico
Apr 1, 2019	14:30-16:00	Common meeting on tt+b-jet backgrounds to ttH(bb)	Indico

Topical Meetings

The activity of the working group entered a new phase in 2014 with a series of topical meetings aimed at:

• fostering discussions and stronger links between the experimental and theoretical communities, involving the relevant leading experts;
• discussing the status of (and plans for) ttH and tH searches in various channels, with emphasis on theory related issues and limitations;
• discussing state-of-the art theory predictions, their present limitations, and possible improvements;
• identifying and prioritizing all needed theoretical improvements.

These meetings prepared and paved the activity of the WG in preparation for Run 2, YR4, and beyond.

Modeling studies in ttH and tt+jets in Preparation for Run 2 (to be collected in YR4)

• Proposal of a standard setup for tt+bjets comparisons at NLO
• Proposal of a standard setup for ttH comparison at NLO+Parton Shower
• Proposal of a standard setup for ttV comparison at NLO

Plans for YR4

• CrossSectionYR4
• ContributionsYR4

The results of these studies are collected in the ttH/tH section of YR4.

ttV recommended cross sections at 13 TeV using fixed scale (mt + mV/2)

Monte Carlo studies for background processes during and after Run 2 (post YR4)

Among the important achievements of the ttH/tH working group collected in YR4 are: 1) the succesful comparison of all existing NLO QCD+parton shower Monte Carlo generators for the simulation of the ttH signal, 2) the first comparison of NLO QCD+parton shower Monte Carlo generators for the simulation of the tt+b jets background, and 3) the recommendation of NLO QCD cross sections for ttW and ttZ background processes.

After YR4, the more recent activity of the ttH/tH working group has focused on background Monte Carlo studies:

• tt+bjets: as documented by the series of meeting in the 2016-2019 period and by the reports presented at the various HXSWG General Assembly Meetings during the same period, this has been the major activity of the WG. Thanks to the collaboration of the Authors of different NLO QCD+parton shower Monte Carlo generators, the comparison is now converging to a substantial agreement which will lead to the possibility of providing the experiments with well-defined recommendations for the use of the corresponding theoretical tools in experimental analyses. A WG note will be completed during 2019. The various stages of this study are documented here:
  • New Rivet analyses and proposal of a standard setup for tt+bjets MC comparisons with top decays
• tt+V (V=W/Z)->multileptons: the study of this background is being prepared and will be the next major focus of the WG, with the goal of presenting preliminary results from this activity at the HXSWG General Assembly Meeting in October 2019.

Subprocess categorization schemes (Run 1 and Run 2)

Note:
1. the jets we used are the selected good jets: Pt>30GeV, |eta|<2.4
2. all the b and c quarks in the MCparticles need to be final state particles and come after top and anti-top in the chain
--------------

Categorization of tt+b/bb:

Step 1: identify all the b quarks, b-from-t and b-not-from-t 
We go through all the MCparticles in each event, identify all the b quarks that come from top decays (b-from-t), 
as well as all the b quarks that are not from top decays(b-not-from-t). We do this by checking the particle's ID 
and its mother's ID.

Step 2: match jets to b-from-t
For each b-from-t, we find the closest jet which has the smallest dR(b, jet). If the dR(b, closest jet) is less than 0.5, 
we say that we find a jet match for this b-from-t and save the corresponding jet to the list of "jet-matched-to-b-from-t".

Step 3: match jets to b-not-from-t
For each b-not-from-t, we do the same dR matching as in step 2. If we find a match and the matched jet doesn't 
match to any b-from-t(not in "jet-matched-to-b-from-t"), we save the b-not-from-t to the list of "matched-b-not-from-t" 
and the jet to the list of "jetmatched- to-b-not-from-t".

Step 4: count of the number of "matched-b-not-from-t" and "jetmatched-to-b-not-from-t"
Sometimes two b quarks are mateched to the same jet, so we remove the duplicates in "jet-matched-to-b-not-from-t" 
before we do the counting. If we only find one "matched-b-not-from-t" which also has a jet match, or we find two 
"matchedb-not-from-t" but only one "jet-matched-to-b-not-from-t" we call this event tt+b. If we find two 
"matched-b-not-from-t" and two "jet-matched-to-b-notfrom- t" or we find three or more "matched-b-not-from-t" we call this
event tt+bb.

--------------
Categorization of tt+cc
Step 1: identify all the b quarks, and c quarks (c-from-bW and cnot-from-bW)
We go throught all the MCparticles in each event, identify all the b quarks regardless of its origin. We aslo identify 
all the c quarks that come from b or W decays (c-from-bW), as well as all the c quarks that are not from b/W decays 
(c-not-from-bW). We do this by checking the particle's ID and its mother's ID.

Step 2: match jets to b quarks
For each b quark, we find the closest jet which has the smallest dR(b, jet). If the dR(b, closest jet) is less than 0.5, 
we say that we find a jet match for this b quark and save the corresponding jet to the list of "jet-matched-to-b".

Step 3: match jets to c-from-bW
For each c-from-bW, we do a similar matching as above. If dR(c, closest jet) is less than 0.5, we say that we find a 
jet match for this c-from-bW and save the corresponding jet to the list of "jetmatched-to-c-from-bW".

Step 4: match jets to c-not-from-bW
For each c-from-bW, we do the same dR matching as in step 3. If we find a match and the matched jet doesn't match 
neither to any b quark(not in "jet-matched-to-b") nor to any c-from-bW(not in "jetmatched-to-c-from-bW"), we save the 
c-not-from-bW to the list of "matched-c-not-from-bW" and the jet to the list of "jet-matched-toc-not-from-bW".

Step 5: count of the number of "matched-c-not-from-bW" and "jetmatched-
bWo-c-not-from-bW" If we find at least one "matched-c-not-from-bW", we call this event
tt+cc.

Take match between b-hadrons not from top with pT > 5 GeV and  particle jets (truth jets) with dR < 0.4.  If this 
particle jet has pT > 15 GeV and |eta| < 2.5, then the event has an additional b.  If there are two such particle jets, 
matched to two b-hadrons not from top, then the event is labeled "bb".  If two b-hadrons not from top are matched 
to one particle jet, it is labelled "B".

In the fit, all b categories are combined and all c categories are combined.  No split between tt+b and tt+bb are 
explicitly formalized by a NP in the profile likelihood, however, the PS systematics, comparisons of generators and NLO 
systematics allow for the normalization of tt+b and tt+bb to vary.  The CMS-like tretment was also tested and found to 
have very little impact on the measurement.

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• CMSttXCategorization.pdf: CMSttXCategorization.pdf