TWiki> LHCPhysics Web>LHCHXSWG1>LHCHWGTTH (revision 51)EditAttachPDF

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

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
Summaries of topical meetings: important aspects and open issues that should be pursued within the framework of the HXSWG will be collected after each meeting in the form of meeting summaries. <!--These summaries will serve as a basis for a preliminary working group report (Jan 2015). They will be continuously updated by the ttH conveners, including input and feedback from the whole ttH group.-->

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)

Plans for YR4

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)

Process XS [fb] scale pdf alpha_S
ttZ 839.3 + 9.6% −11.3% 2.8% 2.8%
ttW+ 397.6 +12.7% −11.4% 2.0% 2.6%
ttW- 203.2 +13.3% −11.7% 2.1% 2.9%
ttW- + ttW+ 600.8 +12.9% -11.5% 2.0% 2.7%
Correlation effects are consistently included in the uncertainties of the combined ttW- + ttW+ cross section.

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:
  • 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)


Here is a handy flowchart for the CMS scheme in Run 1.

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.



In progress...

<!-- ---++ Group Members and Contributors: Incomplete - please contact us if you want to be included. -->

<!-- OLD LIST - How to update
* Pierre Artoisenet, Theory
* Fabio Cascioli, Theory
* Chris Collins-Tooth, ATLAS - ex-oficio group contact
* Sally Dawson, Theory
* Simon Dean, ATLAS - ex-oficio group contact
* Stefan Dittmaier, Theory
* Rikkert Frederix, Theory
* Maria Vittoria Garzelli, Theory
* Stefan Hoeche, Theory
* Joey Huston, ATLAS
* Adam Kardos, Theory
* Frank Krauss, Theory
* Michael Kraemer, Theory
* Kevin Lannon, CMS
* Philipp Maierhoefer, Theory
* Olivier Mattelaer, Theory
* Niccolo Moretti, Theory
* Jim Olsen, CMS - ex-oficio group contact
* Costas Papadopoulos, Theory
* Chris Potter, ATLAS - ex-oficio group contact
* Stefano Pozzorini, Theory
* Robbert Rietkerk, Theory
* Jennifer Thompson, Theory
* Zoltan Trocsanyi, Theory
* Doreen Wackeroth, Theory -->

<!-- ---++ Available Tools -->

<!-- OLD
* HQQ ( M. Spira):
--> <!-- ---++ Documents -->

<!-- OLD
* Set up for Freiburg exercises
* Set up for CERN mtg results
--> <!-- ---++ Previous Meetings -->

<!-- OLD
* CERN InDico Agenda
* Minutes of informal get-acquainted meeting - 18 Feb 2010
* Minutes from meeting dedicated to preparations for Freiburg - 31 March 2010
* Minutes from meeting dedicated to preparations for CERN meeting - 9 June 2010
* Minutes from meeting of May 4, 2012
--> <!-- ---++ Links -->

<!-- OLD
* minute_tth_18_feb_10.txt: minute_tth_18_feb_10.txt --> <!-- * set_up_tth_freiburg-1.txt: set_up_tth_freiburg-1.txt -->

<!-- * minutes_tth_09_jun_10.txt: minutes from 9 June mtg -->

<!-- * set_up_tth_cern.txt: setup for July 2010 CERN mtg results -->

Topic attachments
I Attachment HistorySorted ascending Action Size Date Who Comment
PDFpdf CMSttXCategorization.pdf r1 manage 24.4 K 2014-11-18 - 13:53 ChrisNeu  
Texttxt minutes_tth_050412.txt r1 manage 1.8 K 2012-05-06 - 14:36 LauraReina minutes from May,4 2012 meeting
Texttxt minutes_tth_09_jun_10.txt r1 manage 2.4 K 2010-06-30 - 23:31 ChrisNeu minutes from 9 June mtg
Texttxt minutes_tth_31_mar_10.txt r1 manage 2.5 K 2010-04-06 - 19:22 ChrisNeu  
Texttxt minutes_tth_31_mar_10_v2.txt r1 manage 2.5 K 2010-04-06 - 19:28 ChrisNeu  
Texttxt set_up_tth_cern.txt r1 manage 3.7 K 2010-06-30 - 23:32 ChrisNeu setup for July 2010 CERN mtg results
Edit | Attach | Watch | Print version | History: r66 | r53 < r52 < r51 < r50 | Backlinks | Raw View | Raw edit | More topic actions...
Topic revision: r51 - 2019-05-02 - LauraReina
 
    • Cern Search Icon Cern Search
    • TWiki Search Icon TWiki Search
    • Google Search Icon Google Search

    LHCPhysics All webs login

This site is powered by the TWiki collaboration platform Powered by PerlCopyright & 2008-2022 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
or Ideas, requests, problems regarding TWiki? use Discourse or Send feedback