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ttH/tHq Higgs Associated Production Process

Goals of the group

The ttH/tH group is a subgroup of the LHC Higgs cross-section working group ( LHCHXSWG TWiki). 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:
    • Include associated single-top Higgs searches in the activities of the ttH subgroup
    • 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 subgroup
    • Foster communication between ATLAS and CMS

Group Contacts

ttH Mailing List

Public meetings and general announcements regarding the ttH 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-Nov 2017)

Practical information

  • Meetings will be announced in the mailing list above.(usually Monday's at 17h).
  • 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.

Date Time 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  

Strategy of the Topical Meetings

  • ttH and tH searches involve specific challenges that call for a very close interaction between the experimental and theoretical communities, such as the very high level of background contamination and the critical role of theory uncertainties in the specific framework of experimental analysis techniques that are used to constrain the backgrounds.

  • We thus propose to initiate the activities of the new ttH subgroup by a series of short topical meetings with the following aims:
    • to foster discussions and stronger links between the experimental and theoretical communities, involving the relevant leading experts;
    • to discuss the status of (and plans for) ttH and tH searches in various channels, with emphasis on theory related issues and limitations;
    • to discuss state-of-the art theory predictions, their present limitations, and possible improvements;
    • to identify and prioritize all needed theoretical improvements.

Modeling studies in ttH and tt+jets in Preparation for Run 2

Plans for 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.

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...

Topic attachments
I Attachment History Action Size Date WhoSorted ascending Comment
PDFpdf CMSttXCategorization.pdf r1 manage 24.4 K 2014-11-18 - 13:53 ChrisNeu  
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
Texttxt minutes_tth_050412.txt r1 manage 1.8 K 2012-05-06 - 14:36 LauraReina minutes from May,4 2012 meeting
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Topic revision: r47 - 2018-02-09 - StefanoPozzorini
 
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