# Anatomy of $tthh$ physics at the HL-LHC

## Abstract

The $tthh$ production at colliders contains rich information on the nature of the Higgs boson. In this article, we systematically studied its physics at the high-luminosity Large Hadron Collider (HL-LHC), using exclusive channels with multiple ( $\ge 5$) $b$-jets and one lepton ( $5b1\ell $), multiple ( $\ge 5$) $b$-jets and opposite-sign dilepton ( $5b2\ell $), same-sign dilepton ( $\mathrm{SS}2\ell $), multiple leptons (multi- $\ell $), and ditau resonance ( $\tau \tau $). The scenarios analyzed include: (1) the $tthh$ production in Standard Model; (2) the $tthh$ production mediated by anomalous cubic Higgs self-coupling and $tthh$ contact interaction; (3) heavy Higgs ( $H$) production with $ttH\to tthh$; and (4) pair production of fermionic top partners ( $T$) with $TT\to tthh$. To address the complication of event topologies and the mess of combinatorial backgrounds, a tool of boosted-decision-tree was applied in the analyses. The $5b1\ell $ and $\mathrm{SS}2\ell $ analyses define the two most promising channels. For the nonresonant $tthh$ production, a combination of these exclusive analyses allows for its measurement in the SM with a statistical significance $~0.9\sigma $ (with $S/B>1\%$), and may partially break the sensitivity degeneracy with respect to a varying cubic Higgs self-coupling, a difficulty usually thought to exist in gluon fusion di-Higgs analysis at HL-LHC. These sensitivities were also projected to future hadron colliders at 27 TeV and 100 TeV. For the resonant $tthh$ productions, the heavy Higgs boson in type II two-Higgs-doublet-model could be efficiently searched for between the mass thresholds $2{m}_{h}<{m}_{H}<2{m}_{t}$ and even beyond that, for relatively small $\mathrm{tan}\beta $ (vacuum alignment), while the fermionic top partners in composite Higgs models could be probed up to $~1.5\text{}\text{}\mathrm{TeV}$ and $~1.7\text{}\text{}\mathrm{TeV}$, for $\mathrm{Br}(T\to th)=25\%$ and 50%, respectively.

- Authors:

- Publication Date:

- Research Org.:
- Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC), High Energy Physics (HEP); Research Grants Council (RGC)

- OSTI Identifier:
- 1607819

- Alternate Identifier(s):
- OSTI ID: 1638684

- Report Number(s):
- arXiv:1905.03772; FERMILAB-PUB-19-721-T

Journal ID: ISSN 2470-0010; PRVDAQ; 055043

- Grant/Contract Number:
- AC02-07CH11359; 16312716

- Resource Type:
- Published Article

- Journal Name:
- Physical Review D

- Additional Journal Information:
- Journal Name: Physical Review D Journal Volume: 101 Journal Issue: 5; Journal ID: ISSN 2470-0010

- Publisher:
- American Physical Society (APS)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

### Citation Formats

```
Li, Lingfeng, Li, Ying-Ying, and Liu, Tao. Anatomy of $tthh$ physics at the HL-LHC. United States: N. p., 2020.
Web. https://doi.org/10.1103/PhysRevD.101.055043.
```

```
Li, Lingfeng, Li, Ying-Ying, & Liu, Tao. Anatomy of $tthh$ physics at the HL-LHC. United States. https://doi.org/10.1103/PhysRevD.101.055043
```

```
Li, Lingfeng, Li, Ying-Ying, and Liu, Tao. Tue .
"Anatomy of $tthh$ physics at the HL-LHC". United States. https://doi.org/10.1103/PhysRevD.101.055043.
```

```
@article{osti_1607819,
```

title = {Anatomy of $tthh$ physics at the HL-LHC},

author = {Li, Lingfeng and Li, Ying-Ying and Liu, Tao},

abstractNote = {The tthh production at colliders contains rich information on the nature of the Higgs boson. In this article, we systematically studied its physics at the high-luminosity Large Hadron Collider (HL-LHC), using exclusive channels with multiple (≥5) b-jets and one lepton (5b1ℓ), multiple (≥5) b-jets and opposite-sign dilepton (5b2ℓ), same-sign dilepton (SS2ℓ), multiple leptons (multi-ℓ), and ditau resonance (ττ). The scenarios analyzed include: (1) the tthh production in Standard Model; (2) the tthh production mediated by anomalous cubic Higgs self-coupling and tthh contact interaction; (3) heavy Higgs (H) production with ttH→tthh; and (4) pair production of fermionic top partners (T) with TT→tthh. To address the complication of event topologies and the mess of combinatorial backgrounds, a tool of boosted-decision-tree was applied in the analyses. The 5b1ℓ and SS2ℓ analyses define the two most promising channels. For the nonresonant tthh production, a combination of these exclusive analyses allows for its measurement in the SM with a statistical significance ~0.9σ (with S/B>1%), and may partially break the sensitivity degeneracy with respect to a varying cubic Higgs self-coupling, a difficulty usually thought to exist in gluon fusion di-Higgs analysis at HL-LHC. These sensitivities were also projected to future hadron colliders at 27 TeV and 100 TeV. For the resonant tthh productions, the heavy Higgs boson in type II two-Higgs-doublet-model could be efficiently searched for between the mass thresholds 2mh<mH<2mt and even beyond that, for relatively small tanβ (vacuum alignment), while the fermionic top partners in composite Higgs models could be probed up to ~1.5 TeV and ~1.7 TeV, for Br(T→th)=25% and 50%, respectively.},

doi = {10.1103/PhysRevD.101.055043},

journal = {Physical Review D},

number = 5,

volume = 101,

place = {United States},

year = {2020},

month = {3}

}

https://doi.org/10.1103/PhysRevD.101.055043

Works referenced in this record:

##
Higgs boson pair production at future hadron colliders: From kinematics to dynamics

journal, June 2018

- Gonçalves, Dorival; Han, Tao; Kling, Felix
- Physical Review D, Vol. 97, Issue 11

##
Effective field theory analysis of double Higgs boson production via gluon fusion

journal, August 2015

- Azatov, Aleksandr; Contino, Roberto; Panico, Giuliano
- Physical Review D, Vol. 92, Issue 3

##
Higgs self-coupling as a probe of the electroweak phase transition

journal, September 2008

- Noble, Andrew; Perelstein, Maxim
- Physical Review D, Vol. 78, Issue 6

##
Composite Higgs boson pair production at the LHC

journal, June 2011

- Gröber, R.; Mühlleitner, M.
- Journal of High Energy Physics, Vol. 2011, Issue 6

##
Anomalous couplings in double Higgs production

journal, August 2012

- Contino, Roberto; Ghezzi, Margherita; Moretti, Mauro
- Journal of High Energy Physics, Vol. 2012, Issue 8

##
LHC search of new Higgs boson via resonant di-Higgs production with decays into 4W

journal, June 2018

- Ren, Jing; Xiao, Rui-Qing; Zhou, Maosen
- Journal of High Energy Physics, Vol. 2018, Issue 6

##
Heavy Higgs bosons at 14 TeV and 100 TeV

journal, November 2015

- Hajer, Jan; Li, Ying-Ying; Liu, Tao
- Journal of High Energy Physics, Vol. 2015, Issue 11

##
Light custodians in natural composite Higgs models

journal, March 2007

- Contino, Roberto; Da Rold, Leandro; Pomarol, Alex
- Physical Review D, Vol. 75, Issue 5

##
Search for the standard model Higgs boson produced in association with top quarks and decaying into a $b\overline{b}$ pair in $pp$ collisions at $\sqrt{s}=13\text{\hspace{0.17em}}\text{\hspace{0.17em}}\mathrm{TeV}$ with the ATLAS detector

journal, April 2018

- Aaboud, M.; Aad, G.; Abbott, B.
- Physical Review D, Vol. 97, Issue 7

##
Measurement of the triple Higgs coupling at a HE-LHC

journal, March 2019

- Homiller, Samuel; Meade, Patrick
- Journal of High Energy Physics, Vol. 2019, Issue 3

##
MadGraph 5: going beyond

journal, June 2011

- Alwall, Johan; Herquet, Michel; Maltoni, Fabio
- Journal of High Energy Physics, Vol. 2011, Issue 6

##
Combination of the Searches for Pair-Produced Vectorlike Partners of the Third-Generation Quarks at $\sqrt{s}=13\text{\hspace{0.17em}}\text{\hspace{0.17em}}\mathrm{TeV}$ with the ATLAS Detector

journal, November 2018

- Aaboud, M.; Aad, G.; Abbott, B.
- Physical Review Letters, Vol. 121, Issue 21

##
A brief introduction to PYTHIA 8.1

journal, June 2008

- Sjöstrand, Torbjörn; Mrenna, Stephen; Skands, Peter
- Computer Physics Communications, Vol. 178, Issue 11

##
Heavy Higgs bosons at low tan β: from the LHC to 100 TeV

journal, January 2017

- Craig, Nathaniel; Hajer, Jan; Li, Ying-Ying
- Journal of High Energy Physics, Vol. 2017, Issue 1

##
Scrutinizing the alignment limit in two-Higgs-doublet models: ${m}_{h}=125\text{\hspace{0.17em}}\text{\hspace{0.17em}}\mathrm{GeV}$

journal, October 2015

- Bernon, Jérémy; Gunion, John F.; Haber, Howard E.
- Physical Review D, Vol. 92, Issue 7

##
Fully covering the MSSM Higgs sector at the LHC

journal, June 2015

- Djouadi, A.; Maiani, L.; Polosa, A.
- Journal of High Energy Physics, Vol. 2015, Issue 6

##
Measurements of inclusive and differential fiducial cross-sections of t t ¯ $$ t\overline{t} $$ production with additional heavy-flavour jets in proton-proton collisions at s $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

journal, April 2019

- Aaboud, M.; Aad, G.; Abbott, B.
- Journal of High Energy Physics, Vol. 2019, Issue 4

##
Revisiting the $t\overline{t}hh$ channel at the FCC-hh

journal, October 2019

- Banerjee, Shankha; Krauss, Frank; Spannowsky, Michael
- Physical Review D, Vol. 100, Issue 7

##
Twin Turtles

journal, February 2019

- Asadi, Pouya; Craig, Nathaniel; Li, Ying-Ying
- Journal of High Energy Physics, Vol. 2019, Issue 2

##
Double take on new physics in double Higgs boson production

journal, July 2014

- Chen, Chuan-Ren; Low, Ian
- Physical Review D, Vol. 90, Issue 1

##
DELPHES 3: a modular framework for fast simulation of a generic collider experiment

journal, February 2014

- de Favereau, J.; Delaere, C.; Demin, P.
- Journal of High Energy Physics, Vol. 2014, Issue 2

##
Constraints on the quartic Higgs self-coupling from double-Higgs production at future hadron colliders

journal, October 2019

- Bizoń, Wojciech; Haisch, Ulrich; Rottoli, Luca
- Journal of High Energy Physics, Vol. 2019, Issue 10

##
Measurement of the t t ¯ W $$ t\overline{t}W $$ and t t ¯ Z $$ t\overline{t}Z $$ production cross sections in pp collisions at s = 8 $$ \sqrt{s}=8 $$ TeV with the ATLAS detector

journal, November 2015

- Aad, G.; Abbott, B.; Abdallah, J.
- Journal of High Energy Physics, Vol. 2015, Issue 11

##
Higgs pair production at the LHC with NLO and parton-shower effects

journal, May 2014

- Frederix, R.; Frixione, S.; Hirschi, V.
- Physics Letters B, Vol. 732

##
Resonant heavy Higgs searches at the HL-LHC

journal, September 2019

- Adhikary, Amit; Banerjee, Shankha; Barman, Rahool Kumar
- Journal of High Energy Physics, Vol. 2019, Issue 9

##
Higgs self-coupling measurements at a 100 TeV hadron collider

journal, February 2015

- Barr, Alan J.; Dolan, Matthew J.; Englert, Christoph
- Journal of High Energy Physics, Vol. 2015, Issue 2

##
The minimal composite Higgs model

journal, July 2005

- Agashe, Kaustubh; Contino, Roberto; Pomarol, Alex
- Nuclear Physics B, Vol. 719, Issue 1-2

##
Probing new physics of cubic Higgs boson interaction via Higgs pair production at hadron colliders

journal, January 2016

- He, Hong-Jian; Ren, Jing; Yao, Weiming
- Physical Review D, Vol. 93, Issue 1

##
The strongly-interacting light Higgs

journal, June 2007

- Giudice, Gian Francesco; Grojean, Christophe; Pomarol, Alex
- Journal of High Energy Physics, Vol. 2007, Issue 06

##
Fat Jets for a Light Higgs Boson

journal, March 2010

- Plehn, Tilman; Salam, Gavin P.; Spannowsky, Michael
- Physical Review Letters, Vol. 104, Issue 11

##
Identifying top partners at LHC

journal, November 2009

- Aguilar–Saavedra, J. A.
- Journal of High Energy Physics, Vol. 2009, Issue 11

##
Probing the quartic Higgs boson self-interaction

journal, November 2018

- Liu, Tao; Lyu, Kun-Feng; Ren, Jing
- Physical Review D, Vol. 98, Issue 9

##
Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector

journal, April 2018

- Aaboud, M.; Aad, G.; Abbott, B.
- Physical Review D, Vol. 97, Issue 7

##
Second stop and sbottom searches with a stealth stop

journal, November 2016

- Cheng, Hsin-Chia; Li, Lingfeng; Qin, Qin
- Journal of High Energy Physics, Vol. 2016, Issue 11

##
HE-LHC: The High-Energy Large Hadron Collider: Future Circular Collider Conceptual Design Report Volume 4

journal, July 2019

- Abada, A.; Abbrescia, M.; AbdusSalam, S. S.
- The European Physical Journal Special Topics, Vol. 228, Issue 5

##
Double Higgs production and quadratic divergence cancellation in little Higgs models with T-parity

journal, May 2006

- Dib, Claudio O.; Rosenfeld, Rogerio; Zerwekh, Alfonso
- Journal of High Energy Physics, Vol. 2006, Issue 05

##
HDECAY: a program for Higgs boson decays in the Standard Model and its supersymmetric extension

journal, January 1998

- Djouadi, A.; Kalinowski, J.; Spira, M.
- Computer Physics Communications, Vol. 108, Issue 1

##
Automatic spin-entangled decays of heavy resonances in Monte Carlo simulations

journal, March 2013

- Artoisenet, Pierre; Frederix, Rikkert; Mattelaer, Olivier
- Journal of High Energy Physics, Vol. 2013, Issue 3

##
Search for standard model production of four top quarks with same-sign and multilepton final states in proton–proton collisions at $$\sqrt{s} = 13\,\text {TeV} $$ s = 13 TeV

journal, February 2018

- Sirunyan, A. M.; Tumasyan, A.; Adam, W.
- The European Physical Journal C, Vol. 78, Issue 2

##
Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector

journal, September 2018

- Aaboud, M.; Aad, G.; Abbott, B.
- Physics Letters B, Vol. 784

##
Higgs-boson-pair production $H(\to b\overline{b})H(\to \gamma \gamma )$ from gluon fusion at the HL-LHC and HL-100 TeV hadron collider

journal, November 2019

- Chang, Jung; Cheung, Kingman; Lee, Jae Sik
- Physical Review D, Vol. 100, Issue 9

##
Di-Higgs phenomenology in $t\overline{t}hh$ : The forgotten channel

journal, April 2015

- Englert, Christoph; Krauss, Frank; Spannowsky, Michael
- Physics Letters B, Vol. 743

##
Jet trimming

journal, February 2010

- Krohn, David; Thaler, Jesse; Wang, Lian-Tao
- Journal of High Energy Physics, Vol. 2010, Issue 2

##
Constraining the Higgs self-couplings at e+e− colliders

journal, July 2018

- Maltoni, Fabio; Pagani, Davide; Zhao, Xiaoran
- Journal of High Energy Physics, Vol. 2018, Issue 7

##
Search for new phenomena in events with same-charge leptons and b-jets in pp collisions at s = 13 $$ \sqrt{s}=13 $$ TeV with the ATLAS detector

journal, December 2018

- Aaboud, M.; Aad, G.; Abbott, B.
- Journal of High Energy Physics, Vol. 2018, Issue 12

##
Search for pair production of up-type vector-like quarks and for four-top-quark events in final states with multiple b-jets with the ATLAS detector

journal, July 2018

- Aaboud, M.; Aad, G.; Abbott, B.
- Journal of High Energy Physics, Vol. 2018, Issue 7