Periodic Reporting for period 4 - TheHiggsAndThe7Tops (Mirror Mirror on the Wall, which Higgs is the oddest of them all: Exploring the Top-Higgs Interconnection with ATLAS)
Reporting period: 2024-04-01 to 2025-03-31
The project TheHiggsAndThe7Tops addresses the quesiton on whether we can find new physics in the connection of the two heaviest elementary particles: the top quark and the higgs boson. In particular, it uses all processes that contain a direct top-Higgs connection to probe for CP odd Higgs bosons, which are beyond the standard model. The data analysed by the project is taken by the ATLAS experiment at CERN. To reach the goal of the project, it contains improvements on top and Higgs boosted tagging and event reconstruction as part of the goals.
The project addresses the most fundamental question: what is nature made of and what are the most fundamental laws of nature. These questions have always been part of human's curiosity. It is important for every society to look for the most fundamental. Often applications only result out of researching such questions many decades later.
The overall objectives of the project are:
- Establish novel event-reconstruction tools to enable the first measurement of angular observables
in t t¯H and events, and reach improved sensitivity to reject backgrounds.
- Develop and implement variables sensitive to the QCD colour flow into techniques for identifying
highly collimated decay products of the top and the Higgs (boosted Higgs and top tagging) for the
first time.
- Precisely measure the top-Higgs Yukawa coupling, using processes with 1, 2 and 4 top quarks for
the first time.
- Determine the CP nature of the Higgs boson in the coupling with the top quark for the first time
with a comprehensive analysis using novel observables in events with 1, 2 and 4 top quarks, which
has the potential for ground-breaking insight into the process of electroweak symmetry
breaking.
- Extract detector-corrected novel observables for model-independent studies of new physics,
benefiting the full community.
- Develop and explore extended Higgs sectors with unprecedented sensitivity, in particular probe for
naturally aligned 2HDM models
The project addresses the most fundamental question: what is nature made of and what are the most fundamental laws of nature. These questions have always been part of human's curiosity. It is important for every society to look for the most fundamental. Often applications only result out of researching such questions many decades later.
The overall objectives of the project are:
- Establish novel event-reconstruction tools to enable the first measurement of angular observables
in t t¯H and events, and reach improved sensitivity to reject backgrounds.
- Develop and implement variables sensitive to the QCD colour flow into techniques for identifying
highly collimated decay products of the top and the Higgs (boosted Higgs and top tagging) for the
first time.
- Precisely measure the top-Higgs Yukawa coupling, using processes with 1, 2 and 4 top quarks for
the first time.
- Determine the CP nature of the Higgs boson in the coupling with the top quark for the first time
with a comprehensive analysis using novel observables in events with 1, 2 and 4 top quarks, which
has the potential for ground-breaking insight into the process of electroweak symmetry
breaking.
- Extract detector-corrected novel observables for model-independent studies of new physics,
benefiting the full community.
- Develop and explore extended Higgs sectors with unprecedented sensitivity, in particular probe for
naturally aligned 2HDM models
The project has just finalised, and has been greatly successful.
My project started with 3 postdocs, and has been enhanced to 4 postdocs for the last 1.5 years in order to boost the work on P1.1 (reconstruction methods) and to get the analyses to publication.
Each of the postdocs worked on one of the different aspects of the project.
The main results achieved are:
- Novel event reconstruction methods, in particularly HyPER. HyPer has been published (Phys. Rev. D 111, 032004 (2025)), presented at various ATLAS-internal and community wide workshops and conferences, and has been implemented into the ATLAS software. This for example led to one of my postdocs work on FastFrames (https://zenodo.org/records/15114280(opens in new window)).
- Improved boosted top and Higgs tagging techniques. There results were presented at specific conferences and workshops discussing advancement in boosted tagging. While most of the achievements are internal to ATLAS, a public result can be found here: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2021-035/(opens in new window)
- Measurements of the top-highs Yukawa coupling and the probe for CP-properties: results in 2 and 4 tops have been published in scientific peer-reviewed journals, and presented at various workshops, conferences and in seminars. For 1top, the results are currently in the final stages of ATLAS-internal review before being published in peer-reviewed journals.
- The rare 4top process was observed (after we first achieved evidence, also as part of this project). This result was published and presented at various conferences, including Moriond and ICHEP. In particular, my postdoc Yang Qin, also got various seminar invitations, and the result got presented to the wider public in various articles.
- Several phenomenological studies have been performed together with theorists, all published in peer-reviewed articles. In particular, we worked on accidental symmetries in 2HDMEFT with Apostolos Pilaftsis, and with Eleni Vryonidou on novel observables in tH and ttH for probing new physics via EFTs.
- Searches for extended Higgs sectors have been performed, in particular in 4top events, which are published in peer-reviewed articles.
- The visibility all these different aspects of the project brought to my team has led to all my postdocs acquiring leadership positions within the ATLAS collaboration. Furthermore, all most PhD students and postdocs got invited for presenting ATLAS results at international conferences.
My project started with 3 postdocs, and has been enhanced to 4 postdocs for the last 1.5 years in order to boost the work on P1.1 (reconstruction methods) and to get the analyses to publication.
Each of the postdocs worked on one of the different aspects of the project.
The main results achieved are:
- Novel event reconstruction methods, in particularly HyPER. HyPer has been published (Phys. Rev. D 111, 032004 (2025)), presented at various ATLAS-internal and community wide workshops and conferences, and has been implemented into the ATLAS software. This for example led to one of my postdocs work on FastFrames (https://zenodo.org/records/15114280(opens in new window)).
- Improved boosted top and Higgs tagging techniques. There results were presented at specific conferences and workshops discussing advancement in boosted tagging. While most of the achievements are internal to ATLAS, a public result can be found here: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2021-035/(opens in new window)
- Measurements of the top-highs Yukawa coupling and the probe for CP-properties: results in 2 and 4 tops have been published in scientific peer-reviewed journals, and presented at various workshops, conferences and in seminars. For 1top, the results are currently in the final stages of ATLAS-internal review before being published in peer-reviewed journals.
- The rare 4top process was observed (after we first achieved evidence, also as part of this project). This result was published and presented at various conferences, including Moriond and ICHEP. In particular, my postdoc Yang Qin, also got various seminar invitations, and the result got presented to the wider public in various articles.
- Several phenomenological studies have been performed together with theorists, all published in peer-reviewed articles. In particular, we worked on accidental symmetries in 2HDMEFT with Apostolos Pilaftsis, and with Eleni Vryonidou on novel observables in tH and ttH for probing new physics via EFTs.
- Searches for extended Higgs sectors have been performed, in particular in 4top events, which are published in peer-reviewed articles.
- The visibility all these different aspects of the project brought to my team has led to all my postdocs acquiring leadership positions within the ATLAS collaboration. Furthermore, all most PhD students and postdocs got invited for presenting ATLAS results at international conferences.
The project has advanced the state of the art in multiple areas.
- novel event reconstruction, based on advanced machine learning and improving the reconstruction efficiency, have been achieved, most notably HyPER.
- boosted top and Higgs tagging has been advanced, for example by using tools like transformers
- the sensitivity to CP-odd couplings in ttH has been established and advanced
- the first measurement of tH and a first search for CP-odd Higgs in boosted tH is close to publication
- the world's first observation of 4top events, establishing the possibility to measure ultra-rare events with LHC experiments
- novel phenomenological studies on 2HDMEFT and on sensitive observables in tH and ttH for probing the top-Higgs Yukawa coupling.
- novel event reconstruction, based on advanced machine learning and improving the reconstruction efficiency, have been achieved, most notably HyPER.
- boosted top and Higgs tagging has been advanced, for example by using tools like transformers
- the sensitivity to CP-odd couplings in ttH has been established and advanced
- the first measurement of tH and a first search for CP-odd Higgs in boosted tH is close to publication
- the world's first observation of 4top events, establishing the possibility to measure ultra-rare events with LHC experiments
- novel phenomenological studies on 2HDMEFT and on sensitive observables in tH and ttH for probing the top-Higgs Yukawa coupling.