Periodic Reporting for period 3 - TheHiggsAndThe7Tops (Mirror Mirror on the Wall, which Higgs is the oddest of them all: Exploring the Top-Higgs Interconnection with ATLAS)
Periodo di rendicontazione: 2022-10-01 al 2024-03-31
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
At the moment, the porject is half way through the allocated time and in general going well.
Overall, the work is on track. At the moment the team consists of 3 postdocs, each of them covering the responsibility for woking on one of the physics processes (project part 2.1 2.2 and 2.3 each) and at least one PhD student associated to each process.
Furthermore, work os going on for part 1, where one of the postdocs (Valentina Vecchio) became one of the leaders of the calibration team for flavor tagging and the other two postdocs have leading positions for boosted Higgs tagging.Furthermore we work with theorists to explore the full potential of the top Higgs connection (part 3 of the project).
Since the start of the project, the world's first result of searching for CP odd Higgs bosons in the production of Higgs bosons associated with top pairs, with the Higgs decaying into b quarks (ttH, H to bb), has been released as preliminary result in March 2022 and shown at one of the two most important conferences of the year in the field, Moriond2022 (https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2022-016/). This result was a major achivement for the project. In addition, as part of the project the standard model ttH, H to bb cross section measurement with full current ATLAS data set has been published.
The work on 4 top resulted in the publication of the first evidence for 4top production and a publication of the measurment of its cross section. This result has caught large attention in the community as the cross section is measured two times higher than expected, with a significance close to observation level. The work also resulted in a preliminary result searching for heavier CP odd and even Higgs bosons in 4top processes, which has been shown at Moriond2022 (https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2022-008/).
The work on single top Higgs is ongoing, with results internally being prepared for publication by end of 2022 and a preliminary result for conferences in automn 2022.
The work on boosted top and Higgs taggers is internal to ATLAS at the moment, but improvements are already being used by several groups. A first public result of work involving our team has been released in 2021 (https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2021-035/).
Work on studying the colour-flow sensitive observables (part 1 of the project) is ongoing, and also involves undergraduate MPhys students.
Furthermore, several parts of the overall project has been involving summer interns in summer 2021 (in particular on using ANN techniques for ttH) and undergradute MPhys students, who afterwards went on for PhDs in particle physics.
We have collaborated with theorists within the group, most notably Apostolos Pilaftsis, which resulted in publishing a paper on accidental symmetries in 2HDMEFT. Currently we work with Eleni Veronidou on exploring new physics models using EFT for our top-higgs analyses. This should result in a publication later in the year (part 3 of the project).
Overall, the work is on track. At the moment the team consists of 3 postdocs, each of them covering the responsibility for woking on one of the physics processes (project part 2.1 2.2 and 2.3 each) and at least one PhD student associated to each process.
Furthermore, work os going on for part 1, where one of the postdocs (Valentina Vecchio) became one of the leaders of the calibration team for flavor tagging and the other two postdocs have leading positions for boosted Higgs tagging.Furthermore we work with theorists to explore the full potential of the top Higgs connection (part 3 of the project).
Since the start of the project, the world's first result of searching for CP odd Higgs bosons in the production of Higgs bosons associated with top pairs, with the Higgs decaying into b quarks (ttH, H to bb), has been released as preliminary result in March 2022 and shown at one of the two most important conferences of the year in the field, Moriond2022 (https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2022-016/). This result was a major achivement for the project. In addition, as part of the project the standard model ttH, H to bb cross section measurement with full current ATLAS data set has been published.
The work on 4 top resulted in the publication of the first evidence for 4top production and a publication of the measurment of its cross section. This result has caught large attention in the community as the cross section is measured two times higher than expected, with a significance close to observation level. The work also resulted in a preliminary result searching for heavier CP odd and even Higgs bosons in 4top processes, which has been shown at Moriond2022 (https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2022-008/).
The work on single top Higgs is ongoing, with results internally being prepared for publication by end of 2022 and a preliminary result for conferences in automn 2022.
The work on boosted top and Higgs taggers is internal to ATLAS at the moment, but improvements are already being used by several groups. A first public result of work involving our team has been released in 2021 (https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2021-035/).
Work on studying the colour-flow sensitive observables (part 1 of the project) is ongoing, and also involves undergraduate MPhys students.
Furthermore, several parts of the overall project has been involving summer interns in summer 2021 (in particular on using ANN techniques for ttH) and undergradute MPhys students, who afterwards went on for PhDs in particle physics.
We have collaborated with theorists within the group, most notably Apostolos Pilaftsis, which resulted in publishing a paper on accidental symmetries in 2HDMEFT. Currently we work with Eleni Veronidou on exploring new physics models using EFT for our top-higgs analyses. This should result in a publication later in the year (part 3 of the project).
The measurements published so far, most notably the evidence for 4top and the first result on CP odd Higgs bosons in ttH, H to bb, are beyond state of the art and present novel results. Methologies required to be developed within the project that are going beyond state of the art, as for example the exploration of ANNs and GNNs for reconstruction and keeping the main backgorund under control.
Until the end of the project, refined results are expected for CP odd Higgs boson searches in all the three channels.
Much work is going on in improving the sensitivity of the taggers, including the exporation of colour-flow sensitive observables. This work should result in an improved tagger by end of the project.
The collaboration with theorists is ongoing and work is starting to refine the use of the three processes to enhance the sensitivity to new physics.
Until the end of the project, refined results are expected for CP odd Higgs boson searches in all the three channels.
Much work is going on in improving the sensitivity of the taggers, including the exporation of colour-flow sensitive observables. This work should result in an improved tagger by end of the project.
The collaboration with theorists is ongoing and work is starting to refine the use of the three processes to enhance the sensitivity to new physics.