• External Grants
• Lydia Beresford (YIG)
• Katharina Behr (YIG)
• Sarah Heim (YIG)
• Priscilla Pani (YIG)
• Kerstin Tackmann (ERC)

ATLAS External Grants Katharina Behr (YIG)  · 

Fingerprints of the Vacuum

Helmholtz Young Investigator Group of Katharina Behr (2020-2026)

Research profile

The vacuum of space is not empty. This was impressively demonstrated by the discovery of a Higgs boson in 2012, which showed that the vacuum is permeated by a Higgs field. There are, however, strong reasons to believe that the vacuum is more complex and that additional Higgs bosons exist. These may hold the key to some of the most fundamental questions of particle physics today, such as the nature of dark matter or the matter-antimatter imbalance in the universe.

The Young Investigator Group develops novel experimental techniques to search for rare and challengingly complex signatures of additional Higgs bosons that previous data analyses would not have been able to resolve. It will thereby probe the vacuum structure in a previously unaccessible kinematic regime and, additionally, measure processes predicted by the Standard Model, which may themselves be sensitive to new phenomena, at high precision on the dataset to be collected by the ATLAS experiment until 2023.

Furthermore, the YIG works towards preparing the ATLAS experiment for the high-luminosity phase of the LHC (from 2026) by developing fast, efficient algorithms for the reconstruction of particle trajectories in the new ATLAS tracking detector ITk), which will partly be built at DESY.

You are welcome to contact me if you are interested in pursuing a bachelors, masters or PhD thesis in my group!

Current activities

The group is strongly involved in interference searches for heavy Higgs bosons decaying to a top-antitop quark pair. These searche have unique sensitivity to the high-mass, low tan(beta) region of two-Higgs-doublet models of type 2 but are significantly complicated by the strong interference between the signal and dominant background processes that distort the signal from a simple peak to a peak-dip structure. We have developed novel analysis tools to simulate, identify, and quantify these complex signal shapes. The searches require a precise measurement of the background from strong top pair production. This measurement itself has sensitivity to new phenomena.

The techniques developed in this context are now being used to conduct precision measurements of top quark-antiquark pairs with the goal to unravel the quantum nature of their interactions, such as the quantum entanglement of their spins. Group members have also played a leading role in the recent discovery of a ttbar quasi-bound-state ("toponium") and is now involved in understanding its nature and what it can teach us about hadron formation and, potentially, phenomena beyond the Standard Model.

We are also involved in a search for resonant and non-resonant production of a Higgs boson pair via vector-boson fusion and decaying to four beauty quarks. Our focus is on final states with highly energetic Higgs bosons whose decay products are merged into a single large-radius jet. The group also contributes to various combination and re-interpretation projects within ATLAS, such as the dark matter and heavy resonance combination.

The group also plays a strong role in the area of track reconstruction, focusing on the reconstruction of pixel clusters and tracks in the dense environments found within highly energetic jets. We take leading roles in this area for the upcoming LHC Run 3 data taking and also study the expected tracking performance for the new ATLAS Inner Tracker (ITk) that will be installed before the start of the High-Luminosity LHC (HL-LHC) in 2027. Group members are also involved in the ITk Upgrade project at DESY and in the jet calibrations.

Group members

Teaching

Publications

ATLAS Collaboration, Combination of Searches for Higgs Boson Pair Production in pp Collisions at s=13 TeV with the ATLAS Detector, Phys. Rev. Lett. 133 (2024) 101801

ATLAS Collaboration, Search for pair production of boosted Higgs bosons via vector-boson fusion in the bb¯bb¯ final state using pp collisions at s=13TeV with the ATLAS detector, Phys. Lett. B 858 (2024) 139007

ATLAS Collaboration, Search for heavy neutral Higgs bosons decaying into a top quark pair in 140 fb−1 of proton-proton collision data at √s=13 TeV with the ATLAS detector, JHEP 08 (2024) 013

ATLAS Collaboration, Constraints on dark matter models involving an s-channel mediator with the ATLAS detector in pp collisions at √s = 13 TeV, Eur. Phys. J. C. 84 (2024) 1102

ATLAS Collaboration, Combination of searches for heavy spin-1 resonances using 139 fb−1 of proton-proton collision data at √s = 13 TeV with the ATLAS detector, JHEP 04 (2024) 118

J. K. Behr, Shedding light on the building blocks of matter and the early universe at CERN, Europhysics News 54 (2023) 22–24, https://doi.org/10.1051/epn/2023507

ATLAS Collaboration, Combination and summary of ATLAS dark matter
searches interpreted in a 2HDM with a pseudo-scalar mediator using 139 fb−1 of √s = 13 TeV pp collision data, Sci. Bull. 69 (2024) 3005

J. K. Behr and A. Grohsjean, Dark Matter Searches with Top Quarks, Universe 9 (2023) 16

ATLAS Collaboration,
Search for ttbar resonances in fully hadronic final states in pp collisions at sqrt(s)=13 TeV with the ATLAS detector,
JHEP 10 (2020) 61


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ATLAS conference and public notes

ATLAS Collaboration, ATLAS-CONF-2025-008, Observation of a cross-section enhancement near the production threshold in
TeV collisions with the ATLAS detector

ATLAS Collaboration, ATL-PHYS-PUB-2023-022,
Clustering and Tracking in Dense Environments with the ATLAS Inner Tracker for the High-Luminosity LHC

ATLAS Collaboration, ATLAS-CONF-2022-028,
Combination of searches for heavy resonances using 139 fb^-1 of proton-proton collision data at sqrt(s)=13 TeV with the ATLAS detector

ATLAS Collaboration, ATL-PHYS-PUB-2021-045,
Dark matter summary plots for s-channel and 2HDM+a models

ATLAS Collaboration, ATLAS-CONF-2021-036,
Summary and combination of ATLAS dark matter searches using 139 fb^-1 of sqrt(s)=13 TeV pp collision data and interpreted in a two-Higgs-doublet model with a pseudoscalar mediator

Contact Information

Katharina Behr Phone: E-Mail: Katharina Behr Location: 01C / O1.315 DESY Notkestr. 85, 22607 Hamburg, Germany