About

Professor Keith Baker is the D. Allan Bromley Professor of Physics at Yale University, specializing in experimental particle physics. His research focuses on the energy frontier at the Large Hadron Collider within the ATLAS collaboration, as well as precision studies at sub-eV energies. His current projects include investigations into Axions, Hidden Sector Photons, and the Yale Microwave Cavity Experiment (YMCE). Professor Baker's work encompasses building detectors and conducting machine learning analyses in the discovery of the Higgs boson, as well as pioneering searches for Dark Sector phenomena in exotic Higgs decays. He has contributed to quantum information science in high-energy physics, exploring quantum entanglement and entanglement entropy in proton-proton collisions. His educational background includes a Ph.D. from Stanford University obtained in 1987. Recognized for his outstanding research, he has received numerous honors such as fellowships with the American Academy of Arts and Sciences and the American Physical Society, the Edward Bouchet Award, and the Elmer Imes Award. His contributions have significantly advanced experimental particle physics, particularly in the areas of Higgs boson studies, dark sector searches, and quantum information science applications in high-energy physics.

Research topics

• Physics
• Particle physics
• Nuclear physics
• Computer Science
• Optics
• Quantum mechanics
• Geology
• Astrophysics
• Computer hardware
• Telecommunications
• Statistics
• Real-time computing
• Biology
• Mathematics
• Operating system

Selected publications

• Search for Nearly Mass-Degenerate Higgsinos Using Low-Momentum Mildly Displaced Tracks in $pp$ Collisions at $\sqrt{s}$ = 13 TeV with the ATLAS Detector

  arXiv (Cornell University) · 2024

  • Physics
  • Particle physics
  • Nuclear physics

  Higgsinos with masses near the electroweak scale can solve the hierarchy problem and provide a dark matter candidate, while detecting them at the LHC remains challenging if their mass splitting is $\mathcal{O}(1 \text{GeV})$. This Letter presents a novel search for nearly mass-degenerate Higgsinos in events with an energetic jet, missing transverse momentum, and a low-momentum track with a significant transverse impact parameter using 140 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV collected by the ATLAS experiment. For the first time since LEP, a range of mass splittings between the lightest charged and neutral Higgsinos from $0.3$ GeV to $0.9$ GeV is excluded at 95$\%$ confidence level, with a maximum reach of approximately $170$ GeV in the Higgsino mass.

  DOI

• Inclusive and differential cross-section measurements of $t\bar{t}Z$ production in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector, including EFT and spin-correlation interpretations

  arXiv (Cornell University) · 2023 · 2 citations

  • Physics
  • Particle physics
  • Nuclear physics

  Measurements of both the inclusive and differential production cross sections of a top-quark-top-antiquark pair in association with a $Z$ boson ($t\bar{t}Z$) are presented. Final states with two, three or four isolated leptons (electrons or muons) are targeted. The measurements use the data recorded by the ATLAS detector in $pp$ collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider during the years 2015-2018, corresponding to an integrated luminosity of $140$ fb$^{-1}$. The inclusive cross section is measured to be $\sigma_{t\bar{t}Z}= 0.86 \pm 0.04~\mathrm{(stat.)} \pm 0.04~\mathrm{(syst.)}~$pb and found to be in agreement with the most advanced Standard Model predictions. The differential measurements are presented as a function of a number of observables that probe the kinematics of the $t\bar{t}Z$ system. Both the absolute and normalised differential cross-section measurements are performed at particle level and parton level for specific fiducial volumes, and are compared with NLO+NNLL theoretical predictions. The results are interpreted in the framework of Standard Model effective field theory and used to set limits on a large number of dimension-6 operators involving the top quark. The first measurement of spin correlations in $t\bar{t}Z$ events is presented: the results are in agreement with the Standard Model expectations, and the null hypothesis of no spin correlations is disfavoured with a significance of $1.8$ standard deviations.

  DOI

• A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery

  Nature · 2022 · 371 citations

  • Physics
  • Particle physics
  • Nuclear physics

  . Since then, more than 30 times as many Higgs bosons have been recorded by the ATLAS experiment, enabling much more precise measurements and new tests of the theory. Here, on the basis of this larger dataset, we combine an unprecedented number of production and decay processes of the Higgs boson to scrutinize its interactions with elementary particles. Interactions with gluons, photons, and W and Z bosons-the carriers of the strong, electromagnetic and weak forces-are studied in detail. Interactions with three third-generation matter particles (bottom (b) and top (t) quarks, and tau leptons (τ)) are well measured and indications of interactions with a second-generation particle (muons, μ) are emerging. These tests reveal that the Higgs boson discovered ten years ago is remarkably consistent with the predictions of the theory and provide stringent constraints on many models of new phenomena beyond the standard model.

  DOI

• Search for heavy Higgs bosons decaying into two tau leptons with the ATLAS detector using pp collisions at $\sqrt(s)$ = 13 TeV

  Proceedings of The European Physical Society Conference on High Energy Physics — PoS(EPS-HEP2021) · 2022 · 1 citations

  • Physics
  • Particle physics
  • Nuclear physics

  A search for heavy neutral Higgs bosons is performed using the LHC Run 2 data, corresponding to an integrated luminosity of 139 fb$^{-1}$ of proton-proton collisions at $\sqrt{s}=13$ TeV recorded by the ATLAS detector. The heavy resonance search is performed over the mass range 0.2-2.5~TeV for the $\tau^{+}\tau^{-}$ decay with at least one $\tau$-lepton decaying into handronic final states. The data is in good agreement with the standard model predictions. Results are interpreted in terms of several Minimum Supersymmetry Standard Model scenarios.

  DOI

• Spring statement 2022: quick analysis about standard of living, energy crisis and more – from experts

  2022-03-23

  preprint1st authorCorresponding
  PublisherDOI

• Measurement of the $t\bar{t}t\bar{t}$ production cross section in $pp$ collisions at $\sqrt{s}$=13 TeV with the ATLAS detector

  CERN Document Server (European Organization for Nuclear Research) · 2021 · 2 citations

  • Physics
  • Particle physics
  • Nuclear physics

  A measurement of four-top-quark production using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 139 fb$^{-1}$ is presented. Events are selected if they contain a single lepton (electron or muon) or an opposite-sign lepton pair, in association with multiple jets. The events are categorised according to the number of jets and how likely these are to contain $b$-hadrons. A multivariate technique is then used to discriminate between signal and background events. The measured four-top-quark production cross section is found to be 26$^{+17}_{-15}$ fb, with a corresponding observed (expected) significance of 1.9 (1.0) standard deviations over the background-only hypothesis. The result is combined with the previous measurement performed by the ATLAS Collaboration in the multilepton final state. The combined four-top-quark production cross section is measured to be 24$^{+7}_{-6}$ fb, with a corresponding observed (expected) signal significance of 4.7 (2.6) standard deviations over the background-only predictions. It is consistent within 2.0 standard deviations with the Standard Model expectation of 12.0$\pm$2.4 fb.

• arXiv : Search for exotic decays of the Higgs boson into long-lived particles in $pp$ collisions at $\sqrt{s} = 13$ TeV using displaced vertices in the ATLAS inner detector

  2021 · 1 citations

  • Physics
  • Particle physics
  • Nuclear physics

  A novel search for exotic decays of the Higgs boson into pairs of long-lived neutral particles, each decaying into a bottom quark pair, is performed using 139 fb$^{-1}$ of $\sqrt{s} = 13$ TeV proton-proton collision data collected with the ATLAS detector at the LHC. Events consistent with the production of a Higgs boson in association with a leptonically decaying $Z$ boson are analysed. Long-lived particle (LLP) decays are reconstructed from inner-detector tracks as displaced vertices with high mass and track multiplicity relative to Standard Model processes. The analysis selection requires the presence of at least two displaced vertices, effectively suppressing Standard Model backgrounds. The residual background contribution is estimated using a data-driven technique. No excess over Standard Model predictions is observed, and upper limits are set on the branching ratio of the Higgs boson to LLPs. Branching ratios above 10% are excluded at 95% confidence level for LLP mean proper lifetimes $c\tau$ as small as 4 mm and as large as 100 mm. For LLP masses below 40 GeV, these results represent the most stringent constraint in this lifetime regime.

• Search for new phenomena in three- or four-lepton events in $pp$ collisions at $\sqrt s$ =13 TeV with the ATLAS detector

  2021 · 1 citations

  • Physics
  • Particle physics
  • Nuclear physics

  A search with minimal model dependence for physics beyond the Standard Model in events featuring three or four charged leptons (3ℓ and 4ℓ, ℓ=e,μ) is presented. The analysis aims to be sensitive to a wide range of potential new-physics theories simultaneously. This analysis uses data from pp collisions delivered by the Large Hadron Collider at a centre-of-mass energy of s=13 TeV and recorded with the ATLAS detector, corresponding to the full Run 2 dataset of 139 fb−1. The 3ℓ and 4ℓ phase space is divided into 22 event categories according to the number of leptons in the event, the missing transverse momentum, the invariant mass of the leptons, and the presence of leptons originating from a Z-boson candidate. These event categories are analysed independently for the presence of deviations from the Standard Model. No statistically significant deviations from the Standard Model predictions are observed. Upper limits for all signal regions are reported in terms of the visible cross-section.

• Observation of electroweak production of two jets and a $Z$-boson pair with the ATLAS detector at the LHC

  HAL (Le Centre pour la Communication Scientifique Directe) · 2020 · 16 citations

  • Physics
  • Particle physics
  • Nuclear physics

  Electroweak symmetry breaking explains the origin of the masses of elementary particles through their interactions with the Higgs field. Besides the measurements of the Higgs boson properties, the study of the scattering of massive vector bosons with spin 1 allows the nature of electroweak symmetry breaking to be probed. Among all processes related to vector-boson scattering, the electroweak production of two jets and a Z-boson pair is a rare and important one. Here we report the observation of this process from proton–proton collision data corresponding to an integrated luminosity of 139 fb$^{−1}$ recorded at a centre-of-mass energy of 13 TeV with the ATLAS detector at the Large Hadron Collider. We consider two different final states originating from the decays of the Z-boson pair: one containing four charged leptons and another containing two charged leptons and two neutrinos. The hypothesis of no electroweak production is rejected with a statistical significance of 5.7σ, and the measured cross-section for electroweak production is consistent with the Standard Model prediction. In addition, we report cross-sections for inclusive production of a Z-boson pair and two jets for the two final states.

• Operation of the ATLAS trigger system in Run 2

  Journal of Instrumentation · 2020 · 115 citations

  • Computer Science
  • Computer Science
  • Physics

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  DOI

Frequent coauthors

• L. Schoeffel

  CEA Paris-Saclay

  404 shared

• F. Déliot

  CEA Paris-Saclay

  403 shared

• A. Formica

  CEA Paris-Saclay

  401 shared

• H. Bachacou

  Institut de Recherche sur les Lois Fondamentales de l'Univers

  396 shared

• L. Chevalier

  CEA Paris-Saclay

  395 shared

• M. Saimpert

  Commissariat à l'Énergie Atomique et aux Énergies Alternatives

  385 shared

• A. S. Sharma

  Hiroshima University

  382 shared

• M. Boonekamp

  Université Paris-Saclay

  348 shared

Awards & honors

• Fellow of the American Physical Society
• Edward Bouchet Award - American Physical Society
• Elmer Imes Award for Outstanding Research - Nat. Soc, of Bla…
• US ATLAS Distinguished Researcher - United States ATLAS
• Selected as Distinguished Speaker at five universities (HBCU…