Michael Kagan
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
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Michael Kagan has a total of 1000 co-authors. Here are the top co-authors by number of shared publications:
- Lukas Heinrich
Technical University of Munich
354 shared publications - Ariel Schwartzman
SLAC National Accelerator Laboratory
352 shared publications - Tobias Golling
Université de Genève
352 shared publications - Bogdan Malaescu
Universite Paris Cite
351 shared publications - Ines Ochoa
Laboratory of Instrumentation and Experimental Particle Physics Lisbon Portugal
351 shared publications - A. T. Watson
University of Birmingham
350 shared publications
Latest Publications
- Open Access
- 6 November 2026
- Published by American Physical Society (APS) in Physical Review C
- Vol. 114 (5)
Measurements of longitudinal flow decorrelations in p p and Xe + Xe collisions with the ATLAS detector
Measurements of longitudinal flow decorrelations in 13-TeV p p and 5.44-TeV Xe + Xe collisions with the ATLAS detector are presented. The measurements are performed using the two-particle correlation method, combining charged-particle tracks within | η | < 2.5 with either calorimeter energy clusters or towers within 4.0 < | η | < 4.9 . A template-based subtraction procedure is used to remove nonflow effects in both the p p and the Xe + Xe analyses. The dependence of the longitudinal flow decorrelations on the pseudorapidity separation between the particles is characterized via the slope parameter F n for the elliptic ( n = 2 ) and triangular ( n = 3 ) harmonic moments. The results are reported as a function of charged-particle multiplicity for the p p and Xe + Xe collision systems. Comparing the data to a color string-based model of the initial geometry indicates that in p p and peripheral Xe + Xe collisions, subnucleonic structure, and fluctuations in longitudinal energy deposition are needed to describe the data.
- 6 November 2026
- Published by American Physical Society (APS) in Physical Review C
- Vol. 114 (5)
Open AccessMeasurements of longitudinal flow decorrelations in p p and Xe + Xe collisions with the ATLAS detector
Measurements of longitudinal flow decorrelations in 13-TeV p p and 5.44-TeV Xe + Xe collisions with the ATLAS detector are presented. The measurements are performed using the two-particle correlation method, combining charged-particle tracks within | η | < 2.5 with either calorimeter energy clusters or towers within 4.0 < | η | < 4.9 . A template-based subtraction procedure is used to remove nonflow effects in both the p p and the Xe + Xe analyses. The dependence of the longitudinal flow decorrelations on the pseudorapidity separation between the particles is characterized via the slope parameter F n for the elliptic ( n = 2 ) and triangular ( n = 3 ) harmonic moments. The results are reported as a function of charged-particle multiplicity for the p p and Xe + Xe collision systems. Comparing the data to a color string-based model of the initial geometry indicates that in p p and peripheral Xe + Xe collisions, subnucleonic structure, and fluctuations in longitudinal energy deposition are needed to describe the data.
- Open Access
- 4 November 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (11)
Measurement of J/ψ-jet correlations in pp and Pb+Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV with the ATLAS detectorA bstract: Yields of charmonia, bound states of $$ c\overline{c} $$ quarks, are observed to be strongly suppressed in heavy-ion collisions relative to proton-proton collisions as a result of their interaction with the quark-gluon plasma produced in such collisions. Understanding the mechanisms responsible for this suppression requires a detailed understanding of charmonium production. To constrain the production mechanisms, it is essential to quantify how charmonium production correlates with jet activity. Measurements of J/ψ production in the dimuon decay channel are presented for inclusive J/ψ mesons and for J/ψ mesons that are either isolated or not isolated from jets, separately for prompt and non-prompt production. Non-isolated J/ψ mesons are defined by matching J/ψ candidates to anti- k t jets with R = 0 . 2 and p T > 20 GeV, reconstructed without signal from the J/ψ meson, allowing the quantification of jet activity accompanying J/ψ production. The analysis uses Pb+Pb and pp collisions at $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ TeV recorded by the ATLAS experiment at the LHC, corresponding to integrated luminosities of 1 . 82 nb − 1 and 0 . 26 fb − 1 , respectively. The J/ψ yields in Pb+Pb, cross sections in pp , and nuclear modification factors are presented for non-isolated, isolated, and inclusive J/ψ up to p T = 60 GeV. Isolated fractions and non-prompt fractions are reported in both pp and Pb+Pb collisions. Strong J/ψ suppression is observed to persist up to the highest measured p T values, with differences observed between non-isolated, isolated, and inclusive J/ψ . These results provide new constraints on charmonium production mechanisms and their in-medium suppression.- 4 November 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (11)
Open AccessMeasurement of J/ψ-jet correlations in pp and Pb+Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV with the ATLAS detectorA bstract: Yields of charmonia, bound states of $$ c\overline{c} $$ quarks, are observed to be strongly suppressed in heavy-ion collisions relative to proton-proton collisions as a result of their interaction with the quark-gluon plasma produced in such collisions. Understanding the mechanisms responsible for this suppression requires a detailed understanding of charmonium production. To constrain the production mechanisms, it is essential to quantify how charmonium production correlates with jet activity. Measurements of J/ψ production in the dimuon decay channel are presented for inclusive J/ψ mesons and for J/ψ mesons that are either isolated or not isolated from jets, separately for prompt and non-prompt production. Non-isolated J/ψ mesons are defined by matching J/ψ candidates to anti- k t jets with R = 0 . 2 and p T > 20 GeV, reconstructed without signal from the J/ψ meson, allowing the quantification of jet activity accompanying J/ψ production. The analysis uses Pb+Pb and pp collisions at $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ TeV recorded by the ATLAS experiment at the LHC, corresponding to integrated luminosities of 1 . 82 nb − 1 and 0 . 26 fb − 1 , respectively. The J/ψ yields in Pb+Pb, cross sections in pp , and nuclear modification factors are presented for non-isolated, isolated, and inclusive J/ψ up to p T = 60 GeV. Isolated fractions and non-prompt fractions are reported in both pp and Pb+Pb collisions. Strong J/ψ suppression is observed to persist up to the highest measured p T values, with differences observed between non-isolated, isolated, and inclusive J/ψ . These results provide new constraints on charmonium production mechanisms and their in-medium suppression. - Open Access
- 4 November 2026
- Published by American Physical Society (APS) in PRX Intelligence
- Vol. 1 (2) , 023012
Machine-Learned Particle Flow as a Foundation Model for Collider Physics
The workflow from particle collision to physics analysis passes through a series of reconstruction steps that are traditionally modular and disconnected, with no shared representation linking low-level detector data to high-level analysis tasks. We show that casting event reconstruction as a machine learning problem naturally produces such a shared representation. We repurpose a machine learning model trained for particle-flow reconstruction (MLPF) to perform three distinct analysis tasks: jet flavor identification, jet energy regression, and missing momentum regression. By appending the per-particle latent representations learned during reconstruction as additional input features, we substantially improve over baselines that use conventional particle-level features alone. We further demonstrate that a single linear layer trained using only the latent representations achieves competitive performance against state-of-the-art baseline architectures, and outperforms the baseline for missing momentum regression with approximately 35 times fewer parameters. These results demonstrate that the latent representations learned during reconstruction encode essential physics information needed for downstream analysis, establishing MLPF as a foundation model and offering a concrete step toward an end-to-end pipeline from detector data to physics analysis.
- 4 November 2026
- Published by American Physical Society (APS) in PRX Intelligence
- Vol. 1 (2) , 023012
Open AccessMachine-Learned Particle Flow as a Foundation Model for Collider Physics
The workflow from particle collision to physics analysis passes through a series of reconstruction steps that are traditionally modular and disconnected, with no shared representation linking low-level detector data to high-level analysis tasks. We show that casting event reconstruction as a machine learning problem naturally produces such a shared representation. We repurpose a machine learning model trained for particle-flow reconstruction (MLPF) to perform three distinct analysis tasks: jet flavor identification, jet energy regression, and missing momentum regression. By appending the per-particle latent representations learned during reconstruction as additional input features, we substantially improve over baselines that use conventional particle-level features alone. We further demonstrate that a single linear layer trained using only the latent representations achieves competitive performance against state-of-the-art baseline architectures, and outperforms the baseline for missing momentum regression with approximately 35 times fewer parameters. These results demonstrate that the latent representations learned during reconstruction encode essential physics information needed for downstream analysis, establishing MLPF as a foundation model and offering a concrete step toward an end-to-end pipeline from detector data to physics analysis.
- Open Access
- 28 October 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (10)
Search for dark photons from Higgs boson decays in the gluon-gluon fusion channel in proton-proton collisions at $ \sqrt{s}=13.6 $ TeV with the ATLAS detectorA bstract: This paper presents a search for semi-visible Higgs boson decays in final states with a photon ( γ ) and missing transverse momentum $$ {p}_{\mathrm{T}}^{\mathrm{miss}} $$ . The analysis is optimised for the gluon-gluon fusion production channel and exploits a novel trigger deployed in 2023, with reduced thresholds down to 50 GeV on the photon transverse momentum ( $$ {p}_{\mathrm{T}}^{\gamma } $$ ) and 70 GeV on the $$ {p}_{\mathrm{T}}^{\mathrm{miss}} $$ , in combination with a selection on the transverse mass of the $$ {p}_{\mathrm{T}}^{\mathrm{miss}} $$ -γ system ( m T ) above 80 GeV. The results are interpreted in terms of Higgs boson decays into a γ and a dark photon γ d ( H → γγ d ). The analysis is performed using 135 fb − 1 of Run 3 data collected by ATLAS in 2023 and 2024. A boosted decision tree is used to identify events with misreconstructed primary vertices, which can affect the $$ {p}_{\mathrm{T}}^{\mathrm{miss}} $$ calculation. Data-driven methods are employed to estimate the backgrounds from jets and electrons misidentified as photons, while the backgrounds with genuine photons are taken from Monte Carlo simulations, normalised to data in control regions with muons. A binned maximum-likelihood fit to the m T distribution is performed to evaluate the compatibility of the observed data with the Standard Model expectation. No significant excess is observed over the Standard Model prediction, and an observed (expected) upper limit on the branching ratio of H → γγ d of 1.4% (1.2%) is obtained at 95% confidence level. Combining this result with previous Run 2 searches improves the observed (expected) upper limit to 0.9% (0.9%).- 28 October 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (10)
Open AccessSearch for dark photons from Higgs boson decays in the gluon-gluon fusion channel in proton-proton collisions at $ \sqrt{s}=13.6 $ TeV with the ATLAS detectorA bstract: This paper presents a search for semi-visible Higgs boson decays in final states with a photon ( γ ) and missing transverse momentum $$ {p}_{\mathrm{T}}^{\mathrm{miss}} $$ . The analysis is optimised for the gluon-gluon fusion production channel and exploits a novel trigger deployed in 2023, with reduced thresholds down to 50 GeV on the photon transverse momentum ( $$ {p}_{\mathrm{T}}^{\gamma } $$ ) and 70 GeV on the $$ {p}_{\mathrm{T}}^{\mathrm{miss}} $$ , in combination with a selection on the transverse mass of the $$ {p}_{\mathrm{T}}^{\mathrm{miss}} $$ -γ system ( m T ) above 80 GeV. The results are interpreted in terms of Higgs boson decays into a γ and a dark photon γ d ( H → γγ d ). The analysis is performed using 135 fb − 1 of Run 3 data collected by ATLAS in 2023 and 2024. A boosted decision tree is used to identify events with misreconstructed primary vertices, which can affect the $$ {p}_{\mathrm{T}}^{\mathrm{miss}} $$ calculation. Data-driven methods are employed to estimate the backgrounds from jets and electrons misidentified as photons, while the backgrounds with genuine photons are taken from Monte Carlo simulations, normalised to data in control regions with muons. A binned maximum-likelihood fit to the m T distribution is performed to evaluate the compatibility of the observed data with the Standard Model expectation. No significant excess is observed over the Standard Model prediction, and an observed (expected) upper limit on the branching ratio of H → γγ d of 1.4% (1.2%) is obtained at 95% confidence level. Combining this result with previous Run 2 searches improves the observed (expected) upper limit to 0.9% (0.9%). - Open Access
- 23 October 2026
- Published by Elsevier in Physics Letters B
- Vol. 883
Measurement of isolated photon plus two-jet correlations in Pb+Pb and pp collisions at 5.02 TeV with ATLAS
- 23 October 2026
- Published by Elsevier in Physics Letters B
- Vol. 883
Open AccessMeasurement of isolated photon plus two-jet correlations in Pb+Pb and pp collisions at 5.02 TeV with ATLAS
- Open Access
- 21 October 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (10)
Search for $ t\overline{t} $ resonances in final states with exactly one or two leptons using 140 fb−1 of pp collision data at $ \sqrt{s}=13 $ TeV with the ATLAS experimentA bstract: A search for heavy spin-1 and spin-2 resonances decaying into a top-antitop-quark pair has been performed with 140 fb − 1 of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of $$ \sqrt{s}=13 $$ TeV. Final states with either exactly one electron or muon, or exactly two leptons ( ee , μμ or eμ ), large missing transverse momentum, and two jets, at least one of which must be identified as likely containing a b -hadron decay, are considered. The search targets resonances with both narrow and broad widths relative to the detector resolution, and with masses in the range of 0.4–5.0 TeV. No significant deviation from the Standard Model prediction is observed. Exclusion limits are set on the production cross-section times branching ratio for hypothetical Z′ bosons, Kaluza-Klein gravitons, and Kaluza-Klein gluons that decay into top-quark pairs.- 21 October 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (10)
Open AccessSearch for $ t\overline{t} $ resonances in final states with exactly one or two leptons using 140 fb−1 of pp collision data at $ \sqrt{s}=13 $ TeV with the ATLAS experimentA bstract: A search for heavy spin-1 and spin-2 resonances decaying into a top-antitop-quark pair has been performed with 140 fb − 1 of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of $$ \sqrt{s}=13 $$ TeV. Final states with either exactly one electron or muon, or exactly two leptons ( ee , μμ or eμ ), large missing transverse momentum, and two jets, at least one of which must be identified as likely containing a b -hadron decay, are considered. The search targets resonances with both narrow and broad widths relative to the detector resolution, and with masses in the range of 0.4–5.0 TeV. No significant deviation from the Standard Model prediction is observed. Exclusion limits are set on the production cross-section times branching ratio for hypothetical Z′ bosons, Kaluza-Klein gravitons, and Kaluza-Klein gluons that decay into top-quark pairs. - Open Access
- 21 October 2026
- Published by Springer Nature in The European Physical Journal C
- Vol. 86 (10) , 1200
Publisher Correction: Calibration of the jet energy scale and resolution of small-radius jets using semileptonic $t\bar{t}$ events with the ATLAS detector- 21 October 2026
- Published by Springer Nature in The European Physical Journal C
- Vol. 86 (10) , 1200
Open AccessPublisher Correction: Calibration of the jet energy scale and resolution of small-radius jets using semileptonic $t\bar{t}$ events with the ATLAS detector - Open Access
- 19 October 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (10)
Search for soft unclustered energy patterns containing muons in the final state in pp collisions at $ \sqrt{s}=13 $ TeV with the ATLAS detectorA bstract: Soft unclustered energy patterns (SUEPs) refer to high-multiplicity, isotropic distributions of low-momentum particles that could arise in strongly-coupled hidden sector theories. A search for SUEPs whose decay products contain muons in the final state is presented using 140 fb − 1 of proton–proton collision data at $$ \sqrt{s}=13 $$ TeV collected by the ATLAS detector at the Large Hadron Collider during 2015–2018. The analysis targets SUEP signatures via gluon–gluon fusion production of a scalar mediator in Hidden Valley scenarios. No significant excess over the Standard Model expectation is observed. Exclusion limits are set on the product of the mediator production cross section and the branching fraction for its decay into a SUEP, down to 0.05 fb for a mediator mass of m S = 750 GeV, 0.4 fb for m S = 400 GeV, and 70 fb for m S = 125 GeV; the last value, when identifying the mediator with the Standard Model Higgs boson, translates to an upper limit on the branching fraction of around 0.2%.- 19 October 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (10)
Open AccessSearch for soft unclustered energy patterns containing muons in the final state in pp collisions at $ \sqrt{s}=13 $ TeV with the ATLAS detectorA bstract: Soft unclustered energy patterns (SUEPs) refer to high-multiplicity, isotropic distributions of low-momentum particles that could arise in strongly-coupled hidden sector theories. A search for SUEPs whose decay products contain muons in the final state is presented using 140 fb − 1 of proton–proton collision data at $$ \sqrt{s}=13 $$ TeV collected by the ATLAS detector at the Large Hadron Collider during 2015–2018. The analysis targets SUEP signatures via gluon–gluon fusion production of a scalar mediator in Hidden Valley scenarios. No significant excess over the Standard Model expectation is observed. Exclusion limits are set on the product of the mediator production cross section and the branching fraction for its decay into a SUEP, down to 0.05 fb for a mediator mass of m S = 750 GeV, 0.4 fb for m S = 400 GeV, and 70 fb for m S = 125 GeV; the last value, when identifying the mediator with the Standard Model Higgs boson, translates to an upper limit on the branching fraction of around 0.2%. - Open Access
- 13 October 2026
- Published by Elsevier in Physics Letters B
- Vol. 882
Search for a leptoquark in events with a hadronically decaying τ-lepton and missing transverse momentum using pp collisions at s=13TeV with the ATLAS detector
- 13 October 2026
- Published by Elsevier in Physics Letters B
- Vol. 882
Open AccessSearch for a leptoquark in events with a hadronically decaying τ-lepton and missing transverse momentum using pp collisions at s=13TeV with the ATLAS detector
- Open Access
- 5 October 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (10)
Differential measurements of γγ → ττ and constraints on τ-lepton electromagnetic moments in Pb+Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV with ATLASA bstract: This paper presents the first differential fiducial measurements of γγ → ττ using 1.93 nb − 1 of Pb+Pb data at $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ TeV recorded by the ATLAS detector. Events in which one of the τ -leptons decays into a muon and two neutrinos $$ \tau \to {\nu}_{\tau }{\overline{\nu}}_{\mu}\mu $$ are selected and are categorized into three regions by the presence of an electron or either one or three charged-particle track(s) from the second τ -lepton decay. The measurement is performed in events where both Pb ions remain intact and no neutrons are emitted. Differential cross-sections are measured for seven variables in three fiducial regions at particle level. The measurements are compared to theory predictions with different photon flux models and spin correlation effects. For the fiducial region with one muon and one electron in the final state, comparisons to next-to-leading-order electroweak predictions are also made. The transverse momentum ( p T ) of the decay muon, the p T of the visible decay particles of the other τ -lepton, the total p T , invariant mass, and pseudorapidity of the visible particles from the di- τ system, and the rapidity and acoplanarity of the visible decay particles from either τ -lepton are measured. A maximum-likelihood fit to the muon transverse-momentum distributions in the three regions before unfolding is performed to extract the τ -lepton anomalous magnetic moment a τ and electric dipole moment d τ , the latter for the first time in heavy ion collisions. The observed 95% confidence level intervals are − 0 . 057 < a τ < 0 . 035 and |d τ | < 2 . 7 × 10 − 16 e cm.- 5 October 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (10)
Open AccessDifferential measurements of γγ → ττ and constraints on τ-lepton electromagnetic moments in Pb+Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV with ATLASA bstract: This paper presents the first differential fiducial measurements of γγ → ττ using 1.93 nb − 1 of Pb+Pb data at $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ TeV recorded by the ATLAS detector. Events in which one of the τ -leptons decays into a muon and two neutrinos $$ \tau \to {\nu}_{\tau }{\overline{\nu}}_{\mu}\mu $$ are selected and are categorized into three regions by the presence of an electron or either one or three charged-particle track(s) from the second τ -lepton decay. The measurement is performed in events where both Pb ions remain intact and no neutrons are emitted. Differential cross-sections are measured for seven variables in three fiducial regions at particle level. The measurements are compared to theory predictions with different photon flux models and spin correlation effects. For the fiducial region with one muon and one electron in the final state, comparisons to next-to-leading-order electroweak predictions are also made. The transverse momentum ( p T ) of the decay muon, the p T of the visible decay particles of the other τ -lepton, the total p T , invariant mass, and pseudorapidity of the visible particles from the di- τ system, and the rapidity and acoplanarity of the visible decay particles from either τ -lepton are measured. A maximum-likelihood fit to the muon transverse-momentum distributions in the three regions before unfolding is performed to extract the τ -lepton anomalous magnetic moment a τ and electric dipole moment d τ , the latter for the first time in heavy ion collisions. The observed 95% confidence level intervals are − 0 . 057 < a τ < 0 . 035 and |d τ | < 2 . 7 × 10 − 16 e cm.