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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Octet scalars shaping LHC distributions in 4-jet final states

We study properties of a hypothetical scalar particle, Θ, which is a color octet and an electroweak singlet. At hadron colliders, Θ is pair produced through its QCD coupling to gluons, so that its mass determines the cross section. It decays at tree level into $q\bar{q}$ through dimension-5 operators, and at one loop into gluons. Thus, the main LHC signature of Θ is a pair of dijets of equal invariant mass. The CMS search in this channel shows a 3.6σ excess over the QCD background for a dijet mass M jj ≈ 0.95 TeV, which can be due to Θ : its production cross section (65 fb for a real scalar) and the acceptance of the CMS event selection applied to pp → ΘΘ → ($q\bar{q}$) ($q\bar{q}$) yield a rate consistent with the excess. Furthermore, the shape of the dσ/dM jj signal is in agreement with the CMS result. Given the data-driven background fit performed by CMS, we find that a complex scalar (whose production rate is twice as large) fits better the data than a real scalar. Besides the pair of dijets, testable LHC signals include a trijet-dijet topology, a $t\bar{t}$ pair plus a dijet resonance, as well as final states involving a Higgs, W or Z boson plus jets.

Dobrescu, Bogdan A. [Fermi National Accelerator La↗
DOE OSTI2025

The SRG/eROSITA All-Sky Survey: Constraints on ultralight axion dark matter through galaxy cluster number counts

Ultralight axions are hypothetical scalar particles that influence the evolution of large-scale structures of the Universe. Depending on their mass, they can potentially be part of the dark matter component of the Universe as candidates commonly referred to as fuzzy dark matter. While strong constraints have been established for pure fuzzy dark matter models, the more general scenario where ultralight axions constitute only a fraction of the dark matter has been limited to only a few observational probes. In this work, we use the galaxy cluster number counts obtained from the first All-Sky Survey (eRASS1) of the SRG/eROSITA mission together with gravitational weak lensing data from the Dark Energy Survey, the Kilo-Degree Survey, and the Hyper Suprime-Cam to constrain the fraction of ultralight axions in the mass range 10 −32 eV to 10 −24 eV. We put upper bounds on the ultralight axion relic density Ω a in independent logarithmic axion mass bins by performing a full cosmological parameter inference. We find an exclusion region in the intermediate ultralight axion mass regime with the tightest bounds reported so far in the mass bins around m a = 10 −27 eV with Ω a < 0.0035 and m a = 10 −26 eV with Ω a < 0.0079; both are at a 95% confidence level. When combined with cosmic microwave background probes, these bounds are tightened to Ω a < 0.0030 in the m a = 10 −27 eV mass bin and Ω a < 0.0058 in the m a = 10 −26 eV mass bin, with both at a 95% confidence level. This is the first time that constraints on ultralight axions have been obtained using the growth of structure measured by galaxy cluster number counts. These results pave the way for large surveys, which can be utilized to obtain tight constraints on the mass and relic density of ultralight axions with better theoretical modeling of the abundance of halos.

cosmological parameters↗
DOE OSTI2025

Search for triple Higgs boson production in the 6⁢𝑏 final state using 𝑝⁢𝑝 collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for the production of three Higgs bosons (𝐻⁡𝐻⁡𝐻) in the $b\bar{b}b\bar{b}b\bar{b}$ final state is presented. The search uses 126 fb −1 of proton-proton collision data at $\sqrt{s}$ =13 TeV collected with the ATLAS detector at the Large Hadron Collider. The analysis targets both nonresonant and resonant production of 𝐻⁡𝐻⁡𝐻. The resonant interpretations primarily consider a cascade decay topology of 𝑋 →𝑆⁢𝐻 → 𝐻⁡𝐻⁡𝐻 with masses of the new scalars 𝑋 and 𝑆 up to 1.5 and 1 TeV, respectively. In addition to scenarios where 𝑆 is off-shell, the nonresonant interpretation includes a search for Standard Model 𝐻⁡𝐻⁡𝐻 production, with limits on the trilinear and quartic Higgs self-coupling set. No evidence for 𝐻⁡𝐻⁡𝐻 production is observed. An upper limit of 59 fb is set, at the 95% confidence level, on the cross section for Standard Model 𝐻⁡𝐻⁡𝐻 production.

Artificial neural networks↗
DOE OSTI2025

Weakly supervised anomaly detection with event-level variables

We introduce a new topology for weakly supervised anomaly detection searches, diobject plus X. In this topology, one looks for a resonance decaying to two standard model particles produced in association with other anomalous event activity (X). This additional activity is used for classification. We demonstrate how anomaly detection techniques which have been developed for dijet searches focusing on jet substructure anomalies can be applied to event-level anomaly detection in this topology. To robustly capture event-level features of multiparticle kinematics, we employ new physically motivated variables derived from the geometric structure of a collision’s phase space manifold. As a proof of concept, we explore the application of this approach to several benchmark signals in the di-𝜏 and di-𝜇 plus X final states. We demonstrate that our anomaly detection approach can reach discovery-level significances for signals that would be missed in a conventional bump-hunt approach.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Quantifying scalar field dynamics with DESI 2024 Y1 BAO measurements

Quintessence scalar fields are a natural candidate for evolving dark energy. Unlike the phenomenological w 0 ⁢w a parameterization of the dark energy equation of state, they cannot accommodate the phantom regime of dark energy w⁡(z) <–1, or crossings into the phantom regime. Recent baryon acoustic oscillation (BAO) measurements by the Dark Energy Spectroscopic Instrument (DESI) indicate a preference for evolving dark energy over a cosmological constant, ranging from 2.6⁢σ –3.9⁢σ when fitting to w 0⁢ w a , and combining the DESI BAO measurements with other cosmological probes. In this work, we directly fit three simple scalar field models to the DESI BAO data, combined with cosmic microwave background anisotropy measurements and supernova datasets. We find the best fit model to include a 2–4% kinetic scalar field energy Ω scf,k , for a canonical scalar field with a quadratic or linear potential. However, only the DESY-Y5 supernova dataset combination shows a preference for quintessence over Λ cold dark matter (CDM) at the 95% confidence level. Fitting to the supernova datasets Pantheon, Pantheon+, DES-Y5, and Union3, we show that the mild tension (n σ < 3.4) under Λ ⁢CDM emerges from a BAO preference for smaller values of fractional mass-energy density Ω m < 0.29, while all supernova datasets, except for Pantheon, prefer larger values, Ω m > 0.3. The tension under Λ ⁢CDM remains noticeable (n σ < 2.8), when replacing two of the DESI BAO redshift bins with effective redshifts z eff = 0.51, and z eff = 0.706 with comparable BOSS DR 12 BAO measurements at z eff = 0.51, and z eff = 0.61. Furthermore, canonical scalar fields as dark energy are successful in mitigating that tension.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Search for a Hidden Sector Scalar from Kaon Decay in the Dimuon Final State at ICARUS

We present a search for long-lived particles (LLPs), produced in kaon decays, that decay to two muons inside the ICARUS neutrino detector. This channel would be a signal of hidden sector models that can address outstanding issues in particle physics such as the strong CP problem and the microphysical origin of dark matter. The search is performed with data collected in the Neutrinos at the Main Injector (NuMI) beam at Fermilab corresponding to 2.41 × 10 20 protons-on-target. No new physics signal is observed, and we set world leading limits on heavy QCD axions, as well as for the Higgs portal scalar among dedicated searches. Limits are also presented in a model-independent way applicable to any new physics model predicting the process 𝐾 → 𝜋 + 𝑆⁡(→ 𝜇⁢𝜇), for a LLP 𝑆. This result is the first search for new physics performed with the ICARUS detector at Fermilab. It paves the way for the future program of LLP searches at ICARUS.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Search for events with one displaced vertex from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in 𝑝⁢𝑝 collisions at $\sqrt{𝑠}$ = 13 TeV

A search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using 140 fb −1 of proton-proton collision data at $\sqrt{𝑠}$ =13 TeV recorded in 2015–2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axionlike particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photophobic axionlike particle model considered, this search produces the strongest limits to date for proper decay lengths greater than 𝒪⁡(10) cm.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Lepton flavor violation by three units

The conservation of lepton flavor is a prediction of the Standard Model and is still an excellent approximate symmetry despite our observation of neutrino oscillations. Lepton flavor violation by one or two units has been discussed for decades, with several dedicated experiments exploring the vast model landscape but no discoveries so far. Here, we explore operators and processes that violate at least one lepton flavor by three units and identify testable signatures. In the Standard Model effective field theory, such operators already arise at mass dimension 7 and can be tested through their contributions to Michel parameters in leptonic decays. True neutrinoless charged-lepton flavor violation arises at mass dimension 10 and can realistically only be seen in the tau decay channels 𝜏 → $𝑒⁢𝑒⁢𝑒⁢\bar{𝜇}⁢\bar{𝜇}$ or 𝜏 → $𝜇⁢𝜇⁢𝜇\bar{𝑒}\bar{𝑒}$, for example in Belle II. Testable rates for these tau decays require light new particles and subsequently predict an avalanche of remarkably clean but so-far unconstrained collider signatures.

Feynman diagrams↗
DOE OSTI2025

Search for cascade decays of charged sleptons and sneutrinos in final states with three leptons and missing transverse momentum in 𝑝⁢𝑝 collisions at $\sqrt{𝑠} = 13$ TeV with the ATLAS detector

A search for cascade decays of charged sleptons and sneutrinos using final states characterized by three leptons (electrons or muons) and missing transverse momentum is presented. The analysis is based on a dataset with 140 fb −1 of proton-proton (pp) collisions at a center-of-mass energy of $\sqrt{𝑠} = 13$ TeV recorded by the ATLAS detector at the Large Hadron Collider. This paper focuses on a supersymmetric scenario that is motivated by the muon anomalous magnetic moment observation, dark-mattter relic density abundance, and electroweak naturalness. A mass spectrum involving light Higgsinos and heavier sleptons with a bino at intermediate mass is targeted. No significant deviation from the Standard Model expectation is observed. This search enables us to place stringent constraints on this model, excluding at the 95% confidence level charged slepton and sneutrino masses up to 450 GeV when assuming a lightest neutralino mass of 100 GeV and mass-degenerate selectrons, smuons and sneutrinos.

extensions of Higgs sector↗
DOE OSTI2025

Search for New Resonances Decaying to Pairs of Merged Diphotons in Proton-Proton Collisions at $\sqrt{s}$ = 13 TeV

A search is presented for an extended Higgs sector with two new particles, 𝑋 and 𝜙, in the process 𝑋 → 𝜙⁢𝜙 → (𝛾⁢𝛾)⁢(𝛾⁢𝛾). Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at $\sqrt{s}$ = 13 TeV collected with the CMS detector, corresponding to an integrated luminosity of 138 fb −1 . No evidence of such resonances is seen. Upper limits are set on the production cross section for 𝑚 𝑋 between 300 and 3000 GeV and 𝑚 𝜙 /𝑚 𝑋 between 0.5% and 2.5%, representing the most sensitive search in this channel.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

The pathfinder X-Ray axion telescope for the International Axion Observatory (IAXO) and axion searches at the CERN Axion Solar Telescope (CAST)

The axion, a hypothetical pseudo-scalar particle proposed by Peccei and Quinn to resolve the strong CP problem in quantum chromodynamics, remains one of the most compelling dark matter candidates. Axions and Axion-Like Particles (ALPs) are characterized by a broad and largely unconstrained parameter space in mass and coupling strength, motivating extensive experimental searches. The International Axion Observatory (IAXO) is a next-generation axion helioscope designed to achieve over an order of magnitude improvement in sensitivity to the axion-photon coupling constant gaγ relative to previous experiments such as the CERN Axion Solar Telescope (CAST). IAXO will employ large-scale superconducting magnets, precision x-ray optics, and ultra-low-background detectors to search for solar axions produced primarily via the Primakoff effect. This work presents the design and performance of the IAXO pathfinder x-ray optic, a technological demonstrator that validated the optical concepts for IAXO through axion searches at CAST. Comprehensive ray-tracing simulations and experimental measurements were conducted to assess the optic's effective area, detection efficiency, and background suppression capabilities. Deployed at CAST in conjunction with Micromegas and GridPix detectors, the Pathfinder demonstrated record-setting sensitivity to both gaγ and the axion-electron coupling gae, establishing the most stringent laboratory constraints on solar axions to date. These results confirm the viability of the IAXO optical design and detector concept, providing a critical technological benchmark that informs the ongoing development of the BabyIAXO and full-scale IAXO telescopes.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Testing Scale-Dependent Modified Gravity with DESI DR1

The Dark Energy Spectroscopic Instrument (DESI) provides an unprecedented opportunity to test deviations from general relativity (GR) that introduce a new physical scale within its redshift range. Using the connection between a Yukawa-like potential and the Hu-Sawicki $f(R)$ model, we place strong constraints on the range of a hypothetical fifth force mediated by a massive scalar field. We analyze the power spectrum measurements from DESI Data Release 1 using a baseline EFT model that employs the fkpt approach for the loop integrals. We find no evidence for deviations from GR and obtain the constraint $\log_{10} |f_{R_0}| < -4.59$ (95% C.L.). This corresponds to an upper bound at redshift zero on the scale at which corrections to GR become important, $λ< 17.81$ Mpc, or equivalently, a lower bound on the mass of the additional gravitational mediator of $m_ϕ> 3.60 \times 10^{-31}$ eV. We find that the modified gravity parameter $f_{R_0}$ is largely orthogonal to the cosmological parameters in the model, such that no additional projection effects relative to the GR case are introduced in this Full-Shape analysis. Furthermore, a second modified gravity parameter, the power index $n$, which modulates the time-variation of the associated mass, is found to be consistent with previous analyses that fixed it to unity. Adding DESI BAO data or other cosmological probes does not significantly change these results. The conclusions remain similar if the background evolution is described by evolving dark energy instead of a cosmological constant. Additionally, we test the robustness of the baseline model by varying the maximum wavenumber used in the Full-Shape analysis and analyzing the DESI targets separately. Finally, we analyze the degeneracies between the modified-gravity parameters and the sum of neutrino masses.

Gonzalez, D. [Guanajuato U.; UNAM, CCF] (ORCID:000↗
DOE OSTI2026

Review of Particle Physics

The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,200 new measurements from 903 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Most of the 118 reviews are updated, including many that are heavily revised.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Review of Particle Physics - Scalar Mesons below 1 GeV

The summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,717 new measurements from 869 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Most of the 120 reviews are updated, including many that are heavily revised. The is divided into two volumes. Volume 1 includes the Summary Tables and 97 review articles. Volume 2 consists of the Particle Listings and contains also 23 reviews that address specific aspects of the data presented in the Listings. The complete (both volumes) is published online on the website of the Particle Data Group () and in a journal. Volume 1 is available in print as the . A with the Summary Tables and essential tables, figures, and equations from selected review articles is available in print, as a web version optimized for use on phones, and as an Android app. The 2024 edition of the Review of Particle Physics should be cited as: S. Navas et al. (Particle Data Group), Phys. Rev. D 110, 030001 (2024)© 20242024

Navas, S. [Universidad de Granada]↗
NASA NTRS1975

On the modeling of the scalar correlations necessary to construct a second-order closure description of turbulent reacting flows

A tentative scheme is proposed for constructing second-order closure models of turbulent reacting flows, with particular reference to mixing processes in turbulent diffusion flows. The model is based on the concepts of typical structure and typical eddy, and treats various hypothetical turbulent flame situations, including the time dependence of species mass fractions passing a point in the flame, the most typical occurrence of species mass fractions, and the case of a rather bizarre typical eddy which shows the effects of nonmixedness.

Donaldson, C. DUP.↗
DOE OSTI2025

Search for emerging jets in pp collisions at $\sqrt{s} = 13.6$ TeV with the ATLAS experiment

A search for emerging jets is presented using 51.8 fb −1 of proton–proton collision data at $\sqrt{s} = 13.6$ TeV, collected by the ATLAS experiment during 2022 and 2023. The search explores a hypothetical dark sector featuring ‘dark quarks’ that are charged under a confining gauge group and couple to the standard model (SM) via a new mediator particle. These dark quarks undergo showering and hadronisation within the dark sector, forming long-lived dark mesons that decay back into SM particles. This results in jets that contain multiple displaced vertices known as emerging jets. The analysis targets events with pairs of emerging jets, produced either through a vector mediator, Z′, in the s-channel, or a scalar mediator, Φ, in the t-channel. No significant excess over the SM background is observed. Assuming a dark pion proper decay length between 5 mm and 50 mm, Z′ mediator masses between 600 GeV and 2550 GeV are excluded for quark and dark quark coupling values of 0.01 and 0.1, respectively. For a quark dark-quark coupling of 0.1, Φ mediator masses between 600 GeV and 1375 GeV are excluded. These results represent the first direct search targeting emerging jet pair production via a Z′ mediator, as well as the first study of emerging jet production mediated by a scalar particle exchanged in the t-channel.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Black holes from Fermi ball collapse

Fermi balls are nontopological solitons that can naturally form in an early Universe containing a dark sector with heavy fermions and an attractive interaction mediated by a light scalar field. We compute the Fermi ball mass and radius scaling relations when the potential of the scalar field 𝜑 has a non-negligible quartic coupling 𝜆⁢𝜑4. The resulting Fermi balls reach “saturation” very rapidly, even when their radius is much smaller than the effective Yukawa force range. These objects can therefore grow by mergers or by the accretion of ambient dark fermions until they become so dense that they fall within their Schwarzschild radius and collapse to black holes. This setup, therefore, provides an example of a rather natural and economical dark sector scenario for the formation of primordial black holes.

Hypothetical particle physics models↗
DOE OSTI2024

Search for Soft Unclustered Energy Patterns in Proton-Proton Collisions at 13 TeV

The first search for soft unclustered energy patterns (SUEPs) is performed using an integrated luminosity of 138 fb −1 of proton-proton collision data at $\sqrt{𝑠}$ = 13 TeV, collected in 2016–2018 by the CMS detector at the LHC. Such SUEPs are predicted by hidden valley models with a new, confining force with a large ’t Hooft coupling. In events with boosted topologies, selected by high-threshold hadronic triggers, the multiplicity and sphericity of clustered tracks are used to reject the background from standard model quantum chromodynamics. With no observed excess of events over the standard model expectation, limits are set on the cross section for production via gluon fusion of a scalar mediator with SUEP-like decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗