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DOE OSTI2025

Identification of low-momentum muons in the CMS detector using multivariate techniques in proton-proton collisions at $\sqrt{s}$ = 13.6 TeV

“Soft” muons with a transverse momentum below 10 GeV are featured in many processes studied by the CMS experiment, such as decays of heavy-flavor hadrons or rare tau lepton decays. Maximizing the selection efficiency for these muons, while simultaneously suppressing backgrounds from long-lived light-flavor hadron decays, is therefore important for the success of the CMS physics program. Multivariate techniques have been shown to deliver better muon identification performance than traditional selection techniques. To take full advantage of the large data set currently being collected during Run 3 of the CERN LHC, a new multivariate classifier based on a gradient-boosted decision tree has been developed. It offers a significantly improved separation of signal and background muons compared to a similar classifier used for the analysis of the Run 2 data. The performance of the new classifier is evaluated on a data set collected with the CMS detector in 2022 and 2023, corresponding to an integrated luminosity of 62 fb -1 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Observation of the decay J / ψ → e + e − η ( 1405 ) with η ( 1405 ) → π 0 f 0 ( 980 )

Using a data sample of ( 10087 ± 44 ) × 10 6 J / ψ events collected by the BESIII detector in 2009, 2012, 2018 and 2019, the electromagnetic Dalitz process J / ψ → e + e − η ( 1405 ) is observed via the decay η ( 1405 ) → π 0 f 0 ( 980 ) , f 0 ( 980 ) → π + π − , with a significance of about 9.8 σ . The branching fraction of this decay is measured to be B ( J / ψ → e + e − η ( 1405 ) → e + e − π 0 f 0 ( 980 ) → e + e − π 0 π + π − ) = ( 2.04 ± 0.20 ( stat ) ± 0.08 ( syst ) ) × 10 − 7 . The branching fraction ratio B ( J / ψ → e + e − η ( 1405 ) ) / B ( J / ψ → γ η ( 1405 ) ) is determined to be ( 1.36 ± 0.17 ( stat ) ± 0.06 ( syst ) ) × 10 − 2 . Furthermore, an e + e − invariant mass dependent transition form factor of J / ψ → e + e − η ( 1405 ) is presented for the first time. The obtained result provides input for different theoretical models and is valuable for the improved understanding the intrinsic structure of the η ( 1405 ) meson. Published by the American Physical Society 2024

Astronomy & Astrophysics↗

DOE OSTI2026

Vibrational Spin-Orbit Coupling Contributions to Excited State Decay of Ligand-to-Ligand Charge Transfer States

Controlling excited state relaxation processes is important in a variety of photochemical and photophysical processes, including the generation of ground and excited state spin polarization for quantum information science applications. Here, we address how specific static distortions – based on vibrational spin-orbit active modes at C2v symmetry determined by group theory – in a series of low-symmetry ligand-to-ligand charge transfer complexes enable direct spin-orbit coupling contributions to T1 → S0 excited state decay. These results are used to address spin-vibronic coupling contributions to T1 → S0 decay in a high-symmetry (tBu2bpy)Pt(S,S) (tBu2bpy = 4,4’-di-tert-butyl-2,2’-bipyridine and S,S = benzene-1,2-dithiolate) ligand-to-ligand charge transfer complex with effective C2v symmetry, where T1 relaxation is both spin- and orbitally forbidden due to the direct spin-orbit coupling matrix element being zero by symmetry. Low-frequency vibrations that involve a pyridine-pyridine twisting motion within the bpy ligand generate large ∂/∂Qi values that will contribute significantly to T1 → S0 relaxation. The work advances ligand design strategies for the generation of tailored T1 → S0 relaxation rates, which can be utilized to optimize the generation of electron spin polarization in radical-elaborated ligand-to-ligand charge transfer complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Study of Drell-Yan dimuon production in proton-lead collisions at $\sqrt{s_\mathrm{NN}} =$ 8.16 TeV

Differential cross sections for the Drell-Yan process, including Z boson production, using the dimuon decay channel are measured in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of 8.16 TeV. A data sample recorded with the CMS detector at the LHC is used, corresponding to an integrated luminosity of 173 nb$^{−1}$. The differential cross section as a function of the dimuon mass is measured in the range 15–600 GeV, for the first time in proton-nucleus collisions. It is also reported as a function of dimuon rapidity over the mass ranges 15–60 GeV and 60–120 GeV, and ratios for the p-going over the Pb-going beam directions are built. In both mass ranges, the differential cross sections as functions of the dimuon transverse momentum p$_{T}$ and of a geometric variable ϕ$^{*}$ are measured, where ϕ$^{*}$ highly correlates with p$_{T}$ but is determined with higher precision. In the Z mass region, the rapidity dependence of the data indicate a modification of the distribution of partons within a lead nucleus as compared to the proton case. The data are more precise than predictions based upon current models of parton distributions.[graphic not available: see fulltext]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Generic one-loop matching conditions for rare meson decays

Leptonic and semileptonic meson decays that proceed via flavour-changing neutral currents provide excellent probes of physics of the standard model and beyond. We present explicit results for the Wilson coefficients of the weak effective Lagrangian for these decays in any perturbative model in which these processes proceed via one-loop contributions. We explicitly show that our results are finite and gauge independent, and provide Mathematica code that implements our results in an easily usable form.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Comparative transcriptomics of CAZy enzymes in white- and brown-rot agaricomycetes: Evolutionary insights into lignocellulose degradation and the relevance of GH16 glycoside hydrolase functional divergence

White-rot and brown-rot fungi (WRF and BRF, respectively) decompose lignocellulose, the main structural component of plant biomass, through distinct mechanisms. This study examines the transcriptomic responses of three WRF species (Pleurotus ostreatus, Phanerochaete chrysosporium, and Heterobasidion irregulare) and two BRF species (Fomitopsis schrenkii and Rhodonia placenta) grown on poplar wood (W) and glucose (G) as sole carbon sources. RNA-seq analysis revealed upregulation of carbohydrate-active enzymes (CAZymes) linked to lignocellulose degradation. WRF displayed a broader enzymatic repertoire, whereas BRF employed a more selective approach. Among these responses, GH16 glycoside hydrolases were consistently upregulated across all species, including BRF. Since GH16 enzymes are involved in both plant hemicellulose modification and cell wall remodeling, their wood-induced expression may reflect multiple processes rather than a single conserved wood-decay mechanism. Structural and phylogenetic analyses revealed species-specific divergence, consistent with potential functional specialization. These findings broaden our understanding of fungal enzymatic strategies and highlight GH16 enzymes as candidates for further study. Beyond the immediate context of wood decay, this work has broader implications for fungal ecology, evolutionary biology, and biotechnological applications such as biomass conversion and sustainable bioenergy.

Fungal ecological strategies↗

DOE OSTI2022

Study of alkaline carbonate cooling to mitigate Ex-Vessel molten corium accidents

To mitigate adverse effects from molten corium following a reactor pressure vessel failure (RPVF), some new reactor designs employ a core catcher and a sacrificial material (SM), such as ceramic or concrete, to stabilize the molten corium and avoid containment breach. Existing reactors cannot easily be modified to include these SMs but could be modified to allow injectable cooling materials. Current reactor designs are limited to using water to stabilize the corium, but this can create other issues such as reaction of water with the concrete forming hydrogen gas. Here the novel SM proposed is a granular carbonate mineral that can be used in existing light water reactor plants. The granular carbonate will decompose when exposed to heat, inducing an endothermic reaction to quickly solidify the corium in place and producing a mineral oxide and carbon dioxide. Corium spreading is a complex process strongly influenced by coupled chemical reactions, including decay heat from the corium, phase change, and reactions between the concrete containment and available water. A recently completed Sandia National Laboratories laboratory directed research and development (LDRD) project focused on two research areas: experiments to demonstrate the feasibility of the novel SM concept, and modeling activities to determine the potential applications of the concept to actual nuclear plants. Small-scale experiments using lead oxide (PbO) as a surrogate for molten corium demonstrate that the reaction of the SM with molten PbO results in a fast solidification of the melt due to the endothermic carbonate decomposition reaction and the formation of open pore structures in the solidified PbO from CO 2 released during the decomposition. A simplified carbonate decomposition model was developed to predict thermal decomposition of carbonate mineral in contact with corium. This model was incorporated into MELCOR, a severe accident nuclear reactor code. A full-plant MELCOR simulation suggests that by the introduction of SM to the reactor cavity prior to RPVF ex-vessel accident progression, e.g., core-concrete interaction and core spreading on the containment floor, could be delayed by at least 15 h; this may be enough for additional accident management to be implemented to alleviate the situation.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

DOE OSTI2023

Annihilation-gamma-based diagnostic techniques for magnetically confined electron–positron pair plasma

Efforts are underway to magnetically confine electron–positron pair plasmas to study their unique behaviour, which is characterized by significant changes in plasma time and length scales, supported waves and unstable modes. However, use of conventional plasma diagnostics presents challenges with these low-density and annihilating matter–antimatter plasmas. To address this problem, we propose to develop techniques based on the distinct emission provided by annihilation. This emission exhibits two spatial correlations: the distance attenuation of isotropic sources and the back-to-back propagation of momentum-preserving 2 $\gamma$ annihilation. We present the results of our analysis of the $\gamma$ emission rate and the spatial profile of the annihilation in a magnetized pair plasma from direct pair collisions, from the formation and decay of positronium as well as from transport processes. In order to demonstrate the effectiveness of annihilation-based techniques, we tested them on annular $\gamma$ emission profiles produced by a $\beta ^+$ radioisotope on a rotating turntable. Direct and positronium-mediated annihilation result in overlapping volumetric $\gamma$ sources, and the 2 $\gamma$ emission from these volumetric sources can be tomographically reconstructed from coincident counts in multiple detectors. Transport processes result in localized annihilation where field lines intersect walls, limiters or internal magnets. These localized sources can be identified by the fractional $\gamma$ counts on spatially distributed detectors.

Physics↗

DOE OSTI2022

Search for Majorana neutrinos exploiting millikelvin cryogenics with CUORE

The possibility that neutrinos may be their own antiparticles, unique among the known fundamental particles, arises from the symmetric theory of fermions proposed by Ettore Majorana in 1937. Given the profound consequences of such Majorana neutrinos, among which is a potential explanation for the matter–antimatter asymmetry of the universe via leptogenesis, the Majorana nature of neutrinos commands intense experimental scrutiny globally; one of the primary experimental probes is neutrinoless double beta (0νββ) decay. Here we show results from the search for 0νββ decay of 130 Te, using the latest advanced cryogenic calorimeters with the CUORE experiment3. CUORE, operating just 10 millikelvin above absolute zero, has pushed the state of the art on three frontiers: the sheer mass held at such ultralow temperatures, operational longevity, and the low levels of ionizing radiation emanating from the cryogenic infrastructure. We find no evidence for 0νββ decay and set a lower bound of the process half-life as 2.2 × 10 25 years at a 90 percent credibility interval. We discuss potential applications of the advances made with CUORE to other fields such as direct dark matter, neutrino and nuclear physics searches and large-scale quantum computing, which can benefit from sustained operation of large payloads in a low-radioactivity, ultralow-temperature cryogenic environment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

First-Principles insights into group-V impurities and their impact on germanium detector performance

The outstanding properties of high-purity germanium (HPGe) detectors, such as excellent energy resolution, high energy sensitivity, and a low background-to-signal ratio, make them essential and ideal candidates for detecting particle signatures in nuclear processes such as neutrino-less double beta decay (0νββ). However, the presence of defects and impurities in HPGe crystals can lead to charge trapping, which affects carrier mobility and results in significant energy resolution degradation. In this work, we employ density functional theory with a hybrid functional to study the energetics of possible point defects in Ge. Our findings indicate that group-V impurities form more readily in Ge compared to vacancy and interstitial of Ge. Unlike N dopants, which yield deep trap states, P, As, and Sb create shallow traps close to the conduction band edge of Ge. Furthermore, we predict that group-V defects can condense into defect complexes with Ge vacancies. These vacancy-impurity complexes form deep traps in Ge, similar to Ge vacancies, suggesting that both vacancies and vacancy-impurity complexes contribute to charge trapping in these detectors, thereby diminishing their performance.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Detection efficiency measurement and operational tests of the X-Arapuca for the first module of DUNE far detector

The Deep Underground Neutrino Experiment (DUNE) is a dual-site experiment for long-baseline neutrino oscillation studies, able to resolve the neutrino mass hierarchy and measure δ$_{CP}$. DUNE will also have sensitivity to supernova neutrinos and to processes beyond the Standard Model, such as nucleon decay searches. The Far Detector (FD) will consist of four liquid argon TPC (17.5 kt total mass) with systems for the detection of charge and scintillation light produced by an ionization event. The charge detection system permits both calorimetry and position determination. In addition, the photon-detection system (PDS) enhances the detector capabilities for all DUNE physics drivers. The PDS of the first FD module consists of light collector modules placed in the inactive space between the innermost wire planes of the TPC anode. The light collectors, the so-called X-ARAPUCAS, are functionally a light trap that captures wavelength-shifted photons inside boxes with highly reflective internal surfaces where they are guided to Silicon Photo-multipliers (SiPM) by wavelength-shifting (WLS) bars. Functionality and operational tests of the X-ARAPUCAS to be installed in ProtoDUNE-SP phase II (FD DUNE prototype at the scale 1:20), as well as the measurement of their absolute detection efficiency is reported in this publication.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

The impact of r -process heating on the dynamics of neutron star merger accretion disc winds and their electromagnetic radiation

Neutron star merger accretion discs can launch neutron-rich winds of >10 -2 M⊙. This ejecta is a prime site for r-process nucleosynthesis, which will produce a range of radioactive heavy nuclei. The decay of these nuclei releases enough energy to accelerate portions of the wind by ~0.1c. Here, we investigate the effect of r-process heating on the dynamical evolution of disc winds. We extract the wind from a 3D general relativistic magnetohydrodynamic simulation of a disc from a post-merger system. This is used to create inner boundary conditions for 2D hydrodynamic simulations that continue the original 3D simulation. We perform two such simulations: one that includes the r-process heating, and another one that does not. We follow the hydrodynamic simulations until the winds reach homology (60 s). Using time-dependent multifrequency multidimensional Monte Carlo radiation transport simulations, we then calculate the kilonova light curves from the winds with and without dynamical r-process heating. We find that the r-process heating can substantially alter the velocity distribution of the wind, shifting the mass-weighted median velocity from 0.06c to 0.12c. The inclusion of the dynamical r-process heating makes the light curve brighter and bluer at $\sim 1\, \mathrm{d}$ post-merger. However, the high-velocity tail of the ejecta distribution and the early ($\lesssim 1\, \mathrm{d}$) light curves are largely unaffected.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

First Constraints on the Photon Coupling of Axionlike Particles from Multimessenger Studies of the Neutron Star Merger GW170817

We use multimessenger observations of the neutron star merger event GW170817 to derive new constraints on axionlike particles (ALPs) coupling to photons. ALPs are produced via Primakoff and photon coalescence processes in the merger, escape the remnant, and decay back into two photons, giving rise to a photon signal approximately along the line of sight to the merger. We analyze the spectral and temporal information of the ALP-induced photon signal and use the Fermi Large Area Telescope (Fermi-LAT) observations of GW170817 to derive our new ALP constraints. We also show the improved prospects with future MeV 𝛾-ray missions, taking the spectral and temporal coverage of Fermi-LAT as an example.

Physics↗

DOE OSTI2025

𝐵 → 𝜌⁢ℓ⁢$\bar{v}$ Resonance Form Factors from 𝐵→ 𝜋⁢𝜋⁢ℓ⁢$\bar{v}$ in Lattice QCD

The decay 𝐵 → 𝜌⁢ℓ⁢$\bar{v}$ is an attractive process for determining the magnitude of the smallest Cabibbo-Kobayashi-Maskawa matrix element, |𝑉 𝑢⁢𝑏 |, and can provide new insights into the origin of the long-standing exclusive-inclusive discrepancy in determinations of this standard-model parameter. This requires a nonperturbative QCD calculation of the 𝐵 → 𝜌 form factors 𝑉, 𝐴 0 , 𝐴 1 , and 𝐴 12 . The unstable nature of the 𝜌 resonance has prevented precise lattice QCD calculations of these form factors to date. Here, we present the first lattice QCD calculation of the 𝐵 → 𝜌 form factors in which the 𝜌 is treated properly as a resonance in 𝑃-wave 𝜋⁢𝜋 scattering. To this end, we use the Lellouch-Lüscher finite-volume formalism to compute the 𝐵 → 𝜋⁢𝜋 form factors as a function of both momentum transfer and 𝜋⁢𝜋 invariant mass, and then analytically continue to the 𝜌 resonance pole. This calculation is performed with 2 + 1 dynamical quark flavors at a pion mass of approximately 320 MeV, and demonstrates a clear path toward results at the physical point.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Precision measurement of the neutral pion lifetime

The explicit breaking of the axial symmetry by quantum fluctuations gives rise to the so-called axial anomaly. This phenomenon is solely responsible for the decay of the neutral pion π0 into two photons (γγ), leading to its unusually short lifetime. Here, we precisely measured the decay width Γ of the π 0 → γγ process. The differential cross sections for π0 photoproduction at forward angles were measured on two targets, carbon-12 and silicon-28, yielding Γ(π 0 → γγ)=7.798±0.056(stat.)±0.109(syst.) eV, where stat. denotes the statistical uncertainty and syst. the systematic uncertainty. We combined the results of this and an earlier experiment to generate a weighted average of Γ(π 0 → γγ)=7.802±0.052(stat.)±0.105(syst.) eV. Our final result has a total uncertainty of 1.50% and confirms the prediction based on the chiral anomaly in quantum chromodynamics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2021

Bulk viscosity from Urca processes: npeμ matter in the neutrino-trapped regime

In this work, we extend our previous study of the bulk viscosity of hot and dense npe matter induced by the Urca process in the neutrino trapped regime to npeμ matter by adding the muonic Urca processes as well as the purely leptonic electroweak processes involving electron-muon transition. Here, the nuclear matter is modeled in a relativistic density functional approach with two different parametrizations which predict neutrino dominated matter (DDME2 model) and anti-neutrino dominated matter (NL3 model) at temperatures for which neutrinos/anti-neutrinos are trapped. In the case of neutrino-dominated matter, the main equilibration mechanism is lepton capture, whereas in the case of antineutrino-dominated matter this is due to neutron decay. We find that the equilibration rates of Urca processes are higher than that of the pure leptonic processes, which implies that the Urca bulk viscosity can be computed with the leptonic reactions assumed to be frozen. We find that the bulk viscosity decreases with temperature as ζ~T –2 at moderate temperatures. At high temperatures this scaling breaks down by sharp drops of the bulk viscosity close to the temperature where the proton fraction is density-independent and the matter becomes scale-invariant. This occurs also when the matter undergoes a transition from the antineutrino-dominated regime to the neutrino-dominated regime where the bulk viscosity attains a local maximum. We also estimate the bulk viscous dissipation timescales and find that these are in the range ≳ 1 s for temperatures above the neutrino trapping temperature. These timescales would be relevant only for long-lived objects formed in binary neutron star mergers and hot proto-neutron stars formed in core-collapse supernovas.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Search for η c ( 2 S ) → ω ω and ω ϕ and measurements of χ c J → ω ω and ω ϕ in ψ ( 2 S ) radiative processes

Using ( 2712 ± 14 ) × 10 6 ψ ( 2 S ) events collected with the BESIII detector at the BEPCII collider, we search for the decays η c ( 2 S ) → ω ω and η c ( 2 S ) → ω ϕ via the process ψ ( 2 S ) → γ η c ( 2 S ) . No statistically significant signals are observed. The upper limits of their product branching fractions at the 90% confidence level are determined to be B ( ψ ( 2 S ) → γ η c ( 2 S ) , η c ( 2 S ) → ω ω ) < 1.04 × 10 − 6 and B ( ψ ( 2 S ) → γ η c ( 2 S ) , η c ( 2 S ) → ω ϕ ) < 1.85 × 10 − 7 , respectively. We also update the branching fractions of χ c J → ω ω and χ c J → ω ϕ via the ψ ( 2 S ) → γ χ c J transition. Their branching fractions are determined to be B ( χ c 0 → ω ω ) = ( 10.66 ± 0.11 ± 0.57 ) × 10 − 4 , B ( χ c 1 → ω ω ) = ( 6.43 ± 0.07 ± 0.31 ) × 10 − 4 , B ( χ c 2 → ω ω ) = ( 8.75 ± 0.08 ± 0.42 ) × 10 − 4 , B ( χ c 0 → ω ϕ ) = ( 1.18 ± 0.03 ± 0.07 ) × 10 − 4 , B ( χ c 1 → ω ϕ ) = ( 2.04 ± 0.15 ± 0.11 ) × 10 − 5 , and B ( χ c 2 → ω ϕ ) = ( 9.58 ± 1.07 ± 0.76 ) × 10 − 6 , where the first uncertainties are statistical and the second are systematic. Published by the American Physical Society 2025

Ablikim, M.↗

DOE OSTI2023

Measurement of two-photon decay width of χ c2 (1 P ) in γγ → χ c2 (1 P ) → J/ψγ at Belle

We report the measurement of the two-photon decay width of χ c2 (1P) in two-photon processes at the Belle experiment. We analyze the process γγ → χ c2 (1P) → J/ψγ, J/ψ → ℓ + ℓ - (ℓ = e or μ) using a data sample of 971 fb -1 collected with the Belle detector at the KEKB e + e - collider. In this analysis, the product of the two-photon decay width of χ c2 (1P) and the branching fraction is determined to be ${\Gamma}_{\gamma \gamma}({\chi}_{c2}(1P))\mathcal{B}({\chi}_{c2}(1P)\to J/\psi \gamma) \mathcal{B} (J/\psi \to {\ell}^{+}{\ell}^{-})=$ 14.8 ± 0.3(stat.) ± 0.7(syst.) eV, which corresponds to Γ γγ (χ c2 (1P)) = 653 ± 13(stat.) ± 31(syst.) ± 17(B.R.) eV, where the third uncertainty is from $\mathcal{B}$ (χ c2 (1P) → J/ψγ) and $\mathcal{B}$ (J/ψ → ℓ + ℓ - ).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗