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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2020

Constraints on the $\chi_\mathrm{c1}$ versus $\chi_\mathrm{c2}$ Polarizations in Proton-Proton Collisions at $\sqrt{s} =$ 8 TeV

The polarizations of promptly produced χc1 and χc2 mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at s=8 TeV. The χc states are reconstructed via their radiative decays χc→J/ψγ, with the photons being measured through conversions to e+e−, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χc2 to χc1 yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ→μ+μ- decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Absence of Low-Energy Shape Coexistence in 80 Ge: The Nonobservation of a Proposed Excited 0 2 + Level at 639 keV

The 80 Ge structure was investigated in a high-statistics β-decay experiment of 80 Ga using the GRIFFIN spectrometer at TRIUMF-ISAC through γ, β-e, e-γ and γ-γ spectroscopy. No evidence was found for the recently reported 0 2 + 639-keV level suggested as evidence for low-energy shape coexistence in 80Ge. Large-scale shell model calculations performed in 78,80,82 Ge place the 0 2 + level in 80 Ge at 2 MeV. The new experimental evidence combined with shell model predictions indicate that low-energy shape coexistence is not present in 80 Ge.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Laboratory Resolved Structure of Supercritical Perpendicular Shocks

Supermagnetosonic perpendicular flows are magnetically driven by a large radius theta-pinch experiment. Fine spatial resolution and macroscopic coverage allow the full structure of the plasma-piston coupling to be resolved in laboratory experiment for the first time. Here, a moving ambipolar potential is observed to reflect unmagnetized ions to twice the piston speed. Magnetized electrons balance the radial potential via Hall currents and generate signature quadrupolar magnetic fields. Electron heating in the reflected ion foot is adiabatic.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2022

Nonideal Fields Solve the Injection Problem in Relativistic Reconnection

Magnetic reconnection in relativistic plasmas is well established as a fast and efficient particle accelerator, capable of explaining the most dramatic astrophysical flares. With particle-in-cell simulations, we demonstrate the importance of nonideal fields for the early stages (“injection”) of particle acceleration. Most of the particles ending up with high energies (near or above the mean magnetic energy per particle) must have passed through nonideal regions where the assumptions of ideal magnetohydrodynamics are broken (i.e., regions with E > B or nonzero E ∥ = E ∙ B/B), whereas most of the particles that do not experience nonideal fields end up with Lorentz factors of order unity. So, injection by nonideal fields is a necessary prerequisite for further acceleration. Our results have important implications for the origin of nonthermal particles in high-energy astrophysical sources.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

Search for a Dark Photon and an Invisible Dark Higgs Boson in $μ^+ μ^–$ and Missing Energy Final States with the Belle II Experiment

The dark photon $\textit{A'}$ and the dark Higgs boson $\textit{h'}$ are hypothetical particles predicted in many dark sector models. We search for the simultaneous production of A' and h' in the dark Higgsstrahlung process $e^+e^– → A' h'$ with $A' → μ^+μ^–$ and $\textit{h'}$ invisible in electron-positron collisions at a center-of- mass energy of 10.58 GeV in data collected by the Belle II experiment in 2019. With an integrated luminosity of 8.34 fb –1 , we observe no evidence for signal. We obtain exclusion limits at 90% Bayesian credibility in the range of 1.7-5.0 fb on the cross section and in the range of 1.7 × 10 –8 -200 × 10 –8 on the effective coupling $ε^2 × α_D$ for the $\textit{A'}$ mass in the range of 4.0 GeV/$c^2 < M_{A'}$ < 9.7 GeV/$c^2$ and for the $\textit{h'}$ mass $M_{h'} < M_{A'}$, where $\textit{ε}$ is the mixing strength between the standard model and the dark photon and $α_D$ is the coupling of the dark photon to the dark Higgs boson. Our limits are the first in this mass range. Phtysuc

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for an Invisible Z ' in a Final State with Two Muons and Missing Energy at Belle II

The $L_μ – L_τ$ extension of the standard model predicts the existence of a lepton-flavor-universality-violating Z' boson that couples only to the heavier lepton families. We search for such a Z' through its invisible decay in the process $e^+e^– → μ^+μ^–$Z'. We use a sample of electron-positron collisions at a center- of-mass energy of 10.58 GeV collected by the Belle II experiment in 2019-2020, corresponding to an integrated luminosity of 79.7 fb –1 . We find no excess over the expected standard-model background. We set 90%-confidence-level upper limits on the cross section for this process as well as on the coupling of the model, which ranges from 3 × 10 –3 at low Z' masses to 1 at Z' masses of 8 GeV=$c^2$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Evidence for Modification of $b$ Quark Hadronization in High-Multiplicity $pp$ Collisions at $\sqrt{s}$ = 13 TeV

The production rate of $B^{0}_{s}$ mesons relative to $B^0$ mesons is measured by the LHCb experiment in $pp$ collisions at a center-of-mass energy $\sqrt{s}$ = 13 TeV over the forward rapidity interval 2 < $y$ < 4.5 as a function of the charged particle multiplicity measured in the event. Evidence at the 3.4$σ$ level is found for an increase of the ratio of $B^{0}_{s}$ to $B^0$ cross sections with multiplicity at transverse momenta below 6 GeV /$c$, with no significant multiplicity dependence at higher transverse momentum. Comparison with data from $e^+$ $e^–$ collisions implies that the density of the hadronic medium may affect the production rates of $B$ mesons. This is qualitatively consistent with the emergence of quark coalescence as an additional hadronization mechanism in high-multiplicity collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Search for a τ + τ - Resonance in e + e - → μ + μ - τ + τ - Events with the Belle II Experiment

We report the first search for a nonstandard-model resonance decaying into $τ$ pairs in $e^+e^-$ → $μ^+μ^-τ^+τ^-$ events in the 3.6–10 GeV/c 2 mass range. We use a 62.8 fb -1 sample of $e^+e^-$ collisions collected at a center-of-mass energy of 10.58 GeV by the Belle II experiment at the SuperKEKB collider. The analysis probes three different models predicting a spin-1 particle coupling only to the heavier lepton families, a Higgs-like spin-0 particle that couples preferentially to charged leptons (leptophilic scalar), and an axionlike particle, respectively. We observe no evidence for a signal and set exclusion limits at 90% confidence level on the product of cross section and branching fraction into $τ$ pairs, ranging from 0.7 to 24 fb, and on the couplings of these processes. We obtain world-leading constraints on the couplings for the leptophilic scalar model for masses above 6.5 GeV/c 2 and for the axionlike particle model over the entire mass range.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Precise Measurement of the D s + Lifetime at Belle II

We measure the lifetime of the $D^+_s$ meson using a data sample of 207 fb -1 collected by the Belle II experiment running at the SuperKEKB asymmetric-energy e + e - collider. The lifetime is determined by fitting the decay-time distribution of a sample of 116 × 10 3 $D^+_s$ → φπ + decays. Our result is τ$D^+_s$ = (499.5 ± 1.7 ± 0.9) fs, where the first uncertainty is statistical and the second is systematic. This result is significantly more precise than previous measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Enhanced Production of Λ b 0 Baryons in High-Multiplicity p p Collisions at s = 13 TeV

The production rate of Λ b 0 baryons relative to B 0 mesons in p p collisions at a center-of-mass energy s = 13 TeV is measured by the LHCb experiment. The ratio of Λ b 0 to B 0 production cross sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in e + e − collisions, and increases by a factor of ∼ 2 with increasing multiplicity. At relatively low transverse momentum, the ratio of Λ b 0 to B 0 cross sections is higher than what is measured in e + e − collisions, but converges with the e + e − ratio as the momentum increases. These results imply that the evolution of heavy b quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with several models and implications for the mechanisms enforcing quark confinement are discussed. © 2024 CERN, for the LHCb Collaboration 2024 CERN

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

Observation of Significant Flavor-SU(3) Breaking in the Kaon Wave Function at 12 < Q 2 < 25 GeV 2 and Discovery of the Charmless Decay ψ ( 3770 ) → K S 0 K L 0

We present cross sections for the reaction e + e − → K S 0 K L 0 at center-of-mass energies ranging from 3.51 to 4.95 GeV using data samples collected in the BESIII experiment, corresponding to a total integrated luminosity of 26.5 fb − 1 . The ratio of neutral-to-charged kaon form factors at large momentum transfers ( 12 < Q 2 < 25 GeV 2 ) is determined to be 0.21 ± 0.01 , which indicates a small but significant effect of flavor-SU(3) breaking in the kaon wave function, and, consequently, excludes the possibility that flavor-SU(3) breaking is the primary reason for the strong experimental violation of the pQCD prediction | F ( π ± ) | / | F ( K ± ) | = f π 2 / f K 2 , where F ( π ± ) and F ( K ± ) are the form factors, and f π and f K are the decay constants of charged pions and kaons, respectively. We also observe a significant signal for the charmless decay ψ ( 3770 ) → K S 0 K L 0 for the first time. Within a 1 σ contour of the likelihood value, the branching fraction for ψ ( 3770 ) → K S 0 K L 0 is determined to be B = ( 2.6 3 − 1.59 + 1.40 ) × 10 − 5 , and the relative phase between the continuum and ψ ( 3770 ) amplitudes is ϕ = ( − 0.3 9 − 0.10 + 0.05 ) π . The branching fraction is in good agreement with the S - and D -wave charmonia mixing scheme proposed in the interpretation of the “ ρ π puzzle” between J / ψ and ψ ( 3686 ) decays. Published by the American Physical Society 2024

Physics↗

DOE OSTI2024

Magnetic Dipole Transition in Ca 48

Here, the magnetic dipole transition strength B(M1) of 48 Ca is dominated by a single resonant state at an excitation energy of 10.23 MeV. Experiments disagree about B(M1) and this impacts our understanding of spin flips in nuclei. We performed ab initio computations based on chiral effective field theory and found that B(M1 : 0 + → 1 + ) lies in the range from 7.0 to 10.2 $µ^2_N$. This is consistent with a (γ, n) experiment but larger than results from (e, e') and (p, p') scattering. Two body currents yield no quenching of the B(M1) strength and continuum effects reduce it by about 10%. For a validation of our approach, we computed magnetic moments in 47,49 Ca and performed benchmark calculations in light nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Constraints on Covariant Dark-Matter–Nucleon Effective Field Theory Interactions from the First Science Run of the LUX-ZEPLIN Experiment

The LUX-ZEPLIN (LZ) experiment is a dual-phase xenon time project chamber operating in the Sanford Underground Research Facility in South Dakota, USA. We report on the results of a relativistic extension to the nonrelativistic effective field theory (NREFT) from a 5.5 t fiducial mass and 60 live days of exposure. We present constraints on couplings from covariant interactions arising from the coupling of vector, axial currents, and electric dipole moments of the nucleon to the magnetic and electric dipole moments of the weakly interacting massive particle which cannot be described by recasting previous results described by an NREFT. Using a profile-likelihood ratio analysis, in an energy region between 0 keV nr to 270 keV nr , we report 90% confidence level exclusion limits on the coupling strength of five interactions in both the isoscalar and isovector bases. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Test of Lepton Flavor Universality with B s 0 → ϕ ℓ + ℓ − Decays

Lepton flavor universality in rare b → s transitions is tested for the first time using B s 0 meson decays. The measurements are performed using p p collision data collected by the LHCb experiment between 2011 and 2018, corresponding to a total integrated luminosity of 9 fb − 1 . Branching fraction ratios between the B s 0 → ϕ e + e − and B s 0 → ϕ μ + μ − decays are measured in three regions of dilepton mass squared, q 2 , with 0.1 < q 2 < 1.1 , 1.1 < q 2 < 6.0 , and 15 < q 2 < 19 GeV 2 / c 4 . The results agree with the standard model expectation of lepton flavor universality. © 2025 CERN, for the LHCb Collaboration 2025 CERN

Aaij, R. (ORCID:0000000305331952)↗

DOE OSTI2025

Test of Lepton Flavor Universality with B + → K + π + π − ℓ + ℓ − Decays

The first test of lepton flavor universality between muons and electrons using B + → K + π + π − ℓ + ℓ − ( ℓ = e , μ ) decays is presented. The measurement is performed with data from proton-proton collisions collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb − 1 . The ratio of branching fractions between B + → K + π + π − e + e − and B + → K + π + π − μ + μ − decays is measured in the dilepton invariant-mass-squared range 1.1 < q 2 < 7.0 GeV 2 / c 4 and is found to be R K π π − 1 = 1.3 1 − 0.17 + 0.18 ( stat ) − 0.09 + 0.12 ( syst ) , in agreement with the standard model prediction. The first observation of the B + → K + π + π − e + e − decay is also reported. © 2025 CERN, for the LHCb Collaboration 2025 CERN

Aaij, R. (ORCID:0000000305331952)↗

DOE OSTI2025

Observation of the W -Annihilation Process D s + → ω ρ + and Measurement of D s + → ϕ ρ + in D s + → π + π + π − π 0 π 0 Decays

We present the first amplitude analysis and branching fraction measurement of the decay D s + → π + π + π − π 0 π 0 , using e + e − collision data collected with the BESIII detector at center-of-mass energies between 4.128 and 4.226 GeV corresponding to an integrated luminosity of 7.33 fb − 1 , and report the first observation of the pure W -annihilation decay D s + → ω ρ + with a branching fraction of ( 0.99 ± 0.0 8 stat − 0.07 + 0.05 syst ) % . In comparison to the low significance of the D wave in the decay D s + → ϕ ρ + , the dominance of the D wave over the S and P waves, with a fraction of ( 51.85 ± 7.2 8 stat − 7.90 + 4.83 syst ) % observed in the decay D s + → ω ρ + , provides crucial information for the “polarization puzzle,” as well as for the understanding of charm meson decays. The branching fraction of D s + → π + π + π − π 0 π 0 is measured to be ( 4.41 ± 0.1 5 stat ± 0.1 3 syst ) % . Moreover, the branching fraction of D s + → ϕ ρ + is measured to be ( 3.98 ± 0.3 3 stat − 0.19 + 0.21 syst ) % , and the R ϕ = B ( ϕ → π + π − π 0 ) / B ( ϕ → K + K − ) is determined to be ( 0.222 ± 0.01 9 stat − 0.016 + 0.016 syst ), which is consistent with the previous measurement based on charm meson decays, but deviates from the results from e + e − annihilation and K − N scattering experiments by more than 3 σ . Published by the American Physical Society 2025

Ablikim, M.↗

DOE OSTI2025

First Measurement of Near-Threshold and Subthreshold 𝐽/𝜓 Photoproduction off Nuclei

We report on the first measurement of J/ψ photoproduction from nuclei in the photon energy range of 7 to 10.8 GeV, extending above and below the photoproduction threshold in the free proton of ∼ 8.2 GeV. The experiment used a tagged photon beam incident on deuterium, helium, and carbon, and the GlueX detector at Jefferson Lab to measure the semi-inclusive A(γ, e + e − p) reaction with a dilepton invariant mass M(e + e − ) ∼ m J/ψ = 3.1 GeV. The incoherent J/ψ photoproduction cross sections in the measured nuclei are extracted as a function of the incident photon energy, momentum transfer, and proton reconstructed missing light-cone momentum fraction. Comparisons with theoretical predictions assuming a dipole form factor allow extracting a gluonic radius for bound protons of p $\sqrt4⟨r^2⟩$ = 0.85 ± 0.14 fm. The data also suggest an excess of the measured cross section for sub-threshold production and for interactions with high missing light-cone momentum fraction protons. The measured enhancement can be explained by modified gluon structure for high-virtuality bound-protons.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Physical properties and electronic structure of single-crystal KCo 2 As 2

We present a method for producing high quality KCo 2 As 2 crystals, stable in air and suitable for a variety of measurements. X-ray diffraction, magnetic susceptibility, electrical transport and heat capacity measurements confirm the high quality and an absence of long range magnetic order down to at least 2 K. Residual resistivity values approaching 0.25 µΩ cm are representative of the high quality and low impurity scattering, and a Sommerfeld coefficient γ = 7.3 mJ/mol K 2 signifies weaker correlations than the Fe-based counterparts. Together with Hall effect measurements, angle-resolved photoemission experiments reveal a Fermi surface consisting of electron pockets at the center and corner of the Brillouin zone, in line with theoretical predictions and in contrast to the mixed carrier types of other pnictides with the ThCr 2 Si 2 structure. A large, linear magnetoresistance of 200% at 14 T, together with an observed linear and hyperbolic, rather than parabolic, band dispersions are unusual characteristics of this compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗