Recent lbnl_ps items

Beyond traditional emission-line diagnostics: Using autoencoders to uncover active galactic nuclei in DESI spectra

Tue, 20 Oct 2026 00:00:00 +0000

Context. The growing volume of spectroscopic data in modern surveys motivates the development of data-driven approaches that complement traditional emission-line diagnostics for the identification of active galactic nuclei (AGNs). Aims. We develop and validate a machine-learning (ML) framework for galaxy and AGN classification that exploits the full optical spectrum, using unsupervised learning to capture spectral features within a semi-supervised classification framework that complements classical approaches. Methods. We adapted the SPENDER autoencoder architecture to compress galaxy spectra obtained with the Dark Energy Spectroscopic Instrument (DESI) into a low-dimensional latent space that encodes physically meaningful label-agnostic information. We introduced a quantitative classification method via a k-d tree nearest-neighbor search in latent space. The model was trained on 50 222 spectra from the DESI main survey, corresponding to the internal Guadalupe dataset, released...

Baryon fraction from the BAO amplitude: A consistent approach to parametrizing perturbation growth

Tue, 20 Oct 2026 00:00:00 +0000

Galaxy clustering constrains the baryon fraction Ωb/Ωm through the amplitude of baryon acoustic oscillations and the suppression of perturbations entering the horizon before recombination. This produces a different prerecombination distribution of baryons and dark matter. After recombination, the gravitational potential responds to both components in proportion to their mass, allowing robust measurement of the baryon fraction. This is independent of new-physics scenarios altering the recombination background (e.g. early dark energy). The accuracy of such measurements does, however, depend on how baryons and cold dark matter (CDM) are modeled in the power spectrum. Previous template-based splitting relied on approximate transfer functions that neglected part of information. We present a new method that embeds an extra parameter controlling the balance between baryons and dark matter in the growth terms of the perturbation equations in the camb Boltzmann solver. This approach captures...

Baryon Acoustic Oscillations from the C iv Forest with DESI DR2

Tue, 20 Oct 2026 00:00:00 +0000

We present a measurement of baryon acoustic oscillations (BAO) in the cross correlation of triply ionized carbon (C iv) absorption with the positions of quasars (QSO) and emission-line galaxies (ELGs). We use quasars and ELGs from the second data release (DR2) of the Dark Energy Spectroscopic Instrument survey. Our data sample consists of 2.5 million quasars, 3.1 million ELGs, and the C iv absorption is measured along the line of sight of 1.5 million high-redshift quasars with z > 1.3. We measure the isotropic BAO signal at 4.2σ for the C IV×QSO cross correlation. This translates into a 3.0% precision measurement of the ratio of the isotropic distance scale, DV, and the sound horizon at the drag epoch, rd, with DV/rd(zeff = 1.92) = 30.3 ± 0.9. We make the first detection of the BAO feature in the C IV×ELG cross-correlation at a significance of 2.5σ and find DV/rd(zeff = 1.47) = 24.6 ± 1.0.

Anisotropic flow of light (anti-)(hyper-)nuclei in Pb+Pb collision at s N N = 5.36 TeV

Tue, 20 Oct 2026 00:00:00 +0000

Using the coalescence model with nucleon and Lambda phase-space distributions generated by the hybrid MUSIC framework, we study the elliptic flow (v 2) and triangular flow (v 3) of (anti-)protons, (anti-)deuterons, (anti-)3He, and Λ 3 H in Pb+Pb collisions at s N N = 5.36 TeV. We find that the simple v 2 scaling with the number of constituent nucleons A breaks down at high transverse momentum pT /A > 1.5 GeV/c, while an improved scaling relation holds well up to pT /A ≈ 3 GeV/c. In contrast, v 3 exhibits similar behavior under both scaling prescriptions, with no significant difference. We also make predictions for v 2 and v 3 of the hypertriton and find these flows are insensitive to the Lambda-deuteron ( Λ − d ) distance inside the hypertriton. Our results are compared with preliminary experimental measurements by the ALICE Collaboration and offer insight into the production mechanisms of light (anti-)(hyper-)nuclei in high-energy heavy-ion collisions.

A New Record Census of Dwarf AGN and a Bimodal MBH − M⋆ Scaling Relation with DESI DR1

Mon, 19 Oct 2026 00:00:00 +0000

Using the first spectroscopic data release from the Dark Energy Spectroscopic Instrument (DESI DR1), we conduct the largest systematic search for active galactic nuclei (AGN) signatures in ≈1.7 million low-redshift (0.001 ≤ z ≤ 0.45) line-emitting galaxies. Based on the [N ii]/Hα versus [O iii]/Hβ emission-line ratio diagnostic, we identify AGN in 314,245/1,211,573 (25.9%) high-mass ( log(M⋆/M⊙)>9.5 ) and 9648/467,214 (2.1%) dwarf ( log(M⋆/M⊙)≤9.5 ) galaxies. The AGN fraction in line-emitting galaxies increases monotonically with stellar mass, from ∼1.4% at the low-mass end to ∼93.3% at the high-mass end. Among these AGN, 17,949 exhibit broad Hα emission (BL-AGN), which we use to estimate their black hole (BH) masses via single-epoch virial methods. Leveraging this large BL-AGN sample, we extend the MBH − M⋆ scaling relation down to log(M⋆/M⊙)≈7.8 and log(MBH/M⊙)≈4.4 . We find a bimodal distribution of galaxies in this space, characterized by two distinct empirical relations....

A multi-language auto-differentiation module and its application to a parallel particle-in-cell code on distributed computers

Mon, 19 Oct 2026 00:00:00 +0000

The auto differentiable simulation is a type of simulation that outputs of the simulation include not only the simulation result itself, but also their derivatives with respect to various input parameters. It provides an efficient method to study sensitivity of the simulation results with respect to the input parameters. Furthermore, it can be used in gradient based optimization methods for rapidly optimizing design parameters. In this paper, we present the development of a fast and transparent auto-differentiation module/class designed for easy integration into numerous simulation codes. As an application, this auto-differentiation module is integrated into a parallel particle-in-cell code with message passing interface (MPI) on distributed memory computers.

Observation of a Bc*+ Meson with the ATLAS Detector

Tue, 13 Oct 2026 00:00:00 +0000

The first observation of a new meson state decaying into and a photon is presented using a dataset of collisions at a center-of-mass energy collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of . The mesons are reconstructed from a three-muon final state from decays, along with photons reconstructed via conversions to electron-positron pairs in the detector material. The new state is observed with a significance that exceeds 8 standard deviations. The mass difference between the new meson state and the ground-state meson is measured to be . This corresponds to a mass for the observed state of , where the last uncertainty is due to the precision of the best knowledge of the meson mass. The low mass difference value matches the theory expectations for the lowest vector state of the system, the meson.

Search for anomalies in vector-boson fusion production of the Higgs boson in H(→ γγ)jj events using 164 fb−1 of pp collision data collected at s=13.6 TeV with the ATLAS detector

Tue, 13 Oct 2026 00:00:00 +0000

This article details two studies of Higgs boson properties using the vector-boson fusion production mode and the γγjj final state. Both efforts are based on a data sample corresponding to 164 fb−1 of s=13.6$$ \sqrt{s}=13.6 $$ TeV proton-proton collisions recorded by the ATLAS experiment at the Large Hadron Collider. The first study employs matrix-element-based optimal observables to constrain CP-odd couplings beyond the Standard Model within the Standard Model Effective Field Theory framework, expressed in the Warsaw basis. The second study exploits angular distributions to probe the Higgs boson’s couplings to longitudinally and transversely polarised W and Z bosons in the production of the Higgs boson. To maximise the sensitivity, the constraints of the CP-odd couplings are combined with those from a previous analysis performed in γγjj events in a data sample of proton-proton collisions at s=13$$ \sqrt{s}=13 $$ TeV, corresponding to an integrated luminosity of 140 fb−1. A significant...

Combination of ATLAS and CMS Searches for Higgs Boson Pair Production at s=13 TeV

Tue, 13 Oct 2026 00:00:00 +0000

This Letter presents a combination of searches for Higgs boson pair ( ) production performed by the ATLAS and CMS Collaborations using proton-proton collision datasets recorded at during the Large Hadron Collider Run 2, corresponding to integrated luminosities ranging between 126 and . The upper limit at the 95% confidence level on the total signal strength, defined as the ratio of the measured cross section to the standard model (SM) prediction, corresponds to 2.5, with an expected value of 1.7 (2.8) assuming the absence (presence) of the SM signal. The strength of the signal is measured to be relative to the SM prediction. The observed significance is found to be 1.1 standard deviations whereas 1.3 are expected for the SM signal. Constraints are set on the Higgs boson trilinear self-coupling and on the couplings of two Higgs bosons to two vector bosons, both normalized to the SM predictions and denoted as and , respectively. The observed individual constraints at the...

Measurement of coincident photon-initiated processes in ultra-peripheral Pb+Pb collisions with the ATLAS detector

Tue, 13 Oct 2026 00:00:00 +0000

The Lorentz-contracted electromagnetic fields of the ions in ultra-relativistic heavy-ion collisions generate intense quasi-real photon fluxes. These lead to photon-induced interactions that are observed in ultra-peripheral collisions (UPCs), such as vector meson and lepton-pair production. The high photon flux also enables the occurrence of multiple photon-induced processes in a single collision. Presented is the first measurement of the coincident production of γ γ → μ + μ − and γ + A → ρ 0 + A in UPC Pb+Pb collisions at centre-of-mass energies of 5.02 TeV and 5.36 TeV with the ATLAS detector at the Large Hadron Collider. The coincident ρ 0 is identified via its decay into a π + π − pair, with the selected π + π − sample also containing the non-resonant continuum contribution. The rate of the coincident process relative to the exclusive γ γ → μ + μ − process is measured differentially in intervals of forward event activity, quantified by the Zero Degree Calorimeters. The relative...

Development of a time-of-flight, decay and position-sensitive detector for FIONA

Tue, 6 Oct 2026 00:00:00 +0000

A decay and timing detector for superheavy elements has been developed at Lawrence Berkeley National Laboratory with the goal to become the main measurement detector of FIONA. It combines a double-sided silicon strip detector that provides decay energy and position information with a microchannel plate detector which determines the implantation time of the nuclei on the detector through the detection of secondary electrons emitted from the silicon detector upon impact. This new setup was simulated, constructed and tested offline, in a proof-of-principle setup using a beam of 216Po + , the results of which are presented in this work. The new detector provides, for the first time in FIONA, sensitivity to isotopes beyond α emitters (and fissioning isotopes) and decay time information.

FastPM: a new scheme for fast simulations of dark matter and haloes

Fri, 2 Oct 2026 00:00:00 +0000

We introduce FastPM, a highly scalable approximated particle mesh (PM) N-body solver, which implements the PM scheme enforcing correct linear displacement (1LPT) evolution via modified kick and drift factors. Employing a two-dimensional domain decomposing scheme, FastPM scales extremely well with a very large number of CPUs. In contrast to Comoving-Lagrangian (COLA) approach, we do not require to split the force or track separately the 2LPT solution, reducing the code complexity and memory requirements. We compare FastPM with different number of steps (Ns) and force resolution factor (B) against three benchmarks: halo mass function from friends-of-friends halo finder; halo and dark matter power spectrum; and cross-correlation coefficient (or stochasticity), relative to a high-resolution TreePM simulation. We show that the modified time stepping scheme reduces the halo stochasticity when compared to COLA with the same number of steps and force resolution. While increasing Ns and...

Constraining the astrophysical i process: The Kr87(n,γ)Kr88 reaction rate

Thu, 1 Oct 2026 00:00:00 +0000

Recent astronomical observations indicate that additional nucleosynthesis pathways are required to understand some atypical elemental abundance patterns revealed by new observations. One such process that can help to explain these observations is the intermediate neutron-capture process (i process). The nuclear properties of isotopes involved in this nucleosynthesis pathway are experimentally well constrained with the exception of the neutron-capture reaction rates, which are provided almost entirely by theory. In this paper, the first experimentally constrained reaction rate on the Kr87(n,γ)Kr88 reaction is provided by employing the β-Oslo method. The impact of this reaction on the abundance of rubidium within the i process is investigated.

Magnetic character of the low-energy enhancement in 70Zn

Thu, 1 Oct 2026 00:00:00 +0000

The transition of an atomic nucleus from an excited state to a state of lower energy is typically accompanied by the emission of photons. The likelihood of photon emission is a function of the photon energy and of properties of the initial and final nuclear states and is known as the photon (or γ-ray) strength function (γSF)1,2. Of the features present in the γSF, an enhancement in the low-energy region has been observed in some nuclei, but the electromagnetic nature of this enhancement remains an open question3,4. This low-energy enhancement in the γSF significantly impacts our understanding of how elements are created in stars and the structure of the nucleus5,6. Here we present the results from an experiment on the γSF of 70Zn that show that the enhancement in the γSF of this nucleus is of magnetic nature. This observation helps address a long-open question about γSFs in atomic nuclei and directly impacts our predictive capabilities in nuclear science.

AI@ALS Workshop Report: Machine Learning Needs at the Advanced Light Source

Thu, 1 Oct 2026 00:00:00 +0000

AI@ALS Workshop Report: Machine Learning Needs at the Advanced Light Source

Search for dark mesons decaying to top and bottom quarks in proton-proton collisions at s = 13 TeV with the ATLAS detector