National Institute for Subatomic Physics

Ambient seismic noise beamforming tries to identify the direction (traditional one component beamforming) or the direction and wavetype (three component beamforming) of the incoming ambient noise field. If the signal is weak, either taking longer time intervals or stacking several consecutive time windows is employed to obtain a sharper image of the underlying noise sources. However, this also reduces the temporal resolution of the noise sources and might prevent the identification of distinct sources in the case of a temporally highly variable noise field. In addition, the presence of very local, often station specific, noise sources can compromise the coherence of the seismic noise field, preventing the identification of noise sources. The identification and subsequent removal of either time intervals or single stations with exceptionally low signal correlation could thus also lead to an improvement in the temporal resolution of the seismic noise sources and the classification of the ambient seismic noise field.In this study, we investigate the ambient seismic noise field recorded with different temporary short period seismic networks in the Euregio Meuse-Rhine (EMR). The region is a candidate site for the next generation gravitational wave telescope (Einstein telescope) and characterizing the anthropogenic ambient surface noise field with high spatial and temporal variability containing many different noise sources (e.g. highways, railway lines, industry, wind turbines, urban settlements) is essential. We investigate the spatio-temporal coherence of the seismic wavefield to identify time intervals and regions with high waveform coherence which are then investigated for possible ambient noise sources. The one component and three component (when available) beamforming results are compared with results from matched field processing (MFP) to validate that the sources are outside the recording network and to estimate the possible geographic source area.We observe a clear diurnal character of the coherence of the ambient seismic noise field over a wide frequency range from about 2 to 20 Hz with significantly higher coherence values during night. This indicates the prevalence of very local noise contributions during working hours. In addition, a clear anti-correlation between wavefield coherence and wind speed also indicates the local character of wind generated noise. Limiting beamforming analysis to time windows and stations with high coherence improves the beamforming results and the temporal resolution during time intervals identified as coherent. Beamforming results during time intervals with high waveform coherence often show stable backazimuth directions indicating persistent ambient noise sources. The source location outside the recording network is confirmed by the results of the MFP analysis. This also holds for time intervals during working hours and can be confirmed by MFP processing. Results from such investigations might be used as best practices for the spatio-temporal characterization of ambient noise sources in the case of highly complex noise fields.

The Einstein Telescope (ET), a proposed third-generation underground gravitational-waves observatory requires an acoustically quiet subsurface environment to minimize the effect of seismic ambient noise. A detailed site characterization is currently underway in the Euregion Meuse-Rhine (Germany, Belgium, Netherlands), one of the potential locations for the ET. The site is wedged between the northern margin of the Variscan deformation front and the subsiding Lower Rhine Graben. Subsurface fluid flow, including natural groundwater circulation and drainage constitute sources of induced seismic and gravity-gradient variations. Pre-existing faults and fractures act as preferential flow paths and, critically control potential water inflow into the infrastructure and influence related water management strategies. Consequently, characterizing the relationship between the tectonic stress field and hydraulic characteristics of the host-rock formations is essential for a resilient ET design. In this study, we investigate the evolution of the tectonic stress field (i.e., from paleo- to recent in-situ stresses) and its control on fracture permeability, using an integrated dataset of boreholes drilled in the study area from 2021 to 2025 and down to 250 to 420 m. Paleo-stress conditions are reconstructed from fracture orientations and kinematic indicators observed on drill core material and borehole-televiewer data. The present-day stress-state is evaluated using hydraulic fracturing and hydraulic testing of pre-existing fractures tests. Fracture architectures are characterized using televiewer imagery and core samples, while their hydraulic relevance is assessed through in-situ methods such as impeller flow-meter measurements, temperature logs, and hydraulic packer tests. Slip versus dilation tendency analysis is applied to evaluate deformation modes and associated permeability anisotropies. These results are compared to independent hydraulic indicators to distinguish between hydraulically active and inactive discontinuities. Our findings demonstrate how the complex tectonic history governs the present-day fracture network and associated groundwater pathways, providing key constraints on groundwater management and suitability assessments for the site selection of the ET project in naturally fractured sedimentary host-rocks.

Longitudinal particle production in heavy-ion collisions is influenced both by preferential emission from participating nucleons and by the breakup of spectator matter, yet quantifying these effects experimentally remains challenging. We introduce a Pearson correlation between spectator and charged-particle forward-backward asymmetries as an experimental probe of these phenomena. Using Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV simulated with A Multi-Phase Transport (AMPT) model, we validate that this correlator provides a robust, pseudorapidity-differential measure of the influence of preferential emission on the longitudinal structure of particle production. We further demonstrate that the correlation strength is sensitive to fluctuations in spectator number, which in experiments arise from evaporation and fragmentation of the spectator remnants. The proposed observable therefore offers a data-driven handle for constraining models of preferential emission and spectator breakup, thereby improving our understanding of the mechanisms that shape the final-state longitudinal distributions in heavy-ion collisions.

A bstract The existence of an eV-scale sterile neutrino has been proposed to explain several anomalous experimental results obtained over the course of the past 25 years. The first search for such a sterile neutrino conducted with data from KM3NeT/ORCA — a water Cherenkov neutrino telescope under construction at the bottom of the Mediterranean Sea — is reported in this paper. GeV-scale atmospheric neutrino oscillations are measured by reconstructing the energy and arrival direction of up-going neutrinos that have traversed the Earth. This study is based on a data sample containing 5828 neutrino candidates collected with 6 detection units (5% of the complete detector), corresponding to an exposure of 433 kton-years. From the expected effect of an eV-scale sterile neutrino on the first ν μ → ν τ standard oscillation maximum, simultaneous constraints are put on the magnitude of the U μ 4 and U τ 4 mixing elements assuming $$ \Delta {m}_{41}^2\ge 1 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Δ</mml:mi> <mml:msubsup> <mml:mi>m</mml:mi> <mml:mn>41</mml:mn> <mml:mn>2</mml:mn> </mml:msubsup> <mml:mo>≥</mml:mo> <mml:mn>1</mml:mn> </mml:math> eV 2 . The results are compatible with the absence of mixing between active neutrinos and a sterile state, with | U μ 4 | 2 &lt; 0.138 and | U τ 4 | 2 &lt; 0.076 at a 90% confidence level. Such constraints are compatible with the results reported by other long-baseline experiments, and indicate that with KM3NeT/ORCA it is possible to bring crucial contributions to sterile neutrino searches in the coming years.

Abstract In this paper we report on the production and characterization of a cold beam of BaOH molecules using a cryogenic buffer-gas beam source. BaOH is a highly suitable molecule for studies of the violation of fundamental symmetries, such as the search for the electron’s electric dipole moment. BaOH molecules are synthesized inside the cold source through laser ablation of a barium metal target while water vapor is seeded into the neon buffer gas. The BaOH flux is significantly enhanced (∼11 times) when laser-exciting the barium atoms inside the buffer-gas cell on the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mi/> <mml:mn>1</mml:mn> </mml:msup> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">S</mml:mi> </mml:mrow> <mml:mn>0</mml:mn> </mml:msub> </mml:mrow> </mml:math> – <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mi/> <mml:mn>3</mml:mn> </mml:msup> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">P</mml:mi> </mml:mrow> <mml:mn>1</mml:mn> </mml:msub> </mml:mrow> </mml:math> transition. A similar enhancement has been reported for other alkaline-earth(-like) monohydroxides. For typical source conditions, the molecular beam has an average velocity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>≈</mml:mo> </mml:mrow> <mml:mn>180</mml:mn> </mml:mrow> </mml:math> m s −1 and an intensity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>9</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> molecules s −1 in N = 1, which is comparable to that of cryogenic BaF beams.

Laser cooling of molecules is a powerful technique for producing cold, slow beams for precision measurements and quantum control, yet its implementation remains challenging due to molecular complexity. Here, we combine a cryogenic buffer gas beam, an electrostatic hexapole lens, and 2D transverse Doppler laser cooling to produce a bright beam of barium monofluoride (138Ba19F) molecules. We study both numerically and experimentally the laser cooling effect as a function of laser detuning, laser power, laser alignment, and interaction time. We find a scattering rate of 6.1(1.4) × 105 s−1 on the laser cooling transition (14% of the expected maximum) and identify suboptimal dark Zeeman state remixing, suboptimal laser sideband powers and detunings, and a lack of vibrational repump laser intensity as possible causes of such a low rate. Using 3 tuneable lasers with appropriate sidebands and detuning, each molecule scatters approximately 400 photons during 2D laser cooling, limited by the interaction time and scattering rate. Leaks to dark states are less than 10%. Finally, we use the experimental results to benchmark the trajectory simulations to predict the achievable flux 3.5 m downstream for a planned eEDM experiment. Laser cooling is a powerful technique that enables precision measurements and quantum control, yet its implementation in molecules remains challenging due to their complex structures. Here, the authors apply 2D transverse laser cooling to a focused beam of cold barium monofluoride (138Ba19F) molecules to significantly increase beam brightness.

We present a deep learning pipeline to perform a model-independent, likelihood-free search for anomalous (i.e., non-background) events in the proposed next-generation multi-ton scale liquid xenon-based direct detection experiment, DARWIN. We train an anomaly detector comprising a variational autoencoder (VAE) and a classifier on high-dimensional simulated detector response data and construct a 1D anomaly score to reject the background-only hypothesis in the presence of an excess of non-background-like events. We use simulated validation data to determine the power of the method to reject the background-only hypothesis in the presence of a WIMP dark matter signal, without any model-dependent assumption about the nature of the signal. We show that our neural networks learn relevant features of the events from low-level, high-dimensional detector outputs, avoiding lossy and computationally expensive compression into lower-dimensional observables. Our approach is complementary to the usual likelihood-based analysis, in that it reduces the reliance on many of the corrections and cuts that are traditionally part of the analysis chain, with the potential of achieving higher accuracy and significant reduction of analysis time. We envisage the methodology presented in this work augmenting or complementing likelihood-based and other data-driven methods currently utilized in the DARWIN (and in the future, XLZD) analysis pipeline.

In July 2025 the Large Hadron Collider (LHC) collided 16 O 16 O and 20 Ne 20 Ne isotopes in a quest to understand the physics of ultrarelativistic light ion collisions. One particular feature is that there are many smaller isotopes with the exact same charge over mass ratio that potentially can be produced and contaminate the beam composition. Using the Trajectum framework together with the GEMINI code we provide an estimate of the production cross-section and its consequences. A potential benefit could be the interesting measurement of the multiplicity and mean transverse momentum of 16 O 4 He and 20 Ne 4 He collisions.

An amplitude analysis of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msubsup> <a:mi mathvariant="normal">Ξ</a:mi> <a:mi>c</a:mi> <a:mo>+</a:mo> </a:msubsup> <a:mo stretchy="false">→</a:mo> <a:mi>p</a:mi> <a:msup> <a:mi>K</a:mi> <a:mo>−</a:mo> </a:msup> <a:msup> <a:mi>π</a:mi> <a:mo>+</a:mo> </a:msup> </a:math> decay together with a measurement of the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:msubsup> <e:mi mathvariant="normal">Ξ</e:mi> <e:mi>c</e:mi> <e:mo>+</e:mo> </e:msubsup> </e:math> polarization vector in semileptonic beauty-hadron decays is presented. The analysis is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mn>9</h:mn> <h:mtext> </h:mtext> <h:mtext> </h:mtext> <h:msup> <h:mi>fb</h:mi> <h:mrow> <h:mo>−</h:mo> <h:mn>1</h:mn> </h:mrow> </h:msup> </h:math> . An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. A sizeable <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:msubsup> <j:mi mathvariant="normal">Ξ</j:mi> <j:mi>c</j:mi> <j:mo>+</j:mo> </j:msubsup> </j:math> polarization is found. A large sensitivity of the <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:msubsup> <m:mi mathvariant="normal">Ξ</m:mi> <m:mi>c</m:mi> <m:mo>+</m:mo> </m:msubsup> <m:mo stretchy="false">→</m:mo> <m:mi>p</m:mi> <m:msup> <m:mi>K</m:mi> <m:mo>−</m:mo> </m:msup> <m:msup> <m:mi>π</m:mi> <m:mo>+</m:mo> </m:msup> </m:math> decay to the polarization is seen, making the amplitude model suitable for <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"> <q:msubsup> <q:mi mathvariant="normal">Ξ</q:mi> <q:mi>c</q:mi> <q:mo>+</q:mo> </q:msubsup> </q:math> polarization measurements in other systems.

Modern collider phenomenology requires unprecedented precision for the theoretical predictions, for which slicing techniques provide an essential tool at next-to-next-to-leading order (NNLO) in the strong coupling. The most popular slicing variable is based on the transverse momentum q_{T} of a color-singlet final state, but its generalization to final states with jets is known to be very difficult. Here we propose two generalizations of q_{T} that can be used for jet processes, providing proof of concept with an NLO slicing for pp→2 jets. We present factorization formulas that enable our approach to NNLO, calculate the NNLO collinear-soft function, and demonstrate slicing at this order for e^{+}e^{-}→2 jets. One of these generalizations of q_{T} only applies to planar Born processes, such as pp→2 jets, but offers a dramatic simplification of the soft function. We also discuss how our approach can directly be extended to obtain predictions for the fragmentation of hadrons. This presents a promising path for high-precision QCD calculations with multijet final states.