arXiv subjects

André Rubbia

Publications and source records attributed to André Rubbia.

18 recordsLinked to original sources

arXiv2026

Design and characterization of large-size monolithic layers of 3D-segmented plastic scintillator

Three-dimensional fine-grained plastic scintillator detectors are extensively used in high-energy physics experiments where particle tracking, identification, calorimetry and sub-nanosecond timing information are required. Moreover, the low cost of plastic scintillator makes, in principle, the scalability to multi-tonne detectors possible. In order to circumvent the difficulties related to the long production time and the challenging assembly of millions of tiny independent scintillating voxels, a new technology consisting of gluing a few thousand $9 \times 9 \times 9$ mm$^3$ plastic scintillator cubes in a single large monolithic layer with machining precision, while ensuring an efficient optical separation, was developed and demonstrated. In this work we demonstrate that such technology can be reliably extended to a monolithic layer of $48 \times 48$ optically-isolated scintillating cubes, the size required for future ton-scale detectors, fulfilling the requirements of future neutrino detectors and sampling calorimeters.

physics.ins-det↗

arXiv2026

Towards foundation-style models for energy-frontier heterogeneous neutrino detectors via self-supervised pre-training

Accelerator-based neutrino physics is entering an energy-frontier regime in which interactions reach the TeV scale and produce exceptionally dense, overlapping detector signatures. In this regime, event interpretation becomes impractical for conventional reconstruction approaches, particularly when labelled data are scarce and the analysis spans diverse downstream objectives. We present a sparse ViT framework for learning reusable representations from heterogeneous detector data. Self-supervised pre-training combines masked autoencoder reconstruction with relational voxel-level objectives for hierarchy, ghost and particle identification, and the resulting shared encoder is then jointly fine-tuned across classification and regression tasks. Evaluated on simulated events from the proposed FASERCal concept at the LHC, we find that pre-training consistently improves neutrino flavour and charm-quark identification, momentum regression, and vertex reconstruction over training from scratch, with the addition of relational objectives yielding further gains in the most topologically complex channels. Interpretability analyses further show that pre-training yields a more structured latent space, while detector-subsystem ablations recover physically plausible channel-dependent roles for the heterogeneous inputs. A data-efficiency study shows that, with roughly $10^3$ labelled events, the pre-trained encoder already matches the flavour-classification performance of a randomly initialised model trained on an order of magnitude more data. The learned representations also transfer effectively to publicly available benchmarks spanning different detector technologies and energy scales, matching or exceeding published baselines. These results support self-supervised pre-training on multimodal detector data as a scalable route towards reusable representations for neutrino and particle-detector analysis.

hep-ex↗

arXiv2025

A 3D segmented Water-based Liquid Scintillator for high-precision detection of neutrinos in water

Precision detection of neutrino-nucleus interactions in water with the complete detection of the final state, including leptons and hadrons, is challenging due to water being a non-scintillating medium. This can be a limitation for the next-generation long-baseline neutrino oscillation experiments, such as Hyper-Kamiokande, where the neutrino-nucleus interaction models must reach a few percent-level accuracy. Water-based liquid scintillator can be a game changer for the future near detectors. In this article, we propose a novel design consisting of a 3D highly-segmented water-based liquid scintillator. The water-based liquid scintillator is encapsulated within a highly-segmented rigid but very light structure that provides the optical isolation with a 1 cm$^{3}$ granularity, each read out by orthogonal wavelength shifting fibers, and 81\% of water by mass in the active volume. Such configuration is also suitable for pure liquid scintillator. The detector design, prototyped and validated with cosmic ray data, is described and results are reported. The optical model is studied with Monte Carlo simulations and results are compared with the collected data.

physics.ins-det↗

arXiv2025

Latest neutrino results from the FASER experiment and their implications for forward hadron production

The muon puzzle -- an excess of muons relative to simulation predictions in ultra-high-energy cosmic-ray air showers -- has been reported by many experiments. This suggests that forward particle production in hadronic interactions is not fully understood. Some of the scenarios proposed to resolve this predict reduced production of forward neutral pions and enhanced production of forward kaons (or other particles). The FASER experiment at the LHC is located 480 m downstream of the ATLAS interaction point and is sensitive to neutrinos and muons, which are the decay products of forward charged pions and kaons. In this study, the latest measurements of electron and muon neutrino fluxes are presented using the data corresponding to 9.5 $\mathrm{fb^{-1}}$ and 65.6 $\mathrm{fb^{-1}}$ of proton-proton collisions with $\sqrt{s}=13.6~\mathrm{TeV}$ by the FASER$ν$ and the FASER electronic detector, respectively. These fluxes are compared with predictions from recent hadronic interaction models, including EPOS-LHCr, SIBYLL 2.3e, and QGSJET 3. The predictions are generally consistent with the measured fluxes from FASER, although some discrepancies appear in certain energy bins. More precise flux measurements with additional data will follow soon, enabling validation of pion, kaon, and charm meson production with finer energy binning, reduced uncertainties, and multi-differential analyses.

hep-ex↗

arXiv2025

First Measurement of the Muon Neutrino Interaction Cross Section and Flux as a Function of Energy at the LHC with FASER

This letter presents the measurement of the energy-dependent neutrino-nucleon cross section in tungsten and the differential flux of muon neutrinos and anti-neutrinos. The analysis is performed using proton-proton collision data at a center-of-mass energy of $13.6 \, {\rm TeV}$ and corresponding to an integrated luminosity of $(65.6 \pm 1.4) \, \mathrm{fb^{-1}}$. Using the active electronic components of the FASER detector, $338.1 \pm 21.0$ charged current muon neutrino interaction events are identified, with backgrounds from other processes subtracted. We unfold the neutrino events into a fiducial volume corresponding to the sensitive regions of the FASER detector and interpret the results in two ways: We use the expected neutrino flux to measure the cross section, and we use the predicted cross section to measure the neutrino flux. Both results are presented in six bins of neutrino energy, achieving the first differential measurement in the TeV range. The observed distributions align with Standard Model predictions. Using this differential data, we extract the contributions of neutrinos from pion and kaon decays.

hep-ex↗

arXiv2025

Reconstruction and Performance Evaluation of FASER's Emulsion Detector at the LHC

This paper presents the reconstruction and performance evaluation of the FASER$ν$ emulsion detector, which aims to measure interactions from neutrinos produced in the forward direction of proton-proton collisions at the CERN Large Hadron Collider. The detector, composed of tungsten plates interleaved with emulsion films, records charged particles with sub-micron precision. A key challenge arises from the extremely high track density environment, reaching $\mathcal{O}(10^5)$ tracks per cm$^2$. To address this, dedicated alignment techniques and track reconstruction algorithms have been developed, building on techniques from previous experiments and introducing further optimizations. The performance of the detector is studied by evaluating the single-film efficiency, position and angular resolution, and the impact parameter distribution of reconstructed vertices. The results demonstrate that an alignment precision of 0.3 micrometers and robust track and vertex reconstruction are achieved, enabling accurate neutrino measurements in the TeV energy range.

physics.ins-det↗

arXiv2025

Prospects and Opportunities with an upgraded FASER Neutrino Detector during the HL-LHC era: Input to the EPPSU

The FASER experiment at CERN has opened a new window in collider neutrino physics by detecting TeV-energy neutrinos produced in the forward direction at the LHC. Building on this success, this document outlines the scientific case and design considerations for an upgraded FASER neutrino detector to operate during LHC Run 4 and beyond. The proposed detector will significantly enhance the neutrino physics program by increasing event statistics, improving flavor identification, and enabling precision measurements of neutrino interactions at the highest man-made energies. Key objectives include measuring neutrino cross sections, probing proton structure and forward QCD dynamics, testing lepton flavor universality, and searching for beyond-the-Standard Model physics. Several detector configurations are under study, including high-granularity scintillator-based tracking calorimeters, high-precision silicon tracking layers, and advanced emulsion-based detectors for exclusive event reconstruction. These upgrades will maximize the physics potential of the HL-LHC, contribute to astroparticle physics and QCD studies, and serve as a stepping stone toward future neutrino programs at the Forward Physics Facility.

hep-ex↗

arXiv2025

Beam test results of a fully 3D-printed plastic scintillator particle detector prototype

Plastic scintillators are widely used for the detection of elementary particles, and 3D reconstruction of particle tracks is achieved by segmenting the detector into 3D granular structures. In this study, we present a novel prototype fabricated by additive manufacturing, consisting of a 5 x 5 x 5 array of 1 cm3 plastic scintillator cubes, each optically isolated. This innovative approach eliminates the need to construct complex monolithic geometries in a single operation and gets rid of the traditional time-consuming manufacturing and assembling processes. The prototype underwent performance characterization during a beam test at CERN's Proton-Synchrotron facility. Light yield, optical crosstalk, and light response uniformity, were evaluated. The prototype demonstrated a consistent light yield of approximately 27 photoelectrons (p.e.) per channel, similar to traditional cast scintillator detectors. Crosstalk between adjacent cubes averaged 4-5%, and light yield uniformity within individual cubes exhibited about 7% variation, indicating stability and reproducibility. These results underscore the potential of the novel additive manufacturing technique, for efficient and reliable production of high-granularity scintillator detectors.

physics.ins-det↗

arXiv2024

Shining Light on the Dark Sector: Search for Axion-like Particles and Other New Physics in Photonic Final States with FASER

The first FASER search for a light, long-lived particle decaying into a pair of photons is reported. The search uses LHC proton-proton collision data at $\sqrt{s}=13.6~\text{TeV}$ collected in 2022 and 2023, corresponding to an integrated luminosity of $57.7\text{fb}^{-1}$. A model with axion-like particles (ALPs) dominantly coupled to weak gauge bosons is the primary target. Signal events are characterised by high-energy deposits in the electromagnetic calorimeter and no signal in the veto scintillators. One event is observed, compared to a background expectation of $0.44 \pm 0.39$ events, which is entirely dominated by neutrino interactions. World-leading constraints on ALPs are obtained for masses up to $300~\text{MeV}$ and couplings to the Standard Model W gauge boson, $g_{aWW}$, around $10^{-4}$ GeV$^{-1}$, testing a previously unexplored region of parameter space. Other new particle models that lead to the same experimental signature, including ALPs coupled to gluons or photons, U(1)$_B$ gauge bosons, up-philic scalars, and a Type-I two-Higgs doublet model, are also considered for interpretation, and new constraints on previously viable parameter space are presented in this paper.

hep-ex↗

arXiv2024

First Measurement of the $ν_e$ and $ν_μ$ Interaction Cross Sections at the LHC with FASER's Emulsion Detector

This paper presents the first results of the study of high-energy electron and muon neutrino charged-current interactions in the FASER$ν$ emulsion/tungsten detector of the FASER experiment at the LHC. A subset of the FASER$ν$ volume, which corresponds to a target mass of 128.6~kg, was exposed to neutrinos from the LHC $pp$ collisions with a centre-of-mass energy of 13.6~TeV and an integrated luminosity of 9.5 fb$^{-1}$. Applying stringent selections requiring electrons with reconstructed energy above 200~GeV, four electron neutrino interaction candidate events are observed with an expected background of $0.025^{+0.015}_{-0.010}$, leading to a statistical significance of 5.2$σ$. This is the first direct observation of electron neutrino interactions at a particle collider. Eight muon neutrino interaction candidate events are also detected, with an expected background of $0.22^{+0.09}_{-0.07}$, leading to a statistical significance of 5.7$σ$. The signal events include neutrinos with energies in the TeV range, the highest-energy electron and muon neutrinos ever detected from an artificial source. The energy-independent part of the interaction cross section per nucleon is measured over an energy range of 560--1740 GeV (520--1760 GeV) for $ν_e$ ($ν_μ$) to be $(1.2_{-0.7}^{+0.8}) \times 10^{-38}~\mathrm{cm}^{2}\,\mathrm{GeV}^{-1}$ ($(0.5\pm0.2) \times 10^{-38}~\mathrm{cm}^{2}\,\mathrm{GeV}^{-1}$), consistent with Standard Model predictions. These are the first measurements of neutrino interaction cross sections in those energy ranges.

hep-ex↗

arXiv2024

Neutrino Rate Predictions for FASER

The Forward Search Experiment (FASER) at CERN's Large Hadron Collider (LHC) has recently directly detected the first collider neutrinos. Neutrinos play an important role in all FASER analyses, either as signal or background, and it is therefore essential to understand the neutrino event rates. In this study, we update previous simulations and present prescriptions for theoretical predictions of neutrino fluxes and cross sections, together with their associated uncertainties. With these results, we discuss the potential for possible measurements that could be carried out in the coming years with the FASER neutrino data to be collected in LHC Run 3 and Run 4.

hep-ex↗

arXiv2024

Additive manufacturing of a 3D-segmented plastic scintillator detector for tracking and calorimetry of elementary particles

Plastic-scintillator detectors are devices used for the detection of elementary particles. They provide good particle identification with excellent time resolution, whilst being inexpensive due to the affordability of plastic materials. Particle tracking is achieved by segmenting the scintillator into smaller optically-isolated 3D granular sub-structures which require the integration of multiple types of plastic materials as well as several thousands of tiny holes through a compact volume of several cubic meters. Future particle detectors necessitate larger volumes, possibly with even finer segmentation. However, manufacturing such geometries with current production strategies is challenging, as they involve time-consuming and costly fabrication processes, followed by the assembly of millions of individual parts. The difficulty in scaling up such a workflow can be addressed by additive manufacturing, enabling the construction of complex, monolithic geometries in a single operation. This article presents the fabrication of the first additive manufactured plastic scintillator detector, capable of 3D tracking elementary particles and measuring their stopping power. Its performance is comparable to the state of the art of plastic scintillator detectors. This work paves the way towards a new feasible, time and cost-effective process for the production of future plastic-based scintillator detectors, regardless their size and difficulty in geometry.

physics.ins-det↗

arXiv2024

Deep-learning-based decomposition of overlapping-sparse images: application at the vertex of neutrino interactions

Image decomposition plays a crucial role in various computer vision tasks, enabling the analysis and manipulation of visual content at a fundamental level. Overlapping images, which occur when multiple objects or scenes partially occlude each other, pose unique challenges for decomposition algorithms. The task intensifies when working with sparse images, where the scarcity of meaningful information complicates the precise extraction of components. This paper presents a solution that leverages the power of deep learning to accurately extract individual objects within multi-dimensional overlapping-sparse images, with a direct application in high-energy physics with decomposition of overlaid elementary particles obtained from imaging detectors. In particular, the proposed approach tackles a highly complex yet unsolved problem: identifying and measuring independent particles at the vertex of neutrino interactions, where one expects to observe detector images with multiple indiscernible overlapping charged particles. By decomposing the image of the detector activity at the vertex through deep learning, it is possible to infer the kinematic parameters of the identified low-momentum particles - which otherwise would remain neglected - and enhance the reconstructed energy resolution of the neutrino event. We also present an additional step - that can be tuned directly on detector data - combining the above method with a fully-differentiable generative model to improve the image decomposition further and, consequently, the resolution of the measured parameters, achieving unprecedented results. This improvement is crucial for precisely measuring the parameters that govern neutrino flavour oscillations and searching for asymmetries between matter and antimatter.

cs.CV↗

arXiv2023

TCT investigation of the one-sided depletion of low-temperature covalently bonded silicon sensor P-N diodes

In the context of particle detectors, low-temperature covalent wafer-wafer bonding allows for integration of high-Z materials as absorbing layers with readout chips produced in standard CMOS processes. This enables for instance the fabrication of novel highly efficient X-ray imaging sensors. In order to investigate the effects of the covalent bonding on the signal generated in such sensors, wafer-wafer bonded silicon-silicon P-N pad diodes have previously been produced. The behaviour of these test samples is being investigated with transient current technique (TCT) measurements. In this paper we present an overview of the TCT setup as well as a custom sandwich-type sample holder used for these measurements. A review of the results presented in a previous paper shows, that the bonded P-N structures show a highly asymmetric depletion behaviour under reverse bias. IR edge TCT measurements confirm that only the P-side of the samples is being depleted.

physics.ins-det↗

arXiv2022

Artificial intelligence for improved fitting of trajectories of elementary particles in inhomogeneous dense materials immersed in a magnetic field

In this article, we use artificial intelligence algorithms to show how to enhance the resolution of the elementary particle track fitting in inhomogeneous dense detectors, such as plastic scintillators. We use deep learning to replace more traditional Bayesian filtering methods, drastically improving the reconstruction of the interacting particle kinematics. We show that a specific form of neural network, inherited from the field of natural language processing, is very close to the concept of a Bayesian filter that adopts a hyper-informative prior. Such a paradigm change can influence the design of future particle physics experiments and their data exploitation.

physics.data-an↗

arXiv2022

On the depletion behaviour of low-temperature covalently bonded silicon sensor diodes

Low temperature covalent direct wafer-wafer bonding allows for the fusion of multiple semiconductor wafers without any additional material at the bonding interface. In the context of particle pixel detectors this might provide an alternative to bump-bonding for joining sensors to readout chips. Previous investigations have shown that the amorphous layer formed at the interface during bonding is detrimental to charge propagation. To investigate the influence of the bonding interface on signal collection we have fabricated custom test structures by bonding high-resistivity N to high-resistivity P-type silicon wafers thus forming P-N junctions. Scanning transmission electron microscopy shows indeed the formation of ca. 3nm wide amorphous layer at the interface. Using a scanning transient current technique (TCT) setup we were able to record generated signals. Illuminating our sample with light of different wavelengths and from different sides, indicates that the P side of the bonded structures can be fully depleted, but not the N side. This indicates a strongly asymmetric depletion behaviour which we attribute to the presence of the bonding interface.

physics.ins-det↗

arXiv2021

Neural-network-driven proton decay sensitivity in the $p\rightarrow \barν K^{+}$ channel using large liquid argon time projection chambers

We report on an updated sensitivity for proton decay via $p \rightarrow \barν K^+ $ at large, dual phase liquid argon time projection chambers (LAr TPCs). Our work builds on a previous study in which several nucleon decay channels have been simulated and analyzed [arXiv:hep-ph/0701101]. At the time several assumptions were needed to be made on the detector and the backgrounds. Since then, the community has made progress in defining these, and the computing power available enables us to fully simulate and reconstruct large samples in order to perform a better estimate of the sensitivity to proton decay. In this work, we examine the benchmark channel $p\rightarrow \barν K^{+}$, which was previously found to be one of the cleanest channels. Using an improved neutrino event generator and a fully simulated LAr TPC detector response combined with a dedicated neural network for kaon identification, we demonstrate that a lifetime sensitivity of $ τ/ \text{Br} \left( p \rightarrow \barν K^+ \right) > 7 \times 10^{34} \, \text{years}$ at $90 \, \%$ confidence level can be reached at an exposure of $1 \, \text{megaton} \cdot \text{year}$ in quasi-background-free conditions, confirming the superiority of the LAr TPC over other technologies to address the challenging proton decay modes.

hep-ex↗

arXiv2010

Measurement of the ortho-positronium confinement energy in mesoporous thin films

In this paper, we present measurements of the ortho-positronium emission energy in vacuum from mesoporous films using the time of flight technique. We show evidence of quantum mechanical confinement in the mesopores that defines the minimal energy of the emitted Ps. Two samples with different effective pore sizes, measured with positron annihilation lifetime spectroscopy, are compared for the data collected in the temperature range 50-400 K. The sample with smaller pore size exhibits a higher minimal energy ($73\pm$5 meV), compared to the sample with bigger pores ($48\pm$5 meV), due to the stronger confinement. The dependence of the emission energy with the temperature of the target is modeled as ortho-positronium being confined in rectangular boxes in thermodynamic equilibrium with the sample. We also measured that the yield of positronium emitted in vacuum is not affected by the temperature of the target.

physics.atom-ph↗