arXiv subjects

Matthias Holl

Publications and source records attributed to Matthias Holl.

6 recordsLinked to original sources

arXiv2026

Vertex reconstruction for a search for neutron-antineutron conversions with HIBEAM

The HIBEAM/NNBAR programme (incorporated into the FINESSE/NNBAR programme) at the European Spallation Source is proposed to search for neutrons converting to antineutrons. An important observable is the reconstructed vertex arising from charged particles produced by an antineutron annihilating on a thin target foil and which pass through a time projection chamber. This paper studies track clustering and foil-plane vertex reconstruction for this topology. Both non-machine-learning methods and graph-neural-network methods are tested and compared with each other, including deterministic clustering, trackless projection and a hybrid clustering/graph-neural-network chain with track classification and vertex refinement. We conclude that, for the geometrically simple events in the HIBEAM TPC, classical reconstruction methods perform on-par with machine-learning based methods in terms of vertex coordinate reconstruction. Custom machine-learning based methods can, however, deliver event-shape information that may be important in downstream analyses.

hep-ex↗

arXiv2026

Development and Characterization of a Time Projection Chamber Prototype for Neutron Oscillation Searches at the European Spallation Source

A compact time projection chamber (TPC) prototype was studied for charged-pion tracking in the annihilation detector proposed for the HIBEAM experiment at the European Spallation Source. HIBEAM aims to search for neutron-antineutron oscillations, where a produced antineutron would annihilate on a carbon target and produce a pionic final state. A tracking algorithm was developed and validated using cosmic-particle measurements expected to be dominated by atmospheric cosmic muons, proton elastic-scattering data from the Cyclotron Centre Bronowice, and simulated TPC event data. Cosmic measurements provided a minimum-ionising reference for pion-like tracks, while proton-scattering data tested reconstruction in a more highly ionising environment. Simulated crossing-track events were used as a stress test of complex topologies. The algorithm performed reliably for well-separated tracks, while crossing or overlapping tracks and dense proton-scattering events reduced performance. In experimental data, reconstructed tracks showed sub-millimetre residual widths, robust charge sharing supporting the zigzag-shaped readout, and uniform measured dE/dx across the drift volume. The truncated-mean track-level dE/dx distribution in cosmic data showed an approximately Gaussian peak with a relative width of about 16%, demonstrating how energy-loss information can be used for particle identification. Tilted proton tracks showed broader residuals in yz, because the pad row signal was extended in time. A sub-centroid refit technique was proposed, using the internal ADC time profile within a pad row instead of a single charge-weighted time position. With four equal-y sub-centroids per pad row, the yz residual width was reduced from 1.30 mm to 0.55 mm. These results validate the initial tracking capabilities of the algorithm and prototype, and provide feedback for the next-generation prototype.

physics.ins-det↗

arXiv2026

A Simulation Framework for Ramsey Interferometry

The sensitivity of Ramsey interferometry experiments is governed by the interplay between the beam phase-space distribution and the magnetic field environment through which the spins propagate. Quantitative optimisation thus requires a consistent treatment of optics, magnetics and spin dynamics. We present a simulation framework that enables such an analysis by combining neutron optics simulations in McStas, magnetic field modelling in COMSOL and spin-dynamics simulation in the new RamseyProp program. We describe how important experimental parameters such as adiabaticity, flip angle distributions and Ramsey fringe contrast can be studied. The code is being applied to design an experiment to search for axion-like particles at the European Spallation Source (ESS). We examine how the pulsed time structure of the ESS can be exploited to perform Ramsey interferometry on a broad neutron velocity spectrum. In the absence of velocity or timing restrictions, the standard deviation of the spin flip angle at zero detuning can be reduced from 0.67 to 0.17 radians using time-dependent amplitude modulation. Similarly, the phase sensitivity can be improved by a factor of 4 for a 10 m long setup starting 15 m from the ESS moderator.

physics.ins-det↗

arXiv2025

Advancements in Computing and Simulation Techniques for the HIBEAM-NNBAR Experiment

The HIBEAM-NNBAR program is a proposed two-stage experiment at the European Spallation Source focusing on searches for baryon number violation processes as well as ultralight dark matter. This paper presents recent advancements in computing and simulation, including machine learning for event selection, fast parametric simulations for detector studies, and detailed modeling of the time projection chamber and readout electronics.

physics.ins-det↗

arXiv2022

Beamline Simulation for the NNBAR Experiment at the European Spallation Source

The HIBEAM and NNBAR experiments are a proposed fundamental science experiments at the European Spallation Source, performing high precision searches for neutron conversions in several baryon number violating (BNV) channels. For simulations of the NNBAR beamline, a new sampling method has been developed. The method is based on probability density evaluation and duct source biasing and enables the simulations of the entire NNBAR beamline with high statistics while also preserving correlations of the neutron tracks.

physics.data-an↗

arXiv2016

Coulomb dissociation of $^{20,21}$N

Neutron-rich light nuclei and their reactions play an important role for the creation of chemical elements. Here, data from a Coulomb dissociation experiment on $^{20,21}$N are reported. Relativistic $^{20,21}$N ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the $^{19}\mathrm{N}(\mathrm{n},γ)^{20}\mathrm{N}$ and $^{20}\mathrm{N}(\mathrm{n},γ)^{21}\mathrm{N}$ excitation functions and thermonuclear reaction rates have been determined. The $^{19}\mathrm{N}(\mathrm{n},γ)^{20}\mathrm{N}$ rate is up to a factor of 5 higher at $T<1$\,GK with respect to previous theoretical calculations, leading to a 10\,\% decrease in the predicted fluorine abundance.

nucl-ex↗