arXiv subjects

T. Leontiou

Publications and source records attributed to T. Leontiou.

6 recordsLinked to original sources

arXiv2026

Measurement of Differential Cross Sections and Integrated Luminosity using Proton-Proton Elastic Scattering with HADES at T = 4.53 GeV and T = 1.60 GeV

This work presents an investigation of elastic proton-proton scattering based on data collected with the recently upgraded HADES detector using beams of protons with kinetic energies of $T = 4.53$ GeV and $T = 1.60$ GeV impinging on a liquid hydrogen target. This is the first measurement emerging from the upgraded detector setup, including a Forward Detector with straw-tube tracking planes designed for the PANDA experiment. The well-constrained two-body kinematic relations of elastic scattering have been exploited to study the detector alignment, the beam alignment, and to provide the final measurement of the beam energy. In addition, the recorded luminosity of the experiment has been determined by normalizing the HADES data in a range of the squared four-momentum transfer $t$ that overlaps with measurements by previous experiments worldwide. Furthermore, the differential cross sections have been determined over a large range of $t$ from which the slope parameter $B$ is extracted, yielding $B = 8.98 \pm 0.3$ (GeV/$c$)$^{-2}$ and $7.3 \pm 0.1$ (GeV/$c$)$^{-2}$ at $T = 4.53$ GeV and $1.60$ GeV, respectively. This contribution to the world database on elastic proton-proton scattering provides input to theoretical modeling and serves as a reference for luminosity determinations by future experiments in the same energy range.

hep-ex↗

arXiv2026

Hamiltonian dynamics for stochastic reconstruction in emission tomography

Objective: To develop a practical stochastic reconstruction framework for emission tomography that generates ensembles of data-compatible images and enables uncertainty quantification and assessment of forward-model adequacy. Approach: The framework combines stochastic-gradient descent initialization with Hamiltonian Monte Carlo (HMC) sampling directly in high-dimensional voxel space. Beyond point reconstruction, we introduce a spatially resolved operator-weighted diagnostic, the sampled data-visible variance, which quantifies how image fluctuations propagate through the imaging operator and thereby probes the local conditioning of the inverse problem under realistic acquisition physics. The methodology is evaluated using controlled software phantoms, experimental anthropomorphic phantom measurements, and a clinical DATSCAN SPECT acquisition. Main results: Under ideal conditions, the HMC ensemble mean provides point-estimate accuracy comparable to deterministic reconstruction methods, while the sampled ensemble provides additional physically interpretable information. The ensemble analysis helps distinguish uncertainty associated with the intrinsic ill-posedness of the inverse problem from variability linked to forward-model inadequacy. The clinical example demonstrates applicability under realistic acquisition statistics rather than diagnostic performance. Significance: The proposed stochastic reconstruction framework provides a practical ensemble-based approach for emission tomography that extends conventional point reconstruction with model-conditioned uncertainty estimates and spatially resolved diagnostics of forward-model adequacy.

physics.med-ph↗

arXiv2020

Nucleon axial and pseudoscalar form factors from lattice QCD at the physical point

We compute the nucleon axial and induced pseudoscalar form factors using three ensembles of gauge configurations, generated with dynamical light quarks with mass tuned to approximately their physical value. One of the ensembles also includes the strange and charm quarks with their mass close to physical. The latter ensemble has large statistics and finer lattice spacing and it is used to obtain final results, while the other two are used for assessing volume effects. The pseudoscalar form factor is also computed using these ensembles. We examine the momentum dependence of these form factors as well as relations based on pion pole dominance and the partially conserved axial-vector current hypothesis.

hep-lat↗

arXiv2014

A novel analysis method for excited states in lattice QCD - the nucleon case

We employ a novel method to analyze Euclidean correlation functions entering the calculation of hadron energies in lattice QCD. The method is based on the sampling of all possible solutions allowed by the spectral decomposition of the hadron correlators. We demonstrate the applicability of the method by studying the nucleon excited states in the positive and negative parity channels over a pion mass range of about 400~MeV to 150~MeV. The results are compared to the standard variational approach routinely used to study excited states within lattice QCD. The main advantage of our new approach is its ability to unambiguously determine all excited states for which the Euclidean time correlation function is sensitive on.

hep-lat↗

arXiv2014

Nucleon Excited States in N$_f$=2 lattice QCD

We investigate the excited states of the nucleon using $N_f=2$ twisted mass gauge configurations with pion masses in the range of about 270 MeV to 450 MeV and one ensemble of $N_f=2$ Clover fermions at almost physical pion mass. We use two different sets of variational bases and study the resulting generalized eigenvalue problem. We present results for the two lowest positive and negative parity states.

hep-lat↗

arXiv2013

Nucleon Structure using lattice QCD

A review of recent nucleon structure calculations within lattice QCD is presented. The nucleon excited states, the axial charge, the isovector momentum fraction and helicity distribution are discussed, assessing the methods applied for their study, including approaches to evaluate the disconnected contributions. Results on the spin carried by the quarks in the nucleon are also presented.

hep-lat↗