| |
ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Measurement of t-channel single-top-quark production in pp collisions at √s=5.02 TeV with the ATLAS detector. Phys. Lett. B, 854, 138726–22pp.
Abstract: The observation of the electroweak production of single-top-quarks is made using 255 pb(-1) of proton-proton collision data recorded at root s = 5.02 TeV with the ATLAS detector at the Large Hadron Collider. An event selection is used to identify single-top-quark candidates arising from..-channel production with the top quark decaying semi-leptonically. Events passing the selection are then used to measure the inclusive cross-section for the combined production of single-top-quarks and antiquarks, sigma(tq + (t) over barq), and the ratio R-t between these two. They are measured to be sigma(tq + (t) over barq) = 27.1(-4.1)(+4.4)(stat.)(-3.7)(+4.4)(syst.) pb and R-t = 2.73(-0.82)(+1.43)(stat.)(-0.29)(+1.01)(syst.). The individual single-top-quark (tq) and single-top-antiquark ((t) over barq) production cross-sections are measured to be sigma(tq) = 19.8(-3.1)(+3.9)(stat.)(-2.2)(+2.9)(syst.) pb and sigma((t) over barq) = 7.3(-2.1)(+3.2)(stat.)(-1.5)(+2.8)(syst.) pb. All measurements are in good agreement with the Standard Model predictions.
|
|
del Rio, A., Marañon-Gonzalez, F. J., & Navarro-Salas, J. (2025). Singularity resolution in spherically reduced 2D semiclassical gravity with negative central charge. Phys. Rev. D, 111(4), 045025–11pp.
Abstract: We analyze the semiclassical Schwarzschild geometry in the Boulware quantum state in the framework of two-dimensional (2D) dilaton gravity. The classical model is defined by the spherical reduction of Einstein's gravity sourced with conformal scalar fields. The expectation value of the stress-energy tensor in the Boulware state is singular at the classical horizon of the Schwarzschild spacetime, but when backreaction effects are considered, previous results have shown that the 2D geometry is horizonless and described by a nonsymmetric wormhole with a curvature singularity on the other side of the throat. In this work we show that reversing the sign of the central charge of the conformal matter removes the curvature singularity of the 2D backreacted geometry, which happens to be horizonless and asymptotically flat. This result is consistent with a similar analysis recently performed for the Callan-Giddings-Harvey-Strominger model. We also argue the physical significance of negative central charges in conformal anomalies from a four-dimensional perspective.
|
|
Fanchiotti, H., Garcia Canal, C. A., & Vento, V. (2025). Do heavy monopoles hide from us? Eur. Phys. J. Plus, 140(2), 170–8pp.
Abstract: Dirac demonstrated that the existence of a single magnetic monopole in the universe could explain the discrete nature of electric charge. Magnetic monopoles naturally arise in most grand unified theories. However, the extensive experimental searches conducted thus far have not been successful. Here, we propose a mechanism in which magnetic monopoles bind deeply with neutral states, effectively hiding some of the properties of free monopoles. We explore various scenarios for these systems and analyze their detectability. In particular, one scenario is especially interesting, as it predicts a light state-an analog of an electron but with magnetic charge instead of electric charge-which we refer to as a magnetron.
|
|
Super-Kamiokande and T2K Collaborations(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Molina Bueno, L., & Novella, P. (2025). First Joint Oscillation Analysis of Super-Kamiokande Atmospheric and T2K Accelerator Neutrino Data. Phys. Rev. Lett., 134(1), 011801–13pp.
Abstract: The Super-Kamiokande and T2K Collaborations present a joint measurement of neutrino oscillation parameters from their atmospheric and beam neutrino data. It uses a common interaction model for events overlapping in neutrino energy and correlated detector systematic uncertainties between the two datasets, which are found to be compatible. Using 3244.4 days of atmospheric data and a beam exposure of 19.7(16.3) x 10(20) protons on target in (anti)neutrino mode, the analysis finds a 1.9 sigma exclusion of CP conservation (defined as J(CP) = 0) and a 1.2 sigma exclusion of the inverted mass ordering.
|
|
Valdes-Cortez, C., Mansour, I., Ayala Alvarez, D. S., Berumen, F., Cote, J. S., Ndoutoume-Paquet, G., et al. (2025). Dosimetric impact of physics libraries for electronic brachytherapy Monte Carlo studies. Med. Phys., , 13pp.
Abstract: Background Low-energy x-ray beams used in electronic brachytherapy (eBT) present significant dosimetric challenges due to their high depth-dose gradients, the dependence of detector response on materials, and the lack of standardized dose-to-water references. These challenges have driven the need for Monte Carlo (MC) simulations to ensure accurate dosimetry. However, discrepancies in the physics models used by different MC systems have raised concerns about their dosimetric consistency, particularly in modeling bremsstrahlung interactions. Purpose To assess the dosimetric impact of using different physics approaches in three state-of-the-art MC systems for eBT, focusing on the disagreements observed when different MC methods are used to evaluate bremsstrahlung interactions. Methods The MC studies of the Axxent S700, the Esteya, and the INTRABEAM eBT systems were performed using two EGSnrc applications (egsbrachy and egskerma), TOPAS, and PENELOPE-2018 (PEN18). The fluence spectra and depth doses were compared for simplified x-ray tube models, which maintain the target mode (transmission or reflection), the target material and thickness, and the surface applicators' source-to-surface distance. An extra simulation was made to evaluate the utility of the simplified models as proxies in predicting the most important characteristics of an accurate applicator's simulation (detailed model of INTRABEAM's 30 mm surface applicator). The EGSnrc applications and PEN18 utilized their default bremsstrahlung angular emission approaches. TOPAS used two physics lists: g4em-livermore (TOPAS(liv)) and g4em-penelope (TOPAS(pen)). Results The most significant differences between MC codes were observed for the transmission target mode. The bremsstrahlung component of the fluence spectra differed by about 15% on average, comparing PEN18, EGSnrc applications, and TOPAS(liv), with PEN18's fluences consistently lower. EGSnrc and PEN18 agreed within 3% for their characteristic spectrum components. However, PEN18's characteristic lines overreached TOPAS(liv)'s by 40%. Those spectral characteristics generated depth dose differences, where PEN18, on average, scored 9% lower than EGSnrc and TOPAS(liv). Considering TOPAS(pen) in the transmission mode, PEN18's fluence spectrum presented a lower bremsstrahlung (5%) but a higher characteristic component (10%); these spectral differences compensated, generating depth dose differences within 1% average. In the reflection target mode, EGSnrc and PEN18 agreed within 4% for the bremsstrahlung and characteristic components of the fluence spectra. With TOPAS(pen) in the reflection mode, PEN18 presents 12% lower fluences in the bremsstrahlung component but 6% higher characteristic lines. This spectral behavior diminished the depth dose differences up to 3%. Conclusion This work found considerable disagreements between three state-of-the-art MC systems commonly used in medical applications when simulating bremsstrahlung in eBT. The differences arose when the bremsstrahlung angular distribution and the atomic relaxation processes in the target became relevant. More theoretical and experimental studies are necessary to evaluate the impact of these differences on related calculations.
|
|
|
