In the insides of star forges, the rate of formation of 12C is strongly influenced by the properties of one particular excited state: the so-called Hoyle state, a 0+ which lies at 7.654 MeV of excitation energy. Given its importance, the presence of tensions in the determination of its radiative branching ratio, as the ones posed by some recent experiments, would lead to sizable astrophysical implications. This work presents the results of a low-background charged particle coincidence experiment, aimed to measure the radiative decay branching ratio of the Hoyle state. The obtained radiative decay branching ratio value of Γrad/Γtot = 4.2(6) 10−4 is in agreement with the previously accepted literature values.
^50 Cr and ^53 Cr are very relevant in criticality safety benchmarks related to nuclear reactors. The discrepancies of up to 30 k_eff and k_∞ in criticality benchmarks particularly sensitive to chromium. In this work, the ^50,53 Cr(n, γ ) cross sections are to be determined between 1 and 100 keV with an 8–10 _6 D _6 detectors with very low neutron sensitivity. The highly-enriched samples used are significantly thinner than in previous measurements, thus minimizing the multiple-scattering effects. We have produced, and analysed with the R-matrix analysis code SAMMY, capture yields featuring 33 resonances of ^50 Cr and 51 of ^53 Cr with an accuracy between 5 ^50,53 Cr(n, γ ) cross sections provide a valuable input for upcoming evaluations, which are deemed necessary given that the results presented herein do not support the increase in both cross sections proposed in the recent INDEN evaluation.
Some of the most astonishing and prominent properties of Quantum Mechanics, such as entanglement and Bell nonlocality, have only been studied extensively in dedicated low-energy laboratory setups. The feasibility of these studies in the high-energy regime explored by particle colliders was only recently shown, and has gathered the attention of the scientific community. For the range of particles and fundamental interactions involved, particle colliders provide a novel environment where quantum information theory can be probed, with energies exceeding by about 12 orders of magnitude those employed in dedicated laboratory setups. Furthermore, collider detectors have inherent advantages in performing certain quantum information measurements, and allow for the reconstruction of the state of the system under consideration via quantum state tomography. Here, we elaborate on the potential, challenges, and goals of this innovative and rapidly evolving line of research, and discuss its expected impact on both quantum information theory and high-energy physics.
Abstract The production of single top quarks and top antiquarks via the t-channel exchange of a virtual W boson is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV at the LHC using 140 fb−1 of ATLAS data. The total cross-sections are determined to be $$ \sigma (tq)={137}_{-8}^{+8} $$ σ tq = 137 − 8 + 8 pb and $$ \sigma \left(\overline{t}q\right)={84}_{-5}^{+6} $$ σ t ¯ q = 84 − 5 + 6 pb for top-quark and top-antiquark production, respectively. The combined cross-section is found to be $$ \sigma \left( tq+\overline{t}q\right)={221}_{-13}^{+13} $$ σ tq + t ¯ q = 221 − 13 + 13 pb and the cross-section ratio is $$ {R}_t=\sigma (tq)/\sigma \left(\overline{t}q\right)={1.636}_{-0.034}^{+0.036} $$ R t = σ tq / σ t ¯ q = 1.636 − 0.034 + 0.036 . The predictions at next-to-next-to-leading-order in quantum chromodynamics are in good agreement with these measurements. The predicted value of Rt using different sets of parton distribution functions is compared with the measured value, demonstrating the potential to further constrain the functions when using this result in global fits. The measured cross-sections are interpreted in an effective field theory approach, setting limits at the 95% confidence level on the strength of a four-quark operator and an operator coupling the third quark generation to the Higgs boson doublet: $$ -0.37<{C}_{Qq}^{3,1}/{\Lambda}^2<0.06 $$ − 0.37 < C Qq 3 , 1 / Λ 2 < 0.06 and $$ -0.87<{C}_{\phi Q}^3/{\Lambda}^2<1.42 $$ − 0.87 < C ϕQ 3 / Λ 2 < 1.42 . The constraint |Vtb| > 0.95 at the 95% confidence level is derived from the measured value of $$ \sigma \left( tq+\overline{t}q\right) $$ σ tq + t ¯ q , assuming that the Wtb interaction is a left-handed weak coupling and that |Vtb| ≫ |Vtd|, |Vts|. In a more general approach, pairs of CKM matrix elements involving top quarks are simultaneously constrained, leading to confidence contours in the corresponding two-dimensional parameter spaces.
Differential cross sections for top quark pair ($\mathrm{t\bar{t}}$) production are measured in proton-proton collisions at a center-of-mass energy of 13 TeV using a sample of events containing two oppositely charged leptons. The data were recorded with the CMS detector at the CERN LHC and correspond to an integrated luminosity of 138 fb$^{-1}$. The differential cross sections are measured as functions of kinematic observables of the $\mathrm{t\bar{t}}$ system, the top quark and antiquark and their decay products, as well as of the number of additional jets in the event. The results are presented as functions of up to three variables and are corrected to the parton and particle levels. When compared to standard model predictions based on quantum chromodynamics at different levels of accuracy, it is found that the calculations do not always describe the observed data. The deviations are found to be largest for the multi-differential cross sections.
