Abstract A form-factor-constrained non-factorized transition-GPD reconstruction is developed for the N → Δ ( 1232 ) electromagnetic transition. The production input consists of the published CLAS magnetic multipole amplitude and electric and scalar/Coulomb quadrupole ratios. Additional external low- Q 2 ratio data are retained only as a separate ratio-sector diagnostic. The electroproduction quantities are propagated replica by replica and converted to the dimensionless Jones–Scadron transition form factors G M ∗ , G E ∗ , and G C ∗ . AICc model selection yields a modified dipole for G M ∗ , a dipole for G E ∗ , and a cubic z expansion for G C ∗ . These fits define the imposed positive- x normalization F α ( t ) = 2 G α ∗ ( − t ) for factorized, correlated exponential, Regge-like, and double-distribution-inspired transition-GPD profiles. The upper boundary of the impact-parameter transform is fixed by the largest measured absolute-form-factor point, Q 2 = 6 GeV 2 , so that no high- Q 2 continuation beyond the measured range enters the production reconstruction. The primary transverse localization observable is therefore defined from the small- Q 2 slope of the modeled transition GPD, with finite-window radial moments retained only as secondary core-shape diagnostics. For the slope-defined width, the transition form factor contributes an x -independent channel-dependent offset, while the entire x dependence is fixed by the chosen longitudinal–transverse profile ansatz. The factorized profile is x -independent and the three non-factorized families generate distinct modeled x dependences. The resulting reconstruction separates measured transition-form-factor information from model-dependent longitudinal structure and provides a controlled framework for assessing structural and covariance sensitivity in N → Δ ( 1232 ) transition tomography.
Abstract In this work, we investigate the quantum dynamics of relativistic scalar particles in a (1+1)-dimensional de Sitter spacetime deformed by rainbow gravity, in which the spacetime metric depends explicitly on the energy of the probing particles. We begin by deriving the covariant Klein–Gordon equation in this modified gravitational background and obtain its exact solutions by two independent methods, in terms of Whittaker and Hankel functions. Building upon this formulation, we analyze the corresponding energy spectrum and the semiclassical solutions, and subsequently examine vacuum particle production within the Bogoliubov approach. Both sets of solutions lead to the same particle number density, which takes the form of a thermal Bose–Einstein distribution depending only on the temporal rainbow function f 1 . In the large-mass limit, it reduces to a Boltzmann factor characterized by an effective Gibbons–Hawking temperature T = f 1 H / 2 π , showing that rainbow gravity rescales the de Sitter horizon temperature and can either enhance or suppress particle creation relative to general relativity.
Abstract Nuclear suppression factors quantify the modification of particle production in nuclei relative to free protons and thus provide insight into the properties of nuclear matter and its constituent quarks and gluons. The cross-section for photoproduction of a vector meson on a nucleus is usually determined in nucleus–nucleus collisions, which introduces a two-fold ambiguity because either nucleus can emit the photon. This can be resolved in asymmetric proton–nucleus collisions, where the ratio of photoproduction cross-sections on the proton and nucleus directly measures the nuclear suppression factor with minimal model dependence. Using simulated data corresponding to that already collected at the LHC, it is shown that the nuclear suppression factor can be measured with a statistical precision of 10% using J / ψ mesons and a few percent using ρ mesons. These results demonstrate the potential of proton-lead collisions to provide precise measurements of nuclear suppression factors and motivate future proton-lead running at the LHC.
Identified charged particle production ( pi +/-, K +/-, and p(p & horbar;)) is studied in Pb-Pb collisions at sNN=5.02 TeV and Xe-Xe collisions at sNN=5.44 TeV within the EPOS4 framework. Results obtained with and without the UrQMD hadronic cascade are compared with measurements from the ALICE Collaboration to assess the role of late-stage hadronic interactions. EPOS4 reproduces the overall trends of particle production and the mass-dependent behavior of transverse momentum ( pT) spectra associated with collective expansion. The inclusion of the hadronic phase significantly modifies proton observables, leading to a suppression of low- pT yields and an improved description of the p/pi ratio at intermediate pT, particularly in central collisions. The level of agreement remains dependent on particle species and observable, with only moderate and negligible effects observed for kaons and pions, respectively. The K/pi and p/pi ratios exhibit a clear dependence on pT and event activity, with similar behavior observed in Pb-Pb and Xe-Xe collisions at comparable charged-particle densities. These results indicate that particle production is primarily driven by event activity, while highlighting the essential role of the hadronic phase in shaping proton observables. Overall, EPOS4 with UrQMD provides a more realistic description of the data, although some deviations persist across different observables.
A small series of four caesium hafnium chloride (Cs 2HfCl 6, CHC) crystal scintillators has been measured in a low-background setup at the Gran Sasso National Laboratory of the INFN, Italy. After characterization of the detectors, new measurements concerning the rare alpha activity of natural Hf isotopes have been done. Based on cumulative data collected over 85.23 d, a new half-life value for the 174Hf alpha decay has been obtained: (2.95-0.14+0.15(stat)+/- 0.09(sys)) & times;1016 year. This result is consistent with that reported earlier, which was obtained using one of the CHC crystals employed in the present work, albeit within a different experimental setup. The combined value is T 1/2 = (2.95 +/- 0.16) & times;1016 year. These measurements have resolved the long-standing discrepancy between the previously available experimental values and theoretical predictions. The experimental limits on the half-lives for alpha decay of other natural Hf isotopes have been derived in the range of 1019-1020 year (90% C.L.). The limit for the alpha decay of 180Hf was set for the first time.
