IDS Collaboration(Heideman, J. et al), Algora, A., & Morales, A. I. (2023). Evidence of nonstatistical neutron emission following beta decay near doubly magic Sn-132. Phys. Rev. C, 108(2), 024311–9pp.
Abstract: Models of the beta-delayed neutron emission (beta n) assume that neutrons are emitted statistically via an intermediate compound nucleus post beta decay. Evidence to the contrary was found in an In-134 beta-decay experiment carried out at ISOLDE CERN. Neutron emission probabilities from the unbound states in Sn-134 to known low-lying, single-particle states in Sn-133 were measured. The neutron energies were determined using the time-of-flight technique, and the subsequent decay of excited states in Sn-133 was studied using gamma-ray detectors. Individual beta n probabilities were determined by correlating the relative intensities and energies of neutrons and gamma rays. The experimental data disagree with the predictions of representative statistical models which are based upon the compound nucleus postulate. Our results suggest that violation of the compound nucleus assumption may occur in beta-delayed neutron emission. This impacts the neutron-emission probabilities and other properties of nuclei participating in the r-process. A model of neutron emission, which links the observed neutron emission probabilities to nuclear shell effects, is proposed.
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Magalhaes, R. B., Maso-Ferrando, A., Olmo, G. J., & Crispino, L. C. B. (2023). Asymmetric wormholes in Palatini f (R) gravity: Energy conditions, absorption, and quasibound states. Phys. Rev. D, 108(2), 024063–20pp.
Abstract: We investigate the scalar absorption spectrum of wormhole solutions constructed via the recently developed thin-shell formalism for Palatini f(R) gravity. Such wormholes come from the matching of two Reissner-Nordstrom spacetimes at a timelike hypersurface (shell), which, according to the junction conditions in Palatini f(R), can be stable and have either positive or negative energy density. In particular, we identified a new physically interesting configuration made out of two overcharged Reissner-Nordstrom spacetimes, whose absorption profile departs from that of black holes and other previously considered wormholes in the whole range of frequencies. Unlike in symmetric wormhole solutions, the asymmetry of the effective potential causes the dilution of the resonances associated to the quasibound states for the high -frequency regime. Therefore, slight asymmetries in wormhole space-times could have a dramatic impact on the observable features associated to resonant states.
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IDS Collaboration(Stryjczyk, M. et al.), & Nacher, E. (2023). Simultaneous gamma-ray and electron spectroscopy of 182,184,186Hg isotopes. Phys. Rev. C, 108(1), 014308–20pp.
Abstract: Background: The mercury isotopes around N = 104 are a well-known example of nuclei exhibiting shape coex-istence. Mixing of configurations can be studied by measuring the monopole strength rho^2(E0), however, currently the experimental information is scarce and lacks precision, especially for the I^pi -> I^pi (I not = 0) transitions. Purpose: The goals of this study were to increase the precision of the known branching ratios and internal conversion coefficients, to increase the amount of available information regarding excited states in 182,184,186Hg, and to interpret the results in the framework of shape coexistence using different models. Method: The low-energy structures in 182,184,186Hg were populated in the & beta; decay of 182,184,186Tl, produced at ISOLDE, CERN and purified by laser ionization and mass separation. The & gamma;-ray and internal conversion electron events were detected by five germanium clover detectors and a segmented silicon detector, respectively, and correlated in time to build decay schemes.Results: In total, 193, 178, and 156 transitions, including 144, 140, and 108 observed for the first time in a & beta;-decay experiment, were assigned to 182,184,186Hg, respectively. Internal conversion coefficients were determined for 23 transitions, out of which 12 had an E0 component. Extracted branching ratios allowed the sign of the interference term in 182Hg as well as & rho;2(E 0; 0+2 & RARR; 0+1 ) and B(E2; 0+2 & RARR; 2+1 ) in 184Hg to be determined. By means of electron-electron coincidences, the 0+3 state was identified in 184Hg. The experimental results were qualitatively reproduced by five theoretical approaches, the interacting boson model with configuration mixing with two different parametrizations, the general Bohr Hamiltonian, the beyond mean-field model, and the symmetry-conserving configuration-mixing model. However, a quantitative description is lacking. Conclusions: The presence of shape coexistence in neutron-deficient mercury isotopes was confirmed and evidence for the phenomenon existing at higher energies was found. The new experimental results provide important spectroscopic input for future Coulomb excitation studies.
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Abreu, L. M., Navarra, F. S., Nielsen, M., & Vieira, H. P. L. (2023). Multiplicity of Z(cs)(3985) in heavy ion collisions. Phys. Rev. D, 107(11), 114013–9pp.
Abstract: Using the coalescence model we compute the multiplicity of Z(cs)(3985)(-) (treated as a compact tetraquark) at the end of the quark gluon plasma phase in heavy ion collisions. Then we study the time evolution of this state in the hot hadron gas phase. We calculate the thermal cross sections for the collisions of the Z(cs)(3985)(-) with light mesons using effective Lagrangians and form factors derived from QCD sum rules for the vertices Z(cs)(D) over bar (s)* D and Z(cs)(D) over bar D-s*. We solve the kinetic equation and find how the Z(cs)(3985)(-) multiplicity is affected by the considered reactions during the expansion of the hadronic matter. A comparison with the statistical hadronization model predictions is presented. Our results show that the tetraquark yield increases by a factor of about 2-3 from the hadronization to the kinetic freeze-out. We also make predictions for the dependence of the Z(cs)(3985)(-) yield on the centrality, the center-of-mass energy and the charged hadron multiplicity measured at midrapidity [dN(ch)/d eta(eta < 0.5)].
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Heavy Flavor Averaging Group(Amhis, Y. et al), & Oyanguren, A. (2023). Averages of b-hadron, c-handron, and t-lepton properties as of 2021. Phys. Rev. D, 107(5), 052008–365pp.
Abstract: This paper reports world averages of measurements of b-hadron, c-hadron, and τ-lepton properties obtained by the Heavy Flavor Averaging Group using results available before April 2021. In rare cases, significant results obtained several months later are also used. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, parameters of semileptonic decays, and Cabibbo-Kobayashi-Maskawa matrix elements.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cantero, J., et al. (2023). Production of Upsilon(nS) mesons in Pb plus Pb and pp collisions at 5.02 TeV. Phys. Rev. C, 107(5), 054912–25pp.
Abstract: A measurement of the production of vector bottomonium states, Upsilon(1S), Upsilon(2S), and Upsilon(3S), in Pb + Pb and pp collisions at a center-of-mass energy per nucleon pair of 5.02 TeV is presented. The data correspond to integrated luminosities of 1.38 nb(-1) of Pb + Pb data collected in 2018, 0.44 nb-1 of Pb + Pb data collected in 2015, and 0.26 fb(-1) of pp data collected in 2017 by the ATLAS detector at the Large Hadron Collider. The measurements are performed in the dimuon decay channel for transverse momentum p(T)(mu mu) < 30 GeV, absolute rapidity vertical bar y(mu mu)vertical bar < 1.5, and Pb + Pb event centrality 0-80%. The production rates of the three bottomonium states in Pb + Pb collisions are compared with those in pp collisions to extract the nuclear modification factors as functions of event centrality, p(T)(mu mu), and vertical bar y(mu mu)vertical bar. In addition, the suppression of the excited states relative to the ground state is studied. The results are compared with theoretical model calculations.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cantero, J., et al. (2023). Correlations between flow and transverse momentum in Xe plus Xe and Pb plus Pb collisions at the LHC with the ATLAS detector: A probe of the heavy-ion initial state and nuclear deformation. Phys. Rev. C, 107(5), 054910–28pp.
Abstract: The correlations between flow harmonics v(n) for n = 2, 3, and 4 and mean transverse momentum [pT] in Xe-129 + Xe-129 and Pb-208 + Pb-208 collisions at root s = 5.44 and 5.02 TeV, respectively, are measured using charged particles with the ATLAS detector. The correlations are potentially sensitive to the shape and size of the initial geometry, nuclear deformation, and initial momentum anisotropy. The effects from nonflow and centrality fluctuations are minimized, respectively, via a subevent cumulant method and an event-activity selection based on particle production at very forward rapidity. The v(n)-[p(T)] correlations show strong dependencies on centrality, harmonic number n, pT, and pseudorapidity range. Current models qualitatively describe the overall centrality -and system-dependent trends but fail to quantitatively reproduce all features of the data. In central collisions, where models generally show good agreement, the v(2)-[p(T)] correlations are sensitive to the triaxiality of the quadruple deformation. Comparison of the model with the Pb + Pb and Xe + Xe data confirms that the Xe-129 nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the Xe-129 nucleus from high-energy heavy-ion collisions.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cantero, J., et al. (2023). Measurements of the suppression and correlations of dijets in Pb plus Pb collisions at root s(NN)=5.02 TeV. Phys. Rev. C, 107(5), 054908–31pp.
Abstract: Studies of the correlations of the two highest transverse momentum (leading) jets in individual Pb+Pb colli-sion events can provide information about the mechanism of jet quenching by the hot and dense matter created in such collisions. In Pb+Pb and pp collisions at root NN = 5.02 TeV, measurements of the leading dijet transverse momentum (pT) correlations are presented. Additionally, measurements in Pb+Pb collisions of the dijet pair nuclear modification factors projected along leading and subleading jet pT are made. The measurements are per-formed using the ATLAS detector at the LHC with 260 pb(-1) of pp data collected in 2017 and 2.2 nb(-1) of Pb+Pb data collected in 2015 and 2018. An unfolding procedure is applied to the two-dimensional leading and sublead-ing jet pT distributions to account for experimental effects in the measurement of both jets. Results are provided for dijets with leading jet pT greater than 100 GeV. Measurements of the dijet-yield-normalized xJ distributions in Pb+Pb collisions show an increased fraction of imbalanced jets compared to pp collisions; these measurements are in agreement with previous measurements of the same quantity at 2.76 TeV in the overlapping kinematic range. Measurements of the absolutely normalized dijet rate in Pb+Pb and pp collisions are also presented, and show that balanced dijets are significantly more suppressed than imbalanced dijets in Pb+Pb collisions. It is observed in the measurements of the pair nuclear modification factors that the subleading jets are significantly suppressed relative to leading jets with pT between 100 and 316 GeV for all centralities in Pb+Pb collisions.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cantero, J., et al. (2023). Measurement of muon pairs produced via gamma gamma scattering in nonultraperipheral Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector. Phys. Rev. C, 107(5), 054907–42pp.
Abstract: Results of a measurement of dimuon photoproduction in nonultraperipheral Pb + Pb collisions at root sNN = 5.02 TeV are presented. The measurement uses ATLAS data from the 2015 and 2018 Pb + Pb data-taking periods at the LHC with an integrated luminosity of 1.94 nb-1. The gamma gamma -> mu+mu- pairs are identified via selections on pair momentum asymmetry and acoplanarity. Differential cross sections for dimuon production are measured in different centrality, average muon momentum, and pair rapidity intervals as functions of acoplanarity and k perpendicular to, the transverse momentum kick of one muon relative to the other. Measurements are also made as a function of the rapidity separation of the muons and the angle of the muon pair relative to the second-order event plane to test whether magnetic fields generated in the quark-gluon plasma affect the measured muons. A prior observation of a centrality-dependent broadening of the acoplanarity distribution is confirmed. Furthermore, the improved precision of the measurement reveals a depletion in the number of pairs having small acoplanarity or k perpendicular to values in more central collisions. The acoplanarity distributions in a given centrality interval are observed to vary with the mean pT of the muons in the pair, but the k perpendicular to distributions do not. Comparisons with recent theoretical predictions are made. The predicted trends associated with effects of magnetic fields on the dimuons are not observed.
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DUNE Collaboration(Abud, A. A. et al), Amedo, P., Antonova, M., Barenboim, G., Benitez Montiel, C., Cervera-Villanueva, A., et al. (2023). Impact of cross-section uncertainties on supernova neutrino spectral parameter fitting in the Deep Underground Neutrino Experiment. Phys. Rev. D, 107(11), 112012–25pp.
Abstract: A primary goal of the upcoming Deep Underground Neutrino Experiment (DUNE) is to measure the Oo10 thorn MeV neutrinos produced by a Galactic core-collapse supernova if one should occur during the lifetime of the experiment. The liquid-argon-based detectors planned for DUNE are expected to be uniquely sensitive to the & nu;e component of the supernova flux, enabling a wide variety of physics and astrophysics measurements. A key requirement for a correct interpretation of these measurements is a good understanding of the energy-dependent total cross section & sigma;oE & nu; thorn for charged-current & nu;e absorption on argon. In the context of a simulated extraction of supernova & nu;e spectral parameters from a toy analysis, we investigate the impact of & sigma;oE & nu; thorn modeling uncertainties on DUNE's supernova neutrino physics sensitivity for the first time. We find that the currently large theoretical uncertainties on & sigma;oE & nu; thorn must be substantially reduced before the & nu;e flux parameters can be extracted reliably; in the absence of external constraints, a measurement of the integrated neutrino luminosity with less than 10% bias with DUNE requires & sigma;oE & nu; thorn to be known to about 5%. The neutrino spectral shape parameters can be known to better than 10% for a 20% uncertainty on the cross-section scale, although they will be sensitive to uncertainties on the shape of & sigma;oE & nu; thorn . A direct measurement of low-energy & nu;e-argon scattering would be invaluable for improving the theoretical precision to the needed level.
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