Boso, A. et al, Domingo-Pardo, C., & Perez-Vidal, R. M. (2019). Isospin dependence of electromagnetic transition strengths among an isobaric triplet. Phys. Lett. B, 797, 134835–6pp.
Abstract: Electric quadrupole matrix elements, M-p, for the J(pi) = 2(+) -> 0(+), Delta T = 0, T = 1 transitions across the A = 46 isobaric multiplet Cr-46-V-46-Ti-46 have been measured at GSI with the FRS-LYCCA-AGATA setup. This allows direct insight into the isospin purity of the states of interest by testing the linearity of M-p with respect to T-z. Pairs of nuclei in the T = 1 triplet were studied using identical reaction mechanisms in order to control systematic errors. The M-p values were obtained with two different methodologies: (i) a relativistic Coulomb excitation experiment was performed for Cr-46 and Ti-46; (ii) a “stretched target” technique was adopted here, for the first time, for lifetime measurements in V-46 and Ti-46. A constant value of M-p across the triplet has been observed. Shell-model calculations performed within the fp shell fail to reproduce this unexpected trend, pointing towards the need of a wider valence space. This result is confirmed by the good agreement with experimental data achieved with an interaction which allows excitations from the underlying sd shell. A test of the linearity rule for all published data on complete T = 1 isospin triplets is presented.
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Caputo, A. (2019). Radiative axion inflation. Phys. Lett. B, 797, 134824–7pp.
Abstract: Planck data robustly exclude the simple lambda phi(4) scenario for inflation. This is also the case for models of “Axion Inflation” in which the inflaton field is the radial part of the Peccei-Quinn complex scalar field. In this letter we show that for the KSVZ model it is possible to match the data taking into account radiative corrections to the tree level potential. After writing down the 1-loop Coleman-Weinberg potential, we show that a radiative plateau is easily generated thanks to the fact that the heavy quarks are charged under SU(3)(c) in order to solve the strong CP problem. We also give a numerical example for which the inflationary observables are computed and the heavy quarks are predicted to have a mass m(Q) greater than or similar to 10(2) TeV.
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NA62 collaboration(Cortina Gil, E. et al), & Husek, T. (2019). Searches for lepton number violating K+ decays. Phys. Lett. B, 797, 134794–9pp.
Abstract: The NA62 experiment at CERN reports a search for the lepton number violating decays K+ -> pi(-)e(+)e(+) and K+ -> pi(-)mu(+)mu(+) using a data sample collected in 2017. No signals are observed, and upper limits on the branching fractions of these decays of 2.2 x 10(-10) and 4.2 x 10(-11) are obtained, respectively, at 90% confidence level. These upper limits improve on previously reported measurements by factors of 3 and 2, respectively.
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Guerrero, C., Tessler, M., Paul, M., Lerendegui-Marco, J., Heinitz, S., Maugeri, E. A., et al. (2019). The s-process in the Nd-Pm-Sm region: Neutron activation of Pm-147. Phys. Lett. B, 797, 134809–6pp.
Abstract: The Nd-Pm-Sm branching is of interest for the study of the s-process, related to the production of heavy elements in stars. As Sm-148 and Sm-150 are s-only isotopes, the understanding of the branching allows constraining the s-process neutron density. In this context the key physics input needed is the cross section of the three unstable nuclides in the region: Nd-147 (10.98 d half-life), Pm-147 (2.62 yr) and Pm-148 (5.37 d). This paper reports on the activation measurement of Pm-147, the longest-lived of the three nuclides. The cross section measurement has been carried out by activation at the SARAF LiLiT facility using a 56(2) μg target. Compared to the single previous measurement of Pm-147, the measurement presented herein benefits from a target 2000 times more massive. The resulting Maxwellian Averaged Cross Section (MACS) to the ground and metastable states in Pm-148 are 469(50) mb and 357(27) mb. These values are 41% higher (to the ground state) and 15% lower (to the metastable state) than the values reported so far, leading however to a total cross section of 826(107) mb consistent within uncertainties with the previous result and hence leaving unchanged the previous calculation of the s-process neutron density.
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Jiang, S. J., Sakai, S., Liang, W. H., & Oset, E. (2019). The chi c J decay to phi K*(K)over-bar, phi h(1)(1380) testing the nature of axial vector meson resonances. Phys. Lett. B, 797, 134831–5pp.
Abstract: We perform a theoretical study of the chi(cJ) -> phi K*(K) over bar -> phi K pi(K) over bar reaction taking into account the K*(K) over bar final state interaction, which in the chiral unitary approach is responsible, together with its coupled channels, for the formation of the low lying axial vector mesons, in this case the h(1)(1380) given the selection of quantum numbers. Based on this picture we can easily explain why in the chi(c0) decay the h(1)(1380) resonance is not produced, and, in the case of chi(c1) and chi(c2) decay, why a dip in the K+ pi K-0(-) mass distribution appears in the 1550-1600 MeV region, that in our picture comes from a destructive interference between the tree level mechanism and the rescattering that generates the h(1)(1380) state. Such a dip is not reproduced in pictures where the nominal h(1)(1380) signal is added incoherently to a background, which provides support to the picture where the resonance appears from rescattering of vector-pseudoscalar components.
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Ralet, D. et al, Gadea, A., & Perez, R. M. (2019). Evidence of octupole-phonons at high spin in Pb-207<bold> </bold>. Phys. Lett. B, 797, 134797–6pp.
Abstract: A lifetime measurement of the 19/2(-) state in Pb-207 has been performed using the Recoil Distance Doppler-Shift (RDDS) method. The nuclei of interest were produced in multi-nucleon transfer reactions induced by a Pb-208 beam impinging on a Mo-100 enriched target. The beam-like nuclei were detected<bold> </bold>and identified in terms of their atomic mass number in the VAMOS++ spectrometer while the prompt gamma rays were detected by the AGATA tracking array. The measured large reduced transition probability B(E3, 19/2(-) -> 13/2(+)) = 40(8) W.u. is the first indication of the octupole phonon at high spin in Pb-207. An analysis in terms of a particle-octupole-vibration coupling model indicates that the measured B(E3) value in Pb-207 is compatible with the contributions from single-phonon and single particle E3 as well as E3 strength arising from the double-octupole-phonon 6(+) state, all adding coherently. A crucial aspect of the coupling model, namely the strong mixing between single-hole and the phonon-hole states, is confirmed in a realistic shell-model calculation.
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Bruschini, R., & Gonzalez, P. (2019). Radiative decays in bottomonium beyond the long wavelength approximation. Phys. Rev. D, 100(7), 074001–13pp.
Abstract: We revisit the nonrelativistic quark model description of electromagnetic radiative decays in bottomonium. We show that even for the simplest spectroscopic quark model the calculated widths can be in good agreement with data once the experimental masses of bottomonium states and the photon energy are properly implemented in the calculation. For transitions involving the lower lying spectral states this implementation can be easily done via the long wavelength approximation. For transitions where this approximation does not apply we develop a new method of implementing the experimental energy dependencies.
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Fujita, H. et al, Algora, A., Estevez-Aguado, E., Molina, F., & Rubio, B. (2019). Experimental study of Gamow-Teller transitions via the high-energy-resolution O-18(He-3, t)F-18 reaction: Identification of the low-energy “super” -Gamow-Teller state. Phys. Rev. C, 100(3), 034618–13pp.
Abstract: Using the high-resolution O-18(He-3, t)F-18 reaction at 0 degrees and at 140 MeV/nucleon, Gamow-Teller (GT) transitions were studied. A high energy resolution of 31 keV was achieved by applying dispersion matching techniques. The main part of the observed GT transition strength is concentrated in the transition to the F-18 ground state (g.s.). The absolute values of the reduced GT transition strengths, B(GT), were derived up to E-x = 12 MeV assuming proportionality between the B(GT) values and the reaction cross sections at 0 degrees. The B(GT) value obtained from the beta decay of F-18 (g.s.) -> O-18 (g.s.) was used to determine the proportionality constant. A total B(GT) of 4.06(5) was found and 76(1)% of the strength is concentrated to the ground state of F-18. The obtained B(GT) values were compared with those from the O-18(p, n) F-18 reaction and the mirror symmetric beta(+) decay of Ne-18 -> F-18. The candidates for 1(+) states with isospin T = 1 were identified by comparison with the O-18(p, p') data. The results of shell-model and quasiparticle-random-phase approximation calculations suggest constructive contributions of various configurations to the F-18 ground state, suggesting that this state is the low-energy super GT state.
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Yang, W. Q., Mena, O., Pan, S., & Di Valentino, E. (2019). Dark sectors with dynamical coupling. Phys. Rev. D, 100(8), 083509–11pp.
Abstract: Coupled dark matter-dark energy scenarios arc modeled via a dimensionless parameter xi, which controls the strength of their interaction. While this coupling is commonly assumed to be constant, there is no underlying physical law or symmetry that forbids a time-dependent xi parameter. The most general and complete interacting scenarios between the two dark sectors should therefore allow for such a possibility, and it is the main purpose of this study to constrain two possible and well-motivated coupled cosmologies by means of the most recent and accurate early- and late-time universe observations. We find that CMB data alone prefer xi(z) > 0 and therefore a smaller amount of dark matter, alleviating some crucial and well-known cosmological data tensions. An objective assessment of the Bayesian evidence for the coupled models explored here shows no particular preference for the presence of a dynamical dark sector coupling.
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Campanario, F., Czyz, H., Gluza, J., Jelinski, T., Rodrigo, G., Tracz, S., et al. (2019). Standard model radiative corrections in the pion form factor measurements do not explain the a(mu) anomaly. Phys. Rev. D, 100(7), 076004–5pp.
Abstract: In this paper, we address the question of whether the almost four standard deviations difference between theory and experiment for the muon anomalous magnetic moment a(mu) can be explained as a higher-order Standard Model perturbation effect in the pion form factor measurements. This question has, until now, remained open, obscuring the source of discrepancies between the measurements. We calculate the last radiative corrections for the extraction of the pion form factor, which were believed to be potentially substantial enough to explain the data within the Standard Model. We find that the corrections are too small to diminish existing discrepancies in the determination of the pion form factor for different kinematical configurations of low-energy BABAR, BES-III and KLOE experiments. Consequently, they cannot noticeably change the previous predictions for a(mu) and decrease the deviations between theory and direct measurements. To solve the above issues, new data and better understanding of low-energy experimental setups are needed, especially as new direct a(mu) measurements at Fermilab and J-PARC will provide new insights and substantially shrink the experimental error.
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