IDS Collaboration(Andel, B. et al), Algora, A., & Nacher, E. (2021). New beta-decaying state in Bi-214. Phys. Rev. C, 104(5), 054301–13pp.
Abstract: A new beta-decaying state in Bi-214 has been identified at the ISOLDE Decay Station at the CERN-ISOLDE facility. A preferred I-pi = (8(-)) assignment was suggested for this state based on the beta-decay feeding pattern to levels in Po-214 and shell-model calculations. The half-life of the I-pi = (8) state was deduced to be T-1/2 = 9.39(10) min. The deexcitation of the levels populated in Po-214 by the beta decay of this state was investigated via gamma-gamma coincidences and a number of new levels and transitions was identified. Shell-model calculations for excited states in Bi-214 and Po-214 were performed using two different effective interactions: the H208 and the modified Kuo-Herling particle interaction. Both calculations agree on the interpretation of the new beta-decaying state as an I-pi = 8 – isomer and allow for tentative assignment of shell-model states to several high-spin states in Po-214.
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Belle II Collaboration(Abudinen, F. et al), & Marinas, C. (2021). Search for B+ -> K+nu(nu)over-bar Decays Using an Inclusive Tagging Method at Belle H. Phys. Rev. Lett., 127(18), 181802–10pp.
Abstract: A search for the flavor-changing neutral-current decay B+ -> K+nu(nu) over bar is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The data sample corresponds to an integrated luminosity of 63 fb(-1) collected at the Upsilon(4S) resonance and a sample of 9 fb(-1) collected at an energy 60 MeV below the resonance. Because the measurable decay signature involves only a single charged kaon, a novel measurement approach is used that exploits not only the properties of the B+ -> K+nu(nu) over bar decay, but also the inclusive properties of the other B meson in the Upsilon(4S) -> B (B) over bar event, to suppress the background from other B meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of B+ -> K+nu(nu) over bar of 4.1 x 10(-5) is set at the 90% confidence level.
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Huang, F., Sanz, V., Shu, J., & Xue, X. (2021). LIGO as a probe of dark sectors. Phys. Rev. D, 104(10), 095001–9pp.
Abstract: We show how current LIGO data is able to probe interesting theories beyond the Standard Model, particularly dark sectors where a dark Higgs boson triggers symmetry breaking via a first-order phase transition. We use publicly available LIGO O2 data to illustrate how these sectors, even if disconnected from the Standard Model, can be probed by gravitational wave detectors. We link the LIGO measurements with the model content and mass scale of the dark sector, finding that current O2 data are testing a broad set of scenarios that can be mapped into many different types of dark-sector models where the breaking of SU(N) theories with Nf fermions is triggered by a dark Higgs boson at scales ? similar or equal to 108-109 GeV with reasonable parameters for the scalar potential.
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Godbole, R. M., Maharathy, S. P., Mandal, S., Mitra, M., & Sinha, N. (2021). Interference effect in lepton number violating and conserving meson decays for a left-right symmetric model. Phys. Rev. D, 104(9), 095009–22pp.
Abstract: We study the effect of interference on the lepton number violating (LNV) and lepton number conserving (LNC) three-bodymeson decaysM(1)(+)-> l(i) (+) l(j)(+)pi(+/-) that arise in a TeV-scale left-right symmetric model (LRSM) with degenerate or nearly degenerate right-handed (RH) neutrinos. The LRSM contains three RH neutrinos and a RH gauge boson. The RH neutrinos with masses in the range of M-N similar to (MeV-few GeV) can give resonant enhancement in the semileptonic LNV and LNC meson decays. In the case where only one RH neutrino contributes to these decays, the predicted new physics branching ratios of semileptonic LNV and LNC meson decaysM(1)(+)-> l(i)(+) l(j)(+) pi(-) andM(+) 1 -> l(i)(+)l(j)(-) pi(+) are equal. We find that with at least two RH neutrinos contributing to the process, the LNV and LNC decay rates can differ. Depending on the neutrino mixing angles and CP-violating phases, the branching ratios of LNVand LNC decay channelsmediated by the heavy neutrinos can be either enhanced or suppressed, and the ratio of these two rates can differ from unity.
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Belle II Collaboration(Abudinen, F. et al), & Marinas, C. (2021). Precise Measurement of the D-0 and D+ Lifetimes at Belle II. Phys. Rev. Lett., 127(21), 211801–9pp.
Abstract: We report a measurement of the D-0 and D+ lifetimes using D-0 -> K-pi(+) and D+ -> K-pi(+)pi(+) decays reconstructed in e(+)e(-) -> c (c) over bar data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy e(+)e(-) collider. The data, collected at center-of-mass energies at or near the (sic)(4S) resonance, correspond to an integrated luminosity of 72 fb(-1). The results, (tau)(D-0) = 410.5 +/- 1.1 (stat) +/- 0.8(syst) fs and tau(D-0) = 1030.4 +/- 4.7 (stat) +/- 3.1 (syst) fs, are the most precise to date and are consistent with previous determinations.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2021). Observation of excited Omega(0)(c) baryons in Omega(-)(b) -> Xi(+)(c) K-pi(-) decays. Phys. Rev. D, 104(9), L091102–14pp.
Abstract: The first observation of the Omega(-)(b) -> Xi(+)(c) K-pi(-) decay is reported using p p collision data at center of mass energies of 7, 8, and 13 TeV collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). Four excited Omega(0)(c) baryons are observed in the Xi K-+(c)- mass projection of the Omega(-)(b) -> Xi K-+(c)-pi(-) decays with the significance of each exceeding five standard deviations. They coincide with the states previously observed in prompt pp and e(+)e(-) production. Relative production rates, masses, and natural widths of the states are measured, and a test of spin hypotheses is performed. Moreover, the branching ratio of Omega(-)(b) -> Xi K-+(c)-pi(-) is measured relative to the Omega(-)(b) -> Omega(0)(c)pi(-) decay mode and a precise measurement of the Omega(-)(b) mass of 6044.3 +/- 1.2 +/- 1.1(-0.22)(+0.19) MeV is obtained.
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Fernandez, A. et al, Gadea, A., Perez-Vidal, R. M., Jurado, M., & Domingo-Pardo, C. (2021). Reinterpretation of excited states in Po-212: Shell-model multiplets rather than alpha-cluster states. Phys. Rev. C, 104(5), 054316–19pp.
Abstract: A gamma-ray spectroscopic study of Po-212 was performed at the Grand Accelerateur National d'Ions Lourds, using the inverse kinematics alpha-transfer reaction C-12(Pb-208, Po-212) Be-8 and the AGATA spectrometer. A careful analysis based on gamma gamma coincidence relations allowed us to establish 14 new excited states in the energy range between 1.9 and 3.3 MeV. None of these states, however, can be considered as candidates for the levels with spins and parities of 1(-) and 2(-) and excitation energies below 2.1 MeV, which have been predicted by recent alpha-cluster model calculations. A systematic comparison of the experimentally established excitation scheme of Po-212 with shell-model calculations was performed. This comparison suggests that the six states with excitation energies (spins and parities) of 1744 (4(-)), 1751 (8(-)), 1787 (6(-)), 1946 (4(-)), 1986 (8(-)), and 2016 (6(-)) keV, which previously were interpreted as alpha-cluster states, may in fact be of positive parity and belong to low-lying shell-model multiplets. This reinterpretation of the structure of Po-212 is supported by experimental information with respect to the linear polarization of gamma rays, which suggests a magnetic character of the 432-keV gamma ray decaying from the state at an excitation energy of 1787 keV to the 6(1)(+) yrast state, and exclusive reaction cross sections.
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Hagstotz, S., de Salas, P. F., Gariazzo, S., Pastor, S., Gerbino, M., Lattanzi, M., et al. (2021). Bounds on light sterile neutrino mass and mixing from cosmology and laboratory searches. Phys. Rev. D, 104(12), 123524–20pp.
Abstract: We present a consistent framework to set limits on properties of light sterile neutrinos coupled to all three active neutrinos using a combination of the latest cosmological data and terrestrial measurements from oscillations, beta-decay, and neutrinoless double-beta-decay (0 nu beta beta) experiments. We directly constrain the full 3 + 1 active-sterile mixing matrix elements vertical bar U-alpha 4 vertical bar(2) , with alpha is an element of (e,mu,tau), and the mass-squared splitting Delta m(41)(2) (math) m(4)(2) – m(1)(2). We find that results for a 3 + 1 case differ from previously studied 1 + 1 scenarios where the sterile is coupled to only one of the neutrinos, which is largely explained by parameter space volume effects. Limits on the mass splitting and the mixing matrix elements are currently dominated by the cosmological datasets. The exact results are slightly prior dependent, but we reliably find all matrix elements to be constrained below vertical bar U-alpha 4 vertical bar(2) less than or similar to 10(-3) . Short-baseline neutrino oscillation hints in favor of eV-scale sterile neutrinos arc in serious tension with these bounds, irrespective of prior assumptions. We also translate the bounds from the cosmological analysis into constraints on the parameters probed by laboratory searches, such as m(beta) or m(beta)(beta), the effective mass parameters probed by beta-decay and 0 nu beta beta searches, respectively. When allowing for mixing with a light sterile neutrino, cosmology leads to upper bounds of m(beta) < 0.09 eV and m(beta)(beta )< 0.07 eV at 95% CL, more stringent than the limits from current laboratory experiments.
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Feijoo, A., Liang, W. H., & Oset, E. (2021). (DD0)-D-0 pi(+) mass distribution in the production of the T-cc exotic state. Phys. Rev. D, 104(11), 114015–7pp.
Abstract: We perform a unitary coupled channel study of the interaction of the D*D-+(0), D*D-0(+) channels and find a state barely bound, very close to isospin I = 0. We take the experimental mass as input and obtain the width of the state and the (DD0 pi-)-D-0+ mass distribution. When the mass of the T-cc state quoted in the experimental paper from raw data is used, the width obtained is of the order of the 80 keV, small compared to the value given in that work. Yet, when the mass obtained in an analysis of the data considering the experimental resolution is taken, the width obtained is about 43 keV and both the width and the (DD0 pi+)-D-0 mass distribution are in remarkable agreement with the results obtained in that latter analysis.
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NA64 Collaboration(Andreev, Y. M. et al), & Molina Bueno, L. (2021). Search for pseudoscalar bosons decaying into e(+)e(-) pairs in the NA64 experiment at the CERN SPS. Phys. Rev. D, 104(11), L111102–5pp.
Abstract: We report the results of a search for a light pseudoscalar particle a that couples to electrons and decays to e(+) e(-) perfbnned using the high-energy CERN SPS H4 electron beam. If such light pseudoscalar exists, it could explain the ATOMKI anomaly (an excess of e(+) e(-) pairs in the nuclear transitions of Be-8 and 4 He nuclei at the invariant mass similar or equal to 17 MeV observed by the experiment at the 5 MV Van de Graaff accelerator at ATOMKI, Hungary). We used the NA64 data collected in the “visible mode” configuration with a total statistics corresponding to 8.4 x 10(10) electrons on target (EOT) in 2017 and 2018. In order to increase sensitivity to small coupling parameter epsilon we also used the data collected in 2016-2018 in the “invisible mode” configuration of NA64 with a total statistics corresponding to 2.84 x 10(11) EOT. The background and efficiency estimates for these two configurations were retained from our previous analyses searching for light vector bosons and axionlike particles (ALP) (the latter were assumed to couple predominantly to gamma). In this work we recalculate the signal yields, which are different due to different cross section and lifetime of a pseudoscalar particle a, and perform a new statistical analysis. As a result, the region of the two dimensional parameter space m(a) – epsilon in the mass range from 1 to 17.1 MeV is excluded. At the mass of the central value of the ATOMKI anomaly (the first result obtained on the beryllium nucleus, 16.7 MeV) the values of epsilon in the range 2.1 x 10(-4) < epsilon < 3.2 x 10(-4) are excluded.
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