Wed·Jul 17, 2019Wednesday·July 17, 2019

1. 01*

   Average and recommended half-life values for two-neutrino double beta decay: upgrade-2019

   A.S. Barabash🇷🇺

   All existing positive results on two neutrino double beta decay and two neutrino double electron capture in different nuclei were analyzed. Using the procedure recommended by the Particle Data Group, weighted average values for half-lives of ${}^{48}$Ca, ${}^{76}$Ge, ${}^{82}$Se, ${}^{96}$Zr, ${}^{100}$Mo, ${}^{100}$Mo - ${}^{100}$Ru ($0_1^{+}$), ${}^{116}$Cd, ${}^{130}$Te, ${}^{136}$Xe, ${}^{150}$Nd, ${}^{150}$Nd - ${}^{150}$Sm ($0_1^{+}$), ${}^{238}$U, ${}^{78}$Kr and ${}^{124}$Xe were obtained. Existing geochemical data were analyzed and recommended values for half-lives of ${}^{128}$Te and ${}^{130}$Ba are proposed. I recommend the use of these results as the most currently reliable values for half-lives.

   nucl-exAIP Conf.Proc.(2019)·39 citations
2. 02*

   ${}_{\Lambda }^3\mathrm{H}$ and ${}_{\bar{\Lambda }}^3\bar{\mathrm{H}}$ lifetime measurement in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV via two-body decay

   ALICE Collaboration

   An improved value for the lifetime of the (anti-)hypertriton has been obtained using the data sample of Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV collected by the ALICE experiment at the LHC. The (anti-)hypertriton has been reconstructed via its charged two-body mesonic decay channel and the lifetime has been determined from an exponential fit to the d$N$/d($ct$) spectrum. The measured value, $\tau$ = 242${}_{-38}^{+34}$ (stat.) $\pm$ 17 (syst.) ps, is compatible with all the available theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime puzzle.

   nucl-exhep-exPLB(2019)·80 citations
3. 03*

   New Test of Modulated Electron Capture Decay of Hydrogen-Like ${}^{142}$Pm Ions: Precision Measurement of Purely Exponential Decay

   F. C. Ozturk · B. Akkus · D. Atanasov · H. Beyer · F. Bosch · D. Boutin · C. Brandau · P. Bühler · R. B. Cakirli · R. J. Chen · W. D. Chen · X. C. Chen and 83 other authors

   An experiment addressing electron capture (EC) decay of hydrogen-like ${}^{142}$Pm${}^{60+}$ ions has been conducted at the experimental storage ring (ESR) at GSI. The decay appears to be purely exponential and no modulations were observed. Decay times for about 9000 individual EC decays have been measured by applying the single-ion decay spectroscopy method. Both visually and automatically analysed data can be described by a single exponential decay with decay constants of 0.0126(7) s${}^{-1}$ for automatic analysis and 0.0141(7) s${}^{-1}$ for manual analysis. If a modulation superimposed on the exponential decay curve is assumed, the best fit gives a modulation amplitude of merely 0.019(15), which is compatible with zero and by 4.9 standard deviations smaller than in the original observation which had an amplitude of 0.23(4).

   nucl-exPLB(2019)·23 citations
4. 04*

   Beam induced space-charge effects in Time Projection Chambers in low-energy nuclear physics experiments

   J. S. Randhawa🇨🇦 · M. Cortesi🇺🇸 · Y. Ayyad🇯🇵 · W. Mittig🇺🇸 · T. Ahn🇺🇸 · D. Bazin🇺🇸 · S. Beceiro-Novo🇺🇸 · L. Carpenter🇺🇸 · K. J. Cook🇦🇺 · M. Dasgupta🇦🇺 · S. Henderson🇺🇸 · D. J. Hinde🇦🇺 and 5 other authors

   Tracking capabilities in Time Projection Chambers (TPCs) are strongly dictated by the homogeneity of the drift field. Ion back-flow in various gas detectors, mainly induced by the secondary ionization processes during amplification, has long been known as a source of drift field distortion. Here, we report on beam-induced space-charge effects from the primary ionization process in the drift region in low-energy nuclear physics experiment with Active Target Time Projection Chamber (AT-TPC). A qualitative explanation of the observed effects is provided using detailed electron transport simulations. As ion mobility is a crucial factor in the space-charge effects, the need for a careful optimization of gas properties is highlighted. The impact of track distortion on tracking algorithm performance is also discussed.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2019)·7 citations
5. 05*

   Radiative Corrections to Neutron and Nuclear Beta Decays Revisited

   Andrzej Czarnecki🇨🇦 · William J. Marciano🇺🇸 · Alberto Sirlin🇺🇸

   The universal radiative corrections common to neutron and super-allowed nuclear beta decays (also known as ``inner'' corrections) are revisited in light of a recent dispersion relation study that found $+2.467(22)\%$, i.e.~about $2.4\sigma$ larger than the previous evaluation. For comparison, we consider several alternative computational methods. All employ an updated perturbative QCD four-loop Bjorken sum rule (BjSR) defined QCD coupling supplemented with a nucleon form factor based Born amplitude to estimate axial-vector induced hadronic contributions. In addition, we now include hadronic contributions from low $Q^2$ loop effects based on duality considerations and vector meson resonance interpolators. Our primary result, $2.426(32)\%$ corresponds to an average of a Light Front Holomorphic QCD approach and a three resonance interpolator fit. It reduces the dispersion relation discrepancy to approximately $1.1\sigma$ and thereby provides a consistency check. Consequences of our new radiative correction estimate, along with that of the dispersion relation result, for CKM unitarity are discussed. The neutron lifetime-$g_A$ connection is updated and shown to suggest a shorter neutron lifetime $<879$ s. We also find an improved bound on exotic, non-Standard Model, neutron decays or oscillations of the type conjectured as solutions to the neutron lifetime problem, $\text{BR}(n\to \text{exotics})<0.16\%$.

   ↳ hep-phnucl-exnucl-thPRD(2019)·208 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.