Thu·Dec 19, 2019Thursday·December 19, 2019

1. 01*

   Stable beam experiments in wide energy ranges serving low energy nuclear astrophysics

   Gy. Gyürky🇭🇺

   In experimental nuclear astrophysics it is common knowledge that reaction cross sections must be measured in the astrophysically relevant, low energy ranges or at least as close to them as possible. In most of the cases, however, it is impossible to reach such low energies. The reactions must therefore be studied at higher energies and the cross sections must be extrapolated to lower ones. In this paper the importance of cross section measurements in wide energy ranges are emphasized and a few examples are shown from the areas of hydrogen burning processes and heavy element nucleosynthesis.

   nucl-exastro-ph.SRJ.Phys.Conf.Ser.(2020)·0 citations
2. 02*

   Effective charge from lattice QCD

   Zhu-Fang Cui🇨🇳 · Jin-Li Zhang🇨🇳 · Daniele Binosi🇮🇹 · Feliciano De Soto🇪🇸 · Cédric Mezrag🇫🇷 · Joannis Papavassiliou🇪🇸 · Craig D. Roberts🇨🇳 · Jose Rodríguez-Quintero🇪🇸 · Jorge Segovia🇪🇸 · Savvas Zafeiropoulos🇫🇷

   Using lattice configurations for quantum chromodynamics (QCD) generated with three domain-wall fermions at a physical pion mass, we obtain a parameter-free prediction of QCD's renormalisation-group-invariant process-independent effective charge, $\hat{\alpha }(k^2)$. Owing to the dynamical breaking of scale invariance, evident in the emergence of a gluon mass-scale, this coupling saturates at infrared momenta: $\hat{\alpha }(0)/\pi =0.97(4)$. Amongst other things: $\hat{\alpha }(k^2)$ is almost identical to the process-dependent (PD) effective charge defined via the Bjorken sum rule; and also that PD charge which, employed in the one-loop evolution equations, delivers agreement between pion parton distribution functions computed at the hadronic scale and experiment. The diversity of unifying roles played by $\hat{\alpha }(k^2)$ suggests that it is a strong candidate for that object which represents the interaction strength in QCD at any given momentum scale; and its properties support a conclusion that QCD is a mathematically well-defined quantum field theory in four dimensions.

   ↳ hep-phhep-exhep-latnucl-ex+1CPC(2020)·145 citations
3. 03*

   Lattice QCD Determination of $g_A$

   André Walker-Loud🇺🇸 · Evan Berkowitz🇺🇸 · David A. Brantley🇺🇸 · Arjun Gambhir🇺🇸 · Pavlos Vranas🇺🇸 · Chris Bouchard🇬🇧 · Chia Cheng Chang🇯🇵 · M. A. Clark🇺🇸 · Nicolas Garron🇬🇧 · Bálint Joó🇺🇸 · Thorsten Kurth🇺🇸 · Henry Monge-Camacho🇺🇸 and 4 other authors

   The nucleon axial coupling, $g_A$, is a fundamental property of protons and neutrons, dictating the strength with which the weak axial current of the Standard Model couples to nucleons, and hence, the lifetime of a free neutron. The prominence of $g_A$ in nuclear physics has made it a benchmark quantity with which to calibrate lattice QCD calculations of nucleon structure and more complex calculations of electroweak matrix elements in one and few nucleon systems. There were a number of significant challenges in determining $g_A$, notably the notorious exponentially-bad signal-to-noise problem and the requirement for hundreds of thousands of stochastic samples, that rendered this goal more difficult to obtain than originally thought. I will describe the use of an unconventional computation method, coupled with "ludicrously'" fast GPU code, access to publicly available lattice QCD configurations from MILC and access to leadership computing that have allowed these challenges to be overcome resulting in a determination of $g_A$ with 1% precision and all sources of systematic uncertainty controlled. I will discuss the implications of these results for the convergence of $SU(2)$ Chiral Perturbation theory for nucleons, as well as prospects for further improvements to $g_A$ (sub-percent precision, for which we have preliminary results) which is part of a more comprehensive application of lattice QCD to nuclear physics. This is particularly exciting in light of the new CORAL supercomputers coming online, Sierra and Summit, for which our lattice QCD codes achieve a machine-to-machine speed up over Titan of an order of magnitude.

   ↳ hep-lathep-phnucl-exnucl-thPoS(2020)·42 citations
4. 04*

   123-321 Models of Classical Novae

   Jordi Jose (1,2)🇪🇸 · Steven N. Shore (3) · Jordi Casanova (2) ((1) UPC Barcelona, (2) IEEC Barcelona, (3) U Pisa)

   High-resolution spectroscopy has revealed large concentrations of CNO and sometimes other intermediate-mass elements in the shells ejected during nova outbursts, suggesting that the solar composition material transferred from the secondary mixes with the outermost layers of the underlying white dwarf during the thermonuclear runaway. Multidimensional simulations have shown that Kelvin-Helmholtz instabilities provide self-enrichment of the accreted envelope with material from the outermost layers of the white dwarf, at levels that agree with observations. However, the Eulerian and time-explicit nature of most multidimensional codes used to date and the overwhelming computational load have limited their applicability, and no multidimensional simulation has been conducted for a full nova cycle. This paper explores a new methodology that combines 1-D and 3-D simulations. The early stages of the explosion (i.e., mass-accretion and initiation of the runaway) have been computed with the 1-D hydrodynamic code SHIVA. When convection extends throughout the entire envelope, the structures for each model were mapped into 3-D Cartesian grids and were subsequently followed with the multidimensional code FLASH. Two key physical quantities were extracted from the 3-D simulations and subsequently implemented into SHIVA, which was used to complete the simulation through the late expansion and ejection stages: the time-dependent amount of mass dredged-up from the outer white dwarf layers, and the time-dependent convective velocity profile throughout the envelope. More massive envelopes than those reported from previous models with pre-enrichment have been found. This results in more violent outbursts, characterized by higher peak temperatures and greater ejected masses, with metallicity enhancements in agreement with observations.

   ↳ astro-ph.SRastro-ph.HEnucl-exnucl-thAstron.Astrophys.(2020)·36 citations
5. 05*

   (W)hole new field: the new GEM Time Projection Chamber of ALICE

   Dariusz Miskowiec (for the ALICE Collaboration)🇩🇪

   The ALICE Time Projection Chamber has just been upgraded by replacing the readout chambers, which cover the two ends of the cylinder, with new detectors based on the Gas Electron Multiplier (GEM) technology. We report here on the related activities at GSI Darmstadt: GEM framing and chamber production, as well as the quality assurance accompanying both procedures.

   ↳ physics.ins-detnucl-exJ.Phys.Conf.Ser.(2020)·1 citation
6. 06*

   Global Fit to Modified Neutrino Couplings and the Cabibbo-Angle Anomaly

   Antonio M. Coutinho🇨🇭 · Andreas Crivellin🇨🇭 · Claudio Andrea Manzari🇨🇭

   Recently, discrepancies of up to $4\sigma$ between the different determinations of the Cabibbo angle were observed. This "Cabibbo-angle anomaly" could be explained by lepton flavour universality (LFU) violating New Physics (NP) in the neutrino sector. However, modified neutrino couplings to Standard Model gauge bosons also affect many other observables sensitive to LFU violation which have to be taken into account in order to assess the viability of this explanation. Therefore, we perform a model-independent global analysis in a Bayesian approach and find that the tension in the Cabibbo angle is significantly reduced, while the agreement with other data is also mostly improved. In fact, non-zero modifications of electron and muon neutrino couplings are preferred at more than 99\% CL. Still, since constructive effects in the muon sector are necessary, simple models with right-handed neutrinos (whose global fit we update as a by-product) cannot fully explain data, pointing towards more sophisticated NP models.

   ↳ hep-phhep-exhep-latnucl-ex+1PRL(2020)·135 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.