$^{113}$Cd $β$-decay spectrum and $g_{\rm A}$ quenching using spectral moments
Joel Kostensalo, Eligio Lisi, Antonio Marrone, Jouni Suhonen
备注：
Revised version, results unchanged. Matches version published in PRC (title slightly shortened, text revised, appendices added, figures presented in different order)
We present an alternative analysis of the $^{113}$Cd $β$-decay electron energy spectrum in terms of spectral moments $μ_n$, corresponding to the averaged values of $n^{\rm th}$ powers of the $β$ particle energy. The zeroth moment $μ_0$ is related to the decay rate, while higher moments $μ_n$ are related to the spectrum shape. The here advocated spectral-moment method (SMM) allows for a complementary understanding of previous results, obtained using the so-called spectrum-shape method (SSM) and its revised version, in terms of two free parameters: $r=g_{\rm A}/g_{\rm V}$ (the ratio of axial-vector to vector couplings) and $s$ (the small vector-like relativistic nuclear matrix element, $s$-NME). We present numerical results for three different nuclear models with the conserved vector current hypothesis (CVC) assumption of $g_{\rm V}=1$. We show that most of the spectral information can be captured by the first few moments which are simple quadratic forms (conic sections) in the $(r,\,s)$ plane: an ellipse for $n=0$ and hyperbolae for $n\geq 1$, all being nearly degenerate as a result of cancellations among nuclear matrix elements. The intersections of these curves, as obtained by equating theoretical and experimental values of $μ_n$, identify the favored values of $(r,\,s)$ at a glance, without performing detailed fits. In particular, we find that values around $r\sim 1$ and $s\sim 1.6$ are consistently favored in each nuclear model, confirming the evidence for $g_{\rm A}$ quenching in $^{113}$Cd, and shedding light on the role of the $s$-NME. We briefly discuss future applications of the SMM to other forbidden $β$-decay spectra sensitive to $g_{\rm A}$.
Many-body correlations as the origin of Gamow-Teller quenching in nuclear $β$-decay
School of Physical Science and Technology, Southwest University（西南大学物理科学与技术学院）；School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院）
We examine the leading effects of two-body weak currents from chiral effective field theory on the matrix elements governing neutrinoless double-beta decay. In the closure approximation these effects are generated by the product of a one-body current with a two-body current, yielding both two- and three-body operators. When the three-body operators are considered without approximation, they quench matrix elements by about 10%, less than suggested by prior work, which neglected portions of the operators. The two-body operators, when treated in the standard way, can produce much larger quenching…
In this review the quenching of the weak axial-vector coupling strength, $g_{\rm A}$, is discussed in nuclear $β$ and double-$β$ decays. On one hand, the nuclear-medium and nuclear many-body effects are separated, and on the other hand the quenching is discussed from the points of view of different many-body methods and different $β$-decay and double-$β$-decay processes. Both the historical background and the present status are reviewed and contrasted against each other. The theoretical considerations are tied to performed and planned measurements, and possible new measurements are urged, when…
Relativistic heavy-ion experiments have observed similar quenching effects for (prompt) $D$ mesons compared to charged hadrons for transverse momenta larger than 6-8~GeV, which remains a mystery since heavy quarks typically lose less energies in quark-gluon plasma than light quarks and gluons. Recent measurements of the nuclear modification factors of $B$ mesons and $B$-decayed $D$ mesons by the CMS Collaboration provide a unique opportunity to study the flavor hierarchy of jet quenching. Using a linear Boltzmann transport model combined with hydrodynamics simulation, we study the energy loss …
Detection of the neutrinoless $ββ$ ($0νββ$) decay is of high priority in the particle- and neutrino-physics communities. The detectability of this decay mode is strongly influenced by the value of the weak axial-vector coupling constant $g_{\rm A}$. The recent nuclear-model analyses of $β$ and $ββ$ decays suggest that the value of $g_{\rm A}$ could be dramatically quenched, reaching ratios of $g^{\rm free}_{\rm A}/g_{\rm A}\approx 4$, where $g^{\rm free}_{\rm A}=1.27$ is the free, neutron-decay, value of $g_{\rm A}$. The effects of this quenching appear devastating for the sensitivity of the p…
In this article we present an updated spectrum-shape analysis of the $^{113}$Cd fourfold forbidden non-unique $β$-decay transition in order to address the quenching of the weak axial-vector coupling $g_{\rm A}$ in low-momentum exchange nuclear processes. The experimental data were collected in a dedicated low-threshold run with the COBRA demonstrator at the LNGS and resulted in 44 individual $^{113}$Cd spectra. These data are evaluated in the context of three nuclear model frameworks based on a revised version of the spectrum-shape method and the conserved vector current hypothesis. The novel …
I discuss how the axial current coupling constant $g_A$ renormalized in scale symmetric chiral EFT defined at a chiral matching scale impacts on the axial current matrix elements on beta decays in nuclei with and without neutrinos. The "quenched" $g_A$ observed in nuclear superallowed Gamow-Teller transitions, a long-standing puzzle in nuclear physics, is shown to encode the emergence of chiral-scale symmetry hidden in QCD in the vacuum. This enables one to explore how trace-anomaly-induced scale symmetry breaking enters in the renormalized $g_A$ in nuclei applicable to certain non-unique forb…
The quenching of the axial-vector coupling constant $g_A$ in $β$-decay: joint effects from chiral two-body currents and many-body correlations
Key Laboratory of Beam Technology of Ministry of Education, School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院教育部射线技术重点实验室）；School of Nuclear Science and Technology, Lanzhou University（兰州大学核科学与技术学院）；Frontiers Science Center for Rare isotopes, Lanzhou University（兰州大学稀有同位素前沿科学中心）；Key Laboratory of Beam Technology of Ministry of Education, Institute of Radiation Technology, Beijing Academy of Science and Technology（北京市科学技术研究院辐射技术研究所教育部射线技术重点实验室）；Dipartimento di Fisica, Università degli Studi di Milano, and INFN, Sezione di Milano（米兰大学物理系和意大利国家核物理研究所米兰分部）；RIKEN Nishina Center（理化学研究所西冈中心）；Center for Mathematics and Physics, University of Aizu（会津大学数理研究中心）；Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）
Neutrino nuclear responses associated with medium momentum transfer of q=20-80 MeV for astro neutrinos and double beta decays were studied by using charge exchange reactions on Te128 and Te130. Gamow-Teller and spin dipole nuclear matrix elements are found to be reduced with respect to the pnQRPA matrix elements by the coefficient of around 0.35. The reduction is discussed in terms of the quenching of axial vector coupling (g_A).
We develop a framework to simulate jet quenching in nuclear environments on a quantum computer. The formulation is based on the light-front Hamiltonian dynamics of QCD. The Hamiltonian consists of three parts relevant for jet quenching studies: kinetic, diffusion and splitting terms. In the basis made up of $n$-particle states in momentum space, the kinetic Hamiltonian is diagonal. Matrices representing the diffusion and splitting parts are sparse. The diffusion part of the Hamiltonian depends on classical background gauge fields, which need to be sampled classically before constructing quantu…
