Nuclear Theory·nucl-th

Tuesday·October 5, 2021

16 papers—8 primary·8 cross-listed

09
Parton physics from a heavy-quark operator product expansion: Lattice QCD calculation of the second moment of the pion distribution amplitude
William Detmold🇺🇸 · Anthony Grebe🇺🇸 · Issaku Kanamori🇯🇵 · C.-J. David Lin🇹🇼 · Santanu Mondal🇺🇸 · Robert Perry🇹🇼 · Yong Zhao🇺🇸
The pion light-cone distribution amplitude (LCDA) is a central non-perturbative object of interest for high-energy exclusive processes in quantum chromodynamics. In this article, the second Mellin moment of the pion LCDA is determined as a proof-of-concept calculation for the first numerical implementation of the heavy-quark operator product expansion (HOPE) method. The resulting value for the second Mellin moment, determined in quenched QCD at a pion mass of $m_{π} = 550$ MeV at a factorization scale of 2 GeV is $⟨ ξ^{2} ⟩ = 0.210 \pm 0.013 (stat.) \pm 0.034 (sys.)$ . This result is compatible with those from previous determinations of this quantity.
↳ hep-lathep-phnucl-thPRD(2022)·40 citations
10
Collinear factorization of diphoton photoproduction at next to leading order
Oskar Grocholski🇵🇱 · Bernard Pire🇫🇷 · Paweł Sznajder🇵🇱 · Lech Szymanowski🇵🇱 · Jakub Wagner🇵🇱
We calculate in the framework of collinear factorization the amplitude for the photoproduction of a near forward large mass diphoton at leading twist and next to leading order (NLO) in $α_{s}$ . We demonstrate the validity of factorization at this order, which was never achieved for such a reaction where the coefficient function describes a $2 \to 3$ hard process. While the Born order amplitude was purely imaginary and only probed the $x = \pm ξ$ cross-over line of generalized parton distributions (GPD) domain, the NLO result contains both a real and an imaginary part and probes the whole domain of definition of quark GPDs. The phenomenology of our results for medium (JLab) and higher energy (EIC) experiments will be developed in a future study.
↳ hep-phhep-exnucl-exnucl-thPRD(2021)·35 citations
11
Enhanced symmetry energy bears universality of the r-process
José Nicolás Orce · Balaram Dey · Cebo Ngwetsheni · Srijit Bhattacharya · Deepak Pandit · Brenden Lesch · Andile Zulu
The abundance of about half of the stable nuclei heavier than iron via the rapid neutron capture process or $r$ -process is intimately related to the competition between neutron capture and $β$ -decay rates, which ultimately depends on the binding energy of neutron-rich nuclei. The well-known Bethe-Weizsäcker semi-empirical mass formula\cite{weiz,bethe} describes the binding energy of ground states -- i.e. nuclei with temperatures of $T \approx 0$ MeV -- with the symmetry energy parameter converging between $23 - 27$ MeV for heavy nuclei. Here we find an unexpected enhancement of the symmetry energy at higher temperatures, $T \approx 0.7 - 1.0$ MeV, from the available data of giant dipole resonances built on excited states. Although these are likely the temperatures where seed elements are created -- during the cooling down of the ejecta following neutron-star mergers\cite{mergersnucleo} or collapsars\cite{collapsar} -- the fact that the symmetry energy remains constant between $T \approx 0.7 - 1.0$ MeV, suggests a similar trend down to $T \approx 0.5$ MeV, where neutron-capture may start occurring. Calculations using this relatively larger symmetry energy yield a reduction of the binding energy per nucleon for heavy neutron-rich nuclei and inhibits radiative neutron-capture rates. This results in a substantial close in of the neutron dripline -- where nuclei become unbound -- which elucidates the long sought universality of heavy-element abundances through the $r$ -process; as inferred from the similar abundances found in extremely metal-poor stars and the Sun.
↳ astro-ph.HEnucl-exnucl-thMNRAS(2023)·5 citations
12
Search for $α$ condensed states in $^{13}$ C using $α$ inelastic scattering
K. Inaba · Y. Sasamoto · T. Kawabata · M. Fujiwara · Y. Funaki · K. Hatanaka · K. Itoh · M. Itoh · K. Kawase · H. Matsubara · Y. Maeda · K. Suda and 8 other authors
We searched for the $α$ condensed state in $^{13}$ C by measuring the $α$ inelastic scattering at $E_{α} = 388$ MeV at forward angles including 0 degrees. We performed the distorted-wave Born-approximation calculation with the single-folding potential and the multipole decomposition analysis to determine the isoscalar transition strengths in $^{13}$ C. We found a bump structure around $E_{x} = 12.5$ MeV due to the isoscalar monopole ( $I S 0$ ) transition. A peak-fit analysis suggested that this bump consisted of several $1/ 2^{-}$ states. We propose that this bump is due to the mirror state of the 13.5 MeV-state in $^{13}$ N, which dominantly decays to the $α$ condensed state in $^{12}$ C. It was speculated that the $1/ 2^{-}$ states around $E_{x} = 12.5$ MeV were candidates for the $α$ condensed state, but the $3 α + n$ orthogonality condition model suggests that the $α$ condensed state is unlikely to emerge as the negative parity states. We also found two $1/ 2^{+}$ or $3/ 2^{+}$ states at $E_{x} = 14.5$ and 16.1 MeV excited with the isoscalar dipole ( $I S 1$ ) strengths. We suggest that the 16.1-MeV state is a possible candidate for the $α$ condensed state predicted by the cluster-model calculations on the basis of the good correspondence between the experimental and calculated level structures. However, the theoretical $I S 1$ transition strength for this state is significantly smaller than the measured value. Further experimental information is strongly desired to establish the $α$ condensed state in $^{13}$ C.
↳ nucl-exnucl-thPTEP(2021)·5 citations
13
Competition between $(γ, p)$ and $(γ, n)$ photo-disintegration yields
José Nicolás Orce
A comprehensive analysis of the competition between photo-proton and photo-neutron disintegration yields is undertaken by constraining photo-absorption data with physics principles -- namely, dipole sum rules, decay properties to open channels, isospin selection rules and statistical evaporation from compound nucleus formation. The trend and magnitude of disintegration yields for self-conjugate nuclei are in agreement with the evaporation model of Blatt and Weisskopf. A substantial improvement is found between the exponential trend presented in this work and that determined by Morinaga using a similar approach. This work allows for the evaluation of frequently missing or inconsistent photo-proton contributions, which impacts the photo-disintegration of light and neutron-deficient nuclei, where photo-proton contributions are relevant.
↳ nucl-exnucl-thAtom.Data Nucl.Data Tabl.(2022)·7 citations
14
Exposing the effect of $p$ -wave in pion triplet under the strong magnetic field
Zanbin Xing🇨🇳 · Jingyi Chao🇨🇳 · Lei Chang🇨🇳 · Yu-xin Liu🇨🇳
The static properties, masses and decay constants, of pseudoscalar meson triplet in a strongly magnetized medium are studied through the Dyson-Schwinger equation approach treatment of a contact interaction. Complementary to the usual vector-vector form, a symmetry-preserving formulation of couplings has been proposed in this work, without modifying the quark propagator, to control the strength of the $p$ -wave component of Bethe-Salpeter amplitude. It is found that, with the help of flexible auxiliary interaction, our simple model is able to reproduce the observation in the lattice QCD simulation, where the spectra of the charged pseudo-scalar meson shows a non-monotonic behavior as the magnetic field grows. The discovery of this work implies the strong magnetic field affects the inner structure of mesons dramatically.
↳ hep-phhep-thnucl-thPRD(2022)·10 citations
15
Investigating the low moments of the nucleon structure functions in lattice QCD
K. U. Can🇦🇺 · A. Hannaford-Gunn🇦🇺 · E. Sankey🇦🇺 · R. Horsley🇬🇧 · Y. Nakamura🇯🇵 · H. Perlt🇩🇪 · P. E. L. Rakow🇬🇧 · G. Schierholz🇩🇪 · H. Stuben🇩🇪 · R. D. Young🇦🇺 · J. M. Zanotti🇦🇺
We highlight QCDSF/UKQCD Collaboration's recent developments on computing the Compton amplitude directly via an implementation of the second order Feynman-Hellmann theorem. As an application, we compute the nucleon Compton tensor across a range of photon virtuality at an unphysical quark mass. This enables us to study the $Q^{2}$ dependence of the low moments of the nucleon structure functions in a lattice calculation for the first time. We present some selected results for the moments of the $F_{1}$ , $F_{2}$ and $F_{L}$ structure functions and discuss their implications.
↳ hep-lathep-phhep-thnucl-thPoS(2022)·3 citations
16
Proton inelastic scattering reveals deformation in $^{8}$ He
M. Holl · R. Kanungo · Z. H. Sun · G. Hagen · J. A. Lay · A. M. Moro · P. Navrátil · T. Papenbrock · M. Alcorta · D. Connolly · B. Davids · A. Diaz Varela and 18 other authors
A measurement of proton inelastic scattering of $^{8}$ He at $8.25 A$ ~MeV at TRIUMF shows a resonance at 3.54(6)~MeV with a width of 0.89(11)~MeV. The energy of the state is in good agreement with coupled cluster and no-core shell model with continuum calculations, with the latter successfully describing the measured resonance width as well. Its differential cross section analyzed with phenomenological collective excitation form factor and microscopic coupled reaction channels framework consistently reveals a large deformation parameter $β_{2}$ = 0.40(3), consistent with no-core shell model predictions of a large neutron deformation. This deformed double-closed shell at the neutron drip-line opens a new paradigm.
↳ nucl-exnucl-thPLB(2021)·26 citations

Affiliations

first authorsco-authorsvia INSPIRE