Nuclear Theory·nucl-th

Friday·January 24, 2020

17 papers—10 primary·7 cross-listed

01
The theory of direct laser excitation of nuclear transitions
Lars von der Wense · Pavlo V. Bilous · Benedict Seiferle · Simon Stellmer · Johannes Weitenberg · Peter G. Thirolf · Adriana Pálffy · Georgy Kazakov
A comprehensive theoretical study of direct laser excitation of a nuclear state based on the density matrix formalism is presented. The nuclear clock isomer $^{229 m}$ Th is discussed in detail, as it could allow for direct laser excitation using existing technology and provides the motivation for this work. The optical Bloch equations are derived for the simplest case of a pure nuclear two-level system and for the more complex cases taking into account the presence of magnetic sub-states, hyperfine-structure and Zeeman splitting in external fields. Nuclear level splitting for free atoms and ions as well as for nuclei in a solid-state environment is discussed individually. Based on the obtained equations, nuclear population transfer in the low-saturation limit is reviewed. Further, nuclear Rabi oscillations, power broadening and nuclear two-photon excitation are considered. Finally, the theory is applied to the special cases of $^{229 m}$ Th and $^{235 m}$ U, being the nuclear excited states of lowest known excitation energies. The paper aims to be a didactic review with many calculations given explicitly.
nucl-thphysics.opticsEPJA(2020)·25 citations
02
Bulk medium evolution has considerable effects on jet observables
Yasuki Tachibana🇺🇸 · Chun Shen🇺🇸 · Abhijit Majumder🇺🇸
We consider the case, in QCD, of a single jet propagating within a strongly interacting fluid, of finite extent. Interactions lead to the appearance of a source of energy-momentum within the fluid. The remnant jet that escapes the container is analyzed along with portions of the medium excited by the jet. We study the effect of a static versus a semi-realistic expanding medium, with jets traveling inward versus outward. We consider the medium response via recoils in partonic scatterings based on a weakly-coupled description and its combination with hydrodynamical medium response based on a strongly-coupled description, followed by incorporation into a jet. The effects of these limits on the reconstructed energy, momentum and mass of the jet, as a function of the angle away from the original parton direction are studied. It is demonstrated that different flow velocity configurations in the medium produce considerable differences in jet observables. This work highlights the importance of accurate dynamical modeling of the soft medium as a foundation on which to calculate jet modification, and casts skepticism on results obtained without such modeling.
nucl-thhep-phnucl-exPRC(2022)·43 citations
03
Renormalizability of leading order covariant chiral nucleon-nucleon interaction
Chun-Xuan Wang🇨🇳 · Li-Sheng Geng🇨🇳 · Bingwei Long🇨🇳
In this work, we study the renormalization group invariance (RGI) of the recently proposed covariant power counting (PC) scheme in the case of nucleon-nucleon scattering [Chin.Phys. C42 (2018) 014103] at leading order (LO). We show that unlike the LO Weinberg case, RGI is satisfied in the $^{3} P_{0}$ channel, because a term of $p p^{'}$ appears naturally in the covariant PC scheme at LO. Another interesting feature is that the $^{1} S_{0}$ and $^{3} P_{1}$ channels are correlated. Fixing the two relevant low energy constants by fitting to the $^{1} S_{0}$ phase shifts at $T_{lab.} = 10$ and $25$ MeV with a cutoff $Λ$ of $400 - 650$ MeV, the $^{3} P_{1}$ phase shifts can be described relatively well. In the limit of $Λ \to \infty$ , the $^{1} S_{0}$ channel becomes cutoff independent, while RGI is lost in the $^{3} P_{1}$ channel, consistent with the Wigner bound and the previous observation that the $^{3} P_{1}$ channel better be treated perturbatively. As for the $^{1} P_{1}$ and $^{3} S_{1}$ - $^{3} D_{1}$ channels, RGI is satisfied, similar to the Weinberg approach.
nucl-thhep-phCPC(2021)·20 citations
04
Collisional time and shear relaxation time for interacting QGP
Ankit Anand🇮🇳 · Souvik Paul🇮🇳 · Sarthak Satapathy🇮🇳 · Sabyasachi Ghosh🇮🇳
We have studied the collisional time and relaxation time of a QGP(Quark-Gluon Plasma) by parameterizing them by temperature. From this parameterization we have obtained the decay rate parameterized by temperature which further helps us to calculate and compare the shear viscosity to entropy density ratio of a QGP with the KSS(Kovtun-Son-Starinets) result.
nucl-thhep-phDAE Symp.Nucl.Phys.(2019)·0 citations
05
Improvement Studies of an Effective Interaction for N=Z sd-shell Nuclei by Neural Networks
Serkan Akkoyun · Nadjet Laouet · Fatima Benrachi
The nuclear shell model is one of the successful models in theoretical understanding of nuclear structure. If a convenient effective interaction can be found between nucleons, various observables such as energies of nuclear states are accurately predicted by this model. The basic requirements for the shell model calculations are a set of single particle energies and two-body interaction matrix elements (TBME) which construct the residual interaction between nucleons. This latter could be parameterized in different ways. In this study, we have used a different approach to improve existing USD type Hamiltonians for the shell model calculations of N=Z nuclei in the A=16-40 region. After obtaining the SDNN new effective interaction, shell model calculations have been performed for all N=Z nuclei in sd shell. In which, $^{16} O$ doubly magic nucleus has been assumed as an inert core and active particles are distributed in the $d_{5/2}$ , $s_{1/2}$ and $d_{3/2}$ single particle orbits. The rms deviations from experimental energy values are lower for the newly generated effective interaction than those obtained using the original one for the studied nuclei.
nucl-thBulg.J.Phys.(2021)·7 citations
06
Centrality fluctuations and decorrelations in heavy-ion collisions
Jiangyong Jia🇺🇸 · Chunjian Zhang🇺🇸 · Jun Xu🇨🇳
The centrality or the number of initial-state sources $V$ of the system produced in heavy ion collision is a concept that is not uniquely defined and subject to significant theoretical and experimental uncertainties. We argue that a more robust connection between the initial-state sources with final-state multiplicity could be established from the event-by-event multiplicity correlation between two subevents separated in pseudorapidity, $N_{a}$ vs $N_{b}$ . This correlation is sensitive to two main types of centrality fluctuations (CF): 1) particle production for each source $p (n)$ which smears the relation between $V$ and $N_{a}$ used for experimental centrality, and 2) decorrelations between the sources in the two subevents $V_{b}$ and $V_{a}$ . The CF is analyzed in terms of cumulants of $V_{b}$ and $N_{b}$ as a function of $N_{a}$ , i.e. experimental centrality is defined with $N_{a}$ . We found that the mean values $⟨ V_{b} ⟩_{N_{a}}$ and $⟨ N_{b} ⟩_{N_{a}}$ increase linearly with $N_{a}$ in mid-central collisions, but flatten out in ultra-central collisions. Such non-linear behavior is sensitive to the centrality resolution of $N_{a}$ . In the presence of centrality decorrelations, the scaled variances $⟨(δ V_{b})^{2} ⟩ / ⟨ V_{b} ⟩$ and $⟨(δ N_{b})^{2} ⟩ / ⟨ N_{b} ⟩$ are found to decrease linearly with $N_{a}$ in mid-central collisions, while the $p (n)$ leads to another sharp decrease in the ultra-central region. The higher-order cumulants of $V_{b}$ and $N_{b}$ show interesting but rather complex behaviors which deserve further studies. Our results suggest that one can use the cumulants of the two-dimensional multiplicity correlation, especially the mean and variance, to constrain the particle production mechanism as well as the longitudinal fluctuations of the initial-state sources.
nucl-thhep-phnucl-exPRResearch(2020)·17 citations
07
Efficient method for estimation of fission fragment yields of r-process nuclei
Jhilam Sadhukhan · Samuel A. Giuliani · Zachary Matheson · Witold Nazarewicz
$Background$ More than half of all the elements heavier than iron are made by the rapid neutron capture process (or r process). For very neutron-rich astrophysical conditions, such at those found in the tidal ejecta of neutron stars, nuclear fission determines the r-process endpoint, and the fission fragment yields shape the final abundances of $110 \leq A \leq 170$ nuclei. The knowledge of fission fragment yields of hundreds of nuclei inhabiting very neutron-rich regions of the nuclear landscape is thus crucial for the modeling of heavy-element nucleosynthesis. $Purpose$ In this study, we propose a model for the fast calculation of fission fragment yields based on the concept of shell-stabilized prefragments defined with help of the nucleonic localization functions. $Methods$ To generate realistic potential energy surfaces and nucleonic localizations, we apply Skyrme Density Functional Theory. The distribution of the neck nucleons among the two prefragments is obtained by means of a statistical model. $Results$ We benchmark the method by studying the fission yields of $^{178}$ Pt, $^{240}$ Pu, $^{254}$ Cf, and $^{254, 256, 258}$ Fm and show that it satisfactorily explains the experimental data. We then make predictions for $^{254}$ Pu and $^{290}$ Fm as two representative cases of fissioning nuclei that are expected to significantly contribute during the r-process nucleosynthesis occurring in neutron star mergers. $Conclusions$ The proposed framework provides an efficient alternative to microscopic approaches based on the evolution of the system in a space of collective coordinates all the way to scission. It can be used to carry out global calculations of fission fragment distributions across the r-process region.
nucl-thastro-ph.HEPRC(2020)·21 citations
08
From $K ˉ N$ Interactions to $K ˉ$ -Nuclear Quasi-Bound States
Aleš Cieplý🇨🇿 · Jaroslava Hrtánková🇨🇿 · Jiří Mareš🇨🇿 · Eliahu Friedman🇮🇱 · Avraham Gal🇮🇱 · Àngels Ramos🇪🇸
We review the current status of our study of $K^{-}$ -nuclear interactions and $K^{-}$ -nuclear quasi-bound states. The adopted $K^{-}$ -nuclear optical potential consists of two parts -- the single-nucleon one constructed microscopically from chirally motivated $K ˉ N$ amplitudes, and a phenomenological multi-nucleon one constrained in fits to kaonic atoms data. The inclusion of multi-nucleon absorption in our calculations of $K^{-}$ quasi-bound states in many-body systems leads to huge widths, considerably exceeding the binding energies. If this feature is confirmed the observation of such states is unlikely. Finally, a development of a new microscopical model for in-medium $K^{-} N N$ absorption is discussed as well.
nucl-thAIP Conf.Proc.(2020)·6 citations
09
Exploring Longitudinal Observables with 3+1D IP-Glasma
Scott McDonald🇨🇦 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦
We present a formulation of the initial state of heavy ion collisions that generalizes the 2+1D boost invariant IP-Glasma \cite{Schenke:2012wb} to 3+1D through JIMWLK rapidity evolution of the pre-collision Wilson lines. The rapidity dependence introduced by the JIMWLK evolution leads us to modify the initial condition for the gauge fields, and to solve Gauss' law iteratively in order to allow for temporal evolution on a 3-dimensional lattice. While the transverse physics of QGP has been studied nearly exhaustively, the effect of longitudinal fluctuations introduced by the JIMWLK evolution has yet to be studied in detail phenomenologically. Hence, we couple our 3+1D IP-Glasma model to MUSIC+UrQMD, for completely 3+1D simulations of heavy ion collisions. Specifically, we consider Pb-Pb collisions at $s = 2.76 TeV$ and study the rapidity dependence of the charged hadron $v_{n} (η)$ via the $η$ -dependent flow factorization ratios $r_{n} (η_{a}, η_{b})$ as measured by CMS \cite{Khachatryan:2015oea}, as well as the charged hadron multiplicity $d N_{c h} / d η$ .
nucl-thhep-exhep-phNPA(2021)·28 citations
10
Mass Yields of Fission Fragment of Pt to Ra Isotopes
Krzysztof Pomorski · Artur Dobrowolski · Rui Han · Bozena Nerlo-Pomorska · Michal Warda · Zhigang Xiao · Yongjing Chen · Lilie Liu · Jun-Long Tian
An effective Fourier nuclear shape parametrization which describes well the most relevant degrees of freedom on the way to fission is used to construct a 3D collective model. The potential energy surface is evaluated within the macroscopic-microscopic approach based on the Lublin-Strasbourg Drop (LSD) macroscopic energy and Yukawa-folded single particle potential. A phenomenological inertia parameter is used to describe the kinetic properties of the fissioning system. The fission fragment mass yields are obtained by using an approximate solution of the underlying Hamiltonian. The predicted mass fragmentations for even-even Pt to Ra isotopes are compared with available experimental data. Their main characteristics are well reproduced when the neck rupture probability dependent on the neck radius is introduced.
nucl-thnucl-exPRC(2020)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE