Nuclear Theory·nucl-th

Monday·December 30, 2019

12 papers—7 primary·5 cross-listed

01
In search of the best nuclear data file for proton induced reactions: varying both models and their parameters
E. Alhassan · D. Rochman · A. Vasiliev · R.M. Bergmann · M. Wohlmuther · A.J. Koning · H. Ferroukhi
A lot of research work has been carried out in fine tuning model parameters to reproduce experimental data for neutron induced reactions. This however is not the case for proton induced reactions where large deviations still exist between model calculations and experiments for some cross sections. In this work, we present a method for searching both the model and model parameter space in order to identify the 'best' nuclear reaction models with their parameter sets that reproduces carefully selected experimental data. Three sets of experimental data from EXFOR are used in this work: (1) cross sections of the target nucleus (2) cross sections of the residual nuclei and (3) angular distributions. Selected models and their parameters were varied simultaneously to produce a large set of random nuclear data files. The goodness of fit between our adjustments and experimental data was achieved by computing a global reduced chi square which took into consideration the above listed experimental data. The method has been applied for the adjustment of proton induced reactions on Co-59 between 1 to 100 MeV. The adjusted files obtained are compared with available experimental data and evaluations from other nuclear data libraries.
nucl-thnucl-exphysics.atom-ph0 citations
02
Dense Matter and Neutron Stars: Some Basic Notions
C. J. Pethick
A number of properties of dense matter can be understood semiquantitatively in terms of simple physical arguments. We begin with the outer parts of neutron stars, and consider the density at which pressure ionization occurs, the density at which electrons become relativistic, the density at which neutrons drip out of nuclei, and the size of the equilibrium nucleus in dense matter. Subsequently, we treat the so-called "pasta" phases expected to occur at densities just below the density at which the transition from the crust to the liquid core of a neutron star occurs. We then consider aspects of superfluidity in dense matter. Estimates of pairing gaps in homogeneous nuclear matter are given, and the effect of the dense medium on the interaction between nucleons is described. Finally, we turn to superfluidity in the crust of neutron stars and especially the neutron superfluid density, an important quantity in the theory of sudden speedups of the rotation rate of some pulsars.
nucl-thastro-ph.HEcond-mat.other3 citations
03
A new approach for the wobbling motion in the even-odd isotopes $^{161, 163, 165, 167}$ Lu
A. A. Raduta · R. Poenaru · C. M. Raduta
A new interpretation for the wobbling bands in the even-odd Lu isotopes is given within a particle-triaxial rotor semi-classical formalism. While in the previous papers the bands TSD1, TSD2, TSD3 and TSD4 are viewed as the ground, one, two and three phonon wobbling bands, here the corresponding experimental results are described as the ground band with spin equal to I=R+j, for R=0,2,4,...(TSD1), the ground band with I=R+j and R=1,3,5,...(TSD2), the one phonon excitations of TSD2 (TSD3), with the odd proton moving in the orbit $j = i_{13/2}$ , and the ground band of I=R+j, with R=1,3,5,... and $j = h_{9/2}$ (TSD4). The moments of inertia (MoI) of the core for the first three bands are the same, and considered to be free parameters. Due to the core polarization effect caused by the particle-core coupling, the MoI's for TSD4 are different. The energies and the e.m. transitions are quantitatively well described. Also, the phase diagram of the odd system is drawn. In the parameter space, one indicates where the points associated with the fitted parameters are located, which is the region where the transversal wobbling mode might be possible, as well as where the wobbling motion is forbidden.
nucl-thPRC(2020)·19 citations
04
The electromagnetic field effects in in-out and in-in formalisms
Gaoqing Cao🇨🇳
In this work, we compare the effects of electromagnetic (EM) fields on strong coupling systems in two formalisms: in-out and in-in, which are different from each other when a finite electric field is present. The chiral effective Nambu--Jona-Lasinio model is adopted for this study, and two kinds of EM field distributions are considered: pure electric field and parallel EM (PEM) field with equal electric and magnetic components. For both distributions, we find that the results of in-out and in-in formalisms start to diverge when the electric field $(q E)^{1/2}$ is larger than the chiral effective mass $M = [m^{2} + (π^{0})^{2}]^{1/2}$ , that is, when the Schwinger pair production mechanism becomes important. Besides, the chiral restorations are stiffer in the in-in formalism, especially the transition shifts to first-order instead of the second-order for the PEM field. The neutral collective modes are also explored accordingly: For the PEM field, more precise calculations show nonmonotonic features of their pole masses due to parity mixing, and then the Goldstone-like mode is found to be noneffective at the end of chiral rotation because of chiral anomaly.
nucl-thPLB(2020)·8 citations
05
Theoretical investigation of the antimagnetic rotation in $^{104}$ Pd
Zhen-Hua Zhang
The particle-number-conserving method based on the cranked shell model is used to investigate the antimagnetic rotation band in $^{104}$ Pd. The experimental moments of inertia and reduced $B (E 2)$ transition probabilities are reproduced well. The $J^{(2)} / B (E 2)$ ratios are also discussed. The occupation probability of each orbital close to the Fermi surface and the contribution of each major shell to the total angular momentum alignment with rotational frequency are analyzed. The backbending mechanism of the ground state band in $^{104}$ Pd is understood clearly and the configuration of the antimagnetic rotation after backbending is clarified. In addition, the crossing of a four quasiparticle states with this antimagnetic rotation band is also predicted. By examining the the closing of the four proton hole angular momenta towards the neutron angular momenta, the "two-shears-like" mechanism for this antimagnetic rotation is investigated and two stages of antimagnetic rotation in $^{104}$ Pd are seen clearly.
nucl-thnucl-exCPC(2019)·9 citations
06
Configuration and bandhead spin assignments for the 2-quasiparticle rotational bands in the neutron-rich nuclei $^{154, 156}$ Pm
Shuo-Yi Liu · Miao Huang · Zhen-Hua Zhang
The rotational bands in the neutron-rich nuclei $^{153 - 157}$ Pm are investigated by a particle-number conserving method. The kinematic moments of inertia for the 1-quasiparticle bands in odd- $A$ Pm isotopes $^{153, 155, 157}$ Pm are reproduced quite well by the present calculation. By comparison between the experimental and calculated moments of inertia for the three 2-quasiparticle bands in the odd-odd nuclei $^{154, 156}$ Pm, their configurations and bandhead spins have been assigned properly. For the 2-quasiparticle band in $^{154}$ Pm, the configuration is assigned as $π 5/ 2^{-} [532] \otimes ν 3/ 2^{-} [521]$ ( $K^{π} = 4^{+}$ ) with the bandhead spin $I_{0} = 4ℏ$ . In $^{156}$ Pm, the same configuration and bandhead spin assignments have been made for the 2-quasiparticle band with lower excitation energy. The configuration $π 5/ 2^{+} [413] \otimes ν 5/ 2^{+} [642]$ ( $K^{π} = 5^{+}$ ) with the bandhead spin $I_{0} = 5ℏ$ is assigned for that with higher excitation energy.
nucl-thnucl-exPRC(2019)·5 citations
07
Bremsstrahlung emission from nuclear reactions in compact stars
Sergei P. Maydanyuk (1) · Kostiantyn A. Shaulskyi (2) ((1) Institute for Nuclear Research, National Academy of Sciences of Ukraine, Kyiv, Ukraine, (2) Taras Shevchenko National University of Kyiv, Ukraine)
Bremsstrahlung emission of photons during nuclear reactions inside dense stellar medium is investigated in the paper. For that, a new model of nucleus is developed, where nuclear forces combine nucleons as bound system in dependence on deep location inside compact star. A polytropic model of stars at index $n = 3$ with densities characterized from white dwarf to neutron star is used. Bremsstrahlung formalism and calculations are well tested on existed experimental information for scattering of protons of light nuclei in Earth. We find the following. (1) In neutron stars a phenomenon of dissociation of nucleus is observed --- its disintegration on individual nucleons, starting from some critical distance between this nucleus and center of star with high density. We do not observe such a phenomenon in white dwarfs. (2) In the white dwarfs, influence of stellar medium imperceptibly affects on bremsstrahlung photons. Also, we have accurate description of bremsstrahlung photons in nuclear reactions in Sun. (3) For neutron stars, influence of stellar medium is essentially more intensive and it crucially changes the bremsstrahlung spectrum. The most intensive emission is from bowel of the star, while the weakest emission is from periphery.
nucl-thastro-phastro-ph.HEastro-ph.SR+1CPC(2025)·0 citations
08
The $σ$ and $ρ$ coupling constants for the charmed and beauty mesons
Hee-Jin Kim🇰🇷 · Hyun-Chul Kim🇰🇷
We investigate the $σ$ and $ρ$ coupling constants for the $D D$ and $D^{*} D^{*}$ interactions, based on correlated $2 π$ exchange in the $D D$ and $D^{*} D^{*}$ interactions. Starting from the $D D ˉ \to π π$ and $D^{*} D ˉ^{*} \to π π$ amplitudes derived in the pseudophysical region ( $4 m_{π}^{2} \leq t \leq 52 m_{π}^{2}$ ) with the $S$ - and $P$ -wave $2 π$ correlations considered, we obtain the spectral functions for the $D D \to D D$ and $D^{*} D^{*} \to D^{*} D^{*}$ amplitude with correlated $S$ - and $P$ -wave $2 π$ exchanges. Using the pole approximation, we estimate the $D D σ$ , $D D ρ$ , $D^{*} D^{*} σ$ , and $D^{*} D^{*} ρ$ coupling constants. We extended phenomenologically the present results to the region in $t \leq 0$ and compare them with those from lattice QCD. The results are also compared with those of other models. We also present the results of the $B B σ$ , $B B ρ$ , $B^{*} B^{*} σ$ , and $B^{*} B^{*} ρ$ coupling constants. We observe that it is unlikely that the $σ$ and $ρ$ coupling constants for the $B$ and $B^{*}$ mesons are the same as those for the $D$ and $D^{*}$ mesons. On the contrary, they are quite larger than those for the charmed mesons.
↳ hep-phhep-exhep-latnucl-thPRD(2020)·9 citations
09
Triangle singularity appearing as an $X (3872)$ -like peak in $B \to (J / ψ π^{+} π^{-}) K π$
Satoshi X. Nakamura (University of Science and Technology of China)🇨🇳
We consider a triangle diagram for $B^{0} \to (J / ψ π^{+} π^{-}) K^{+} π^{-}$ where an $X (3872)$ peak has been observed experimentally. We demonstrate that a triangle singularity inherent in the triangle diagram creates a sharp peak in the $J / ψ π^{+} π^{-}$ invariant mass distribution when the final $(J / ψ π^{+} π^{-}) π$ invariant mass is at and around the $D^{*} D ˉ^{*}$ threshold. The position and width of the peak is 3871.68 MeV (a few keV above the $D^{* 0} D ˉ^{0}$ threshold) and $\sim$ 0.4 MeV, respectively, in perfect agreement with the precisely measured $X (3872)$ mass and width: $3871.69 \pm 0.17$ MeV and $< 1.2$ MeV. This remarkable agreement is virtually parameter-free. The result indicates that the considered mechanism has to be understood in advance when separating an $X (3872)$ -pole contribution from $B^{0} \to (J / ψ π^{+} π^{-}) K^{+} π^{-}$ data; the separation yields an $X (3872) π$ lineshape that could be used to determine the $X (3872)$ mass. We suggest a method to set a constraint on the triangle mechanism by analyzing a charge analogous process $B^{0} \to (J / ψ π^{0} π^{-}) K^{+} π^{0}$ where a similar triangle singularity generates an $X^{-} (3876)$ -like peak.
↳ hep-phhep-exnucl-thPRD(2020)·23 citations
10
Analysis of $^{4}$ He( $γ, p)$ T and $^{4}$ He( $γ, n)$ $^{3}$ He Reactions with Linearly Polarized Photons in the Energy Range up to 100\,MeV
Yu.P.Lyakhno
In a number of investigations, one can find the data on the $^{4}$ He( $γ$ ,p)T and $^{4}$ He( $γ$ ,n) $^{3}$ He reaction cross sections in the collinear geometry, which are due to spin {\it S}=1 transitions of the final-state particles. The ratio of the differential cross section in the collinear geometry to the differential reaction cross section at the nucleon emission angle $θ_{N}$ =90 $^{\circ}$ , and specified by the {\it S}=0 electric dipole transition at photon energies in the range 20 $\leq E_{γ} \leq$ 100\,MeV, is independent of the photon energy, within the experimental error. In the meantime, experiments were made to measure the asymmetry of the cross section $Σ (θ_{N})$ , for the mentioned reactions with linearly polarized photons. It has been found that in the energy range between 20 and 90\,MeV, the $Σ (θ_{N})$ value is also independent of the photon energy, within the experimental error. These data are in agreement with the assumption that transitions with spin {\it S}=1 can be due to the contribution of $^{3} P_{0}$ states of the $^{4}$ He nucleus, and are inconsistent with the assumption that the spin-flip of the particle system occurred during the reaction as a result of the meson exchange current contribution. The available measured data on the collinear geometry reaction cross sections and the ones on the cross-section asymmetry of the reaction with linearly polarized photons do not agree between themselves. The above mentioned reactions seem to be more convenient for measuring the degree of photon beams linear polarization than the deuteron photodisintegration reactions.
↳ nucl-exnucl-th0 citations
11
Exclusive Hard Processes for Studying Hadron Structures at J-PARC
Wen-Chen Chang🇹🇼
With an appropriate hard scale, exclusive hadronic processes could provide novel information of the internal quark-gluon configurations of hadrons. The availability of 10-20 GeV secondary meson beam in the coming high-momentum beam line of Hadron Hall at J-PARC offers an unique opportunity to carry out the measurements of the exclusive hard processes. We address this interesting approach by two possibilities: (a) $π^{-} p \to K^{0} Λ (1405)$ for the constituent quark structure of $Λ (1405)$ , and (b) exclusive pion-induced Drell-Yan process $π^{-} p \to γ^{*} n \to l^{+} l^{-} n$ for the generalized parton distributions (GPDs) of nucleons. Realization of such measurements at J-PARC will open up a new way of accessing the internal quark structure of exotic hadrons and also the nucleon GPDs based on a solid theoretical foundation of perturbative QCD.
↳ nucl-exhep-phnucl-thJPS Conf.Proc.(2021)·0 citations
12
Photoproduction of hidden-bottom pentaquark and related topics
Xu Cao🇨🇳 · Feng-Kun Guo🇨🇳 · Yu-Tie Liang🇨🇳 · Jia-Jun Wu🇨🇳 · Ju-Jun Xie🇨🇳 · Ya-Ping Xie🇨🇳 · Zhi Yang🇨🇳 · Bing-Song Zou🇨🇳
Due to the discovery of the hidden-charm pentaquark $P_{c}$ states by the LHCb collaboration, the interests on the candidates of hidden-bottom pentaquark $P_{b}$ states are increasing. They are anticipated to exist as the analogues of the $P_{c}$ states in the bottom sector and predicted by many models. We give an exploration of searching for a typical $P_{b}$ in the $γ p \to Υ p$ reaction, which shows a promising potential to observe it at an electron-ion collider. The possibility of searching for $P_{b}$ in open-bottom channels are also briefly discussed. Meanwhile, the $t$ -channel non-resonant contribution, which in fact covers several interesting topics at low energies, is systematically investigated.
↳ hep-phnucl-thPRD(2020)·37 citations

Affiliations

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