Nuclear Theory·nucl-th

Tuesday·April 21, 2015

14 papers—9 primary·5 cross-listed

01
Central depressions in the charge density profiles of the nuclei around $^{46}$ Ar
Jun Ling Song · Qiang Zhao · Wen Hui Long
The occurrence of the proton bubble-like structure has been studied within the relativistic Hartree-Fock-Bogoliubov (RHFB) and relativistic Hartree-Bogoliubov (RHB) theories by exploring the bulk properties, the charge density profiles and single proton spectra of argon isotopes and $N = 28$ isotones. It is found that the RHFB calculations with PKA1 effective interaction, which can properly reproduce the charge radii of argon isotopes and the $Z = 16$ proton shell nearby, do not support the occurrence of the proton bubble-like structure in argon isotopes due to the prediction of deeper bound proton orbit $π 2 s_{1/2}$ than $π 1 d_{3/2}$ . For $N = 28$ isotones, $^{42}$ Si and $^{40}$ Mg are predicted by both RHFB and RHB models to have the proton bubble-like structure, owing to the large gap between the proton $π 2 s_{1/2}$ and $π 1 d_{5/2}$ orbits, namely the $Z = 14$ proton shell. Therefore, $^{42}$ Si is proposed as the potential candidate of proton bubble nucleus, which has longer life-time than $^{40}$ Mg.
nucl-th1 citation
02
Octupole deformation in light actinides within an analytic quadrupole octupole axially symmetric model with Davidson potential
Dennis Bonatsos · Andriana Martinou · N. Minkov · S. Karampagia · D. Petrellis
The analytic quadrupole octupole axially symmetric model, which had successfully predicted 226Ra and 226Th as lying at the border between the regions of octupole deformation and octupole vibrations in the light actinides using an infinite well potential (AQOA-IW), is made applicable to a wider region of nuclei exhibiting octupole deformation, through the use of a Davidson potential (AQOA-D). Analytic expressions for energy spectra and B(E1), B(E2), B(E3) transition rates are derived. The spectra of 222-226Ra and 224,226Th are described in terms of the two parameters phi_0 (expressing the relative amount of octupole vs. quadrupole deformation) and beta_0 (the position of the minimum of the Davidson potential), while the recently determined B(EL) transition rates of 224Ra, presenting stable octupole deformation, are successfully reproduced. A procedure for gradually determining the parameters appearing in the B(EL) transitions from a minimum set of data, thus increasing the predictive power of the model, is outlined.
nucl-thPRC(2015)·29 citations
03
Thermonuclear Processes for Three Body System in the Potential Cluster Model
S.B. Dubovichenko · A.V. Dzhazairov-Kakhramanov
The manuscript is devoted to the description of the results obtained in the frame of the modified potential cluster model with the classification of states according to Young tableaux for neutron and proton radiative capture processes on 2H at thermal and astrophysical energies. It demonstrates methods of application that were obtained on the basis of phase shift analysis and characteristics of the bound states of 2H potentials for consideration of the radiative capture processes. First reaction of the proton capture directly takes part in the pp solar cycle, where it is the second reaction. The neutron capture is not a part of usual thermonuclear cycles in the Sun and stars, but can take part in the processes of primordial nucleosynthesis, following at formation and evolution of our entire Universe.
nucl-thNPA(2015)·26 citations
04
Microscopic study of low-lying spectra of $Λ$ hypernuclei based on a beyond-mean-field approach with covariant energy density functional
H. Mei🇯🇵 · K. Hagino🇯🇵 · J.M. Yao🇯🇵 · T. Motoba🇯🇵
We present a detailed formalism of the microscopic particle-rotor model for hypernuclear low-lying states based on a covariant density functional theory. In this method, the hypernuclear states are constructed by coupling a hyperon to low-lying states of the core nucleus, which are described by the generator coordinate method (GCM) with the particle number and angular momentum projections. We apply this method to study in detail the low-lying spectrum of $_{Λ}^{13}$ C and $_{Λ}^{21}$ Ne hypernuclei. We also briefly discuss the structure of $_{Λ}^{155}$ Sm as an example of heavy deformed hypernuclei. It is shown that the low-lying excitation spectrum with positive parity states of the hypernuclei, which are dominated by $Λ$ hyperon in $s$ -orbital coupled to the core states, are similar to that for the corresponding core states, while the electric quadrupole transition strength, $B (E 2)$ , from the 2 $_{1}^{+}$ state to the ground state is reduced according to the mass number of the hypernuclei. Our study indicates that the energy splitting between the first 1/2 $^{-}$ and 3/2 $^{-}$ hypernuclear states is generally small for all the hypernuclei which we study. However, their configurations depend much on the properties of a core nucleus, in particular on the sign of deformation parameter. That is, the first $1/ 2^{-}$ and $3/ 2^{-}$ states in $_{Λ}^{13}$ C are dominated by a single configuration with $Λ$ particle in the $p$ -wave orbits and thus providing good candidates for a study of the $Λ$ spin-orbit splitting. On the other hand, those states in the other hypernuclei exhibit a large configuration mixing and thus their energy difference cannot be interpreted as the spin-orbit splitting for the $p$ -orbits.
nucl-thnucl-exPRC(2015)·35 citations
05
Ground-state energies and charge radii of $^{4}$ He, $^{16}$ O, $^{40}$ Ca, and $^{56}$ Ni in the unitary-model-operator approach
Takayuki Miyagi · Takashi Abe · Ryoji Okamoto · Takaharu Otsuka
We study the nuclear ground-state properties by using the unitary-model-operator approach (UMOA). Recently, the particle-basis formalism has been introduced in the UMOA and enables us to employ the charge-dependent nucleon-nucleon interaction. We evaluate the ground-state energies and charge radii of $^{4}$ He, $^{16}$ O, $^{40}$ Ca, and $^{56}$ Ni with the charge-dependent Bonn potential. The ground-state energy is dominated by the contributions from the one- and two-body cluster terms, while, for the radius, the one-particle-one-hole excitations are more important than the two-particle-two-hole excitations. The calculated results reproduce the trend of experimental data of the saturation property for finite nuclei.
nucl-thPTEP(2015)·3 citations
06
Shape phase transition in the odd Sm nuclei: effective order parameter and odd-even effect
Yu Zhang · Xin Guan · Yin Wang · Yan Zuo · Li-na Bao · Feng Pan
Some binding-energy-related quantities serving as effective order parameters have been used to analyze the shape phase transition in the odd Sm nuclei. It is found that the signals of phase transition in the odd Sm nuclei are greatly enhanced in contrast to the even Sm nuclei. A further analysis shows that the transitional behaviors related to pairing in the Sm nuclei can be well described by the mean field plus pairing interaction model, with a monotonic decrease in the pairing strength $G$ .
nucl-thCPC(2015)·4 citations
07
Triaxial dynamics in the quadrupole-deformed rotor
Qiu-Yue Li · Xiao-Xiang Wang · Yan Zuo · Yu Zhang · Feng Pan
The triaxial dynamics of the quadrupole-deformed rotor model of both the rigid and the irrotational type have been investigated in detail. The results indicate that level patterns and E2 transitional characters of the two types of the model can be matched with each other to the leading order of the deformation parameter $β$ . Especially, it is found that the dynamical structure of the irrotational type with most triaxial deformation ( $γ = 3 0^{\circ}$ ) is equivalent to that of the rigid type with oblate deformation ( $γ = 6 0^{\circ}$ ), and the associated spectrum can be classified into the standard rotational bands obeying the rotational $L (L + 1)$ -law or regrouped into a new ground- and $γ$ -band with odd-even staggering in the new $γ$ -band commonly recognized as a signature of the triaxiality. The differences between the two types of the model in this case are emphasized especially on the E2 transitional characters.
nucl-thCPC(2016)·6 citations
08
Electromagnetic Structure of Few-Nucleon Ground States
L.E. Marcucci🇮🇹 · F. Gross🇺🇸 · M.T. Pena🇵🇹 · M. Piarulli🇺🇸 · R. Schiavilla🇺🇸 · I. Sick🇨🇭 · A. Stadler · J.W. Van Orden🇺🇸 · M. Viviani🇮🇹
Experimental form factors of the hydrogen and helium isotopes, extracted from an up-to-date global analysis of cross sections and polarization observables measured in elastic electron scattering from these systems, are compared to predictions obtained in three different theoretical approaches: the first is based on realistic interactions and currents, including relativistic corrections (labeled as the conventional approach); the second relies on a chiral effective field theory description of the strong and electromagnetic interactions in nuclei (labeled $χ$ EFT); the third utilizes a fully relativistic treatment of nuclear dynamics as implemented in the covariant spectator theory (labeled CST). For momentum transfers below $Q ≲ 5$ fm $^{- 1}$ there is satisfactory agreement between experimental data and theoretical results in all three approaches. However, at $Q ≳ 5$ fm $^{- 1}$ , particularly in the case of the deuteron, a relativistic treatment of the dynamics, as is done in the CST, is necessary. The experimental data on the deuteron $A$ structure function extend to $Q ≃ 12$ fm $^{- 1}$ , and the close agreement between these data and the CST results suggests that, even in this extreme kinematical regime, there is no evidence for new effects coming from quark and gluon degrees of freedom at short distances.
nucl-thnucl-exJ.Phys.G(2016)·67 citations
09
Three-pion exchange nucleon-nucleon potentials with virtual $Δ$ -isobar excitation
N. Kaiser🇩🇪
The nucleon-nucleon interaction arising from the exchange of three pions and the excitation of $Δ (1232)$ -isobars in intermediate states is studied. Approximating the $Δ$ -propagator by the inverse $Δ$ N mass-splitting, analytical expressions are derived for the spectral-functions of the isoscalar and isovector central, spin-spin and tensor NN-potentials in momentum-space. A trans- lation of the spectral-functions into coordinate-space potentials reveals that the main effect of these specific exchange and excitation mechanisms is a repulsive isoscalar central NN-potential.
nucl-thPRC(2015)·6 citations
10
Energy Dependence of Direct-Quarkonium Production in pp Collisions from Fixed-Target to LHC Energies: Complete One-Loop Analysis
Yu Feng🇨🇳 · Jean-Philippe Lansberg🇫🇷 · Jian-Xiong Wang🇨🇳
We compute the energy dependence of the P_T-integrated cross section of directly produced quarkonia in pp collisions at next-to-leading order (NLO), namely up to alpha_s^3, within nonrelativistic QCD (NRQCD). Our analysis is based on the idea that the P_T-integrated and the P_T-differential cross sections can be treated as two different observables. The colour-octet NRQCD parameters needed to predict the P_T-integrated yield can thus be extracted from the fits of the P_T-differential cross sections at mid and large P_T. For the first time, the total cross section is evaluated in NRQCD at full NLO accuracy using the recent NLO fits of the P_T-differential yields at RHIC, the Tevatron and the LHC. Both the normalisation and the energy dependence of the J/psi, psi' and Upsilon(1S), we obtained, are in disagreement with the data irrespective of the fit method. The same is true if one uses CEM-like colour-octet NRQCD parameters. If, on the contrary, one disregards the colour-octet contribution, the existing data in the TeV range are well described by the alpha_s^3 contribution in the colour-singlet model --which, at alpha_s^4, however shows an unphysical energy dependence. A similar observation is made for eta(c,b). This calls for a full NNLO or for a resummation of the initial-state radiation in this channel. In any case, past claims that colour-octet transitions are dominantly responsible for low-P_T quarkonium production are not supported by our results. This may impact the interpretation of quarkonium suppression in high-energy proton-nucleus and nucleus-nucleus collisions.
↳ hep-phhep-exnucl-exnucl-thEPJC(2015)·65 citations
11
Lepton-pair production in ultraperipheral collisions at AFTER@LHC
J.P. Lansberg🇫🇷 · L. Szymanowski🇵🇱 · J. Wagner🇵🇱
We investigate the potentialities offered by the study of lepton-pair production in ultraperipheral collisions at a fixed-target experiment using the proton and ion LHC beams. In these collisions, exclusive or semi-exclusive lepton-pair production can be used as luminosity monitor as well as a check of the equivalent-photon approximation, via the measurement of the Bethe-Heitler cross section. It can also serve as a probe of the inner hadron structure via the measurement of the lepton-pair azimuthal asymmetry which is sensitive to the timelike virtual Compton scattering. We also briefly discuss the possibility offered by the study of eta(c) production. Finally, we outline the possibilities for lepton-pair production by Pomeron-Odderon fusion in exclusive pp and pA collisions.
↳ hep-phhep-exnucl-exnucl-thJHEP(2015)·22 citations
12
Selecting specific initial configuration using spectator neutrons in U+U collisions
Vipul Bairathi🇮🇳 · Md. Rihan Haque🇮🇳 · Bedangadas Mohanty🇮🇳
We present a method to select events with specific initial configuration, namely body-tip, in heavy-ion collisions using deformed Uranium nuclei. We propose to use asymmetry in spectator neutron numbers to filter out these body-tip events from the unbiased configurations in U+U collisions. We have used a variable S_eta to differentiate between the body-tip and unbiased configurations. We have calculated the second order azimuthal anisotropy, namely elliptic flow (v2), for this body-tip configuration in the framework of a transport model and found it to be consistently lower compared to that in unbiased configurations as we expected. The purity of selecting such events in a real experiment is also discussed.
↳ nucl-exhep-phnucl-thPRC(2015)·14 citations
13
Exploring the proton spin structure
Cédric Lorcé (SLAC and Liège U.)🇺🇸
Understanding the spin structure of the proton is one of the main challenges in hadronic physics. While the concepts of spin and orbital angular momentum are pretty clear in the context of non-relativistic quantum mechanics, the generalization of these concepts to quantum field theory encounters serious difficulties. It is however possible to define meaningful decompositions of the proton spin that are (in principle) measurable. We propose a summary of the present situation including recent developments and prospects of future developments.
↳ hep-phnucl-thSpringer Proc.Phys.(2016)·1 citation
14
Interpreting Single Jet Measurements in Pb+Pb Collisions at the LHC
Martin Spousta🇨🇿 · Brian Cole🇺🇸
Results are presented from a phenomenological analysis of recent measurements of jet suppression and modifications of jet fragmentation functions in Pb+Pb collisions at the LHC. Particular emphasis is placed on the impact of the differences between quark and gluon jet quenching on the transverse momentum ( $p_{T}^{j e t}$ ) dependence of the jet $R_{AA}$ and on the fragmentation functions, $D (z)$ . Primordial quark and gluon parton distributions were obtained from PYTHIA8 and were parameterized using simple power-law functions and extensions to the power-law function which were found to better describe the PYTHIA8 parton spectra. A simple model for the quark energy loss based on the shift formalism is used to model $R_{AA}$ and $D (z)$ using both analytic results and using direct Monte-Carlo sampling of the PYTHIA parton spectra. The model is capable of describing the full $p_{T}^{j e t}$ , rapidity, and centrality dependence of the measured jet $R_{AA}$ using three effective parameters. A key result from the analysis is that the $D (z)$ modifications observed in the data, excluding the enhancement at low- $z$ , may result primarily from the different quenching of the quarks and gluons. The model is also capable of reproducing the charged hadron $R_{AA}$ at high transverse momentum. Predictions are made for the jet $R_{AA}$ at large rapidities where it has not yet been measured and for the rapidity dependence of $D (z)$ .
↳ hep-phnucl-thEPJC(2016)·110 citations

Affiliations

first authorsco-authorsvia INSPIRE