Nuclear Theory·nucl-th

Tuesday·July 30, 2019

17 papers—9 primary·8 cross-listed

01
$^{15}$ C: from Halo-EFT structure to the study of transfer, breakup and radiative-capture reactions
Laura Moschini · Jiecheng Yang · Pierre Capel
Aside from being a one-neutron halo nucleus, $^{15}$ C is interesting because it is involved in reactions of relevance for several nucleosynthesis scenarios. The aim of this work is to analyze various reactions involving $^{15}$ C, using a single structure model based on Halo EFT. To develop a Halo-EFT model of $^{15}$ C at NLO, we first extract the ANC of its ground state by analyzing $^{14}$ C(d,p) $^{15}$ C transfer data at low energy. Using this Halo-EFT description, we study the $^{15}$ C Coulomb breakup at high (605AMeV) and intermediate (68AMeV) energies using eikonal models with a consistent treatment of nuclear and Coulomb interactions at all orders, and proper relativistic corrections. Finally, we study the $^{14}$ C(n, $γ$ ) $^{15}$ C radiative capture. Our theoretical cross sections are in good agreement with experimental data for all reactions, thereby assessing the robustness of the $^{15}$ C Halo-EFT model. Since a simple NLO description is enough to reproduce all data, the only nuclear-structure observables that matter are the binding energy and its ANC, showing that all the reactions considered are purely peripheral. In particular, it confirms the ANC value obtained for the $^{15}$ C ground state: 1.59 $\pm$ 0.06fm $^{- 1}$ . Our model provides also a new estimate of the radiative-capture cross section at astrophysical energy (23.3keV): 4.66 $\pm$ 0.14 $μ$ b. Including a Halo-EFT description of $^{15}$ C within precise models of reactions is confirmed to be an excellent way to relate the nucleus reaction cross sections and structure. Its systematic expansion enables us to deduce which nuclear-structure observables are actually probed in the collision. From this, we can infer valuable information on both the structure of $^{15}$ C and its synthesis through the $^{14}$ C(n, $γ$ ) $^{15}$ C radiative capture at astrophysical energies.
nucl-thPRC(2019)·30 citations
02
Coherent-Nuclear Pion Photoproduction and Neutron Radii
Gerald A. Miller🇺🇸
{ {\bf Background:} Knowing the difference between the neutron and proton densities of nuclei is a significant topic because of its importance for understanding neutron star structures and cooling mechanisms. The coherent-nuclear photoproduction of pions, $(\g, π^{0})$ , combined with elastic electron scattering, has been suggested to be a very accurate probe of density differences. {\bf Purpose:} Study the $(\g, π^{0})$ reaction mechanism so as to better access the uncertainties involved in extracting the neutron density. {\bf Methods:} Include the effects of final-state pion-nucleus charge-exchange reactions on the cross section and study the influence of the non-zero spatial extent of the proton. {\bf Results:} The effects of final-state charge-exchange increase the cross section between 6\% and 5\%, generally decreasing as the momentum transfer increases. This leads to an increase of the extracted neutron skin distance by about 50\%. The validity of the previous treatments of the proton size is confirmed. {\bf Conclusion:} The model dependence of the theoretically computed cross section increases the total systematic uncertainty (experiment plus theory) in extracting the neutron skin from the $(\g, π^{0})$ cross section by at least a factor of three. }
nucl-thhep-phnucl-exPRC(2019)·11 citations
03
Removing the Wigner bound in non-perturbative effective field theory
Saar Beck🇮🇱 · Betzalel Bazak🇮🇱 · Nir Barnea🇮🇱
The Wigner bound, setting an upper limit on the scattering effective range, is examined at different orders of contact effective field theory. Using cutoff regulator we show that the bound loosens when higher orders of the theory are considered. For a sharp and a Gaussian regulators, we conjecture an analytic formula for the dependence of the Wigner bound on the theory's order. It follows that the bound vanishes in the limit of infinite order. Using a concrete numerical example we demonstrate that the above surmise still holds after renormalization at finite cutoff. Studying the 3-body system with this example, we have found that limiting the permissible range of cutoffs by the Wigner bound, we avoid the Thomas collapse, and don't need to promote the 3-body force to leading order.
nucl-thPLB(2020)·9 citations
04
The effect of single-particle space-momentum angle distribution on two-pion HBT correlation in high-energy heavy-ion collisions
Hang Yang🇨🇳 · Qichun Feng · Yanyu Ren · Jingbo Zhang🇨🇳 · Lei Huo
Using several source models, we analyze the transverse momentum dependence of HBT radii in the relativistic heavy-ion collisions. The results indicate that the single-particle space-momentum angle distribution plays an important role in the transverse momentum dependence of HBT radii. In a cylinder source, we use several formulas to describe the transverse momentum dependence of HBT radii and the single-particle space-momentum angle distribution. We also make a numerical connection between them in the transverse plane.
nucl-thCPC(2020)·3 citations
05
Hybrid star within the framework of a lowest-order constraint variational method
S. Khanmohamadi🇮🇷 · H.R. Moshfegh🇮🇷 · S.Atashbar Tehrani🇮🇷
The hadron-quark phase transition in the core of heavy neutron star (NS) has been studied. For the hadronic sector, we have used the lowest-order constraint variational method by employing $A V_{18}$ , $A V_{14}$ , $U V_{14}$ , and Reid $68$ two-body nucleon-nucleon forces supplemented by the phenomenological Urbana-type three-body force. We have adopted the MIT bag model as well as three-flavor version of the Nambu- Jona-Lasinio (NJL) model to describe the quark phase. The equation of state (EOS) of a hybrid star (HS) is presented by combining two EOS of the hadronic sector and quark sector of a star, which are derived from independent models or theories. The hadron-quark transition is constructed by considering a sharp phase transition, i.e., Maxwell construction. The structure of the HS is calculated and reported by solving Tolman-Oppenheimer-Volkoff equations. Finally the radii and tidal deformability of purely NS and HS for the mass of $1.4 M_{⊙}$ is computed and new constraints on these quantities are checked. The maximum mass of HS is found more than $2 M_{⊙}$ for both the NJL and MIT bag models. However, the maximum mass of $1.796 M_{⊙}$ ( $1.896 M_{⊙}$ ) was the best result that would be calculated for a stable HS with the pure quark core within the MIT (NJL) model. All the hybrid EOS fulfill the constraints on radii and tidal deformability extracted from the binary GW170817 for HSs. A comprehensive analysis on the structure of purely NS and HS and also compactness, tidal Love number, and tidal deformability for the star with the mass of 1.4 $M_{⊙}$ has been conducted for various EOS of the hadron sector and several parameter sets of the quark EOS. The results achieved in this study are in good concurrence with the other calculations reported on this subject.
nucl-thastro-ph.HEhep-phPRD(2020)·12 citations
06
Energy loss of heavy quarks in the isotropic collisional hot QCD medium
Mohammad Yousuf Jamal🇮🇳 · Vinod Chandra🇮🇳
Collisional energy loss of heavy partons (charm and bottom quarks) has been determined within the framework of semi-classical transport theory implying Bhatnagar-Gross-Krook (BGK) collisional kernel. Hot QCD medium effects have been incorporated while employing a quasi-particle description of the medium in terms of effective gluons, quarks and antiquarks with respective temperature dependent effective fugacities. The momentum dependence of the energy loss for charm and bottom quark has been investigated. It is observed that with the increase in momentum of the heavy quarks, the loss increases sharply for the smaller values and reaches a saturation later. Further, as compared to the charm quark, bottom quark losses less energy at a particular momentum and collisional frequency. The energy loss is seen to increase with increasing collisional frequency. We also provide a comparative study of the results obtained using BGK-kernel than those using relaxation time approximation (RTA)-kernel and found them consistent with each other. The medium effects in all the situations are seen to play quite significant role.
nucl-thhep-phEPJC(2019)·21 citations
07
Smallest QCD Droplet and Multiparticle Correlations in pp Collisions
Seyed Farid Taghavi🇩🇪
The collective evolution of produced matter in heavy-ion collisions is effectively described by hydrodynamics from time scales greater than the inverse of the temperature, $τ ≳ 1/ T$ . In the context of the Gubser solution, I show that the hydrodynamization condition $τ T ≳ 1$ is translated into an allowed domain in the spatial system size and the final multiplicity for hydrodynamics applicability. It turns out that the flow measurements in pp collisions are inside the domain of validity. I predict that by approaching the boundaries of the allowed domain the hydrodynamic response to the initial ellipticity changes its sign. I follow a rather model-independent approach for the initial state where, instead of modeling the initial energy density of individual events, the initial system size and ellipticity event-by-event fluctuation are modeled. The model, initial state fluctuation+Gubser solution+Cooper-Frye freeze-out, describes the multiplicity and transverse momentum dependence of two-point and four-point correlation functions ( $c_{2} {2}$ and $c_{2} {4}$ ) in an accurate agreement with pp collision experimental measurements. In particular, the sign of the four-point correlation function is the same as the observation, which failed to be described correctly in previous studies. I also predict a signal for the sign change in the hydrodynamic response that can be inspected in future experimental measurements of two-point and four-point correlation functions at lower multiplicities.
nucl-thhep-phnucl-exPRC(2021)·11 citations
08
Structure of 16C from analyses of proton scattering data and the B(E2) problem
S. Karataglidis🇿🇦 · K. Murulane🇿🇦
The B(E2) value for the decay of the 2+_1 state in 16C to ground has been the subject of much discussion. Analyses assuming a simple model of two neutrons coupled to a 14C core of the available data, which extend over an order of magnitude,gives reasonable agreement but with an inclusion of a large effective charge for the neutrons. To assess this situation, a large scale (2+4)hw shell model calculation of 16C has been made from which the wave functions have been used to obtain the B(E2) value. As a check, comparison is made with available data on the spectrum of 16C and intermediate-energy elastic proton scattering.
nucl-thPRC(2020)·3 citations
09
Ruling out the supersoft high-density symmetry energy from the discovery of PSR J0740+6620 with mass $2.1 4_{- 0.09}^{+ 0.10} M_{⊙}$
Ying Zhou🇨🇳 · Lie-Wen Chen🇨🇳
Using the very recently reported mass $2.1 4_{- 0.09}^{+ 0.10} M_{⊙}$ of PSR J0740+6620 together with the data of finite nuclei and the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions, we show that the symmetry energy $E_{sym} (n)$ cannot be supersoft so that it becomes negative at suprasaturation densities in neutron stars (NSs) and thus may make the NS have a pure neutron matter core. This is in contrast to the fact that using the mass $2.01 \pm 0.04 M_{⊙}$ of PSR J0348+0432 as the NS maximum mass cannot rule out the supersoft high-density $E_{sym} (n)$ . Furthermore, we find the stiffer high-density $E_{sym} (n)$ based on the existence of $2.14 M_{⊙}$ NSs leads to a strong constraint of $Λ_{1.4} \geq 34 8_{- 51}^{+ 88}$ for the dimensionless tidal deformability of the canonical $1.4 M_{⊙}$ NS.
nucl-thastro-ph.HEastro-ph.SRhep-ph+1ApJ(2019)·33 citations

Affiliations

first authorsco-authorsvia INSPIRE