Nuclear Theory·nucl-th

Monday·September 24, 2018

9 papers—4 primary·5 cross-listed

01
Role of charged particle emission on the evaporation residue formation in the $^{82}$ Se+ $^{138}$ Ba reaction leading to the $^{220}$ Th compound nucleus
G. Mandaglio · A. K. Nasirov · A. Anastasi · F. Curciarello · G. Fazio · G. Giardina
We present detailed results of a theoretical investigation on the production of evaporation residue nuclei obtained in a heavy ion reaction when charged particles (proton and $α$ -particle) are also emitted with the neutron evaporation along the deexcitation cascade of the formed compound nucleus. The almost mass symmetric $^{82}$ Se+ $^{138}$ Ba reaction has been studied since there are many experimental results on individual evaporation residue (ER) cross sections after few light particle emissions along the cascade of the $^{220}$ Th compound nucleus (CN) covering the wide 12--70 MeV excitation energy range. Our specific theoretical results on the ER cross sections for the $^{82}$ Se+ $^{138}$ Ba are in good agreement with the available experimental measurements, but our overall theoretical results concerning all possible relevant contributions of evaporation residues are several times greater than the ERs measured in experiment. The discrepancy could be due to the experimental difficulties in the identification of ER nuclei after the emission of multiple neutral and charged particles, nevertheless the analysis of ER data is very important to test the reliability of the model and to stress the importance on the investigation of ER nuclei also obtained after charged particle emissions.
nucl-thNPA(2018)·3 citations
02
Current Status of Very-Large-Basis Hamiltonian Diagonalizations for Nuclear Physics
Calvin W. Johnson🇺🇸
Today there are a plethora of many-body techniques for calculating nuclear wave functions and matrix elements. I review the status of that reliable workhorse, the interacting shell model, a.k.a. configuration-interaction methods, a.k.a. Hamiltonian diagonalization, and survey its advantages and disadvantages. With modern supercomputers one can tackle dimensions up to about 20 billion! I discuss how we got there and where we might go in the near future.
nucl-th5 citations
03
Towards the determination of heavy-quark transport coefficients in quark-gluon plasma
Shanshan Cao🇺🇸 · Gabriele Coci🇮🇹 · Santosh Kumar Das🇮🇳 · Weiyao Ke🇺🇸 · Shuai Y.F. Liu🇺🇸 · Salvatore Plumari🇮🇹 · Taesoo Song🇩🇪 · Yingru Xu🇺🇸 · Jörg Aichelin🇫🇷 · Steffen Bass🇺🇸 · Elena Bratkovskaya🇩🇪 · Xing Dong🇺🇸 and 7 other authors
Several transport models have been employed in recent years to analyze heavy-flavor meson spectra in high-energy heavy-ion collisions. Heavy-quark transport coefficients extracted from these models with their default parameters vary, however, by up to a factor of 5 at high momenta. To investigate the origin of this large theoretical uncertainty, a systematic comparison of heavy-quark transport coefficients is carried out between various transport models. Within a common scheme devised for the nuclear modification factor of charm quarks in a brick medium of a quark-gluon plasma, the systematic uncertainty of the extracted drag coefficient among these models is shown to be reduced to a factor of 2, which can be viewed as the smallest intrinsic systematical error band achievable at present time. This indicates the importance of a realistic hydrodynamic evolution constrained by bulk hadron spectra and of heavy-quark hadronization for understanding the final heavy-flavor hadron spectra and extracting heavy-quark drag coefficient. The transverse transport coefficient is less constrained due to the influence of the underlying mechanism for heavy-quark medium interaction. Additional constraints on transport models such as energy loss fluctuation and transverse-momentum broadening can further reduce theoretical uncertainties in the extracted transport coefficients.
nucl-thhep-phnucl-exPRC(2019)·200 citations
04
Diffusion of charm and beauty in the Glasma
Marco Ruggieri🇨🇳 · Santosh Kumar Das🇮🇳
Relativistic nuclear collisions offer a unique way to study strong interactions at very high energy. The collision process can be described within the gluon saturation framework as the interaction of two colored glasses, and because of this interaction strong longitudinal gluon fields, namely the Glasma, are produced immediately after the collision. Besides, heavy quarks are also produced in the very early stage and because of their large mass and small concentration, their motion does not affect the evolution of the Glasma, thus behaving as ideal probes of the Glasma itself. We study the evolution of the heavy quarks in the Glasma allegedly produced in high energy p-Pb collisions by solving consistently the equations of motion of the quarks in the evolving Glasma fields. We find that this motion can be understood in terms of diffusion in momentum space, similarly to the random motion of a heavy probe in a hot thermalized medium. We show how the diffusion of heavy probes affects the nuclear modification factor of D and B mesons in p-Pb collisions.
nucl-thhep-phEPJ Web Conf.(2018)·10 citations
05
$Ξ (1690)^{-}$ production in the $K^{-} p \to K^{+} K^{-} Λ$ reaction process near threshold
Jung Keun Ahn🇰🇷 · Seung-il Nam🇰🇷
We investigate $Ξ (1690)^{-}$ production from the $K^{-} p \to K^{+} K^{-} Λ$ reaction within the effective Lagrangian approach at the tree-level Born approximation. We consider the $s$ - and $u$ -channel $Σ/Λ$ ground states and resonances for the $Ξ$ -pole contributions, in addition to the $s$ -channel $Λ$ , $u$ -channel nucleon pole, and $t$ -channel $K^{-}$ -exchange for the $ϕ$ -pole contributions. The $Ξ$ -pole includes $Ξ (1320)$ , $Ξ (1535)$ , $Ξ (1690) (J^{p} = 1/ 2^{-})$ ,and $Ξ (1820) (J^{p} = 3/ 2^{-})$ . We calculate the Dalitz plot density of $(d^{2} σ / d M_{K^{+} K^{-}} d M_{K^{-} Λ}$ at 4.2 GeV $/ c$ ) and the total cross sections for the $K^{-} p \to K^{+} K^{-} Λ$ reaction near the threshold. The calculation results are in good agreement with previously acquired experimental data. Using the parameters from the fit, we present the total and differential cross sections for the two-body $K^{-} p \to K^{+} Ξ (1690)^{-}$ reaction near the threshold. In our calculation, a strong enhancement at backward $K^{+}$ angles is predicted because of the dominant $u$ -channel contribution. We also demonstrate that the Dalitz plot analysis for $p_{K^{-}} = 1.915 - - 2.065$ GeV/c enables us to access direct information regarding $Ξ (1690)^{-}$ production, which can be tested by future $K^{-}$ beam experiments. The possible spin-parity states of $Ξ (1690)^{-}$ are briefly discussed as well.
↳ hep-phhep-exnucl-thPRD(2018)·4 citations
06
Pentaquark states with the $QQQq q ˉ$ configuration in a simple model
Shi-Yuan Li🇨🇳 · Yan-Rui Liu🇨🇳 · Yu-Nan Liu🇨🇳 · Zong-Guo Si🇨🇳 · Jing Wu🇨🇳
We discuss the mass splittings for the $S$ -wave triply heavy pentaquark states with the $QQQq q ˉ$ $(Q = b, c; q = u, d, s)$ configuration which is a mirror structure of $Q Q ˉ q q q$ . The latter configuration is related with the nature of $P_{c} (4380)$ observed by the LHCb Collaboration. The considered pentaquark masses are roughly estimated with a simple method. One finds that such states are probably not narrow even if they do exist. This leaves room for molecule interpretation for a state around the low-lying threshold of a doubly heavy baryon and a heavy-light meson, e.g. $Ξ_{cc} D$ , if it were observed. As a by product, we conjecture that upper limits for the masses of the conventional triply heavy baryons can be determined by the masses of the conventional doubly heavy baryons.
↳ hep-phhep-exhep-latnucl-thEPJC(2019)·29 citations
07
Probing axial quark generalized parton distributions through exclusive photoproduction of a $γ π^{\pm}$ pair with a large invariant mass
G.Duplančić🇭🇷 · K.Passek-Kumerički🇭🇷 · B.Pire🇫🇷 · L.Szymanowski🇵🇱 · S.Wallon🇫🇷
Exclusive photoproduction of a $γ π^{\pm}$ pair in the kinematics where the pair has a large invariant mass and the final nucleon has a small transverse momentum is described in the collinear factorization framework. The scattering amplitude is calculated at leading order in $α_{s}$ and the differential cross sections for the process are estimated in the kinematics of the JLab~12-GeV experiments. The order of magnitude of the predicted cross-sections seems sufficient for a dedicated experiment to be performed. The process turns out to be very sensitive to the axial generalized parton distribution combination $H ~_{u} - H ~_{d}$ .
↳ hep-phhep-exnucl-exnucl-thJHEP(2018)·58 citations
08
Dense matter equation of state for neutron star mergers
S. Lalit🇺🇸 · M. A. A. Mamun🇺🇸 · C. Constantinou🇺🇸 · M. Prakash🇺🇸
In simulations of binary neutron star mergers, the dense matter equation of state (EOS) is required over wide ranges of density and temperature as well as under conditions in which neutrinos are trapped, and the effects of magnetic fields and rotation prevail. Here we assess the status of dense matter theory and point out the successes and limitations of approaches currently in use. A comparative study of the excluded volume (EV) and virial approaches for the $n p α$ system using the equation of state of Akmal, Pandharipande and Ravenhall for interacting nucleons is presented in the sub-nuclear density regime. Owing to the excluded volume of the $α$ -particles, their mass fraction vanishes in the EV approach below the baryon density 0.1 fm $^{- 3}$ , whereas it continues to rise due to the predominantly attractive interactions in the virial approach. The EV approach of Lattimer et al. is extended here to include clusters of light nuclei such as d, $^{3}$ H and $^{3}$ He in addition to $α$ -particles. Results of the relevant state variables from this development are presented and enable comparisons with related but slightly different approaches in the literature. We also comment on some of the sweet and sour aspects of the supra-nuclear EOS. The extent to which the neutron star gravitational and baryon masses vary due to thermal effects, neutrino trapping, magnetic fields and rotation are summarized from earlier studies in which the effects from each of these sources were considered separately. Increases of about $20% (≳ 50%)$ occur for rigid (differential) rotation with comparable increases occurring in the presence of magnetic fields only for fields in excess of $1 0^{18}$ Gauss. Comparatively smaller changes occur due to thermal effects and neutrino trapping. Some future studies to gain further insight into the outcome of dynamical simulations are suggested.
↳ astro-ph.HEnucl-thEPJA(2019)·27 citations
09
Chiral Cherenkov and chiral transition radiation in anisotropic matter
Kirill Tuchin🇺🇸
A significant contribution to the electromagnetic radiation by a fast electric charge moving in anisotropic chiral matter arises from spontaneous photon radiation due to the chiral anomaly. While such a process, also known as the "vacuum Cherenkov radiation", is forbidden in the QED vacuum, it can occur in chiral matter, where it is more appropriate to call it the "chiral Cherenkov radiation". Its contribution to the radiation spectrum is of order $α^{2}$ compared to $α^{3}$ of the bremsstrahlung. I derive the frequency spectrum and the angular distribution of this radiation in the high energy limit. The quantum effects due to the hard photon emission and the fermion mass are taken into account. The obtained spectra are analyzed in the case the quark-gluon plasma and a Weyl semimetal.
↳ hep-phcond-mat.mes-hallnucl-thPRD(2018)·18 citations

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