Nuclear Theory·nucl-th

Tuesday·September 15, 2020

17 papers—8 primary·9 cross-listed

01
Nuclear resonance fluorescence of $^{208}$ Pb in heavy-ion colliders
Uliana Dmitrieva (1 and 2)🇷🇺 · Igor Pshenichnov (1 and 2) ((1) Moscow Institute of Physics and Technology, Dolgoprudny, Russia, (2) Institute for Nuclear Research, Russian Academy of Sciences, Moscow, Russia)🇷🇺
In ultraperipheral collisions (UPC) of nuclei the impact of Lorentz-contracted electromagnetic fields of collision partners leads to their excitations. In case of heavy nuclei the emission of neutrons is a main deexcitation channel and forward neutrons emitted in UPC were detected at the Relativistic Heavy-Ion Collider (RHIC) and at the Large Hadron Collider (LHC) by means of Zero Degree Calorimeters. However, the excitation of low-lying discrete nuclear states is also possible in UPC below the neutron separation energy. In this work by means of the Weizsacker-Williams method the data on nuclear resonance fluorescence (NRF) induced by real photons in 208 Pb are used to model the excitations of discrete levels in colliding nuclei. Due to Lorentz boosts one can expect that deexcitation photons with energies up to 40 GeV and 300 GeV are emitted in very forward direction, respectively, at the LHC and at the Future Circular Collider (FCC-hh). Energy, rapidity and angular distributions of such photons are calculated in the laboratory system, which can be used for monitoring of collider luminosity or triggering particle production in UPC.
nucl-thnucl-exEPJA(2021)·4 citations
02
Lattice calculation of transport coefficient $q^$ in pure gluon plasma and (2+1)-flavor QCD plasma
Amit Kumar (Wayne State University USA)🇺🇸 · Abhijit Majumder (Wayne State University USA)🇺🇸 · Johannes Heinrich Weber (Michigan State University USA)🇺🇸
The transport coefficient $q^$ is a leading coefficient that controls the modification of the hard parton traversing QGP, and hence, responsible for the suppression of the high transverse momentum (transverse to the beam direction) charged-hadrons in heavy-ion collisions. In this article, we present the first unquenched lattice QCD calculation of $q^$ . The calculation is carried out using (2+1)-flavor of quarks, using the highly improved staggered quark action (HISQ) and tree-level Symanzik improved gauge action. The calculation is performed in a wide range of temperatures, ranging from 200 MeV $< T <$ 800 MeV using MILC code package. We considered a leading-order process where a hard parton scatters off the glue field of a thermal QCD medium by exchanging a Glauber gluon (whose transverse momentum is larger than its longitudinal components). The hard scale associated with the jet parton allows the coupling of the gluon to that parton to be treated in perturbation theory. The coupling of the gluon to the medium is treated non-perturbatively. This non-perturbative part is expressed in terms of a non-local (two-point) field-strength-field-strength operator product which can be Taylor expanded after analytic continuation to the deep Euclidean region. Such an expansion allows us to write $q^$ in terms of a series of local operators, which are suppressed by factors of the hard parton energy. The calculated $q^$ and its temperature dependence demonstrates reasonable agreement with the phenomenological extraction carried out by the JET collaboration.
nucl-thhep-latnucl-exPoS(2021)·2 citations
03
Influence of triaxial deformation on wobbling motion in even-even nuclei
Bin Qi · Hui Zhang · Shou Yu Wang · Qi Bo Chen
The influence of triaxial deformation $γ$ on the purely collective form of wobbling motion in even-even nuclei are discussed based on the triaxial rotor model. It is found that the harmonic approximation is realized well when $γ = 3 0^{\circ}$ for the properties of energy spectra and electric quadrupole transition probabilities, while this approximation gets bad when $γ$ deviates from $3 0^{\circ}$ . A recent data from Coulomb excitation experiment, namely $3_{1}^{+}$ and $2_{2}^{+}$ for the $^{110}$ Ru are studied and might be suggested as the bandhead of the wobbling bands. In addition, two types of angular momentum geometries for wobbling motion, stemming from different $γ$ values, are exhibited by azimuthal plots.
nucl-thJ.Phys.G(2021)·13 citations
04
Nature of $S$ -wave $NN$ interaction and dibaryon production at nucleonic resonance thresholds
V. I. Kukulin🇷🇺 · O. A. Rubtsova🇷🇺 · M. N. Platonova🇷🇺 · V. N. Pomerantsev🇷🇺 · H. Clement🇩🇪 · T. Skorodko🇩🇪
Phase shifts and inelasticity parameters for $N N$ scattering in the partial-wave channels $^{3} S_{1}$ -- $^{3} D_{1}$ and $^{1} S_{0}$ at energies $T_{lab}$ from zero to about 1 GeV are described within a unified $N N$ potential model assuming the formation of isoscalar and isovector dibaryon resonances near the $N N^{*} (1440)$ threshold. Evidence for these near-threshold resonances is actually found in the recent WASA experiments on single- and double-pion production in $N N$ collisions. There, the excitation of the Roper resonance $N^{*} (1440)$ exhibits a structure in the energy dependence of the total cross section, which corresponds to the formation of dibaryon states with $I (J^{π}) = 0 (1^{+})$ and $1 (0^{+})$ at the $N N^{*} (1440)$ threshold. These two $S$ -wave dibaryon resonances may provide a new insight into the nature of the strong $N N$ interaction at low and intermediate energies.
nucl-thEPJA(2020)·20 citations
05
Cumulants of net-charge distribution from particle-antiparticle sources
Igor Altsybeev🇷🇺
It is shown how high-order cumulants of net-charge distribution in hadronic collisions at LHC energies can be expressed via lower-order terms under the assumption that particle-antiparticle pairs are produced in independent local processes. It is argued and tested with HIJING model that this assumption is typically valid for net-proton fluctuations in the case when no critical behaviour is present in the system. Values estimated in such a way can be considered as baselines for direct measurements of high-order net-charge fluctuations in real data.
nucl-thhep-phnucl-exActa Phys.Polon.Supp.(2021)·1 citation
06
Higher-rank discrete symmetries in the IBM. III Tetrahedral shapes
Piet Van Isacker🇫🇷 · Abdelhamid Bouldjedri🇩🇿 · Salima Zerguine🇩🇿
In the context of the sf-IBM, the interacting boson model with s and f bosons, the conditions are derived for a rotationally invariant and parity-conserving Hamiltonian with up to two-body interactions to have a minimum with tetrahedral shape in its classical limit. A degenerate minimum that includes a shape with tetrahedral symmetry can be obtained in the classical limit of a Hamiltonian that is transitional between the two limits of the model, U_f(7) and SO_{sf}(8). The conditions for the existence of such a minimum are derived. The system can be driven towards an isolated minimum with tetrahedral shape through a modification of two-body interactions between the f bosons. General comments are made on the observational consequences of the occurrence of shapes with a higher-rank discrete symmetry in the context of algebraic models.
nucl-thNPA(2020)·1 citation
07
Relativistic hydrodynamics with momentum dependent relaxation time
Sukanya Mitra
A second order relativistic hydrodynamic theory has been derived using momentum dependent relaxation time in the relativistic transport equation. In order to do that, an iterative technique of gradient expansion approach, namely Chapman-Enskog (CE) expansion of the particle distribution function has been employed. The key findings of this work are, (i) momentum dependent relaxation time in collision term results in an extended Landau matching condition for the thermodynamic variables, (ii) the result from numerical solution of Boltzmann equation lies somewhere in between the two popular extreme limits : linear and quadratic ansatz, indicating a fractional power of momentum dependence in relaxation time to be appropriate, (ii) an equivalence has been established between the iterative gradient expansion method like CE and the well known moment approach like Grad's 14-moment method.
nucl-thPRC(2021)·22 citations
08
Limiting masses and radii of neutron stars and their implications
Christian Drischler🇺🇸 · Sophia Han🇺🇸 · James M. Lattimer🇺🇸 · Madappa Prakash🇺🇸 · Sanjay Reddy🇺🇸 · Tianqi Zhao🇺🇸
We combine equation of state of dense matter up to twice nuclear saturation density ( $n_{sat} = 0.16 fm^{- 3}$ ) obtained using chiral effective field theory ( $χ$ EFT), and recent observations of neutron stars to gain insights about the high-density matter encountered in their cores. A key element in our study is the recent Bayesian analysis of correlated EFT truncation errors based on order-by-order calculations up to next-to-next-to-next-to-leading order in the $χ$ EFT expansion. We refine the bounds on the maximum mass imposed by causality at high densities, and provide stringent limits on the maximum and minimum radii of $\sim 1.4 M_{⊙}$ and $\sim 2.0 M_{⊙}$ stars. Including $χ$ EFT predictions from $n_{sat}$ to $2 n_{sat}$ reduces the permitted ranges of the radius of a $1.4 M_{⊙}$ star, $R_{1.4}$ , by $\sim 3.5 km$ . If observations indicate $R_{1.4} < 11.2 km$ , our study implies that either the squared speed of sound $c_{s}^{2} > 1/2$ for densities above $2 n_{sat}$ , or that $χ$ EFT breaks down below $2 n_{sat}$ . We also comment on the nature of the secondary compact object in GW190814 with mass $≃ 2.6 M_{⊙}$ , and discuss the implications of massive neutron stars $> 2.1 M_{⊙} (2.6 M_{⊙})$ in future radio and gravitational-wave searches. Some form of strongly interacting matter with $c_{s}^{2} > 0.35 (0.55)$ must be realized in the cores of such massive neutron stars. In the absence of phase transitions below $2 n_{sat}$ , the small tidal deformability inferred from GW170817 lends support for the relatively small pressure predicted by $χ$ EFT for the baryon density $n_{B}$ in the range $1 - 2 n_{sat}$ . Together they imply that the rapid stiffening required to support a high maximum mass should occur only when $n_{B} ≳ 1.5 - 1.8 n_{sat}$ .
nucl-thastro-ph.HEPRC(2021)·181 citations

Affiliations

first authorsco-authorsvia INSPIRE