Nuclear Theory·nucl-th

Wednesday·October 4, 2017

13 papers—8 primary·5 cross-listed

01
Exciting Nucleons in Compton Scattering and Hydrogen-Like Atoms
Franziska Hagelstein (JGU Mainz)🇩🇪
This PhD thesis is devoted to the low-energy structure of the nucleon (proton and neutron) as seen through electromagnetic probes, e.g., electron and Compton scattering. The research presented here is based primarily on dispersion theory and chiral effective-field theory. The main motivation is the recent proton radius puzzle, which is the discrepancy between the classic proton charge radius determinations (based on electron-proton scattering and normal hydrogen spectroscopy) and the highly precise extraction based on first muonic-hydrogen experiments by the CREMA Collaboration. The precision of muonic-hydrogen experiments is presently limited by the knowledge of proton structure effects beyond the charge radius. A major part of this thesis is devoted to calculating these effects using everything we know about the nucleon electromagnetic structure from both theory and experiment. The thesis consists of eight chapters. The first and last are, respectively, the introduction and conclusion. The remainder of this thesis can roughly be divided into the following three topics: finite-size effects in hydrogen-like atoms, real and virtual Compton scattering, and two-photon-exchange effects.
nucl-thhep-phnucl-exphysics.atom-ph12 citations
02
Dynamical initial state model for relativistic heavy-ion collisions
Chun Shen🇺🇸 · Björn Schenke🇺🇸
We present a fully three-dimensional model providing initial conditions for energy and net-baryon density distributions in heavy ion collisions at arbitrary collision energy. The model includes the dynamical deceleration of participating nucleons or valence quarks, depending on the implementation. The duration of the deceleration continues until the string spanned between colliding participants is assumed to thermalize, which is either after a fixed proper time, or a fluctuating time depending on sampled final rapidities. Energy is deposited in space-time along the string, which in general will span a range of space-time rapidities and proper times. We study various observables obtained directly from the initial state model, including net-baryon rapidity distributions, 2-particle rapidity correlations, as well as the rapidity decorrelation of the transverse geometry. Their dependence on the model implementation and parameter values is investigated. We also present the implementation of the model with 3+1 dimensional hydrodynamics, which involves the addition of source terms that deposit energy and net-baryon densities produced by the initial state model at proper times greater than the initial time for the hydrodynamic simulation.
nucl-thhep-phnucl-exPRC(2018)·220 citations
03
Universal strangeness production and size fluctuactions in small and large systems
P.Castorina🇮🇹 · M.Floris🇨🇭 · S.Plumari🇮🇹 · H.Satz🇩🇪
Strangeness production in high multiplicity events gives indications on the transverse size fluctuactions in nucleus-nucleus ( $AA$ ), proton-nucleus ( $p A$ ) and proton-proton ( $pp$ ) collisions. In particular the behavior of strange particle hadronization in "small" ( $pp, p A$ ) and "large" ( $AA$ ) initial configurations of the collision can be tested for the specific particle species, for different centralities and for large fluctuations of the transverse size in $p A$ and $pp$ by using the recent ALICE data. A universality of strange hadron production emerges by introducing a dynamical variable proportional to the initial parton density in the transverse plane.
nucl-thhep-phPoS(2017)·2 citations
04
Uncertainty of the astrophysical $^{17, 18}$ O( $α$ ,n) $^{20, 21}$ Ne reaction rates and the applicability of the statistical model for nuclei with $A ≲ 20$
Peter Mohr
Background: The ( $α$ ,n) and ( $α$ , $γ$ ) reactions on $^{17, 18}$ O have significant impact on the neutron balance in the astrophysical $s$ -process. In this scenario stellar reaction rates are required for relatively low temperatures below $T_{9} ≲ 1$ . Purpose: The uncertainties of the $^{17, 18}$ O( $α$ ,n) $^{20, 21}$ Ne reactions are investigated. Statistical model calculations are performed to study the applicability of this model for relatively light nuclei in extension to a recent review for the $20 \leq A \leq 50$ mass range. Method: The available experimental data for the $^{17, 18}$ O( $α$ ,n) $^{20, 21}$ Ne reactions are compared to statistical model calculations. Additionally, the reverse $^{20}$ Ne(n, $α$ ) $^{17}$ O reaction is investigated, and similar studies for the $^{17}$ F mirror nucleus are provided. Results: It is found that on average the available experimental data for $^{17}$ O and $^{18}$ O are well described within the statistical model, resulting in reliable reaction rates above $T_{9} ≳ 1.5$ from these calculations. However, significant experimental uncertainties are identified for the $^{17}$ O( $α$ ,n $_{0}$ ) $^{20}$ Ne(g.s.) channel. Conclusions: The statistical model is able to predict astrophysical reaction rates for temperatures above 1 GK with uncertainties of less than a factor of two for the nuclei under study. An experimental discrepancy for the $^{17}$ O( $α$ ,n) $^{20}$ Ne reaction needs to be resolved.
nucl-thPRC(2017)·12 citations
05
Transverse expansion of hot magnetized Bjorken flow in heavy ion collisions
M. Haddadi Moghaddam🇮🇷 · B. Azadegan🇮🇷 · A. F. Kord🇮🇷 · W. M. Alberico🇮🇹
We argue that the existence of an inhomogeneous external magnetic field can lead to radial flow in transverse plane. Our aim is to show how the introduction of a magnetic field generalizes the Bjorken flow. We investigate the effect of an inhomogeneous weak external magnetic field on the transverse expansion of in-viscid fluid created in high energy nuclear collisions. In order to simplify our calculation and compare with Gubser model, we consider the fluid under investigation to be produced in central collisions, at small impact parameter; azimuthal symmetry has been considered. In our model, we assume an inhomogeneous external magnetic field following the power-law decay in proper time and having radial inhomogeneity perpendicular to the radial velocity of the in-viscid fluid in the transverse plane; then the space time evolution of the transverse expansion of the fluid is obtained. We also show how the existence of an inhomogeneous external magnetic field modifies the energy density. Finally we use the solutions for the transverse velocity and energy density in the presence of a weak magnetic field, to estimate the transverse momentum spectrum of protons and pions emerging from the Magneto-hydrodynamic solutions.
nucl-thhep-phEPJC(2019)·4 citations
06
Consistent optical potential for incident and emitted low-energy $α$ particles. II. $α$ -emission in fast-neutron induced reactions on Zr isotopes
V. Avrigeanu · M. Avrigeanu
Background: Challenging questions of the $α$ -particle optical-model potential (OMP) are still pointed out by recent high-precision measurements of $α$ -induced reaction data below the Coulomb barrier. Moreover, the reliability of a previous OMP for $α$ -particles on nuclei within the mass number range 45 $\leq$ $A$ $\leq$ 209 has been recently proved for emitted $α$ particles as well, but only in the case of proton-induced reactions on Zn isotopes [Phys. Rev. C {\bf 91}, 064611 (2015), Paper I]. Purpose: Analysis of most recent $(α, γ)$ reaction data for Ge and Zr isotopes, which provides an additional validation of the above-mentioned potential, is related to a further account of $α$ -particle emission in neutron-induced reactions on Zr isotopes, at the same time with a suitable description of all competitive processes. Methods: A consistent parameter set, established or validated by independent analysis of recent various data, particularly $γ$ -ray strength functions, have been involved within model calculation of the $(α, γ)$ as well as $(n, α)$ reaction cross sections. The latter are part of the whole analysis of the neutron activation of Zr isotopes, in order to avoid any error compensation or latent ambiguity. Results: The aforesaid potential provides a consistent description of recent $α$ -induced reaction data with no empirical rescaling factors of the $γ$ and/or nucleon widths. On the other hand, its use leads to underestimated predictions of the pre-equilibrium emission and statistical models for the $(n, α)$ reaction cross sections. Conclusions: An optical potential with a volume imaginary component seems to be needed to describe the low-energy $α$ -particle evaporation, while only surface absorption occurs in $α$ -induced reactions at similar energies.
nucl-thPRC(2017)·11 citations
07
Event patterns extracted from anisotropic spectra of charged particles produced in Pb-Pb collisions at 2.76 TeV
Ya-Hui Chen🇨🇳 · Fu-Hu Liu🇨🇳
Event patterns extracted from anisotropic spectra of charged particles produced in lead-lead collisions at 2.76 TeV are investigated. We use an inverse power-law resulted from the QCD calculus to describe the transverse momentum spectrum in the hard scattering process, and a revised Erlang distribution resulted from a multisource thermal model to describe the transverse momentum spectrum and anisotropic flow in the soft excitation process. The pseudorapidity distribution is described by a three-Gaussian function which is a revision of the Landau hydrodynamic model. Thus, the event patterns at the kinetic freeze-out are displayed by the scatter plots of the considered particles in the three-dimensional velocity, momentum, and rapidity spaces.
nucl-thhep-exhep-phnucl-exEPJA(2017)·4 citations
08
Beyond the Unified Model
Stefan Frauendorf
The key elements of the Unified Model are reviewed and checked against modern experimental data. For medium-mass or heavy nuclei it is found that separation between collective and intrinsic degrees freedom becomes invalid for after exciting five to ten collective quanta along the yrast line and two quanta above it. The microscopic derivation of the Bohr Hamiltonian by means of adiabatic time-dependent mean field theory is presented and results compared with experiment. The description of the strong coupling between the rotational and intrinsic degrees of freedom in framework of the rotating mean field is described from a conceptual point of view. The classification of rotational bands as configurations of rotating quasiparticles is introduced. Using the concept of spontaneous symmetry breaking the microscopic underpinning of the rotational degrees is refined. Resulting phenomena, as tilted-axis rotation, transverse wobbling, chirality, magnetic rotation, and band termination are discussed.
nucl-thPhys.Scripta(2018)·57 citations
09
A fast and accurate method for perturbative resummation of transverse momentum-dependent observables
Daekyoung Kang🇺🇸 · Christopher Lee🇺🇸 · Varun Vaidya🇺🇸
We propose a novel strategy for the perturbative resummation of transverse momentum-dependent (TMD) observables, using the $q_{T}$ spectra of gauge bosons ( $γ^{*}$ , Higgs) in $pp$ collisions in the regime of low (but perturbative) transverse momentum $q_{T}$ as a specific example. First we introduce a scheme to choose the factorization scale for virtuality in momentum space instead of in impact parameter space, allowing us to avoid integrating over (or cutting off) a Landau pole in the inverse Fourier transform of the latter to the former. The factorization scale for rapidity is still chosen as a function of impact parameter $b$ , but in such a way designed to obtain a Gaussian form (in $ln b$ ) for the exponentiated rapidity evolution kernel, guaranteeing convergence of the $b$ integral. We then apply this scheme to obtain the $q_{T}$ spectra for Drell-Yan and Higgs production at NNLL accuracy. In addition, using this scheme we are able to obtain a fast semi-analytic formula for the perturbative resummed cross sections in momentum space: analytic in its dependence on all physical variables at each order of logarithmic accuracy, up to a numerical expansion for the pure mathematical Bessel function in the inverse Fourier transform that needs to be performed just once for all observables and kinematics, to any desired accuracy.
↳ hep-phnucl-thJHEP(2018)·26 citations
10
Radiative resonance couplings in $γ π \to π π$
Martin Hoferichter🇺🇸 · Bastian Kubis🇩🇪 · Marvin Zanke🇩🇪
Studies of the reaction $γ π \to π π$ , in the context of the ongoing Primakoff program of the COMPASS experiment at CERN, give access to the radiative couplings of the $ρ (770)$ and $ρ_{3} (1690)$ resonances. We provide a vector-meson-dominance estimate of the respective radiative width of the $ρ_{3}$ , $Γ_{ρ_{3} \to π γ} = 48 (18)$ keV, as well as its impact on the $F$ -wave in $γ π \to π π$ . For the $ρ (770)$ , we establish the formalism necessary to extract its radiative coupling directly from the residue of the resonance pole by analytic continuation of the $γ π \to π π$ amplitude to the second Riemann sheet, without any reference to the vector-meson-dominance hypothesis.
↳ hep-phhep-exnucl-thPRD(2017)·81 citations
11
Roper resonances and quasi-normal modes of Skyrmions
C. Adam🇪🇸 · M. Haberichter🇩🇪 · T. Romanczukiewicz🇵🇱 · A. Wereszczynski🇵🇱
Radial vibrations of charge one hedgehog Skyrmions in the full Skyrme model are analysed. We investigate how the properties of the lowest resonance modes (quasi normal modes) - their frequencies and widths - depend on the form of the potential (value of the pion mass as well as the addition of further potentials) and on the inclusion of the sextic term. Then we consider the inverse problem, where certain values for the frequencies and widths are imposed, and the field theoretic Skyrme model potential giving rise to them is reconstructed. This latter method allows to reproduce the physical Roper resonances, as well as further physical properties of nucleons, with high precision.
↳ hep-thnucl-thJHEP(2018)·11 citations
12
New results from a number operator interpretation of the compositeness of bound and resonant states
J.A. Oller🇪🇸
A novel theoretical approach to the problem of the compositeness ( $X$ ) of a resonance or bound state is developed on the basis of the expectation values of the number operators of the free particles in the continuum. This formalism is specially suitable for effective field theories in which the bare elementary states are integrated out but that give rise to resonance and bound states when implemented in nonperturbative calculations. We demonstrate that $X = 1$ for finite-range energy-independent potentials, either regular or singular. A non-trivial example for an energy-dependent potential is discussed where it is shown that $X$ is independent of any type of cutoff regulator employed. The generalization of these techniques to relativistic states is developed. We also explain how to obtain a meaningful compositeness with respect to the open channels for resonances, even if it is complex in a first turn, by making use of suitable phase-factor transformations. Defining elementariness as $X = 0$ , we derive a new universal criterion for the elementariness of a bound state. Along the same lines, a necessary condition for a resonance to be qualified as elementary is given. The application of the formalism here developed might be of considerable practical interest.
↳ hep-phhep-lathep-thnucl-thAnnals Phys.(2018)·58 citations
13
Entropy and Multifractality in Relativistic Ion-Ion Collisions
Shaista Khan🇮🇳 · Shakeel Ahmad🇮🇳
Entropy production in multiparticle systems is investigated by analysing the experimental data on ion-ion collision at AGS and SPS energies and comparing the findings with those reported earlier for hadron-hadron, hadron-nucleus and nucleus-nucleus collisions. It is observed that the entropy produced in limited and full phase space, when normalised to maximum rapidity exhibits a kind of scaling which is nicely supported by Monte Carlo model \hij. Using the Rényi's order-q information entropy, multifractal characteristics of particle production are examined in terms of Generalized dimensions, D $_{q}$ . Nearly the same values of multifractal specific heat, $c$ observed in hadronic and ion-ion collisions over a wide range of incident energies suggest that the quantity $c$ may be used as a universal characteristic of multiparticle production in hadron-hadron, hadron-nucleus and nucleus-nucleus collisions.
↳ hep-phnucl-thAdv.High Energy Phys.(2018)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE