Nuclear Theory·nucl-th

Wednesday·July 15, 2015

12 papers—4 primary·8 cross-listed

01
Microscopic derivation of the quadrupole collective Hamiltonian for shape coexistence/mixing dynamics
Kenichi Matsuyanagi · Masayuki Matsuo · Takashi Nakatsukasa · Kenichi Yoshida · Nobuo Hinohara · Koichi Sato
Assuming that the time-evolution of the self-consistent mean field is determined by five pairs of collective coordinate and collective momentum, we microscopically derive the collective Hamiltonian for low-frequency quadrupole modes of excitation. We show that the five-dimensional collective Schrödinger equation is capable of describing large-amplitude quadrupole shape dynamics seen as shape coexistence/mixing phenomena. We focus on basic ideas and recent advances of the approaches based on the time-dependent mean-field theory, but relations to other time-independent approaches are also briefly discussed.
nucl-thJ.Phys.G(2016)·18 citations
02
Relativistic Effects in 3-Nucleon Forces for Nuclear Matter and Finite Nuclei
A.H. Lippok · H. Müther
In order to simulate the relativistic effects of the Dirac Brueckner Hartree Fock approach for finite nuclei the part of the Urbana 3 nucleon (3N) force is considered, which represents the enhancement of the small components of the Dirac spinors for the nucleons in the nuclear medium. This 3N force is included in a Brueckner Hartree Fock calculation with rearrangement terms using a realistic model for the NN interaction. The strength of the 3N force is adjusted to reproduce the empirical saturation point of nuclear matter and then used in corresponding studies of the closed shell nuclei $^{16}$ O and $^{40}$ Ca. Special attention is paid to a consistent treatment of the spectrum of particle states in the NN propagator of the Bethe-Goldstone equation.
nucl-thPRC(2015)·6 citations
03
Dirac Coupled Channel Analyses of Proton Inelastic Scattering from $^{40}$ Ar Nucleus
Sugie Shim
0.8 GeV proton inelastic scatterings from $^{40}$ Ar nucleus are analyzed using an optical potential model in the Dirac coupled channel formalism. A rotational collective model is used to obtain the transition optical potentials for the low lying excited states of the rotational band. The optical potential parameters of a Woods-Saxon shape and the deformation parameters of the excited states are searched phenomenologically to reproduce the experimental differential cross-section data by using the sequential iteration method. The effect of a multistep process is investigated by including the channel coupling between two excited states in addition to the couplings between the ground state and the excited states. The calculated deformation parameters of the excited states are compared with those obtained by using the nonrelativistic calculations. The results of the Dirac coupled channel calculations are found to show pretty good agreements with the experimental data of the ground state and the low-lying excited states. The multistep excitation process via the channel coupling with the second $2^{+}$ state is found to be important for the excitation of the $4^{+}$ state at the inelastic scatterings from the deformed nucleus, $^{40}$ Ar.
nucl-thJ.Korean Phys.Soc.(2015)·1 citation
04
Collision Geometry and Flow in Uranium+Uranium Collisions
Andy Goldschmidt🇺🇸 · Zhi Qiu🇺🇸 · Chun Shen🇨🇦 · Ulrich Heinz🇺🇸
Using event-by-event viscous fluid dynamics to evolve fluctuating initial density profiles from the Monte-Carlo Glauber model for U+U collisions, we report a "knee"-like structure in the elliptic flow as a function of collision centrality, located around the 0.5% most central collisions as measured by the final charged multiplicity. This knee is due to the preferential selection of tip-on-tip collision geometries by a high-multiplicity trigger. Such a knee structure is not seen in the STAR data. This rules out the two-component MC-Glauber model for initial energy and entropy production. Hence an enrichment of tip-tip configurations by triggering solely on high-multiplicity in the U+U collisions does not work. On the other hand, by using the Zero Degree Calorimeters (ZDCs) coupled with event-shape engineering such a selection is possible. We identify the selection purity of body-body and tip-tip events in full-overlap U+U collisions. By additionally constraining the asymmetry of the ZDC signals we can further increase the probability of selecting tip-tip events in U+U collisions.
nucl-thnucl-exPRC(2015)·53 citations
05
Analytic Boosted Boson Discrimination
Andrew J. Larkoski🇺🇸 · Ian Moult🇺🇸 · Duff Neill🇺🇸
Observables which discriminate boosted topologies from massive QCD jets are of great importance for the success of the jet substructure program at the Large Hadron Collider. Such observables, while both widely and successfully used, have been studied almost exclusively with Monte Carlo simulations. In this paper we present the first all-orders factorization theorem for a two-prong discriminant based on a jet shape variable, $D_{2}$ , valid for both signal and background jets. Our factorization theorem simultaneously describes the production of both collinear and soft subjets, and we introduce a novel zero-bin procedure to correctly describe the transition region between these limits. By proving an all orders factorization theorem, we enable a systematically improvable description, and allow for precision comparisons between data, Monte Carlo, and first principles QCD calculations for jet substructure observables. Using our factorization theorem, we present numerical results for the discrimination of a boosted $Z$ boson from massive QCD background jets. We compare our results with Monte Carlo predictions which allows for a detailed understanding of the extent to which these generators accurately describe the formation of two-prong QCD jets, and informs their usage in substructure analyses. Our calculation also provides considerable insight into the discrimination power and calculability of jet substructure observables in general.
↳ hep-phhep-exnucl-thJHEP(2016)·179 citations
06
Universal range corrections to the Efimov trimer for a class of paths to the unitary limit
A. Kievsky · M. Gattobigio
Using potential models we analyze range corrections to the universal law dictated by the Efimov theory of three bosons. In the case of finite-range interactions we have observed that, at first order, it is necessary to supplement the theory with one finite-range parameter, $Γ_{n}^{3}$ , for each specific $n$ -level [Kievsky and Gattobigio, Phys. Rev. A {\bf 87}, 052719 (2013)]. The value of $Γ_{n}^{3}$ depends on the way the potentials is changed to tune the scattering length toward the unitary limit. In this work we analyze a particular path in which the length $r_{B} = a - a_{B}$ , measuring the difference between the two-body scattering length $a$ and the energy scattering length $a_{B}$ , results almost constant. Analyzing systems with very different scales, as atomic or nuclear systems, we observe that the finite-range parameter remains almost constant along the path with a numerical value of $Γ_{0}^{3} \approx 0.87$ for the ground state level. This observation suggests the possibility of constructing a single universal function that incorporate finite-range effects for this class of paths. The result is used to estimate the three-body parameter $κ_{*}$ in the case of real atomic systems brought to the unitary limit thought a broad Feshbach resonances. Furthermore, we show that the finite-range parameter can be put in relation with the two-body contact $C_{2}$ at the unitary limit.
↳ cond-mat.quant-gasnucl-thPRA(2015)·15 citations
07
Gyromagnetic g_s factors of the spin-1/2 particles in the (1/2+,1/2-,3/2-) triad of the four-vector spinor, \psi_\mu, irreducibility, and linearity
E. G. Delgado Acosta🇲🇽 · V. M. Banda Guzmán🇲🇽 · M. Kirchbach🇲🇽
We show that the spin (1/2-) particle from the (1/2,1)+(1,1/2) Lorentz irreducible sector of the four-vector spinor can not be described within a linear formalism but behaves as a genuinely quadratic fermion satisfying the generalized Feynman-Gell-Mann equation with a gyromagnetic factor of (-2/3). In contrast, spin (1/2 +) from the (1/2,0)+(0,1/2) sector is confirmed as a genuine linear Dirac fermion whose gyromagnetic factor takes the value of two units.We calculate Compton scatterings off each one of the two targets and obtain both times well behaved cross sections in the ultra relativistic limit and in accord with unitarity.
↳ hep-phnucl-thIJMPE(2015)·4 citations
08
Light $Ξ$ hypernuclei
H. Garcilazo🇲🇽 · A. Valcarce🇪🇸
Arguments in favor of a light $Ξ N N$ hypernucleus with $(I) J^{P} = (3/2) 1/ 2^{+}$ are presented, within the uncertainties of our knowledge of the baryon-baryon strangeness $- 2$ interactions. If bound, this $Ξ N N$ state, being decoupled from the lowest $N ΛΛ$ system, would be stable. It will also benefit from additional binding due to the electromagnetic interaction what makes it worthwhile to look for. We show how the equivalent state with $J = 3/2$ could never be bound in spite of the attractive interaction of the two-body subsystems. We illustrate our discussion with a full-fledged Faddeev calculation of the $Ξ N N$ system using simple potentials that mimic more elaborate interactions. We also make contact with different recent phenomenological interactions from the literature, like the ESC08 Nijmegen potential or quark-model based potentials.
↳ hep-phnucl-thPRC(2015)·15 citations
09
Constituent-quark model description of triply heavy-baryon nonperturbative lattice QCD data
J. Vijande🇪🇸 · A. Valcarce🇪🇸 · H. Garcilazo🇲🇽
This paper provides results for the spectra of triply charmed and bottom baryons based on a constituent quark model approach. We take advantage of the assumption that potential models are expected to describe triply heavy baryons to a similar degree of accuracy as the successful results obtained in the charmonium and bottomonium sectors. The high precision calculation of the ground state and positive and negative parity excited states recently reported by nonperturbative lattice QCD provides us with a unique opportunity to confront model predictions with data. This comparison may also help to build a bridge between two difficult to reconcile lattice QCD results, namely, the lattice SU(3) QCD static three-quark potential and the recent results of nonperturbative lattice QCD for the triply heavy-baryon spectra.
↳ hep-phhep-exhep-latnucl-thPRD(2015)·38 citations
10
Heavy-baryon quark model picture from lattice QCD
J. Vijande🇪🇸 · A. Valcarce🇪🇸 · H. Garcilazo🇲🇽
The ground state and excited spectra of baryons containing three identical heavy quarks, $b$ or $c$ , have been recently calculated in nonperturbative lattice QCD. The energy of positive and negative parity excitations has been determined with high precision. Lattice results constitute a unique opportunity to learn about the quark-confinement mechanism as well as elucidating our knowledge about the nature of the strong force. We analyze the nonperturbative lattice QCD results by means of heavy-quark static potentials derived using SU(3) lattice QCD. We make use of different numerical techniques for the three-body problem.
↳ hep-phhep-exhep-latnucl-thPRD(2014)·20 citations
11
Moments of $ϕ$ meson spectral functions in vacuum and nuclear matter
Philipp Gubler🇮🇹 · Wolfram Weise🇮🇹
Moments of the $ϕ$ meson spectral function in vacuum and in nuclear matter are analyzed, combining a model based on chiral SU(3) effective field theory (with kaonic degrees of freedom) and finite-energy QCD sum rules. For the vacuum we show that the spectral density is strongly constrained by a recent accurate measurement of the $e^{+} e^{-} \to K^{+} K^{-}$ cross section. In nuclear matter the $ϕ$ spectrum is modified by interactions of the decay kaons with the surrounding nuclear medium, leading to a significant broadening and an asymmetric deformation of the $ϕ$ meson peak. We demonstrate that both in vacuum and nuclear matter, the first two moments of the spectral function are compatible with finite-energy QCD sum rules. A brief discussion of the next-higher spectral moment involving strange four-quark condensates is also presented.
↳ hep-phhep-exnucl-exnucl-thPLB(2015)·51 citations
12
Bottomonia suppression in 2.76 TeV Pb-Pb collisions
Brandon Krouppa🇺🇸 · Radoslaw Ryblewski🇵🇱 · Michael Strickland🇺🇸
We compute the QGP suppression of Upsilon(1s), Upsilon(2s), Upsilon(3s), chi_b1, and chi_b2 states in sqrt(s_NN)=2.76 TeV Pb-Pb collisions. Using the suppression of each of these states, we estimate the inclusive R_AA for the Upsilon(1s) and Upsilon(2s) states as a function of N_part, y, and p_T including the effect of excited state feed down. We find that our model provides a reasonable description of preliminary CMS results for the N_part-, y-, and p_T-dependence of R_AA for both the Upsilon(1s) and Upsilon(2s). Comparing to our previous model predictions, we find a flatter rapidity dependence, thereby reducing some of the tension between our model and ALICE forward-rapidity results for Upsilon(1s) suppression.
↳ hep-phnucl-exnucl-thPRC(2015)·98 citations

Affiliations

first authorsco-authorsvia INSPIRE