Nuclear Theory·nucl-th

Monday·February 27, 2017

8 papers—4 primary·4 cross-listed

01
[Submitted on 24 Feb 2017]
The Glauber model and heavy ion reaction and elastic scattering cross sections
Ajay Mehndiratta · Prashant Shukla
We revisit the Glauber model to study the heavy ion reaction cross sections and elastic scattering angular distributions at low and intermediate energies. The Glauber model takes nucleon-nucleon cross sections and nuclear densities as inputs and has no free parameter and thus can predict the cross sections for unknown systems. The Glauber model works at low energies down to Coulomb barrier with very simple modifications. We present new parametrization of measured total cross sections as well as ratio of real to imaginary parts of the scattering amplitudes for pp and np collisions as a function of nucleon kinetic energy. The nuclear (charge) densities obtained by electron scattering form factors measured in large momentum transfer range are used in the calculations. The heavy ion reaction cross sections are calculated for light and heavy systems and are compared with available data measured over large energy range. The model gives excellent description of the data. The elastic scattering angular distributions are calculated for various systems at different energies. The model gives good description of the data at small momentum transfer but the calculations deviate from the data at large momentum transfer.
Comments:
25 pages, 13 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1702.07459 [pdf]
NPA(2017)·19 citations
02
[Submitted on 24 Feb 2017]
Weak Magnetism Correction to Allowed Beta-decay for Reactor Antineutrino Spectra
X.B. Wang · A.C. Hayes
The weak magnetism correction and its uncertainty to nuclear beta-decay play a major role in determining the significance of the reactor neutrino anomaly. Here we examine the common approximation used for one-body weak magnetism in the calculation of fission antineutrino spectra, wherein matrix elements of the orbital angular momentum operator contribution to the magnetic dipole current are assumed to be proportional to those of the spin operator. Although we find this approximation invalid for a large set of nuclear structure situations, we conclude that it is valid for the relevant allowed beta-decays between fission fragments. In particular, the uncertainty in the fission antineutrino due to the uncertainty in the one-body weak magnetism correction is found to be less than 1%. Thus, the dominant uncertainty from weak magnetism for reactor neutrino fluxes lies in the uncertainty in the two-body meson-exchange magnetic dipole current.
Comments:
10 page, 9 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1702.07520 [pdf]
PRC(2017)·19 citations
03
[Submitted on 24 Feb 2017]
New approach to initializing hydrodynamic fields and mini-jet propagation in quark-gluon fluids
Michito Okai🇯🇵 · Koji Kawaguchi🇯🇵 · Yasuki Tachibana🇨🇳 · Tetsufumi Hirano🇯🇵
We propose a new approach to initialize the hydrodynamic fields such as energy density distributions and four flow velocity fields in hydrodynamic modeling of high-energy nuclear collisions at the collider energies. Instead of matching the energy-momentum tensor or putting the initial conditions of quark-gluon fluids at a fixed initial time, we utilize a framework of relativistic hydrodynamic equations with source terms to describe the initial stage. Putting the energy and momentum loss rate of the initial partons into the source terms, we obtain hydrodynamic initial conditions dynamically. The resultant initial profile of the quark-gluon fluid looks highly bumpy as seen in the conventional event-by-event initial conditions. In addition, initial random flow velocity fields also are generated as a consequence of momentum deposition from the initial partons. We regard the partons that survive after the dynamical initialization process as the mini-jets and find sizable effects of both mini-jet propagation in the quark-gluon fluids and initial random transverse flow on the final momentum spectra and anisotropic flow observables. We perform event-by-event $(3 + 1)$ -dimensional ideal hydrodynamic simulations with this new framework that enables us to describe the hydrodynamic bulk collectivity, parton energy loss, and interplay among them in a unified manner.
Comments:
9 pages, 8 figures; v2: published version, title changed
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1702.07541 [pdf]
PRC(2017)·60 citations
04
[Submitted on 24 Feb 2017]
Probing QCD critical fluctuations from light nuclei production in relativistic heavy-ion collisions
Kai-Jia Sun🇨🇳 · Lie-Wen Chen🇨🇳 · Che Ming Ko🇺🇸 · Zhangbu Xu🇨🇳
Based on the coalescence model for light nuclei production, we show that the yield ratio $O_{p-d-t} = N_{^{3} H} N_{p} / N_{d}^{2}$ of $p$ , d, and $^{3}$ H in heavy-ion collisions is sensitive to the neutron relative density fluctuation $Δ n = ⟨(δ n)^{2} ⟩ / ⟨ n ⟩^{2}$ at kinetic freeze-out. From recent experimental data in central Pb+Pb collisions at $s_{N N} = 6.3$ ~GeV, $7.6$ ~GeV, $8.8$ ~GeV, $12.3$ ~GeV and $17.3$ ~GeV measured by the NA49 Collaboration at the CERN Super Proton Synchrotron (SPS), we find a possible non-monotonic behavior of $Δ n$ as a function of the collision energy with a peak at $s_{N N} = 8.8$ ~GeV, indicating that the density fluctuations become the largest in collisions at this energy. With the known chemical freeze-out conditions determined from the statistical model fit to experimental data, we obtain a chemical freeze-out temperature of $\sim 144$ MeV and baryon chemical potential of $\sim 385$ MeV at this collision energy, which are close to the critical endpoint in the QCD phase diagram predicted by various theoretical studies. Our results thus suggest the potential usefulness of the yield ratio of light nuclei in relativistic heavy-ion collisions as a direct probe of the large density fluctuations associated with the QCD critical phenomena.
Comments:
6 pages, 1 figure, 2 tables. Correlations between neutron and proton density fluctuations considered and presentation improved. Accepted version to appear in PLB
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1702.07620 [pdf]
PLB(2017)·136 citations
05
[Submitted on 21 Feb 2017] (cross-list from hep-ph)
A toy model of elastic scattering of high energy protons
I.M. Dremin🇷🇺
The ratio of elastic to total proton cross sections is related to the darkness of the spatial profile of inelastic interactions by a single parameter in the framework of a simple analytical model. Their critical values at LHC energies are discussed. Two possible variants of their asymptotical behavior are described.
Comments:
11 p
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1702.06304 [pdf]
5 citations
06
[Submitted on 23 Feb 2017] (cross-list from hep-ph)
Dispersion relation for hadronic light-by-light scattering: two-pion contributions
Gilberto Colangelo🇨🇭 · Martin Hoferichter🇺🇸 · Massimiliano Procura🇨🇭 · Peter Stoffer🇩🇪
In this third paper of a series dedicated to a dispersive treatment of the hadronic light-by-light (HLbL) tensor, we derive a partial-wave formulation for two-pion intermediate states in the HLbL contribution to the anomalous magnetic moment of the muon $(g - 2)_{μ}$ , including a detailed discussion of the unitarity relation for arbitrary partial waves. We show that obtaining a final expression free from unphysical helicity partial waves is a subtle issue, which we thoroughly clarify. As a by-product, we obtain a set of sum rules that could be used to constrain future calculations of $γ^{*} γ^{*} \to π π$ . We validate the formalism extensively using the pion-box contribution, defined by two-pion intermediate states with a pion-pole left-hand cut, and demonstrate how the full known result is reproduced when resumming the partial waves. Using dispersive fits to high-statistics data for the pion vector form factor, we provide an evaluation of the full pion box, $a_{μ}^{π -box} = - 15.9 (2) \times 1 0^{- 11}$ . As an application of the partial-wave formalism, we present a first calculation of $π π$ -rescattering effects in HLbL scattering, with $γ^{*} γ^{*} \to π π$ helicity partial waves constructed dispersively using $π π$ phase shifts derived from the inverse-amplitude method. In this way, the isospin- $0$ part of our calculation can be interpreted as the contribution of the $f_{0} (500)$ to HLbL scattering in $(g - 2)_{μ}$ . We argue that the contribution due to charged-pion rescattering implements corrections related to the corresponding pion polarizability and show that these are moderate. Our final result for the sum of pion-box contribution and its $S$ -wave rescattering corrections reads $a_{μ}^{π -box} + a_{μ, J = 0}^{π π, π -pole LHC} = - 24 (1) \times 1 0^{- 11}$ .
Comments:
70 pages, 14 figures, Mathematica notebook with full expressions for the basis change included as supplementary material. Version accepted for publication in JHEP
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1702.07347 [pdf]
JHEP(2017)·555 citations
07
[Submitted on 24 Feb 2017] (cross-list from cond-mat.quant-gas)
Semisuper Efimov effect of two-dimensional bosons at a three-body resonance
Yusuke Nishida
Wave-particle duality in quantum mechanics allows for a halo bound state whose spatial extension far exceeds a range of the interaction potential. What is even more striking is that such quantum halos can be arbitrarily large on special occasions. The two examples known so far are the Efimov effect and the super Efimov effect, which predict that spatial extensions of higher excited states grow exponentially and double exponentially, respectively. Here, we establish yet another new class of arbitrarily large quantum halos formed by spinless bosons with short-range interactions in two dimensions. When the two-body interaction is absent but the three-body interaction is resonant, four bosons exhibit an infinite tower of bound states whose spatial extensions scale as $R_{n} \sim e^{(π n)^{2} /27}$ for a large $n$ . The emergent scaling law is universal and is termed a semisuper Efimov effect, which together with the Efimov and super Efimov effects constitutes a trio of few-body universality classes allowing for arbitrarily large quantum halos.
Comments:
5 pages; published version
Subjects:
Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th)
arXiv:
1702.07532 [pdf]
PRL(2017)·20 citations
08
[Submitted on 24 Feb 2017] (cross-list from hep-ph)
Tensor-polarized structure function $b_{1}$ by convolution picture for deuteron
W. Cosyn🇧🇪 · Yu-Bing Dong🇨🇳 · S. Kumano🇯🇵 · M. Sargsian🇺🇸
There are polarized structure functions $b_{1 - 4}$ for the spin-1 deuteron. We calculated the leading-twist tensor structure function $b_{1}$ by using convolution description for the deuteron. We found large differences between our theoretical functions and HERMES experimental data on $b_{1}$ . Although higher-twist effects should be considered in obtaining experimental $b_{1}$ , it suggests a possible existence of new hadron physics mechanism for spin-1 hadrons. Furthermore, we found that there are significant distributions at large Bjorken $x$ . In future, an experimental measurement is planned at JLab for $b_{1}$ and there is a possibility of a proton-deuteron Drell-Yan experiment at Fermilab with the tensor-polarized deuteron, so that further theoretical studies are needed for clarifying the physics origin of tensor structure in terms of quark and gluon degrees of freedom.
Comments:
4 pages, 2 eps figures, 22nd International Spin Symposium (Spin-2016), University of Illinois, Champaign, Illinois, USA, September 25-30, 2016
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1702.07594 [pdf]
1 citation

Affiliations

first authorsco-authorsvia INSPIRE