Nuclear Theory·nucl-th

Thursday·December 3, 2015

8 papers—2 primary·6 cross-listed

01
Complex suppression patterns distinguish between major energy loss effects in Quark-Gluon Plasma
Magdalena Djordjevic🇷🇸
Interactions of high momentum partons with Quark-Gluon Plasma created in relativistic heavy-ion collisions provide an excellent tomography tool for this new form of matter. Recent measurements for charged hadrons and unidentified jets at the LHC show an unexpected flattening of the suppression curves at high momentum, exhibited when either momentum or the collision centrality is changed. Furthermore, a limited data available for B probes indicate a qualitatively different pattern, as nearly the same flattening is exhibited for the curves corresponding to two opposite momentum ranges. We here show that the experimentally measured suppression curves are well reproduced by our theoretical predictions, and that the complex suppression patterns are due to an interplay of collisional, radiative energy loss and the dead-cone effect. Furthermore, for B mesons, we predict that the uniform flattening of the suppression indicated by the limited dataset is in fact valid across the entire span of the momentum ranges, which will be tested by the upcoming experiments. Overall, the study presented here, provides a rare opportunity for pQCD theory to qualitatively distinguish between the major energy loss mechanisms at the same (nonintuitive) dataset.
nucl-thnucl-exPLB(2016)·6 citations
02
Antimatter $_{Λ}^{4}$ H Hypernucleus Production and the $_{Λ}^{3}$ H/ $^{3}$ He Puzzle in Relativistic Heavy-Ion Collisions
Kai-Jia Sun🇨🇳 · Lie-Wen Chen🇨🇳
We show that the measured yield ratio $_{Λ}^{3}$ H/ $^{3}$ He ( $_{Λ}^{3} H$ / $^{3} He$ ) in Au+Au collisions at $s_{N N} = 200$ GeV and in Pb+Pb collisions at $s_{N N} = 2.76$ TeV can be understood within a covariant coalescence model if (anti-) $Λ$ particles freeze out earlier than (anti-)nucleons but their relative freezeout time is closer at $s_{N N} = 2.76$ TeV than at $s_{N N} = 200$ GeV. The earlier (anti-) $Λ$ freezeout can significantly enhance the yield of (anti)hypernucleus $_{Λ}^{4}$ H ( $_{Λ}^{4} H$ ), leading to that $_{Λ}^{4} H$ has a comparable abundance with $^{4} He$ and thus provides an easily measured antimatter candidate heavier than $^{4} He$ . The future measurement on $_{Λ}^{4}$ H ( $_{Λ}^{4} H$ ) would be very useful to understand the (anti-) $Λ$ freezeout dynamics and the production mechanism of (anti)hypernuclei in relativistic heavy-ion collisions.
nucl-thastro-ph.COhep-phnucl-exPRC(2016)·31 citations
03
Exploring central opacity and asymptotic scenarios in elastic hadron scattering
D. A. Fagundes🇧🇷 · M. J. Menon🇧🇷 · P. V. R. G. Silva🇧🇷
In the absence of a global description of the experimental data on elastic and soft diffractive scattering from the first principles of QCD, model-independent analyses may provide useful phenomenological insights for the development of the theory in the soft sector. With that in mind, we present an empirical study on the energy dependence of the ratio $X$ between the elastic and total cross sections; a quantity related to the evolution of the hadronic central opacity. The dataset comprises all the experimental information available on proton-proton and antiproton-proton scattering in the c.m. energy interval 5 GeV - 8 TeV. Generalizing previous works, we discuss four model-independent analytical parameterizations for $X$ , consisting of sigmoid functions composed with elementary functions of the energy and three distinct asymptotic scenarios: either the standard black disk limit or scenarios above or below that limit. Our two main conclusions are the following: (1) although consistent with the experimental data, the black disk does not represent an unique solution; (2) the data reductions favor a semi-transparent scenario, with asymptotic average value for the ratio $X ˉ$ = 0.30 $\pm$ 0.12. In this case, within the uncertainty, the asymptotic regime may already be reached around 1000 TeV. We present a comparative study of the two scenarios, including predictions for the inelastic channel (diffraction dissociation) and the ratio associated with the total cross-section and the elastic slope. Details on the selection of our empirical ansatz for $X$ and physical aspects related to a change of curvature in this quantity at 80 - 100 GeV, indicating the beginning of a saturation effect, are also presented and discussed.
↳ hep-phhep-exnucl-thNPA(2016)·26 citations
04
Parametric Instability of Classical Yang-Mills Fields in an Expanding Geometry
Shoichiro Tsutsui🇯🇵 · Teiji Kunihiro🇯🇵 · Akira Ohnishi🇯🇵
We investigate the instability of classical Yang-Mills field in an expanding geometry under a color magnetic background field within the linear regime. We consider homogeneous, boost-invariant and time-dependent color magnetic fields simulating the glasma configuration. We introduce the conformal coordinates which enable us to map an expanding problem approximately into a nonexpanding problem. We find that the fluctuations with finite longitudinal momenta can grow exponentially due to parametric instability. Fluctuations with finite transverse momenta can also show parametric instability, but their momenta are restricted to be small. The most unstable modes start to grow exponentially in the early stage of the dynamics and they may affect the thermalization in heavy-ion collisions.
↳ hep-phnucl-thPRD(2016)·5 citations
05
Light mesons in QCD and unquenching effects from the 3PI effective action
Richard Williams🇩🇪 · Christian S. Fischer🇩🇪 · Walter Heupel🇩🇪
We investigate the impact of unquenching effects on QCD Green's functions, in the form of quark-loop contributions to both the gluon propagator and three-gluon vertex, in a three-loop inspired truncation of the three-particle irreducible (3PI) effective action. The fully coupled system of Dyson-Schwinger equations for the quark-gluon-, ghost-gluon- and three-gluon vertices, together with the quark propagator, are solved self-consistently; our only input are the ghost and gluon propagators themselves that are constrained by calculations within Lattice QCD. We find that the two different unquenching effects have roughly equal, but opposite, impact on the quark-gluon vertex and quark propagator, with an overall negative impact on the latter. By taking further derivatives of the 3PI effective action, we construct the corresponding quark-antiquark kernel of the Bethe-Salpeter equation for mesons. The leading component is gluon exchange between two fully-dressed quark-gluon vertices, thus introducing for the first time an obvious scalar-scalar component to the binding. We gain access to time-like properties of bound-states by analytically continuing the coupled system of Dyson--Schwinger equations to the complex plane. We observe that the vector axial-vector splitting is in accord with experiment and that the lightest quark-antiquark scalar meson is above 1 GeV in mass.
↳ hep-phhep-latnucl-thPRD(2016)·225 citations
06
Neutron and proton electric dipole moments from $N_{f} = 2 + 1$ domain-wall fermion lattice QCD
Eigo Shintani🇯🇵 · Thomas Blum🇺🇸 · Taku Izubuchi🇺🇸 · Amarjit Soni🇺🇸
We present a lattice calculation of the neutron and proton electric dipole moments (EDM's) with $N_{f} = 2 + 1$ flavors of domain-wall fermions. The neutron and proton EDM form factors are extracted from three-point functions at the next-to-leading order in the $θ$ vacuum of QCD. In this computation, we use pion masses 0.33 and 0.42 GeV and 2.7 fm $^{3}$ lattices with Iwasaki gauge action and a 0.17 GeV pion and 4.6 fm $^{3}$ lattice with I-DSDR gauge action, all generated by the RBC and UKQCD collaborations. The all-mode-averaging technique enables an efficient and high statistics calculation. Chiral behavior of lattice EDM's is discussed in the context of baryon chiral perturbation theory. In addition, we also show numerical evidence on relationship of three- and two-point correlation function with local topological distribution.
↳ hep-lathep-phnucl-thPRD(2016)·51 citations
07
Observation of Large Enhancement of Charge Exchange Cross Sections with Neutron-Rich Carbon Isotopes
I. Tanihata · S. Terashima · R. Kanungo · F. Ameil · J. Atkinson · Y. Ayyad · D. Cortina-Gil · I. Dillmann · A. Estradé · A. Evdokimov · F. Farinon · H. Geissel and 21 other authors
Production cross sections of nitrogen isotopes from high-energy carbon isotopes on hydrogen and carbon targets have been measured for the first time for a wide range of isotopes. The fragment separator FRS at GSI was used to deliver C isotope beams. The cross sections of the production of N isotopes were determined by charge measurements of forward going fragments. The cross sections show a rapid increase with the number of neutrons in the projectile. Since the production of nitrogen is mostly due to charge exchange reactions below the proton separation energies, the present data suggests a concentration of Gamow-Teller and Fermi transition strength at low excitation energies for neutron-rich isotopes. It was also observed that the cross sections were enhanced much more strongly for neutron rich isotopes in the C-target data.
↳ nucl-exnucl-thPTEP(2016)·10 citations
08
Hyperon elastic electromagnetic form factors in the space-like momentum region
Helios Sanchis-Alepuz🇦🇹 · Christian S. Fischer🇩🇪
We present a calculation of the electric and magnetic form factors of ground-state octet and decuplet baryons including strange quarks. We work with a combination of Dyson-Schwinger equations for the quark propagator and covariant Bethe-Salpeter equations describing baryons as bound states of three (non-perturbative) quarks. Our form factors for the octet baryons are in good agreement with corresponding lattice data at finite $Q^{2}$ ; deviations in some isospin channels for the magnetic moments can be explained by missing meson cloud effects. At larger $Q^{2}$ our quark core calculation has predictive power for both, the octet and decuplet baryons.
↳ hep-phhep-exnucl-thEPJA(2016)·24 citations

Affiliations

first authorsco-authorsvia INSPIRE