Nuclear Theory·nucl-th

Tuesday·February 7, 2017

16 papers—9 primary·7 cross-listed

01
Fluctuations in ultra-relativistic heavy ion collisions
Aleksas Mazeliauskas🇺🇸
Fluctuations are one of the main probes of the physics of the new state of hot and dense nuclear matter called the Quark Gluon Plasma (QGP) which is created in the ultra-relativistic heavy ion collisions. In this dissertation we extend and improve upon the existing descriptions of heavy ion collisions in three different directions: we study the new signatures of initial state fluctuations, the propagation of perturbations in the early stages of the collision, and the effect of thermal fluctuations on the hydrodynamic expansion of the QGP. First, we use Principal Component Analysis (PCA) to study event-by-event fluctuations in the spectrum of harmonic flow, $v_{n} (p_{T})$ for $n = 0 - 5$ , in hydrodynamic simulations of Pb+Pb collisions at the CERN Large Hadron Collider ( $s_{N N} = 2.76 TeV$ ). The PCA procedure finds two dominant contributions to the two-particle correlation function: the leading component is identified with the standard event plane $v_{n} (p_{T})$ and the subleading component is responsible for factorization breaking and reflects the radial excitation in the initial state. Second, we use leading order effective kinetic theory (accurate at weak coupling) to simulate the pre-equilibrium evolution of transverse energy and flow perturbations. We construct the linear response Green functions, which map initial perturbations to the energy momentum tensor at a time when hydrodynamics becomes applicable. Finally, we develop a set of kinetic equations for thermal noise correlators which are equivalent to nonlinear hydrodynamics with noise. We use the hydro-kinetic equations to analyze thermal fluctuations for a Bjorken expansion and determine the coefficient of the first fractional power ( $\propto 1/ (τ T)^{3/2}$ ) of the nonlinear noise corrections to energy momentum tensor.
nucl-thhep-ph2 citations
02
Structure and reactions of 11Be: many-body basis for single-neutron halo
F. Barranco · G. Potel · R.A. Broglia · E. Vigezzi
The exotic nucleus 11Be has been extensively studied and much experimental information is available on the structure of this system. Treating, within the framework of empirically renormalised nuclear field theory in both configuration and 3D-space, the mixing of bound and continuum single-particle states through the coupling to collective particle-hole (p,h) and pairing vibrations of the 10Be core, as well as Pauli principle acting not only between the particles explicitly considered and those participating in the collective states, but also between fermions involved in two-phonon virtual states it is possible, for the first time, to simultaneously and quantitatively account for the energies of the 1/2+,1/2- low-lying states, the centroid and line shape of the 5/2+ resonance, the one-nucleon stripping and pickup absolute differential cross sections involving 11Be as either target or residual nucleus, and the dipole transitions connecting the 1/2+ and 1/2- parity inverted levels as well as the charge radius, thus providing a unified and exhaustive characterisation of the many-body effects which are at the basis of this paradigmatic one-neutron halo system.
nucl-thPRL(2017)·32 citations
03
Effect of bulk viscosity on interferometry correlations in ultrarelativistic heavy-ion collisions
Piotr Bozek🇵🇱
A temperature dependent bulk viscosity coefficient is used in 3+1D hydrodynamic simulations. I study the effect of the increase of bulk viscosity around the critical temperature on the system dynamics in central Pb+Pb collisions at $s_{N N} = 2760$ ~GeV. With increasing bulk viscosity the life-time of the system increases slightly. Also the shape of the freeze-out hypersurface changes, the outer layers of the fireball live longer. This effect causes a small reduction of the ratio of two interferometry radii $R_{o u t} / R_{s i d e}$ , improving the agreement with experimental data.
nucl-thPRC(2017)·13 citations
04
Hydrodynamic fluctuations near a critical endpoint and Hanbury Brown-Twiss interferometry
Christopher Plumberg🇺🇸 · Joseph I. Kapusta🇺🇸
The field of high energy nuclear collisions has witnessed a surge of interest in the role played by hydrodynamic fluctuations. Hydrodynamic fluctuations may have significant effects on matter created in heavy-ion accelerators whose trajectories in the plane of temperature versus chemical potential pass near a possible critical endpoint. We extend previous studies to explore the impact of these fluctuations on Hanbury Brown-Twiss interferometry of identical hadrons. With an appropriately defined correlation function we find that the fluctuations increase substantially when the trajectory passes near a critical endpoint, and also displays a damped oscillatory behavior in the rapidity distance $Δ y$ unlike that originating from initial-state fluctuations.
nucl-thPRC(2017)·16 citations
05
Spin asymmetry for proton-deuteron Drell-Yan process with tensor-polarized deuteron
S. Kumano🇯🇵 · Qin-Tao Song🇯🇵
Tensor structure of the deuteron can be studied by deep inelastic scattering and Drell-Yan process to understand it in terms of quark and gluon degrees of freedom. It probes interesting features in the deuteron including a D-wave contribution. In the charged-lepton DIS, twist-two structure functions $b_{1}$ and $b_{2}$ are expressed by tensor-polarized parton distribution functions (PDFs). We note that the HERMES experimental measurement of $b_{1}$ seems to be much different from a conventional theoretical prediction. This puzzling situation should be significantly improved in the near future by an approved experiment to measure $b_{1}$ at JLab. On the other hand, the tensor-polarized PDFs, especially antiquark distributions, could be measured by spin asymmetries in the Drell-Yan process with a tensor-polarized deuteron at Fermilab. In this work, we estimate tensor-polarization asymmetries for the Fermilab Drell-Yan experiment by using a parametrization for the tensor-polarized PDFs to explain the HERMES $b_{1}$ data. Obtained spin asymmetries are typically a few percent order and they could be measured by the Fermilab-E1039 experiment. Since the tensor-polarized antiquark distributions will play an important role to solve the puzzle, further theoretical and experimental efforts are needed toward the Drell-Yan experiment at Fermilab and other hadron facilities.
nucl-thhep-lathep-phnucl-ex7 citations
06
A combined mean-field and three-body model tested on the $^{26}$ O-nucleus
D. Hove · E. Garrido · P. Sarriguren · D.V. Fedorov · H.O.U. Fynbo · A.S. Jensen · N.T. Zinner
We combine few- and many-body degrees of freedom in a model applicable to both bound and continuum states and adaptable to different subfields of physics. We formulate a self-consistent three-body model for a core-nucleus surrounded by two valence nucleons. We treat the core in the mean-field approximation and use the same effective Skyrme interaction between both core and valence nucleons. We apply the model to $^{26}$ O where we reproduce the known experimental data as well as phenomenological models with more parameters. The decay of the ground state is found to proceed directly into the continuum without effect of the virtual sequential decay through the well reproduced $d_{3/2}$ -resonance of $^{25}$ O.
nucl-thPRC(2017)·8 citations
07
Nuclear suppression of $ϕ$ meson yields with large $p_{T}$ at the RHIC and the LHC
Wei Dai🇨🇳 · Xiao-Fang Chen🇨🇳 · Ben-Wei Zhang🇨🇳 · Han-Zhong Zhang🇨🇳 · Enke Wang🇨🇳
We calculate $ϕ$ meson transverse momentum spectra in p+p collisions as well as their nuclear suppressions in central A+A collisions both at the RHIC and the LHC in LO and NLO with the QCD-improved parton model. We have included the parton energy loss effect in hot/dense QCD medium with the effectively medium-modified $ϕ$ fragmentation functions in the higher-twist approach of jet quenching. The nuclear modification factors of $ϕ$ meson in central Au+Au collisions at the RHIC and central Pb+Pb collisions at the LHC are provided, and a nice agreement of our numerical results at NLO with the ALICE measurement is observed. Predictions of yield ratios of neutral mesons such as $ϕ / π^{0}$ , $ϕ / η$ and $ϕ / ρ^{0}$ at large $p_{T}$ in relativistic heavy-ion collisions are also presented for the first time.
nucl-thhep-exEPJC(2017)·13 citations
08
Relative flow fluctuations as a probe of initial state fluctuations
Giuliano Giacalone🇫🇷 · Jacquelyn Noronha-Hostler🇺🇸 · Jean-Yves Ollitrault🇫🇷
Elliptic flow, $v_{2}$ , and triangular flow, $v_{3}$ , are to a good approximation linearly proportional to the corresponding spatial anisotropies of the initial density profile, $ε_{2}$ and $ε_{3}$ . Using event-by-event hydrodynamic simulations, we point out when deviations from this linear scaling are to be expected. When these deviations are negligible, relative $v_{n}$ fluctuations are equal to relative $ε_{n}$ fluctuations, and one can directly probe models of initial conditions using ratios of cumulants, for instance $v_{n} {4} / v_{n} {2}$ . We argue that existing models of initial conditions tend to overestimate flow fluctuations in central Pb+Pb collisions, and to underestimate them in peripheral collisions. We make predictions for $v_{3} {6}$ in noncentral Pb+Pb collisions, and for $v_{3} {4}$ and $v_{3} {6}$ in high-multiplicity p+Pb collisions.
nucl-thhep-phnucl-exPRC(2017)·101 citations
09
Higher-order anisotropies in the Blast-Wave Model - disentangling flow and density field anisotropies
Jakub Cimerman🇨🇿 · Boris Tomasik🇨🇿 · Mate Csanad🇭🇺 · Sandor Lokos🇭🇺
We formulate a generalisation of the blast-wave model which is suitable for the description of higher order azimuthal anisotropies of the hadron production. The model includes anisotropy in the density profile as well as an anisotropy in the transverse expansion velocity field. We then study how these two kinds of anisotropies influence the single-particle distributions and the correlation radii of two-particle correlation functions. Particularly we focus on the third-order anisotropy and consideration is given to the averaging over different orientation of the event plane.
nucl-thhep-exhep-phEPJA(2017)·23 citations
10
Angular Momentum Conservation Law in Light-Front Quantum Field Theory
Kelly Yu-Ju Chiu🇺🇸 · Stanley J. Brodsky🇺🇸
We prove the Lorentz invariance of the angular momentum conservation law and the helicity sum rule for relativistic composite systems in the light-front formulation. We explicitly show that $j^{3}$ , the $z$ -component of the angular momentum remains unchanged under Lorentz transformations generated by the light-front kinematical boost operators. The invariance of $j^{3}$ under Lorentz transformations is a feature unique to the front form. Applying the Lorentz invariance of the angular quantum number in the front form, we obtain a selection rule for the orbital angular momentum which can be used to eliminate certain interaction vertices in QED and QCD. We also generalize the selection rule to any renormalizable theory and show that there exists an upper bound on the change of orbital angular momentum in scattering processes at any fixed order in perturbation theory.
↳ hep-thnucl-thPRD(2017)·27 citations
11
Review of experimental and theoretical status of the proton radius puzzle
Richard J. Hill🇨🇦
The discrepancy between the measured Lamb shift in muonic hydrogen and expectations from electron-proton scattering and regular hydrogen spectroscopy has become known as the proton radius puzzle, whose most "mundane" resolution requires a $> 5 σ$ shift in the value of the fundamental Rydberg constant. I briefly review the status of spectroscopic and scattering measurements, recent theoretical developments, and implications for fundamental physics.
↳ hep-phnucl-thphysics.atom-phEPJ Web Conf.(2017)·43 citations
12
World-line construction of a covariant chiral kinetic theory
Niklas Mueller🇩🇪 · Raju Venugopalan🇺🇸
We discuss a novel world-line framework for computations of the Chiral Magnetic Effect (CME) in ultrarelativistic heavy-ion collisions. Starting from the fermion determinant in the QCD effective action, we show explicitly how its real part can be expressed as a supersymmetric world-line action of spinning, colored, Grassmanian particles in background fields. Restricting ourselves for simplicity to spinning particles, we demonstrate how their constrained Hamiltonian dynamics arises for both massless and massive particles. In a semi-classical limit, this gives rise to the covariant generalization of the Bargmann-Michel-Telegdi equation; the derivation of the corresponding Wong equations for colored particles is straightforward. In a previous letter we outlined how Berry's phase arises in a non-relativistic adiabatic limit for massive particles. We extend the discussion here to systems with a finite chemical potential. We discuss a path integral formulation of the relative phase in the fermion determinant that places it on the same footing as the real part. We construct the corresponding anomalous world-line axial vector current and show in detail how the chiral anomaly appears. Our work provides a systematic framework for a relativistic kinetic theory of chiral fermions in the fluctuating topological backgrounds that generate the CME in a deconfined quark-gluon plasma. We outline some further applications of this framework in many-body systems.
↳ hep-phhep-thnucl-thPRD(2017)·89 citations
13
Cooling of neutron stars with stiff stellar matter
H. Grigorian · D. N. Voskresensky · D. Blaschke
Recent evidence for high masses ( $\sim 2 M_{⊙}$ ) pulsars PSR J1614-2230 and PSR J0348-0432 requires neutron star matter to have a stiff equation of state (EoS). The thermal evolution of compact stars (CS) with stiff hadronic EoS necessitates the application of the "nuclear medium cooling" scenario with a selection of appropriate proton gap profiles together with in-medium effects (like pion softening) on cooling mechanisms in order to achieve a satisfactory explanation of all existing observational data for the temperature-age relation of CS. Here we focus on two examples from \cite{Grigorian:2016leu} for a stiff hadronic EoS without (DD2 EoS) and with (DD2vex) excluded volume correction.
↳ astro-ph.HEnucl-thActa Phys.Polon.Supp.(2017)·1 citation
14
Characterizing the mechanism(s) of heavy element synthesis
W. Loveland
A review of the current state of our understanding of complete fusion reaction mechanisms is presented, from the perspective of an experimentalist. For complete fusion reactions, the overall uncertainties in predicting heavy element synthesis cross sections are examined in terms of the uncertainties associated with the calculations of capture cross sections, fusion probabilities and survival probabilities.
↳ nucl-exnucl-thEPJA Web of Conferences 131, 04003 (2016)·0 citations
15
Concurrent application of ANC and THM to assess the $^{13} C (α, n)^{16} O$ absolute cross section at astrophysical energies and possible consequences for neutron production in low-mass AGB stars
Oscar Trippella · Marco La Cognata
The $^{13} C (α, n)^{16} O$ reaction is considered to be the main neutron source responsible for the production of heavy nuclides (from $Sr$ to $Bi$ ) through slow $n$ -capture nucleosynthesis ( $s$ -process) at low temperatures during the asymptotic giant branch (AGB) phase of low mass stars ( $≲ 3 - 4 M_{⊙}$ , or LMSs). In recent years, several direct and indirect measurements have been carried out to determine the cross section at the energies of astrophysical interest (around $190 \pm 40 keV$ ). However, they yield inconsistent results causing a highly uncertain reaction rate and affecting the neutron release in LMSs. In this work we have combined two indirect approaches, the asymptotic normalization coefficient (or ANC) and the Trojan Horse Method (THM), to unambiguously determine the absolute value of the $^{13} C (α, n)^{16} O$ astrophysical factor. Therefore, we have determined a very accurate reaction rate to be introduced into astrophysical models of $s$ -process nucleosynthesis in LMSs. Calculations using such recommended rate have shown limited variations in the production of those neutron-rich nuclei (with $86 \leq A \leq 209$ ) receiving contribution only by slow neutron captures.
↳ astro-ph.SRnucl-exnucl-thApJ(2017)·34 citations
16
Baryon interactions from lattice QCD with physical masses -- Overview and $S = 0, - 4$ sectors --
Takumi Doi🇯🇵 · Sinya Aoki🇯🇵 · Shinya Gongyo🇯🇵 · Tetsuo Hatsuda🇯🇵 · Yoichi Ikeda🇯🇵 · Takashi Inoue🇯🇵 · Takumi Iritani🇯🇵 · Noriyoshi Ishii🇯🇵 · Takaya Miyamoto🇯🇵 · Keiko Murano🇯🇵 · Hidekatsu Nemura🇯🇵 · Kenji Sasaki🇯🇵
Nuclear forces and hyperon forces are studied by lattice QCD. Simulations are performed with (almost) physical quark masses, $m_{π} ≃ 146$ MeV and $m_{K} ≃ 525$ MeV, where $N_{f} = 2 + 1$ nonperturbatively $O (a)$ -improved Wilson quark action with stout smearing and Iwasaki gauge action are employed on the lattice of $(96 a)^{4} ≃ (8.1 \mbox f m)^{4}$ with $a^{- 1} ≃ 2.3$ GeV. In this report, we give the overview of the theoretical framework and present the numerical results for two-nucleon forces ( $S = 0$ ) and two- $Ξ$ forces ( $S = - 4$ ). Central forces are studied in $^{1} S_{0}$ channel, and central and tensor forces are obtained in $^{3} S_{1}$ - $^{3} D_{1}$ coupled channel analysis.
↳ hep-lathep-phnucl-thPoS(2017)·29 citations

Affiliations

first authorsco-authorsvia INSPIRE