Nuclear Theory·nucl-th

Wednesday·August 12, 2015

13 papers—8 primary·5 cross-listed

01
Strong diquark correlations inside the proton
Jorge Segovia🇪🇸
Quantum Chromodynamics is thought to be the relativistic quantum field theory that describes the strong interaction of the Standard Model. This interaction produces mesons but it is also able to generate quark-quark (diquark) correlations inside baryons. In this work, we employ a continuum approach to QCD based on Dyson-Schwinger equations to calculate the electromagnetic form factors of the proton and analyze in a deeper way the consequences of having strong diquark correlations. Comparison with the experimental data reveals that the presence of strong diquark correlations within the proton is sufficient to understand empirical extractions of the flavour-separated form factors. The explained reduction of the ratios $F_{1}^{d} / F_{1}^{u}$ and $F_{2}^{d} / F_{2}^{u}$ at high $Q^{2}$ in the quark-diquark picture are responsible of the precocious scaling of the $F_{2}^{p} / F_{1}^{p}$ observed experimentally.
nucl-thhep-exhep-lathep-ph+1EPJ Web Conf.(2016)·0 citations
02
Conserved Charge Susceptibilities in a Chemically Frozen Hadronic Gas
Jackson Ang'ong'a🇺🇸 · Todd Springer🇺🇸
In a hadronic gas with three conserved charges (electric charge, baryon number, and strangeness) we employ the hadron resonance gas model to compute both diagonal and off-diagonal susceptibilities. We model the effect of chemical freeze-out in two ways: one in which all particle numbers are conserved below the chemical freeze-out temperature and one which takes into account resonance decays. We then briefly discuss possible implications these results may have on two active areas of research, hydrodynamic fluctuations and the search for the QCD critical point.
nucl-thhep-ph0 citations
03
Sensitivity of flow harmonics to sub-nucleon scale fluctuations in heavy ion collisions
Jacquelyn Noronha-Hostler (Columbia U.)🇺🇸 · Jorge Noronha (Sao Paulo U. & Columbia U.)🇺🇸 · Miklos Gyulassy (Columbia U.)🇺🇸
In this paper a new procedure to smooth out the initial energy densities of hydrodynamics is employed to show that the initial spatial eccentricities $ε_{m, n}$ , which drive the final state flow harmonics $v_{n}$ , are remarkably robust with respect to variations of the underlying scale of initial energy density spatial gradients, $λ$ , in nucleus-nucleus collisions. For $s = 2.76$ TeV Pb+Pb collisions, the $ε_{m, n}$ 's (across centrality classes) change by less than $10%$ if the scale of fluctuations is varied from $0.1$ to $1$ fm. We show, using the 2+1 Lagrangian hydrodynamic code, v-USPhydro, that this robustness is transferred to the final $v_{n}$ 's computed within event by event viscous hydrodynamics. This indicates that the flow harmonics in nucleus-nucleus collisions are not yet particularly sensitive to the underlying microscopic sub-nucleon physics below the confinement scale. On the other hand, the eccentricities of top $1%$ high multiplicity $s = 5.02$ TeV p+Pb collisions are found to be very sensitive to sub-nucleonic scale fluctuations, which should be contrasted with the robustness found in peripheral Pb+Pb collisions with the same multiplicity.
nucl-thhep-phnucl-exPRC(2016)·84 citations
04
New sum rule for the nuclear magnetic polarizability
Mikhail Gorchtein🇩🇪
I extend the well-known photonuclear sum rule that relates the strength of the photoexcitation of the giant dipole resonance in a nucleus to the number of elementary scatterers-nucleons to the case of virtual photons. The new sum rule relates the size of the magnetic polarizability of a nucleus to the slope of the transverse virtual photoabsorption cross section integrated over the energy in the nuclear range. I check this sum rule for the deuteron where necessary data is available, discuss possible applications and connection with other sum rules postulated in the literature.
nucl-thhep-phnucl-exPRL(2015)·8 citations
05
Electron transport through nuclear pasta in magnetized neutron stars
D. G. Yakovlev
We present a simple model for electron transport in a possible layer of exotic nuclear clusters (in the so called nuclear pasta layer) between the crust and liquid core of a strongly magnetized neutron star. The electron transport there can be strongly anisotropic and gyrotropic. The anisotropy is produced by different electron effective collision frequencies along and across local symmetry axis in domains of exotic ordered nuclear clusters and by complicated effects of the magnetic field. We also calculate averaged kinetic coefficients in case local domains are freely oriented. Possible applications of the obtained results and open problems are outlined.
nucl-thastro-ph.HEMNRAS(2015)·33 citations
06
Test of the notch technique for determining the radial sensitivity of the optical model potential
Lei Yang · Cheng-Jian Lin · Hui-ming Jia · Xin-Xing Xu · Nan-Ru Ma · Li-Jie Sun · Feng Yang · Huan-Qiao Zhang · Zu-Hua Li · Dong-Xi Wang
Detailed investigations on the notch technique are performed on the ideal data generated by the optical model potential parameters extracted from the 16O+208Pb system at the laboratory energy of 129.5 MeV, to study the sensitivities of this technique on the model parameters as well as the experimental data. It is found that, for the perturbation parameters, a sufficient large reduced fraction and an appropriate small perturbation width are necessary to determine the accurate radial sensitivity; while for the potential parameters, almost no dependence was observed. For the experimental measurements, the number of data points has little influence for the heavy target system, and the relative inner information of the nuclear potential can be derived when the measurement extended to a lower cross section.
nucl-thnucl-exCPC(2016)·4 citations
07
Quasiparticle Theory of Transport Coefficients for Hadronic Matter at Finite Temperature and Baryon Density
M. Albright🇺🇸 · J. I. Kapusta🇺🇸
We develop a flexible quasiparticle theory of transport coefficients of hot hadronic matter at finite baryon density. We begin with a hadronic quasiparticle model which includes a scalar and a vector mean field. Quasiparticle energies and the mean fields depend on temperature and baryon chemical potential. Starting with the quasiparticle dispersion relation, we derive the Boltzmann equation and use the Chapman-Enskog expansion to derive formulas for the shear and bulk viscosities and thermal conductivity. We obtain both relaxation time approximation formulas and more general integral equations. Throughout the work, we explicitly enforce the Landau-Lifshitz conditions of fit and ensure the theory is thermodynamically self-consistent. The derived formulas should be useful for predicting the transport coefficients of the hadronic phase of matter produced in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) and at other accelerators.
nucl-thPRC(2016)·89 citations
08
Properties of Lithium-11 and Carbon-22 at leading order in halo effective field theory
Bijaya Acharya · Daniel Phillips
We study the $^{11} Li$ and $^{22} C$ nuclei at leading order (LO) in halo effective field theory (Halo EFT). Using the value of the $^{22} C$ rms matter radius deduced in Ref. [1] as an input in a LO calculation, we simultaneously constrained the values of the two-neutron (2 $n$ ) separation energy of $^{22} C$ and the virtual-state energy of the $^{20} C -$ neutron system (hereafter denoted $^{21}$ C). The 1 $- σ$ uncertainty of the input rms matter radius datum, along with the theory error estimated from the anticipated size of the higher-order terms in the Halo EFT expansion, gave an upper bound of about 100 keV for the 2 $n$ separation energy. We also study the electric dipole excitation of 2 $n$ halo nuclei to a continuum state of two neutrons and the core at LO in Halo EFT. We first compare our results with the $^{11} Li$ data from a Coulomb dissociation experiment and obtain good agreement within the theoretical uncertainty of a LO calculation. We then obtain the low-energy spectrum of $B (E 1)$ of this transition at several different values of the 2 $n$ separation energy of $^{22} C$ and the virtual-state energy of $^{21} C$ . Our predictions can be compared to the outcome of an ongoing experiment on the Coulomb dissociation of $^{22} C$ to obtain tighter constraints on the two- and three-body energies in the $^{22} C$ system.
nucl-thEPJ Web Conf.(2016)·7 citations
09
Employing Helicity Amplitudes for Resummation
Ian Moult🇺🇸 · Iain W. Stewart🇺🇸 · Frank J. Tackmann🇩🇪 · Wouter J. Waalewijn🇳🇱
Many state-of-the-art QCD calculations for multileg processes use helicity amplitudes as their fundamental ingredients. We construct a simple and easy-to-use helicity operator basis in soft-collinear effective theory (SCET), for which the hard Wilson coefficients from matching QCD onto SCET are directly given in terms of color-ordered helicity amplitudes. Using this basis allows one to seamlessly combine fixed-order helicity amplitudes at any order they are known with a resummation of higher-order logarithmic corrections. In particular, the virtual loop amplitudes can be employed in factorization theorems to make predictions for exclusive jet cross sections without the use of numerical subtraction schemes to handle real-virtual infrared cancellations. We also discuss matching onto SCET in renormalization schemes with helicities in $4$ - and $d$ -dimensions. To demonstrate that our helicity operator basis is easy to use, we provide an explicit construction of the operator basis, as well as results for the hard matching coefficients, for $pp \to H + 0, 1, 2$ jets, $pp \to W / Z / γ + 0, 1, 2$ jets, and $pp \to 2, 3$ jets. These operator bases are completely crossing symmetric, so the results can easily be applied to processes with $e^{+} e^{-}$ and $e^{-} p$ collisions.
↳ hep-phnucl-thPRD(2016)·50 citations
10
Di-photon "Ridge" in p+p and p+A collisions at RHIC and the LHC
Alex Kovner🇺🇸 · Amir H. Rezaeian🇨🇱
We obtain prompt di-photon cross-section in proton-nucleus collisions in Hamiltonian light-cone approach within a hybrid approximation, treating the projectile proton in the parton model and the target nucleus in the Color-Glass-Condensate approach. We study in details the di-photon correlations in quark-nucleus and proton-nucleus collisions at RHIC and the LHC. We show that the single fragmentation di-photon produces the away side correlations peak, and the double fragmentation component of prompt di-photon is responsible for the near-side peak, and the long-range in rapidity near-side azimuthal collimation, the so-called "ridge" structure. We study the transverse momentum, density and energy dependence of the di-photon ridge and show that it strongly depends on the kinematics and saturation dynamics. We show that while di-photon ridge exists at the LHC in quark-nucleus collisions, the effect disappears in proton-nucleus collisions at the LHC. At RHIC the ridge-type structure persists at low transverse momenta of di-photon even in proton-nucleus collisions. We argue that di-photon correlation measurments in p+A collisions can help to discriminate among models and understand the true origin of the observed di-hadron ridge in p+A collisions. We also show that in addition to the ridge structure, prompt di-photon correlation also exhibits some distinct novel features, including the emergence of away side double-peak structure at intermediate transverse momenta.
↳ hep-phhep-exnucl-exnucl-thPRD(2015)·22 citations
11
The Nonclassical Diffusion Approximation to the Nonclassical Linear Boltzmann Equation
Richard Vasques
We show that, by correctly selecting the probability distribution function $p (s)$ for a particle's distance-to-collision, the nonclassical diffusion equation can be represented exactly by the nonclassical linear Boltzmann equation for an infinite homogeneous medium. This choice of $p (s)$ preserves the $t r u e$ mean-squared free path of the system, which sheds new light on the results obtained in previous work.
↳ math-phmath.MPnucl-thAppl.Math.Lett.(2016)·3 citations
12
Effects of kinematic cuts on net-electric charge fluctuations
Frithjof Karsch🇩🇪 · Kenji Morita🇯🇵 · Krzysztof Redlich🇩🇪
The effects of kinematic cuts on electric charge fluctuations in a gas of charged particles are discussed. We consider a very transparent example of an ideal pion gas with quantum statistics, which can be viewed as a multi-component gas of Boltzmann particles with different charges and masses. Cumulants of net-electric charge fluctuations $χ_{n}^{Q}$ are calculated in a static and expanding medium with flow parameters adjusted to the experimental data. We show that the transverse momentum cut, $p_{t_{min}} \leq p_{t} \leq p_{t_{max}}$ , weakens the effects of Bose statistics, i.e. contributions of effectively multi-charged states to higher order moments. Consequently, cuts in $p_{t}$ modify the experimentally measured cumulants and their ratios. We discuss the influence of kinematic cuts on the ratio of mean and variance of electric charge fluctuations in a hadron resonance gas, in the light of recent data of the STAR and PHENIX Collaborations. We find that the different momentum cuts of $p_{t_{min}} = 0.2$ ~GeV (STAR) and $p_{t_{min}} = 0.3$ ~GeV (PHENIX) are responsible for more than 30\% of the difference between these two data sets. We argue that the $p_{t}$ cuts imposed on charged particles will influence the normalized kurtosis { $κ_{Q} σ_{Q}^{2} = χ_{4}^{Q} / χ_{2}^{Q}$ } of the electric charge fluctuations. In particular, the reduction of $κ_{Q} σ_{Q}^{2}$ with increasing $p_{t_{min}}$ will lead to differences between PHENIX and STAR data of $O (6%)$ which currently are buried under large statistical and systematic errors. We furthermore introduce the relation between momentum cut-off and finite volume effects, which is of relevance for the comparison between experimental data and lattice QCD calculations.
↳ hep-phhep-latnucl-exnucl-thPRC(2016)·49 citations
13
Exclusive decays $B \to ℓ^{-} ν ˉ$ and $B \to D^{(*)} ℓ^{-} ν ˉ$ in the covariant quark model
Mikhail A. Ivanov🇷🇺 · Jürgen G. Körner🇩🇪 · Chien-Thang Tran🇷🇺
We study the exclusive leptonic and semileptonic $B$ decays $B \to ℓ^{-} ν ˉ$ and $B \to D^{(*)} ℓ^{-} ν ˉ$ in the framework of the covariant quark model with built-in infrared confinement. We compute the relevant form factors in the full kinematical momentum transfer region. The calculated form factors are used to evaluate branching fractions and polarization observables of the above transitions. We compare our results with experimental data and results from other theoretical studies.
↳ hep-phhep-exnucl-thPRD(2015)·71 citations

Affiliations

first authorsco-authorsvia INSPIRE