Nuclear Theory·nucl-th

Friday·December 4, 2015

10 papers—4 primary·6 cross-listed

05
Calculating Soft Radiation at One Loop
Tomas Kasemets🇳🇱 · Wouter J. Waalewijn🇳🇱 · Lisa Zeune🇳🇱
We present an efficient way to calculate the effect of soft QCD radiation at one loop, which is needed for predictions at next-to-next-to-leading logarithmic accuracy. We use rapidity coordinates and isolate the divergences in the integrand. By performing manipulations with cumulative variables, we avoid complications from plus distributions. We address rapidity divergences, divergences with an azimuthal dependence, complicated jet boundaries and multi-differential measurements. The process and measurements can be easily adjusted, as we demonstrate by reproducing many existing soft functions. The results for a general LHC process with multiple Wilson lines are obtained by treating Wilson lines that are not back-to-back using a boost. We also obtain, for the first time, the N-jettiness soft function for generic jet angularities, and the collinear-soft function for the measurement of two angularities.
↳ hep-phnucl-thJHEP(2016)·20 citations
06
Model-independent determination of the shear viscosity of a trapped unitary Fermi gas: Application to high temperature data
Marcus Bluhm (North Carolina State University) · Thomas Schaefer (North Carolina State University)
Determinations of the shear viscosity of trapped ultracold gases suffer from systematic, uncontrolled uncertainties related to the treatment of the dilute part of the gas cloud. In this work we present an analysis of expansion experiments based on a new method, anisotropic fluid dynamics, that interpolates between Navier-Stokes fluid dynamics at the center of the cloud and ballistic behavior in the dilute corona. We validate the method using a comparison between anisotropic fluid dynamics and numerical solutions of the Boltzmann equation. We then apply anisotropic fluid dynamics to the expansion data reported by Cao et al. In the high temperature limit we find $η = 0.282 (m T)^{3/2}$ , which agrees within about 5\% with the theoretical prediction $η = 0.269 (m T)^{3/2}$ .
↳ cond-mat.quant-gasnucl-thPRL(2016)·38 citations
07
Real and virtual $N N ˉ$ pair production near the threshold
V. F. Dmitriev🇷🇺 · A. I. Milstein🇷🇺 · S. G. Salnikov🇷🇺
Nucleon-antinucleon optical potential, which explains the experimental data for the processes $e^{+} e^{-} \to p p ˉ$ and $e^{+} e^{-} \to \mbox p i o n s$ near the threshold of $p p ˉ$ pair production, is suggested. To obtain this potential we have used the available experimental data for $p p ˉ$ scattering, $p p ˉ$ pair production in $e^{+} e^{-}$ annihilation, and the ratio of electromagnetic form factors of a proton in the timelike region. It turns out that final-state interaction via the optical potential allows one to reproduce the available experimental data with good accuracy. Our results for the cross sections of $e^{+} e^{-} \to 6 π$ process near the threshold of $p p ˉ$ pair production are in agreement with the recent experiments.
↳ hep-phnucl-thPRD(2016)·27 citations
08
Pion Production via Proton Synchrotron Radiation in Strong Magnetic Fields in Relativistic Field Theory: Scaling Relations and Angular Distributions
Tomoyuki Maruyama🇯🇵 · Myung-Ki Cheoun🇯🇵 · Toshitaka Kajino🇯🇵 · Grant J. Mathews🇺🇸
We study pion production by proton synchrotron radiation in the presence of a strong magnetic field when the Landau numbers of the initial and final protons are $n_{i, f} \sim 1 0^{4} - 1 0^{5}$ . We find in our relativistic field theory calculations that the pion decay width depends only on the field strength parameter which previously was only conjectured based upon semi-classical arguments. Moreover, we also find new results that the decay width satisfies a robust scaling relation, and that the polar angular distribution of emitted pion momenta is very narrow and can be easily obtained. This scaling implies that one can infer the decay width in more realistic magnetic fields of $1 0^{15}$ G, where $n_{i, f} \sim 1 0^{12} - 1 0^{13}$ , from the results for $n_{i, f} \sim 1 0^{4} - 1 0^{5}$ . The resultant pion intensity and angular distributions for realistic magnetic field strengths are presented and their physical implications discussed.
↳ astro-ph.HEhep-phnucl-thPLB(2016)·8 citations
09
Pion-induced production of the $Z_{c} (3900)$ off a nuclear target
Yin Huang🇨🇳 · Jun He🇨🇳 · Xiang Liu🇨🇳 · Hong Fei Zhang🇨🇳 · Ju Jun Xie🇨🇳 · Xu Rong Chen🇨🇳
We investigate the possibility to study the charmoniumlike state $Z_{c} (3900)$ through the pion-induced production off a nuclear target. By using a high-energy pion beam, the $Z_{c} (3900)$ can be produced off a proton or nucleus though the Primakoff effect. The production amplitude is calculated in an effective Lagrangian approach combined with the vector dominance model. The total cross sections of the $p (π^{-}, Z_{c}^{-} (3900))$ and $p (π^{-}, Z_{c}^{-} (3900) \to J / ψ π^{-})$ reactions are calculated, and their order of magnitude is about 0.1 and 0.01nb, respectively, with an assumption of branch ratio 10\% for the $Z_{c} (3900)$ decay in $J / ψ π$ channel. If the proton target is replaced by a nuclear target, the production of the $Z_{c} (3900)$ enhances obviously. The predicted total cross sections for the $A (π^{-}, Z_{c}^{-} (3900))$ and $A (π^{-}, Z_{c}^{-} (3900) \to J / ψ π^{-})$ reactions with $A =^{12}$ C or $^{208}$ Pb are on the order of magnitude of 100 and 10 nb, respectively, which is about one thousand times larger than the cross sections off a proton target. Based on these the results, we suggest the experimental study of the $Z_{c} (3900)$ by using high-energy pion beams with a nuclear target at facilities such as COMPASS and J-PARC.
↳ hep-phhep-exnucl-exnucl-thPRD(2016)·8 citations
10
Axial form factors of the octet baryons in a covariant quark model
G. Ramalho🇧🇷 · K. Tsushima🇧🇷
We study the weak interaction axial form factors of the octet baryons, within the covariant spectator quark model, focusing on the dependence of four-momentum transfer squared, Q^2. In our model the axial form factors G_A(Q^2) (axial-vector form factor) and G_P(Q^2) (induced pseudoscalar form factor), are calculated based on the constituent quark axial form factors and the octet baryon wave functions. The quark axial current is parametrized by the two constituent quark form factors, the axial-vector form factor g_A^q(Q^2), and the induced pseudoscalar form factor g_P^q(Q^2). The baryon wave functions are composed of a dominant S-state and a P-state mixture for the relative angular momentum of the quarks. First, we study in detail the nucleon case. We assume that the quark axial-vector form factor g_A^q(Q^2) has the same function form as that of the quark electromagnetic isovector form factor. The remaining parameters of the model, the P-state mixture and the Q^2-dependence of g_P^q(Q^2), are determined by a fit to the nucleon axial form factor data obtained by lattice QCD simulations with large pion masses. In this lattice QCD regime the meson cloud effects are small, and the physics associated with the valence quarks can be better calibrated. Once the valence quark model is calibrated, we extend the model to the physical regime, and use the low Q^2 experimental data to estimate the meson cloud contributions for G_A(Q^2) and G_P(Q^2). Using the calibrated quark axial form factors, and the generalization of the nucleon wave function for the other octet baryon members, we make predictions for all the possible weak interaction axial form factors G_A(Q^2) and G_P(Q^2) of the octet baryons. The results are compared with the corresponding experimental data for G_A(0), and with the estimates of baryon-meson models based on SU(6) symmetry.
↳ hep-phhep-exhep-latnucl-ex+1PRD(2016)·32 citations

Affiliations

first authorsco-authorsvia INSPIRE

Calculating Soft Radiation at One Loop

Model-independent determination of the shear viscosity of a trapped unitary Fermi gas: Application to high temperature data

Real and virtual NNˉ pair production near the threshold

Pion Production via Proton Synchrotron Radiation in Strong Magnetic Fields in Relativistic Field Theory: Scaling Relations and Angular Distributions

Pion-induced production of the Zc​(3900) off a nuclear target

Axial form factors of the octet baryons in a covariant quark model

Affiliations

Real and virtual $N N ˉ$ pair production near the threshold

Pion-induced production of the $Z_{c} (3900)$ off a nuclear target