Mon·Dec 29, 2014Monday·December 29, 2014

1. 01*

   Direct photon and neutral pion production in pp and Pb-Pb collisions measured with the ALICE experiment at LHC

   Dmitri Peressounko (for the ALICE collaboration)🇷🇺

   Measurements of direct photon and neutral pion production in heavy-ion collisions provide a comprehensive set of observables characterizing properties of the hot QCD medium. Direct photons provide means to test the initial stage of an AA collision and carry information about the temperature and space-time evolution of the hot medium. Neutral pion suppression probes the parton energy loss in the hot medium. Measurements of neutral meson spectra in pp collisions at LHC energies $\sqrt{s}=$0.9, 2.76, 7 TeV serve as a reference for heavy-ion collisions and also provide valuable input data for parameterization of the QCD parton Fragmentation Functions. In this talk, results from the ALICE experiment on direct photon and neutral pion production in pp and Pb-Pb collisions are summarized.

   nucl-ex1 citation
2. 02*

   Searching for isovector signatures in the neutron-rich oxygen and calcium isotopes

   Wei-Chia Chen🇺🇸 · J. Piekarewicz🇺🇸

   We search for potential isovector signatures in the neutron-rich oxygen and calcium isotopes within the framework of a relativistic mean-field theory with an exact treatment of pairing correlations. To probe the isovector sector we calibrate a few relativistic density functionals using the same isoscalar constraints but with one differing isovector assumption. It is found that under certain conditions, the isotopic chain in oxygen can be made to terminate at the experimentally observed ${}^{24}$O isotope and in the case of the calcium isotopes at ${}^{60}$Ca. To produce such behavior, the resulting symmetry energy must be soft, with predicted values for the symmetry energy and its slope at saturation density being $J=(30.92\pm 0.47)$ MeV and $L=(51.0\pm 1.5)$ MeV, respectively. As a consequence, the neutron-skin thickness of ${}^{208}$Pb is rather small: $R_{\mathrm{skin}}^{208}=(0.161\pm 0.011)$ fm. This same model - labelled "FSUGarnet" - predicts $R_{1.4}=(13.1\pm 0.1)$ km for the radius of a "canonical" 1.4$M_{\odot }$ neutron star, yet is also able to support a two-solar-mass neutron star.

   ↳ nucl-thnucl-exPLB(2015)·148 citations
3. 03*

   Theoretical investigation of the decay of the $N(2120)$ resonance to nucleon resonances near 1.7 GeV

   Yin Huang🇨🇳 · Jun He🇨🇳 · Xu-Rong Chen🇨🇳 · Rong Wang🇨🇳 · Jun-Jun Xie🇨🇳 · Hong-Fei Zhang🇨🇳

   Background: Until now the knowledge about nucleon resonances with a mass higher than 2 GeV has been scarce. Huge amounts of experimental data of the multipion photoproduction have been accumulated, and more can be expected in the future in facilities such as JLab 12 GeV. It makes it possible to investigate the decay of a nucleon resonance into another nucleon resonance. Purpose: The possibility to research the decay of the $N(2120)$ to nucleon resonances near 1.7 GeV in the three-pion photoproduction will be explored to provide useful information for future experimental study. Method: The pion and radiative decay amplitudes of nucleon resonances are studied within the constituent quark model, which is used to calculate the couplings constants, especially for the decay of a nucleon resonance near 2.1 GeV to another nucleon resonance near 1.7 GeV. The three-pion photoproduction off the neutron target, i.e.,$\gamma n\to {\pi }^{-}{\pi }^{-}{\Delta }^{++}\to {\pi }^{-}{\pi }^{-}{\pi }^{+}p$, is investigated based on the effective Lagrangian method with the coupling constant obtained form the decay amplitudes. Results: The resonance contribution with a state $N{(}^2{P}_M){\frac{3}{2}}^{-}$ near 2.1 GeV decaying to a state $N{(}^4{P}_M){\frac{5}{2}}^{-}$ near 1.7 GeV, i.\ e., $N(2120)\to N(1675)\pi$ is dominant in the process considered. The total cross section from the resonance contribution is at the order of 1 $\mu$b and can be easily distinguished from the background. Conclusions: Our results suggest it is practicable to research the decay of the $N(2120)$ to the $N(1675)$ in experiment.

   ↳ nucl-thhep-phnucl-exPRC(2015)·2 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.