Fri·Jan 29, 2016Friday·January 29, 2016

1. 01*

   Probing neutron-proton dynamics by pions

   Natsumi Ikeno🇯🇵 · Akira Ono🇯🇵 · Yasushi Nara🇯🇵 · Akira Ohnishi🇯🇵

   In order to investigate the nuclear symmetry energy at high density, we study the pion production in central collisions of neutron-rich nuclei ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ at 300 MeV/nucleon using a new approach by combining the antisymmetrized molecular dynamics (AMD) and a hadronic cascade model (JAM). The dynamics of neutrons and protons is solved by AMD, and then pions and $\Delta$ resonances in the reaction process are handled by JAM. We see the mechanism how the $\Delta$ resonance and pions are produced reflecting the dynamics of neutrons and protons. We also investigate the impacts of cluster correlations as well as of the high-density symmetry energy on the nucleon dynamics and consequently on the pion ratio. We find that the ${\Delta }^{-}/{\Delta }^{++}$ production ratio agrees very well with the neutron-proton squared ratio $(N/Z{)}^2$ in the high-density and high-momentum region. We show quantitatively that $\Delta$ production ratio, and therefore $(N/Z{)}^2$, are directly reflected in the ${\pi }^{-}/{\pi }^{+}$ ratio, with modification in the final stage of the reaction.

   ↳ nucl-thnucl-exPRC(2016)·69 citations
2. 02*

   Probing the transversity spin structure of a nucleon in neutrino-production of a charmed meson

   B. Pire🇫🇷 · L. Szymanowski🇵🇱 · J. Wagner🇵🇱

   Including O(m_c) terms in the coefficient functions and/or O(m_D) twist 3 contributions in the heavy meson distribution amplitudes leads to a non-zero transverse amplitude for exclusive neutrino production of a D pseudoscalar charmed meson on an unpolarized target. We work in the framework of the collinear QCD approach where chiral-odd transversity generalized parton distributions (GPDs) factorize from perturbatively calculable coefficient functions.

   ↳ hep-phhep-exnucl-exnucl-thEPJ Web Conf.(2016)·8 citations
3. 03*

   Examination of directed flow as a signature of the softest point of the equation of state in QCD matter

   Yasushi Nara🇯🇵 · Harri Niemi🇩🇪 · Akira Ohnishi🇯🇵 · Horst Stoecker🇩🇪

   We analyze the directed flow of protons and pions in high-energy heavy-ion collisions in the incident energy range from $\sqrt{s_{NN}}=7.7$ to 27 GeV within a microscopic transport model. Standard hadronic transport approaches do not describe the collapse of directed flow below $\sqrt{s_{NN}}\simeq 20$ GeV. By contrast, a model which simulates effects of a softening of the equation of state, well describes the behavior of directed flow data recently obtained by the STAR Collaboration~\cite{STARv1}. We give a detailed analysis of how directed flow is generated. Particularly, we found that softening of effective equation of state at the overlapping region of two nuclei, i.e. the reaction stages where the system reaches high baryon density state, is needed to explain the observed collapse of proton directed flow within a hadronic transport approach.

   ↳ hep-phhep-exnucl-exnucl-thPRC(2016)·96 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.