Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session EL: JPS Award Talks by Distinguished Young Researchers |
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Sponsoring Units: JPS Chair: Hideyuki Sakai, University of Tokyo Room: Ritz-Carlton Hotel Plantation 1/2/3 |
Wednesday, September 21, 2005 9:00AM - 9:30AM |
EL.00001: Hadron Physics at RHIC Invited Speaker: From the first five years of the relativistic heavy ion runs at RHIC, several key experimental discoveries brought a new understanding of the matter at the high temperature and energy density. Among the rich data from four experiments (BRAHMS, PHENIX, PHOBOS, and STAR), the following results are important to characterize the matter created in central Au+Au collisions at RHIC: (1) large hadron yield suppression at high $p_T$, (2) disappearance (or broadening) of back-to-back jet, (3) ``baryon anomaly'' at intermediate $p_T$, and (4) large event anisotropy and its quark number scaling behavior. We will review those experimental results along with the context of a possible formation of the strongly interacting quark-gluon plasma. We will also present the most recent systematic studies on hadron production at RHIC, such as single particle spectra and elliptic flow in different beam energies and colliding systems (p+p, d+ Au, Cu+Cu), which may give us a further understanding of the in- medium effects and their evolutions. [Preview Abstract] |
Wednesday, September 21, 2005 9:30AM - 10:00AM |
EL.00002: Experimental finding of the anomalous quadrupole collectivity in unstable nucleus $^{16}$C Invited Speaker: The electric quadrupole transition from the first 2$^+$ state to the ground 0$^+$ state in $^{16}$C is studied through measurements of the lifetime. The measured mean lifetime $\tau$ is $77 \pm 14$ (stat) $\pm 19$ (syst)~ps. The central value of $\tau$ corresponds to a $B$($E2;2_1^+\rightarrow 0^+$) value of $0.63 e^2$fm$^4$, or $0.26$ Weisskopf units~[1]. The transition strength is found to be smaller than the empirically predicted value by one order of magnitude. \\ This is the first application of recoil shadow method (RSM) to the lifetime measurement using an intermediate-energy RI beam. For nuclei located far from the stability line, the method of the intermediate energy Coulomb excitation has widely been used for their $B$($E2$) measurements. In the case of small $Z$ nuclei, however, a cross section of the nuclear excitation is comparable with that of the Coulomb excitation. To avoid difficult treatment of the nuclear excitation, we adopted the RSM for measurements of $\tau$, which is inversely proportional to $B$($E2$).\\ To account for the quenched $B$($E2$) value, two theoretical pictures have been proposed. One is based on the shell model calculation. The other is on the antisymmetrized molecular dynamics (AMD) calculation. The shell model treatment has mainly ascribed the quenching to the combined effects of increased proton sub-shell gap between $1p_{3/2}$ and $1p_{1/2}$ and reduced $E2$ effective charges for neutrons, while the AMD treatment has ascribed it mainly to the difference between favored deformed shapes for protons and neutrons. Both calculations reproduce the sudden decrease of $B$($E2$) in carbon isotopes. \\ I will show the detailed experimental setup and the experimental result together with the theoretical works. \\ {\bf Ref.} [1] N.\ Imai et al., Phys. Rev. Lett. {\bf 92}, 06251(2004). [Preview Abstract] |
Wednesday, September 21, 2005 10:00AM - 10:30AM |
EL.00003: Partial restoration of chiral symmetry in the nuclear medium Invited Speaker: Study of pionic atom has been revisited by a recent discovery of deeply bound pionic states in the context of possible sensitivity to the partial chiral restoration in the nuclear medium. The chiral symmetry breaking in QCD is considered to be a driving mechanism of how hadrons acquire their masses. Exploring the QCD phase diagram towards high density regime is believed to experience highly non-trivial chiral phase transition. A quark condensate, $\langle \bar{q}q \rangle$, is an ``order parameter'' of this symmetry breaking and is expected to diminish as a consequence of chiral symmetry restoration. Efforts of detecting this precursor are being made intensively these days. The deeply bound pionic atom provides unique laboratory in this context. In the hadrons mass spectrum as quasi particle excitations of the condensate, pions are identified to be Nambu-Goldstone bosons, which are the lowest energy excitation modes. Isovector part of their s-wave interaction with nucleons is determined by the pion decay constant, $f_{\pi}^2$, which is directly connected to the magnitude of $\langle \bar{q}q \rangle$ through the Gell-Mann-Oaks-Renner relation. Since the pionic orbits of low-lying states have certain overlap with nucleus, a property of pion can be influenced by a nuclear medium. We performed a systematic measurement of 1s $\pi^-$ states in $^{115,119,123}$Sn by hiring $^{ 116,120,124}$Sn(d,$^3$He) reactions at GSI SIS-FRS system, from which we determined the 1s binding energies and widths precisely. These are used to deduce the isovector s-wave interaction, $b_1 = 0.115 \pm 0.005 m_{\pi}^{-1}$. The observed magnitude is significantly enhanced over the free $\pi N$ value, which is translated into a reduction of $\langle \bar{q}q \rangle$ by $\sim$35\% at normal nuclear density. [Preview Abstract] |
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