Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session CD: Mini-Symposium on Meson-Nucleus Systems and the Partial Restoration of Chiral Symmetry I |
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Chair: Satoru Hirenzaki, Nara Womens University Room: Kohala 4 |
Thursday, October 15, 2009 9:00AM - 9:30AM |
CD.00001: Recent topics of hadrons in nuclei Invited Speaker: The investigation of the properties of hadrons in nuclei is one of the important subjects of contemporary nuclear physics. Especially, production and confirmation of meson-nucleus bound systems are challenging both in experimental and theoretical points of view. With the structure of the (quasi)bound states, one can learn the in-medium properties of individual hadrons, and also universal consequences among the in-medium effects on the hadrons, such as the in-medium quark condensate. In this talk, I briefly review the recent topics of hadrons in nuclei. First, I will show that the in-medium properties of pion do relate to the quark condensate in finite density based on an exact sum rule derived recently by exploiting operator relations in QCD. We will discuss the consequences obtained in the deeply bound pionic atoms based on the sum rule. For the mesonic nuclei, I emphasize that, to understand physics of mesons in nuclei, detailed knowledge of baryon resonances is also important, since the meson inside the nucleus excites one of the nucleons and creates a baryon resonance. The interesting examples are $N(1535)$ in the eta mesonic nuclei and $\Lambda(1405)$ in the kaon and nucleus systems. For the $\eta$ mesonic nuclei, I discuss a possibility of the level crossing between the eta and $N(1535)$-hole modes caused by the reduction of the mas gap between $N$ and $N(1535)$ in the context of partial restoration of chiral symmetry. For the kaonic nuclei, reviewing the present status of $\Lambda(1405)$, I discuss the important role of $\Lambda(1405)$ and possible hadronic molecular states with multiple kaons. [Preview Abstract] |
Thursday, October 15, 2009 9:30AM - 9:45AM |
CD.00002: $\eta$ meson production in nucleus and observation of in-medium behavior of $N^*(1535)$ Hideko Nagahiro, Daisuke Jido, Satoru Hirenzaki The study of the in-medium hadron properties is one of the important subjects in nuclear physics. It would provide us useful information on chiral symmetry in finite density. In this contribution, we investigate the properties of the $\eta$-nucleus interaction in chiral models and discuss the possible observation of the in-medium behavior of the $N^*(1535) $ resonance in experiments. The strong coupling of the $\eta N$ system to $N^*$ enables us to investigate the in-medium properties of $N^*$ through the $\eta$ meson production in nuclei. For in-medium properties of $N^*$, there are some theoretical models paying respects to chiral symmetry. In the chiral doublet model, in which $N^*$ is regarded as a chiral partner of nucleon, the effect of the partial restoration of chiral symmetry reduces the mass difference of $N$ and $N^*$ in the nuclear medium. On the other hand, the chiral unitary model, in which $N^*$ is introduced as a resonance dynamically generated by meson- baryon scattering, predicts almost no mass shift of $N^*$ in nuclear matter. To investigate the in-medium properties of $N^*$, we would like to discuss the formation probability of the $\eta$ mesic nuclei by using the missing mass spectroscopy and also investigate the production reaction of the $\eta$ meson off nuclei that has a different kinematics from the former reaction. [Preview Abstract] |
Thursday, October 15, 2009 9:45AM - 10:00AM |
CD.00003: Recent results on in-medium properties of the omega meson Volker Metag Data on the photo production of $\omega $ mesons on nuclei have been re-analyzed. For incident photon energies of 900 -- 2200 MeV, $\omega$ mesons have been identified via the $\pi ^{0}\gamma $ channel using the CBELSA/TAPS detector. A new procedure has been developed which allows a model-independent background determination in shape and absolute magnitude directly from the data. Applying this method, an earlier claim of an in-medium lowering of the $\omega $ mass [1] can not be confirmed. Because of the strong in-medium broadening of the $\omega $ meson, deduced from a transparency ratio measurement [2], the fraction of in-medium $\omega \quad \to \quad \pi ^{0}\gamma $ decays is correspondingly reduced and the experiment becomes less sensitive to in-medium mass shifts. A higher sensitivity is expected for incident energies close to the production threshold [3]. A measurement at incident photon energies of 800-1400 MeV has been performed. Results of this experiment, including an analysis of the $\omega$ excitation function, will be presented \\[4pt] [1] D. Trnka et al., PRL 94 (2005)192303.\\[0pt] [2] M. Kotulla et al., PRL 100 (2008) 192302.\\[0pt] [3] K. Gallmeister et al., Prog. Part. Nucl. Phys. 61 (2008) 283. [Preview Abstract] |
Thursday, October 15, 2009 10:00AM - 10:15AM |
CD.00004: Coherent $\pi^+$ Photoproduction on $^3$He Rakhsha Nasseripour, Barry Berman Comparing an elementary meson-production process on a free nucleon with the same process inside a nucleus has been an interesting problem in nuclear physics. Studying these processes are useful in developing our understanding of nuclear structure and the long-range part of the nucleon-nucleon interaction described by the one-pion-exchange model. In the present analysis, we have measured the differential cross section for the $\gamma$$^3$He$\rightarrow \pi^+ t$ reaction channel. Studying this channel is ideal for understanding the interaction of pions with nuclei and for searching for possible effects mediated by nucleon resonances in nuclear matter. The $^3$He target contains the lightest nucleus on which one can observe coherent (elastic) $\pi^+$ photoproduction with charge exchange that also leads to a well defined final state that can be easily identified. This reaction was studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. Real photons produced with the Hall-B bremsstrahlung tagging system in the energy range from 0.35 to 1.55 GeV were incident on a cryogenic liquid $^3$He target. The differential cross sections for the $\gamma$$^3$He$\rightarrow \pi^+ t$ reaction were measured as a function of photon-beam energy and pion-scattering angle in the center- of-mass frame. Our results will be presented and discussed. [Preview Abstract] |
Thursday, October 15, 2009 10:15AM - 10:30AM |
CD.00005: Precision Spectroscopy of Pionic Atom in ($d$,$^3$He) Reaction at RIKEN-RIBF Satoshi Itoh Spectroscopy of pionic atoms has been contributing to understanding of the origin of hadron masses. The hadron masses dynamically grow as the chiral symmetry is partially broken. The order of the symmetry breaking is parameterized by the magnitude of the quark condensate. The objective of our experiment is to evaluate the magnitude of the quark condensate through precise experimental determination of the in-medium isovector interaction strength between the pion and the nucleus. Previous results of the pionic atom spectroscopy yielded the first quantitative estimation of its reduction at the normal nuclear density to be about $33\%$ compared to that in the vacuum. However, the value of $33\%$ definitely needs more careful and precise evaluation. The next experiment will be performed at RIKEN-RIBF. In this experiment, we use the dispersion matching to minimize the effect of the incident beam momentum spread. After fulfilling the necessary technical issues, we will achieve about twice better resolution of $150-200$ keV compared to the previous. In this contribution, we introduce the next experiment and report the present status. [Preview Abstract] |
Thursday, October 15, 2009 10:30AM - 10:45AM |
CD.00006: Deeply Bound Pionic 1$s$ and 2$s$ Sates in Sn at RIBF Natsumi Ikeno, Junko Yamagata-Sekihara, Hideko Nagahiro, Daisuke Jido, Satoru Hirenzaki Deeply bound pionic states are interesting exotic systems since we can observe the properties of NG boson in nucleus and deduce clear information on the partial restoration of chiral symmetry around normal nuclear density. Recently it has been reported that the (d,3He) reaction at recoilless kinematics efficiently populates these states. New experiments will be performed at a new facility, RIKEN RIBF, in near future with significantly better energy resolution than those in the previous experiments. There, one expects to observe the 2$s$ atomic state, which has not been observed so far, in addition to the deepest 1$s$ state. In this contribution, we discuss physical implications of the new data obtained in simultaneous observation of the 1$s$ and 2$s$ states with high energy resolution. It is known that only information of pionic atom yrast levels hardly provides the pion properties at different nuclear densities. We expect that the pion in the 2$s$ state can probe different nuclear densities from the yrast levels. Thus, we perform a systematic evaluation of the effective nuclear densities which can be probed by pions in various atomic states. We explore the possibilities to deduce the pion properties at different nuclear densities by observing the different atomic states, and discuss the importance of the 2$s$ pionic states in Sn isotopes. [Preview Abstract] |
Thursday, October 15, 2009 10:45AM - 11:00AM |
CD.00007: Precision spectroscopy of kaonic atom x rays at DA$\Phi$NE with silicon drift detectors in SIDDHARTA (III) Hexi Shi The SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research by Timing Application) project is currently in progress at the DA$\Phi$NE $e^{+}e^{-}$ collider in LNF (Laboratori Nazionali di Frascati), Italy. In this experiment, the $K$-series x rays of kaonic hydrogen atom will be measured to a precision below 10 eV to determine the strong-interaction shift and width of the kaonic hydrogen atom $1s$ state with the best accuracy ever, which is important for the understanding of the kaon nucleon interaction. A gaseous target is used to stop the kaons produced resonantly through $\Phi\rightarrow K^{+}K^{-}$ at DA$\Phi$NE interaction point. And the specifically designed SDDs with a time resolution at micro-second order in addition to an energy resolution of about 150 eV FWHM at 6 keV, were introduced to achieve both a good timing selection to reduce background and a high energy resolution. The array of 144 such SDDs each with 1 cm$^2$ effective surface will cover a large sensitive area, leading to a better acceptance of kaonic x rays. Preliminary results of the measurement carried out in 2009 will be discussed. [Preview Abstract] |
Thursday, October 15, 2009 11:00AM - 11:15AM |
CD.00008: $K^{-}$\textit{pp} studied with Coupled-Channel Complex Scaling Method Akinobu Dote, Takashi Inoue $K^{bar}$ nuclei (nuclear system with anti-kaon) might have lots of interesting properties due to the strong $K^{bar}N$ attraction in $s$-wave isoscalar channel. Recently, people are focusing on the most essential $K^{bar}$ nucleus ``$K^{-}$\textit{pp}''. A variational calculation with an effective $K^{bar}N$ potential derived from chiral SU(3) theory, performed by one of authors (A. D.), concluded the shallow binding of $K^{-}$\textit{pp}. (only 20 MeV) However, a Faddeev (AGS) calculation, also constrained by chiral SU(3) theory, reported 80 MeV binding energy. Such a large discrepancy is considered to be caused by the \underline {\textit{$\pi \Sigma $N}}\underline { three-body dynamics}. Since the \textit{$\pi \Sigma $} degree is not explicitly dealt with in the variational calculation and is incorporated in the effective $K^{bar}N$ potential, the \textit{$\pi \Sigma $N} three-body dynamics might be lack in the previous study. We will perform a coupled channel calculation treating \underline {the }\underline {\textit{$\pi \Sigma $N}}\underline { channel explicitly}. Since the obtained $K^{-}$\textit{pp}-\textit{$\pi \Sigma $N} coupled state is expected to appear above the \textit{$\pi \Sigma $N} threshold as \underline {a resonant state}, we employ ``Complex Scaling Method'' (CSM) which has succeeded in the treatment of resonances in nuclear physics. Studying $K^{-}$\textit{pp} with ``\textbf{\textit{Coupled-Channel Complex Scaling Method}}'' using a reliable \textit{NN} potential (Av18 potential) and theoretical/phenomenological $K^{bar}N$ potentials, we will report its binding energy and decay width. Then, analyzing the CSM wave function, detailed property of $K^{-}$\textit{pp} will be investigated. [Preview Abstract] |
Thursday, October 15, 2009 11:15AM - 11:30AM |
CD.00009: Search for kaonic nuclear state using p+p reaction Ken Suzuki Since so-called ``kaonic hydrogen puzzle'' has been solved about 10 years ago with a modern X-ray measurement of kaonic hydrogen, and $KN$ interaction has been reasonably well constrained from the experimental data, a possible existence of exotic nuclear systems involving $K$ as a constituent has been a hot topic for theory and experiment. Such systems are said to have peculiar features compared to conventional nuclear systems, namely high binding energy ($>50$ MeV), bound states like $K^-pp$, $K^-ppp$ due to strong $I=0$ $KN$ interaction, density that does not saturate at normal nuclear density. We plan an experimental program to aim at the first high statistics, low background measurement in order to examine unambiguously the existence of the prototype kaonic nuclear state, $K^-pp$ using $p+p\rightarrow K^+ + K^-pp$ reaction at $T_p=3$ GeV. The experiment employs the FOPI apparatus at GSI (Germany) and beamtime is scheduled in August 2009. In the talk, an impression of quick analysis will be reported as well. [Preview Abstract] |
Thursday, October 15, 2009 11:30AM - 11:45AM |
CD.00010: $\Lambda (1405)$-induced non-mesonic decay in kaonic nuclei Takayasu Sekihara, Junko Yamagata-Sekihara, Daisuke Jido, Yoshiko Kanada-En'yo The non-mesonic decay of kaonic nuclei is studied under the $\Lambda (1405)$-doorway picture, in which the $\bar{K}$ absorption to the nuclei takes place through the $\Lambda (1405)$ resonance, owing to the presence of the $\Lambda (1405)$ just below the $\bar{K} N$ threshold. For the study of the $\Lambda (1405)$-doorway non-mesonic decay of kaonic nuclei, we calculate the $\Lambda (1405) N \to Y N$ transition in uniform nuclear matter using one-meson exchange model. In the present calculation we find that the non-mesonic decay ratio $\Gamma _{\Lambda N} / \Gamma _{\Sigma^{0} N}$ depends strongly on the ratio of the couplings $\Lambda (1405) $-$\bar{K} N$ and $\Lambda (1405) $-$\pi \Sigma$. Especially a larger $\Lambda (1405)$-$\bar{K} N$ coupling leads to enhancement of the decay to $\Lambda N$. Using the chiral unitary approach for description of the $\bar{K} N$ amplitudes, we obtain $\Gamma _{\Lambda N} / \Gamma _{\Sigma^{0} N} \approx 1.2$ almost independently of the nucleon density, and find the total two-nucleon absorption of the $\bar{K}$ in uniform nuclear matter to be 22 MeV at the normal density. We also show the two-nucleon absorption stpectrum of the $(K^{-} , \, N)$ reaction in our approach. [Preview Abstract] |
Thursday, October 15, 2009 11:45AM - 12:00PM |
CD.00011: $\Lambda^*$-hyper-nuclei with chiral dynamics Toshitaka Uchino, Tetsuo Hyodo, Makoto Oka Bound states of $\Lambda^*=\Lambda(1405)$ in nuclei, the $\Lambda^*$-hyper-nuclei, are studied from the viewpoint of chiral dynamics. As the $\Lambda^*$ is formed by a strong attraction between $\bar{K}$ and the nucleon, the $\Lambda^*$- hyper-nuclei can be a main component of the $\bar{K}$ nucleon bound states. We use an extension of the Nijmegen one-boson- exchange potential for the interaction between $\Lambda^*$ and nucleon. The coupling constants concerning the $\Lambda^*$ are determined by a microscopic theory based on chiral dynamics of meson-baryon systems. We discuss the level structure of the $\Lambda^*$-hyper-nuclei in the case when the $\Lambda^*$ is described as a superposition of two states. [Preview Abstract] |
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