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 EK: Strange Baryon and Meson Production |
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Sponsoring Units: DNP JPS Chair: Dan Carman, Ohio University Room: Ritz-Carlton Hotel Maui |
Wednesday, September 21, 2005 9:00AM - 9:15AM |
EK.00001: $\Xi$ spectroscopy in photoproduction on a proton target at Jefferson Lab Lei Guo The CLAS Collaboration at Jefferson Lab conducted a photoproduction experiment on a proton target using a tagged photon beam with an energy range of 1.6-3.8~GeV during May-July 2004. With an integrated luminosity of about 70 $pb^{-1}$, this experiment provides the largest data set for photon-proton reactions ever collected. The reaction $\gamma p \rightarrow K^+K^+\Xi^{-}(1320)$ has been investigated with the two $K^+$'s detected by CLAS and $\Xi^{-}(1320)$ constructed from missing four momentum. The preliminary results of the cross section measurement of $\Xi^-(1320)$ for the photon energy range of 2.7-3.8~GeV will be presented. In search for excited cascade states, the reaction of $\gamma p \rightarrow K^+K^+\pi^-(\Xi^0(1320))$ has been explored. Preliminary results of excited cascade states decaying into $\Xi^{0}\pi^{-}$ will be shown. The feasibility of searching for pentaquark cascade states in photoproduction on a proton target will also be discussed. [Preview Abstract] |
Wednesday, September 21, 2005 9:15AM - 9:30AM |
EK.00002: Diffractive $\phi$ photo-production off the Deuteron Near Threshold in LEPS/SPring-8 Manabu Miyabe, Keito Horie, Suguru Shimizu, Wen Chen Chang Measurement of $\phi$ photo-production off the deuteron at forward angles investigate an unique way of studying the reaction mechanisms. Close to production threshold, meson-exchange processes such as exchange of $\pi$ or $\eta$ shows up, other than the dominating channel of Pomeron exchange in the high energy region. The isovector $\pi$-meson exchange can be eliminated in coherent photoproduction from the deuteron as an isoscalar target. In the SPring-8/LEPS experiment, we have measured photo-production of $\phi$ from liquid deuteron target with a photon energy from production threshold to 2.4 GeV. Linearly polarized photon beam was generated by backward Compton scattering. In this talk, we will report preliminary results of differential cross section and decay asymmetry for both coherent and incoherent production. [Preview Abstract] |
Wednesday, September 21, 2005 9:30AM - 9:45AM |
EK.00003: $\Lambda(1405)$ and $\Sigma(1385)$ Photoproduction at LEPS/SPring-8 Deuk Soon Ahn, Takashi Nakano, Jung Keun Ahn We have measured d$\sigma$/dt for $\gamma + p$ $\rightarrow$ $K^{+}$ + $\Lambda{(1405)}$ and $\gamma + p$ $\rightarrow$ $K^{+}$ + $\Sigma{(1385)}$ reactions on the Liquid Hydrogen target at $E_{\gamma}$ = 1.5 - 2.4 GeV by using a linearly polarized photon beam. From the t - distribution we have estimated the contribution of t - channel kaon exchange in the $\Sigma{(1385)}$ and $\Lambda {(1405)}$ photoproduction processes. [Preview Abstract] |
Wednesday, September 21, 2005 9:45AM - 10:00AM |
EK.00004: $\Lambda(1405)$ photoproduction at SPring8/LEPS Hisako Fujimura, Masayuki Niiyama The structure of $\Lambda(1405)$ is a long standing question in hadron physics whether $\Lambda(1405)$ is the spin-multiplet partner of $J^P=\frac{3}{2}^-$ $\Lambda(1520)$ or a Meson-Baryon resonance. Recent theoritical works based on chiral dynamics predict its lineshape to be different in the $\Sigma^+\pi^-$ and $\Sigma^-\pi^+$ channels due to interfence of I=0 and I=1 amplitudes. The same model predicts the modification of mass spectrum of $\Lambda(1405)$ in nuclear medium. The hyperon photoproduction experiment were performed at SPring-8/LEPS with polyethylene, carbon and copper targets. The energy range of the backward Compton scattering photon was 1.5 - 2.4 GeV. In this talk, I will report the experimental details and status of the analysis of $\Lambda(1405)$ lineshape from proton and carbon. [Preview Abstract] |
Wednesday, September 21, 2005 10:00AM - 10:15AM |
EK.00005: Nucleon Motion Effects for Hyperon Production Reactions Shintaro Hashimoto, Michio Kohno, Kazuyuki Ogata, Yukinobu Watanabe, Mitsuji Kawai Single-particle potentials of hyperon, e.g. $\Lambda,~\Sigma,~\Xi$, in nuclei are determined from analysis of $^{32}$Si$(\pi^{\pm},K^+)$ at 1.2 GeV/c and $^{12}$C$(K^-,K^+)$ at 1.65 GeV/c. We use the semiclassical distorted wave (SCDW) model to accurately describe these reactions. As an important advantage of the use of the SCDW model, the Fermi motion of a struck nucleon in the target nucleus is explicitly taken into account. Consequently, the $\Sigma$-$^{32}$Si potential derived from $^{32}$Si$(\pi^-,K^+)$ with the SCDW model is significantly different from a result of previous analysis, where a rather simple reaction-model was adopted. In the present paper we discuss effects of the Fermi motion of a struck target-nucleon on the energy spectrum of the outgoing particle in detail and aim to clarify the reaction mechanisms of the inclusive $(\pi^{\pm},K^+)$ and $(K^-,K^+)$ reactions. We will also discuss the role of multistep processes, which can easily be included in the SCDW model analysis, in the study of the hyperon single-particle potential. [Preview Abstract] |
Wednesday, September 21, 2005 10:15AM - 10:30AM |
EK.00006: Electron population during the cascade of kaonic nitrogen atoms Takahisa Koike The Particle Data Group assigned 493.677 $\pm$ 0.013 MeV to the charged kaon mass as a world average, but there is a serious disagreement between the most two recent mass values deduced from kaonic atom x-rays, which differ 60 keV although their uncertainties are $\sim$10 keV[1]. In order to settle this discrepancy, new precise kaon mass measurement using kaonic nitrogen atom x-rays in a gaseous target is planned at the DA$\Phi$NE[2,3]. For the determination of the kaon mass within the 10 keV error, the electron screening effect on the kaonic x-ray energy becomes crucial issue to be calculated correctly. It needs the knowledge of the electron population at the moment of x-ray emission, which depends on the balance between Auger electron emission and electron refilling during the atomic cascade process. In preparation for the forthcoming kaon mass measurement, we are developing the atomic cascade code for kaonic nitrogen atoms, which enables us to determine the electron population at each kaon atomic level. Our cascade model has been improved to get further details of the electron configuration during the cascade[4]. We will report our recent results of the cascade calculation, including the density dependence. \\ 1. S. Eidelman {\it et al.}, Phys. Lett. B592, 1 (2004). \\ 2. G. Beer {\it et al.}, Phys. Lett. B535, 52 (2002). \\ 3. T. Ishiwatari {\it et al.}, Phys. Lett. B593, 48 (2004). \\ 4. T. Koike, Genshikaku Kenkyu, Vol.49 no.6, 159 (2005). [Preview Abstract] |
Wednesday, September 21, 2005 10:30AM - 10:45AM |
EK.00007: Formation reaction of $\eta'(958)$-mesic nuclei and $U_A(1)$ anomaly at finite density in NJL model Hideko Nagahiro, Makoto Takizawa, Satoru Hirenzaki The huge mass of the $\eta'(958)$ meson is believed to have close connection with the breaking of the axial $U(1)$ symmetry at the quantum level referred as {\it the $U_A(1)$ anomaly}. There are many theoretical studies for the effects of the $U_A(1)$ anomaly on the $\eta'$ meson, not only in vacuum, but also at finite temperature and finite density, which suggest the possible character changes of $\eta'$ at finite temperature and/or finite density. At the present time, however, there exists no experimental information on the property and behavior of the $U_A(1)$ anomaly at finite density. In this presentation, we propose the formation reaction of the $\eta'$-mesic nuclei in order to investigate the $\eta'$ properties, especially its mass shift, at finite density. We apply the NJL model to describe $\eta'$ properties in nuclear medium, and show the clear relations between NJL parameters and expected reaction spectra, which should be the first step to get deeper insights on $U_A(1)$ anomaly at finite density from experimental data. The $\eta'$ mass in the medium should provide us important information on the properties of the $U_A(1)$ anomaly in the nuclear medium. [Preview Abstract] |
Wednesday, September 21, 2005 10:45AM - 11:00AM |
EK.00008: Neutron spectra from the in-flight $^{16}$O($K^-,n$) and $^{12}$C($K^-,n$) reactions T. Hayakawa, T. Kishimoto, A. Sakaguchi, S. Ajimura, Y. Shimuzu, T. Itabashi, Y. Mitoma, K. Terai, F. Khanam, H. Noumi$^{a}$, H. Takahashi$^{a}$, T. Fukuda$^{b}$, S. Minami$^{b}$, W. Imoto$^{b}$ We carried out an experiment to study kaonic nuclei at K2 beam line of KEK 12GeV Proton Synchrotron in this spring. We employed the in-flight ($K^-,N$) reaction to excite the kaonic nuclear state since expected that almost the highest energy nucleon made background ineffective. Water, carbon, and polyethylene were used as targets. We would like to show the preliminary result of the missing mass spectra of the $^{16}$O($K^-,n$) and $^{12}$C($K^-,n)$ reaction and discuss kaonic nuclei by spectra in the bound region. [Preview Abstract] |
Wednesday, September 21, 2005 11:00AM - 11:15AM |
EK.00009: Semirelativistic calculations of exotic systems Hidekatsu Nemura, Choki Nakamoto Recent experimental report on a new observation of strange tribaryon $S^0(3115)$ has had a significant impact on nuclear physics. The existence of deeply bound $\bar{K}$-nuclear systems has been predicted by Akaishi and Yamazaki, based on an assumption of $\Lambda(1405)$ being a bound state of $\bar{K}+N$. However, the $S^0(3115)$ is different from that was originally predicted since the isospin ($I=1$) of $S^0(3115)$ determined by the isospin conservation does not match the isospin ($I=0$) predicted by the theory. Moreover, the mass of $S^0(3115)$ is about 100 MeV lighter than the value by the theoretical prediction. Towards a description of the strange tribaryon, we calculate the exotic systems (e.g., $\Lambda(1405)$) using a semi-relativistic hamiltonian, that includes a semi-relativistic form of the kinetic energy ($\sqrt{p^2+m^2}$). [Preview Abstract] |
Wednesday, September 21, 2005 11:15AM - 11:30AM |
EK.00010: Search for eta bound states in nuclei M. Shindo, K. Gomikawa, R.S. Hayano, N. Ono, H. Outa, K. Itahashi, M. Iwasaki, K. Suzuki, K. Lindberg, P.-E. Tegner, I. Zartova, A. Trzcinska, H. Geissel, G. Munzenberg, Yu.A. Litvinov, H. Weick, A. Gillitzer S214 experment is scheduled in July, 2005 at GSI. The goal of this experiment is to study properties of eta bound to nuclei. Recently S160 group succeeded in searching for the bound states of $\pi^-$ to the nuclei at GSI. The local part of the $\pi$- nucleus optical potential parameters was determined through the detailed analysis. The determined potential is translated to the effective $\pi$ mass in nuclear matter. For better understanding of the meson properties in nuclear medium systematically, we study eta-nucleus bound states. This experimental search is challenging due to the small signal cross section ($\sim$ 1 Hz) and the large background ($\sim 10^8$ Hz). We develop a new type high resolution Cherenkov detector, TORCH, to overcome these difficulties. In this talk, we will report the latest result of an analysis. [Preview Abstract] |
Wednesday, September 21, 2005 11:30AM - 11:45AM |
EK.00011: In search of the $\sigma$ resonance in $\pi^0\pi^0$ production by $\pi^-$ and $K^-$ Bernard M.K. Nefkens, Serguei Prakhov, John W. Price, Alexander Starostin The identification of the light scalar mesons, in particular the $\sigma$ state also called the $f_0(600)$ with $I^G(J^{PC}) = 0^+(0^{++})$, is a long-standing puzzle. The main $\sigma$ decay mode is to two pions. The study of the process $K^-p \to \pi^0\pi^0\Lambda$ is especially attractive because the $\pi^0\pi^0$ pair is a pure $I=0$ state. This is in contrast to $\pi^+\pi^-$, which features $I=0$ and 1. Extensive new data have become available recently from the Crystal Ball at the AGS [1] on $\pi^-p \to \pi^0\pi^0n$, $K^-p\to\pi^0\pi^0\Lambda$, and $K^-p\to\pi^0\pi^0\Sigma^{0}$, which cast doubts on the picture of the $\sigma$ being a simple $2\pi^0$ state with $m\sim600$~MeV, as recommended in recent editions of the Review of Particle Physics. The latest experimental data have fully measured kinematics, so the four-dimensional variable space has been determined in its entirety; there is major structure in the $\pi^0\pi^0$ invariant mass which varies with the $\pi^0\pi^0$ angle and the incident energy.\\ Reference: S. Prakhov \emph{et al.}\ (Crystal Ball Collaboration), Phys.\ Rev.\ C \textbf{69}, 042202 (2004); S. Prakhov \emph{et al.}\ (Crystal Ball Collaboration), Phys.\ Rev.C \textbf{69}, 045202 (2004); S. Prakhov \emph{et al.}\ (Crystal Ball Collaboration), Phys.\ Rev.\ C \textbf{70}, 034605 (2004). [Preview Abstract] |
Wednesday, September 21, 2005 11:45AM - 12:00PM |
EK.00012: Search for medium effects on light vector mesons Rakhsha Nasseripour, Chaden Djalali, Clarisse Tur, Michael Wood, Dennis Weygand Theoretical calculations predict the modifications of properties of vector mesons such as their masses and widths in dense nuclear matter. These modifications can be related to more fundamental physics such as partial restoration of chiral symmetry at high density. An experiment was performed using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The data were taken with a tagged photon beam of energies up to 4 GeV on various nuclear targets. The properties of light vector mesons, $\rho$, $\omega$, and $\phi$, have been investigated through their rare leptonic decay to $e^+e^-$. This decay channel is preferred over the hadronic modes in order to eliminate the final state interactions in the nuclear matter. Preliminary results will be shown and discussed. [Preview Abstract] |
Wednesday, September 21, 2005 12:00PM - 12:15PM |
EK.00013: Study of two pion photoproduction on deuteron Kentarou Hirose We studied the $\gamma d \rightarrow p n \pi^+ \pi^-$ reaction at $E_\gamma = 0.8 \sim 1.1$~GeV. It was carried out at the tagged photon facility of the Laboratory of Nuclear Science, Tohoku University. Neutral Kaon Spectrometer was used for detection of charged particles and liquid deuterium was used for a target. The spectrometer consists of a pair of drift chambers in the 0.5~T magnetic field, inner and outer scintillation hodoscopes. Four veto counters were installed to reduce QED background. The geometrical acceptance of the spectrometer is $\pi$ sr. The $p \pi^+ \pi^-$ events in the final state were selected. The $\gamma d \rightarrow p n \pi^+ \pi^-$ events were derived by missing mass distribution. The neutron momentum was used to determine whether the reaction was a quasi-free kinematics or not. Since the detection threshold for protons is about 0.2~GeV/c, the proton spectator reaction cannot be measured. The $N\pi$ invariant mass spectra suggest that the $\gamma d \rightarrow \Delta^{++} \pi^- n_{sp}$ reaction is dominant in the quasi-free kinematics region and the $\gamma d \rightarrow \Delta^{++} \Delta^{-}$ reaction may exist in the non quasi- free kinematics region. From detailed comparison of the measured data with the results of Monte Carlo simulations, we're going to deduce the total cross section for the reaction $\gamma d \rightarrow \Delta^ {++} \Delta^{-}$. [Preview Abstract] |
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