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 EE: Mini-symposium on Pentaquarks II |
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Sponsoring Units: DNP JPS Chair: Atsushi Hosaka, RCNP Osaka University Room: Ritz-Carlton Hotel Amphitheatre |
Wednesday, September 21, 2005 9:00AM - 9:15AM |
EE.00001: Pentaquark Mass and Structure Terry Goldman, Jialun Ping, Fan Wang The Extended Quark Delocalization, Color Screening Model reproduces ground state baryons and the deuteron with good accuracy. The model includes all meson exchange contributions to hadronic interactions using explicit pions and quark wavefunctions distorted from their configurations in isolated baryons. We apply the model to calculate the masses of pentaquark states for various structures. A tetrahedal configuration of light quarks centered on the strange antiquark is found to have a lower mass than the configurations proposed by both Jaffe-Wilczek and Lipkin-Karliner for the $\Theta^+$. [Preview Abstract] |
Wednesday, September 21, 2005 9:15AM - 9:30AM |
EE.00002: Four- and five-body calculation of resonance and scattering states of exotic hadoron systems Hiyama Emiko, Kamimura Masayasu, Hosaka Atsushi, Toki Hiroshi, Yahiro Masanobu Scattering problem of uudd$\bar{s}$ system, in the standard non- relativistic quark model, is for the first time, by treating the large five-body modelspace including the NK scattering channel accurately with the Gaussian expansion method and Kohn- type coupled-channel variational method. The NK scattering phase shift calculated shows no resonance corresponding to the reported pentaquark $\Theta^+(1540)$ MeV. The phase shift does show two resonance at energies much higher than the $\Theta^+$ (1540) MeV energy region; one is a broad $1/2^+$ resonance with width of $\Gamma \approx 110$ MeV located at $\approx$ 535 MeV above the NK threshold, and the other is a sharp $1/2^-$ resonance with $\Gamma =0.24$ MeV at 539 MeV. We also will report the structure of X(3872)which has been reproted by the Belle gourp. [Preview Abstract] |
Wednesday, September 21, 2005 9:30AM - 9:45AM |
EE.00003: Quantum Monte Carlo studies of pentaquark states Mark Paris We study states of four light quarks of isospin zero and a strange antiquark for a variety of wave functions with a non-relativistic constituent quark model (NRCQM) whose parameters are fixed from light baryon spectroscopy. The many-body Schrodinger equation is solved using the variational Monte Carlo technique. Improvements over previous NRCQM include full antisymmetrization of the state of the four light quarks, sometimes neglected, relaxed assumptions for the spin state of the four light quarks, and the inclusion of correlations between pairs of quarks which depend on their isospin-spin-color state. Masses are calculated for negative and positive parity pentaquark states and found to be considerably higher than 1.5 GeV. The structure of the wave function is studied in terms of short range correlations. [Preview Abstract] |
Wednesday, September 21, 2005 9:45AM - 10:00AM |
EE.00004: Analysis of the pentaquark mass and decay width in a constituent quark model Hideki Matsumura, Yasuyuki Suzuki After the discovery of the pentaquark $\Theta^+$ by the LEPS collaboration at Spring-8 in Japan, its existence was further investigated by other experimental groups. Though the mass and width for $KN$ decay reported by several experimental groups are consistent each other to some extent, its spin and parity are not yet determined. Several models have been proposed to predict the spin and parity of $\Theta^+$. There are two representative studies on the pentaquark in a constituent quark model. First one is the Jaffe-Wilczek model ($ud-ud-\bar{s}$), the other one is the Karliner-Lipkin model ($ud-ud\bar{s}$). As these models are restricted to a special degree of freedom of spin, isospin, and color, they may be insufficient to describe the pentaquark more accurately. For the purpose, we use explicitly correlated basis functions as the orbital wave function, and take into account all possible spin, isospin, and color channels, then present a precise 5-body calculation for $\Theta^+$, By using a real stabilization method, we identify a $\Theta^+$ resonance in the continuum. In this way, we analyze the pentaquark mass and $NK$ decay width for spin and parity states. [Preview Abstract] |
Wednesday, September 21, 2005 10:00AM - 10:15AM |
EE.00005: Non-interacting \textit{KN} contribution in the QCD sum rule for the pentaquark $\Theta ^{+}$ (1540) Youngshin Kwon, Atsushi Hosaka, Su Houng Lee We perform a QCD sum rule analysis for the pentaquark baryon $\Theta ^{+}$ with the non-interacting \textit{KN} contribution treated carefully. The coupling of the $\Theta ^{+}$ current to the \textit{KN} state is evaluated by applying the soft kaon theorem and vacuum saturation. When using a five-quark current including scalar and pseudo-scalar diquarks, the\textit{ KN }contribution turns out not to be very important and the previous result of the negative parity $\Theta ^{+}$ is reproduced again. The Borel analysis of the correlation function for $\Theta ^{+}$ with the \textit{KN} continuum states subtracted yields the mass of the J$^{P}$= 1/2$^{-} \quad \Theta ^{+}$ around 1.5 GeV. [Preview Abstract] |
Wednesday, September 21, 2005 10:15AM - 10:30AM |
EE.00006: Two-Hadron-Irreducible Qcd Sum Rule for Pentaquark Baryon Osamu Morimatsu, Yoshihiko Kondo, Tetsuo Nishikawa We point out that naive pentaquark correlations function include two-hadron-reducible contributions, which are given by convolution of baryon and meson correlation functions and have nothing to do with pentaquark. We show that the two-hadron- reducible contributions are large in the operator product expansion of the correlation functions of three existing works on the pentaquark. Therefore, it is dangerous to draw a conclusion from the sum rules using naive pentaquark correlation functions with naive ansatz for the spectral function under the dispersion integral. Instead, we propose to use the two-hadron- irreducible correlation function, which is obtained by subtracting the two-hadron-reducible contribution from the naive correlation function. [Preview Abstract] |
Wednesday, September 21, 2005 10:30AM - 10:45AM |
EE.00007: $\Lambda$(1405) as a pentaquark Sachiko Takeuchi, Kiyotaka Shimizu Recent findings of the strangeness +1 particle gives new light to q$^4{\overline{\rm q}}$ systems. Here we apply this method to investigate the features of the old but not-fully-understood baryon: $\Lambda$(1405). From the quark model view points, $\Lambda$(1405) has been considered as the flavor-singlet q$^3$ state with the orbital excitation. On the other hand, it has been reported that the state can also be understood as N${\overline{\rm K}}$ and $\Sigma \pi$ states [1]. Recent works of hyperuclei also suggest that $\Lambda$(1405) may have a more complicated structure than a simple baryon [2]. It is known that the N${\overline{\rm K}}$ (TJ$^P$)=(0 1/2$^-$) state does not have a repulsion from the color-magnetic interaction, CMI. By introducing the mixing among the q$^4{\overline{\rm q}}$ flavor multiplets, we have found that there are two states where CMI are strongly attractive and may form a resonance below the N${\overline{\rm K}}$ theshold. It is also interesting what kind of states they become when the system is bound in nuclei. In the present talk, we will discuss the features of the q$^4{\overline{\rm q}}$ systems with the strangeness $-$1 (TJ$^P$)=(0 1/2$^-$), and argue that this component may be important and should be mixed to the q$^3$ state.\\ \noindent {}[1] V.K.Magas, {\it et.al.}\ hep-ph/0503043.\\ {}[2] T.Suzuki, {\it et.al.}\ PL{\bf B597}(04)263; Y.Akaishi and T.Yamazaki, PR{\bf C65}(02)044005. [Preview Abstract] |
Wednesday, September 21, 2005 10:45AM - 11:00AM |
EE.00008: Magnetic moment of $\Lambda(1405)$ as a S-shell pentaquark Takashi Inoue \def \mate<#1|#2|#3>{\mbox{$\langle {#1}|\,{#2}\,|{#3}\rangle$}} Many theoretical interpretations have been given for exotic baryons, $\Theta^+$ and $\Xi^{--}$ in various scenarios: chiral quark soliton, hadron bound state, valence pentaquark and so on. The simplest pentaquark model is the S-shell pentaquarks where all quarks and an anti-quark are in the ground S-wave state. There is an experimental indication of the $\Theta^+$ being iso- scalar. If we take this indication into S-shell pentaquarks, the $\Theta^+$ become a member of flavor SU(3) anti-decuplet with $J^P = 1/2^-$ and $3/2^-$. In this model, there are also accompanying flavor SU(3) octets with $J^P = 1/2^-$ and $3/2^-$. These octets include one $\Lambda$ hyperon as the ground state octet. The structure of observed $\Lambda(1405)$ with $J^P=1/2^-$ have been given in scenarios: p-wave excited 3-quark, meson-baryon quasi-bound state and so on. Now, we have one another scenario: a S-shell pentaquark. In this paper, we study $\Lambda(1405)$ in this scenario, especially its magnetic moment. Magnetic moment of the $\Lambda$ pentaquark is given by $\mu_{\Lambda} = \sum_{i=1}^{5} \mate<\Lambda| \hat{\mu}_i Q_i \sigma_i^3 |\Lambda>$ because all valence particles are in the ground state S-wave orbit. Using the fit to ground state baryons, we obtain $\mu_{\Lambda (1405)} = 0.427 \mu_N$. This prediction is in contrast with that of p-wave excited 3- quark model: $\mu_{\Lambda(1405)} = -0.13 \mu_N$. It is interesting that the present result agree with the prediction $\mu_{\Lambda(1405)} = +0.25 \sim 0.45 \mu_N$ in the meson-baryon resonance approach. It seems natural because both two approaches share five-quark valence contents for the hyperon. Further discussions will be given at the conference. [Preview Abstract] |
Wednesday, September 21, 2005 11:00AM - 11:15AM |
EE.00009: Measurement of charged $\overline{\Sigma}$ Baryons at RHIC-PHENIX Christopher Pinkenburg The PHENIX experiment at RHIC has the ability to detect the annihilation signal of anti neutrons with its highly segmented large acceptance electromagnetic calorimeter. Utilizing this capability, a measurement of $\overline{\Sigma}^{\pm}\rightarrow\overline{n}\pi^{\pm}$ is technically feasible. Charged pions are measured in the central arm spectrometer of the PHENIX detector which provides excellent particle identification up to high transverse momentum. The major challange of this analysis is therfore to understand the response of the PHENIX electromagnetic calorimeter for anti neutrons which is currently derived from the observed response for identified anti protons. Over the last years PHENIX took high statistics datasets for a variety of systems (p-p, d-Au, Cu-Cu, Au-Au) at various energies. This provides an ideal basis for the development of such an analysis. Due to the similarity of the measurement this analysis can serve to set an upper limit on a possible anti--Pentaquark production ($\overline{\Theta}^- \rightarrow\overline{n}K^-$). We will present the method and the current status of the analysis. [Preview Abstract] |
Wednesday, September 21, 2005 11:15AM - 11:30AM |
EE.00010: Nucleon structure from lattice QCD with domain wall fermions quarks Shigemi Ohta We review RBC lattice numerical calculations of nucleon structure with domain wall fermions (DWF) quarks. DWFs allow arbitrarily accurate and continuum-like chiral and flavor symmetries at finite lattice spacing. This allows fully non-perturbative renormalization of relevant currents. Helped also by rectangular improved DBW2 gauge action that facilitates the use of DWF at relatively coarser lattice spacings, the RBC Collaboration have successfully reproduced such quantities as the ratio of isovector vector and axial charges, $(g_A/g_V)$, and the ratio of the first moments of structure functions ($\langle x \rangle_{u-d}/\langle x \rangle_{\Delta u - \Delta d$). First moments of some other structure functions are calculated as well. And 2-flavor dynamical domain wall results exist for many of these quantities, though some of them are yet to be renormalized. [Preview Abstract] |
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