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 DD: Mini-Symposium on Meson-Nucleus Systems and the Partial Restoration of Chiral Symmetry II |
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Chair: Kenneth H. Hicks, Ohio University Room: Kohala 4 |
Thursday, October 15, 2009 7:00PM - 7:30PM |
DD.00001: Meson Properties at Finite Density Invited Speaker: Quantum Chromodynamics (QCD), the theory of the strong interaction, has been remarkably successful in describing high-energy and short-distance-scale experiments involving quarks and gluons. However, applying QCD to low energy and large-distance-scale experiments has been a major challenge. The symmetries of QCD (such as Chiral Symmetry) provide guiding principles to deal with strong interaction phenomena in the non-perturbative domain. Various QCD-inspired models predict a modification of the properties of hadrons in nuclear matter from their free-space values. A review of experiments searching for the in-medium modifications of light mesons will be given trying to assess if they confirm or refute these theoretical predictions. The majority of experiments both with relativistic heavy-ion reactions as well as with elementary reactions observe a substantial broadening of the width of light vector mesons inside the nuclear medium, with no evidence of a mass shift. Several complementary high statistics experiments are planned at JLab, GSI, JPARC and RHIC to further study the properties of mesons in the medium. [Preview Abstract] |
Thursday, October 15, 2009 7:30PM - 7:45PM |
DD.00002: Formation of Slow Heavy Mesons in Nuclei Satoru Hirenzaki Meson - nucleus systems such as mesic atoms and mesic nuclei have been studied systematically for a long time. The binding energies and widths of these bound states provide us unique and valuable information on the meson-nucleus interactions. In addition, the measurements of light vector meson spectra in nucleus as the invariant mass of lepton pairs have also provided interesting information. So far, the properties of relatively light mesons have been studied well both theoretically and experimentally. In this contribution, to extend our studies to a domain of heavier mesons, we would like to report recent research activities on the formation of heavy mesons in nuclei with small momenta. We think it is very interesting to consider the in-medium properties of heavier mesons including heavy quark contents. As a first step to heavier mesons, we will report our studies on formation of slow $phi$ meson in nuclei. In-medium properties of $phi$ meson have been studied theoretically, which have close relation to $K$ and $K$-bar meson properties in medium because of the strong coupling of $phi$ to $K$ and $K$-bar. The study of QCD sum rule and the data taken at KEK suggested 3 percent mass reduction of $phi$ at the normal nuclear density, while the $phi$ meson selfenergy calculated in some effective models indicated a significantly smaller attractive potential for $phi$. We will show the calculated spectra for some reactions. [Preview Abstract] |
Thursday, October 15, 2009 7:45PM - 8:00PM |
DD.00003: Studying the Medium Effects of the $\omega$ and $\phi$ Mesons at JLab Michael Wood, Rakhsha Nasseripour, Chaden Djalali, Dennis Weygand The E01-112 experiment at Jefferson Lab (JLab) in Newport News, VA, USA is an investigation of the properties of the $\rho$, $\omega$, and $\phi$ mesons in dense nuclear matter. The vector mesons are produced by a high-intensity photon beam, with energies up to 4~GeV, incident on targets ranging from $^{2}$H to Pb. Using the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B at TJNAF, the mesons are reconstructed by means of their rare leptonic decay to $e^{+}e^{-}$, eliminating any hadronic final state interactions. These data make possible an analysis of the in-medium widths of the $\omega$ and $\phi$ mesons. The in-medium widths can be accessed by measuring the amount of absorption inside the nucleus. An increase in the in-medium $\omega$N and $\phi$N cross sections leads to an increase in the number of absorbed mesons. The signature of absorption is a decrease of the nuclear transparencies as a function of the number of target nucleons. The results indicate a substantial widening of the $\omega$ and $\phi$ mesons in the medium. The CBELSA/TAPS Collaboration has published transparency ratios for the channel $\omega \rightarrow \pi^{0}\gamma$, that also shows an increase in the in-medium width. The JLab results show a greater absorption than what was measured by CBELSA/TAPS. [Preview Abstract] |
Thursday, October 15, 2009 8:00PM - 8:15PM |
DD.00004: $\phi$ Meson Photoproduction on Nuclear Targets at Jefferson Lab Dennis Weygand Theoretical calculations predict a shift of vector meson masses within the nuclear medium due to partial restoration of chiral symmetry. Experimental data from KEK on the $\phi$ meson suggests such a shift. Experiment E01-112 at Jefferson Lab produced $\phi$ mesons using a tagged bremsstrahlung photon beam up to $4$ GeV incident on a range of nuclear targets. The $\phi$ mesons were observed via the rare leptonic $e^+e^-$ decay, which is devoid of final state interactions, as well as the dominant hadronic mode $K^+K^-$. As the $\phi$ decay is near the $K^{+}K^{-}$ production threshold energy, a small change in the meson mass will result in a sharp change in the ratio of the two branching ratios. Preliminary results will be shown. [Preview Abstract] |
Thursday, October 15, 2009 8:15PM - 8:30PM |
DD.00005: Development of GEM detectors for a large acceptance phi meson spectrometer Yosuke Watanabe, Kazuya Aoki, Hideto Enyo, Taku Gunji, Hideki Hamagaki, Yasuto Hori, Yusuke Komatsu, Shinichi Masumoto, Kyoichiro Ozawa, Tamotsu Sato, Michiko Sekimoto, Tomoya Tsuji, Kazuki Utsunomiya, Satoshi Yokkaichi New experiment is being proposed at J-PARC to study chiral properties and meson mass modification in nucleus. Mass modification of $\phi$ meson in nucleus can be considered as a signal of partial chiral symmetry restoration. Experimentally, the first observation of $\phi$ mass modification is reported by KEK-E325. However, several possibilities for the origin of the mass modification exist. Thus, the next generation experiments are highly required to distinguish several physics processes. For such purpose, large acceptance spectrometer and high intensity beam line are needed. We are developing a new spectrometer using GEM detectors to cover a large acceptance and cope with high counting rates. A prototype is reconstructed and tested using electron beam. Test experiments are performed at FUJI test beam line at KEK and at LNS GeV-Gamma beam line at Tohoku University. Detailed evaluation of position resolutions at several conditions is performed. Currently, a position resolution of 100 $\mu$m is achieved. We will report details of the proto type and results of beam tests. [Preview Abstract] |
Thursday, October 15, 2009 8:30PM - 8:45PM |
DD.00006: A development of a Hadron Blind Detector for J-PARC E16 experiment Kazuya Aoki, Hideto Enyo, Taku Gunji, Hideki Hamagaki, Yasuto Hori, Yusuke Komatsu, Shnichi Masumoto, Kyoichiro Ozawa, Tamotsu Sato, Michiko Sekimoto, Tomoya Tsuji, Kazuki Utsunomiya, Yousuke Watanabe, Satoshi Yokkaichi Spontaneous breaking of the chiral symmetry is considered to be the origin of hadron mass, however, the experimental confirmation is not given yet. J-PARC E16 experiment was proposed to investigate the origin of the mass through the mass modification of vector mesons in a finite density environment. The mass of the vector mesons are measured through electron-positron decay. A cherenkov detector with a high rate capability and fine segmentation is required for the electron identification. Hadron Blind Detector (HBD) is ideal for the purpose, which is a windowless cherenkov detector with a stack of GEMs on top of which CsI is evaporated. CF$_{4}$ works as amplification gas and cherenkov radiator in the HBD. We developed a prototype of HBD for J-PARC E16 experiment. It is constructed with a stack of an CsI-evaporated LCP-GEM with a thickness of 100$\mu$m and double kapton-GEMs with a thickness of 50$\mu$m. Very stable operation without severe damage from sparks is possible due to the lower voltage operation compared to triple 50$\mu$m kapton-GEMs. A beam test was performed with an electron beam at Tohoku Univ. The performance of the prototype will be reported and discussed. [Preview Abstract] |
Thursday, October 15, 2009 8:45PM - 9:00PM |
DD.00007: Relativistic chiral mean field model and chiral property of finite nuclei and nuclear matter Hiroshi Toki, Yoko Ogawa, Jinniu Hu We study the role of pion in finite nuclei and nuclear matter with the relativistic chiral mean field (RCMF) model. In the RCMF model, we use the linear sigma model Lagrangian, which contains the nucleon field and sigma and pion fields in chiral symmetric way. We introduce further the omega meson coupling in order to include necessary repulsion to form nucleus. We take first the mean field approximation and obtain meson fluctuation terms to be treated in the 2p-2h space so that the pion exchange interaction is fully taken into account. The pion exchange interaction provides major contribution to the nuclear binding. We calculate $^4$He, $^{12}$C and $^{16}$O and nuclear matter. For finite nuclei, we obtain more than a half of the attraction from the pion exchange interaction. We get an extra binding for $^{12}$C than $^{16}$O due to the pion exchange interaction coming from the Pauli-blocking effect. We find the nucleon mass is reduced about 20\% from the free space value in the interior of finite nuclei. We calculate also chiral condensate in nuclear matter, which has a similar behavior to the model independent expression as a function of density. This behavior agrees with the behavior of isovector s-wave parameter extracted from deeply bound pionic atoms. [Preview Abstract] |
Thursday, October 15, 2009 9:00PM - 9:15PM |
DD.00008: Softening of the dynamical $\sigma$ meson Tetsuo Hyodo, Daisuke Jido, Teiji Kunihiro We study the structure of the lowest lying scalar meson with $I=J=0$, the sigma meson, through the softening phenomena associated with partial restoration of chiral symmetry. We formulate two-flavor dynamical chiral models with a finite pion mass to describe the $\pi\pi$ scattering. Several structures of the sigma meson can be realized, such as the chiral partner of pion, or a dynamically generated resonance by $\pi\pi$ attraction. We show that, when the chiral symmetry is partially restored, the dynamically generated sigma meson shows qualitatively different softening pattern from the behavior of the chiral partner, reflecting the nature of an s-wave resonance. Investigating the properties with large symmetry restoration, we find that the mass of the dynamical sigma meson approaches the pion mass and that the coupling to $\pi\pi$ scattering state is proportional to the pion mass. Although the dynamical sigma meson consists of mesonic molecule, the behavior near the restoration limit is similar to that of the chiral partner. This suggests an interesting possibility of the dynamical sigma meson as the chiral partner of the pion. [Preview Abstract] |
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