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 CG: Electromagnetic Interactions I |
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Sponsoring Units: DNP JPS Chair: Marc van der Haeghen, College of William and Mary Room: Ritz-Carlton Hotel Plantation 2 |
Tuesday, September 20, 2005 2:00PM - 2:15PM |
CG.00001: A Study of the Spin Dependence of Pion Electro-Production near the $\Delta$-Excitation Region Yuan Xiao The BLAST collaboration recently finished an experiment measuring the spin dependence of pion electro-production near the $\Delta$-excitation region. The experiment used the polarised electron beam from the MIT-Bates Linear Accelerator Facility and a target of vector polarized atomic hydrogen produced by an Atomic Beam Source (ABS). The polarized hydrogen was injected into an internal target cell on the South Hall Electron Storage Ring. Data for various kinematics and different reaction channels were collected simultaneously by the BLAST (Bates Large Acceptance Spectrometer Toroid) detector. By flipping the target spin direction and the electron beam helicity, asymmetries were constructed from the measured rates with different spin combinations. The resulting asymmetries were obtained for longitudinal and transverse target spin orientations (with respect to the momentum transfer direction) and cover an invariant mass ($W$) range of 1.1 to 1.4 $GeV/c^{2}$. With less background and fewer assumptions than results from other inclusive channels, this spin depend study of the exclusive channels, pion electro-production near the $\Delta$-excitation region, will cast light on the spin structure of protons. Preliminary experimental results of spin-correlated parameters and a comparison between the experiment and a unitary iosbar model (MAID) will be presented. [Preview Abstract] |
Tuesday, September 20, 2005 2:15PM - 2:30PM |
CG.00002: Progress in 3N Response Functions Using the LIT Technique Edward Tomusiak, Victor Efros, Winfried Leidemann, Giuseppina Orlandini Our earlier results \footnote{V.D.Efros, W.Leidemann, G.Orlandini, E. Tomusiak, Phys.Rev. C69 (2004) 044001} for the longitudinal response functions of $^3$He and $^3$H began to display frame dependence at q=500 MeV/c. This is a manifestion of the non- relativistic framework of our calculations. We have found a method of extending such calculations to regions of higher q while drastically reducing the frame dependence. The method hinges on the choice of a particular frame and/or the details of the kinematical input. Results for the longitudinal response will be shown for q up to 700 MeV/c. In addition we will show our results to date for the transverse response functions of the trinucleons. [Preview Abstract] |
Tuesday, September 20, 2005 2:30PM - 2:45PM |
CG.00003: Magnetic moment of the Delta(1232)-resonance in chiral EFT Vladimir Pascalutsa, Marc Vanderhaeghen The $\Delta(1232)$-isobar is the most distinguished and well-studied nucleon resonance. However, such a fundamental property as its magnetic dipole moment (MDM) has thusfar escaped a precise determination. The problem is generic to any unstable particle whose lifetime is too short for its MDM to be measurable in the usual way through spin precession experiments. A measurement of the MDM of such an unstable particle can apparently be done only indirectly, in a three-step process, where the particle is first produced, then emits a low-energy photon which plays the role of an external magnetic field, and finally decays. In this way the MDM of $\Delta^{++}$ is accessed in the reaction $\pi^+ p \to \pi^+ p \gamma$ while the MDM of $\Delta^+$ can be determined using the radiative pion photoproduction ($\gamma p \to \pi^0 p \gamma^\prime$). In this paper we will present a new chiral effective field theory calculation of the radiative pion photoproduction ($\gamma p \rightarrow \pi^0 p \gamma'$) in the $\Delta$-resonance region. This work is aimed at a model-independent extraction of the $\Delta^+$ magnetic moment from new precise measurements of this reaction. It also predicts the chiral behavior of $\Delta$'s magnetic moment, which can be used to extrapolate the recent lattice QCD results to the physical point. [Preview Abstract] |
Tuesday, September 20, 2005 2:45PM - 3:00PM |
CG.00004: Electroproduction of pi0 from Delta(1232) at high Q2 with CLAS Maurizio Ungaro, Paul Stoler We report the analysis of exclusive single $\pi^0$ electroproduction in the $\Delta(1232)$ resonance region at Jefferson Lab in the $Q^2$ range 2 to 5 $GeV^2/c^2$. The electron beam energy was $5.75$ $GeV$, impinging on a cryogenic Hydrogen target. The CLAS spectrometer was used to detect the scattered electrons and final state protons, and the $\pi^0$'s were reconstructed by the missing mass technique. $\pi^0$ angular distributions are obtained over the entire $4 \pi$ $cm$ solid angle. The c.m. differential cross section ${d\sigma}/{d\Omega^*_{\pi^0}}$ is measured, the $M_{1+}$, $R_{em} = E_{1+}/M_{1+}$ and $Rsm = S_{1+}/M_{1+}$ multipoles for the delta resonance are extracted using the JANR unitary isobar model, along with the form factor $G^*_M$. [Preview Abstract] |
Tuesday, September 20, 2005 3:00PM - 3:15PM |
CG.00005: New Measurements of the Low $Q^2$ Behavior of the $\gamma^*p\rightarrow\Delta$ Reaction Sean Stave Data were taken using a polarized electron beam at the Mainz Microtron for the $ p(\vec{e}, e^{'} p)\pi^{0}$ reaction in the $\Delta$ region at $Q^{2} = 0.06~{\rm GeV}^{2}$ utilizing out of plane magnetic spectrometers. Results for the EMR = E2/M1 and CMR = C2/M1 ratios and the magnitude of the M1 amplitude will be shown and compared with reaction models. Non-zero quadrupole amplitudes demonstrate non-spherical components in nucleon and $\Delta$ structure. The data test the dynamical model descriptions of the $Q^2$ evolution in the long range, low $Q^2$ region where the pion cloud is predicted to be primarily responsible for non-spherical structure components. The EMR and CMR are extracted using resonant multipole fits of the separated cross sections $\sigma_{0} \equiv \sigma_{T} + \epsilon \sigma_{L}, \sigma_{TL}, \sigma_{TT}$. Background multipoles are tested through measurement of the fifth structure function $\sigma_{TL^{'}}$. The experiment was performed by an Athens, Mainz A1, and MIT collaboration. [Preview Abstract] |
Tuesday, September 20, 2005 3:15PM - 3:30PM |
CG.00006: Separated Structure Functions in $K^+\Lambda$ and $K^+\Sigma^0$ Electroproduction Daniel S. Carman Data analysis from an extensive program of kaon electroproduction from the proton utilizing electron beams from 2.5 to 5.7~GeV is presently underway in Hall B at Jefferson Laboratory. Cross sections for the $K^+\Lambda$ and $K^+\Sigma^0$ final states have been measured using the CLAS spectrometer. The data reported here were collected at beam energies of 2.6 and 4.2~GeV and span a range of kinematics in $W$ from threshold to 2.5~GeV, $Q^2$ from 0.5 to 2.5~(GeV/c)$^2$, while covering nearly the full center-of-mass angular range for the kaon. As part of this analysis, the structure functions $\sigma_U = \sigma_T + \epsilon \sigma_L$, $\sigma_{TT}$, and $\sigma_{LT}$ have been extracted from the $\phi$- and $\epsilon$-dependent differential cross sections. These structure functions have strong sensitivity to disentangle the resonant contributions in the $s$, $t$, and $u$ reaction channels from the non-resonant strength. Differences in the production dynamics for the $\Lambda$ and $\Sigma^0$ hyperons will be discussed and the data will be compared with available theoretical calculations for these processes. These measurements are part of the larger $N^*$ program of CLAS. [Preview Abstract] |
Tuesday, September 20, 2005 3:30PM - 3:45PM |
CG.00007: Measurement of $\sigma_T$, $\sigma_L$, and the ratio $\sigma_L/\sigma_T$ in kaon electroproduction using CLAS Brian Raue Measurements of the differential cross section $\frac{d\sigma}{d\Omega_K}$ for $p(e,e'K^+)\Lambda/\Sigma^0$ have been done using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The data were taken with beam energies of 2.567, 4.056, and 4.247 GeV and covered the kinematic ranges of $0.5\leq Q^2\leq 2.5$ GeV$^2$ and $W$ from threshold up to 2.5 GeV. The overlap in $Q^2$ and $W$ for the different beam energies allows a separation of the longitudinal and transverse contributions to the unpolarized cross section. The separation was done using both the Rosenbluth technique and a simultaneous $\epsilon-\phi$ fit. These results cover a wide range of $\cos\theta_K^*$ and are the first to include measurements away from $\cos\theta_K^*=1$. The results of this analysis will be compared to previous results obtained by Rosenbluth separations as well as results obtained from hyperon transferred polarization measurements at 2.567 GeV. We will also show comparisons to current theoretical descriptions of kaon electroproduction and discuss the implications. [Preview Abstract] |
Tuesday, September 20, 2005 3:45PM - 4:00PM |
CG.00008: Photoproduction of neutral kaons on deuterons in the threshold region Kyo Tsukada Until now, the investigation of kaon photo-/electro-production have been carried out in $p(\gamma, K^+)\Lambda$, $p(\gamma,K^+)\Sigma^0$ and $p(\gamma,K^0)\Sigma^+$ reactions among six isospin channels. However, no data have been measured for the other three channels on a neutron. The elementary processes of strangeness photoproduction are far from well understood. It is believed that measurements of these three strangeness production channels provide much information on the strangeness photoproduction mechanism. In particular, the $n(\gamma,K^0)\Lambda$ reaction is expected to play an essential role since it is unique in the sense that no charge is involved. Therefore, we carried out the experiment of the $d(\gamma,K^0)$ reaction in the threshold region, $E_\gamma = 0.8 \sim 1.1$ GeV. $K^0$'s were measured in $\pi^+ \pi^-$ decay mode by Neutral Kaon Spectrometer (NKS) which we installed in the Laboratory of Nuclear Science of Tohoku University (LNS-Tohoku). $K^0$ momentum spectra were compared with theoretical spectra calculated assuming representative isobar models. The present experiment demonstrated a usefulness of neutral kaon detection for the investigation of photo strangeness production reaction. [Preview Abstract] |
Tuesday, September 20, 2005 4:00PM - 4:15PM |
CG.00009: $\Lambda$ photoproduction on the neutron Pawel Nadel-Turonski Of the two elementary $\gamma $n $\to $ K$\Lambda $ reactions, the $\gamma $p $\to $ K$^{+}\Lambda $ channel has been studied extensively, but for $\gamma $n $\to $ K$^{0}\Lambda $ there are no data at all. It is very important to measure the cross section for this latter process because this production channel is one of the main reaction channels that can be used to identify missing N* resonances.$^{1}$ We have measured exclusive K$^{0}\Lambda $ photoproduction by detecting all four charged particles from the K$^{0} \quad \to \quad \pi ^{+}\pi ^{-}$ and $\Lambda \quad \to $ p$\pi ^{-}$ decays and reconstructing the invariant masses of both strange particles. The experiment was performed in Hall B at Jefferson Lab using tagged photons having energy up to 3.6 GeV and a liquid deuterium target. Events where the proton is a spectator were clearly identified. The recoil polarization of the lambda was also measured. $^{1}$ T. Mart and C. Bennhold, Phys. Rev. C \textbf{61}, 012201 (2000) [Preview Abstract] |
Tuesday, September 20, 2005 4:15PM - 4:30PM |
CG.00010: $\eta$ electroproduction at high momentum transferred with CLAS Maurizio Ungaro, Kyungseon Joo This analysis presents high quality angular distributions of the $p(\vec{e}, e'p)\eta$ reaction for full coupled-channel analysis purpose. The c.m. differential cross section ${d\sigma}/{d\Omega^*_{\eta}}$ will be extracted, and the unpolarized $\sigma_T$, $\sigma_L$, $\sigma_{LT}$, $\sigma_{TT}$ will be calculated. The measurement of the polarized longitudinal-transverse structure function $\sigma_{LT'}$ will provide new and useful information for untangling the $N^*$ states and to probe the interference between resonant and non-resonant processes. The CLAS spectrometer was used to detect the scattered electrons and final state protons, and the $\eta$'s were reconstructed by the missing mass technique. The angular distributions are obtained over the $4 \pi$ $c.m.$ solid angle. The beam polarization was $\sim 70\% $. \\ Preliminary data will be discussed. [Preview Abstract] |
Tuesday, September 20, 2005 4:30PM - 4:45PM |
CG.00011: Measurement of the $\pi^+$-meson polarizabilities via the $\gamma p \to \gamma \pi^+ n$ reaction D.L. Hornidge, R. Beck, D. Krambrich, M. Rost, Th. Walcher, S.N. Cherepnya, L.V. Fil'kov, V.L. Kashevarov, I. Giller, M. Moinester An experiment on the radiative $\pi^+$ meson photoproduction from the proton ($\gamma p \to \gamma \pi^+ n$) was carried out at the Mainz Microtron MAMI in the kinematic region 537~MeV $< E_\gamma <$ 817~MeV, $140^\circ \le \theta^{cm}_{\gamma\gamma^\prime} \le 180^\circ$. The $\pi^+$ meson polarizabilities have been determined from a comparison of the data with the predictions of two different theoretical models. Validity of the models has been verified by comparing the predictions with the present experimental data in the kinematic region where the pion polarizability contribution is negligible and where the difference between the predictions of the two models does not excede 3\%. Results will be presented and discussed. [Preview Abstract] |
Tuesday, September 20, 2005 4:45PM - 5:00PM |
CG.00012: Longitudinal and Transverse Response Functions from Kaon Electroproduction off Hydrogen Pete Markowitz Exclusive H(e,e'K)Lambda data were taken in 2001 - 2002 in Hall A at the Thomas Jefferson National Accelerator Facility during experiment E98-108. Electrons and kaons were detected in coincidence with the two High Resolution Spectrometers (HRS) in Hall A. The kaon arm was specially equipped with two aerogel \c{C}erenkov threshold detectors, designed to separately provide pion and proton particle separation thus allowing kaon identification. Data were taken close to t=t$_{min}$, or at a minimum angle between the kaon and the virtual photon, $\theta _{CM}^{k\gamma }$ $\Rightarrow $ 0. This talk presents the final results of a Rosenbluth separation of the cross section and the longitudinal and transverse responses. The data have been compared to calculations using various kaon electromagnetic form factors. Longitudinal and transverse responses show separate sensitivity to varying the form factor at the kinematics of the experiment. This comparison constrains the kaon form factor, albeit in a model dependent fashion. [Preview Abstract] |
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