Session E7: Hadronic Physics I

Exclusive Kaon Electroproduction in Hall C at JLab

The additional flavor degree of freedom in the H(e,e'K+)$\Lambda $ and H(e,e'K+)$\Sigma $0 reactions provides a unique opportunity to study the reaction mechanism underlying strangeness production and the transition from hadronic to partonic degrees of freedom in exclusive processes. However, due to experimental challenges the potential of these reactions has not been fully unexploited to date. One such challenge is the separation of kaons from pion and proton backgrounds. At high momenta, a kaon aerogel Cerenkov detector is the simplest and most economical way of addressing this issue. At CUA, we are building such a detector for Hall C ~at the 12 GeV Jefferson Lab. Desirable properties are high light output for kaons, and good efficiency in the collecting and converting the light using cost-effective PMTs. Computational optimizations using simulations have been performed and component testing has begun. In this talk, I will discuss the importance of kaon production for hadron structure and the detectors needed to address the experimental challenges.   

Measuring two-photon exchange in elastic electron-proton scattering with OLYMPUS

Polarization-transfer measurements of the ratio of the proton's electric and magnetic form factors disagree substantially at large momentum-transfers from ratios obtained through unpolarized experiments. This discrepancy may be resolved by additional contributions to the elastic cross-section beyond the single-photon Born Approximation. The OLYMPUS experiment will test this hypothesis by measuring the two-photon contribution to elastic scattering. This contribution will be detected by measuring the ratio of cross-sections for electron-proton to positron-proton elastic scattering in the Q$^{2}$ range 0.5--2.5~GeV/c$^2$ at DESY, in Hamburg, Germany. Installation of the OLYMPUS experiment in the DORIS storage ring is under way in anticipation of dedicated running in the spring of 2012. A description of the experiment as well as a status report will be presented.   

Pair-Symmetric Background of Spin Asymmetries of the Nucleon Experiment (Jefferson Lab E07-003)

The Spin Asymmetries of the Nucleon Experiment (SANE) at the Thomas Jefferson Lab National Accelerator Facility measured inclusive double spin asymmetries by scattering longitudinally polarized electrons on a longitudinally and transversely polarized NH3 target. The measurements were done at momentum transfer of 2.5 $\le $ Q$^{2 }\le $ 6.5 GeV$^{2}$ and Bjorken x of 0.3 $\le $ x $\le $ 0.8. Data were also taken at 0.2 $<$ x $<$ 0.3. Preliminary analysis of the pair-symmetric background used to extract asymmetries from this low x data will be discussed.   

Charged Particle Tracking for the GlueX Detector

The GlueX experiment is a new experiment under construction at the Thomas Jefferson National Accelerator Facility designed to study gluonic degrees of freedom via the production of ``hybrid'' mesons with exotic quantum numbers. At full luminosity, the trigger rate is expected to be on the order of 150 kHz and the data rate to tape is expected to be on the order of 300 MB/s. In order to reduce the reconstruction time, the current GlueX analysis framework is multi-threaded such that multiple events can be analyzed in parallel on multi-core machines. The tracking code presents the largest bottleneck in the event reconstruction. By taking advantage of Single-Instruction, Multiple-Data (SIMD) instructions in the three-vector and matrix operations needed in the tracking code, the reconstruction can be sped up considerably. The current status of the tracking reconstruction for GlueX will be presented.   

Offline Computing for the GlueX Experiment at Jefferson Lab

The GlueX Experiment in Hall D at Jefferson Lab is scheduled to start commissioning in the Summer of 2015. The new detector will record events created with a new beamline that will deliver tagged, coherent bremsstrahlung photons with an endpoint of 11 GeV and a prominent coherent peak at 9 GeV. Reconstruction software will have to output both charged and neutral particles. To facilitate a partial wave analysis of final states, high-single particle efficiency will be required. The general approach to offline software will be presented, including resource requirements and technology choices.   

Strangeness photoproduction near the threshold at ELPH-Tohoku

Strangeness photoproduction processes near the threshold offers invaluable opportunity for the investigation of hadron structure and coupling constants that involve strangeness in hadron physics. The process had been intensively studied by measuring $K^{+}$ such as $\gamma+p \to K^{+}+\Lambda (\Sigma^{0})$. However, there had been no reliable data on the neutron and the theoretical investigation suffered seriously from the lack of the data. We have been making an effort to measure the $\gamma+d \to K^{0}(\Lambda)$+X reaction in the $\pi^{+}\pi^{-}$ (p$\pi^{-})$ decay channel of $K^{0}_{S}(\Lambda)$, using a liquid D$_{2}$ target and internally-tagged photon beams (E$_{\gamma }$= 0.8-1.1 GeV) at Research Center for Electron Photon Science (ELPH), Tohoku University. Having succeeded to collect exploratory data of $K^{0}$ with the original NKS spectrometer [1], we have renewed the spectrometer (NKS2) and taken data in 2005-2007, obtaining the differential and total cross-section of $K^{0}_{S}$ and $\Lambda$. The results are compared with recent theoretical studies (Isobar models and a Regge-plus-resonance model). The comparison suggests a backward angular distribution of $K^{0}_{S}$ in CM. Further upgrade of the NKS2 spectrometer specifically in the vertex region has been completed and the data taking is under way. \\[4pt] [1] K. Tsukada et al., Phys.Rev.C78 (2008) 014001, and Erratum 2011   

Search for Missing Resonances in $\gamma p\to K^+\Lambda$ using circularly polarized photons on longitudinally polarized target

Focus in the search for missing baryon resonances has been directed toward the prospect of performing a full partial wave analysis using all single and double polarization observables across multiple decay channels. In particular, the possibility of resonances coupling strongly to decay channels with strangeness is encouraging. Double polarization data has been taken in Jefferson Lab's CLAS detector using circularly polarized photons on a longitudinally polarized frozen-spin butanol target. Measurements of the double polarization observables $E$ (beam-target) and $L_x$ and $L_z$ (target-recoil) for the $\gamma p\to K^+\Lambda$ channel will be presented and compared with model predictions.   

Preliminary Measurement of Longitudinal Spin Asymmetry $A_1^{^3He}$

Recent measurements of the nucleon-virtual photon longitudinal spin asymmetry $A_1$ for the proton and neutron have called into question the perturbative QCD prediction that the ratio of polarized-to-unpolarized down-quark PDFs, $\Delta d/d$, approaches 1 at large $x$. As part of Experiment E06-014 in Hall A of Jefferson Lab, double-spin asymmetries were measured in the scattering of a polarized electron beam from a polarized $^3$He target in the deep inelastic scattering region, allowing the eventual extraction of the neutron asymmetry $A_1^n$. We will discuss our analysis of data with beam energies of 5.9 and 4.7 GeV and present preliminary results for the nuclear asymmetry $A_1^{^3He}$ as measured with 4.7-GeV electrons for $0.2 < x < 0.65$ and $2$ GeV$^2 < Q^2 < 5$ GeV$^2$. Once corrections for nuclear effects have been completed, the resulting measurements of $A_1^n$ will provide a test of previous experimental results in advance of anticipated data from upcoming experiments at Jefferson Lab.   

Pion Structure from Lattice QCD

We present moments of the quark distribution functions of the pion, $$, from lattice QCD. The calculation is done for a range of pion masses between 290 and 500 MeV with attention to effects caused by the nonzero lattice spacing and finite volume. We also investigate how the pion structure is modified within a Bose-condensed medium of either pions or kaons. This modification is the mesonic analog of the EMC effect, which we hope to explore for light nuclei in the future.