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Nuclear Interaction Group - Research Highlights, 2005~2006 Introduction Bates JLab MAINZ Posters INTRODUCTION At the Nuclear Interactions Group (NIG), we carry out our research at Bates, Mainz and JLab. We are sponsors of many experiments at these facilities and our group provides a great deal of the leadership for the programs. Our work includes substantial and novel facility development as part of a collaborative contribution. The major thrusts of our research program are: Structure of the Nucleon, Free and Bound: at Bates & JLab The nucleon and its structure is simply another component of the strong interaction many-body problem and its study is integrated into the program as a free and as a bound nucleon. It must be understood from both points of view to extract with precision the currents in complex nuclei. The Two-Body Problem and It's Currents: at Bates & JLab The two-body system is fundamental to an understanding of the interactions and currents needed in the structure of more complex systems. The progression through the three- and four-body systems is essential because these add growing complexity and can be calculated with the greatest precision. Testing Modern Models of Light Nuclei:  at Bates, Mainz & JLab The Spin Structure of the Nucleon:  at JLab  Study of the nucleon spin structure of the nucleon, espically the contribution from valence quarks, could reveil the source of nucleon spin, you can find an interesting story about it from our previous Ph.D. student. Multi-Nucleon Currents and Correlations in Nuclei. at Bates & JLab  The nucleon-nucleon short-range correlations are responsible for approximately 40% of the nuclear wave function and we know essentially nothing about these structures and the associated currents. This page summarizes all activities we have participated in since year 2004. Previous activities can be found in "Privious Programs". go to top MIT-BATES At the MIT-Bates Laboratory, the entire year of 2004 was devoted to data taking with the BLAST detector. Our student, Chi Zhang, has obtained the most precise and extensive data set on the tensor polarization of the deuteron, T20, induced by elastic electron scattering. The preliminary data, together with the world data and several theoretical predictions of this quantity as a function of the transferred momentum are displayed in right. T20 is a fundamental quantity that is required for the separation of the elastic electric and quadrupole form factors of the deuteron. It provides stringent conditions on theoretical models. (* click figure to enlarge) Our second student at Bates, Yuan Xiao, has obtained the first data set of the double-polarization (in this case, both beam and target are polarized) asymmetry in the electroproduction of pi+ off the proton in the Delta(1232) resonance region. These unique data are important to the understanding of the small quadrupole amplitudes in the gamma* p -> Delta+ -> pi+ n, the isospin partner of the more commonly-studied gamma* p -> Delta0 -> pi0 n transition. These very preliminary data are displayed together with predictions of 2 commonly-used models, MAID2003 and that of Sato-Lee. go to top Jefferson Lab Scientists from across the country and around the world visit the Thomas Jefferson National Accelerator Facility to advance mankind's understanding of the atom's nucleus and thus of matter itself.  Their tools for probing nuclei are: continuous beams of high-energy electrons from CEBAF - Jefferson Lab's unique Continuous Electron Beam Accelerator Facility - and the advanced particle-detection and ultra-high-speed-data acquisition equipment in CEBAF's three experimental halls. You can find more interesting stuff through Nuclear Physics at Jefferson Lab. At JLab, we have performed two experiments in 2005. Our student, Yi Qiang, has performed in Hall A the best resolution (approximately 3.5 MeV), most precise and most extensive search to date of 3 pentaquark partners of the Theta+, experiment E04-012. The existence of the latter, as well of its anti-decuplet partners is one of the most hotly debated issues in nuclear physics. Mr. Qiang was able to put preliminary upper limits on the electroproduction cross sections of the Theta++(1540), N0(1650) and Sigma0(1750) - 3nb, 8nb, and 11nb respectively. We note that the production cross section for the Theta+ as reported by CLAS, another large collabration in Jefferson Lab Hall B, is about 50nb. In this context, the fact that the electroproduction cross sections of these three partners are so low provides a significant input to this debate. Our student, Peter Monaghan, has just completed his experiment aimed at studying the short-distance behavior in nuclei by using the triple-coincidence 12C(e,e'pp) and 12C(e,e'pn) reactions. This experiment E01-015 in Hall A employed favorable kinematics including high transferred momentum, Q2, and high xB (1.2-1.3), the Bjorken scaling variable, in order to minimize competing processes that plagued previous measurements.The (e,e'p) process was measured with the aid of the standard 2 high-resolution spectrometer configuration in Hall A. The second proton in the (e,e'pp) reaction was detected with the Bigbite spectrometer, newly constructed and commissioned for the purpose of this measurement (and many future ones). The neutron in the (e,e'pn) reaction was detected with a neutron wall, constructed specifically for the purpose of this measurement as well. These major undertakings, in which our group played a major role, were well worth it as triple-coincidence events with both protons and neutrons were observed already "on line". Very preliminary and partial data of triple coincidence with both protons and neutrons are displayed. The timing peak for pp correlated events can be seen in TDC channel 2500 (left panel), and that of the np peak in channel 300 (right panel). These values were set arbitrarily. go to top Mainz Microtron (MAMI) Studies on 3He and 4He nuclei have also been the subject of a comprehensive research program at MAMI where we are members of the A1 collaboration which operates three high-resolution magnetic spectrometers suitable for precise measurements of nuclear structure and reactions.  The response of these nuclei to longitudinally and transversely-polarized virtual photons are sensitive to components of the wave functions that are not generated by mean field and to details of the electromagnetic nuclear currents.  Data over a wide kinematical range provide accurate tests for modern model of electromagnetic interactions with three- and four-nucleon systems.  The laboratory has high quality beam characteristics and detection apparatus similar to those of JLAB, albeit at a maximum beam energy of 1.5 GeV, and it has been undergoing a major upgrade which is near completion.  Additional experiments on these and other nuclear and nucleon targets are planned at a time scale relevant to new incoming graduate students. go to top Poster Collection Posters for Measurement of A1n at large xB Posters for Short Range Correlation Posters for Pentaquark Partners go to top