Bulletin of the American Physical Society
2006 Division of Nuclear Physics Annual Meeting
Wednesday–Saturday, October 25–28, 2006; Nashville, Tennessee
Session GA: Topics In Nuclear Physics |
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Sponsoring Units: DNP Chair: Richard Milner, Massachusetts Institute of Technology Room: Gaylord Opryland Tennessee C |
Saturday, October 28, 2006 9:00AM - 9:36AM |
GA.00001: The Diffuse Supernova Neutrino Background Invited Speaker: The cosmic stellar birth rate can be measured by standard astronomical techniques. It can also be probed via the cosmic stellar death rate, though until recently, this was much less precise. However, new results based on measured supernova rates, and importantly, also on the attendant diffuse fluxes of neutrinos and gamma rays, have become competitive, and a concordant history of stellar birth and death is emerging. The neutrino flux from all past core-collapse supernovae, while faint, is realistically within reach of detection in Super-Kamiokande, and a useful limit has already been set. I will discuss predictions for this flux, the prospects for neutrino detection, the implications for understanding core-collapse supernovae, and a new limit on the contribution of type-Ia supernovae to the diffuse gamma-ray background. [Preview Abstract] |
Saturday, October 28, 2006 9:36AM - 10:12AM |
GA.00002: First Physics Results from the MuCap Experiment at PSI Invited Speaker: The MuCap experiment will measure the rate of the muon capture reaction $\mu $ + p $\to $ n + $\nu $ on the free proton to 1{\%} precision. This directly determines the pseudoscalar form factor g$_{P }$at q$^{2}$ = -0.88 m$_{\mu}^{2}$ to 7{\%}. The pseudoscalar is the least well-known of the basic nucleon form factors characterizing the structure of its charged electro weak current. Modern effective theories based on the chiral symmetry of QCD and its breaking can calculate g$_{P}$ to 3{\%}. In spite of efforts spanning the last 30 years, experimental results are still controversial and subject to large uncertainties in their interpretation. While the first radiative muon capture experiment on hydrogen recently observed a four standard deviation discrepancy from the precise chiral prediction, new results on muonic atomic physics processes in hydrogen underscore the model dependence of the present g$_{P}$ determinations. The resulting uncertainty in g$_{P}$ is as large as 50 percent. The MuCap experiment is designed to overcome the problems that plagued earlier efforts. The method requires a combination of novel and challenging detector techniques. The capture rate will be determined from the difference of the $\mu ^{+}$ and $\mu ^{-}$ lifetimes measured after muons are stopped in a time projection chamber operating with 10 bar hydrogen gas. Electrons from muon decay are reconstructed with an electron tracking system. A sophisticated gas system maintains and monitors the ultra-high purity of the deuterium-depleted H$_{2}$ gas used as an active target. In 2004 the hardware for the complex detector was commissioned and 20{\%} of our final statistics was recorded. After additional performance upgrades in 2005, the experiment successfully reached the proposed goal of 10$^{10}$ events in 2006. The 2004 data analysis is at an advanced stage. The data surpass all previous experiments both in statistics and in reduction of systematic uncertainties. First results on the $\mu $p capture rate will be presented at this conference. As a possible second stage, we are exploring a precision measurement of the related muon capture reaction on deuterium. A measurement at the 1{\%} level could be compared with recent high-precision calculations, provide direct information on the two-nucleon axial current and calibrate fundamental neutrino reactions. [Preview Abstract] |
Saturday, October 28, 2006 10:12AM - 10:48AM |
GA.00003: Observation of unique radioactivity in spinning silver Invited Speaker: Radioactivity or spontaneous decay of atomic nuclei has been much studied ever since Becquerel discovered natural radioactivity in 1896. For proton-rich nuclei, one- and two-proton radioactivity were predicted in 1960 [1], with the former observed in 1982 [2]. Two-proton radioactivity has also recently been detected, e. g. by experimentally studying the decay of Fe-45 [3, 4], but identification of two protons is missing from these experiments. We have measured proton-proton correlations in two-proton radioactivity of the high-spin isomer (21+) in Ag-94 [5] which is also known to undergo one-proton decay [6] thus making the unique nuclear decay case. Striking 2p decay features are the proton-proton energy correlations and the unexpectedly large decay probability. These data can only be interpreted in a meaningful way by assuming simultaneous two-proton emission. Our results exclude sequential emission of protons via the intermediate nucleus Pd-93. The two-proton decay pattern can be explained by assuming that the parent nucleus is strongly cigar-like (prolate) deformed emitting the protons either from the same or from opposite ends of the cigar. This first measurement of correlations in 2p radioactivity, the nuclear-structure implications and plans for further experimental and theoretical studies of the properties of this truly exotic isomer will be presented. [1] Goldansky, V.I., Nucl. Phys. 19, 482 (1960). [2] Hofmann, S. et al., Z. Phys. A 305, 111 (1982). [3] Pfutzner, M. et al,. Eur. Phys. J. A 14, 279 (2002). [4] Giovinazzo, J. et al., Phys. Rev. Lett. 89, 102501 (2002). [5] I. Mukha et al., Nature 479, 298 (2006). [6] I. Mukha et al., Phys. Rev. Lett. 95, 022501 (2005). [Preview Abstract] |
Saturday, October 28, 2006 10:48AM - 11:24AM |
GA.00004: Deep Virtual Compton Scattering Results from Hall A at JLab Invited Speaker: At JLab Hall A, we have measured the $\vec{e} p \rightarrow e p \gamma$ reaction at $Q^2= 1.5$, $1.9$, and $2.3$ GeV$^2$. The amplitude for this reaction is the coherent superposition of the Compton (radiation from the target) and Bethe-Heitler (radiation from the electron) amplitudes. In the deep virtual Compton scattering (DVCS) limit of large $Q^2$ and small invariant momentum transfer $t$ to the target, the compton amplitude factorizes into the convolution of a perturbative hard scattering kernel with matrix elements of quark and gluon operators, known as generalized parton distributions (GPDs). Measurements of the GPDs can determine the transverse spatial profile of quarks and gluons, as a function of their lightcone momentum fractions $x$. We measured the $H(\vec{e},e\gamma)p$ cross sections for positive and negative beam helicity with good control of exclusivity and full acceptance in the azimuth of the final photon around the electron scattering momentum transfer direction ${\bf q}$. I will present our evidence for factorization, and our results for the Real and Imaginary parts of the BH$\cdot$DVCS interference. [Preview Abstract] |
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