Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session X11: Precision Measurements of Nucleons and Nuclei |
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Sponsoring Units: DNP Chair: Dave Mack, Jefferson National Laboratory Room: Marriott Tampa Waterside Room 7 |
Tuesday, April 19, 2005 10:45AM - 11:21AM |
X11.00001: Probing Medium Effects on Hadronization in Heavy Ion Collisions Invited Speaker: The first four years of studies of heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory brought a number of exciting discoveries about the high temperature and energy density matter created in the collisions. Among those, one of the most significant observations is the hadron yield suppression at high transverse momenta ($p_T >$ 2 GeV/$c$) in central Au+Au collisions. Another discovery, unpredicted by theory, is that protons and anti-protons behave differently: no suppression is present at intermediate $p_T$ (2 - 5 GeV/$c$). This ``baryon anomaly'' at RHIC invoked new theoretical frameworks to describe the hadronization process in the presence of quark- gluon plasma. A survey of experimental data on identified hadron yields, jet correlations, and elliptic flow in p+p, d+Au, and Au+Au collisions will be presented and compared to theoretical models with the goal to reveal the dynamics of the hadronization process and the effects of the underlying medium. [Preview Abstract] |
Tuesday, April 19, 2005 11:21AM - 11:57AM |
X11.00002: Measurements of the Longitudinal to Transverse Cross Section Ratio and Separated Structure Functions on Nucleons and Nuclei Invited Speaker: The ratio R of longitudinal (L) to transverse (T) electron scattering off the nucleon is a fundamental quantity that should be measured with the best possible accuracy. Recent data from experiments in Hall C at Jefferson Lab have measured precision inclusive elastic, quasi-elastic, resonance, and deep inelastic cross sections from nucleons and nuclei over the four-momentum transfer range 0.05 $<$ Q$^{2} \quad <$ 5.50 GeV$^ {2}$. This new data has been used to accurately perform over 200 Rosenbluth- type L/T separations. These separations have allowed for the longitudinal component of the electron-nucleon(us) cross section to be extracted, for the first time in many cases, and for the inelastic structure functions F$_{1}$, F$_{2}$, and F$_{L}$ to be obtained. One surprising observation is that R is large at the larger W, low Q values, where it is typically assumed to go to zero. Other physics issues addressed by the new data include: the nuclear dependence of the longitudinal structure function; quark-hadron duality; structure function moment extractions; a search for nuclear pions; improved measurements of F$_{2}$; and modeling the vector contribution to neutrino cross sections. [Preview Abstract] |
Tuesday, April 19, 2005 11:57AM - 12:33PM |
X11.00003: Fundamental Symmetries Probed by Precision Nuclear Mass Measurements at ISOLTRAP Invited Speaker: Mass measurements on rare isotopes can play an important role in testing the nature of fundamental interactions. Precise mass values together with decay data are required for critical tests of the conserved vector current (CVC) hypothesis and the standard model. Substantial progress in Penning trap mass spectrometry has made this technique the best choice for precision measurements on rare isotopes, by providing high accuracy and sensitivity even for short-lived nuclides. The pioneering facility in this field is ISOLTRAP at ISOLDE/CERN. ISOLTRAP is a mass spectrometer capable to determine nuclear binding energies with an uncertainty of 10$^{-8}$ on nuclides that are produced with yields as low as a few 100 ions/s and at half-lives well below 100 ms. It is used for mass measurements relevant for a better understanding of nuclear structure and the nucleosynthesis of the elements. It is also used for the determination of masses that are important for the test of CVC, the unitary of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, and for putting constrains on the existence of scalars currents. Measurements along this line include $^{74}$Rb (T$_{1/2}$=65 ms), which is the shortest-lived nuclide studied in a Penning trap. The Q$_{EC}$ values of $^{74}$Rb, determined with a precision of 6$\cdot $10$^{-8}$, serves as a test of CVC or of related theoretical corrections [1]. Masses of $^{32}$Ar and $^{33}$Ar have been determined with uncertainties of 6.0 $\cdot $ 10$^{{\-}8}$ and 1.4 $\cdot $ 10$^{-8}$ [2]. The improved mass for $^{32}$Ar helps to provide a better constraint on scalar contributions to the weak interaction and both argon data serve as the most stringent test of isobaric multiplet mass equation IMME. $^{34}$Ar, another CVC test candidate, has been studied with an uncertainty of 1.1$\cdot $10$^{{\-}8}$ ($\delta $m = 0.41 keV). Similar precision has been achieved for $^{22}$Mg and neighboring $^{21}$Na and $^{22}$Na [4]. The importance of these results is twofold: First, an Ft value has been obtained for the super-allowed $\beta $ decay of $^{22}$Mg to further test the CVC hypothesis. Second, the resonance energy for the astrophysically relevant $^{21}$Na proton-capture reaction has been independently determined. [1] A. Kellerbauer et al., Phys. Rev. Lett. 93 (2004) 072502 [2] K. Blaum et al.,~Phys. Rev. Lett. 91 (2003) 260801 [3] F. Herfurth et al, Eur. Phys. J. A15 (2002) 17 [4] M. Mukherjee et al., Phys. Rev. Lett. 93 (2004) 150801 [Preview Abstract] |
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