Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session H2: New Directions in Hadron Dynamics |
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Sponsoring Units: GHP Chair: Les Bland, Brookhaven National Laboratory Room: Thurgood Marshall East |
Sunday, February 14, 2010 10:45AM - 11:21AM |
H2.00001: Physics for Future Facilities for QCD Invited Speaker: Quantum Chromo Dynamics (QCD) is the theory of the strong nuclear force. In the US, there are currently two facilities focused on unveiling its mysteries. At RHIC, nuclear matter can be studied at extreme temperatures (quark gluon plasma) in high-energy collisions between gold ions. With the 12 GeV upgrade, Jefferson Lab will be able to precisely map the behavior of the three valence quarks confined by the strong force within protons and neutrons by scattering electrons on various nuclei. The next generation facility would be a machine capable of colliding electrons and nuclei to probe the sea of virtual quarks, and directly measure the glue that constitutes the strong force, providing a more complete map of the spatial and spin landscape of the nucleon, and the transition from quarks and gluons into protons and other hadrons. [Preview Abstract] |
Sunday, February 14, 2010 11:21AM - 11:57AM |
H2.00002: Baryons and Evidence for Direct Hadron Production in Heavy Ion Collisions Invited Speaker: Baryon and anti-baryon production in heavy ion collisions is enhanced compared to pion production for transverse momentum greater than 2GeV/c. Conventionally, hadron production at these momenta is thought to be dominated by fragmentation of partons from 2$\to$2 scattering into final state hadrons. The particle composition in heavy ion collisions should then be similar to p+p collisions, in contrast to the observed increased fraction of baryons in heavy ion collisions. However, there is evidence that an alternate method of hadron production, from color transparent higher-twist QCD processes where the final state hadron is produced directly in the hard subprocess, is important over a wide momentum range. The color transparent hadrons traverse the hot nuclear matter without interacting with it, in contrast to colored partons. Pions, which are abundantly produced in fragmentation, are observed to be suppressed in heavy ion collisions because the parent partons interact with the matter and lose some of their energy. Thus, the matter produced in heavy ion collisions could act as a filter, enhancing the fraction of observed hadrons which were produced in higher-twist subprocesses. Baryon and anti-baryon production, heavily suppressed in fragmentation, is naturally enhanced by this mechanism. We discuss the evidence for this from RHIC data including $x_T$ scaling of particle yields and correlations, and discuss how measurements in the near future can help understand the role of higher-twist effects in heavy ion collisions and also provide insight into hadron production in p+p collisions. [Preview Abstract] |
Sunday, February 14, 2010 11:57AM - 12:33PM |
H2.00003: Forward particle production in d+Au collisions Invited Speaker: Parton distribution functions have been determined by perturbative QCD (pQCD) fits to experimental data. Due to QCD bremsstrahlung, gluon density quickly rises and dominate as the momentum fraction of partons bound within a nucleon (Bjorken x) becomes small. However, gluon density cannot grow forever and it is expected to saturate when the density is high enough that recombination effects cannot be ignored. In pQCD picture, forward particle production at a hadron collider probes asymmetric parton collisions of high-x quark and low-x gluon. During FY08, RHIC had d+Au collisions, in addition to p+p collisions. The expectation that gluon saturation occurs at larger x in a heavy nucleus may make it to possible to search gluon saturation by RHIC energy, while the deuteron provides dilute partons as a probe of saturation. Both the STAR and the PHENIX experiments at RHIC had major detector upgrades in the forward region, making forward particle production at RHIC an excellent place to study low-x gluons. A summary of new experimental results from FY08 d+Au collisions at RHIC will be presented. [Preview Abstract] |
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