E-906/SeaQuest: Parton Energy Loss and Antishadowing Benjamin W. Miller of Abilene Christian University For E-906/SeaQuest Abstract In addition to measuring Drell-Yan di-muon cross sections for extracting d-bar to u-bar asymmetry in the nucleon, E-906/SeaQuest, a fixed target experiment using Fermilab's Main Injector, will make several other important measurements. To fully understand partonic energy loss in hot nuclear matter, it is important to understand energy loss in cold nuclear matter. Since the effects of parton energy loss are proportional to 1/s, SeaQuest will be much more sensitive to energy loss effects than E-866/NuSea, which placed upper limits on such parton energy loss at 800 GeV. SeaQuest will also further our understanding of nuclear anti-shadowing and extend the Drell-Yan measurements into the EMC effect region. This experiment will improve on Fermilab E-772 data. SeaQuest will have significantly better precision and extension over a much larger range in Bjorken-x, where the competing models diverge strongly from each other. The predictions for the experiment are shown by the red circles and the associated error bars (statistical only.) The ranges expected by CTEQ are shown. Previously, there have been very poor constraints above x=.20. SeaQuest will improve this significantly, and provide much better data to structure function calculations groups, such as MRST, GRV, and CTEQ. Conclusion Collaborators all across the globe are currently in the process of detector construction and software development. SeaQuest is expected to have low-rate beam by September, and to start collecting data in late This research is funded in part by the U.S. Department of Energy under grants DE-PS02_09ER09-02, DE-FG03-94ER , the National Science Foundation MRI Program, and the ACU Research Council. Introduction Special Thanks to: Donald Isenhower, Paul Reimer, and Shon Watson. Drell-Yan process Fermilab E-906/SeaQuest is a fixed target experiment using a focusing spectrometer. Its main objective is measure di-muon pairs from the Drell-Yan process to determine the light antiquark ratio at high Bjorken x. However, this is only one of the measurements SeaQuest will explore. Physicists around the globe are studying the behavior of partons in hot nuclear matter. Little is known of parton energy loss in cold nuclear matter. SeaQuest will make new measurements to provide data in kinematic regions that have not been accessible before. These new results are important for the interpretation of high energy experiment results, such as those being conducted at Brookhaven’s Relativistic Heavy Ion Collider (RHIC) and soon to be made measurements at CERN’s Large Hadron Collider. SeaQuest is more than the d-bar/u-bar asymmetry! Why it’s Important Shadowing and antishadowing was seen in the EMC experiment [J. Ashman et al., Phys. Lett. B 202, 603 (1982), M. Arneodo et al., Phys Lett. B 211, 493 (1988)] in the x>0,1 region as seen in the figure below. Brodsky and Lu [Brodsky and Lu, PRL 84,1342 (1990)] pointed out that their analysis of interpreting these effects as antiquark-nucleus multiscattering could be extended to Drell-Yan and other fusion processes. These would require taking into account the separate dependencies on the valence and sea quarks. Thus SeaQuest will be able to add important information on understanding shadowing and antishadowing. But, don’t forget… The partons of the incident proton interact strongly with the nuclear medium and lose energy prior to annihilation. Energy loss is seen as a shift in beam quark Bjorken-x (x 1 ) in heavy nuclei relative to light nuclei. E-866 Drell-Yan data show no apparent shift in x 1 and place upper limits on parton energy loss in cold nuclear matter. Partonic energy loss in hot nuclear matter is important to understand RHIC data. Models of this process must be tested in cold nuclear matter. Parton energy loss is proportional to 1/s, thus at 120 GeV, Since backgrounds scale with energy the same way, SeaQuest will also be able to run at much higher luminosities than E- 772 or E-866. These two factors combine to make SeaQuest much more sensitive to these effects. The figure below shows the cross sections ratios of Fe and W relative to Be showing the effect of the heavier nucleus (PRL 83 (1999) 2304). Energy loss of partons traveling through cold nuclear matter Fermilab E-772 did not see an increase in antiquarks in heavy nuclei relative to deuterium (blue squares). The red curve represents the theoretical expectation before the E-772 data, while the other curves represent postdictions of the effect. E906 will greatly improve the precision and extend the range in x of the data (red circles). What We Will Learn Nuclear Antishadowing Shadowing and antishadowing have been studied in Deep Inelastic Scattering (DIS) experiments. Shadowing is a destructive interference effect decreasing the number of interactions in the interior and back face of the nucleus. Antishadowing is observed when the number of interactions in the interior increases rather than decrease. Abilene Christian University Academia Sinica Argonne National Laboratory University of Colorado Fermi National Accelerator Laboratory University of Illinois KEK Kyoto University Ling-Tung University Los Alamos National Lab University of Maryland University of Michigan National Kaohsiung Normal University RIKEN Rutgers University Texas A & M University Thomas Jefferson National Accelerator Facility Tokyo Tech Yamagata University