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theses

ETD_10174

Ph.D.

Includes bibliographical references

Fermilab E906/SeaQuest is an experiment aimed at studying the anti-quark distributions of nucleons and nuclei. The experiment uses a 120 GeV/c proton beam extracted from the Main Injector at Fermilab to collide with various solid and cryogenic targets to study a variety of physics topics. The experiment takes advantage of the Drell-Yan process in order to probe specifically the high-x anti-quark distributions of the target nucleus. The acceptance of the spectrometer is tuned to explore the unprecedentedly high Bjorken-x region, thereby extending our knowledge of the anti-quark sea structure of nucleons and nuclei.
A new Intensity-Extrapolation method was developed to counter the rate dependence challenge at SeaQuest. Using this method, the ratio of cross sections of liquid deuterium and liquid hydrogen, σpd(x)/2σpp(x), was measured in the range0.1≤xT≤0.45. The results have been found to be consistently above 1 for all values of the measured range of xT. Also, a first look at ̄d(x)/ ̄u(x) is presented. The trend of the data points indicate that the ratio is consistently above 1 for the measured range of xT. These results (when combined with more data) will provide a key input in constraining many theoretical models that attempt to explain the origin of the nucleon sea.
Using the same method, the nuclear dependence of the per-nucleon cross section ratio, RpA, of carbon, iron and tungsten versus deuterium studied as a function of xT, pT, and xF are reported. The results for xT are consistent with E772 indicating little nuclear dependence. A striking A (atomic mass) dependence in which there is a depletion of low-pT dimuons and an excess of high-pT dimuons relative to deuterium is reported. Also, an A dependence for the drop in RpA(xF) for increasing xF is presented. An analysis with and without the cut xT>0.16 (which removes the effects of the shadowing) gives consistent results indicating that the effects of shadowing are small. These results (when combined with more data) will address important questions on the modification of anti-quark distributions in nuclei and in modeling energy loss for partons traversing a cold nuclear medium.

doi:10.7282/t3-2ccn-7w70

ETD doctoral

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