Lower limits on large extra dimensions in the Drell-Yan process in proton-antiproton collisions at center of mass energy = 1.8 TeV.

Abstract

This thesis describes a test of a theory of low-scale quantum gravity featuring large extra compact spatial dimensions, using data collected with the Collider Detector at Fermilab experiment of the Fermilab Tevatron Collider. This theory was introduced to solve the hierarchy problem, the unresolved large difference between the strengths of gravity and the other forces in nature. The gravitational force is observed to be much weaker than the other forces thereby creating a hierarchy of force strengths, which leads to a self-consistency problem in the Standard Model (SM) theory. The hierarchy problem has been the motivation for a large body of work. Current theoretical extensions to the SM attempt to solve the hierarchy problem by removing the problems associated with the self-consistency. Recently, the theory of Large Extra Dimensions (LED) by Arkani-Hamed, Dimopoulos, and Dvali, another extension to the SM, was proposed to solve the hierarchy problem by removing the hierarchy itself. In the LED theory, <italic>n</italic> compact, extra dimensions, with characteristic size as large a millimeter, are theorized where gravity is allowed to propagate while the particles of the SM are restricted to a four dimensional plane in the full 4 + <italic>n</italic> dimensional space (four for space and time and <italic>n</italic> LEDs). In the 4 + <italic>n</italic> dimensions, the strength of gravity, characterized by <italic>M_s</italic>, the fundamental Planck scale in the LEDs, is theorized to be near the strength of the electroweak force (<italic>M_s</italic> &sim; 1 TeV). At the same time, in our four dimensions, the gravitational strength is maintained, <italic> i.e.</italic> much weaker than the other forces. We place limits on the LED parameter <italic>M_s</italic>. We search for evidence of the LED theory in dielectron events; one consequence of the LED theory is to enhance the high-mass production cross-section of the Drell-Yan process (dilepton production). We select dielectron events from data collected in 1.8 TeV center-of-mass <italic>pp&macr;</italic> collisions. We fit the data to the predicted SM and LED Drell-Yan invariant mass distributions which scale as 1/ M4s . Using standard statistical techniques, we set 95% confidence level lower limits on the fundamental Planck scale in the LED theory, <italic>M_s</italic> > 826 GeV for lambda = -1, and <italic>M_s</italic> > 808 GeV for lambda = +1 in the LED convention of Hewett.