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B.A., 1976, Carleton College. M.S., 1979, University of Chicago. PhD., 1984, University of Chicago. Research Associate, Stanford Linear Accelerator Center, 1984-1988. Assistant Professor, Cornell University, 1988-1993; Associate Professor, Cornell University, 1993-1998; Professor, Cornell University, 1998-present; Director of Graduate Studies, Physics Department, Cornell University, 2001-2006. Presidential Young Investigator, 1990-1996. Visiting Foreign Scholar, KEK, Japan, 1997-1998. Fellow, American Physical Society, 1999. Director, Laboratory for Elementary-Particle Physics, 2006-present.

Research Areas
Experimental particle physics, Beyond the Standard Model physics, LHC, ILC, particle detector technology and instrumentation

Current Research
Why does the Standard Model work? What is beyond the Standard Model? What is the Higgs mass, and what keeps it there? What gives the Higgs potential its unique and all-important shape?
Thoughts of this sort have lead physicists to invent countless scenarios for New Physics, scenarios which sometimes require additional spatial dimensions, sometimes new "fermionic" dimensions of spacetime, and invariably predict new particles and new interactions. But until we get real data from very high energy collisions, we can't know what the right scenario is. Even then we will have to work very hard to figure out what the data are telling us!
Our group has joined the CMS Collaboration at CERN. In 2009 the LHC will begin physics operations, and soon we should start to see the first trickle of data from collisions at center of mass energies of 14 TeV -- high enough to probe convincingly the crucial region where new physics should show up. This should lead to an explosion of new data and new phenomena, and the number of questions that can be pursued in this environment will be enormous. Here are just a few of the things which interest me most and are likely to dominate my research directions:

• If the new physics is Supersymmetry (this is where the fermionic spacetime dimensions come in) then what are the masses of the neutralinos and charginos? What are the best strategies for extracting these signals from the data? Where in the vast parameter space of Supersymmetry does the pattern of masses seem to put us? Is the lightest neutralino a possible candidate for the Dark Matter of our universe? In fact, is the pattern of observations consistent with "R-parity" conservation? This is needed for there to be a dark matter candidate in the first place. Can we be clever enough to extract from the complicated and incomplete LHC data any information at all -- even hints -- about the couplings of the new particles, or their spin?
  
• If the new physics is the existence of "extra" spatial dimensions, can we distinguish this from Supersymmetry? Many of the phenomena will look rather similar, especially in LHC data. Will our initially very limited view up the Kaluza-Klein towers allow us to count the number of extra dimensions or measure their size, even roughly? What is the dark matter candidate in this case? What symmetry keeps it from decaying, and can we see evidence for this symmetry?
  
• Beyond the question of the neutralinos and charginos, in the Supersymmetric scenario, what other supersymmetric partners do we see, and what are their masses? Can we see sleptons and squarks? The heavy Higgs particles H, A, and H+, H-?
  
• And last but not least, what if the world beyond the Standard Model is nothing like the usual suspects would have it? What are the phenomena? Do we see missing energy events? If not, what shall we do about Dark Matter? Do we at least see the Standard Model Higgs? If not.... what should we be looking for? What are the issues that matter if everything we have thought of for the last 25 years has to be set aside??

These questions are just some of the many that one could pursue. They attract me both because of their close connection to cosmology and the unresolved identity of Dark Matter (which plays such a crucial role in the evolution of the universe), and because of their access -- their experimental access -- to the staggeringly fundamental question of what spacetime actually is, and how many dimensions (of what type!) there are in the universe we inhabit.

Graduate Student
Xin Shi