James Alexander

Professor of Physics

318 Physical Sciences Building
Cornell University
Ithaca NY 14853

(607) 255-5259

jpa6@cornell.edu
personal website

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.

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?

Thoughts of this sort have led 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!

We are doing that now. Working at the Large Hadron Collider at CERN, the Cornell particle physics group is focusing heavily on the search for New Physics. Here are just a few of the things which interest me most and 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 traditional neutralino 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 masses or spin of the new particles?
  • 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? We have not seen missing energy events yet, but don't yet know what this means. If they continue to be AWOL, what shall we do about Dark Matter?  

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.

As a starting point in this vast landscape of questions and unknowns, I began working on the problem of mass determination of New Physics particles produced under conditions where incomplete information severely complicates the problem of mass measurement. Two graduate students, Nic Eggert and Nathan Mirman, and two undergraduates, Ben Nachman and Adam Dishaw have carried on these studies. We are now moving into new areas, searching (a) for New Physics that might have a close association to the top quark, but not so much missing energy, and (b) for New Physics that might exhibit the long-awaited missing energy, but be produced in ways that make it less prominent in the data. Four new undergraduates are engaged in these programs: Caroline Aust, Jared Claypoole, Xiaoyue (Mandy) Guo, and Yimin Wang. In addition, graduate student Shao Min Tan is joining the group.

In the background, I have projects in detector development both for future CMS tracking and for ILC accelerator diagnostics. I also enjoy outreach projects and have a strong commitment to our undergraduate research program.

Graduate Students
Nic Eggert (CMS), Nathan Mirman (CMS) and Shao Min Tan (CMS)

  • Spotlight

    Dionysios Anninos was recently an undergraduate physics major at Cornell. "The range of possibilities offered at Cornell is overwhelming. One can end up studying the most disparate fields and end up well versed in them. Personally, I tried to exploit this feature to the maximum. I ended up learning a lot of great physics by sampling a large set of physics courses offered at a unique level, as well as exploring economics and mathematics." "Furthermore, through its advanced courses and research opportunities, Cornell offers the student a unique ... read more