Dr. Joel Walker, Sam Houston State University Associate Professor of Physics, has been awarded $75,000 over three years from the National Science Foundation (NSF) for his research proposal: “RUI: Supersymmetric Theory, Phenomenology, and Tool-Building.” In keeping with the NSF’s educational mission, the Research at Undergraduate Institutions (RUI) designation of this project indicates that Walker’s work will involve students in the research process at the earliest possible juncture, increasing their chances of securing a space in a competitive particle physics graduate program.

Walker emphasizes that SHSU is uniquely poised to fulfill the mission of promoting opportunities for a career in physics to traditionally underserved constituencies, including first-generation and economically disadvantaged students. As a primarily undergraduate institution, we are able to focus our first attentions on enriching the educational experience of students who are at the very early stages of establishing what paths their professional lives will follow. However, there is a trade-off, as it takes a significant amount of time to train undergraduate students to the point that they can be useful in a major research project.

Recently, Walker has taken on four new students (Llamo-Cohen, Fantahun, Fernando, and Schachtner) who are already reaping the benefits of the grant funding. Weekly two-hour meetings have been initiated with these students, constituting a “crash course” on essential elements of particle and collider physics, and external reading and preparatory projects have been assigned. Walker’s hope is that the students will soon have developed enough foundational knowledge to begin participating in well-defined aspects of his research program. The longer term goal is that these individuals will actively participate in the publication of a peer-reviewed journal article before graduating. New students will be rolled sequentially into the project to offset graduations, and it is anticipated that around 8 students will have directly benefitted from the grant funding by the end of the three-year timeline.


The overarching theme of the project addresses aspects of the theory of Supersymmetry (SUSY), especially as applicable to ongoing experiments at the Large Hadron Collider (LHC) in Geneva, Switzerland. In the first experimental run of the LHC, the Higgs boson was discovered, leading to a Nobel Prize in 2013. While direct evidence of SUSY has not yet materialized, the theory may help explain why light particles such as the Higgs can exist, by hypothesizing the symmetric cancellation of effects that would otherwise push their mass up to higher scales.

These cancellations occur naturally, if one mirrors each known particle with a new “super partner” having the same charge but a different angular momentum. However, for the SUSY idea to be effective in explaining the natural emergence and stabilization of our low energy world, these partners cannot be too heavy. After a long break, proton collisions at the LHC have recently resumed at almost twice the kinetic energy of the original run, potentially allowing for much more massive particles to be created and explored. According to Walker, if the idea of low energy SUSY is correct, there is a good argument that the super partners could now be visible at the LHC.

One aspect of the project that is well-suited for student participation involves the application of software tools engineered by Walker for implementing generic event “selection cuts” on simulated collider data. Walker explains that the result of most collisions at the LHC will necessarily be of comparatively low interest, because interactions that happen with great frequency are by their nature already very well understood. In any collider analysis, one then has to establish criteria for cutting out the dominant background noise (and unavoidably some signal also) so that what is left of the signal can compete on equal footing with the background.


An example of the text-driven operating instructions for Walker’s program, AEACuS, which automates the computation of statistics and application of event selection cuts on simulated collider data.

Simulated collider data is very useful in this context for refining specific hypotheses regarding the interactions and masses of particles associated with new physics. By graphically revealing ways in which the background is distinct from signal, the tools that Walker has developed help researchers to efficiently make optimized decisions about what cuts to place on various event variables for potentially testing a given model at the LHC. Alternatively, by replicating event selections employed by the major LHC experimental collaborations, it is possible to compare the outcome of a simulation to existing data; while this approach can very effectively rule out a hypothesis that is inconsistent with experiment, confirming a hypothesis is much more difficult. Walker will additionally devote efforts to multiplying the impact of his software tools by marketing them to researchers and students at other institutions.


An example of the graphical output of Walker’s program, RHADAManTHUS, for analyzing trends of signal and background in simulated collider data.

An additional research theme that Walker is currently exploring involves the search for coherent nuclear scattering of very light weakly-interacting particles called neutrinos. The proposed experiment would place pioneering high-sensitivity Germanium and Silicon detectors developed by collaborators Mahapatra and Mirabolfathi at Texas A&M University (TAMU) in close proximity to the local research-scale nuclear reactor, which radiates more than a hundred-million-billion neutrinos per second during normal operation. A small fraction of these neutrinos are expected to scatter off of dense nuclei in the detector material, producing an extremely faint recoil, the observation of which would be a first-in-the-world accomplishment.

In particular, Walker was invited by theorists Dutta and Strigari at the TAMU Mitchell Institute for Fundamental Physics and Astronomy to assist in the calculation of scattering rates for this experiment, and to help ascertain the potential sensitivity of the experiment to search for new physics interactions.  Examples of new physics hypotheses that could be tested include potential magnetic properties of the neutrino, a “Z-prime” boson (a heavier sibling of the known Z particle related to the weak nuclear force), and the existence of an even more weakly interacting “sterile” neutrino variety (potentially visible via the 2015 Nobel-prize neutrino “oscillation” effect).

Walker emphasizes that these collaborations, and similar long-term professional relationships with TAMU/Mitchell professors, including Toback and Nanopoulos, provide SHSU faculty and students the opportunity to interact with a much larger, research-oriented department and to participate in studies and analyses that they would be unable to undertake in isolation. He adds that the NSF is very supportive of these large/small, graduate/undergraduate crossovers and the world-class research integration that they bring to the smaller departments.

Walker, cantu, and Ellsworth    Walker and Voth

(Left) Walker with students Jesse Cantu and William Ellsworth in the University of Pittsburgh Cathedral of Learning, 2014 Phenomenology Conference. (Right) Walker with student Trenton Voth at the Carnegie Museum of Natural History, 2015 University of Pittsburgh Phenomenology Conference.

Walker believes that consideration for the grant benefitted greatly from the maintenance of a very active travel schedule, with heavy participation in conferences, lectures, and workshops alongside leading figures in the field. Key goals of such networking, according to Walker, include establishing and legitimizing Sam Houston’s name in the particle physics community, and developing two-way professional awareness. Beyond this, though, the global community of research scientists is ultimately a collection of individuals, and becoming a functioning part of that community necessarily includes getting to know faces and names, and having personal human interactions with as many of those individuals as possible, meeting them and letting them meet you.

Finally, Walker expresses his appreciation to the Office of Research and Sponsored Programs, including Executive Director Delia Gallinaro and Associate Director Dee Myall, for help received while applying for funding. Walker said that Myall “has been incredibly helpful with the practicalities of how one prepares a budget and generates the various properly formatted supporting documents that necessarily accompany any grant proposal”. Myall and Walker worked patiently for 4 annual submission cycles, pursuing the grant funding which finally materialized for the current project. Walker suggests that persistence and responsiveness to sponsor feedback have now paid off in the form of a very constructive award.