Searches for baryon-number and lepton-number violating B meson decays. I initiated and conducted the search for decays of a B meson to a baryon and lepton. The baryon is either a Lambda or Lambda_c and the lepton is either a muon or electron. The hypothesis is that bosons which violate both baryon- and lepton-number might couple weakly to 1st generation quarks and leptons, and so further suppress proton decay beyond the suppression that comes from the mass scale of the interaction. If this was so, then these processes might be observed in reactions involving b or c quarks. No signal was observed and we set the first upper limits on the branching fraction for these reactions.
Search for CP violation in the decays of B mesons to 3 pions. While at Stanford, I worked with a graduate student, Tomo Miyashita, on his thesis analysis: a Dalitz plot analysis of a B meson decaying to 3 pions. This decay procedes primarily through B --> rho pi. The 3 rho's overlap in the corners of the Dalitz plot and interfere with one another. As the B meson propagates, its amplitude oscillates between a neutral B and a neutral anti-B meson. CP violation will show up as a changing interference in the rho overlap bands as a function of time. This analysis is ongoing and is aiming for a 2012 publication.
Jefferson Lab analyses
Searches for missing baryon resonances using partial wave analysis. My thesis at RPI and and post-doctoral research at CMU focused on mapping the spectrum of non-strange baryon, excited states of the proton and neutron. For over 30 years, experimentalists have looked for a particular class of baryons which were predicted by theory but which have not been observed. Data is analyzed from Jefferson Laboratory in Newport News, VA, where high energy photons were scattered off of a liquid hydrogen target. The analysis involves a multitude of final states including p pi+ pi-, p omega, K Lambda, K sigma, p eta, p eta'. By performing a partial wave analysis (PWA), where the energies and angles at which the final state particles are produced are analyzed, the amplitudes are extracted for any intermediate resonances which contribute to these reactions.
Our group at CMU extended the PWA framework I wrote (and extended myself from previous analysis tools) and brought with me from RPI. In the end, we put out multiple papers mapping out the differential cross sections and polarization observables for many of these reactions. While the full coupled-channel analysis required to definitely identify or rule out the missing baryon states was not completed, preliminary PWA work suggests structure which indicate that these baryons resonances in fact do exist.
- "Differential cross sections and recoil polarizations for the reaction gamma p ---> K+ Sigma0", (2010) Phys. Rev. C.
- "Differential crosss ections for the reactions gamma p ---> p eta and gamma p ---> p eta-prime.", (2009) Phys. Rev. C
- "Differential cross section and recoil polarization measurements for the gamma p to K+ Lambda reaction using CLAS at Jefferson Lab.", (2010), Phys. Rev. C
- "Differential cross sections and spin density matrix elements for the reaction gamma p ---> p omega", (2009), Phys. Rev. C
- "Partial wave analysis of the reaction gamma p ---> p omega and the search for nucleon resonances.", (2009), Phys. Rev. C
Cross checks of previous pentaquark observations. I was very involved with analyses using data at Jefferson Lab in the search for a pentaquark, a predicted particle which contains 5-quarks. I performed comprehensive parallel analysis to check new hypothesis regarding the production of this state. Following these checks by myself and others, the original claims of an observation have since been reassessed and the general consensus is that a narrow pentaquark has not been observed. I worked with the analysis group to use the Feldman-Cousins method to calculate the upper-limits on pentaquark production.
- "Search for the Theta+ pentaquark in the reactions gamma p ---> anti-K0 K+n and gamma p ---> anti-K0 K0p.", (2006), Phys. Rev. D
- "Search for Theta+(1540) pentaquark in high statistics measurement of gamma p ---> anti-K0 K+ n at CLAS.", (2006), Phys. Rev. Letters
CoGeNT analysis of public data
The CoGeNT experiment is a search for dark matter headed up by Juan Collar at University of Chicago. This experiment aims to detect dark matter particles interacting through the weak nuclear force in their detector, where they detect the ionization produced by the nuclear recoils off the dark matter particles.
In 2011, the collaboration published results that showed that their data could be fit by a function that included a term that was consistent with a dark matter signal. In addition, this fit suggested an annual modulation, consistent with models in which our solar system moves through the dark matter halo of the galaxy.
The CoGeNT group, in an exceptional show of scientific honesty and open collaboration, made their data public, along with explanatory documents so that others might analyze it and come up with alternative hypotheses. I have been analyzing this data since the summer of 2011 and have written analysis tools based on RooFit that allow the user to easily try different fit components and modulation hypotheses. Results will be discussed further on this website or on the arXiv, as they become available.
Service work tasks
In any sizable collaboration, service work must be parceled out to the members of the collaboration, beyond the immediate analysis upon which we work. Here I list some of my broader contributions to these groups.
BaBar collaboration (SLAC)
- Documentation Working Group Manager
- Monte Carlo Production Manager
CLAS collaboration (Jefferson Lab)
- Drift Chamber alignment for eg3 run.
- Determination of fiducial cuts for g1c and g11 run.
Other professional activities
The Second Banff Statistics Challenge (2010). The Banff challenge was submitted to the general HEP community to address the subtlties of discovery significance in particle physics experiments. With Douglas Applegate, I wrote a nearest-neighbor algorithm and incorporated bootstrapping techniques to account for the finite statistics in the Monte Carlo samples. We acquitted ourselves very well, as can be seen in the summary document. In all, about a dozen groups participated.
High Energy Physics Congressional Visit, (2010), Washington D.C.