Research Interests

In spite of the astounding successes of the Standard Model of Particle Physics (SM) in both predicting the existence of particles years before they were detected (like the top quark and Higgs boson) and providing the most comprehensive framework for explaining how the universe works, its shortcomings are becoming more glaring. The SM among other things, fails to incorporate gravity, does not account for the masses of neutrinos and to date has not been reconciled with general relativity. In fact, the SM deals only with baryonic matter which comprises a mere 5% of our universe with the remaining 95% being the mysterious dark matter and dark energy. Perhaps the most curious for us as humans is the failure of the SM to account for our existence since there is no known mechanism for breaking the matter-antimatter symmetry of the universe. Particle physics is at an important juncture and a whole field of "Beyond the Standard Model" (BSM) physics has arisen. Of particular interest to me is a subset of experiments which seek to measure basic parameters of the SM while testings the limits of its predictions by looking for signatures of unaccounted for forces and particles. These experiments provide an expansion of our knowledge of how things work inside the SM framework while probing for its shortcomings. Two such fields that I have become involved in having this dual appeal are neutrino physics and parity-violating physics.

Parity-violating physics
The parity operation is one that reverses the direction of every coordinate in a system, for example taking x to -x, y to -y and z to -z. Practically speaking, the parity operation working on physics processes looks like a mirror image. Intuitively we would expect that physics processes and their mirror image would behave identically. In the Standard Model, the weak force (and only the weak force) violates parity meaning that performing and experiment and its mirror image will produce different results. Measuring the small differences arising from parity violation is a useful tool for investigating the weak force, nuclear structure and even processes in neutron stars. More recently it has become a tool for probing BSM physics. The SM makes very precise predictions of parity-violating processes and parameters and deviations from these predictions could be a signal of BSM physics. Precision measurements of key SM parameters gives sensitivity to certain types of new physics at scales well beyond that currently available even at colliders like the Large Hadron Collider at CERN in Switzerland. Given the current funding challenges, physics measurements like these at the precision frontier create a feasible (much cheaper) method to search for BSM physics processes only directly observable at much higher energies.

My Ph.D. research was primarily on the Qweak experiment which ran in Hall C at Jefferson Lab, providing the world's first determination of the weak charge of the proton and a precision test of the SM prediction for this value. The Qweak collaboration has submitted its final result for publication.

I am also involved in the PREXII and CREX experiments tentatively scheduled to run in Hall A at Jefferson Lab in 2019. These experiments, which utilize parity violation to investigate the neutron structure in the nuclei of calcium-48 and lead, are of interest to the astrophysics community for their implications on the structure of neutron stars.

Perhaps the flagship precision experiment of the future is the MOLLER experiment which aims to measure the weak charge of the electron to unprecedented precision. Although not yet officially funded, this experiment, which would run in Hall A at Jefferson Lab, has received CD0 status from the Department of Energy and even made it into the Long Range Plan of the Nuclear Science Advisory Committee. I am currently involved in research for reaching beam polarimetry measurements at the <0.5% precision level required for this experiment.

Neutrino physics
Although the existence of neutrinos was first postulated in the 1930's, their existence was not confirmed until almost three decades later due to the difficulty of detecting them. Since in the SM neutrinos only interact via the weak force, the cross section for their interaction with matter is so small that a beam of these particles could pass through a wall of lead a light year thick and most of them come out the other side. It was not until the turn of the millennium that scientists were able to conclusively confirm that neutrinos have mass, albeit tiny compared to other SM particles. Over the past few decades much research has gone into studying neutrino oscillation, a quantum mechanical phenomenon that allows neutrinos of one flavor to turn into another flavor purely as a consequence of their different masses.

Reactor neutrino physics, a subfield of neutrino physics that utilizes nuclear reactors as a source of antineutrinos, has of late generated interest due to discrepancies between the calculated and measured flux of reactor antineutrinos as well as their expected energy spectrum. One proposed solution to the flux discrepancy is the existence of a BSM particle termed a sterile neutrino that has no SM interaction with ordinary matter but which still participates in oscillation via quantum mechanics. I am involved in the PROSPECT experiment which aims to help unravel this discrepancy. The PROSPECT detector which I am currently helping to build at Yale University, will be deployed at Oak Ridge National Lab late this year and begin taking data in early 2018. This experiment will look for evidence of a sterile neutrino in the parameter space currently favored by world data. PROSPECT also aims to perform the world's best measurement of the U-235 antineutrino spectrum from a highly enriched nuclear reactor to help determine the source of the discrepancy between measured and calculated reactor spectrum shapes.

Key Publications

1. Seasonal variation of the underground cosmic muon flux observed at Daya Bay. Daya Bay collaboration, Journal of Cosmology and Astroparticle Physics (2018, Jan)

2. Evolution of the reactor antineutrino flux and spectrum at Daya Bay. Daya Bay collaboration. Phys. Rev. Lett. (2017, Jun)

3. Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment. Daya Bay Collaboration. Phys. Rev. D (2017, Apr)

4. Improved measurement of the reactor antineutrino flux and spectrum at Daya Bay} Chinese Physics C (2017)

5. A novel comparison of Møller and Compton electron-beam polarimeters. Jefferson Lab Hall C polarimetry group. Elsevier, (2017, Jan)

6. Precision Electron-Beam Polarimetry at 1 GeV Using Diamond Microstrip Detectors. Jefferson Lab Hall C polarimetry group. Phys. Rev. X Vol. 6 (2016, Feb)

7. The PROSPECT Physics Program. PROSPECT collaboration. Journal of Physics G: Nuclear and Particle Physics (2016)

8. The Qweak experimental apparatus. Qweak collaboration. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 781, 105-133. (2015, May )

9. Measurement of parity violation in electron-quark scattering. PVDIS collaboration. Nature 506, 67-70 (2014, Feb)

10. Measurement of Parity-Violating Asymmetry in Electron-Deuteron Inelastic Scattering. PVDIS Collaboration. Physical Review C. (2015)

11. Precision Compton polarimetry for Hall C at Jefferson Lab. Paper presented at XVth International Workshop on Polarized Sources, Targets, and Polarimetry. Donald Jones. Proceedings of Science. (2013, Sep).

12. First determination of the weak charge of the proton. Qweak collaboration Phys. Rev. Lett. 111, 141803. (2013, Oct)
​
13. New precision limit on the strange vector form factors of the proton. HAPPEX collaboration. Phys. Rev. Lett. 108, 102001. (2012, Mar)