Overview: The Standard Model of Particle Physics (SM) has been incredibly successful with all of its predictions validated by observations. The discovery of the Higgs boson (H) in 2012 by ATLAS and CMS experiments at Large Hadron Collider (LHC) was a triumph of the SM. Since its discovery, many measurements of the Higgs boson’s properties have been carried out, and so far all the results agree with the SM predictions within uncertainties. However, in order to fully characterize the Higgs boson, it is necessary to measure its coupling to itself (Higgs self-coupling), a property that has cosmological consequences. The quartic Higgs self-coupling is not possible in any current experimental facility, but the trilinear Higgs boson self-coupling can be accessed in events with pair-produced Higgs bosons (HH) at the LHC. Any deviation from the SM prediction in the HH production cross-section will be an unmistakable sign of new physics. On the contrary, if the experimental results agree with the SM predictions, then several new theories, built to address the shortcomings of the SM and that predict enhancements of the HH cross-section will be ruled out as feasible models of Nature. The proposed research aims to search for pair-produced Higgs bosons in the proton-proton collision data recorded by the ATLAS detector at the LHC.

Intellectual Merit: ATLAS is a general-purpose particle detector built cylindrically around the proton-proton collision point around the LHC. It measures the resulting particles from the proton-proton collision at the highest achievable energies in a laboratory. The LHC completed the first run (2008-2013), second run (2015-2018), and has completed year one of its third run (Run3). It is expected to deliver a few hundred fb-1 of data by the end of Run3, providing much needed data statistics for more precise measurements. Researchers in the Shrestha Lab will analyze this data to search for HH bosons in the bbWW channel. Previously deemed impossible due to large, irreducible top-quark background, this channel has made significant progress in the past few years, and is poised to contribute significantly to the measurement of Higgs boson self-coupling. In order to enhance sensitivity to the HH signal, Washington College (WAC) ATLAS group will lead the efforts to enhance trigger efficiency for the HH signal and event selection, improve background modeling, and suppress background through kinematic fitting and other multivariate analysis. In addition, we will continue to study the performance of the b-jet trigger, necessary for several physics analyses, including HH searches. Finally, WAC students will contribute to the hardware of the BCM’, a sub-detector critical for the safety of ATLAS and for luminosity measurement. These projects will advance the physics program of ATLAS for Run3, and give us deeper insight into the working of nature at the most fundamental scales.

Broader Impacts:The Shrestha Lab aims to establish a research and education program in particle physics at WAC, an undergraduate institution with a student body of roughly 1000, of which 20% identify as the underrepresented minorities. WAC has successfully attracted and trained students from diverse backgrounds in physics and prepared them for successful careers in science. In the Shrestha Lab, WAC students will participate in an international scientific collaboration, analyzing LHC data and testing the frontiers of detector technology, and in the process will contribute to the fundamental understanding of nature. Though WAC is a small institution, it plays a significant role in educating some of the brightest students for productive careers in cutting-edge fields that contribute to the well-being and economic security of the U.S.