Dark Matter

Ordinary matter only represents about 5% of the observed energy density of the universe. A new particle with weak-scale mass and couplings could account for the additional "dark" (lacking electromagnetic interactions) matter, which has only been inferred based on it's gravitational interaction.


Momentum Imbalance

Being invisible to the ATLAS detector, dark matter can't be observed directly. Instead, I search for an apparent momentum imbalance among final state particles that recoil against the invisible dark matter.

Monojet

The "monojet" topology, with a single jet recoiling against dark matter, results when dark matter is produced in association with radiation from an initial state particle.

Complementarity

The monojet topology is an extremely powerful and model-independent probe of dark matter at the LHC. While direct-detection experiments are more sensitive to the existence of heavy dark matter, the monojet search dominates for small dark matter mass.

Extra Spatial Dimensions

The monojet search is also a probe of the existence of of Supersymmetry (with a compressed mass spectrum) and extra dimensions.

The Hierarchy Problem

The mass of the Higgs boson is extremely sensitive to quantum corrections, particularly those due to the top quark. Naively, these corrections should drive the mass of the Higgs boson to the Planck scale at O(1018) GeV. However, the experimentally observed value is only mH=125 GeV. The vast and unexpected gulf between these values is referred to as the "Hierarchy Problem."


Conventional Solutions

Conventional solutions of the hierarchy problem (most prominently Supersymmetry and Composite Higgs models) predict the existence of a top quark partner that should be accessible at the LHC. However, despite over 25 years worth of effort, no evidence for the existence of such a particle has been observed.

Exotic Higgs Decays

In the abscence of evidence supporting conventional solutions to the hierarchy problem, interest in unconventional solutions has exploded. The concept of "neutral naturalness" has been proposed as an alternative solution, which does not require top quark partners that would be accessible at the LHC. Instead, the smoking gun signature for such models are exotic decays of the Higgs boson to pairs of "long-lived" particles X, each of which decay to bottom quarks.

Long-Lived Particles

Most heavy particles decay to light, detector-stable particles with an extremely short lifetime, which emanate from the primary vertex (in the center of the ATLAS detector). However, long-lived particles can decay travel a macroscopic distance before decaying, producing a "displaced" secondary vertex millimeters to meters from the privary vertex.

Displaced Vertex Search

My group recently performed a search for decays of the Higgs boson resulting in pairs of displaced vertices in the ATLAS inner detector. Unfortunately, the observed number of events (0) is compatible with the expected background yield of 1.3 ± 0.08 (stat.) ± 0.27 (sys.).

Jon Dale Nichols


Graduate Student

Connor Waits


Graduate Student

Open Position


Graduate Student

Noah
Reidy

Post-Baccalaureate

Bianca
Azaratsh

Post-Baccalaureate

Zach
Yarbrough

Undergraduate Student

Isabella
Campbell

Undergraduate Student

Contact Me

Are you interested in dark matter or the hierarchy problem? Do you have questions about ATLAS or the LHC? Are you interested in joining my research group?

Don't hesitate to reach out!