in UC Santa Barbara
LUX-ZEPLIN(LZ)
The most popular model of dark matter is Weakly Interacting Massive Particles(WIMPs). It does not mean their interaction is weak; it means that they interact via the weak force. Therefore, if they exist, WIMPs can be detected by measuring interactions with atomic nuclei, in this case liquid xenon. The first science results of LZ can be seen here.
in Korea University
SUBMET
Is the charge of an electron (or a quark) the smallest charge possible? Probably, but not necessarily. Unlike the energy of light for example, the Standard Model does not force charges to be separated out in to discrete units. Some suggest that the existence of milli-charged particles can explain the temperature drops of the early universe. We seek to probe charges under 10-4e using scintillator based detectors.
Long-lived Particle Search
Currently, all the particles of our interest (in the LHC) decay very rapidly after its formation. So in today’s collider experiments, it is normal to assume that all particles are converted into more stable particles before they enter the tracker volume. But if certain invisible particles escape the tracker and decay a few meters away from the vertex, they can leave a distinct decay signature. I’m involved in the analysis to catch these signatures using HCAL timing information.
Data-driven Background Estimation with Neural Nets
The ABCD background estimation relies on the assumption that the two parameters of our choice are independent. But sometimes, finding such sets of parameters are difficult, let alone validating them. With Prof. Suyong Choi, we are developing a model to accurately estimate backgrounds with correlated variables. Our model is based on Bayesian neural network which can be easily extended to arbitrarily high dimensions.
Others
Event Simulation with GAN
The traditional method of simulating particle collisions is through Monte-Carlo. But since we need huge quantities of simulated data to predict signal events (which are very rare), our computing power cannot keep up with future HL-LHC experiments. So as a small project, I tried using generative adversarial networks to simulate $Z\to\mu\mu$ events.
CMB Anisotropies
Cosmic Microwave Backgrounds are thermal relics from the very early universe. It is very uniform–the closest thing to a black body in the real world–but by analyzing very small deviations in temperature, we can extract vital information about the early universe. In this project, I used the pixel-likelihood method to check whether the low multipole moments of our CMB measurements can give meaningful constraints to $\Lambda$-CDM model parameters.
Super Massive Black Holes
Supermassive Black Holes are black holes that have more than 106 times the mass of the sun, and sit in center of galaxies. Recently, observations showed that there exists black holes that are too massive to be explained by conventional dynamics. So there is a possibility that dark matter also fuels the growth of SMBH through gravitational attraction. I studied the different feasible mechanics of SMBH growth and gave a presentation (as a group).
Supernova Ia
Supernovae Ia are formed when white dwarfs exceed a critical mass. This makes them a standard candle, meaning that they all have the same intrinsic brightness. By observing their brightness and redshift, we can measure the relation between their speed (which is caused by the expansion of the universe) and distance. Supernovae observations were the first to reveal the accelerating nature of our universe. I analyzed the discrepancy between supernovae and CMB measurements and calculated wether the effects from our local gravitational environment can be a cause.