As a member of CMS collaboration, the following are the current research projects our group is involved in:
RPV SUSY search in 1-lepton final state
Search for long-lived particles using HCAL timing
Search for SM 4top process in all hadronic final state
Performance of HCAL local reconstruction algorithms and noise filters
We are also interested in searches for particles with non-integer electric charges. Please check below for the details!
Most Supersymmetry(SUSY) searches require missing transverse energy(MET) because the conservation of R-parity requires that the LSP be stable, which gives MET. The high MET region is well covered by existing searches, but low MET regions are not. So, our team also searches for new physics without a MET requirement. This is well motivated in the context of R-parity violated scenarios where SUSY particles can directly decay to SM particles without an LSP at the end of the decay chain. The model we focus on is gluino pair production where the gluino decays to top, bottom, and strange quarks (gluino→ tbs) motivated by minimal flavor violating SUSY. The result with the 2016 data was published in Phys. Lett. B where mgluino<1.6 TeV is excluded at 95% CL. We are improving the analysis method to be less sensitive to systematic effects for the results with the full Run2 data. We will discover new physics or (sadly) push the gluino mass limit to ~2 TeV.
Team: Chang Hwan Jung and Yongho Jeong in collaboration with David Stuart's group at UCSB
No evidence for new physics has been seen at the LHC so far and the increase of the amount of data accumulated will be slower than before. This project aims to search long-lived particles, which belong to a phase space that is not so thoroughly searched. If these particles are massive and weakly interacting, they can travel a considerable distance before decaying into visible particles and leave a signal of displaced non-prompt jets. A signal of this nature can be detected with the timing information and missing transverse momentum measurements.
Recently, there was an attempt to detect these decay patterns using the timing capabilities of the CMS electromagnetic calorimeter(ECAL). With the upcoming upgrade to the hadronic calorimeter(HCAL), we can take advantage of its new timing measurements to extend the limits of such particle searches.
Team: Jeong Hwa Kim and Jayashri Padmanaban in collaboration with Matthew Citron (UCSB)
The 4-top production is a rare Standard Model process, but its cross section needs to be measured precisely because it is a background in searches for BSM models with multiple top quarks. It also provides a promising probe of top-quark Yukawa coupling.
In CMS there are efforts to study this process in different final states. We are interested in all-hadronic channel where all W bosons from the top quarks decay to two quarks. We search for this process in the region of many jets and many b-jets with high energy requirements.
Team: Chang Hwan Jung in collaboration with Prof. Suyong Choi's group at KU and Joe Incandela's group at UCSB
Many new physics scenarios, for example, gluino pair production, come with large hadronic activity. They may carry large MET due to LSPs. Therefore, a robust measurement of hadronic activity is crucial, not only to estimate its size but also to calculate MET correctly. This means that the HCAL reconstruction algorithm should extract the energy of hadrons accurately. It should also run fast enough for the algorithm to be used at the high-level trigger (HLT). We have been working on the improvement and maintenance of the local reconstruction algorithms, noise filters, and the simulation for HCAL. The current focus is to optimize the local reconstruction algorithm for Run3 and documenting its performance in Run2 data.
Team: Jayashri Padmanaban
As part of the CMS Phase 2 upgrade, MIP Timing Detector is planned to be installed in order to mitigate the impact of pileup that is expected to reach 200 in HL-LHC. In the endcap region, silicon-based Low Gain Avalanche Detector (LGAD) sensors that allow timing resolution of a few tens of picoseconds are used. The sensor design needs to be optimized considering several factors, including radiation resistance, uniformity of gain, and long-term stability. At Korea University, we have set up a testing facility using a laser and started testing prototypes.
Team: Jayashri Padmanaban, Insung Hwang, Byeong Jin Hong
The existence of particles with non-integer electric charge (millicharged particles, mCPs) is not strictly excluded in the Grand Unified Theories and mCPs may a viable dark matter (DM) candidate (at least some fraction of DM). We are studying the feasibility of detecting mCPs with a scintillator-based detector in a fixed target p-p experiment.
Our study focuses exclusively in the near detector site at J-PARC. We seek to optimize the detector configuration (size, material, design, etc.) to achieve sensitivity down to charges near O(5x10^-5) times the electron charge.
Team: Jeong Hwa Kim , Insung Hwang, Taegyu Lee
Research projects prior to joining KU:
SUSY search in 1L final state using MJ
Evidence of H->WW->2l2v
HCAL operations
milliQan experiment
