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Search for SUSY with Delayed Photons at the Compact Muon Solenoid


Kopp, Gillian Baron (2018) Search for SUSY with Delayed Photons at the Compact Muon Solenoid. Senior thesis (Major), California Institute of Technology. doi:10.7907/G4D7-G385.


The Compact Muon Solenoid (CMS) experiment records data from proton-proton (pp) and heavy ion (Pb-Pb and Pb-p) collisions at the Large Hadron Collider (LHC) to search for physics beyond the Standard Model, test theories of supersymmetry (SUSY), and measure properties of known particles with higher precision. In 2025, the LHC will be upgraded to the High Luminosity LHC (HL-LHC), where the luminosity will be increased by a factor of 10. This will increase the number of pile-up collisions to 140-200 events per proton-proton bunch crossing, compared to the current 40 events per crossing (where each bunch crossing occurs every 25 ns). In order to fully exploit the sensitivity of the CMS experiment, the current detectors must be upgraded to mitigate the effects of the large number of pileup interactions expected in collisions at the HL-LHC. New capabilities, such as precision timing measurements in calorimetric devices and minimum ionizing detectors, have been shown to effectively mitigate the effects due to pileup, and are expected to benefit the overall physics reach of the experiment. In addition to mitigating pileup and increasing the detector capabilities, precision timing is beneficial in the search for particles beyond the Standard Model. A simulation of a benchmark long lived neutralino SUSY search is presented, and it is shown that the generator particle flight times can be faithfully reconstructed using the detector-level information. Identification algorithms for the SUSY model have been significantly improved with the use of a Boosted Decision Tree, and it is demonstrated that this algorithm has many benefits as compared to cut based IDs. With use of the BDT for the long lived neutralino SUSY model, the background rejection is increased significantly, with constant signal acceptance of 53.6%. This is an improvement in the significance of the signal selection by a factor of 2.38. Further improvement is seen with the inclusion of detector timing information in the BDT – with this contributing ≈25% of the information used in signal event identification. We thus demonstrate that with the BDT, the SUSY neutralino search can be performed with increased signal identification significance, and the searches’ sensitivity is expected to improve with the time resolution attained by the upgraded CMS calorimeter.

Item Type:Thesis (Senior thesis (Major))
Subject Keywords:LHC, CMS, precision timing, machine learning, BDT, long lived particles, neutralino, SUSY, GMSB, photon identification, delayed photons
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Awards:Library Friends Senior Thesis Prize Finalist, 2018. D.S. Kothari Prize in Physics, 2018.
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Spiropulu, Maria (advisor)
  • Pena Herrera, Cristian (co-advisor)
Group:Senior Undergraduate Thesis Prize
Thesis Committee:
  • Stone, Edward C. (chair)
  • Libbrecht, Kenneth George
  • Frautschi, Steven C.
  • Politzer, Hugh David
  • Refael, Gil
Defense Date:22 May 2018
Record Number:CaltechTHESIS:05222018-110636485
Persistent URL:
Kopp, Gillian Baron0000-0001-8160-0208
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10924
Deposited By: Gillian Kopp
Deposited On:24 May 2018 22:00
Last Modified:02 Aug 2022 21:38

Thesis Files

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