A Caltech Library Service

Search for Beyond Standard Model Physics at BaBar


Li, Yunxuan (2022) Search for Beyond Standard Model Physics at BaBar. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/tz7n-d662.


This thesis reports searches for beyond Standard Model physics in e+e collisions in two directions.

We report the first search for a dark matter bound state. The existence of dark matter bound states could arise in a simple dark sector model in which a dark photon (A) is light enough to generate an attractive force between dark fermions. We report herein a search for a JPC = 1 − − darkonium state, the ΥD, produced in the reaction e+e → γΥD, ΥD → AAA, where the dark photons subsequently decay into pairs of leptons or pions, using data collected with the BaBar detector. No significant signal is observed, and we derive limits on the γ − A kinetic mixing (ϵ) as a function of the dark sector coupling constant for 0.001 < mA < 3.16 GeV and 0.05 < mΥD < 9.5 GeV. Bounds on the mixing strength ϵ down to 5 × 10 − 5 − 10 − 3 are set for a large fraction of the parameter space.

We also report a measurement of R(D) = B(B → τν̄τ)/B(B → ν̄) and R(D*) = B(B → *τν̄τ)/B(B → *ν̄), where refers to either an electron or muon. We select samples by reconstructing tag-side B mesons in semileptonic decays and signal-side τ in a purely leptonic decay. Using data collected with the BaBar detector, we measure R(D) = 0.316 ± 0.062(stat) ± 0.019(syst) and R(D*) = 0.226 ± 0.022(stat) ± 0.012(syst), which agree with the Standard Model expectations by 0.26σ and 1.10σ, respectively. Taken together, the results are in agreement with the Standard Model within 1.51σ level.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Beyond Standard Model Physics, Electron-Positron Collider, BaBar Collaboration, High Energy Physics, Dark Matter, B Meson Decays
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Minor Option:Computer Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Hitlin, David G.
Thesis Committee:
  • Porter, Frank C. (chair)
  • Hitlin, David G.
  • Patterson, Ryan B.
  • Wise, Mark B.
  • Echenard, Bertrand
Defense Date:20 May 2022
Non-Caltech Author Email:yxli528 (AT)
Record Number:CaltechTHESIS:05232022-144829107
Persistent URL:
Li, Yunxuan0000-0001-9004-2471
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14598
Deposited By: Yunxuan Li
Deposited On:27 May 2022 23:21
Last Modified:04 Aug 2022 23:21

Thesis Files

[img] PDF - Final Version
See Usage Policy.


Repository Staff Only: item control page