Date of Award

August 2016

Degree Type


Degree Name

Doctor of Philosophy (PhD)




Tomasz Skwarnicki


Hadrons, LHC, LHCb, Pentaquarks

Subject Categories

Physical Sciences and Mathematics


The observation of structures consistent with charmonium-pentaquark states decaying to $J/\psi p$ in $\Lambda_b^0 \rightarrow J/\psi K^- p$ decays is presented. The data sample analyzed corresponds to an integrated luminosity of 3 $fb^{-1}$ acquired with the LHCb detector from 7 and 8 TeV $pp$ collisions. An amplitude analysis was performed which utilized all six kinematic degrees of freedom in the decay. It was shown that adequate descriptions of the data are unattainable with only $K^- p$ resonances in the amplitude model. For satisfactory fits of the data, it was found to be necessary to include two $J/\psi p$ resonances, with each having significances of over 9 standard deviations. One has a mass of $4449.8\pm1.7\pm2.2$ MeV and a width of $39\pm5\pm16$ MeV, while the second is broader, with a mass of $4380\pm8\pm29$ MeV and a width of $205\pm18\pm87$ MeV. The $J^P$ assignments could not be uniquely determined, though there is a preference for one to have spin $3/2$ and the other spin $5/2$ with an opposite parity to the first. The data sample was also inspected in a model-independent way for the presence of $J/\psi p$ or $J/\psi K^-$ contributions. It was demonstrated at more than 9 standard deviations that the data cannot be described with $K^- p$ contributions alone, and that $J/\psi p$ contributions play a dominant role in this incompatibility. These model-independent results support the model-dependent evidence for $P_c^+\rightarrow J/\psi p$ charmonium-pentaquark states provided by the amplitude analysis.


Open Access