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Excited nucleon states are established as an important milestone to understand quantum chromodynamics in the non-perturbative region. Even after decades of study, not all of the excited states predicted by different theoretical approaches have been verified. The disparity between the predicted states and the verified states is known as the “missing baryon problem". The verified states were mostly established using pion beam data or through Nπ decay channels, but are not sufficient to address the missing baryon problem. In recent years, new experiments were conducted worldwide at CLAS in Jefferson Lab, ELSA in Bonn, MAMI in Mainz, and so on, using electromagnetic probes that also included the study of multiple channels with different states. Since excited baryon states are broad and overlap, they are difficult to disentangle using cross-section data alone. Thus, polarization observables can play a crucial role in the identification of missing baryons.
The current work uses CLAS g12 data, which were obtained from a circularly polarized photon beam incident upon an unpolarized hydrogen target, γp −> K+Λ, from CLAS at Jefferson Lab. Due to the weak decay of the hyperon, it is possible to measure the polarization observables from decay products, particularly pπ−with a 64% branching ratio. We measured the transferred polarization observables Cxand Cz, and the induced polarizationP. The measurement covers the center-of-mass energy range from 1.75 GeV to 3.33 GeV, expanding previous coverage by roughly 500 MeV for the Pobservable and 800 MeV for the Cxand Czobservables. We produced results for polarization observables via two topologies, K+p π−and K+p(π−), and found excellent agreement between them.
The current analysis data, along with the previously published photo- and electro- production cross section and polarization observables from CLAS, SAPHIR, and GRAAL, are needed in a coupled-channel analysis to find the predicted excited states. The results at higher energies are important for determining the contributions from non-resonant processes, which is a dominant background in the lower energy baryon resonance region.
Adhikari, Shankar Dayal, "Polarization Observables for γp −> K+Λ at Photon Energies up to 5.45 GeV" (2018). FIU Electronic Theses and Dissertations. 3908.
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