Resonance Production through the Two Neutral-Pion Channel

Thesis/Dissertation · Wed Jan 30 04:00:00 EST 2002

DOI:https://doi.org/10.2172/824914· OSTI ID:824914

Philips, Sasha A. ^[1]

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1. George Washington Univ., Washington, DC (United States)

We have obtained data for the γp → π⁰π⁰ reaction with the CLAS at Jefferson Lab for photon energies 0.4 < E_γ < 1.7 GeV. These data extend previous total-cross-section measurements of the γp → π⁰π⁰ channel beyond E_γ = 800 MeV, and show a strong enhancement of resonance production at E_γ ~ 1.1 GeV (W_cms ~ 1.7 GeV). The proton and forward-going π⁰ were detected in the CLAS, while the backward π⁰ has been reconstructed from missing mass. An intermediate Δ state can be reconstructed from the proton and the backward π⁰, which provides information on the sequential decay of the γp → N* → Δ⁺ π⁰ → π⁰ π⁰ process. The Δ⁺ π⁰ intermediate state is a significant part of the cross section at center-of-mass energies of W ~ 1700 MeV and W ~ 1930 MeV. The enhancement at W ~ 1.7 GeV is broad, and coincides with the structure seen in the total cross-section measurement. This is most likely the signature of a nucleon resonance having a mass of 1650-1750 MeV, with strong Δπ and γp couplings. The enhancement at W ~ 1.9 GeV, however, is narrow and therefore is unlikely to arise from resonance production or the interference of a resonance with non-resonant background. The proximity of the enhancement to the pn' threshold (W = 1896 MeV), as well as evidence from other analyses for the presence of a resonance at this mass, suggests a cusp phenomenon. There is also evidence for the γp → (N* → D₁₃(1520) π⁰) → (p π⁰) π⁰ two-step process, that is enhanced at W approx. 1.83 GeV. No resonances have been previously observed at this energy. Finally, for events that did not proceed through the two decay chains mentioned above, there is an enhancement at W approx. 1.7 GeV. This could possibly be the signature of a resonance decaying via the γp → pσ → p(π⁰ π⁰) process. If this enhancement arises from the same resonance in the Δπ channel, then its branching fraction would be roughly 1/2 that of the Δπ channel.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Energy Research (ER)
• DOE Contract Number: AC05-84ER40150
• OSTI ID: 824914
• Report Number(s): JLAB-PHY--02-107; DOE/ER/40150--2758
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
CROSS SECTIONS
CUSPED GEOMETRIES
DECAY
MESONS
MISSING MASS
NUCLEONS
PHOTONS
PRODUCTION
PROTONS
RESONANCE
TOTAL CROSS SECTIONS