A study of 3π production in γp → n^-π⁺π⁺π^- and γ-p → Δ⁺⁺π⁺π^-π^- with CLAS at Jefferson Lab ->n

Thesis/Dissertation · Mon Feb 22 00:00:00 EST 2016

DOI:https://doi.org/10.2172/1351257· OSTI ID:1351257

Tsaris, Aristedis ^[1]

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1. Florida Intl Univ., Miami, FL (United States)

Apart from the mesons that the constituent quark model predicts, QCD allows for additional states beyond the qq system. Previous experiments have performed partial wave analysis on pion-production data and claim observation of an exotic J^PC = 1^-+ state decaying via p-π. The g12 experiment took place at Jefferson Lab using the CLAS spectrometer, a liquid hydrogen target was used and a tagged photon beam. By studying the reactions γp → n^-π⁺π⁺π^- and γp → Δ⁺⁺π⁺π^-π^-, the photoproduction of mesons decaying to 3-pi was studied using two different but complimentary channels. Events are selected with low four-momentum transfer to the baryon, in order to enhance one pion exchange production. For both 3-pi systems the data exhibit two intermediate decays, p-pi and f₂π. For the γp → n^-π⁺π⁺π^- reaction over 600k events were acquired resulting in the largest 3 photoproduction dataset to date. The exotic J^PC = 1^-+ partial wave does not show resonant behavior and more so it is strongly consistent with a non-resonant non-interfering wave relative to a resonant π₂(1670). Furthermore, the partial wave analysis shows production of the a₂(1320) and π₂(1670) mesons. For the first time we report observation of a photoproduced a₁(1260) meson. For the γp → Δ⁺⁺π⁺π^-π^- reaction nearly 350k events were analyzed. A partial wave analysis was performed for the first time on this channel. The a1(1260), a2(1320), and the 2(1670) mesons were observed. Observation of the a1(1260) confirms the result first reported in γp → n^-π⁺π⁺π^- reaction.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-84ER-40150
• OSTI ID: 1351257
• Report Number(s): JLAB-PHY-16-2443; DOE/OR/23177-4115
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS