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Search for the $$Theta^{+}$$ pentaquark via the $$pi^-prightarrow K^-X$$ reaction at 1.92 GeV/$$c$$

1.92GeV/$$c$$$$pi^-prightarrow K^-X$$反応による$$Theta^{+}$$ペンタクォークの探索

白鳥 昂太郎; 今井 憲一; 佐甲 博之; 佐藤 進; 他64名*

Shirotori, Kotaro; Imai, Kenichi; Sako, Hiroyuki; Sato, Susumu; 64 of others*

J-PARCにおいて$$Theta^+$$ペンタクォークの探索実験を1.4MeV/$$c^2$$の高分解能の$$pi^-prightarrow K^-X$$を用いて行った。1.92GeV/$$c$$$$pi$$中間子ビームを液体水素標的に照射し生成を試みた。しかしながら、ミッシングマススペクトルに明瞭なピーク構造を観測することはできなかった。質量領域1.51-1.55GeV/$$c^2$$にて、微分生成断面積の上限値を$$K$$の散乱角度2$$^{circ}$$から15$$^{circ}$$の範囲で求め0.26$$mu$$b/srを得た。この生成断面積の上限値から$$Theta^+$$の幅の上限値をeffective Lagrangianによる理論計算を用いて求め、スピンパリティに応じ、0.72MeV/$$c^2(1/2^+)$$と3.1MeV/$$c^2(1/2^-)$$を得た。

The $$Theta^+$$ pentaquark baryon was searched for via the $$pi^-prightarrow K^-X$$ reaction in a missing-mass resolution of 1.4 MeV/$$c^2$$ (FWHM) at J-PARC. $$pi^-$$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$$c$$. No peak structure corresponding to the $$Theta^+$$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2$$^{circ}$$ to 15$$^{circ}$$ in the laboratory frame was obtained to be 0.26 $$mu$$b/sr in the mass region of 1.51$$-$$1.55 GeV/$$c^2$$. The upper limit of the $$Theta^+$$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$$c^2$$ and 3.1 MeV/$$c^2$$ for $$J^P_{Theta}=1/2^+$$ and $$J^P_{Theta}= 1/2^-$$, respectively.

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