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First observation of S N decay of S= -2 system

First observation of S N decay of S= -2 system. Brief status report of E373 Analysis of S N decay event Event topology Analysis Discussion Summary. T. Watanabe ( Gifu University ) and KEK-E373 Collaborators. K +. K -. Λ. Λ. o. r. H. X -. p ⇒. -. X. LL + 28 MeV. Λ.

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First observation of S N decay of S= -2 system

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  1. First observation of SN decay of S=-2 system • Brief status report of E373 • Analysis of SN decay event • Event topology • Analysis • Discussion • Summary T. Watanabe (Gifu University) and KEK-E373 Collaborators

  2. K+ K- Λ Λ o r H X- p ⇒ - X LL + 28MeV Λ X - A Λ A*(S=-2) Λ Λ X-atom Λ Λ o r H KEK-E373 experiment X- capture events • 570 (±90) events [preliminary] estimated by the number of events of single-L hypernuclei in relation to that obtained by the previous exp. (KEK-E176). • Double-L hypernucleus (cand.) : 6 • Twin single-L hypernucleus : 2 • # X-stop is about 60 % of expected value • Come from emulsion scanning efficiency • 2nd analysis is underway

  3. A Event topology #1 X- #3 #2 10 5 0 0 5 10 (mm) B

  4. A B Particle identification of track #3 • At point B • if mesonic decay of LH (#2) 2 charged particles should be seen at B only 1 particle, denied • if non mesonic decay of LH(#2) #3 is proton: Tp > 200 MeV Q-value of LH ~170 MeV Tp is too large, denied #1 X- #3 #2 10 5 0 Track#3 is p from weak decay of hyperon. remul. = 1.60 MeV.g-1.cm2 (by SRIM2000) Tp = 66.0±2.0 MeV (by dE/dx fitting, c2=5.1) To confirm this method, apply it to p of the NAGARA event Tp = 26.1 ± 0.5 MeV (by dE/dx fitting, c2=3.4) Tp = 27.3 ± 0.5 MeV (by range, c2=4.0) consistent 0 5 10 (mm)

  5. p :KE=66.0±2.0 (MeV) q= 153.48±0.43o p(#2) n:???? (MeV) A KE(p) = 68 MeV M(S-) = 1197MeV M(S+) = 1189MeV KE(p) = 64 MeV B  T(#2):22.6~29.6 MeV for S- 14.7~20.6 MeV for S+ Mass reconstruction of #2 #1 X- #3 #2 10 5 0 0 5 10 (mm)

  6. A B Event reconstruction at point A(1) • Possibility of K- absorption from • K- + 12C  K+ + K- + 12LB • pK-(beam)= 1.67 GeV/c (momentum bite 3.6%) • pK+ = 0.987 GeV/c (smax.=20 MeV/c) • qK- = 14.3° • TK- = 0.321 GeV • Required beam momentum is too high, denied #1 K- X- #3 #2 10 5 0 0 5 10 (mm)

  7. A B Event reconstruction at point A(2) • Track is truly X- from (K-,K+) reaction? • (miss connection SciFi  emulsion) • X- candidates are rescanned 5 times • 11 candidates are picked up • No event of X- stop is found except this event #1 X- X- from (K-,K+) is absorbed at point A #3 #2 X- +(p)  X + Q1, X  S- + p(included in #1) + Q2 X : LLor H 10 5 0 KE(S-) :22.6~29.6MeV  KE(S-) + KE(p): 51.8~67.8 MeV 0 5 10 (mm) So far, the mass of X is not known.  more analysis is still needed.

  8. discussion • The first observation of an event • X- + (p)  (X)  S-+ p. • X- capture as rest : 570 (±90) events • several tens S=-2 nuclei ( estimated from KEK-E176) Theoretical approach ?? H-dibaryon resonance ?? (KEK-E522) • Decay rate (LL S-p)for 6LLHe [unit GL]: ~10-3 • (NOT H-dibaryon) References: 1) K.Itonaga, T.Ueda and T.Motoba; NP. A691(2001) 197 2) A.Parreno, A.Ramos and C.Bennhold; PRC65(2002) 015205 3) K.Sasaki, T.Inoue and M.Oka; NP. A726 (2003) 349 [4) H.Nemura, S.Shinmura, Y.Akaishi and K.S.Myint PRL94(2005) 202502] • Decay rate(H  S-p ) : several×10 % Possibilities of 1) mixing LL  H 2) H-nucleus Invariant mass of LL produced by (K-,K+) reaction in Scifi target. A peak is seen at the threshold.

  9. Summary • An event showing weak interaction of double strangeness was observed for the first time. • We can probably get information for the mixing. • We attempt to do particle identification of absorbed particle from track profile in the emulsion • track volume • multiple scattering angle • Near future • 2nd scan of KEK E373 ( #Xstop: 560 (±90)  103(designed value) ) • J-PARC E07 ( #Xstop : 104 )

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