First observation of S N decay of S= -2 system
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Transcript of First observation of S N decay of S= -2 system
First observation of N decay of S= system
T. Watanabe (Gifu University)
and KEK-E373 Collaborators
Brief status report of E373 Analysis of N decay event
– Event topology– Analysis
Discussion Summary
KEK-E373 experiment - capture events• 570 (90) events [preliminary]
estimated by the number of events of single- hypernuclei
in relation to that obtained by the previous exp. (KEK-E176).
– Double- hypernucleus (cand.) : 6– Twin single- hypernucleus : 2
– # stop is about 60 % of expected value
• Come from emulsion scanning efficiency
• 2nd analysis is underway
atom
28MeV
Hor
Λ
ΛΛ
ΛΛor H
p ⇒
Λ
Λ Λ
A
(S=-2)
5
6ΛΛHe
4He
t
Ξ -
p
π -
ΛHe
10μm500
10
5
Event topology
A
B0 5 10
(m)
10
5
0
#1
#3
#1
5.3±0.5m preliminary
#2
56.6±1.2mpreliminaryDecay angle #2#3:153.48±0.43o
#3
15539 m
Escaping from emulsion
#2
Particle identification of track #3
A
B0 5 10
(m)
10
5
0
#1
#2 #3
At point B• if mesonic decay of H (#2)
2 charged particles should be seen at Bonly 1 particle, denied
if non mesonic decay of H(#2)#3 is proton: Tp > 200 MeVQ-value of H ~170 MeVTp is too large, denied
Track#3 is from weak decay of hyperon. emul. = 1.60 MeV.g-1.cm2 (by SRIM2000) T = 66.0 ± 2.0 MeV (by dE/dx fitting, =5.1) To confirm this method,apply it to of the NAGARA event Tp = 26.1 ± 0.5 MeV (by dE/dx fitting, 2=3.4) Tp = 27.3 ± 0.5 MeV (by range, 2=4.0) consistent
Mass reconstruction of #2
A
B0 5 10
(m)
10
5
0
#1
#2 #3
= 153.48±0.43o
p (#2)
: KE=66.0±2.0 (MeV)
n: ???? (MeV)
KE() = 64 MeV
KE() = 68 MeV
M() = 1197MeV
M() = 1189MeV
T(#2): 22.6~29.6 MeV for
14.7~20.6 MeV for
Event reconstruction at point A(1)
A
B0 5 10
(m)
10
5
0
#1
#2 #3
Possibility of K absorption fromK- + 12C K+ + K- + 12
B• pK
-(beam)= 1.67 GeV/c (momentum bite 3.6%)
• pK+ = 0.987 GeV/c (max.=20 MeV/c)
• K- = 14.3°• TK- = 0.321 GeVRequired beam momentum is too high, denied
K
Event reconstruction at point A(2)
Track is truly - from (K-,K+) reaction?(miss connection SciFi emulsion)• candidates are rescanned 5 times• 11 candidates are picked up• No event of stop is found except this event
KE() : 22.6~29.6MeV KE() + KE(p) : 51.8~67.8 MeV
from (K-,K+) is absorbed at point A
+(p) X + Q1, X + p(included in #1) + Q2
X : or H
So far, the mass of X is not known. more analysis is still needed.
A
B0 5 10
(m)
10
5
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#1
#2 #3
discussion• The first observation of an event
+ (p) (X) + p. capture as rest : 570 (±90) events
– several tens S=-2 nuclei ( estimated from KEK-E176)
Invariant mass of produced by (K-,K+) reaction in Scifi target.A peak is seen at the threshold.
?? H-dibaryon resonance ??(KEK-E522)
Theoretical approach
Possibilities of 1) mixing H 2) H-nucleus
• Decay rate ( p) for 6He [unit ]: ~10-3
(NOT H-dibaryon)References:1) K.Itonaga, T.Ueda and T.Motoba; NP. A691(2001) 1972) A.Parreno, A.Ramos and C.Bennhold; PRC65(2002) 0152053) 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 p ) : several×10 %
Summary• An event showing weak interaction of double strangeness wa
s observed for the first time.• We can probably get information for the mixing.• We attempt to do particle identification of absorbed particle fr
om track profile in the emulsion– track volume– multiple scattering angle
• Near future– 2nd scan of KEK E373
( #stop: 560 (±90) 103 (designed value) )– J-PARC E07 ( #stop : 104 )