(K+,p+)反応によるPenta

21世紀COE外国旅費補助出張報告会
IX International Conference on
Hypernulear and Strange Particle Physics
(HYPE2006)
“Search for Q+ via K+p -> p+X reaction with highresolution spectrometer system”
原子核ハドロン物理学研究室
大樂誠司
E559 collaboration
Gifu U.
T. Kameyama, K. Nakazawa, T. Watanabe
KEK
S. Ishimoto, T. Nagae, H, Noumi, Y. Sato, S. Sawada,
M. Sekimoto, S. Suzuki, H. Takahashi, T. Takahashi, N. Tanaka,
A. Toyoda
Kyoto U.
S. Dairaku, H. Funahashi, K. Imai*, K. Miwa, K. Shoji, M. Hayata,
M. Miyabe, M. Niiyama, N. Saito, Y. Seki
Ohio U.
K. Hicks, R. Zavislak
Osaka U.
S. Ajimura
Osaka EC U.
T. Fukuda
RCNP
T. Nakano, M. Yosoi
RIKEN
M. Naruki, K. Tanida
Tohoku U.
S. Kinoshita, T. Koike, Y. Ma, Y. Miura, K. Shirotori, H. Tamura
U. Paris-Sud
J. Arvieux
U. Tokyo H. Fujioka, T. Maruta, D. Nakajima, T. N. Takahashi
The
+
Q
baryon
Theoretical prediction
• Diakonov et al.
– Chiral soliton model
– Anti-decuplet
– M=1530 MeV, < 15MeV
Experiment
• LEPS at Spring-8
– n  -Q  -n
– M=154010 MeV
– <25 MeV
LEPS
Purpose
 Search for Q+ Pentaquark ( E559 at KEK-PS K6)
 if Q+ exists, < 1 MeV/c2 (M=1530 - 1540 MeV/c2)
 High Resolution spectrometer SKS & K6beamline
⇒resolution ： 2.4 MeV/c2 (FWHM)
 High statistics
 Hadronic reaction K+p -> p+X
 1.2 GeV/c K+ beam and liquid H2 target
 Determination of decay angle distribution
 Large solid angle Drift Chamber & Range Counter
downstream of target
 Spin and Parity
Setup
SKS
1.6 T
π+(0.5 - 0.6 GeV/c)
p+
K+ (1.2GeV/c)
mass2(GeV/c2)2
For π+veto
p+
Solid angle
0 - 60 deg
K+
Data set
RUN1 ( 2005/5/24 - 2005/7/1 )
H(K+,p+) run
@1.2GeV/c for Q+
K+ yield : 2.79x109
Empty target run @1.2GeV/c for B.G.
H(p+,K+) run
@1.1GeV/c for S+
RUN2 ( 2005/12/13 - 2005/12/28 )
H(K+,p+) run
@1.2GeV/c for Q+
Empty target run @1.2GeV/c for B.G.
H(p+,K+) run
@1.1GeV/c for S+
K+ yield : 2.09x109
Resolution for S+ and Q
1st run
M=1189.31 ± 0.03 MeV/c2
=2.03 ± 0.06 MeV/c2
Resolution
K6 : p/p = 0.047% (FWHM)
SKS : p/p = 0.43% (FWHM)
Mass(GeV/c2)
(simulation) for S+ 1.98 MeV/c2 (FWHM)
This is consistent with real data
(simulation) for Q 2.4 MeV/c2 (FWHM)
2nd run
M=1189.33±0.03 MeV/c2
=1.94±0.07 MeV/c2
Missing mass value
Mass(GeV/c2)
1st run is consistent
with 2nd run
Vertex distribution (before B.G. cut)
1st run
2nd run
(K+, p+)
(K+, p+)
(p+, p+)
vertex z(mm)
(p+, p+)
vertex z(mm)
(K+, p+) reaction : large background from K+ decay
Suppression of K+ decay events
(SDC1 analysis cut)
π+veto
K+
Aerogel
Beam line chamber
π+
Target
vertex
SKS
SDC1
analysis
K+pSDC1
reaction
event cut
SDC2
RC
drift chamber
K+ decay event
98.0% of K+ decay
events are suppressed
+
(simulation)K
K+
Even charged &
( to SKS )
( to SKS )
p
p
70.1% of Q+ production events remain
Large scattered angle
(simulation
--- assume isotropic angular distribution)
vertex distribution (after B.G. cut)
2nd run
1st run
vertex z(mm)
16900 event (-30<z<100)
vertex z(mm)
11900 event (-40<z<85)
Missing Mass (ppX)
Sum of 1st and 2nd runs
Assumption
1530MeV/c2
s=50mb
isotropic distribution
Expected peak
under assumption
Preliminary
Missing Mass (ppX)
Preliminary
170 ( 90% C.L. upper limit)
Upper limit
NQ
s
N tgt  N K   (efficiency)
NQ
Counts(90% C.L.)
Ntgt
NK+
5.04x1023
90% C.L.9 upper limit
4.88x10
Survival rate
0.858
Interaction factor
0.94
K6 efficiency
0.935(K6 tracking)
SKS efficiency
SDC1 analysis cut
0.953(SdcOut)x0.875(SdcIn)
x0.93(SksTrack)=0.775
90% C.L. upper limit
0.701 ( assume angular distribution )
vertex cut
0.85
Trigger efficiency
0.95(LC)x0.99(TOF)
Acceptance
0.11sr(Laboratory frame)
0.0293(assume angular distribution)
Preliminary
Cross section of H(K+,π+) reaction
=1MeV
√s=1.89GeV ( E559 exp. )
gK*NQ= ＋gKNQ
gK*NQ= －gKNQ
gK*NQ= 0
W/O F.F.
Y. Oh et al.
Phys. Rev. D 69, 074016
L=1.2GeV
Cross section of H(K+,π+) reaction
=1MeV
gK*NQ= ＋gKNQ
gK*NQ= －gKNQ
gK*NQ= 0
Y. Oh et al.
Phys. Rev. D 69, 074016
Preliminary
E559 exp.
90% C.L. upper limit
W/O F.F.
L=1.2GeV
Summary
 Search for Q+ via H(K+, p+) reaction
at KEK-PS K6 beamline
 K+ beam yield 4.88x109
reaction event 28800 (after SDC1 cut)
 No significant peak (1520 － 1560 MeV/c2)
 cross section 7.0mb, 1.9mb/sr
90% C. L. upper limit
(assume angular distribution)
much smaller than theoretical value
under K* exchange (calculated by Y.Oh )
END

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