Transcript The gp K+L and gp K+S0 reactions at SPring

Hyperon Photoproduction by
Linearly Polarized Photons at
SPring-8/LEPS
Mizuki Sumihama
RCNP, Osaka Univ.
for the LEPS collaboration
SPIN2006 Oct. 6th 2006
Physics motivation
Missing resonances N* and D* in s-channel
• It is essential to fully know
N* and D* to understand
baryon structure.
g
• Many nucleon resonances
predicted by quark model
are still missing.
p
• D13(1900) resonance in
SAPHIR / CLAS data was
found.
K+
N, N*, D*
Y(L, S0)
Some resonances should couple to KL or KS channel.
Kaon photoproduction is good means
to search for missing resonances.
Meson exchange in t-channel
Eg = 1.5 - 2.4 GeV
Transition region, s-channel  t-channel
Contribution of t-channel meson exchange
becomes large above 2GeV.
g
K+
K*, K, K1
p
Y(L, S0)
Photon-beam asymmetry S
natural parity exchange (K*)  S = + 1
unnatural parity exchange (K, K1)  S =－1
at t = 0 and large Eg.
LEPS spectrometer
– forward acceptance
Aerogel
Cherenkov
(n=1.03)
TOF
wall
Dipole Magnet
(0.7 T)
Start counter
Liquid Hydrogen
Target (50 mm thick)
Linearly polarized
g
Silicon Vertex
Detector
MWDC 3
MWDC 1
MWDC 2
1m
Particle identification
by time-of-flight and momentum measurements
Momentum resolution
~0.8% for 2GeV/c Kaons.
Time resolution ~150 ps.
K+ Missing mass spectrum
g p  K+L(1116)
g p  K+S0(1193)
Z-vertex distribution
LH2 target
K+
Photon asymmetry –L(1116)
data
Positive sign
Phys. Rev. C68, 058201 (2003)
K+K*-exchange (K*-exchange is dominant) by M. Guidal.
0412097
Isobar + Regge by T. Mart and C. Bennhold. nucl-th
/ SNP2004
Gent isobar model by T. Corthals. Phys. Rev. C73, 045207 (2006)
Agreement is not so bad, but still need fine optimization.
Photon asymmetry –S0(1193)
data
Positive sign
Phys. Rev. C68, 058201 (2003)
 K+K*-exchange (K*-exchange is dominant) by M. Guidal.
nucl-th 0412097 / SNP2004
Isobar by T.Mart and C.Bennhold.
Gent isobar model by T. Corthals Phys. Rev. C73, 045207 (2006)
Agreement is not so bad, but still need fine optimization.
Differential cross sections –L(1116)
Resonance-like structure
LEPS
SAPHIR
CLAS
LEPS data agree with
SAPHIR and CLAS at
cosQ = 0.75, 0.85
but discrepancy for
SAHIR data is large
at cosQ = 0.95.
LEPS data shows a small
bump at W= 1960MeV.
Regge K+K*-exchange
Isobar (with D13)+Regge
by T.Mart and C.Bennhold.
Good agreement.
W (GeV)
Differential cross sections –S0(1193)
Good agreement with
CLAS.
Slightly smaller than
SAPHIR.
Small bump structure
around W = 2070 MeV.
LEPS
SAPHIR
CLAS
Regge K+K*-exchange
Isobar model by
T.Mart and C.Bennhold.
Gent isobar model
by T. Corthals
Good agreement
W (GeV)
Differential cross sections –L(1116)
- angular dependence
CLAS
LEPS
Forward peaking
Cannot be reproduced
By Feynman diagram
only, at Eg>2GeV.
Need Regge poles.
Regge model K+K*-exchange
K-exchange makes forward peak for KL channel.
Isobar (Feynman) only
Isobar (Feynman) + Regge
by T.Mart and C.Bennhold.
Differential cross sections –S0(1193)
- angular dependence
CLAS
LEPS
No forward peaking.
Can be explained by
Feynman diagram only.
Regge model K+K*-exchange
K*-exchange is dominate for KS channel.
Isobar (Feynman)
by T. Mart and C. Bennhold.
Differential cross sections
for gp  pp0
- Check photon normalization
LEPS data
Old data
Curves SAID
(fit data at Eg < 2GeV)
Good agreement with SAID  Photon normalization is OK.
Summary
• The K+ photoproduction was measured by linearly polarized
photons at SPring-8/LEPS.
• Photon beam asymmetry is good tool to define theoretical
models. Theoretical models are still needed to be optimized.
• Differential cross sections were obtained at very forward
angles, up to cosQcm = 0.975.
• Bump structure was seen at W=1960 MeV in the K+L mode.
• We see a forward peaking in K+L while no peaking in K+S0.
• In order to fit the forward-angle data, a Regge pole is
necessary in addition to s-channel resonances and t-channel
K and K*-exchanges.
• Combination of isobar (Feynman) and Regge is successful to
explain this forward peaking in K+L.
• Photon normalization was checked by gp  pp0 cross sections.
The data show a good agreement with SAID. LEPS photon
normalization is OK.
PRC73, 035214 (2006) / PRL 91, 092001-1 (2003).
LEPS collaboration
D.S. Ahn, J.K. Ahn, H. Akimune, Y. Asano, W.C. Chang, S. Date, H. Ejiri, H. Fujimura, M.
Fujiwara, K. Hicks, K. Horie, T. Hotta, K. Imai, T. Ishikawa, T. Iwata, Y.Kato, H. Kawai, Z.Y.
Kim, K. Kino, H. Kohri, N. Kumagai, Y.Maeda, S. Makino, T. Matsumura, N. Matsuoka, T.
Mibe, M. Miyabe, Y. Miyachi, M. Morita, N. Muramatsu, T. Nakano, Y. Nakatsugawa, M.
Niiyama, M. Nomachi, Y. Ohashi, T. Ooba, H. Ookuma, D. S. Oshuev, C. Rangacharyulu, A.
Sakaguchi, T. Sasaki, T. Sawada, P. M. Shagin, Y. Shiino, H. Shimizu, S. Shimizu, Y. Sugaya,
M. Sumihama H. Toyokawa, A. Wakai, C.W. Wang, S.C. Wang, K. Yonehara, T. Yorita, M.
Yosoi and R.G.T. Zegers,
a Research Center for Nuclear Physics (RCNP), Ibaraki, Osaka 567-0047, Japan
b Department of Physics, Pusan National University, Pusan 609-735, Korea
c Department of Physics, Konan University, Kobe, Hyogo 658-8501, Japan
d Japan Atomic Energy Research Institute, Mikazuki, Hyogo 679-5148, Japan
e Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
f Japan Synchrotron Radiation Research Institute, Mikazuki, Hyogo 679-5198, Japan
h School of physics, Seoul National University, Seoul, 151-747 Korea
i Department of Physics, Ohio University, Athens, Ohio 45701, USA
j Department of Physics, Kyoto University, Kyoto, Kyoto 606-8502, Japan
k Laboratory of Nuclear Science, Tohoku University, Sendai 982-0826, Japan
l Department of Physics, Yamagata University, Yamagata, Yamagata 990-8560, Japan
m Department of Physics, Chiba University, Chiba, Chiba 263-8522, Japan
n Wakayama Medical College, Wakayama, Wakayama 641-0012, Japan
o Department of Physics, Nagoya University, Nagoya, Aichi 464-8602, Japan
p Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
q Department of Physics, University of Saskatchewan, Saskatoon, S7N 5E2, Canada
r Department of Applied Physics, Miyazaki University, Miyazaki 889-2192, Japan
Photon asymmetry
-difference between L and S0
L(1116) / S0(1193)
Photon asymmetry
-energy dependence
L(1116) / S0(1193)
Eg (GeV)