Transcript Differetial cross section of K photoproduction at Spring

Differential cross sections
for K+ photoproduction
at SPring-8/LEPS.
Mizuki Sumihama
Department of physics
Tohoku university
For LEPS collaboration
JPS meeting at Kochi 9.27 2004
The LEPS collaboration
Research Center for Nuclear Physics, Osaka University
D.S. Ahn, M. Fujiwara, T. Hotta, K. Kino,
H. Kohri, T. Matsumura, T. Mibe, T. Nakano, A. Shimizu,
M. Sumihama
Pusan National University
J.K. Ahn
Konan University
H. Akimune
Japan Atomic Energy Research Institute / SPring-8
Y. Asano, N. Muramatsu
Institute of Physics, Academia Sinica, Taiwan
W.C. Chang, T.H. Chang, D.S. Oshuev, C.W. Wang, S.C.
Wang
Japan Synchrotron Radiation Research Institute (JASRI)
/ SPring-8
S. Date, H. Ejiri, N. Kumagai, Y. Ohashi, H. Ookuma,
H.Toyokawa, T. Yorita
Ohio University
K. Hicks
Kyoto University
K. Imai, M. Miyabe, M. Niiyama, T. Sasaki, M. Yosoi
Chiba University
H. Kawai, T. Ooba, Y. Shiino
Yamagata University
T. Iwata
Wakayama Medical University
S. Makino
Nagoya University
T. Fukui
Osaka University
H. Nakamura, M. Nomachi, A. Sakaguchi, Y. Sugaya,
University of Saskatchewan
C. Rangacharyulu
Institute for High Energy Physics (IHEP), Moscow
P. Shagin
Laboratory of Nuclear Science, Tohoku University
H. Shimizu, T. Ishikawa
University of Michigan
K. Yonehara
Michigan State University
R.G.T. Zegers
Seoul National University
H. Fujimura
Miyazaki University
T. Matsuda, Y. Toi
Physics motivations
• Missing baryon resonance search (D13, ….)
• Meson exchange in t-channel (K, K*, K1)
Eg = 1.5 - 2.4 GeV at LEPS
Data of Kaon photoproduction at sub-GeV energy
 Cross section from SAPHIR, CLAS
 Recoil polarization from SAPHIR, CLAS
 Photon beam asymmetry from LEPS
There still remains a controversy
in theoretical descriptions.
Discrepancy
between Bonn/SAPHIR and Jlab/CLAS
g+p
K+ + L
g+p
K+ + S0
It is important to
solve the discrepancy between SAPHIR and CLAS, and
obtain the data overall energy and angle range.
Experiment
•
•
•
•
Photon energy 1.5 – 2.4 GeV.
Liquid hydrogen target with a 5 cm.
~1x1011 photons at the target.
K+ angle cos(Qcm) = 0.75, 0.85, 0.925, 0.975.
g+p
g+p
K+ + L (2.2x104 events)
K+ + S0 (1.5x104 events)
Detected by spectrometer.
Data analysis
g+p
g+p
K+ + L
K+ + S 0
Event selection
1
2
3
4
5
6
K+ selection with Mass (3s).
Reject decay-in-flight with c2 of track fitting.
Reject e+e- cut (remove events in-plane).
Proton selection with z-vertex point.
Photon selection at tagging counter.
Hyperon selection with missing mass (2s).
Differential cross sections
a(NK+ - b)
ds
=
NB・NT・d(cosQcm)
d(cosQcm)
NK+ : number of selected K+ events
NB : number of protons
NT : number of photons
a = acceptance of K+ and detectors
b = background contaminations
(pions, protons, start counter)
< 2.2%
< 6.5%
Results of differential cross sections
g+p
SAPHIR CLAS LEPS
K+ + L
g+p
K+ + S 0
Theoretical models I
g+p
K+ + L
g+p
K+ + S 0
K + K* and K* : Regge theory by Guidal (NPA627, 645,1997)
Isobar model with missing resonance of D13 (PRC65,015201, 2002)
Theoretical models II
g+p
K+ + L
g+p
K+ + S 0
Regge, Feynman (D13), Mix by Bennhold and Mart
Theoretical models III
g+p
K+ + L
g+p
K+ + S 0
Regge, Feynman (D13), Mix by Bennhold and Mart
Summary
• Differential cross sections of K+ photoproduction
at Eg = 1.5 – 2.4 GeV and forward angles.
• LEPS data shows a good agreement with CLAS data.
Solve the discrepancy between SAPHIR and CLAS.
• Resonance structure at W=1.86 GeV and
forward peaking can be seen in g + p K+ + L.
No resonance nor forward peaking in g + p K+ + S0.
• Refitting with new LEPS data and CLAS data
and LEPS photon asymmetries data.
LEPS detector
Aerogel
Cerenkov
(n=1.03)
TOF
wall
Dipole Magnet
(0.7 T)
Start counter
Liquid Hydrogen
Target (50mm thick)
g
Silicon Vertex
Detector
MWDC 1
MWDC 3
MWDC 2
1m
Photon beam asymmetry