Differential cross sections for K+ photoproduction

at SPring-8/LEPS.

Mizuki SumihamaDepartment 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

• Missing baryon resonance search (D13, ….)

• Meson exchange in t-channel (K, K*, K1)

Physics motivations

Data of Kaon photoproduction at sub-GeV energy Cross section from SAPHIR, CLAS Recoil polarization from SAPHIR, CLAS Photon beam asymmetry from LEPS

E = 1.5 - 2.4 GeV at LEPS

There still remains a controversy in theoretical descriptions.

Discrepancy between Bonn/SAPHIR and Jlab/CLAS

It is important to solve the discrepancy between SAPHIR and CLAS, and obtain the data overall energy and angle range.

+ p K+ + + p K+ +

Experiment

• Photon energy 1.5 – 2.4 GeV.

• Liquid hydrogen target with a 5 cm.

• ~1x1011 photons at the target.

• K+ angle cos(cm) = 0.75, 0.85, 0.925, 0.975.

+ p K+ + (2.2x104 events) + p K+ + (1.5x104 events)

Detected by spectrometer.

Event selection1 K+ selection with Mass (3). 2 Reject decay-in-flight with of track fitting.3 Reject e+e- cut (remove events in-plane). 4 Proton selection with z-vertex point. 5 Photon selection at tagging counter. 6 Hyperon selection with missing mass (2).

Data analysis

+ p K+ + + p K+ +

d(coscm)a(NK+ - b)d

NB ・ NT ・ d(coscm)=

Differential cross sections

NK+ : number of selected K+ eventsNB : number of protonsNT : 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

+ p K+ + + p K+ +

SAPHIR CLAS LEPS

Theoretical models I

+ p K+ + + p K+ +

K + K* and K* : Regge theory by Guidal (NPA627, 645,1997)

Isobar model with missing resonance of D13 (PRC65,015201, 2002)

Theoretical models II

+ p K+ + + p K+ +

Regge, Feynman (D13), Mix by Bennhold and Mart

Theoretical models III

+ p K+ + + p K+ +

Regge, Feynman (D13), Mix by Bennhold and Mart

Summary• Differential cross sections of K+ photoproduction at E = 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 + p K+ + . No resonance nor forward peaking in + p K+ + .• Refitting with new LEPS data and CLAS data and LEPS photon asymmetries data.

LEPS detector

1m

TOFwall

MWDC 2

MWDC 3

MWDC 1

Dipole Magnet (0.7 T)

Liquid HydrogenTarget (50mm thick)

Start counter

Silicon VertexDetector

AerogelCerenkov(n=1.03)

Photon beam asymmetry