K

+ L

and K

+ S 0

photoproduction at SPring-8/LEPS Mizuki Sumihama Department of physics Osaka Univ.

for LEPS collaboration

1. Introduction 2. Experiment 3. Data analyses 4. Experimental results 5. Summary

LEPS collaboration

M. Nomachi, A. Sakaguchi, Y. Sugaya, M. Sumihama

Dept. of physics Osaka Univ.

H. Fujimura, M. Fujiwara, T. Hotta, H. Kohri, T. Matsumura, N. Matsuoka, T. Mibe, M. Morita, T. Nakano, R.G.T.Zegers

RCNP Osaka Univ.

K. Imai, M. Miyabe, M. Niiyama, M. Yosoi

Dept. of physics Kyoto Univ.

D.S. Ahn, J.K. Ahn

Pusan Nat’l Univ.. Korea

T. Iwata

Dept. of physics Yamagata Univ.

Y. Asano,N. Matsumura

JAERI

T. Ishikawa, H. Shimizu

Tohoku Univ.

H. Kawai, T. Ooba, Y. Shiino

Chiba Univ.

S. Date, N. Kumagai, Y. Ohashi, H. Ookuma, T. Yorita

JASRI

W.C. Chang, D.S. Oshuev, C.W. Wang, S.C. Wang

Academia Sinica, Taiwan

A. Wakai

Akita Industry Promotion Foundation

K. Hicks

Ohio Univ.USA

C. Rangacharyulu

Univ.. of Saskatchewan Canada

H. Akimune

Konan Univ.

P. Shagin

Minnesota Univ.

S. Makino

Wakayama Med. Univ.

1. Introduction

Missing resonances N * and D * in strangeness channels • • • Information on nucleon resonances mainly comes from the p N channel.

Many nucleon resonances predicted by quark model are still missing.

It is essential to fully know N * and D * to understand the structure of baryons.

g p N, N * , D * K + Y( L, S ) Some resonances may couple to K L or K S channel.

K + photoproduction is good means to search missing resonances.

Resonance structure?

• Resonance like structure in the total cross section for p( g ,K + ) L from SAPHIR and CLAS.

• Missing resonance D 13 (1960) ?

without D 13 with D 13 calculations by Mart and Bennhold • There still remains a controversy of the theoretical description.

• Only cross section data is not conclusive .

~ 1.9 GeV SAPHIR data Additional observables are required .

Photon beam asymmetry is one of the candidates .

Theoretical predictions of photon asymmetry

by Mart & Bennhold without D 13 (1960) with D 13 (1960) by Janssen

et al

Hadronic form factor A B C Davidson&Workman Haberzettl A) Small cut-off mass B) L * in u-channel C) No restriction on g KYp With D 13 (1960) Need more study to fix parameters.

Photon beam asymmetry is sensitive to model differences.

2.

Experiment

• 2000.12 ~ 2001.6

• Liquid hydrogen target : 5cm • Linearly polarized photons Tagged photons 1.5 ~ 2.4 GeV Resolution 15 MeV Beam intensity 5 x 10 5 cps (Tagged photons) High polarization ~92% at 2.4 GeV ~55% at 1.5 GeV • 52% data with vertical polarization 48% data with horizontal polarization • 2 x 10 12 photons at the target Photon beam asymmetries for the p( g ,K + ) L and p( g ,K + ) S 0 reactions

3. Data analyses

Event selections for p( g ,K + ) L and p( g ,K + ) S 0

• Tagged photons •

recoil electron by Tagging counter

• Events from the proton target

z-vertex point of K + contamination from the trigger counter ~ 8% < 2% q q lab lab < 5 > 5 o o

• K

+

events

mass distribution by tracking and TOF c 2 probability cut - confidence level 98% p and proton contaminations ~ 2% L

and

S 0

events

missing mass of p( g , K + )X L and S 0 contamination < 1% Beam

Missing mass spectrum

• p( g ,K + ) L (1116) 72,500 events • p( g ,K + ) S 0 (1193) 48,900 events • 1.5 ~ 2.4 GeV • 0.6 < cos q cm < 1 Photon beam asymmetry

Photon beam asymmetry

S • Vertical = [ 1 + P • Horizontal = [ 1 - P d s W v h d s unpol d W unpol g g S S cos(2 cos(2 f f ) ] ) ]

N = F

acc d s d W nN v nN v - N h + N h

= P

g S

cos(2

f • N : K + photoproduction yield

)

• f • P g : K + azimuthal angle : Polarization of photon • n : Normalization factor for N v For all events

4. Experimental results

•Correction 1 p & proton contaminations DS < 0.03

•Correction 2 TRG contaminations DS < 0.02

•Systematic error 1 from pol. degree & angle 1.5% •Systematic error 2 from normalization factor DS ~ 0.03

•Positive sign •Different angular distribution •Increase as the E g increases p( g ,K + ) L p( g ,K + ) S 0

L S 0

Comparison with models

by Mart & Bennhold without D 13 (1960) with D 13 (1960) by Janssen

et al

Hadronic form factor A B C Davidson&Workman Haberzettl A) Small cut-off mass B) L * in u-channel C) No restriction on g KYp with D 13 (1960) Currently, no models reproduce our data, perfectly.

5. Summary

• K + photoproduction is good means to search missing resonances.

• Photon beam asymmetries were obtained for the p( g ,K + ) L and p( g ,K + ) S 0 reactions at the first time in E g = 1.5 ~ 2.4 GeV at SPring-8/LEPS. Positive sign • Our data will stimulate the further development of the theoretical models and extend our knowledge of this reaction including missing resonances.