K+and K+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. SumihamaDept. 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.ZegersRCNP Osaka Univ.

K. Imai, M. Miyabe, M. Niiyama, M. YosoiDept. of physics Kyoto Univ.

D.S. Ahn, J.K. AhnPusan Nat’l Univ.. Korea

T. IwataDept. of physics Yamagata Univ.

Y. Asano,N. MatsumuraJAERI

T. Ishikawa, H. ShimizuTohoku Univ.

H. Kawai, T. Ooba, Y. ShiinoChiba 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. WakaiAkita Industry Promotion Foundation

K. HicksOhio Univ.USA

C. RangacharyuluUniv.. of Saskatchewan Canada

H. AkimuneKonan Univ.

P. ShaginMinnesota Univ.

S. MakinoWakayama Med. Univ.

1. IntroductionMissing resonances N* and *in strangeness channels

• Information on nucleon resonances mainly comes from the N channel.

• Many nucleon resonances predicted by quark model are still missing.

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

K+

Y()p

N, N*, *

Some resonances may couple to K or K channel.

K+ photoproduction is good means to search missing resonances.

Resonance structure?• Resonance like structure in the

total cross section for p(,K+) from SAPHIR and CLAS.

• Missing resonance D13(1960) ?

without D13

with D13

calculations by Mart and Bennhold

• There still remains a controversy

of the theoretical description.

• Only cross section data is not conclusive.

SAPHIR data

~ 1.9 GeV

Additional observables are required.

Photon beam asymmetry is one of the candidates.

Theoretical predictions of photon asymmetry

by　 Janssen et alby Mart & Bennhold

Hadronic form factor A B C Davidson&Workman Haberzettl

A) Small cut-off massB) * in u-channel C) No restriction on gKYp

without D13(1960)

with D13(1960)

With D13(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 105 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 1012 photons at the target

Photon beam asymmetries for the p(,K+) and p(,K+)0 reactions

3. Data analyses

• Tagged photons recoil electron by Tagging counter• Events from the proton target z-vertex point of K+

contamination from the trigger counter ~ 8% lab< 5o

< 2% lab> 5o

• K+ events mass distribution by tracking and TOF 2probability cut - confidence level 98% and proton contaminations ~ 2% • and 0events missing mass of p(, K+)X and 0contamination < 1%

Event selections for p(,K+)and p(,K+)0

Beam

Missing mass spectrum

• p(,K+)72,500

events• p(,K+)0 (1193)

48,900 events

• 1.5 ~ 2.4 GeV

• 0.6 < coscm < 1

Photon beam asymmetry

Photon beam asymmetry

• Vertical = [ 1 + Pcos(2) ]

• Horizontal = [ 1 - Pcos(2) ]

N = Facc

= Pcos(2)

• N : K+ photoproduction yield• : K+ azimuthal angle• P : Polarization of photon

• n : Normalization factor for Nv

ddv

ddunpol

ddunpol

ddh

dd

nNv 　 - Nh

nNv 　 + Nh

For all events

4. Experimental results

•Correction 1 & proton contaminations < 0.03•Correction 2 TRG contaminations< 0.02•Systematic error 1 from pol. degree & angle 1.5%•Systematic error 2 from normalization factor~ 0.03

•Positive sign•Different angular distribution •Increase as the E increases

p(,K+)

p(,K+)0

Comparison with models

Currently, no models

reproduce our data, perfectly.

by Mart & Bennhold

without D13(1960)with D13(1960)

by　 Janssen et al

Hadronic form factor A B C Davidson&Workman Haberzettl

A) Small cut-off massB) * in u-channel C) No restriction on gKYp

with D13(1960)

5. Summary• K+ photoproduction is good means

to search missing resonances.• Photon beam asymmetries were obtained

for the p(,K+) and p(,K+)0 reactions

at the first time in E= 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.