Hyperon Photoproduction by Linearly Polarized

Photons at SPring-8/LEPS

Mizuki SumihamaRCNP, Osaka Univ.

for the LEPS collaboration

SPIN2006 Oct. 6th 2006

Physics motivation

• It is essential to fully know N* and * to understand baryon structure.

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

• D13(1900) resonance in SAPHIR / CLAS data was found

K+

Y()p

N, N*, *

Some resonances should couple to K or Kchannel.Kaon photoproduction is good means

to search for missing resonances.

Missing resonances N* andMissing resonances N* and * * in s-channelin s-channel

Meson exchange in t-channelMeson exchange in t-channel

K+

Y()p

K*, K, K1

E = 1.5 2.4 GeVTransition region, s-channel t-

channelContribution of t-channel meson

exchangebecomes large above 2GeV.

Photon-beam asymmetry natural parity exchange (K*) = + 1unnatural parity exchange (K, K1) =－ 1 at t = 0 and large E.

LEPS spectrometer – forward acceptance

1m

TOFwall

MWDC 2

MWDC 3MWDC 1

Dipole Magnet (0.7 T)

Liquid HydrogenTarget (50 mm thick)

Start counter

Silicon VertexDetector

AerogelCherenkov(n=1.03)

Linearly polarized

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

K+

p K+(1116) p K+0(1193)

Z-vertex distribution

LH2 target

Photon asymmetry 　– (1116)

K+K*-exchange (K*-exchange is dominant) by M. Guidal.Isobar + Regge by T. Mart and C. Bennhold.Gent isobar model by T. Corthals.

Agreement is not so bad, but still need fine optimization.

Positive sign data

nucl-th 0412097 / SNP2004

Phys. Rev. C68, 058201 (2003)

Phys. Rev. C73, 045207 (2006)

Photon asymmetry 　– (1193)

K+K*-exchange (K*-exchange is dominant) by M. Guidal.Isobar by T.Mart and C.Bennhold.Gent isobar model by T. Corthals Agreement is not so bad, but still need fine optimization.

Positive sign data

nucl-th 0412097 / SNP2004

Phys. Rev. C68, 058201 (2003)

Phys. Rev. C73, 045207 (2006)

Differential cross sections –(1116)

LEPS data agree with SAPHIR and CLAS at cos = 0.75, 0.85 but discrepancy for SAHIR data is large at cos = 0.95. LEPS data shows a small bump at W= 1960MeV.Regge K+K*-exchangeIsobar (with D13)+Regge by T.Mart and C.Bennhold.Good agreement.

Resonance-like structure

W (GeV)

SAPHIR CLAS LEPS

Differential cross sections –(1193)

Good agreement with CLAS.Slightly smaller than SAPHIR. Small bump structure around W = 2070 MeV.

Regge K+K*-exchangeIsobar model by T.Mart and C.Bennhold.Gent isobar model by T. CorthalsGood agreement

W (GeV)

LEPS SAPHIR CLAS

Differential cross sections –(1116)

Regge model K+K*-exchange K-exchange makes forward peak for K channel.Isobar (Feynman) only Isobar (Feynman) + Regge by T.Mart and C.Bennhold.

Forward peakingCannot be reproduced By Feynman diagram only, at E>2GeV.Need Regge poles.

CLAS LEPS

- angular dependence

Differential cross sections –0(1193)

Regge model K+K*-exchange K*-exchange is dominate for K channel.Isobar (Feynman) by T. Mart and C. Bennhold.

No forward peaking.Can be explained by Feynman diagram only.

- angular dependence CLAS LEPS

Differential cross sections for p p0

-Check photon normalization

LEPS dataOld dataCurves SAID(fit data at E < 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 coscm = 0.975.• Bump structure was seen at W=1960 MeV in the K+ mode. • We see a forward peaking in K+while no peaking in K+0.• 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+.• Photon normalization was checked by p p0 cross

sections. The data show a good agreement with SAID. LEPS photon

normalization is OK. PRC73, 035214 (2006) / PRL 91, 092001-1 (2003).

LEPS collaborationD.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, Koreac Department of Physics, Konan University, Kobe, Hyogo 658-8501, Japan

d Japan Atomic Energy Research Institute, Mikazuki, Hyogo 679-5148, Japane Institute of Physics, Academia Sinica, Taipei 11529, Taiwan

f Japan Synchrotron Radiation Research Institute, Mikazuki, Hyogo 679-5198, Japanh School of physics, Seoul National University, Seoul, 151-747 Koreai Department of Physics, Ohio University, Athens, Ohio 45701, USA

j Department of Physics, Kyoto University, Kyoto, Kyoto 606-8502, Japank Laboratory of Nuclear Science, Tohoku University, Sendai 982-0826, Japan

l Department of Physics, Yamagata University, Yamagata, Yamagata 990-8560, Japanm Department of Physics, Chiba University, Chiba, Chiba 263-8522, Japan

n Wakayama Medical College, Wakayama, Wakayama 641-0012, Japano Department of Physics, Nagoya University, Nagoya, Aichi 464-8602, Japan

p Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japanq 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 and

Photon asymmetry 　 -energy dependence

E (GeV)