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Single Single 0 0 photoproduction photoproduction at SPring-8/LEPSat SPring-8/LEPS

Mizuki SumihamaOsaka university, RCNP

JPS meeting March 2007

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Introduction Introduction • Pion photoproduction is well studied experimentally

and theoretically as a spectroscopy of N* and * resonances. The proprieties of many resonances are determined at W < 1.7 GeV. However above the resonance region, the production mechanism is not well studied partly due to lack of data.

• We measured single 0 photoproduction in 1.9-2.3 GeV in total energy at backward angles where less experimental data.

• The production mechanism will be investigated in a transition range from nucleon-meson degrees of

freedom to quark-gluon degrees of freedom.• High mass resonances, u-channel contribution, quark

counting rule…

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Diagram in tree levelDiagram in tree level

0

p pp

0

p p

0

p pp

0

p pN*, *

P33(1232),P11(1440), D13(1520),S11(1535), S31(1620), S11(1650), D15(1675), F15(1680), D33(1700), P13(1720), F35(1905),P31(1910) and F37(1950) in MAID2005.

W < 1.7 GeV Models are well established. Data are well explained by four-star N* and *. W ~1.9 GeV There are one or two star N* and * but doubtful. W > 1.9 GeV at very backward angles non-resonant u-channel is expected to be dominant. Much higher, W > 3 GeV in 60s, 70s. Regge baryon pole explains data well.

Regge ~s2(u)-2 at u~small,

follow quark counting rule.(JLab)

t-channel(forward)

1.9 – 2.3 GeV+Backward - medium

s-channel

u-channel s-channel

List of four-star nucleon resonancesBorn term

pp

Detect protons By spectrometer

in missing mass

Measurement ofMeasurement of + p + p p + p + 00

•Detect protons by LEPS spectrometer at forward angles•Identify 0 in missing mass spectrum. •Measure differential cross sections and photon beam asymmetries at backward anglesbackward angles -1 < coscm < -0.6.•Polarization degree is ~95% at the maximum E, 2.4 GeV.

Linearly polarized photons

Liquid hydrogen

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LEPS spectrometer LEPS spectrometer – forward acceptance– 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

+-~10o in y+-~20o in x

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Particle identificationParticle identification by time-of-flight and momentum measurementsby time-of-flight and momentum measurements

Proton selection with 4.Kaon/pion contamination is negligible.

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Missing mass spectrum Missing mass spectrum pppXpX

Z-vertex distribution

LH2 target

1/10 total statistics

~18000 counts

Measurement region:1.5 < E < 2.4 GeV1.9 < W < 2.3 GeV-1 < coscm < -0.6

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Background reactionsBackground reactions

1.1. p p p p 2. p p 3. p p 4. p p

Missing mass square

No-scale!

2 cut (~ 0.13)

•2,3 reactions are above the 2 cut point. •4 is much less than pion production by ~2-3 orders.

(demonstration)

Data

MC

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Background subtractionBackground subtraction

Single pion and double pion productions generated by MC simulation are fitted to data by a template fit. Systematic uncertainty was estimated by doing a fits by Gaussians for 0 peaks with 2 and 1.5 cuts.

Example of results of template fits

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Systematic error

1. Target protons 1.0% (fluctuation of temp. and pressure) 2. Photon normalization 1.2%, Photon transmission 3%3. AC over veto 1.6% 4. Background subtraction, < 5%

•Obtain yield by subtracting two-pion photoproduction.•Detector acceptance is obtained Monte Carlo simulation based on GEANT3.•Photon normalization is obtained by tagging counter.

Determine differential cross sectionDetermine differential cross section

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Differential cross section,Differential cross section, E E LEPS data Existing data. Eur.Phys.J.A26(2005)399, PRL,94(2005)012503, PLB,48(1974)463, NPB60(1973)267…

SAID -partial-wave analysis (fit of existing data) PRC66,055213(2002)MAID2005 - isobar model nucl-th/0603012

•Good agreement with existing data (SAID).

•Not follow ~s2(u)-2(Regge), ~s7(counting rule) at E > 1.8 GeV.

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Differential cross section cosDifferential cross section coscmcm

LEPS data Existing data.

SAID MAID2005

•Change angular distribution drastically at E~1.8GeV1.8GeV, •Backward peakingBackward peaking, small bump structure 1.85<E<1.95GeV.

•Discrepancy with MAID becomes large at higher energy.

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Photon beam asymmetry Photon beam asymmetry

nNv Nh

nNv + Nh

Pcos(2) = LEPS data Existing data. PLB544(2002)113 NPB104(1976)253… SAID

MAID2005

•Data show a good agreement with SAID/MAID.•Strong angular dependence above 1.8GeV1.8GeV.

Positive sign: Negative sign:

2.1 GeV < W < 2.3 GeV

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SummarySummary• Differential cross sections at very backward angles have been measured and new data at E> 1.8 GeV.

Photon beam asymmetries have been measured at the first time at backward angles E> 1.5 GeV.

• Angular dependence of both observables changes at E 1.8 GeV1.8 GeV. A strong angular dependence strong angular dependence is seen at E> 1.8 GeV. Energy dependence cannot be explain by nucleon Regge pole nor scaling. • At low energy region, the data is explained with models

including well-known-nucleon resonances, but the strong angular dependence at high energy cannot be explained.

• Can the data be explained by Born term only? Does u-channel contribution dominate? Quark-hadron duality? High spin states? Challenge to theorists.

• Measurement at side angles and higher photon energy, Homework to experimentalist.

LEPS collaborationLEPS 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. Zegersa 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 15