Article

Differential Cross Section and Photon-Beam Asymmetry for the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mover accent="true"><mml:mrow><mml:mi>γ</mml:mi></mml:mrow><mml:mrow><mml:mo stretchy="false">→</mml:mo></mml:mrow></mml:mover><mml:mi>p</mml:mi><mml:mtext> </mml:mtext><mml:mo stretchy="false">→</mml:mo><mml:mtext> </mml:mtext><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mrow><mml:mi mathvariant="normal">Δ</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mo stretchy="false">(</mml:mo><mml:mn>1232</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math> Reaction at Forward <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>π</mml:mi><mml:mo>−</mml:mo></mml:msup></mml:math> Angles for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>E</mml:mi></mml:mrow><mml:mrow><mml:mi>γ</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>1.5</mml:mn><mml:mo>–</mml:mo><mml:mn>2.95</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>GeV</mml:mi></mml:mrow></mml:math>

H. KohriInstitute of Physics, Academia Sinica, Taipei 11529, TaiwanS. H. ShiuDepartment of Physics, National Central University, Taoyuan City 32001, TaiwanW. C. ChangInstitute of Physics, Academia Sinica, Taipei 11529, TaiwanY. YanaiResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanD. S. AhnRIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, JapanJ. K. AhnDepartment of Physics, Korea University, Seoul 02841, Republic of KoreaJ Y ChenLight Source Division, National Synchrotron Radiation Research Center, Hsinchu 30076, TaiwanS. DatéJapan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5143, JapanH. EjiriResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanH. FujimuraM̄. FujiwaraNational Institutes for Quantum and Radiological Science and Technology, Tokai, Ibaraki 319-1195, JapanS. FukuiResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanW. GohnDepartment of Physics, University of Connecticut, Storrs, Connecticut 06269-3046, USAK. HicksDepartment of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USAAtsushi HosakaResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanT. HottaResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanSanghoon HwangKorea Research Institute of Standards and Science (KRISS), Daejeon 34113, Republic of KoreaK. ImaiAdvanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, JapanT. IshikawaResearch Center for Electron Photon Science, Tohoku University, Sendai, Miyagi 982-0826, JapanK. JooDepartment of Physics, University of Connecticut, Storrs, Connecticut 06269-3046, USAYuji KatōKobayashi-Maskawa Institute, Nagoya University, Nagoya, Aichi 464-8602, JapanY. KonResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanH. S. LeeRare Isotope Science Project, Institute for Basic Science, Daejeon 34047, KoreaY. MaedaProton Therapy Center, Fukui Prefectural Hospital, Fukui 910-8526, JapanT. MibeHigh Energy Accelerator Organization (KEK), Tsukuba, Ibaraki 305-0801, JapanM. MiyabeResearch Center for Electron Photon Science, Tohoku University, Sendai, Miyagi 982-0826, JapanY. MorinoHigh Energy Accelerator Organization (KEK), Tsukuba, Ibaraki 305-0801, JapanN. MuramatsuResearch Center for Electron Photon Science, Tohoku University, Sendai, Miyagi 982-0826, JapanT. NakanoResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanY. NakatsugawaHigh Energy Accelerator Organization (KEK), Tsukuba, Ibaraki 305-0801, JapanSeung-il NamDepartment of Physics, Pukyong National University (PKNU), Busan 608-737, Republic of KoreaM. NiiyamaDepartment of Physics, Kyoto University, Kyoto 606-8502, JapanH. NoumiResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanYoji OhashiJapan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5143, JapanT. OhtaResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanMakoto OkaResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanJ. D. ParkerDepartment of Physics, Kyoto University, Kyoto 606-8502, JapanC. RangacharyuluDepartment of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, CanadaS. Y. RyuResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanT. SawadaInstitute of Physics, Academia Sinica, Taipei 11529, TaiwanH. ShimizuResearch Center for Electron Photon Science, Tohoku University, Sendai, Miyagi 982-0826, JapanE. A. StrokovskyJoint Institute for Nuclear Research, Dubna, Moscow Region 142281, RussiaY. SugayaResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, JapanM. SumihamaDepartment of Education, Gifu University, Gifu 501-1193, JapanT. TsunemiDepartment of Physics, Kyoto University, Kyoto 606-8502, JapanM. UchidaDepartment of Physics, Tokyo Institute of Technology, Tokyo 152-8551, JapanM. UngaroDepartment of Physics, University of Connecticut, Storrs, Connecticut 06269-3046, USAS. Y. WangInstitute of Physics, Academia Sinica, Taipei 11529, TaiwanM. YosoiResearch Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan

2018lv

ABI

Abstract

Differential cross sections and photon-beam asymmetries for the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\mathrm{\ensuremath{\Delta}}}^{++}(1232)$ reaction have been measured for $0.7<\mathrm{cos}{\ensuremath{\theta}}_{\ensuremath{\pi}}^{\mathrm{c}.\mathrm{m}.}<1$ and ${E}_{\ensuremath{\gamma}}=1.5--2.95\text{ }\text{ }\mathrm{GeV}$ at SPring-8/LEPS. The first-ever high statistics cross-section data are obtained in this kinematical region, and the asymmetry data for $1.5<{E}_{\ensuremath{\gamma}}(\mathrm{GeV})<2.8$ are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure $u\overline{u}$ quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at ${E}_{\ensuremath{\gamma}}=1.5--1.8\text{ }\text{ }\mathrm{GeV}$. The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of $\ensuremath{\pi}$ exchange in the $t$ channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions producing a $d\overline{d}$ or an $s\overline{s}$ quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural-parity exchanges are needed to reproduce the present data.

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Identifiers

DOI: 10.1103/physrevlett.120.202004

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Cited by 20 references

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