電子・陽子衝突による新粒子の探索と陽子構造の研究

• Project/Area Number: 11206201
• Research Category: Grant-in-Aid for Scientific Research on Priority Areas
• Allocation Type: Single-year Grants
• Review Section: Science and Engineering
• Research Institution: 高エネルギー加速器研究機構
• Principal Investigator: 徳宿 克夫 高エネルギー加速器研究機構, 素粒子原子核研究所, 助教授 (80207547)
• Co-Investigator(Kenkyū-buntansha): 椎野 二男 高エネルギー加速器研究機構, 素粒子原子核研究所, 助手 (20092231) ; 山崎 祐司 高エネルギー加速器研究機構, 素粒子原子核研究所, 助手 (00311126) ; 久世 正弘 東京工業大学, 大学院・理工系研究科, 助教授 (00225153) ; 山田 作衛 東京大学, 名誉教授 (70011658) ; 鶴貝 達政 明治学院大学, 法学部, 教授 (50267366)
• Project Period (FY): 1999 – 2003
• Project Status: Completed (Fiscal Year 2003)
• Budget Amount: ¥139,300,000 (Direct Cost: ¥139,300,000); Fiscal Year 2003: ¥24,300,000 (Direct Cost: ¥24,300,000); Fiscal Year 2002: ¥25,200,000 (Direct Cost: ¥25,200,000); Fiscal Year 2001: ¥24,800,000 (Direct Cost: ¥24,800,000); Fiscal Year 2000: ¥34,000,000 (Direct Cost: ¥34,000,000); Fiscal Year 1999: ¥31,000,000 (Direct Cost: ¥31,000,000)
• Keywords: 電子・陽子衝突 / HERA / ZEUS / レプトクォーク / クォークの半径 / 偏極陽電子 / 回折反応 / ジェット / 電子・陽子の衝突 / 陽子の構造 / クォーク・グルーオン分布 / 強い相互作用の結合定数 / 励起フェルミオン / レプトン・フレーバーの流れ / 新粒子探索 / 陽子構造 / クォーク / 深非弾性散乱 / 高精度シリコン飛跡検出器

Research Abstract

ドイツ電子シンクロトロン研究所(DESY)に建設した電子・陽子衝突型加速器HERAを用いて、電子陽子間の相互作用を精密に測定し、新粒子の探索と陽子構造を測定することがこの研究の目的である。測定に用いるZEUS実験装置は、我々を含む14カ国の国際共同により建設し改良を加えた。
ビームと残留ガスとの反応によるバックグランドが非常に大きくなる問題が生じたが、これに対処するためにビーム衝突点付近の加速器改造を行い、10月から定常運転を始めた。実験条件は格段に良くなり問題点を解決できた。3月には瞬間衝突輝度が3×10^<31>cm^<-2>s^<-1>まで上がり、改造前の2倍以上を達成した。今後さらに改良していく計画である。我々の担当しているシリコン高精度飛跡検出器とトリガーシステムは順調に稼動している。この定常運転で収集した偏極陽電子と陽子の衝突反応を解析して、特に高い運動量移行(Q^2>200GeV^2)での中性流及び荷電流での断面積の測定を進めた。
平成12年までに収集した無偏極のデータの解析は順調に進んだ。高い運動量移行(Q^2>200GeV^2)での解析は完了した。これらのデータの中から新粒子の探索を進めた。例を挙げると、レプトンとハドロンの性質をあわせ持った粒子であるレプトクォーク等、標準模型を超える理論で予測される新粒子の探索を、平成6年から12年までのすべてのデータを用いて行った。探索の結果このような粒子は発見されず、質量200GeVから400GeVの広い範囲で結合定数の上限を得た。また、陽子を構成するクォークの大きさを測定した。その半径は0.85×10^<-16>cmより小さいことがわかり、この精度でクォークが構造の無い素粒子であることがわかった。
回折反応では、包括断面積、ベクター中間子の生成断面積の測定を進めた。ジェット生成断面積の測定に着手し、量子色力学のモデルとの比較を進めている。

Research Products

• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Measurement of proton-dissociative diffractive photoproduction of vector mesons at large momentum transfer at HERA"The European Physical Journal. C26. 389-409 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Measurement of high-Q^2 e-p neutral current cross sections at HERA and the extraction of xF_3"The European Physical Journal. C28. 175-201 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Leading proton production in e+p collisions at HERA"Nuclear Physics. B658. 3-46 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Measurement of event shapes in deep inelastic scattering at HERA"The European Physical Journal. C27. 531-545 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Scaling violations and determination of alpha_s from jet production in gamma p interactions at HERA"Physics Letters. B560. 7-23 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Search for single-top production in ep collisions at HERA"Physics Letters. B559. 153-170 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Dijet angular distributions in photoproduction of charm at HERA"Physics Letters. B565. 87-101 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "A search for resonance decays to lepton+jet at HERA and limits on leptoquarks"Physical Review. D68. 052004 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Jet production in charged current deep inelastic e+p scattering at HERA"The European Physical Journal. C31. 149-164 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Measurement of deeply virtual Compton scattering at HERA"Physics Letters. B573. 46-62 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Measurement of high-Q^2 charged current cross sections in e+p deep inelastic scattering at HERA"The European Physical Journal. C32. 1-16 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Measurement of the open-charm contribution to the diffractive proton structure function"Nuclear Physics. B672. 3-35 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Observation of K^0_sK^0_s resonances in deep inelastic scattering at HERA"Physics Letters. B578. 33-44 (2003)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Measurement of D^*± production in deep inelastic e±p scattering at HERA"Physical Review. D69. 012004 (2004)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Bose-Einstein correlations in one and two dimensions in deep inelastic scattering"Physics Letters. B583. 231-246 (2004)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Dijet production in neutral current deep inelastic scattering at HERA"The European Physical Journal. C23. 13-27 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Searches for excited fermions in ep collisions at HERA"Physics Letters. B549. 32-47 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Measurement of the photon-proton total cross section at a center-of-mass energy of 209 GeV at HERA"Nuclear Physics. B627. 3-28 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "High-mass dijet cross sections in photoproduction at HERA"Physics Letter. B531. 9-27 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Dijet photoproduction at HERA and the structure of the photon"The European Physical Journal. C23. 615-631 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Search for lepton-flavor violation in e^+p collisions at HERA"Physical Review. D65. 092004 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Exclusive photoproduction of J/Psi mesons at HERA"The European Physical Journal. C25. 345-360 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Measurement of the Q^2 and energy dependence of diffractive interactions at HERA"The European Physical Journal. C25. 169-187 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Leading Neutron production in e^+p collisions at HERA"Nuclear Physics. B637. 3-56 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Measurement of high-Q^2 charged current cross sections in ep deen inelastic scattering at HERA"Physics Letters. B539. 197-217 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Measurement of diffractive production of D^<*±>(2010) mesons in deep inelastic scattering at HERA"Physics Letters. B545. 244-260 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "A ZEUS next-to-leading-order QCD analysis of data on deep inelastic scattering"Physical Review. D67. 012007 (2003)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Inclusive jet cross sections in the Breit frame in neutral current deep inelastic scattering at HERA and determination of α_s"Physics Letters. B547. 164-180 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Measurements of inelastic J/psi and J/psi' photoproduction at HERA"The European Physical Journal. C27. 173-188 (2002)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Study of the azimuthal asymmetry of jets in neutral current deep inelastic scattering at HERA"Physics Letters. B551. 226-240 (2003)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Observation of the strange sea in the proton via inclusive φ-meson production in neutral current deep inelastic scattering at HERA"Physics Letters. B553. 141-158 (2003)
• [Publications] ZEUS Collaboration, S. Chekanov et al.: "Measurement of subjet multiplicities in neutral current deep inelastic scattering at HERA and determination of αs"Physics Letters. B558. 41-58 (2003)
• [Publications] ZEUS Collaboration, J. Breitweg et al.: "Search for resonance decays to an anti-neutrino plus jet in e^+p scattering at DESY HERA"Physical Review. D63. 052002 (2001)
• [Publications] ZEUS Collaboration, J. Breitweg et al.: "Measurement of dijet cross sections for events with a leading neutron in photoproduction at HERA"Nucl. Phys. B. 596. 3-29 (2001)
• [Publications] ZEUS Collaboration, J. Breitweg et al.: "Measurement of open beauty production in photoproduction at HERA"Euro. Phys. J.. C18. 625-637 (2001)
• [Publications] ZEUS Collaboration, J. Breitweg et al.: "Measurement of dijet production in neutral current deep inelastic scattering at high Q^2 and determination of α_s"Physics Letters. B507. 70-88 (2001)
• [Publications] ZEUS Collaboration, J.Breitweg et al.: "Study of the effective transverse momentum of partons in the proton using prompt photons in photoproduction at HERA"Physics Letters. B511. 19-32 (2001)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Multiplicity moments in deep inelastic scattering at HERA"Physics Letters. B510. 36-54 (2001)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Measurement of the neutral current cross section and F_2 structure function for deep inelastic e^+p scattering at HERA"Euro. Phys. J.. C21. 443-471 (2001)
• [Publications] ZEUS Collaboration, S.Chekanov et al.: "Three-jet production in diffractive deep inelastic scattering at HERA"Physics Letters. B516. 273-292 (2001)
• [Publications] ZEUS Collaboration, J.Breitweg et al.: "Properties of hadronic final states in diffractive deep inelastic scattering at HERA"Physical Review. D63. 052001 (2002)
• [Publications] ZEUS Collaboration,J.Breitweg et al.: "Search for Contact Interactions in Deep Inelastic e+p→e+X Scattering at HEAR"Euro.Phys.J.. C14. 239-254 (2000)
• [Publications] ZEUS Collaboration,J.Breitweg et al.: "Measurement of inclusive prompt photon photoproduction at HERA"Phys.Lett.. B472. 175-188 (2000)
• [Publications] ZEUS Collaboration,J.Breitweg et al.: "The Q^2 Dependence of Dijet Cross Sections in gamma p Interactions at HERA"Physics Letters. B479. 37-52 (2000)
• [Publications] ZEUS Collaboration,J.Breitweg et al.: "Measurement of Inclusive D_s^<+-> Photoproduction at HERA"Physics Letters. B481. 213-227 (2000)
• [Publications] ZEUS Collaboration,J.Breitweg et al.: "Measurement of the Proton Structure Function F_2 at Very Low Q^2 at HERA"Physics Letters. B487. 53-73 (2000)
• [Publications] ZEUS Collaboration,J.Breitweg et al.: "Measurement of high-Q2 charged-current e+p deep inelastic scattering cross sections at HERA"Ero.Phys.J.. C11. 411-428 (2000)
• [Publications] ZEUS Collaboration,J.Breitweg et al.: "Measurement of high-Q2 neutral-current e+p deep inelastic scattering cross sections at HERA"Ero.Phys.J.. C11. 427-445 (1999)
• [Publications] ZEUS Collaboration,J.Breitweg et al.: "W production and the search for events with an isolated high-energy lepton and missing transverse momentum at HERA"Phys. Lett.. B471. 411-428 (2000)