406
886-2-2789-6794
changwc [at] phys.sinica.edu.tw
406
886-2-2789-6794
changwc [at] phys.sinica.edu.tw
Su, Jing-Xuan / 886-2-2789-6784
(1) | 西元年:2018 研究人員(中):章文箴、郡英輝、許軒豪 研究人員(英):CHANG, WEN-CHEN, Hideki Kohri,Shiuan-Hal Shiu 研究成果名稱(中):Δ^(++) 共振態的光致生成過程的精準量測 研究成果名稱(英):High precision information of photo-production of Δ^(++) Resonances 簡要記述(中):透過質子靶的 Δ^(++) 共振態的光致生成過程(γp→π^- Δ^(++)),能研究uu ̅夸克對的激發機制。反應截面和束流極化方向不對稱性的資料,將有助確認新型核子共振態和低能量強子反應的研究。利用日本SPring-8設施產生1.5-2.95 GeV背向康普頓散射的高極化線性光子,2018年5月18日, LEPS實驗組在Physics Review Letters (PRL 120, 202004 (2018)). 發表在前置方向和低能量區間的量測結果。 量測結果發現反應截面高度集中在前置方向,並透過束流極化方向不對稱性的資料確認,是符合π介子t通道交換的機制。束流極化方向不對稱性為負號,這與對應dd ̅ 和 ss ̅ 夸克對生成的π^+ 和 K^+ 光致生成過程的所量測性質相反,相類似的結果也有趣地出現在 pp 和 ep 反應生成π^- 、 π^+ 和 K^+的橫向自旋不對稱性,其中的關連性還有需進一步的探討。這項精準的資料將可提供理論上描述低能量區間強子作用模式,和新型核子共振態的確認。 簡要記述(英):The photo-production of Δ^(++) resonances from the proton target (γp→π^- Δ^(++)) is an interesting channel of studying the uu ̅ pair excitation. The production cross sections and beam asymmetries of this process also offers important information in gauging new nucleon resonances and understanding the low-energy hadronic interactions. Such data at the forward production direction and in low-energy regime becomes available recently from the LEPS experiment, using unique 1.5-2.95 GeV linearly-polarized Compton-backward scattered photon beam at SPring-8 facility, Japan. The results are published in Physics Review Letters (PRL 120, 202004 (2018)) on May 18, 2018. Strong forward-peaking production from the t-channel π-exchange is confirmed in the high precision data of differential cross sections and beam asymmetries. The measured negative beam asymmetries are opposite to those from π^+ and K^+ photo-production, corresponding to the production of dd ̅ and ss ̅ pairs. It is intriguing that analogous results are observed in the measurements of the transverse single-spin asymmetries in the pp and ep reactions. Further investigations are needed to clarify any fundamental connection. These precise data will surely improve the theoretical modeling of the low-energy hadronic interactions as well as the identification of new nucleon resonances. |
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(2) | 西元年:2017 研究人員(中):章文箴、朱明禮、謝佳諭、連昱翔、林志勳、澤田廣崇、鄧宇勝 研究人員(英):CHANG, WEN-CHEN, Ming-Lee Chu, Chia-Yu Hsieh, Yu-Shiang Lian, Chih-Hsun Lin, Takahiro Sawada and Yu-Sheng Teng 研究成果名稱(中):測定質子Sivers函數在極化Drell-Yan過程發生變號 研究成果名稱(英):Observation of sign change in Drell-Yan Sivers function 簡要記述(中):對於質子內部夸克組成的瞭解,已經由一維縱向動量分布,加入了橫向空間或橫向動量的資訊,進入了細緻的多維分布描述。其中,Sivers 函數是描述整體質子橫向自旋,與其內部夸克橫向動量的關連性,它會反映出夸克的橫向軌道運動效果,我們已經在SIDIS過程中發現Sivers 函數的強度是不為零,這也意味著夸克的橫向軌道運動的存在。透過量子色動力學(QCD)對於強作用力的描述,因為強作用力在SIDIS和Drell-Yan這兩個過程的時間方向是相反的,據此做出一個重要的預測:透過這二反應所得到的Sivers 函數的符號將是相反的。為了檢證這個預測,在2015年CERN COMPASS實驗組進行了首次橫向極化Drell-Yan過程的量測,實驗的結果的確與QCD的預測是相符的,為整體質子夸克橫向動量動量分布研究的正確性提供了極重要的實驗證據。 簡要記述(英):Our understanding of the partonic structures of protons has been deepened from the one-dimension longitudinal momentum distributions to multi-dimensional distributions with additional dependency on transverse size or transverse momentum. Among the transverse momentum dependent parton distributions (TMDs), Sivers function describes the correlation between the transverse spin of the parent proton and the transverse momentum of the probed quark. A nonzero Sivers function is considered to be the strong evidence of quark orbital motion. The effects of a nonzero Sivers function have been observed in the semi-inclusive deep inelastic scattering (SIDIS) process. A fundamental prediction based on the factorization of Quantum Chromodynamics (QCD) is a sign change of Sivers functions between SIDIS and Drell-Yan processes due to their opposite time directions of the strong interaction involved. This milestone test has been recently accomplished by the COMPASS collaboration in 2015 transversely-polarized Drell-Yan run. The observed sign of Sivers functions is found to be consistent with the prediction of QCD. This work provides the essential experimental validation of the overall study of TMD partonic structures of protons.
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