{"title":"在[公式省略]TeV波长的Pb-Pb对撞中测量相干ρ0光生成中与撞击参数相关的方位各向异性","authors":"","doi":"10.1016/j.physletb.2024.139017","DOIUrl":null,"url":null,"abstract":"<div><p>This Letter presents the first measurement of the impact-parameter dependent angular anisotropy in the decay of coherently photoproduced <span><math><msup><mrow><mi>ρ</mi></mrow><mrow><mn>0</mn></mrow></msup></math></span> mesons. The <span><math><msup><mrow><mi>ρ</mi></mrow><mrow><mn>0</mn></mrow></msup></math></span> mesons are reconstructed through their decay into pion pairs. The measured anisotropy corresponds to the amplitude of the <span><math><mi>cos</mi><mo></mo><mo>(</mo><mn>2</mn><mi>ϕ</mi><mo>)</mo></math></span> modulation, where <em>ϕ</em> is the angle between the two vectors formed by the sum and the difference of the transverse momenta of the pions, respectively. The measurement was performed by the ALICE Collaboration at the LHC using data from ultraperipheral Pb–Pb collisions at a center-of-mass energy of <span><math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mspace></mspace><mo>=</mo><mspace></mspace><mn>5.02</mn></math></span> TeV per nucleon pair. Different impact-parameter regions are selected by classifying the events in nuclear-breakup classes. The amplitude of the <span><math><mi>cos</mi><mo></mo><mo>(</mo><mn>2</mn><mi>ϕ</mi><mo>)</mo></math></span> modulation is found to increase by about one order of magnitude from large to small impact parameters. Theoretical calculations describe the measured <span><math><mi>cos</mi><mo></mo><mo>(</mo><mn>2</mn><mi>ϕ</mi><mo>)</mo></math></span> anisotropy and its impact-parameter dependence as the result of a quantum interference effect at the femtometer scale, arising from the ambiguity regarding which of the nuclei is the photon source in the interaction.</p></div>","PeriodicalId":20162,"journal":{"name":"Physics Letters B","volume":null,"pages":null},"PeriodicalIF":4.3000,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0370269324005756/pdfft?md5=b7a0c85833b0c6b9af41ae853f4f2124&pid=1-s2.0-S0370269324005756-main.pdf","citationCount":"0","resultStr":"{\"title\":\"Measurement of the impact-parameter dependent azimuthal anisotropy in coherent ρ0 photoproduction in Pb–Pb collisions at sNN=5.02 TeV\",\"authors\":\"\",\"doi\":\"10.1016/j.physletb.2024.139017\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>This Letter presents the first measurement of the impact-parameter dependent angular anisotropy in the decay of coherently photoproduced <span><math><msup><mrow><mi>ρ</mi></mrow><mrow><mn>0</mn></mrow></msup></math></span> mesons. The <span><math><msup><mrow><mi>ρ</mi></mrow><mrow><mn>0</mn></mrow></msup></math></span> mesons are reconstructed through their decay into pion pairs. The measured anisotropy corresponds to the amplitude of the <span><math><mi>cos</mi><mo></mo><mo>(</mo><mn>2</mn><mi>ϕ</mi><mo>)</mo></math></span> modulation, where <em>ϕ</em> is the angle between the two vectors formed by the sum and the difference of the transverse momenta of the pions, respectively. The measurement was performed by the ALICE Collaboration at the LHC using data from ultraperipheral Pb–Pb collisions at a center-of-mass energy of <span><math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mspace></mspace><mo>=</mo><mspace></mspace><mn>5.02</mn></math></span> TeV per nucleon pair. Different impact-parameter regions are selected by classifying the events in nuclear-breakup classes. The amplitude of the <span><math><mi>cos</mi><mo></mo><mo>(</mo><mn>2</mn><mi>ϕ</mi><mo>)</mo></math></span> modulation is found to increase by about one order of magnitude from large to small impact parameters. Theoretical calculations describe the measured <span><math><mi>cos</mi><mo></mo><mo>(</mo><mn>2</mn><mi>ϕ</mi><mo>)</mo></math></span> anisotropy and its impact-parameter dependence as the result of a quantum interference effect at the femtometer scale, arising from the ambiguity regarding which of the nuclei is the photon source in the interaction.</p></div>\",\"PeriodicalId\":20162,\"journal\":{\"name\":\"Physics Letters B\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":4.3000,\"publicationDate\":\"2024-09-12\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://www.sciencedirect.com/science/article/pii/S0370269324005756/pdfft?md5=b7a0c85833b0c6b9af41ae853f4f2124&pid=1-s2.0-S0370269324005756-main.pdf\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Physics Letters B\",\"FirstCategoryId\":\"101\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0370269324005756\",\"RegionNum\":2,\"RegionCategory\":\"物理与天体物理\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"ASTRONOMY & ASTROPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Physics Letters B","FirstCategoryId":"101","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0370269324005756","RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ASTRONOMY & ASTROPHYSICS","Score":null,"Total":0}
引用次数: 0
摘要
这封信首次测量了相干光生ρ0介子衰变中与撞击参数相关的角各向异性。ρ0介子是通过它们衰变成对来重建的。测量到的各向异性对应于cos(2j)调制的振幅,其中j分别是由离子横向矩的和与差形成的两个矢量之间的角度。测量是由 ALICE 协作在大型强子对撞机上利用超外围 Pb-Pb 对撞的数据进行的,对撞的质心能量为每核子对 sNN=5.02 TeV。通过对核裂变事件进行分类,选择了不同的撞击参数区域。结果发现,cos(2j)调制振幅从大到小的撞击参数增加了大约一个数量级。理论计算将测量到的 cos(2ϕ) 各向异性及其对撞击参数的依赖性描述为飞秒尺度量子干涉效应的结果,这种量子干涉效应是由于在相互作用中哪个原子核是光子源的模糊性引起的。
Measurement of the impact-parameter dependent azimuthal anisotropy in coherent ρ0 photoproduction in Pb–Pb collisions at sNN=5.02 TeV
This Letter presents the first measurement of the impact-parameter dependent angular anisotropy in the decay of coherently photoproduced mesons. The mesons are reconstructed through their decay into pion pairs. The measured anisotropy corresponds to the amplitude of the modulation, where ϕ is the angle between the two vectors formed by the sum and the difference of the transverse momenta of the pions, respectively. The measurement was performed by the ALICE Collaboration at the LHC using data from ultraperipheral Pb–Pb collisions at a center-of-mass energy of TeV per nucleon pair. Different impact-parameter regions are selected by classifying the events in nuclear-breakup classes. The amplitude of the modulation is found to increase by about one order of magnitude from large to small impact parameters. Theoretical calculations describe the measured anisotropy and its impact-parameter dependence as the result of a quantum interference effect at the femtometer scale, arising from the ambiguity regarding which of the nuclei is the photon source in the interaction.
期刊介绍:
Physics Letters B ensures the rapid publication of important new results in particle physics, nuclear physics and cosmology. Specialized editors are responsible for contributions in experimental nuclear physics, theoretical nuclear physics, experimental high-energy physics, theoretical high-energy physics, and astrophysics.