{"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}
引用次数: 0
Abstract
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.