Measurement of the phase between strong and electromagnetic amplitudes of J/ψ decays

BESIII Collaboration

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Using 16 energy points of e + e annihilation data collected in the vicinity of the J/ψ resonance with the BESIII detector and with a total integrated luminosity of around 100pb −1 , we study the relative phase between the strong and electromagnetic amplitudes of J/ψ decays. The relative phase between J/ψ electromagnetic decay and the continuum process (e + e annihilation without the J/ψ resonance) is confirmed to be zero by studying the cross section lineshape of μ + μ production. The relative phase between J/ψ strong and electromagnetic decays is then measured to be (84.9±3.6) or (−84.7±3.1) for the 2(π + π 0 final state by investigating the interference pattern between the J/ψ decay and the continuum process. This is the first measurement of the relative phase between J/ψ strong and electromagnetic decays into a multihadron final state using the lineshape of the production cross section. We also study the production lineshape of the multihadron final state ηπ + π with η→π + π π 0 , which provides additional information about the phase between the J/ψ electromagnetic decay amplitude and the continuum process. Additionally, the branching fraction of J/ψ→2(π + π 0 is measured to be (4.73±0.44)% or (4.85±0.45)%, and the branching fraction of J/ψ→ηπ + π is measured to be (3.78±0.68)×10 −4 . Both of them are consistent with the world average values. The quoted uncertainties include both statistical and systematic uncertainties, which are mainly caused by the low statistics.

Original languageEnglish (US)
Pages (from-to)375-384
Number of pages10
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
StatePublished - Apr 10 2019

Bibliographical note

Funding Information:
We thank the authors of the babayaga and mcgpj generators for their kind help and constructive discussion. The BESIII collaboration thanks the staff of BEPCII and the IHEP computing center for their strong support. This work is supported in part by Ministry of Science and Technology of China on the joined China-Italian project under Contract No. 2015DFG02380, National Key Basic Research Program of China under Contract No. 2015CB856700 , 2015NSFC11375206 ; National Natural Science Foundation of China (NSFC) under Contracts Nos. 11235011 , 11335008 , 11425524 , 11625523 , 11635010 ; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; the CAS Center for Excellence in Particle Physics (CCEPP); Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under Contracts Nos. U1332201 , U1532257 , U1532258 ; CAS under Contracts Nos. KJCX2-YW-N29 , KJCX2-YW-N45 ; CAS Key Research Program of Frontier Sciences under Contracts Nos. QYZDJ-SSW-SLH003 , QYZDJ-SSW-SLH040 ; 100 Talents Program of CAS ; National 1000 Talents Program of China ; INPAC and Shanghai Key Laboratory for Particle Physics and Cosmology ; German Research Foundation DFG under Contracts Nos. Collaborative Research Center CRC 1044 , FOR 2359 ; Istituto Nazionale di Fisica Nucleare , Italy; Koninklijke Nederlandse Akademie van Wetenschappen (KNAW) under Contract No. 530-4CDP03 ; Ministry of Development of Turkey under Contract No. DPT2006K-120470 ; National Natural Science Foundation of China (NSFC) under Contracts Nos. 11505034 , 11575077 ; National Science and Technology fund ; The Swedish Research Council ; U. S. Department of Energy under Contracts Nos. DE-FG02-05ER41374 , DE-SC-0010118 , DE-SC-0010504 , DE-SC-0012069 ; University of Groningen (RuG) and the Helmholtzzentrum fuer Schwerionenforschung GmbH (GSI), Darmstadt; WCU Program of National Research Foundation of Korea under Contract No. R32-2008-000-10155-0 .


  • Electromagnetic amplitude
  • J/ψ decay
  • Phase
  • Strong amplitude

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