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Two-photon exchange model for production of neutral meson pairs in e+e- annihilation

6

002 nJu 31 1v5516060/hp-pe:hviXraFebruary2,2008

neutralTwo-photonvectorexchangemesonpairsmodelinfore+eproduction annihilation

ofM.Daviera,M.Peskinb,andA.Snyderb1

aLaboratoire

del’Acc´el´erateurLin´eaire,

IN2P3-CNRSetUniversit´edeParis-Sud11,91898Orsay,France

bStanford

LinearAcceleratorCenter,Stanford,California94309,USA

Abstract

Avector-dominancetwo-photonexchangemodelisproposedtoexplainthere-centlyobservedproductionofρ0ρ0andρ0φpairsine+e annihilationat10.58GeV

withtheBaBardetector.Alltheobservedfeaturesofthedata—angularanddecaydistributions,rates—areinagreementwiththemodel.Predictionsaremadeforyet-unobserved nalstates.

1Introduction

Sofarallobservedhadronicprocessesine+e annihilationareinagreementwithone-photonexchangeleadingtoC= 1 nalstates.However,theBaBarCollaborationhasrecentlypresentedthe rstmeasurementofe+e annihilationintopairsofneutralvectormesonsat10.58GeVcentre-of-massenergy[1].The nalstatesρ0ρ0andρ0φareobservedwithcrosssections

σ(e+e →ρρ)=(20.7±(1) →ρφ)=(5.7±00.5.7stat±2.7syst)fb,σ(e+estat±0.8syst)fb

(2)

inthecentre-of-massangularrange|cosθ|<0.8.TheseprocessescharacterizedbyC=+1 nalstatescannotoriginatefromone-photonexchangefollowedbyquark-antiquarkfragmentation.

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