The First Transverse Single Spin Measurement in High Energy Polarized Proton-Nucleus Collision at the PHENIX experiment at RHIC

摘要

LargesinglespinasymmetriesinveryforwardneutronproductionseenusingthePHENIXzero-degreecalorimetersarealongestablishedfeatureoftransverselypolarizedproton-protoncollisionsatRHIC.Neutronproductionnearzerodegreesiswelldescribedbytheone-pionexchangeframework.TheabsorptivecorrectiontotheOPEgeneratestheasymmetryasaconsequenceofaphaseshiftbetweenthespinflipandnon-spinflipamplitudes.However,theamplitudepredictedbytheOPEistoosmalltoexplainthelargeobservedasymmetries.Amodelintroducinginterferenceofpionanda1-Reggeonexchangeshasbeensuccessfulinreproducingtheexperimentaldata.DuringtheRHICexperimentinyear2015,RHICdeliveredpolarizedprotoncollisionswithAuandAlnucleiforthefirsttime,enablingtheexplorationofthemechanismoftransversesingle-spinasymmetrieswithnuclearcollisions.TheobservedasymmetriesshowedsurprisinglystrongA-dependenceintheinclusiveforwardneutronproduction,whiletheexistingframeworkwhichwassuccessfullinp+ponlypredictsmoderateA-dependence.Thustheobserveddataareabsolutelyunexpectedandunpredicted.Inthisreport,experimentalandtheoreticaleffortsarediscussedtodisentangletheobservedA-dependenceusingsomewhatsemi-inclusivetypemeasurementsandMonte-Carlostudy,respectively...