The Neutrino World：中微子的世界

TheNeutrinoRevolution(1998–…)Neutrinoshavenonzeromasses!Leptonsmix!Thesediscoveriescomefromtheobservationofneutrinooscillation.ThePhysicsofNeutrinoOscillationNeutrinosComeinatLeastThreeFlavorsTheknownneutrinoflavors:e,,Eachoftheseisassociatedwiththecorrespondingcharged-leptonflavor:e,,TheMeaningofthisAssociationeDetectoreeWbosonShortJourneyeWWOvershortdistances,neutrinosdonotchangeflavor.WShortJourneyDoesNotOccurButifneutrinoshavemasses,andleptonsmix,neutrinoflavorchangesdooccurduringlongjourneys.LetUsAssumeNeutrinoMassesandLeptonicMixingNeutrinomass—Thereissomespectrumof3ormoreneutrinomasseigenstatesi:(Mass)21234Mass(i)miLeptonicmixing—WhenW+l++,theproducedneutrinostate|is|=U*i|i.NeutrinoofflavorNeutrinoofdefinitemassmiLeptonicMixingMatrixlee,l,le,,oriAnotherwaytolookatWdecay:Agivenl+canbeaccompaniedbyanyi.Amp(W+l++i)=U*iis|=U*i|i.Theneutrinostate|producedtogetherwithl+iAccordingtotheStandardModel,extendedtoincludeneutrinomassandleptonicmixing—Thenumberofdifferentiisthesameasthenumberofdifferentl.ThemixingmatrixUis3x3andunitary:UU†=U†U=1.Somemodelsinclude“sterile”neutrinos—neutrinosthatexperiencenoneoftheknownforcesofnatureexceptgravity.Insuchmodels,thereareN3i,andUisNxN,butstillunitary.Justaseachneutrinoofdefiniteflavorisasuperpositionofmasseigenstatesi,soeachmasseigenstateisasuperpositionofflavors.From|=iU*i|iandtheunitarityofU,|i=Ui|.Theflavor-fractionofiis—||i|2=|Ui|2.TheStandardModel(SM)descriptionofneutrinointeractions(notmassesorleptonicmixing)iswell-confirmed.Wewillassumeitistrue,andextendittoincludemixing.FortheleptoncouplingstotheWboson,wethenhave—MacintoshPICTimageformatisnotsupportedLeft-handedTakingmixingintoaccountInsertExplanationofNeutrinoOscillationExperimentalEvidenceEvidenceForFlavorChangeNeutrinosSolarReactor(L~180km)AtmosphericAccelerator(L=250and735km)Stopped+DecayLSNDL30mEvidenceofFlavorChangeCompellingCompellingCompellingCompellingUnconfirmed()Solare/isnowwellestablished.Themechanismforthisflavorconversionisthe—LargeMixingAngleversionofthe—MikheyevSmirnovWolfenstein—Effect.Thisoccursastheneutrinosstreamoutwardthroughsolarmaterial.Itrequiresbothinteractionswithmatterandneutrinomassandmixing.WhatHappensToSolarNeutrinosHowDoestheLargeMixingAngleMSWEffectWork?Thesolarmattereffectisimportantforthehigh-energy8Bneutrinos,notthelow-energyppneutrinos.Since3couplesatmostfeeblytoelectrons(tobediscussed),andsolarneutrinosareborne,thesolarneutrinosaremixturesofjust1and2.(Convention:2heavierthan1).Thisisa2-neutrinosystem.Solarneutrinoflavorchangeisex,wherexissomecombinationofand.Inthesun,Atthecenterofthesun,√2GFNe≈0.75×10-5eV2/MeV.Form2sol≈8×10-5eV2andtypical8Bneutrinoenergyof~8MeV,m2sol/4E≈0.25×10-5eV2/MeV.TheinteractionterminHdominates,andeisapproximatelyaneigenstateofH.*MacintoshPICTimageformatisnotsupportedexex*Forthe(E~0.2MeV)ppneutrinos,HVacdominates.The8Bsolarneutrinopropagatesoutwardadiabatically.Itremainstheslowly-changingheaviereigenstateoftheslowly-changingH.ItemergesfromthesunastheheaviereigenstateofHVac,2.*Itstays2untilitreachestheearth.Nothing“oscillates”!Since2=esinsol+xcossol,(See22Umatrix)Prob[Seeeatearth]=sin2sol.*Goodto91%(Nunokawa,Parke,Zukanovich-Funchal)