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10
StandardandNon-standardNeutrinoOscillationsInvolvingTauNeutrinos
Figure1.1.
NuMIneutrinofluxesasseenbytheon-axisexper-
imentsMINOSandMINOS+andoff-axisexperimentNOvA.
highenoughneutrinoenergiesarerequiredtoobservethisprocess.Suchneutrinoscanbefound
inthespectrumofneutrinosproducedintheatmosphereoftheEarthandcanbeproducedin
accelerators.Mostofcurrentacceleratorneutrinoexperimentshowever,havebeamenergytoolow
tostudyτappearance.TheexceptionistheMINOS+experimentwithmeanbeamenergyabout
6.5GeV(Fig.1.1).ItislocatedontheNuMIbeamaxis,whileotheracceleratorexperimentscurrently
analysingdata,T2K[31]andNOvA[32],aresituatedoffthebeamaxis.Neutrinoenergydistributions
intheseoff-axisexperimentshavemaximumclosetotheoscillationmaximumandmostofthefluxin
theregionswherecrosssectionforcharged-currentinteractionsofVτisverysmall(Figs.1.1and1.2).
OPERA(OscillationProjectwithEmulsion-tRackingApparatus),theonlyexperimentthat
presentedevidenceofappearanceofVτwithasignificancelargerthan5σ,usedthebeamofmean
energyabout17GeV.ThisexperimentwasexposedtotheCNGSneutrinobeamfromCERNto
theGranSassoLaboratoryintheyears2008–2012.ThemaingoaloftheOPERAexperimentwas
toshowtheevidenceofappearanceoftauneutrinosproducedduetotheoscillationsofaccelerator
muonneutrinos,onthelong,730kmwayfromthesourcetothedetector.Thankstotheunique
spacialresolutionofnuclearemulsionitwaspossibletoselecttauleptonanditsdecayproducts.
Figure1.2.
Bottom:NeutrinofluxesasproducedbytheJapan
ProtonAcceleratorResearchComplex(J-PARC)seenatdif-
ferentanglesfromtheneutrinobeamaxis.T2Kexperimentis
located2
.
5
◦
offthebeamaxis.Top:Muonneutrinosurvival
probabilityattheT2Klocation(
L
=295km).Imagefrom[