neutrino physics

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1、NeutrinophysicsL.WolfensteinDepartmentofPhysics,CarnegieMellonUniversity,Pittsburgh,Pennsylvania15213Theneutrinowasthe®rstelementaryparticleproposedthatwasnotaconstituentofordinarymatter.Becauseneutrinosinteractonlyweakly,theyplayauniqueroleinparticlephysics,astrophysics,andcosmology.Theposs

2、ibilitythatneutrinoshaveamassandoscillatefromoneformtoanotherhasledtoagreatvarietyofongoingexperiments.[S0034-6861(99)01202-7]I.NEUTRINOHISTORY:THETRAILOFPAULIANDheadedtowardtheearthallbutonewouldemergeonFERMItheotherside.Detectionofneutrinosseemedimpos-sible.Nevertheless,afterWorldWarII,Fre

3、dReinesandTheneutrinowasinventedbyWolfgangPauliin1930ClydeCowanatLosAlamostookupthechallenge.Attoexplainaproblemconcerningnuclearbetadecay.The®rsttheythoughttousetheneutrinosfromanuclearemittedelectronshadacontinuousenergyspectrum,bombexplosion,butthentheydecidedtodetectthewhereastheywereexp

4、ectedtohaveoneorpossiblyalargeÅn¯uxfromthe®ssionproductsofanuclearreac-fewdiscreteenergiescorrespondingtotheenergyofthetor.Theirde®nitiveexperimentsweredoneatthenewnucleartransition.PauliproposedthataneutralparticleSavannahRiverreactorinSouthCarolinaandan-wasemittedtogetherwiththeelectronsot

5、hatthesumnouncedin1956.Intheirexperimenttheneutronfromoftheenergiesofthisparticleandtheelectronwases-reaction(1.3b)wasdetectedviaacapturegammaraysentiallyconstant.andthepositronfromthetwoannihilationgammarays.Aftertheneutronwasdiscovered,EnricoFermiIn1995,longafterCowanhaddied,Reines®nallyre

6、-namedthisparticletheneutrino(littleneutron)andfor-ceivedtheNobelPrize.mulatedin1933atheoryofbetadecay.Thistheoryin-Fermi'soriginalpaperdiscussestheeffectoftheneu-volvedanewinteractioninwhichtheneutronchangedtrinomassontheshapeoftheelectronspectrumattheintoaproton,andanelectronandanantineutr

7、ino.Inhigh-energyendpoint.Fromthishededucedthatthethelanguageofquantum®eldtheorythiswasdescribedneutrinomasswasmuchlessthantheelectronmass.byaninteractionHamiltonian,Manyexperimentsoverthepast50yearshavestudiedthespectrum,particularlythatof3H,which