dcpv dif b kpi bk
TRANSCRIPT
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Nature452,332‐335(20March2008)
11June2008,HoriiYasuyuki
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Contents
• Motivation• DecaysBKπ• BelleExperiment
• Methods
• CPasymmetries
• Conclusion
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– EqualamountsofmatterandantimatterarepredictedtohavebeenproducedintheBigBang.
– Sakharovconditionsformatterdominance• Baryonnumberviolation
• C‐symmetryandCP‐symmetryviolation• Interactionsoutofthermalequilibrium
– CPVinquarksectorcanbeexplainedusingKobayashi‐Maskawamechanism.
1964:IndirectCPV1999:DirectCPV(forneutralkaons)
FirstObservations
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• Dominantcontributions(SM)
• CPviolationviaso‐calledVub CPasymmetries:Weobserve.
dominatedbyvirtualtop
WecanchoosethequarkphasessothatlargecomplexphasesappearsonlyinVubandVtd.
*
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• RelativeamplitudesandtheCPasymmetry
• PhaseδstrongcanbedifferentforthechargedandneutralBdecays.• Similarvaluesofδstrongmakethetwoasymmetriesclosetoeachother.
weakphase:δweak=arg(Vub*)
strongphase:δstrong
A(b),A(b) _
A(a)
A(a) _
Differentmagnitudes!!=CPasymmetry
*
δweak+δstrong
-δweak+δstrong
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• SincethedecaysBKπarestronglysuppressed,wemustproducemanyBmesonsanddetectthemwithhighefficiency. KEKBacceleratorandBelledetectoraredesignedforsuchapurpose.
KEKBaccelerator
・周長:3km ・重心系:10.58GeV (Υ(4S)レゾナンス)
Belledetector
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• K±,π±,andπ0arereconstructedusingtheinformationprovidedbytheBelledetector.– π0:reconstructedfromtwophotons.
• Thedominante+e‐qqbackgroundissuppressedbyemploying– eventshapevariablesand
– Bflavortagginginformation.» UnambiguousflavorassignmentLikelytobeaBBevent.
• CPasymmetriesareextractedbyfittingMbc‐ΔEdistribution.
_
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MbcProjectionΔEProjection|ΔE|<0.06GeVforKπMbc>5.27GeV/c2
‐0.14<ΔE<0.06GeVforothers
FitResult 535MillionBBpairs
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• Systematicerrorcomesfrom– fittingand
Estimatebyfittingaftervaryingeachparameters.
– biasduetodetectorresponse.(Detectorismadefrommatter.)K±π:Usedecayswhoseasymmetryisnegligible.h±π0:UseBGasymmetries.
4.8σ
±
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• ForthedecayBπ±π0,thecontributionfromthepenguindiagramvanishesbyisospinsymmetry.
• CPasymmetryisexpectedtobeverysmall.
Obtainedresultisconsistentwiththisexpectation.
CPAsymmetryforBπ±π0
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• Contributionsfromaandb ΔA≒0.
• Enhancementofthecolor‐suppressedtreec?– (Couldexacerbateanotherpuzzle:ΔSpuzzle.)
• Enhancementoftheelectroweakpenguind?– CanpickupaCP‐violatingphasefromnewphysicsasaloopamplitude.
DifferenceofCPAsymmetriesforBKπDecays
4.4σ
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• TherateforB0decaystocharmlessstateswhichisexpectedtobedominatedbypenguindiagrams,suchasB0K0π0,aretoosmallcomparedtotheexpectation:ΔSPuzzle.
• Ifcolor‐suppressedtreediagramisenhanced,ΔSpuzzlecanbeexacerbated.
• MoredataareneededtoconfirmΔSproblem.– OnecanmeasuredirectCPasymmetryofB0K0π0,andcompareit
withtheasymmetriesforB±K±π0andBK±π.
ΔSPuzzle
±
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• CPasymmetriesforBK±π,K±π0,andπ±π0aremeasuredusing535millionBBpairs.
• DirectCPviolationinB±K±πandlargedeviationbetweenandareobserved.
• ThedeviationcouldbeanindicationofnewsourcesofCPviolationbeyondtheSM.
±
±