Nature452,332‐335(20March2008)

11June2008,HoriiYasuyuki

Contents

•  Motivation•  DecaysBKπ•  BelleExperiment

•  Methods

•  CPasymmetries

•  Conclusion

– EqualamountsofmatterandantimatterarepredictedtohavebeenproducedintheBigBang.

– Sakharovconditionsformatterdominance•  Baryonnumberviolation

•  C‐symmetryandCP‐symmetryviolation•  Interactionsoutofthermalequilibrium

– CPVinquarksectorcanbeexplainedusingKobayashi‐Maskawamechanism.

1964:IndirectCPV1999:DirectCPV(forneutralkaons)

FirstObservations

•  Dominantcontributions(SM)

•  CPviolationviaso‐calledVub CPasymmetries:Weobserve.

dominatedbyvirtualtop

WecanchoosethequarkphasessothatlargecomplexphasesappearsonlyinVubandVtd.

*

•  RelativeamplitudesandtheCPasymmetry

•  PhaseδstrongcanbedifferentforthechargedandneutralBdecays.•  Similarvaluesofδstrongmakethetwoasymmetriesclosetoeachother.

weakphase:δweak=arg(Vub*)

strongphase:δstrong

A(b),A(b) _

A(a)

A(a) _

Differentmagnitudes!!=CPasymmetry

*

δweak+δstrong

-δweak+δstrong

•  SincethedecaysBKπarestronglysuppressed,wemustproducemanyBmesonsanddetectthemwithhighefficiency. KEKBacceleratorandBelledetectoraredesignedforsuchapurpose.

KEKBaccelerator

・周長：3km ・重心系：10.58GeV 　（Υ(4S)レゾナンス）

Belledetector

•  K±,π±,andπ0arereconstructedusingtheinformationprovidedbytheBelledetector.–  π0:reconstructedfromtwophotons.

•  Thedominante+e‐qqbackgroundissuppressedbyemploying– eventshapevariablesand

– Bflavortagginginformation.»  UnambiguousflavorassignmentLikelytobeaBBevent.

•  CPasymmetriesareextractedbyfittingMbc‐ΔEdistribution.

_

MbcProjectionΔEProjection|ΔE|<0.06GeVforKπMbc>5.27GeV/c2

‐0.14<ΔE<0.06GeVforothers

FitResult 535MillionBBpairs

•  Systematicerrorcomesfrom–  fittingand

Estimatebyfittingaftervaryingeachparameters.

–  biasduetodetectorresponse.(Detectorismadefrommatter.)K±π:Usedecayswhoseasymmetryisnegligible.h±π0:UseBGasymmetries.

4.8σ

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•  ForthedecayBπ±π0,thecontributionfromthepenguindiagramvanishesbyisospinsymmetry.

•  CPasymmetryisexpectedtobeverysmall.

Obtainedresultisconsistentwiththisexpectation.

CPAsymmetryforBπ±π0

•  Contributionsfromaandb ΔA≒0.

•  Enhancementofthecolor‐suppressedtreec?–  (Couldexacerbateanotherpuzzle:ΔSpuzzle.)

•  Enhancementoftheelectroweakpenguind?–  CanpickupaCP‐violatingphasefromnewphysicsasaloopamplitude.

DifferenceofCPAsymmetriesforBKπDecays

4.4σ

•  TherateforB0decaystocharmlessstateswhichisexpectedtobedominatedbypenguindiagrams,suchasB0K0π0,aretoosmallcomparedtotheexpectation:ΔSPuzzle.

•  Ifcolor‐suppressedtreediagramisenhanced,ΔSpuzzlecanbeexacerbated.

•  MoredataareneededtoconfirmΔSproblem.–  OnecanmeasuredirectCPasymmetryofB0K0π0,andcompareit

withtheasymmetriesforB±K±π0andBK±π.

ΔSPuzzle

±

•  CPasymmetriesforBK±π,K±π0,andπ±π0aremeasuredusing535millionBBpairs.

•  DirectCPviolationinB±K±πandlargedeviationbetweenandareobserved.

•  ThedeviationcouldbeanindicationofnewsourcesofCPviolationbeyondtheSM.

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