Hyperon Semileptonic Decays and CKM Unitarity

We perform a new numerical analysis of hyperon semileptonic decays emphasizing the systematic uncertainties. The poor understanding of SU(3) symmetry breaking effects at second order in the vector form factor translates into a large error of |V(us)|. Using

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002 voN 3 2v7710150/hp-pe:hviXraHyperonSemileptonicDecaysandCKMUnitarity

V.Mateua

a

DepartamentdeF´ sicaTe`orica,IFIC,UniversitatdeVal`encia-CSICApt.Correus22085,E-46071Val`encia,Spain

Weperformanewnumericalanalysisofhyperonsemileptonicdecaysemphasizingthesystematicuncertainties.ThepoorunderstandingofSU(3)symmetrybreakinge ectsatsecondorderinthevectorformfactortranslatesintoalargeerrorof|Vus|.Usingourdetermination|Vus|=0.226±0.005togetherwiththosecomingfromothersourceswetesttheunitarityoftheCKMmatrix.

1.Introduction

OneofthemostinvolvedsectorsoftheStan-dardModelisits avourstructure.TheproblemsofCPviolation[1]andtheunitarityoftheCKMmatrix[2,3,1,4]aretwomajorissuesthatdeservetobeclari ed.Inordertoachievethisgoal,averyaccuratecontrolofsystematicuncertaintiesbecomesmandatory.

Sincethenumericalvalueof|Vub|2isnegligible,totesttheunitarityiftheCKMmatrix[5]inits rstrow,thevaluesof|Vud|and|Vus|owetoberatherwell xed.Duetorecentchangesontheexperimentalside,thevaluesof|Vud|and|Vus|havesu eredstrong uctuations.Inthecaseofhy-

|Vud|,whiledatafromsuperallowednuclearbetaperonintoanotherspin-

1

2

decayremainsunchanged[4],thisisnotthecaseforneutrondecay[6,7].Concerningof|Vus|,newexperimentsonK→πlν ndbranchingratioslargerthanpreviousresults[8,9,10,11].

Datafromhadronicτdecaysarestableanditcanbeusedtoobtainanaccuratedetermina-tionof|Vus|[12].BesideskaonandhadronicτMσ

µν

qdecays,thereexistsanother,inprinciplelessac-Bν+

f3(q2)

1

curate,determinationof|Vus|.Hyperondecaysarea ectedbylargertheoreticalandexperimen-taluncertainties.However,onecan ndtwore-centanalyses[13,14]thatclaimaccuraciescom-petitivewithpreviousdeterminations.Moreover,Mσ

µν

q+

g3(q2

Hyperon Semileptonic Decays and CKM Unitarity

)

Bν1

usingthesamedata,theyobtaindi erentcentral

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