Hard Exclusive Electroproduction of Pions

We investigate the exclusive electroproduction of pi^+ mesons from nucleons. To leading twist, leading order alpha_s accuracy the corresponding production amplitude can be decomposed into pseudovector and pseudoscalar parts. Both can be expressed in terms

8

9

9

1

c

e

D

1

2

1

v

76

4

2

1

8

9

/

h

p

-

p

e

:hv

i

X

r

aTUM/T39-98-33HardExclusiveElectroproductionofPions L.Mankiewiczab,G.PilleraandA.Radyushkincd aPhysikDepartment,TechnischeUniversit¨atM¨unchen,D-85747Garching,GermanybN.CopernicusAstronomicalCenter,ul.Bartycka18,PL–00-716Warsaw,PolandcPhysicsDepartment,OldDominionUniversity,Norfolk,VA23529,USAdJe ersonLab,NewportNews,VA23606,USAAbstractWeinvestigatetheexclusiveelectroproductionofπ+mesonsfromnucleons.Tolead-ingtwist,leadingorderαsaccuracythecorrespondingproductionamplitudecanbedecomposedintopseudovectorandpseudoscalarparts.Bothcanbeexpressedintermsofquarkdoubledistributionfunctionsofthenucleon.Whilethepseudovectorcontributionisconnectedtoordinarypolarizedquarkdistributions,thepseudoscalar

partcanberelatedtoonepiont-channelexchange.Weobservethatthepseudovec-torpartoftheproductionamplitudeisimportantatxBj<0.1.Ontheotherhand,for0.1<xBj<0.4contributionsfromonepionexchangedominate.