Future Measurements of Transversity

A review of envisaged future quark transversity measurements is presented.

FutureMeasurementsofTransversity1

V.A.Korotkova,bandW.-D.Nowaka

a

DESYZeuthen,D-15735Zeuthen,Germanyb

IHEP,RU-142284Protvino,Russia

Abstract:Areviewofenvisagedfuturequarktransversitymeasurementsispresented.

arXiv:

h

e

p

-

ph/0102015v1 2 Feb 2001

1Introduction

Aquarkofagiven avorinthenucleonischaracterizedbythreetwist-twoquarkdistributions:thenumberdensitydistributionq(x),thehelicitydistribution q(x),andtheexperimentallyunknowntransversitydistributionδq(x),whichcharacterizesthedistributionofthequark’stransversespininatransverselypolarizednucleon.Fornon-relativisticquarksδq(x)= q(x)canbeexpected,butgenerallybothdistributionfunctionsareindependent.So er’sinequal-ityforeachquark avor,2|δq(x,Q2)|≤q(x,Q2)+ q(x,Q2),restrictspossiblevaluesofthetransversitydistributions.

Thetransversitydistributionwas rstdiscussedbyRalstonandSoper[1]indoublytrans-versepolarizedDrell-Yan(DY)scattering.ItsmeasurementisoneofthemaingoalsofthespinprogramatRHIC.Thetransversitydistributionsδq(x)arenotaccessibleininclusiveDIS,becausetheyarechiral-oddandonlyoccurincombinationswithotherchiral-oddobjects.Insemi-inclusiveDISofunpolarizedleptonso transverselypolarizednucleonsseveralmethodshavebeenproposedtoaccessδq(x)viaspeci csingletarget-spinasymmetries.

2Measurementofδq(x)inppCollisions

AnevaluationoftheDYasymmetryATT～e2¯i(x)wascarriedout[2]byassumingiδqi(x)δq

thesaturationofSo er’sinequalityforthetransversitydistributions.ThemaximumpossibleasymmetryatRHICenergieswasestimatedtobeATT=1÷2%(seeAtsmallerenergies,

(√e.g.forapossible xed-targetexperimentHERA-N

TalkpresentedbyV.A.KorotkovattheInternationalWorkshop”SymmetriesandSpin,Praha-Spin-2000”,

Prague,July17-22,2000

1

1

A review of envisaged future quark transversity measurements is presented.

]

e

cn%[a|)tpeM(cTcTaA|

[GeV]M[GeV]

MFigure1:ProjectionsformeasurementswithPHENIX(

√

M

≈

1

A review of envisaged future quark transversity measurements is presented.

A(x)

~

10

x

0.510

x

1

Figure2:ProjectionsforameasurementatHERMESofa)twist-3asymmetryforπ++π pro-duction(dash-dottedcurve—δq(x)=0,dashedcurve—saturationoftheSo er’sinequality,solidcurve—δq(x)= q(x)),b)two-pionasymmetry.

thesumofπ+andπ productiononaprotontarget:

√

2Mx2ygT(x)+h1(x)/3x (1 y/2)g1(x)

A(x,y,φ)=cosφ···

Q21+(1 y)2

gT(x)=g1(x)+g2(x),andφistheazimuthalanglebetween

theleptonscatteringplaneandthespinplane.Theprojectionsforameasurementofthis

(x,y)=twist-3pionasymmetryatHERMESareshownin g.2a,wheretheasymmetryA

PB·PT·A(x,y,φ)/cosφisshownforconvenience.

Two-MesonCorrelationswithTransverseSpin.Ashasbeennotedabove,theasymmetryinthiscasedependsontheunknownchiral-oddinterferencequarkFFδq I(z),

2a

I(z).A⊥ ～aeaδqa(x)δq

AmaximallypossibleasymmetrywithrespecttotheinterferenceFFcanbeobtainedwithitsupperbound.Forπ+π pairproductionataprotontargetthemaximalasymmetrytakestheform:

2

2

ieiδqi(x),

Amax

δuv(x) π

= cosφsin(δ0 δ1)Dnn

(u(x)+u¯(x))+32

11

A review of envisaged future quark transversity measurements is presented.

Collinse ect.Inthecaseofanunpolarizedbeamandatransverselypolarizedtargetthefollowingweightedasymmetry[12]providesaccesstothequarktransversitydistributionviatheCollinse ect:

AT(x,y,z)≡

dφ d2Ph⊥

|Ph⊥|

dφ d2Ph⊥(dσ↑+dσ↓)

,(3)

wherePh⊥isthepion’stransversemomentumandtheazimuthalanglesarede nedinthetransversespacegivingtheorientationoftheleptonplane(φ )andtheorientationofthe

hadronplane(φ h=φh φ)orspinvector(φs=φs φ)withrespecttotheleptonplane.Theasymmetry(3)canbeestimatedfrom

AT(x,y,z)=PT·Dnn·

q

e2qδq(x)H1

⊥(1)q

(z)

u(x)

·

H1

⊥(1)u

(z)

A review of envisaged future quark transversity measurements is presented.

3.2TheExperimentTESLA-N

ThebasicTESLA-N

[13]ideaistouseoneofthearmsofthepresentlyplannede+e colliderTESLAatDESYtoaccomplishcollisionsoflongitudinallypolarizedelectrons(E=250GeV,PB=90%)withapolarizedsolid-state xedtarget.Presently,thetargetmaterialsNH3(PT=0.8,f=0.176)and6LiD(PT=0.3,f=0.44)appearasthebestchoicestostudyelectronscatteringo polarizedprotonsanddeuterons,respectively.

Thephysicsprojectionspresentedbelowarebasedonanintegratedluminosityof100fb 1.Thisrepresentsaconservativeestimateforoneyearofdatataking.

Measurementsofsingletarget-spinasymmetriesduetotheCollinse ectintheproduction

+,π

ofpositiveandnegativepionsonprotonanddeuterontargets(Aπ)allow,underreasonablep,d

assumptions,thesimultaneousreconstructionoftheshapesoftheunknownfunctionsδq(x,Q2)

⊥(1)

andH1(z)/D1(z).Againtherelativenormalizationcannotbe xedwithoutanindependentmeasurementorafurtherassumption.Thisambiguitycanberesolvedbyrelatingδq(x)to q(x)atsmallvaluesofQ2.Followingref.[14],thenormalizationambiguityisresolvedby

2

assumingδu(x0,Q20)= u(x0,Q0)atx0=0.25.

Theprojectionsforthemeasurementofδuv(x,Q2)atTESLA-Nareshownin g.4.Abroadrangeof0.003<x<0.7canbeaccessedinconjunctionwith1<Q2<100GeV2.A

¯isattainedsimultaneousreconstructionofthequarktransversitydistributionsδdv,δu¯,andδd

withasomewhatloweraccuracy.Projectionsfortheaccuraciesofameasurementoftheu-andd-quarktensorchargesare±0.01and±0.02atthescaleof1GeV2,respectively.Atthesametime,precisevalueswouldbemeasuredfortheratioofpolarizedandunpolarizedfavore …… 此处隐藏：5147字，全部文档内容请下载后查看。喜欢就下载吧 ……