Measurements with Polarized Hadrons

Measurements with Polarized Hadrons

T.-A. Shibata

Tokyo Institute of Technology

Aug 15, 2003Lepton-Photon 2003

T.-A. Shibata 2

Introduction: Spin of Proton

Polarized Deep Inelastic Lepton-Nucleon Scattering

1. Flavor Separation of Quark Helicity Distributions

2. Deeply Virtual Compton Scattering

3. Single-Spin Azimuthal Asymmetries

in Semi-Inclusive Deep Inelastic Scattering

Polarized Proton-Proton Collisions

Contents:

T.-A. Shibata 3

Introduction:


‘Explore spin structure of hadrons and further　 develop QCD using Spin’

QCD was successful, both in perturbative and

non-perturbative regions, but spin of the nucleon still needs

to be studied in many aspects to be fully explained with QC

D.

T.-A. Shibata 4

Introduction : Spin of Proton

Sum of Spins of u u d Quarks = Spin of Proton

2

1

2

1

2

1

2

1

+ +

SU(6) Quark Wave Functions of Baryons1 / 2

1 / 2- 1 / 2

1 / 2

2

106800470060

2

1 ...)( sdu

)%( 14912

EMC Experiment (1988)

20 – 30 % of Nucleon Spin

Gqq

JLsdu )(2

1

2

1

=

‘Nucleon Spin Problem’

T.-A. Shibata 5

Introduction:

Fixed Target Experiments :

Polarized Targets + (Polarized) Beams

Nucleon (p, n) + e+/e- HERMES

e- SLAC, JLab

COMPASS Collider Experiments :

Polarized Proton - Proton Collisions RHIC


Experimental Methods: Lepton-Hadron Scattering, Hadron-Hadron Collision

/

T.-A. Shibata 6

Deep Inelastic Scattering, Semi-inclusive Measurements

Semi-inclusive measurement,

e’ and

... pp,K,,

)()(),( zDxqezx hq

qqh 2

( quark distribution ) x ( fragmentation function )

e

e’

Flavor tagging

Inclusive measurement, e’

)()( xqexq

q 2

/hEz

T.-A. Shibata 7

Detectors

Target

HERMES @DESY- HERA1995 --

27.6 GeV

Polarized Internal gas targets

(3He, H, D)

e

T.-A. Shibata 8

Compass Set-up

2002-2003

polarized target

magnets

RICH

muon filter

GeV160

@ CERN

Gluon Spin ContributionD’s identified in 2002.

)(xGc

c

Photon Gluon Fusion

N

T.-A. Shibata 9

1. Flavor Separation of Quark Helicity Distributions

)(),(),(),(),( xsxdxuxdxu

T.-A. Shibata 10

Quark Helicity Distributions, Flavor Separation

Double-spin asymmetry

)()(

)()(),(

xx

xxzxA

1

XeNe

Beam and target, both polarized

....

.... ....

....NucleonVirtual photon

T.-A. Shibata 11

Quark Helicity Distributions, Flavor Separation

x

Ah1(x)

K+

K-

asymmetries similar to inclusive asymmetry,except asymmetry.

Double-spin asymmetries Ah1 (d) from semi-inclusive DIS

K,-K

Hadron identification for the first time

HERMES

x

T.-A. Shibata 12

Quark Helicity Distributions , Flavor Separation

)()(),( zDxqezx hq

qqh 2

Semi-inclusive DIS cross section

Double-spin asymmetry

/hEz

q

hqq

q

hqq

hh

hhh

zDxqe

zDxqe

zxzx

zxzxzxA

)()(

)()(

),(),(

),(),(),( 2

2

1

)()()( xQxPxA

1 ),,,,()(s

s

d

d

u

u

d

d

u

uxQ

XmeNe

)()()( xqxqxq )()()( xqxqxq Quark Helicity Distributions

Quark Density Distributions

)(K),( susu unconstraineds

N = p, d m =

unpol. PDF and FF from data of unpol. semi-inclusive DIS

T.-A. Shibata 13

Flavor Separation, 　Quark Helicity Distributions

Result:

x

ux

dx

ux

dx

sx QCD fits to inclusive measurements

etc.11

xasd

d

• X bin by bin analysis except

for smearing correction.

• No functional forms are

assumed.

• No first moments are assume

d.

• Helicity conservation not

assumed

0u0d0q

HERMES

x

Error band – systematic error

T.-A. Shibata 14

2. Deeply Virtual Compton Scattering -- Generalized (Off-forward) Parton Distributions

T.-A. Shibata 15

Deeply Virtual Compton Scattering (DVCS) -- Exclusive production of a real photon

Deeply Virtual Compton Scattering

GPD

p

p

x x

Im

Coss section for inclusive deep inelasticscattering

:Light cone momentum fraction

:Exchanged longitudinal momentum fraction

:Momentum transfertBJ

BJ

x

x

2

x

T.-A. Shibata 16

Generalized (Off-Forward) Parton Distributions

Generalized Parton Distributions (GPD)

Deep InelasticScattering


Electromagnetic Form Factors( Elastic Scattering )

Total Angular Momentum Jq

qqqq EHEH~

,~

,,

Exclusive Meson Production ,,,

21 FF ,

qq ,

Orbital Angular Momentum Lq

T.-A. Shibata 17

Generalized Parton Distributions

),,(~

),,,(~

),,,(),,,( txEtxHtxEtxH qqqq

),()( xq,x,Hq 00 )()(~

xq,x,Hq 00

Sum rules, x – integral, sum over q

),(),,( tFtxHq1 )(),,( tFtxE q

2

),(),,(~

A tgtxHq )(),,(~

A thtxE q

Dirac and Pauli Nucleon Form Factors

Axial-vector and Pseudo- scalar Form Factors

qqq

t

JtxEtxHxdx

1

10 2

1)],,(),,([lim

qz

q LqJ 2

1

Ordinary QuarkDistributions

Forward limit ,0t

Total angular momentum

Orbital angular momentum

2nd moment

T.-A. Shibata 18


Beam-spin asymmetry by HERMES and CLASBeam-charge asymmetry by HERMES -- DVCS-BH Interference, Real and Imaginary

Deeply Virtual Compton Scattering Bethe-Heitler Process, known calculable

DVCS Cross Section by ZEUS and H1

IAAAAxQt

2222

4

||||||dddd

dBHDVCSBHDVCS

Ipe Imsinp)e(-)(LU �

Ipepech Recos)(-)(

How to measure DVCS

T.-A. Shibata 19

HERMES (2001) CLAS (2001)


LUA

First observation of beam-spin asymmetry of DVCS

~ 30% effect

T.-A. Shibata 20

Beam-Spin Asymmetry

Deeply Virtual Compton Scattering, Generalized Parton Distributions

Momentsin HERMES

XM

Missing Mass Resolution 0.8 GeV

T.-A. Shibata 21

Deeply Virtual Compton Scattering, Generalized Parton Distributions

Missing Mass Resolution 0.8 GeV

Momentcos Beam-Charge AsymmetryHERMES

XM

T.-A. Shibata 22

How to extend

GPD

GPD

Quantum number of final state Select different GPD

,,

Pseudo scalar meson Vector meson

Exclusive Meson Productions

),,(~

),,,(~

txEtxH qq ),,(),,,( txEtxH qq HERMES’s data

T.-A. Shibata 23

　 3. Single-Spin Azimuthal Asymmetry in Semi-inclusive Deep Inelastic Scattering ‘Quark Transversity Distributions ’)(xq

T.-A. Shibata 24

Last unmeasured leading twist distribution:q

3 leading twist quark distributions

　　　　 Quark Density Distributions

Quark Helicity Distributions

Quark Transversity Distributions

Single-Spin Azimuthal Asymmetries in Semi-Inclusive DIS, Transversity

is Chiral Odd. Not accessible with inclusive DIS It is accessible with semi-inclusive DIS,accompanied with a Chiral Odd Fragmentation Function does not couple with gluon. ( Collins FF ) Q2 evolution is different from

)(xq

)(xq)(),( xqxq

)()( , zHxqeAh

qq

qh 1

2

)(xq

)(xq

)(xq

Spin averaged, vector charge

Helicity difference, axial charge

Helicity flip, tensor charge

)(zH 1

|)()(||)(| xqxqxq 2

1

Soffer bound

T.-A. Shibata 26

Single-Spin Azimuthal Asymmetries in Semi-Inclusive DIS

LongitudinallyPolarized Target

TransverselyPolarizedTarget

XmeNe

150

12

.sin

yQ

xMS

T

Azimuthal Angle

sAzimuthal Angle

NN HERMES, JLab

HERMES, COMPASS, JLab

dependence

s s

dependence

dependence

with respect to

T.-A. Shibata 27

Xmede

Single-Spin Azimuthal Asymmetries in Semi-Inclusive DIS

Longitudinally polarized target ,Target Spin Asymmetry AUL

LNLN

LNLN

pA

L /)(/)(

/)(/)(

||)(UL

1

sin1P

221 sinsin PP

ULA

π

0π

π

K

HERMES

sinULA positive for

Increases with x nearly zero for

K,, 0

2sin moment ~ 0

T.-A. Shibata 28

　　 (Quark transversity distribution) x (Chiral odd FF )

HERMES (2002--) focused on it. 700K D.I.S. events recorded.

Further data taking 2003-- . COMPASS data at higher Q2, JLab

UTs )(sin UTs )(sin moment: Collins Effect

moment: Sivers Effect

Transversely polarized target data can distinguish between the two. becomes dominant.

UTTULLUL SSA sinsin~sin

sinOrigins of moment, Longitudinally polarized target0S

)()(~ , zHxqe q

q q 1

2

)()(~ T zDxfe q

q q 112

TS

))(~

)()()((~sin ,, zHxhz

zHxheQ

qL

qqL

qqUL

112 11

UT sin

Q2 evolution of ),( 2Qxq

Sivers Effect: 　　　　　　　　　　　　　　

Collins Effect:

( see also polarized pp collisions )

T.-A. Shibata 29

Polarized Proton-Proton Collisions

T.-A. Shibata 30

g

jet

q

Polarized Proton-Proton Collision

Gluon spin contribution to the nucleon spin

Gluon Compton scattering

LLLL axq

xq

xG

xGA ˆ

)(

)(

)(

)(

2

2

1

1

qqg 2 jet production

qq

qg

jetjetgg

)(

Inclusivemeasurement

p

p

q

Polarized Parton-Parton Collision

Polarized pp Collisions at RHIC

100 GeV + 100 GeV

2001/2002 P = ~0.2, Int L ~ 0.3 pb-1, transverse

- May 2003 P = ~0.3, Int L ~ 0.8 pb-1, transverse + longitudinal

Physics Goal P = 0.7, Int L = 320 pb-1 , at 100 + 100 GeV

800 pb-1 , at 250 + 250 GeV

T.-A. Shibata 32

STAR

p + p + X ,

s = 200 GeV

Single-Spin Asymmetry, Transversely Polarized Beam

PHENIX and STAR collected data of inclusive production

Polarized pp Collisions at RHIC

Similar to the earlier Fermilab data at s=20 GeV, pT = 0.5-2.0 GeV/c

Forward , small pT

Double spin asymmetry, ALL,at large pT will becomeavailable soon

T.-A. Shibata 33

Conclusions 1

To understand hadrons in terms of QCD, Spin Structure of the

Nucleon is an important subject.

Many experiments are currently running with beams

at different labs in the world.

Flavor separation of quark helicity distributions has been mad

e.

Deeply Virtual Compton Scattering provides access to Generalized

Parton Distributions.

Single-spin azimuthal asymmetries in semi-inclusive DIS have bee

n

observed. Quark Transversity Distributions is a new subject

which is being investigated. Results from transversely polarized

targets will become available soon.

... p,,,e

q

q

T.-A. Shibata 34

Conclusions 2

Polarized proton-proton collider has now longitudinally as well as

transversely polarized beams. Single-spin asymmetries in

productions at small angles from transversely polarized

beam have been obtained. The asymmetries at large pT are being

analyzed.

Spin physics with the nucleon is a rapidly expanding field. Many

new ideas of measurements are being proposed. High precision

data as well as new surprises are expected.

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Measurements with Polarized Hadrons