1 Probing Spin and Flavor Structures of the Nucleon with Hadron Beams Flavor and spin structures of...

1

Probing Spin and Flavor Structures of the Nucleon with Hadron Beams

• Flavor and spin structures of the nucleons– Overview and recent results

• Future prospects – Fermilab, RHIC, J-PARC

Jen-Chieh Peng

Workshop on Hadron Physics in China and Opportunities with 12 GeV JLab

Lanzhou University, July 31-August 1, 2009

University of Illinois

Outline

2

Flavor and spin structures of the nucleons

• 99.97% of the visible mass of the Universe is composed of protons and neutrons

• Quantum Chromodynamics (QCD) at the confinement scale remains to be understood

• The progress of lattice QCD calculations allow direct comparison between the experiments and theory

• They provide crucial inputs for describing hard processes in high energy collisions such as at LHC (p+p collider)

Why is it interesting?

3

Electron beam as a powerful tool for probing partonic structure in nucleon

SLAC e p e’ X (DIS)

(elastic)eq e q

DIS data vs. QCD calculation

4

Some open questions on nucleon partonic structures

• What are the flavor structures of valence and sea quarks?

• What are the origins of sea quarks in nucleons and nuclei?

• Where does the proton’s spin come from?• How are the quark’s transverse spin distributions

different from the helicity distributions?• What are the characteristics of various transverse-

momentum-dependent (TMD) quark distribution functions?

5

Flavor structure of the parton distributions in the proton

( ) 2 ( )?

( ) ( )?

( ) ( )?

( ) ( )?

( ) ( )?

( ) ( )?

V V

p n

p n

Is u x d x

Is u x d x

Is s x u x

Is s x s x

Is u x d x

Is

Questio

u d x

ns

x

(From the textbook of F. Close)

6

Complimentality between DIS and Drell-Yan

Both DIS and Drell-Yan process are tools to probe the quark and antiquark structure in hadrons

DIS Drell-Yan

7

/ flavor asymmetry from Drell-Yand u

2 2

1/ 2 (1 ( ) / ( )Dr )

2ell-Yan: pd pp d x u x

2 2

21 2 1 2

1 2 1 2. .

4( ) ( ) ( ) ( )

9 a a a a aaD Y

de q x q x q x q x

dx dx sx x

1 2 :at x x

800 GeV proton beam

on hydrogen and deuterium

mass spectrum

8

0

0

Sullivan Processed in DIS

| | | |

( )

( )

Goldstone bosons couple to va

Meson cloud in the nucleon

Orig

s

Chir

lence qua

al quark

ins of ( ) ( )?

model

rks

p p a N b

p ud n

p ud

u d

u K s

u x d x

The pion cloud is a source for antiquarks in the proton,

and it leads to d u

9

Meson cloud model

Thomas / Brodsky and Ma

Analysis of neutrino DIS data

( )x s s

NuTeV, PRL 99 (2007) 192001

( ) ( ) ?s x s x

p K (( ))us uds

10

Predictions for sea-quark polarizations

0 ( ) (

( )

)

( ) ( ) 0

u uu u u K us

u x

s

d x s x

( ) ( ) ( ) ( )u x d x d x u x

• Meson Cloud Model

• Chiral-Quark Soliton Model

Remain to be tested …..

11

What's next for / ?d u2

21 2 1 2

1 2 1 2

4[ ( ) ( ) ( ) ( )

1]

3DY

i ii

de q x q

sx q x q x

dx dx x x

J-PARC 50 GeV

Intriguing / behavior at large

can be studied at lower beam energies

d u x DY cross section is 16 times larger

at 50 GeV than at 800 GeV

120 GeV proton bea

Fermilab E-906

(P. Reimer, D. Geesaman et al.)

J-PARC P-04

(J. Peng, S. Sawada et

m

50 GeV proton

al

be

.)

am

12

Fermilab E906 dimuon experiment (expected to run ~2010-2011)

13

/ from W production at RHICd u production in collisi (Generalized Drell-Yan)o nW p p

p p W x p p W x

( )u d W ( )d u W

No nuclear effects

No assumption of charge-symmetry

Large Q2 scale

21

21

( )( )

(

( )(

( ) ))

( )

FF

F

dpp W X

dx u xR x

d d xpp

d x

uW xXdx

14

u d

u d

Using recent PDFs

R. Z. Yang and JCP arXiv 0905.3783.

( 0.16) ( 0.16) ( 0.16)( 0) 2

( 0.16) ( 0.16) ( 0.16)F

u x d x d xR x

d x u x u x

/ from W production at RHICd u/ ( )

( ) at 500 GeV/ ( )

FF

F

d dx pp W xR x s

d dx pp W x

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Charge Symmetry Violation in PDF?

2 2

Charge symmetry : rotation around isospin axis by 180

Charge symmetry in PDF is generally assumed, bu

( ; .)

A compari

t not tested

son of with shows upper limit o f

n

y

p n pp n u d u d u d u d etc

F F

I

The NuTeV anomaly in the Weinberg angle could be partly

explained b

(Lon

y ch

CS breaking

of 5 1

arge symmetry vio

dergan and

latio

Thomas, hep-ph/0407247)

(Londergan and Thomas,

n

0%

P

L B558

(2003) 132)

See recent review of Londergan, Peng, and Thomas (arXiv:0907.2352)

16

Charge Symmetry violation from MRST Global fits

(Eur. Phys. J. C35, 325 (2004))

4 0.5(

(

) (1 ) ( 0.0

) ( ) ( )

Best fit: 0.2

0.8 0.65 (90%

( ) ( ) ( )

( )

C.L.)

90

(

9

)

)

( )

V V

p nV V V

p nV V V

u x d x f x

d x d x u x

u x u

f x x x

x

x

x d

Best fit: 0.08

(8% of C

0.08 0.18 (90

( ) ( )[

BV

1 ]

( ) ( )[

fo

% C

1 ]

r

.L

.

!

)

sea )

n p

n p

u x d x

d x u x

CSV for sea quarks

CSV for valence quarks

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Comparison between MRST and quark-model calculation

Charge symmetry violation for valence quarks

MRST Quark-model

(Rodionov, Thomas, Londergan)Eur. Phys. J. C35, 325 (2004)

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CSV from W production at RHIC2 / ( )

( ) at 500 GeV/ ( )

FF

F

d dx pp W xR x s

d dx pd W x

2 2

2 2

/ ( )( )

2 / ( )

( ) ( )11

2 (

for 0, ( ) is sensitive to

valence-quar

) ( )

k CSV

FF

F F

F

d dx pd W xR x

d dx pp W x

d x d x

u x u x

x R x

(S. Yoon and Peng, 2006)

Charge-symmetric

Charge symmetry violating

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Gluon distributions in proton versus neutron?

E866data: ( ) / 2 ( )p d X p p X

/ 2 [1 ( ) / ( )] / 2:

/ , : / 2 [1 ( ) / ( )] / 2

pd pp

pd ppn p

d x uDrell Y x

g

an

J x g x

Lingyan Zhu et al., PRL, 100 (2008) 062301 (arXiv: 0710.2344)

Gluon distributions in proton and neutron are very similar

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Three parton distributions describing quark’s transverse momentum and/or transverse spin

1) Transversity

2) Sivers function

3) Boer-Mulders function

Correlation between and q Ns S

Correlation between and q qs k

Correlation between and N qS k

Three transverse quantities:

1) Nucleon transverse spin

2) Quark transverse spin

3) Qaurk transverse

mo

Three diff

me

er

ntum

ent correlations

N

q

q

S

s

k

21

4

26 4

Q

sxd

),()(])1(1{[ 211

,

22 h

qq

qqq PzDxfey

22 (1) 2

1 12,

22 (1) 2

1 12,

2 21 1

,

cos(2 )

sin(2 )

(1 ) ( ) ( , )4

| |

s

(1 ) ( ) ( , )4

| | (1 ) ( ) (in( )) ,

q qhq h

q qN h

q qhL q L h

q qN h

q

lh

lh

l lh

qhST q h

q qh

Py e h x H z P

z M M

PS y e h x H z P

z M M

PS y e h x H z P

zM

2 2 (1) 21 1

,

32 (2) 2

1 13 2,

2 21 1

,

1| | (1 ) ( ) ( , )

2

| | (1 ) ( ) ( , )6

1| | (1 ) ( ) ( , )

2

1| | (1 )

sin( )

sin(3 )

co ( )2

s

q qhT q T h

q qN

q qhT q T h

q qN h

q qe L q h

q q

he T

N

l lh S

l lh S

l lh S

PS y y e f x D z P

zM

PS y e h x H z P

z M M

S y y e g x D z P

PS y y e

zM

2 (1) 2

1 1,

( ) ( , )}q qq T h

q q

g x D z P

Unpolarized

Polarized target

Polarzied beam and

target

SL and ST: Target Polarizations; λe: Beam Polarization

Sivers

Transversity

Boer-Mulders

Transversity and TMD PDFs are probed in Semi-Inclusive DIS

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Transversity and TMD PDFs are also probed in Drell-Yan

1 1

1

- Unpolarized Drell-Yan:

- Single transverse spin asymmetry in polarized Drell

Boer-Mulders

-Yan:

cos

functions:

Sivers functions:

Transversity

(2 )

( ) ( )

distributio

DY

DYN T q q q

d h h

A f x f x

1 1

- Double transverse spin asymmetry in polarized Drell-Yan:

Drell-Yan and SIDIS involve different combinations of TMDs

Drell-Yan does not require

ns:

kno

( ) (

wledge of the fra

)DYTT q qA h x h x

gmentation functions

T-odd TMDs are predicted to change sign from DIS to DY

(Boer-Mulders and Sivers functions)

Remains to be tested experimenta ! lly

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Boer-Mulders function h1┴

1

1

1 represents a correlation between quark's and

transverse spin in an unpolarized hadron (ana

is a time-reversal odd, chiral-o

logous to Coll

dd TMD p

ins fu

arton distributio

nction)

n

T

h

h

h k

can lead to an azimuthal cos(2 ) dependence in SIDIS and

Drell-Yan

Boer, PRD 60 (1999) 014012

● Observation of large cos(2Φ) dependence in Drell-Yan with pion beam

● How about Drell-Yan with proton beam?

252 GeV/c π + W

2 21 31 cos sin 2 cos sin cos 2

4 2

d

d

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cos2Φ Distribution in p+p and p+d Drell-Yan

E866 Collab., Lingyan Zhu et al., PRL 99 (2007) 082301; PRL 102 (2009) 182001

Sea-quark BM functions are much smaller than valence BM

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Polarized Drell-Yan with polarized proton beam?

• Polarized Drell-Yan experiments have never been done before

• Provide unique information on the quark (antiquark) spin

Quark helicity distribution

Quark transversity distribution

Can be measured at RHIC, J-PARC, FAIR etc.

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• Does Sivers function change sign between DIS and Drell-Yan?

• Does Boer-Mulders function change sign between DIS and Drell-Yan?

• Are all Boer-Mulders functions alike (proton versus pion Boer-Mulders functions)

• Flavor dependence of TMD functions• Independent measurement of transversity

with Drell-Yan

Outstanding questions in TMD to be addressed by future Drell-Yan experiments

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Future prospect for Drell-Yan experiments• Fermilab p+p, p+d, p+A

– Unpolarized beam and target

• RHIC– Polarized p+p collision

• COMPASS– π-p and π-d with polarized targets

• FAIR– Polarized antiproton-proton collision

• J-PARC– Possibly polarizied proton beam and target

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Summary• The Deep-Inelastic Scattering, together

with Drell-Yan process in hadron collisions, have provide much information (and surprises) on the partonic structures of the hadrons

• New Drell-Yan (and W-production) experiments using pion, proton, and antiproton beams will further elucidate the flavor and spin structures of the nucleons.

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Double-spin asymmetry in polarized p-p at J-PARC

1) Double-spin asymmetry (ALL) with longitudinally polarized beam/target in Drell-Yan probe Quark helicity distributions

21 2 1 2

21 2 1 2

[ ( ) ( ) ( ) ( )]

[ ( ) ( ) ( ) ( )]a a a a aDY a

LLa a a a aa

e q x q x q x q xA

e q x q x q x q x

2) Double-spin asymmetry (ATT) with transversely polarized beam/target in Drell-Yan probe quark transversity distribution

21 1 1 2

21 2

( ) ( )ˆ

( ) ( )

q qqq

TT TTqq

e h x h xA a

e q x q x

P24 proposal, Goto et al.

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/ from W production at PHENIXd u

R. Z. Yang and Peng (2007)

/ ( )( ) at 500 GeV

/ ( )

d dy pp W x l xR y s

d dy pp W x l x

detectione

detection

u d

u d

950 pb-1 integrated luminosity

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Leading-Twist Quark Distributions

No K┴ dependence

K┴ - dependent, T-odd

K┴ - dependent, T-even

( A total of eight distributions)

32

Spin and flavor are closely connected

0 ( ( )) u Ku uu u us s

,L R LR RR LL du u d d u ud

( ) ( ) ( ) ( )u x d x d x u x

( ) ( ) ( ) ( )u x d x d x u x

• Meson Cloud Model

• Pauli Blocking Model

A spin-up valence quark would inhibit the probability of generating a spin-down antiquark

• Instanton Model

• Chiral-Quark Soliton Model

• Statistical Model

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1

0Predictions of [ ( ) ( )]u x d x dx

Peng, Eur. Phys. J. A18 (2003) 395