1

Partonic Substructure of Nucleons and Nuclei with Dimuon Production

• Partonic structures of the nucleons and nuclei with dimuon production– Overview and recent results

• Future prospects – Fermilab, RHIC, J-PARC, FAIR ...

Jen-Chieh Peng

Workshop on Achievements and New Directions in Subatomic Physics

CSSM, Adelaide, February 15-19, 2010

University of Illinois

Outline

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Observation of scaling behavior in deep-inelastic scattering

νW2 is the “form factor” for the deep-inelastic scattering, and is found to be independent of Q2 2 / 3

3

1( ) ( )

(2 )iq rf r F q e d q

3

Proton structure function from DIS• Important features:

– Q2-dependence is due to the quark-gluon coupling– Observed Q2 dependence can be well described by QCD

• Challenges:– Compositions of various quarks and antiquarks– Spin structure of the proton – New types of structure functions – Models and lattice calculations for PDFs– Modifications of PDFs in nuclei

4

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

McGaughey, Moss, JCP,

Ann.Rev.Nucl. Part. Sci. 49 (1999) 217

5

Lepton-pair production provides unique information on parton distributions

194 GeV/c

W X

800 GeV/c

p W X

1.8 TeV

p p l l X

Probe antiquark distribution in nucleon Probe antiquark

distribution in pion Probe antiquark

distributions in antiproton

Unique features of D-Y: antiquarks, unstable hadrons…

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Fermilab Dimuon Spectrometer(E605 / 772 / 789 / 866 / 906)

1) Fermilab E772

"Nuclear Dependence of Drell-Yan and Quarkonium Production"

2) Fermilab E78

(proposed in 1986 and completed in 1988)

(proposed in 1989 and completed in 19919

"Search for Two-Body a

)

Dec

ys of Heavy Quark Mesons"

3) Fermilab E866

"Determination of / Ratio of the Proton via Drell-Yan"

4) Fermilab E906

(proposed in 1993 and completed in 1996)

(proposed in 1999, will run in 2010?)

"Drell

d u

-Yan with the FNAL Main Injector"

Physics results from Fermilab dimuon experiments

Antiquarks in nuclei and nucleons

Drell-Yan angular distribu

Quark energy loss in nuclear medium

Pronounced nuclear dependence

Production mechn

tions

1) Drell -Yan process :

2) Quarkonium production :

Gluon distributions in the nucl

ism and polarizations

Open charm production

B-meson product

ons

ion

e

3) Heavy quark production :

8

Is in the proton? u d

The Gottfried Sum Rule 1

2 20

1

0

[( ( ) ( )) / ]

1 2( ( ) ( ))

3 3

( )1

3 p p

p nG

p p

S F x F x x dx

u x d

i

x dx

f u d

In 1992, New Muon Collaboration (NMC) obtainsSG = 0.235 ± 0.026

( Significantly lower than 1/3 ! )

=Expect if sea quarks

are produced in

d u

g qq

?d u

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“A Limit on the Pionic Component of the Nucleon through SU(3) Flavor Breaking in the Sea”

A.W. Thomas, Phys. Lett. 126B (1983) 97-100

"... it is rather distrurbing that no one has yet provided

direct experimental evidence of a p

"Clearly the pion excha

ionic component

in t

nge process of fig. 1 do

he nucleon."

es predict

".... the lack of experimental infor

that the excess of D to U should be i

mation about the shapes

of s(x), s(

n th

x) a

e ratio of 5 to 1

i

nd [d(x) - u(x)]."

n the proton."

"It is therefor

e appropriate to close with a plea for better

measurements of these three quantities in the free proton."

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/ 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

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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(Piller and Thomas)

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Meson Cloud Models Chiral-Quark Soliton Model Instantons

• nucleon = chiral soliton

• expand in 1/Nc

• Quark degrees of freedom in a pion mean-field

Theses models also have implications on• asymmetry between and ( )s x ( )s x• flavor structure of the polarized sea

Meson cloud has significant contributions to sea-quark distributions

(For reviews, see Speth and Thomas (1997), Kumano (hep-ph/9702367 ), Garvey and Peng (nucl-ex/0109010))

Theory: Thomas, Miller, Kumano, Ma, Londergan, Henley, Speth, Hwang, Melnitchouk, Liu, Cheng/Li, etc.

Origins of ( ) ( )?u x d x

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Meson cloud model

Signal and Thomas, 1987

Analysis of neutrino DIS data

( )x s s

NuTeV, PRL 99 (2007) 192001

( ) ( ) ?s x s x

p K (( ))us uds

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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

Eur. Phys. J. A18 (2003) 395

First measurements are now available (Talk by Don Geesaman)

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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 6 times larger

at 120 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

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/ 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

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u d

u d

Using recent PDFs

Yang, Peng, Perdekamp, Phys. Lett. B680, 231 (2009)

/ from W production at RHICd u/ ( )

( ) at 500 GeV/ ( )

FF

F

d dx pp W xR x s

d dx pp W x

A comparison with D-Y could lead to extraction of CSV effect

( ) ( )? ( ) ( )? etc.p n p nIs u x d x u x d x

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Three parton distributions describe 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) Quark transverse

mo

Three diff

me

er

ntum

ent correlations

N

q

q

S

s

k

20

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 Transverse Momentum Dependent PDFs are probed in Semi-Inclusive DIS

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Transversity and Transverse Momentum Dependent PDFs are also probed in Drell-Yan

1 1

1

a) Boer-Mulders functions:

b) Sivers functions

- Unpolarized Drell-Yan:

- Single transverse spin asymmetry in polarized Drell-Yan:

:

c) Transv

( ) ( ) cos(2 )

( ) ( )

e

DY q q

DYN T q q q

d h x h x

A f x f x

1 1

rsity distributions:

Drell-Yan does not require knowledge of the fragmentation functions

T-odd TMDs are pre

- Double transverse spin asymmetry in polarized Drell-Yan:

(

d

) ( )DYTT q qA h x h x

icted to change sign from DIS to DY

(Boer-Mulders and S

Remains to be te

ivers functions)

sted 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 hadro

is a time-reversal odd, chiral-odd TMD parton distributio

can lea

n

d

n

to an azimuthal cos(2

T

h

h

h

k

) dependence in 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?

194 GeV/c π + W

2 21 31 cos sin 2 cos sin cos 2

4 2

d

d

1 1 ( ) ( )q qh x h x

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With Boer-Mulders function h1┴:

ν(π-Wµ+µ-X)~ [valence h1┴(π)] * [valence

h1┴(p)]

ν(pdµ+µ-X)~ [valence h1┴(p)] * [sea h1

┴(p)]

Azimuthal 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 quarks

Smallνis observed for p+d and p+p D-Y

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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: Burkardt)?

• Flavor dependence of Transverse Momentum Dependent distribution functions

• Independent measurements of transversity and sea-quark polarization with Drell-Yan

Outstanding questions to be addressed by future Drell-Yan experiments

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Modification of Parton Distributions in NucleiEMC effect observed in DIS

How are the antiquark distributions modified in nuclei?

F2 contains contributions from quarks and antiquarks

(Ann. Rev. Nucl. Part. Phys., Geesaman, Saito and Thomas)

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Drell-Yan on nuclear targets

The x-dependence of can be directly measured( ) / ( )A Nu x u x

( )

( )

pAA

pdN

u x

u x

PRL 64 (1990) 2479 PRL 83 (1999) 2304

No evidence for enhancement of antiquark in niclei !?

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Cloet, Bentz, and Thomas, arXiv:0901.3559

Isovector mean-field generated in Z≠N nuclei can modify nucleon’s u and d PDFs in nuclei

Is / asymmetry also modified in nuclei?d u

Flavor dependence of the EMC effects

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The Drell-Yan Process: pN X

2 2 /

1 /

pA

pd

Z N d u

A A d u

Assuming dbar/ubar = 1.5 for the nucleons at x=0.15, then the above ratios are:

1.0 for 40Ca, 1.042 for 208Pb

Drell-Yan ratios for p-A /p-d :

Can probably be measured at Fermilab E906

Can one measure / in nuclei?d u

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Nuclear modification of spin-dependent PDF?

Bentz, Cloet, Thomas et al., arXiv:0711.0392

EMC effect for g1(x)

Remains to be tested by experiments

Measure the nuclear modification of Boer-Mulders functions with Drell-Yan ?

(only unpolarized Drell-Yan is required)

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Summary• Unique information on hadron structures has been

obtained with dilepton production experiments using hadron beams.

• On-going and future dilepton production experiments at various hadron facilities can address many important unresolved issues in the spin and flavor structures of nucleons and nuclei.

• Many of the accomplishments and future plans were inspired by Tony’s ideas.