1

Hadron Structure with Dilepton Production

• Brief historical review • Recent highlights • Future prospects

Jen-Chieh Peng

Workshop on “High-energy Hadron Physics with Hadron Beams”, KEK, January 6-8, 2010

University of Illinois at Urbana-Champaign

Outline

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First Dimuon Experiment

29 GeV protonp U X

Lederman et al. PRL 25 (1970) 1523

• Experiment originally designed to search for neutral weak boson (Z0)

• Missed the J/Ψ signal !

3

Lepton-pair production is a powerful tool for finding new particles

0/J e e Z e e

4

The Drell-Yan Process

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

5

Lepton-pair production also 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…

6

Deep-Inelastic Scattering versus Drell-Yan

Drell-Yan cross sections are well described by NLO calculations

DIS Drell-Yan

(hep-ph/9905409)

7

Quarkonium production provides complementary information

2

1

2 2 2

2 2

1/ 2

1

1

2

2/ ( / ) 2 ( , ; ) /(

where

4 )

/ and

F PT F

F

d dx J F d H x x m x

m s x x x

21 2 1 2

, ,

22

2

1

21( ) ( )

(

{ ( ) ( ) ( ) ( )} ( ; )

,

( ;

; )

)i i i iP T P T

i u

T

s

PT

d

PG x G x

q x q x q x q

gg QQ

x

H x

m

m

q QQ

m

q

x

Gluon-gluon fusion

Quark-antiquark annihilation

Calculations versus data

Schuler, Vogt, PL B 387(1996)181

• Proceed via strong interaction

• Sensitive to gluons

Color evaporation model

F is the “fudge factor”

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Meson East Spectrometer(E605/772/789/866)

Open-aperture Closed-aperture Beam-dump (Cu)

J/ΨJ/Ψ

Ψ’

σ(J/ψ) ~ 15 MeV σ(J/ψ) ~ 150 MeVσ(J/ψ) ~ 300 MeV

800 GeV proton beam

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Physics with High-Mass Dimuon Production

Antiquarks in nuclei and nucleons

Quark energy loss in nuclear medium

Drell-

1) Drell-Yan process:

2) Quarkonium

Yan angular distributions

Pronounced nuclear dependence

produ

Produc

c

t

ti

io

on

n mechn

:

3) Heavy qua

ism and pola

rk productio

rizations

Gluon distributions in the nucleons

Open charm production

B-meson produc

n:

tion

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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

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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/ 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

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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 Kumano (hep-ph/9702367 ), Garvey and Peng (nucl-ex/0109010))

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

Origins of ( ) ( )?u x d x

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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

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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

First results are obtained from polarized DIS. Remain to be tested by W-production at RHIC

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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 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

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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

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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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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

( ) ( )[

SV

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)

x(uVp-dV

n)

x(dVp-uV

n)

Pion-induced D-Y can measure CSV effect(See arXiv:0907.2352 for a recent review on CSV and

possible experimental tests)

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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

22

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. (see talk by Goto)

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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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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, Sato and Thomas)

Extensive study by Kumano et al. and Strikman et al.

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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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Can there be other nuclear effects in Drell-Yan?

1) DIS 2) Drell-Yan

3) Semi-inclusive DIS

• No initial state rescattering

• No final state rescattering

• No initial state rescattering

• Possible final state rescattering

• Possible initial state rescattering

• No final state rescattering

e

e’

e

e’

• Possible initial state rescattering effects in Drell-Yan need to be identified (and subtracted)

• Drell-Yan is analogous to semi-inclusive DIS (rather than DIS)

h

h

μ+μ-

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How to identify initial-state interaction in Drell-Yan?

• Interaction would degrade the longitudinal momentum of the dimuons

• dσ/dxF would shift to more negative xF for Drell-Yan on nuclei

• Nuclear dependence would drop below 1 as xF -> 1

E772 Drell-Yan data

Nuclear modification of PDF depends on x2, initial-state effect depends on xF

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D-Y measurement at lower energies is importantFractional energy loss is larger at 50 GeV

Garvey and JCP, PRL 90 (2003) 092302

Very sensitive measurement of quark energy loss at J-PARC is possible

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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 nucleons

Is / asymmetry modified in nuclei?d u

What are the flavor dependences of the EMC effects?

(first considered by Kumano et al.)

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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 be measured at J-PARC

Can one measure / in nuclei?d u

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Nuclear modification of spin-dependent PDF?

Bentz, Cloet et al., arXiv:0711.0392

EMC effect for g1(x)

Very difficult to measure !

Easier to measure the nuclear modification of Boer-Mulders functions (only unpolarized targets are required)? (See Bianconi and Radici, J. Phys. G31 (2005) 645)

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Can one measure gluon distribution in nuclei with quarkonium production?

p + A at 800 GeV/cE772 data σ(p+A) = Aασ(p+N)

Strong xF - dependence

Nuclear effects scale with xF, not x2 → Effects other than parton distribution modification need to be separated.

See talk by Leitch

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Targets (Z = -24.0”)0 = Empty1 = 0.502 “ Copper2 = 2.036 “ Beryllium3 = 1.004 “ Copper

High-pT Single Muon Trigger

Single muon measurement in E866 p+AThesis of Stephen Klinksiek

High-pT single muon events are dominated by D-meson decays

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Preliminary E866 results on the single-muon (open-charm) nuclear-dependence

Cu / Be Ratios

PT (GeV/C) Rapidity (y)

PT and XF (y) dependences have similar trend as J/Ψ

Can be further studied at J-PARC

Thesis of S. Klinksiek

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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.