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
2
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…
6
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
9
“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."
10
/ 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
11
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)
12
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
13
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
14
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
15
1
0Predictions of [ ( ) ( )]u x d x dx
Eur. Phys. J. A18 (2003) 395
First measurements are now available (Talk by Don Geesaman)
16
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
17
/ 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
18
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
19
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
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
21
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!
22
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
23
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
24
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.
25
• 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
26
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)
27
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 !?
28
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
29
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
30
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)
31
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.