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Transcript of 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
15
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
17
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)
18
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
19
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
20
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
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
22
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
23
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
24
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
25
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.
26
• 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
27
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
28
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.
29
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.
30
/ 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
31
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
33
1
0Predictions of [ ( ) ( )]u x d x dx
Peng, Eur. Phys. J. A18 (2003) 395