Parton Distribution Functions · • The progress of lattice QCD calculations allow direct...
Transcript of Parton Distribution Functions · • The progress of lattice QCD calculations allow direct...
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Parton Distribution Functions
• Unpolarized parton distrbutions
– Flavor structures of the valence and sea quark
contents of the nucleons and nuclei
• Transverse momentum dependent (TMD)
distributions
– Transversity and other novel TMDs
Jen-Chieh Peng
2014 Long-range Plan Joint Town Meetings on QCD
Temple University, Philadelphia, Sept. 13-15, 2014
University of Illinois at Urbana-Champaign
Outline
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Flavor and spin structures of the nucleons
• 99.97% of the visible mass of the Universe is composed of protons and neutrons
• QCD at the confinement scale remains to be better 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?
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Flavor structure of the proton sea
From Frank
Close’s textbook
(1980)
There was a time when nucleon was nice
and simple……
Actually, the nucleon is full of surprises !!
( ) ( ) ( ) ( ) (3) symmetric seau x d x s x s x SU
Is ( ) 2 ( )?
Is ( ) ( )?
Is ( ) ( )?
Is ( ) (
Quest
)?
Is ( ) ( )?
Is ( ) ( )?
ions
V V
p n
p n
u x d x
u x d x
s x u x
s x s x
u x d x
g x g x
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The Gottfried Sum Rule 1
2 20
1
0
[( ( ) ( )) / ]
1 2( ( ) ( ))
3 3
( )1
3p p
p n
G
p p
S F x F x x dx
u x d
i
x dx
f u d
New Muon Collaboration (NMC) obtains
SG = 0.235 ± 0.026
( Significantly lower than 1/3 ! )
= Expect if sea quarks
are produced in
d u
g qq
?d u
Is in the Proton?u d
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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
2
1 2 1 2
1 2 1 2. .
4( ) ( ) ( ) ( )
9a a a a a
aD Y
de q x q x q x q x
dx dx sx x
800 GeV proton beam
on hydrogen and deuterium
mass spectrum
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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
Meson cloud has significant contributions to
sea-quark distributions
Some Theoretical Models for / Asymmetryd u
Asymmetry between
These models a
(
Asymmetry between ( ) and (
lso have specific
)
) and ( )
predictions on
s x s
d x
x
u x
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SeaQuest Experiment ( Unpolarized Drell-Yan using 120 GeV proton beam)
Main goals:
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1) Measure / fla
) Measure EMC ef
vor asymmet
fect of ant
ry up to
iquarks u p to 0.4
0.4
5
5d u x
x
Is there a sign-reversal for ( ) ( ) at large ?d x u x x
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Is the sea-quark polarization flavor symmetric?
W production at RHIC clearly shows ( ) / ( ) asymmetryu x d x
Data show ( ) 0 and ( ) 0 in agreement with chiral soliton model u x d x
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0, 0 1, 0 1, 1
1, 0 1, 1
2
2
1) SU(6) sy
1 1 1| ( ) ( ) ( )
32 18
1 2( ) ( )
3 3
mmetry
2) Dominance of 0 diquark configu
rations (Close, Carlitz)
1 2
2
3
I
Z Z Z
Z Z
S S S S S S
S
n
S S S
p
Fd
u F
p u ud u ud u ud
d uu uu
S
d
2
2
2
2
2) Dominance of 0 diquark configurations (Farrar,
gnoring terms with 1 diquarks, then
Ignoring terms with 1 diquarks, then
1
Jack
04
1 3
s )
5 7
n
o
n
Z
p
n
p
Z
S
S
Fd
u F
Fd
u F
S
Ratios of ( ) / ( ) at large ?d x u x x
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– Extract F2n/F2
p from ratio of
measured 3He/3H structure
functions
How to make a precise measurement of ( ) / ( )?d x u x
1) “spectator tagging”
(BONUS experiment)
2) “Super ratio 3He/3H”
(Marathon experiment)
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Meson cloud model
Thomas / Brodsky and Ma
Analysis of neutrino DIS data
( )x s s
NuTeV, PRL 99 (2007) 192001
Is ( ) ( ) ?s x s x
p K (( ))us uds
x x
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( ) ( ) from NNPDF global fitss x s x
NNPDF2.0 analysis includes fixed-target
Drell-Yan and Tevatron W and Z data
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What is the -dependence of [ ( ) ( )] / [ ( ) ( )]?x s x s x u x d x
A strong dependence for the [ ( ) ( )] / [ ( ) ( )] rati
Ne
CTEQ6.6 suggests an SU(3) symmetric sea at smal
w kaon semi-inclusive DIS data at JLab 12 GeV and at EIC
will be crucia
o
l ?
?
l
x s x s x u x
x
d x
P. Jimenez-Delgado, E. Reya, PRD 89 (2014) 074049
xuv
xdv
x(d u)
x(s s )
x(u u)
x(d d )
x(s s )
xg
Proton parton distributions from JR14
Nuclear binding
Fermi motion
of the nucleon
Shadowing
Anti-shadowing
Nuclear Modifications of Structure Function F2
Connection with SRC? Flavor-dependent EMC effect?
F2 & Drell-Yan data
for nuclei
region of existing nuclear data
Existing Nuclear Data are limited in Q2 and x
EIC and p-A collision will
explore new region
Measure Meson PDF with Drell-Yan Process
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CEDAR
(CErenkov Differential counter with
Achromatic Ring focus)
Hadron beam at COMPASS
Projected D-Y events in 140 days
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Transverse structures of the nucleons
• Transverse degrees of freedom offer new insights on the nucleon structure
• TMDs provide stringent tests for various nucleon models
• The progress of lattice QCD calculations allow direct comparison with the experiments
• Novel parton distributions are accessible by experiments using lepton as well as hadron beams
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Why is it interesting?
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Three parton distributions describing
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
momentum
Three different correlations
N
q
q
S
s
k
4
26 4
Q
sxd
•
),()(])1(1{[ 2
11
,
22
h
q PzDxfey
22 (1) 2
1 12,
22 (1) 2
1 12,
2 2
1 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
l
h
l
h
l l
h
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) 2
1 1
,
32 (2) 2
1 13 2,
2 2
1 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 q
e L q h
q q
he T
N
l l
h S
l l
h S
l l
h 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 q
q 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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Extraction of Transversity and Collins fragmentation
function from SIDIS and Belle data
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Torino group, Anselmino et al., PRD 87, 094019 (2013)
SIDIS
on p
SIDIS
on pSIDIS
on d
Belle
ee
Extraction of Transversity and Collins fragmentation
function from SIDIS and Belle data
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Torino group, Anselmino et al., PRD 87, 094019 (2013)
Transversity Collins pion FF
quarku
quarkd
Favored
Unfavored
Extraction of nucleon tensor charge
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Torino group, Anselmino et al., PRD 87, 094019 (2013)
1
1 10[ ( ) ( )]q qq h x h x dx
1 : Extractions from global fits
(using two different Collins FF
parameterizations)
2-10: Predictions from various
models (including LQCD)
u d
0.787 0.319u d
Tensor charges are smaller
than axial charge
Difference between data and theory
could be partly caused by neglecting
sea transversity in the extraction?
Recent progress in LQCD suggests the possibility to
calculate the x-dependence of parton distributions
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The -dependence of
the quark and antiquark
transversity distributions
can be calculated (not
just their moments)
x
Predicts large sea-quark transversity!
Transversity at Jlab 12-GeV
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Hall-B
Extensive SIDIS program
with SoliD in Hall-A
Extraction of Sivers function from SIDIS data
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Torino group, Anselmino et al.,
Eur. Phys. J. A39 (2009) 89
(2013)
and -quark Sivers functions have opposite signs
Sea-quark Sivers functions are non-zero (from data)
u d
K
• Does Sivers function change sign between DIS and Drell-Yan?
• Sign and magnitude of the sea-quark Sivers functions?
• Q2-evolution of the Sivers function?
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Outstanding questions on Sivers function
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Polarized Drell-Yan with 190 GeV/c pion beam
(Sivers asymmetry)
Polarized target
Expect data-taking in 2014-2015
Proposal to measure Sivers in polarized
Drell-Yan at Fermilab
• Propose using the existing dimuon spectrometer
• Possibility of polarized target is also being considered 31
Proposal (P-1027) ( Polarized Drell-Yan with polarized proton beam)
Main goals:
2) T
1) Accelerate polarized p
est "sign-change" of T-od
roton b
d Siver
eam at the Main Injector
s function in Drell-Yan
(W. Lorenzon, P. Reimer, et al.)
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Another proposal to measure sea-quark Sivers in
polarized Drell-Yan at Fermilab
Global interest in polarized Drell-Yan measurements
• Fermilab (proton beam, unpolarized, polarized beam/target possible)
• COMPASS (pion beam, polarized target)
• FAIR (polarized antiproton beam)
• RHIC (polarized proton beam)
• J-PARC (proton beam, polarzied beam possible)
• JINR NICA (proton beam)
Fermilab COMPASS J-PARC NICA RHIC
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Summary
• Significant progress has been made in
measuring and understanding the flavor and
momentum dependencies of parton
distributions in the nucleon.
• Exciting physics opportunities await us with
existing and future electron and hadron
facilities to further advance our knowledge
on hadron structure and QCD.