Transcript Slide 1

More observables to study the nucleon structure with EIC
Harut Avakian (JLab)
Electron Ion Collider Users Meeting,
June 24-27, 2014 at Stony Brook University
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Outline
•Introduction
•Hard scattering processes and 3D PDFs
•Target fragmentation
•Hard exclusive pseudoscalar meson production
•Medium modification of 3D PDFs
•Summary
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12 GeV Approved Experiments by Physics Topics
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xq(x)
Generalizing 1D PDFs
To understand better the dynamics we need
• Study orbital motion, move from 1D to 3D
• Study interactions and correlations of spin, longitudinal and
transverse degrees of freedom
• medium modifications of 3D PDFs
1D+3D+medium
3D PDFs in nucleons and nuclei
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Single hadron production in hard scattering
xF>0 (current fragmentation)
h
xF<0 (target fragmentation)
xF - momentum
in the CM frame
Target fragmentation
Current fragmentation
semi-inclusive
exclusive
h
FF h
M
-1
Fracture Functions
DA
DA
h
PDF
0
kT-dependent PDFs
GPD
1
Generalized PDFs
Wide kinematic coverage of large acceptance detectors allows studies
of hadronization both in the target and current fragmentation regions
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xF
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3D structure of the nucleon
Non-perturbative distributions in hard scattering
TMDs
GPDs
✖
✖
Wigner Distributions
✖
✖
Fracture Functions
unpol. quarks in long. pol. nucleon related to OAM!
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SIDIS kinematical plane and observables
Cross section is a function of
scale variables x,y,z
n = E-E’
y = n /E
x = Q2 /2Mn
z = Eh /n
U unpolarized
L long.polarized
T trans.polarized
z
Target polarization
Beam polarization
TMD structure functions accessible as
moments in the azimuthal distributions
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L production in the target fragmentation region
L – unique tool for polarization study due to
self-analyzing parity violating decay
probability to produce the hadron h
when a quark q is struck in a proton target
M. Anselmino, V. Barone and A. Kotzinian, Phys. Lett. B 699 (2011) 108
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L production in the target fragmentation region
polarization tranfer coefficient
60 days of CLAS12
data taking
Projected results of the longitudinal spin transfer as a function of xF (red
full circles) compared with the CLAS preliminary data and the ISM prediction
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L production in the target fragmentation region at EIC
(LEPTO 4x60)
e
direct L
1Λ 2
e’
p
p-
hyperon decay L
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Dihadron production asymmetries
M. Anselmino, V. Barone and A. Kotzinian, Physics Letters B 713 (2012)
The beam–spin asymmetry appears, at
leading twist and low transverse momenta, in
the deep inelastic inclusive lepto-production
of two hadrons, one in the target
fragmentation region and one in the current
fragmentation region.
Target fragmentation may be used to tag the flavor in current fragmentation
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3D structure: GPDs
epe’pp0
CLAS e1dvcs
DVCS asymmetries measured
at HERMES & JLAB
More measurements at
JLab, Compass
Transverse photon dominates the xsection for exclusive p0 production
Lattice (QCDSF)
Spin-azimuthal asymmetries in hard exclusive production of
photons and pions give access to underlying GPDs
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SSAs in exclusive pion production
P.Kroll & S. Goloskokov arXiv:0906.0460
Transverse photon matters
•The production amplitude at large Q2 factorizes into
the hard subprocess and GPDs
•Within the handbag approach g*Tp transitions are
related to transversity (helicity-flip) GPDs
accompanied by a twist-3 pion wave function
Hard partonic subprocess
HERMES
•CLAS12 can measure Q2 dependence of HT SSAs significantly extending the range of CLAS
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Exclusive kaon production
Unlike p+ the K+ x-section
is totally dominated by the
transverse photon
pole contribution
negligible
Exclusive production of KL and KS provide access to different combinations of chiral-odd GPDs
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SSAs in exclusive kaon production
Goloskokov&Kroll
KS asymmetries are
predicted to be large and
with opposite sign to KL
Goldstein, Hernandez, & Liuti
Beam and target
asymmetries in exclusive
production of KL and KS are
very sensitive to chiral-odd
GPDs.
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K/K* and L/S separation
L
S
Due to detector resolution
clean separation of
different channels (L,S,K*)
will require detection of 4
particles
K+
q
L
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kT in medium and FSI
Tang,Wang & Zhou
Phys.Rev.D77:125010,2008
total transverse momentum
broadening squared
kT-distributions
wider in nuclei?
the intrinsic transverse momentum of partons arises naturally from
multiple soft gluon interaction inside the nucleon or nucleus.
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Approximations on TMDs in medium
assume “maximal two gluon approximation” in
accounting all higher-twist nuclear multiple parton
correlations.
simple estimation can reproduce the main features of the data
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Medium modification and spin observables
I. Cloet
H.A.,Brodsky,Yuan & Deur
•In medium quarks are more relativistic
•lower components of quark wavefunctions enhanced
•quark lower components have larger angular momentum
•quark spin  orbital angular momentum in medium
•observables sensitive to orbital motion
will have strongest medium modifications
•q- most sensitive to orbital motion
•medium modifies the orbital motion
Gao, Liang & Wang
arXiv:1308.1159
CLAS Preliminary
spin and azimuthal asymmetries provide important
information on partonic distributions in bound nucleons.
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From JLab12 to EIC
Q2
JLab@12GeV (25/50/75)
0.1<xB<0.7 : valence quarks
EIC √s = 140, 50, 15 GeV
10-4<xB<0.3: gluons and quarks, higher
PT and Q2.
EIC@Jlab/BNL
Aybat,Prokudin&Rogers hep:1112.4423
Sun & Yuan arXiv:1304.5037
EIC@HIAF
ENC@FAIR
JLab12
•Study of high x domain requires high luminosity, low x higher energies
•Wide range in Q2 is crucial to study the evolution
•Overlap of EIC and JLab12 in the valence region will be crucial for the TMD program
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Sivers effect in the target fragmentation
A.Kotzinian
Significant effect predicted in the target fragmentation region, in
particular for baryons (target remnant also asymmetric)
EIC will allow studies of Q2 dependence of the Sivers
effect in the target fragmentation region
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Summary
•EIC provides a unique possibility to study the nucleon structure in target
fragmentation region and correlations of target and current fragmentation
regions
•Orbital motion in medium modifies, making medium modifications of
observables sensitive to spin orbit correlations (SSAs) more important for
studies of proton structure
•Combination of DVCS measurements with measurements of hardexclusive pseudoscalar mesons with unpolarized, longitudinally and
transversely polarized targets would allow precision measurement of all
chiral-even and chiral-odd GPDs
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Support slides….
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TMDs in medium: Predictions for CLAS12
Modification of multiplicity in medium and the double-spin asymmetry in
medium (A=7) using Eqs.42,45,50 for x = 0.3 and z = 0.5.
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TMDs in medium: modifications of SSAs
SSA are very sensitive to the relative
widths of involved nucleon TMDs
spin and azimuthal asymmetries provide
important information on partonic
distributions in bound nucleons.
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Correlations of spin, longitudinal and transverse degrees
•How kT distributions of partons depending on spin and flavor modify in
medium?
•How studies of proton transverse structure will improve our
understanding of medium effects?
•How studies of medium modifications will improve our understanding of
the proton structure?
Tools:
•Polarized and unpolarized SIDIS resolve flavor and spin effects
•Polarized SIDIS will help to resolve the spin-orbital effects in medium
Joint analysis of polarized and unpolarized target data is crucial for studies of
orbital effects in general and medium modification in particular
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1D Structure of the Nucleon (+twist-3)
nucleon polarization
quark polarization
Quark polarized in the x-direction right after
scattering feels a force in the y-direction
e
g1
gT
hL
~
Burkardt (2008)
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flavor and spin effects on kT
B.Musch et al
arXiv:1011.1213
g1q=Dq=(q+-q-)/2
Higher probability to find a quark anti-aligned with
proton spin, also more d-quarks at large kT
N.Makke
0
0.5
1.0
P. Schweitzer et al arXiv:1210.1267
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TMD factorization
TMD factorization theorem separates a transversely
differential cross section into a perturbatively calculable part
and several well-defined universal factors
TMDs may in general contain a mixture of
both perturbative and non-perturbative
contributions
corrections for the
region of large kT~Q
Aybat,Collins,Qiu,Rogers 2012
pertutbatively calculable
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Azimuthal moments in SIDIS
quark polarization
Higher Twist PDFs
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Experiment for a given target
polarization measures all
moments simultaneously 30
Hadronization in current and target regions
h1
h2
Anselmino/Barone/Kotzinian
arXiv:1107.2292 (2011)
Fracture Function:
h1
h2
conditional probabilities to find a
quark with certain polarization and
longitudinal momentum fraction xB
and transverse momentum kT inside
a nucleon fragmenting into a hadron
carrying a fraction z of the nucleon
longitudinal momentum and a
transverse momentum PT
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Forces and binding effects in the partonic medium
Interaction dependent parts
“Wandzura-Wilczek approximation” is equivalent to setting functions with a tilde to zero.
Quark polarized in the x-direction with
kT in the y-direction
Interpreting HT (quark-gluon-quark
correlations) as force on the quarks
(Burkardt hep-ph:0810.3589)
Boer-Mulders Force on the active
quark right after scattering (t=0)
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SSAs in exclusive pion production
Transverse
photon matters
Ahmad,Liuti & Goldstein: arXiv:0805.3568
Gloskokov & Kroll :
arXiv:0906.0460
HERMES
CLAS Preliminary
•HT SSAs are expected to be very significant
•Wider coverage (CLAS12,EIC) would allow
measurements of Q2 dependence of HT SSAs
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