Single Spin Asymmetries: from JLab12 to EIC
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Transcript of Single Spin Asymmetries: from JLab12 to EIC
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Single Spin Asymmetries: from JLab12 to EIC
Harut Avakian *) Jefferson Lab
Introduction Semi-Inclusive processes and TMD distributions Hard exclusive processes and GPDs Summary
Single-Spin Asymmetries Workshop, BNL June 1-3, 2005
*) In collaboration with V. Burkert and L. Elouadrhiri
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PDFs fpu(x), g1, h1 FFs F1p
u(t),F2pu(t)..
d2k
T
=0,
t=0 dx
Wpu(x,k,r) “Parent” Wigner distributions
d3 r
d 2kT(FT) GPD
Measure momentum transfer to quark
Measure momentum transfer to target
Probability to find a quark u in a nucleon P with a certain polarization in a position r and momentum k
kT-integrated PDFs same in exclusive and semi-inclusive analysis
Analysis of SIDIS and DVMP are complementary
TMD
TMD PDFs fpu(x,kT),
GPDs Hpu(x,,t)..
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BNL June 3 3
CLAS12
High luminosity polarized CW
beam
Wide physics acceptance
(exclusive, semi-inclusive current and target fragmentation)
Wide geometric acceptance
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BNL June 3 4
ep→e’X: kinematic coverage at 11 GeV
Acceptance in Q2,Mx,PT gained with high luminosity and energy upgrade (at 6GeV Mx<2.5GeV, Q2<4.5GeV2, PT<1GeV)
test factorization in a wide kinematical rangestudy the transition between the non-perturbative and perturbative regimes of QCDmeasure PDFs and study higher twists
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com
pass
herm
es JLab (upgraded)
clas
Q2
EIC– Collider measurements,
requiring high luminosity (L~1034-1035cm-2 sec-1), and wide coverage, will vastly increase the kinematics and the scope of observables.
EIC
–Large Q2 may be crucial for precision studies of hard exclusive meson production.
EIC: large acceptance high luminosity
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Mechanisms for SSA
L=1
FSI (Brodsky et al.)
Sivers Distribution
Collins Fragmentation
String fragmenation (Artru)
• L/R SSA generated in fragmentation
•Unfavored SSA with opposite sign
•No effect in target fragmenation
•L/R SSA generated in distribution
•Hadrons from struck quark have the same sign SSA
•Opposite effect in target fragmentation
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Collins Effect
UT ~Collins
Study the Collins fragmentation for all 3 pions with a transversely polarized target and measure the transversity distribution function. JLAB12 cover the valence region.
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From CLAS12 to EIC: Transversity projections
AUT ~Collins
Simultaneous measurement of, exclusive with a transversely polarized target
The background from vector mesons very different for CLAS12 and EIC.
EIC
10-3
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Collins Effect and Kotzinian-Mulders Asymmetry
Study the Collins fragmentation with longitudinally polarized target.Measure the twist-2 Mulders TMD (real part of interference of L=0 and L=1 wave functions)
UL ~KM
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From CLAS12 to EIC: Mulders TMD projections
Simultaneous measurement of, exclusive with a longitudinally polarized target important to control the background.
UL ~KM
EIC
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Sivers effect
UT ~Sivers
Requires: non-trivial phase from the FSI + interference between different helicity statesProvides: info about the space-time structure of the nucleon
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Sivers function extraction from AUT (0) does not require information on fragmentation function. It is free of HT and diffractive contributions.
F1T=∑qeq2f1T
┴q
AUT (0) on proton and neutron will allow flavor decomposition w/o info on FF.
In large Nc limit:
f1Tu = -f1T
d
Efremov et al(large xB behavior of
f1T from GPD E)
CLAS12projected
CLAS12projected
From CLAS12 to EIC: Sivers effect projections
EIC
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Nonperturbative TMD Perturbative region
PT-dependence of beam SSA
sinLU(UL) ~FLU(UL)~ 1/Q (Twist-3)
In the perturbative limit 1/PT
behavior expected (F.Yuan SIR-2005)
Study for SSA transition from non-perturbative to perturbative regime.
EIC will significantly increase the PT range.
2.0
EIC
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BNL June 3 14
Flavor decomposition of T-odd g┴
)z(D)x(fe/yy qqq
q,qUU 11
22 21
)z(D)x(xgeyyQ
MS qq
qq,q
LsinLU 1
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With SSA measurements for on neutron and proton ()
In jet SIDIS with massless quarks contributions from H1┴,E vanish
Beam SSA measurements at EIC will allow to study the Q2 dependence of twist-3 g┴ (generated by gauge link)
44154 /udAduA)x(xg n,LUp,LU
u
44154 /duAudA)x(xg p,LUn,LU
d
ALU (g┴) like A1 (g1) and Sivers AUT (f1┴) depend on D1(z)
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BNL June 3 15
Transversity in double pion production
Dihadron production provides an alternative, “background free” access to transversity
h1
h2
quark
RT
“Collinear” dihadron fragmentation described by two functions at leading twist:
D1(z,cosR,M),H1R(z,cosR,M)
...Hh)sin(A RSRUT
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The angular distribution of two hadrons is sensitive to the spin
of the quark
relative transverse momentum of the two hadrons replaces the PT in single-pion production (No transverse momentum of the pair center of mass involved )
Collins et al, Ji, Jaffe et al, Radici et al.
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BNL June 3 16
SIDIS: target fragmentation
xF<0 (target fragmentation, TFR)
xF>0 (current fragmentation)
xF - momentum in the CM frame
Wide kinematical coverage of a large acceptance detector allows studies of hadronization both in the current and target fragmentation region
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Sivers effect in the target fragmentation
Significant effect predicted in the target fragmentation region, in particular for baryons (target remnant also asymmetric)
A.Kotzinian
EIC will allow studies of Q2 dependence of the Sivers effect in the target fragmentation region
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polarization in the target fragmentation
xF - momentum
in the CM frame
Wide kinematic coverage of CLAS12 allows studies of hadronization in the target fragmentation region
p
e
Λ1 2
e’
– unique tool for polarization study due to self-analyzing parity violating decay
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DVCSDVCS DVMPDVMP
Hard Exclusive Processes and GPDs
hard vertices
hard gluon
DVCS – for different polarizations of beam and target provide access to different combinations of GPDs H, H, E
long. only
DVMP for different mesons is sensitive to flavor contributions ( select H, E, for u/d flavors, , K select H, E)
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Separating GPDs through polarization
LU~ sin{F1H + (F1+F2)H +kF2E}d~
Polarized beam, unpolarized target:
Unpolarized beam, longitudinal target:
UL~ sin{F1H+(F1+F2)(H + … }d~
Unpolarized beam, transverse target:
UT~ sin{k(F2H – F1E) + …. }d
= xB/(2-xB)
k = t/4M2
H, H, E
Kinematically suppressed
H, H~
H, E
A =
=
~
ep ep
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BNL June 3 21
CLAS12 - DVCS/BH Beam Asymmetry
L = 1x1035
T = 2000 hrsQ2 = 1 GeV2
x = 0.05
E = 11 GeV
Selected Kinematics
Sensitive to GPD H
LU~sinIm{F1H+.}d
e p ep
Acceptance of protons for EIC studied using Roman Pots (60% efficiency)
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BNL June 3 22
GPDs H from expected DVCS ALU data
bval=bsea=1
MRST02 NNLOdistribution
Q2=3.5 GeV2
Other kinematics measured concurrently
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BNL June 3 23
CLAS12 - DVCS/BH Target Asymmetry
e p ep
<Q2> = 2.0GeV2
<x> = 0.2<-t> = 0.25GeV2
CLAS preliminary
E=5.75 GeVAUL
Longitudinally polarized target
~sinIm{F1H+(F1+F2)H...}d~
E = 11 GeVL = 2x1035 cm-2s-1
T = 1000 hrsQ2 = 1GeV2
x = 0.05
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BNL June 3 24
CLAS12 - DVCS/BH Target Asymmetry
Asymmetry highly sensitive to the u-quark contributions to proton spin.
Transverse polarized target
e p ep
~ sinIm{k1(F2H – F1E) +…}d
Q2=2.2 GeV2, xB = 0.25, -t = 0.5GeV2E = 11 GeVSample kinematics
AUTx Target polarization in scattering plane
AUTy Target polarization perpedicular to scattering plane
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BNL June 3 25
Exclusive production on transverse target
2 (Im(AB*))/ T
t/4m2) - ReUT
A ~ 2Hu + Hd
B ~ 2Eu + Ed0
K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001
Q2=5 GeV2
Eu, Ed needed forangular momentum sum rule.
0
B
A ~ Hu - Hd
B ~ Eu - Ed+
EIC
Higher Q2 of EIC may be crucial
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BNL June 3 26
Exclusive + production Exclusive + production e- p e- n+π+π0
Exclusive +n separated by invariant and missing masses. n+
Provide access to different combinations of orbital momentum contributions Ju,Jd
-> 2Ju + Jd
-> Ju - Jd
2Ju - Jd
•Significant transverse target SSA predicted also for exclusive
(Goeke et al hep-ph/0106012)
CLAS5.7 GeV
Doesn’t require detection of recoil nucleon
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BNL June 3 27
Transversity GPDs with exclusive +
Long distance part described by GPD HT
GPD
•Large momentum transfer, large rapidity gap•Virtual photon replaced with 2 gluons
hard
hard
Smaller rapidity gap selects quark antiquark
exchange with the nucleon.
(courtesy M. Vanderhaeghen)
Ivanov et al. Phys.Part.Nucl.35:S67-S70,2004
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CLAS12 a full acceptance, general purpose detector for high luminosity electron scattering experiments, is essential for high precision
measurements of GPDs and TMDs in the valence region. Provide new insight into
- quark orbital angular momentum contributions to the nucleon spin- 3D structure of the nucleon’s interior and correlations- quark flavor polarization
EIC will extend studies of 3D nucleon structure, to low x and high Q2 , important for all processes of interest:
- deeply virtual exclusive processes (DVCS, DVMP) - semi-inclusive meson production with polarized beam and polarized targets
Summary