Transcript Semi-inclusive DIS at 12 GeV H.Avakian (JLab) For the semi-inclusive working group JLAB PAC January 10, 2005 Semi-inclusive processes Factorization at low energies Large-x behavior of.

Semi-inclusive DIS at 12 GeV
H.Avakian (JLab)
For the semi-inclusive working group
JLAB PAC January 10, 2005
Semi-inclusive processes
Factorization at low energies
Large-x behavior of valence PDFs and flavor asymmetries of the sea
Transversity and transverse momentum dependent distributions
Target fragmentation and intrinsic strangeness
Summary
Semi-Inclusive Deep Inelastic Scattering (SIDIS)
DIS: Major source of QCD tests and PDF studies
• Probes only the sum of quarks and anti-quarks
• Requires assumptions on sea
• No access to transversity effect in LO
SIDIS: “Tagging” to distinguish different quark flavors.
•Provide access to quark distributions with
fragmentation acting as a weight factor:
•Probes orbital motion of quarks.
Main focus of SIDIS studies:
orbital angular momentum of quarks
parton distributions at large x
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SIDIS kinematic plane and relevant variables
  E  E'
Q2  4EE' sin( / 2)
x  Q 2 / 2M
y  / E
z  Eh / 
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SIDIS at leading twist
e
Unpolarized target
Mulders et al.
e
Longitudinally
pol. target
p
Boer
Mulders
Transversely
pol. target
e
p
Sivers
transversity
Off-diagonal PDFs vanish if quarks only in s-state! In addition
T-odd PDFs require FSI (Brodsky et al., Collins, Ji et al. 2002)
Factorization of kT-dependent PDFs proven at low PT of
hadrons (Ji et al)
Universality of kT-dependent distribution and fragmentation
functions proven (Collins,Mets…)
Wpu(x,k,r) “Parent” Wigner distributions
Probability to find a
quark u in a
nucleon P with a
certain polarization
in a position r and
momentum k
GPD
TMD PDFs: fpu(x,kT),..
Measure momentum
transfer to quark
kT distributions also
important for
exclusive studies
PDFs fpu(x),…
GPDs: Hpu(x,x,t), …
FFs F1pu(t),F2pu(t)..
Measure momentum
transfer to target
Exclusive meson data
important in
understanding of
SIDIS measurements
Some PDFs same in exclusive and semi-inclusive analysis
Analysis of SIDIS and DVMP are complementary
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ep→e’pX: 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 kinematic range
study the transition between the nonperturbative and perturbative
regimes of QCD
measure PDFs and study higher twists
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p
Collinear Fragmentation
quark
The only fragmentation function at leading twist
for pions in eN→e’pX is D1(z)
Ee =5.7 GeV
Hall-C Ee =5.5 GeV
No significant variation observed in p+/p ratio and in z distributions
of p+ for different x ranges (0.4<z<0.7, MX>1.5)
A1p f-kinematic dependence for p+/-/0
1
N +  N ++
A 
PB PT fDLL ( y ) N + + N ++
p
1
A1p
CLAS 5.7 GeV
A1p
• No significant z-dependence of A1 in the range 0.4<z<0.7 (p+p0)
•x dependence of CLAS A1p (A2=0) consistent with HERMES data at x3
higher Q2 and with PEPSI (LUND)MC.
Polarized PDFs
Ee =11 GeV NH3+He3
g1u=u,g1d=d….
Jlab @11 GeV
•Asymmetry measurements with different hadrons (p+p) and
targets (p,n) allow flavor separation
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Flavor decomposition: polarized sea
• Predictions:
– Instantons (QSM):
•First data from HERMES
u  d
JLab @11 GeV
0
More data expected from RHIC W±
production in future
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Longitudinally polarized Target SSA for p+
Measurement of kT dependent twist-2
distribution provides an independent test of
the Collins fragmentation.
Real part of interference of wave
functions with L=0
and L=1
In noncollinear singlehadron fragmentation
q h
H11(z,k
additional FF H
T()z )
p
kT
quark
Efremov et al.
•Study the PT – dependence of AULsin2f
•Study the possible effect of large unfavored
Collins function.
Transversely polarized target SSA
transversely polarized
quarks in a transversely
polarized nucleon.
Collins
AUT ~
H1qπ0  21 (H1qπ + + H1qπ  )
Interpretation requires
large unfavored spin
dependent fragmentation.
•No success so far in describing consistently
Collins SSA for all 3 pions at least in QSM!
•More data needed, new observables GSI, CERN
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Transverse Target SSA @11 GeV
CLAS @ 11GeV (NH3)
Collins
p+
AUT ~
p0
pf1T┴, requires final
state interactions +
interference between
different helicity states
Sivers
AUT ~
Simultaneous (with pion SIDIS) measurement of,
exclusive r,r+,w with a transversely polarized
target important
to control the background.
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Jan 10, 2005
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Transversity in double pion production
The angular distribution of two
hadrons is sensitive to the spin
of the quark
AUT  sin(  R +  S )h1 H
R
1
+ ...
“Collinear” dihadron fragmentation described by
two functions at leading twist:
D1(z,cosR,Mpp),H1R(z,cosR,Mpp)
h1
RT
quark
h2
Collins et al,
Ji, Jaffe et al,
Radici et al.
relative transverse momentum of the two hadrons
replaces the PT in single-pion production (No transverse
momentum of the pair center of mass involved )
Dihadron production provides an alternative,
free” access to transversity
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10, 2005
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SIDIS: target fragmentation
xF>0 (current fragmentation)
xF - momentum in the
CM frame
xF<0 (target fragmentation, TFR)
Wide kinematic coverage at 11 GeV allows studies of
hadronization in the target fragmentation region
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Λ in target fragmentation
e’
e
1Λ 2
π
p
L – unique tool for polarization study due
to self-analyzing parity violating decay
(ud)-diquark is a spin and isospin singlet →
s-quark carries whole spin of L L  uds
L polarization in TFR provides
information on contribution of
6strange sea to proton spin
W.Melnitchouk and A.W.Thomas ‘96
J.Ellis, D.Kharzeev, A. Kotzinian ‘96
Polarized beam gives unique possibility to perform
an “acceptance independent” measurement of L
polarization in electroproduction.
JLab at 12 GeV
Complementarity
of high luminosity
and wide geometric
acceptance halls
High luminosity
polarised CW
beam
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Wide physics
acceptance
(exclusive, semiinclusive current and
target fragmentation)
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Summary
Semi-inclusive measurements at 12 GeV will
• provide precise information on the polarized valence
distributions in the nucleon
• test the expected flavor asymmetry in the polarized sea
distributions
• determine the essentially unknown transversity and Sivers
functions with high precision and in a variety of channels
sensitivity to orbital motion of quarks
• improve the understanding of the fragmentation process
and give access to the poorly understood target
fragmentation region
Essential for understanding the structure of the nucleon !
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support slides…..
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PT-dependence of beam SSA
ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3)
In the perturbative limit
1/PT behavior expected
Nonperturbative TMD
Perturbative region
Asymmetries from kT-odd and kT-even (g1) distribution functions are
expected to have a very different
behavior
(flat A1p(PT) observed at 5.7 GeV).
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Jan 10, 2005
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Measuring the Q2 dependence of SSA
ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3)
For fixed x, 1/Q
behavior expected
Wide kinematic coverage allows to check the higher twist nature
of beam and longitudinal target SSAs
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g1/f1: PT-dependence
Constant in
perturbative limit
Asymmetries from kT-odd (f1┴, h1┴, gT..) and kT-even (g1) distribution
functions are expected to have a very different behavior
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Transversity
Sub-leading pion
opposite to leading
(into page)
Simple string fragmentation
(Artru model)
L=1
r production may produce
an opposite sign AUT
r
Leading r opposite to
leading p(into page)
SIDIS @11 GeV: 2 pions
p+p0(r+)
Understanding of 2 pion
asymmetries will help to
understand transversity
mesurements
p+p(r0)
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Λs in target fragmentation
e’
e
1Λ 2
P and p- kinematics
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π
p