New results on SIDIS SSA from JLab Physics Motivation Double spin asymmetries Single Spin...
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Transcript of New results on SIDIS SSA from JLab Physics Motivation Double spin asymmetries Single Spin...
New results on SIDIS SSA from JLab
Physics MotivationDouble spin asymmetries Single Spin AsymmetriesFuture measurementsSummary
H. Avakian *
* In collaboration with P.Bosted, V.Burkert and L.Elouadrhiri
DIS-2005 Apr 28
Jefferson Lab
Semi-Inclusive Deep Inelastic Scattering (SIDIS):
• Probes orbital motion of quarks through quark transverse momentum distribution• Access to new PDFs not accessible in inclusive DIS.
kT-dependent parton distributions
Sivers transversity
Mulders
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…)
H. Avakian, DIS-2005 3
SIDIS kinematic plane and relevant variables
Ey /
)/(sinEEQ ' 24 22
MQx 2/2
'EE
/Ez h
)()()( zFFxDFyK
H. Avakian, DIS-2005 4
The CLAS Detector
Scattering of 5.7 GeV polarized electrons off polarized NH3
~8M + in DIS kinematics,SIDIS Q2>1.1GeV2, W2>4GeV2, y<0.85, beam polarization 73% target polarization 72% (f=0.2)x x
A1p
-kinematic dependence for +/-/0
CLAS 5.7 GeV
NN
NN
)y(fDPPA
LLTB
p 11
A1p A1
p
• No significant z-dependence of A1 in the range 0.4<z<0.7 ()•x dependence of CLAS A1
p (A┴=0) consistent with HERMES data at 3 times
higher Q2 and with PEPSI (LUND)MC.
CLAS PRELIMINARY
1
1
f
g
H. Avakian, DIS-2005 6
SIDIS: factorization studies
• A1 inclusive, from sum and are consistent (in range 0.4<z<0.7 )• A1
p dependence can serve an important check of HT effects and applicability of simple partonic description.•There is an indication that A1
p of +is lower than inclusive at large z.
GRVS
A1+-
H. Avakian, DIS-2005 7
Longitudinally polarized Target SSA
Measure the kT dependent twist-2
distribution and provides an independent test of the Collins fragmentation.
Real part of interfe-rence of wave functions with L=0 and L=1
UL ~KM
8•Study the Collins fragmentation mechanism with long. polarized target• For - and 0 SSA is sensitive to unfavored fragmentation
)()( 12
,
sin zHxxheQ
MS q
Lqqq
LUL
)()( 112
,
sin zDxfeS qqTq
qqTUT
SSA: x-dependence
HT–SSA significant for + and 0 (non-Collins?)
q
qqq
q
qqLq
ULTUL zDxfe
zHxhe
DPA)()(
)()(
112
112
2sin
AUL ( 0) ~ H1favore+H1
unfavored
PRELIMINARY 5.7 GeV
For Collins fragmentation use chirally invariant Manohar-Georgi model (Bacchetta et al)
Systematic error only from unknown ratio of favored and unfavored Collins functions (R= H1
d→/H1u→), band
correspond to -2.5<R<0
- and 0 SSA will also give access to h1Ld ( If R ≈ -1 deuteron data could be crucial)
CLAS-5.7GeV
First glimpse of Twist-2 TMD h1L┴
PRELIMINARY
•More data required with - & 0 •Exclusive 2 pion background may be important
Distribution functions fromQSM from Efremov et al
H. Avakian, DIS-2005 10
0 in Semi-inclusive DIS
1) SIDIS0 production is not contaminated by diffractive2) HT effects and exclusive 0 suppressed3) Simple PID by 0-mass (no Kaon contamination)4) Provides complementary to +/- information on PDFs
disadvantages: reconstruction efficiency (requires detection of 2)
advantages:
H. Avakian, DIS-2005 11
CLAS+Inner Calorimeter (IC)
IC at CLAS opens new avenue for studies of spin and azimuthal
asymmetries of exclusive and semi-inclusive
CLAS
CLAS+IC
CLAS
IC
424 PbWO4 ……..crystals
Reconstruction efficiency of high energy 0 with IC increases ~ 4 times due to small angle coverage
IC E/E=0.0034/E+0.038/√E+0.022
12
UL ~KM
Longitudinally polarized target SSA using CLAS+IC
•Provide measurement of SSA for all 3 pions, extract the Mulders TMD and study Collins fragmentation with longitudinally polarized target•Allows also measurements of 2 pion asymmetries
Hunf=-1.2Hfav
Hunf=-5Hfav
Hunf=0
50 days of CLAS+IC (5.7GeV)
curves, QSM from Efremov et al
H. Avakian, DIS-2005 13
Summary
Spin and azimuthal asymmetries measured at 5.7 GeV with longitudinally polarized target.
•Double spin asymmetries of pions are consistent with factorization and partonic picture
• sinandsin2 SSA measured, providing access to the twist-2 TMD h1L distribution and testing the Collins fragmentation
Studies of spin and azimuthal asymmetries at CLAS will significantly improve the error bars for charged pions and will provide a superior measurements with neutral pions allowingprecision measurement of the twist-2 kT-dependent PDF.
H. Avakian, DIS-2005 15
Longitudinally Pol Target: SSA for +
•sin2 moment (Kotzinian-Mulders asymmetry) is a clean source of Collins SSA
P1= 0.0110±0.0024P2=-0.0065±0.0025
Significant sin2 term in the long.pol. x-section compared to ALU
H. Avakian, DIS-2005 16
Collins effect and 2 pion production
Simple string fragmentation (Artru model)
Sub-leading pion opposite to leading
(into page)
L=1
production may produce an opposite sign AUT
Leading opposite to leading (into page)
Understanding of 2 pion asymmetries will help to understand single pion mesurements
+
0
H. Avakian, DIS-2005 17
•sin SSA + increases with PT and is consistent with HERMES measurement.
AULSSA: PT-dependenceHT –SSA significant for + and 0
CLAS PRELIMINARY
H. Avakian, DIS-2005 18
•sin SSA + increases with PT and is consistent with HERMES measurement.
AULSSA: z-dependenceHT –SSA significant for + and 0
CLAS PRELIMINARY
H. Avakian, DIS-2005 19
Longitudinally polarized target+IC: +
Reconstruction efficiency with IC decreases ~ 40%
H. Avakian, DIS-2005 20
Longitudinally polarized target+IC: -
Reconstruction efficiency with IC decreases ~ 10%
H. Avakian, DIS-2005 21
Exclusive + production Exclusive + production
Exclusive +n separated by invariant and missing masses.
n+
e- p e- n+π+π0
Provide access to different combinations of orbital momentum contributions Ju,Jd
-> 2Ju + Jd
-> Ju - Jd
•Significant transverse target SSA predicted for exclusive
accesible with long.pol. Target with effective polarization ~20%
CLAS5.7 GeV
H. Avakian, DIS-2005 22
Missing mass of pions in ep→e’X
In accessible kinematics (Q2>1.5,W2>4) low MX(large z) for 0 are suppressed by current CLAS acceptance.
-0
+n
0
++
H. Avakian, DIS-2005 23
SIDIS: factorization studies
• A1 inclusive, from sum and are consistent (in range 0.4<z<0.7 )• A1
p dependence can serve an important check of HT effects and applicability of simple partonic description.•There is an indication that A1
p of +is lower than inclusive at large z.
A1+A1
-
___________ 1+
from-MCGRVS
A1+-=