Spin and azimuthal asymmetries in SIDIS at JLAB
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Transcript of Spin and azimuthal asymmetries in SIDIS at JLAB
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P. Bosted, DNP 2005 1
Spin and azimuthal asymmetries in SIDIS at JLAB
Physics MotivationJlab kinematics and factorization Single Spin AsymmetriesFuture measurementsSummary
P. Bosted *
* In collaboration with H. Avakian, V.Burkert and L.Elouadrhiri
DNP-2005
Jefferson Lab
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P. Bosted, DNP 2005 2
h
Single pion production in hard scattering
Target fragmentation Current fragmentation
Fracture FunctionsxF
M
0-1 1
h
h
PDF GPD
kT-dependent PDFs Generalized PDFs
Wide kinematic coverage of large acceptance detectors allows studies of hadronization both in the target and current fragmentation regions
xF - momentum in
the CM frame
xF>0 (current fragmentation)
h
xF<0 (target fragmentation)
h
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P. Bosted, DNP 2005 3
Polarized Semi-Inclusive DISCross section is a function of scale variables x,y,z
Parton-Hadron transition: by
fragmentation function D+( (z):
probability for a u-quark to produce a +(-) with momentum
fraction z
Hadron-Parton transition: by distribution function f1
u(x): probability to find a u-quark
with a momentum fraction x
1u
= E-E’y = /Ex = Q2 /2M z = Eh /
z
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P. Bosted, DNP 2005 4
Transverse momentum of quarks
To study orbital motion of quarks in semi-inclusive DIS measurements in a wide range of x,z,PT, are required.
•kT – led to introduction of kT dependent PDFs (TMDs)•kT – crucial for orbital momentum and spin structure studies
–led to SSA in hard scattering processes•kT - important for cross section description
- PT distributions of hadrons in DIS- exclusive photon production (DVCS)- hard exclusive vector meson cross section- pp → 0X (E704,RHIC) cross sections
Spin-Azimuthal Asymmetries: sensitive to kT
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P. Bosted, DNP 2005 5
SIDIS (*p→X) cross section at leading twist (Ji et al.)
structure functions = pdf × fragm × hard × soft (all universal)
eUnpolarized target
Longitudinally pol. target
Transversely pol. target e
e
p
p
Off diagonal PDFs related to interference between L=0 and L=1 light-cone wave functions.
Boer-Mulders1998
Kotzinian-Mulders1996
Collins-1993
To observe the transverse polarization of quarks in SIDIS spin dependent fragmentation
is required!
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P. Bosted, DNP 2005 6
JLab Kinematics and Facorization
Traditional DIS: W>2 GeV, Q2>1.1 GeV2
Berger criteriium for current fragmentation dominance is z>0.4 Require z<0.7 to avoid diffractive rho meson contributions (and keep Mx>1.4 GeV)
Pt<1 GeV (approximately exponential region)
Study if factorization broken for these cuts using unpolarized data from E00-108 in Hall C
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P. Bosted, DNP 2005 7
Z-Dependence of unpolarized cross sections
Pretty good agreement with prediction using CTEQ5M PDFs and Binnewies fragmentation functions, except for z>0.7, or Mx>1.4 GeV.
X=0.3, Q2=2.5 GeV2, W=2.5 GeV
Jlab E00-108, Preliminary, E=5.5 GeV
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CLAS Experiment Setup and Kinematics
Scattering of 5.7 GeV polarized electrons off polarized NH3, ND3
~8M + in SIDIS kinematics
x x
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• Target polarization PT about 0.7 (0.3) for NH3 (ND3)• Beam polarization PB about 0.7• Dilution factor f varies from 0.1 to 0.3: used Lund model for n/p ratio and preliminary Hall B data for A-dependence• Depolarization factor DLL(y) evaluated assuming R same as for inclusive.• Assumed Aperp=0 (not measured, probably small)• No radiative corrections applied (expected to be small)• “+” and “-” include some K+, K- for P>1.5 GeV • 0 events cleanly identified with two photons
Experimental Overview
++−+
++−+
+−
≈NN
NN
)y(fDPPA
LLTB
p 11
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P. Bosted, DNP 2005 10
SIDIS: factorization studies
g1/F1 inclusive, for the sum of , and for are consistent with each other in the range 0.4<z<0.7, as expected in LO if factorization works and current fragmentation dominance. Data at 6 GeV with Mx>1.4 GeV support this.
GRVS
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P. Bosted, DNP 2005 11
z-depenence of SIDIS g1/F1
CLAS 5.7 GeV
PRELIMINARY
No significant z-dependence seen 0.3<z<0.7, as expected for factorization and current fragmentation dominance
Good agreement with PEPSI predictions (including dropoff at high z for -)
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P. Bosted, DNP 2005 12
Longitudinally Polarized Target SSA
Clear dependence seen for proton target and +, 0
Fit A*sin() + B*sin(2) for Twist-3 and Twist-2 respectively
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P. Bosted, DNP 2005 13
• Significant SSA measured for pions with longitudinally polarized target• Complete azimuthal coverage crucial separation of sinsin2moments
SSA measurements at CLAS
p1sin+p2sin2
0.12<x<0.48
Q2>1.1 GeV2
PT<1 GeV
ep→e’XW2>4 GeV2
0.4<z<0.7MX>1.4 GeV
y<0.85
CLAS PRELIMINARY
p1= 0.059±0.010p2=-0.041±0.010
p1=-0.042±0.015p2=-0.052±0.016
p1=0.082±0.018p2=0.012±0.019
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P. Bosted, DNP 2005 14
)()( 12
,
sin zHxxheQ
MS q
Lqqq
LUL⊥
−Σ∝φσ
SSA: x-dependence
∑∑ ⊥⊥
=
q
q
qqL
ULTUL zDxf
zHxh
DPA)()(
)()(
11
112sin φ
PRELIMINARY 5.7 GeV
Twist-2 Higher Twist
Data in rough agreement with Efremov et al.predictions, exceptfor 0 sin() term(evidence for termsnot involving Collinsfragmentation?)
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P. Bosted, DNP 2005 15
For Collins fragmentation function use HERMES data
Systematic error only from unknown ratio of favored and unfavored Collins functions (R= H1
d→/H1u→), band
correspond to -2.5<R<0
CLAS-5.7GeV
First glimpse of Twist-2 TMD h1L┴
PRELIMINARY
•More data required with - & 0 •Exclusive 2 pion background may be important: analysis in progress.
Distribution functions fromQSM from Efremov et al
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P. Bosted, DNP 2005 16
•sin SSA + increases with PT and is consistent with HERMES measurement.
AULSSA: PT-dependenceHT –SSA significant for + and 0
CLAS PRELIMINARY
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P. Bosted, DNP 2005 17
Higher Twist SSAs
Target sin SSA (Bacchetta et al. 0405154)
Beam sin SSA
In jet SIDIS only contributions ~ D1 survive
Discussed as main sources of SSA due to the Collins fragmentation
With H1┴ (0)≈0 (or measured) Target and Beam SSA can be a valuable source of info on HT T-odd distribution functions
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P. Bosted, DNP 2005 18
Future: more 0 data in SIDIS
1) SIDIS0 production is not contaminated by diffractive
2) 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:
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P. Bosted, DNP 2005 19
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 σE/E=0.0034/E+0.038/√E+0.022
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P. Bosted, DNP 2005 20
σUL ~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
curves, QSM from Efremov et al
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P. Bosted, DNP 2005 21
CLAS12 High luminosity polarized
(~80%) CW beam
Wide physics acceptance(exclusive, semi-inclusive current
and target fragmentation)
Wide geometric acceptance
12GeV significantly increase the kinematic acceptance (x10 lumi)
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P. Bosted, DNP 2005 22
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: may be used in future NLO QCD fits.
• sinandsin2 SSA measured, providing access to the twist-2 TMD h1L distribution and testing the Collins fragmentation function
•Future measurements with IC will greatly improve 0 data, and charged pions too. Much greater improvements for all reactions possible with 12 GeV upgrade due to much larger coverage of DIS kinematics.
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P. Bosted, DNP 2005 23
support slides…..
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P. Bosted, DNP 2005 24
AULSSA: z-dependence
CLAS PRELIMINARY
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P. Bosted, DNP 2005 25
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
++
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P. Bosted, DNP 2005 26
Collinear Fragmentation
quarkThe only fragmentation function at leading twist for pions in eN→e’X is D1(z)
Ee =5.7 GeV
No significant variation observed in z distributions of + for different x ranges (0.4<z<0.7, MX>1.5) and for A1p as a function of PT
∑∑
=
q
qqq
LLTLL zDxf
zDxg
DPA)()(
)()(
11
11
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P. Bosted, DNP 2005 27
SIDIS: factorization studies
JLab data at 6GeV are consistent with factorization and partonic description for variety of ratio observables
P.Bosted
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P. Bosted, DNP 2005 28
Collins Effect: azimuthal modulation of the fragmentation function
D(z,PT)=D1(z,PT)+H1┴(z,PT) sin(hS’)
spin of quark flips wrt y-axisS’ = -S sin(hS)
C
S
STy
x
h
PT sT
S’
C
FUT∞h1H1┴
S’ = -S = -h
S
y
x
h
PTsT
S’
C
sT(p×kT)↔ h1┴
FUU∞h1 ┴ H1┴
S = +h
sT(q×PT)↔ H1┴
S’ = -S = -h
xsin(2h)
sTPT
h
C
S=h
y
FUL∞h1L H1┴┴
(sTkT)(pSL)↔ h1L┴
sinC=sin(hS’)
cos(2h)
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P. Bosted, DNP 2005 29
Flavor decomposition of T-odd f┴
( ) )z(D)x(fe/yy qqq
q,qUU 11
22 21−
Σ+−∝σ
)()(1 12
,
sin zDxxfeyyQ
MS qq
Lqqq
LUL⊥
−Σ−∝φσ
( ) ( )[ ]4/4)( ,,154 udAduAxxf nULpUL
uL +−+=⊥ ππ
( ) ( )[ ]4/4)( ,,154 duAudAxxf pULnUL
dL +−+=⊥ ππ
With SSA measurements for and on neutron and proton
() assuming Hfav=Hu→+ ≈ -Hu→-=-Hunfav
)()(1 12
,
sin zHxxheyyQ
MS qq
Lqqq
LUL⊥
−Σ−∝φσ
In jet SIDIS with massless quarks contributions from H1┴ vanish
gauge link contribution
L
With H1┴ (0)≈0 (or measured) target and beam HT SSAs can be a valuable source of info on HT T-odd distribution functions
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P. Bosted, DNP 2005 30
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