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Spin and azimuthal asymmetries in SIDIS at JLAB
Physics MotivationJlab kinematics and factorizationDouble spin asymmetries Single Spin AsymmetriesFuture measurementsSummary
P. Bosted *
* In collaboration with H. Avakian, V.Burkert and L.Elouadrhiri
SIR-2005
Jefferson Lab
P. Bosted, SIR-2005 2
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,This talk
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)
This talk
P. Bosted, SIR-2005 3
SIDIS kinematic plane and relevant variables
Ey /ν=
)/(sinEEQ ' 24 22 θ=
νMQx 2/2=
'EE−=ν
ν/Ez h=
P. Bosted, SIR-2005 4
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
P. Bosted, SIR-2005 5
Hall C E00-108 dataExperiment ran in August 2003 Close-to-final data analysis Small Q2 variation not corrected yet
No visual “bumps and valleys” in pion ratios off deuterium x = 0.32
x = 0.32
PRELIMINARY
PRELIMINARY
P. Bosted, SIR-2005 6
From E00-108 deuterium data: D-/D+ = (4 – N+/N
-)/(4N+/N
- - 1)
D-/D+ ratio should be independent of x, and data supports this for W=2.5 GeV, Q2=2.5 GeV2, pt<0.3 GeV
but should depend on z Find similar slope versus z as HERMES, but slightly larger values (could be due to lower average photon energy)
z = 0.55
x = 0.32
PRELIMINARY
PRELIMINARY
7
CLAS Experiment Setup and Kinematics
Scattering of 5.7 GeV polarized electrons off polarized NH3, ND3
~8M + in SIDIS kinematics
x x
8
• 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)• No radiative corrections applied• “+” and “-” include some K+, K- for P>1.5 GeV • 0 events cleanly identified with two photons
Determination of g1/F1 (approximately A1)
++−+
++−+
+−
≈NN
NN
)y(fDPPA
LLTB
p 11
P. Bosted, SIR-2005 9
x-depenence of SIDIS g1/F1
• Good agreement with HERMES + data at 3x higher Q2
• x-dependence follows PEPSI (Lund) Monte Carlo using GRSV polarized PDFs (LO)
• Magnitude also in good agreement with simulation
P. Bosted, SIR-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 with factorizationand current fragmentation dominance
GRVS
P. Bosted, SIR-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 -)
P. Bosted, SIR-2005 12
pt-depenence of SIDIS g1/F1
No pt dependence expectedin LO if current fragmentationdominance and factorization
Slight pt dependence seen(but results quite sensitiveto pt dependence of A-dependence needed for dilution factor)
Reasonable agreement with PEPSI predictions.
PRELIMINARY
CLAS 5.7 GeV
13
SIDIS g1/F1 for Deuteron
Results don’t agree as well with PEPSI using GRSV, more sensitive to un-favored fragmentation functionand NLO corrections than proton (although errorsare about a factor of two larger)
NLO QCD fits including new SIDIS CLAS data canhelp constrain polarized PDFs in valence region
PRELIMINARYCLAS 5.7 GeV
P. Bosted, SIR-2005 14
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
P. Bosted, SIR-2005 15
)()( 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?)
P. Bosted, SIR-2005 16
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
Distribution functions fromQSM from Efremov et al
P. Bosted, SIR-2005 17
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:
P. Bosted, SIR-2005 18
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
19
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
P. Bosted, SIR-2005 20
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, if approved, will greatly improve 0 data. Much greater improvements for all reactions possible with 12 GeV upgrade due to much larger coverage of DIS kinematics.
P. Bosted, SIR-2005 21
support slides…..
P. Bosted, SIR-2005 22
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
P. Bosted, SIR-2005 23
•sin SSA + increases with PT and is consistent with HERMES measurement.
AULSSA: PT-dependenceHT –SSA significant for + and 0
CLAS PRELIMINARY
P. Bosted, SIR-2005 24
AULSSA: z-dependence
CLAS PRELIMINARY
P. Bosted, SIR-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
++