1. Spin and azimuthal asymmetries in SIDIS at JLAB
P. Bosted *
Jefferson Lab
DNP-2005
Physics Motivation
Jlab kinematics and factorization
Single Spin Asymmetries
Future measurements
Summary
Note mes
* In collaboration with H. Avakian, V.Burkert and L.Elouadrhiri
P. Bosted, DNP 2005

2. Single pion production in hard scattering
xF>0 (current fragmentation)
Single pion production in hard scattering h
xF<0 (target fragmentation)
xF - momentum in the CM frame
Target fragmentation
Current fragmentation h h h h M
PDF
PDF
GPD 1 -1 xF
Fracture Functions
kT-dependent PDFs
Generalized PDFs
Wide kinematic coverage of large acceptance detectors allows studies of hadronization both in the target and current fragmentation regions
P. Bosted, DNP 2005

3. Polarized Semi-Inclusive DIS
Cross section is a function of scale variables x,y,z
n = E-E’
y = n /E
x = Q2 /2Mn
z = Eh /n
Hadron-Parton transition: by distribution function f1u(x): probability to find a u-quark with a momentum fraction x
Parton-Hadron transition: by fragmentation function Dp+(p-) (z): probability for a u-quark to produce a p+(p-) with momentum fraction z z 1u
P. Bosted, DNP 2005

4. Transverse momentum of quarks
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 → p0X (E704,RHIC) cross sections
Spin-Azimuthal Asymmetries: sensitive to kT
To study orbital motion of quarks in semi-inclusive DIS measurements in a wide range of x,z,PT, f are required.
P. Bosted, DNP 2005

5. SIDIS (g*p→pX) cross section at leading twist (Ji et al.)
Unpolarized target
Longitudinally pol. target
Transversely pol. target e p
Boer-Mulders
1998
Kotzinian-Mulders
1996
Collins-1993
structure functions = pdf × fragm × hard × soft (all universal)
Off diagonal PDFs related to interference between L=0 and L=1 light-cone wave functions.
To observe the transverse polarization of quarks in SIDIS spin dependent fragmentation is required!
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 E in Hall C
P. Bosted, DNP 2005

7. Z-Dependence of unpolarized cross sections
Jlab E00-108, Preliminary, E=5.5 GeV
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
P. Bosted, DNP 2005

8. CLAS Experiment Setup and Kinematics
Scattering of 5.7 GeV polarized electrons off polarized NH3, ND3
~8M p+ in SIDIS kinematics x x
P. Bosted, DNP 2005

9. Experimental Overview
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)
“p+” and “p-” include some K+, K- for P>1.5 GeV
p0 events cleanly identified with two photons
P. Bosted, DNP 2005

10. SIDIS: factorization studies
GRVS
g1/F1 inclusive, for the sum of p+ ,p- , and for p0 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.
P. Bosted, DNP 2005

11. z-depenence of SIDIS g1/F1
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-)
CLAS 5.7 GeV
PRELIMINARY
P. Bosted, DNP 2005

12. Longitudinally Polarized Target SSA
Clear f dependence
seen for proton
target and p+, p0
Fit A*sin(f) + B*sin(2f)
for Twist-3 and Twist-2
respectively
P. Bosted, DNP 2005

13. SSA measurements at CLAS
ep→e’pX
W2>4 GeV2
p1sinf+p2sin2f
CLAS PRELIMINARY
Q2>1.1 GeV2
y<0.85
0.4<z<0.7
MX>1.4 GeV
PT<1 GeV
0.12<x<0.48
p1= 0.059±0.010
p2=-0.041±0.010
p1=-0.042±0.015
p2=-0.052±0.016
p1=0.082±0.018
p2=0.012±0.019
Significant SSA measured for pions with longitudinally polarized target
Complete azimuthal coverage crucial separation of sinf, sin2f moments
P. Bosted, DNP 2005

14. SSA: x-dependence Twist-2 Higher Twist Data in rough agreement with
Efremov et al.
predictions, except
for p0 sin(f) term
(evidence for terms
not involving Collins
fragmentation?)
5.7 GeV
PRELIMINARY
P. Bosted, DNP 2005

15. First glimpse of Twist-2 TMD h1L┴
For Collins fragmentation function use HERMES data
Distribution functions from cQSM from Efremov et al
PRELIMINARY
CLAS-5.7GeV
Systematic error only from unknown ratio of favored and unfavored Collins functions (R= H1d→p+/H1u→p+), band correspond to -2.5<R<0
More data required with p- & p0
Exclusive 2 pion background may be important: analysis in progress.
P. Bosted, DNP 2005

16. AULSSA: PT-dependence
HT –SSA significant for p + and p 0
CLAS PRELIMINARY
sinf SSA p + increases with PT and is consistent with HERMES measurement.
P. Bosted, DNP 2005

17. Higher Twist SSAs
Discussed as main sources of SSA due to the Collins fragmentation
Target sinf SSA (Bacchetta et al )
In jet SIDIS only contributions ~ D1 survive
Beam sinf SSA
With H1┴ (p0)≈0 (or measured) Target and Beam SSA can be a valuable source of info on HT T-odd distribution functions
P. Bosted, DNP 2005

18. Future: more p0 data in SIDIS
advantages:
SIDIS p0 production is not contaminated by diffractive r
HT effects and exclusive p0 suppressed
Simple PID by p0-mass (no kaon contamination)
Provides complementary to p+/- information on PDFs
disadvantages:
reconstruction efficiency (requires detection of 2g)
P. Bosted, DNP 2005

19. CLAS+Inner Calorimeter (IC)
424 PbWO4 ……..crystals
CLAS+Inner Calorimeter (IC) IC
IC sE/E=0.0034/E+0.038/√E+0.022
CLAS+IC
CLAS
Reconstruction efficiency of high energy p0 with IC increases ~ 4 times due to small angle coverage
CLAS
IC at CLAS opens new avenue for studies of spin and azimuthal asymmetries of exclusive and semi-inclusive g, p0,h,r+
P. Bosted, DNP 2005

20. Longitudinally polarized target SSA using CLAS+IC
sUL ~ KM
50 days of CLAS+IC
curves, cQSM from Efremov et al
Hunf=-5Hfav
Hunf=-1.2Hfav
Hunf=0
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
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)
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.
sinf and sin2f SSA measured, providing access to the twist-2 TMD h1L distribution and testing the Collins fragmentation function
Future measurements with IC will greatly improve p0 data, and charged pions too. Much greater improvements for all reactions possible with 12 GeV upgrade due to much larger coverage of DIS kinematics.
P. Bosted, DNP 2005

23. support slides…..
P. Bosted, DNP 2005

24. AULSSA: z-dependence
CLAS PRELIMINARY
P. Bosted, DNP 2005

25. Missing mass of pions in ep→e’pX
D++ p- D0
In accessible kinematics (Q2>1.5,W2>4) low MX(large z) for p0 are suppressed by current CLAS acceptance.
P. Bosted, DNP 2005

26. Collinear Fragmentationp
quark
Collinear Fragmentation
The only fragmentation function at leading twist for pions in eN→e’pX is D1(z)
Ee =5.7 GeV
No significant variation observed in z distributions of p+ for different x ranges (0.4<z<0.7, MX>1.5) and for A1p as a function of PT
P. Bosted, DNP 2005

27. SIDIS: factorization studies
P.Bosted
JLab data at 6GeV are consistent with factorization and partonic description for variety of ratio observables
P. Bosted, DNP 2005

28. Collins Effect: azimuthal modulation of the fragmentation function
FUT∞h1H1┴
sT(q×PT)↔ H1┴ y fS ST fC PT fC sT
D(z,PT)=D1(z,PT)+H1┴(z,PT) sin(fh- fS’) fh
spin of quark flips wrt y-axis
fS’ = p-fS
sin(fh+fS)
fS’ x
sT(p×kT)↔ h1┴
FUU∞h1 ┴ H1┴ sT PT fh fC
fS=fh y
FUL∞h1L H1┴ ┴
(sTkT)(pSL)↔ h1L y x fh PT sT
fS’ fC
sinfC=sin(fh- fS’)
cos(2fh)
The Collins Effect is the correlation of the transverse spin of the fragmenting quark and the transverse momentum of the produced hadron. It leads to an azimuthal modulation of the fragmentation function, with a sin\phi_Collins term.
The virtual photon here is in the z-direction pointing out of plane.
-m-
To define the azimuthal angle of the fragmenting quark we need the azimuthal angle of the initial struck quark, which in case of the transverse polarized target is defined by the direction of the transverse polarization of the nucleon.
There is a simple relation between azimuthal angles before and after scattering in leading order for massless quarks and after a simple arithmetics we get a well known expression for the Collins effect for the transversely polarized target.
In this case transversity function is responsible for the transversely polarized quarks and the Collins effect is just a product of transversity and Collins function.
Similar situation exist for the longitudinal target. The only difference is that quarks are polarized in the direction
Of their transverse momentum, which in average coincide with the transverse momentum of the final hadron.
The Collinse angle in this case is simply 2\phi_hadron.
Collins effect for longitudinally polarized target therefore lead to a sin2f moment in the cross section. fS fC
fS = p/2+fh x
sin(2fh)
fS’ = p-fS = p-fh
fS’ = p-fS = p/2-fh
P. Bosted, DNP 2005
sin(2fh)

29. Flavor decomposition of T-odd f┴
In jet SIDIS with massless quarks contributions from H1┴ vanish
gauge link contribution
With SSA measurements for p++p- and p0 on neutron and proton (p=p++p-) assuming Hfav=Hu→p+ ≈ -Hu→p-=-Hunfav
With H1┴ (p0)≈0 (or measured) target and beam HT SSAs can be a valuable source of info on HT T-odd distribution functions
P. Bosted, DNP 2005

30. Collins effect and 2 pion production
Sub-leading pion opposite to leading (into page)
Simple string fragmentation (Artru model)
L=1
Leading r opposite to leading p(into page)
r production may produce an opposite sign AUT r r+
Understanding of 2 pion asymmetries will help to understand single pion mesurements r0
P. Bosted, DNP 2005