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

qq

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

++