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 14

support slides…..

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+-=