Spin and azimuthal asymmetries in SIDIS at JLAB

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


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)

PDF

h

xF<0 (target fragmentation)

h


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


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


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!


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


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


CLAS Experiment Setup and Kinematics

Scattering of 5.7 GeV polarized electrons off polarized NH3, ND3

~8M + in SIDIS kinematics

x x


• 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


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


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 -)


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


• 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


)()( 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?)


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


•sin SSA + increases with PT and is consistent with HERMES measurement.

AULSSA: PT-dependenceHT –SSA significant for + and 0

CLAS PRELIMINARY


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


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:


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


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


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)


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.


support slides…..


AULSSA: z-dependence

CLAS PRELIMINARY


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

++


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

qq

LLTLL zDxf

zDxg

DPA)()(

)()(

11

11


SIDIS: factorization studies

JLab data at 6GeV are consistent with factorization and partonic description for variety of ratio observables

P.Bosted


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)


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


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

Documents

Spin and azimuthal asymmetries in SIDIS at JLAB