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### Target Single-Spin Asymmetry in Semi-Inclusiven↑(e, e’p+/-)

Outline

Describe the complex nucleon structure in terms of partonic degrees of freedom of QCD

- Physics motivation
- Transverse Momentum Distributions (TMDs) of quarks and spin-azimuthal asymmetries in semi-inclusive DIS
- SIDIS results from JLab at 6 GeV
- Tests of the applicability of the partonic picture
- Studies of spin-orbit correlations with CLAS
- Measurements of TMDs at 6 GeV
- Longitudinally polarized proton target measurements (E05-113)
- Transversely polarized 3He (E06-010/011) and proton targets (E08-015)
- Summary

IWHSS09, Apr 1

SIDIS kinematical plane and observables

z

U unpolarized

L long.polarized

T trans.polarized

sin2f moment of the cross section for unpolarized beam and longitudinal target

Transverse spin effects are observable as correlations of transverse spin and transverse momentum of quarks.

IWHSS09, Apr 1

Wpu(k,rT) “Mother” Wigner distributions

d2kT

d2rT

GPDs/IPDs

TMD PDFs f1u(x,kT), .. h1u(x,kT)

d2kT

Structure of the Nucleonquark polarization

PDFs f1u(x), .. h1u(x)

- Gauge invariant definition (Belitsky,Ji,Yuan 2003)
- Universality of kT-dependent PDFs (Collins,Metz 2003)
- Factorization for small kT. (Ji,Ma,Yuan 2005)

IWHSS09, Apr 1

e

p-

p+

2

SIDIS with CLAS at 6 GeV

Scattering of 5.7 GeV electrons off unpolarized and polarized proton and deuteron targets

- DIS kinematics,

Q2>1 GeV2, W2>4 GeV2, y<0.85

- 0.4>z>0.7, MX2>2 GeV2

- Polarized NH3/ND3 (~5 days)
- Polarized H 30+30 days (2001/2005)

epX

IWHSS09, Apr 1

p multiplicities in SIDIS

ep→e’pX

M.Aghasyan

Hall-C

DSS (Q2=2.5GeV2)

DSS (Q2=25GeV2)

p+/- multiplicities at large z diverge from SIDIS predictions

p0 multiplicities less affected by higher twists

0.4

IWHSS09, Apr 1

Tests of partonic picture with p+/p- ratios

Hall-C @ 6 GeV

Rpd+

Rpd-

Both ratios agree with PDF models for z<0.7 (Mx>1.4 GeV)

IWHSS09, Apr 1

constituent quark model (Pasquini et al).A1 PT-dependence in SIDIS

m02=0.25GeV2

mD2=0.2GeV2

M.Anselmino et al hep-ph/0608048

Como-2005

In perturbative limit predicted to be constant

p+ ALL can be explained in terms of broader kT distributions for f1 compared to g1

IWHSS09, Apr 1

Quark longitudinal polarization

BBS/LSS no OAM

q

Dq

Du/u

JMR model

MR, R=s,a

(dipole formfactor), J.Ellis, D-S.Hwang, A.Kotzinian

BBS/LSS with OAM

Effect of the orbital motion on the q- may be significant (H.A.,S.Brodsky, A.Deur,F.Yuan 2007)

For given xthesignof the polarization is changing at large kT

IWHSS09, Apr 1

A1 PT-dependence in SIDIS

0.4

M.Anselmino et al hep-ph/0608048

m02=0.25GeV2

mD2=0.2GeV2

p+ A1 suggests broader kT distributions for f1 than for g1

p- A1 may require non-Gaussian kT-dependence for different helicities and/or flavors

IWHSS09, Apr 1

Fits to unpolarized data

Anselmino et al

Collins et al

Extracting widths from A1Assuming the widths of f1/g1 x,z and flavor independent

IWHSS09, Apr 1

A1 PT-dependence

Anselmino

Collins

CLAS data suggests that width of g1 is less than the width of f1

IWHSS09, Apr 1

ST

Intial quark polarization

fS

fS’ = p-fS

sin(fh+fS)

spin of quark flips wrt y-axis

y

PT

fS= p/2+fh

fS

fh

x

y

PT

fS=fh

fh

x

fh

y

PT

fS=p

x

Collins Effect: azimuthal modulation of the fragmentation functionFUT∞h1H1┴

sT(q×PT)↔H1┴

y

fC

PT

fC

sT

D(z,PT)=D1(z,PT)+H1┴(z,PT)sin(fh- fS’)

fh

hadronizing quark

fS’

x

fC

sin(2fh)

IWHSS09, Apr 1

TMD PDFsSIDIS (g*p->pX) x-section at leading twist

- Measure Boer-Mulders distribution functions and probe the polarized fragmentation function
- Measurements from different experiments consistent

IWHSS09, Apr 1

Kotzinian-Mulders asymmetry

Transversely polarized quarks in the longitudinally polarized nucleon

curves, cQSM from Efremov et al

More data needed to clarify the situation with negative pions

- Data indicate that spin-orbit correlations with long.pol. target may be significant
- Provide measurement of SSA for all 3 pions, extract the RSMT TMD (Ralston-Soper (1979), Mulders-Tangerman (1995)

16

IWHSS09, Apr 1

What comes next

- Hall-A Transversely polarized 3He target measurement
- (E06-010/011)

Hall-B Longitudinally polarized proton (NH3) target measurement

(E05-113)

Hall-B Transversely polarized proton target measurement

(E08-015)

Calibrating

Currently running

September 2011

Fixed bins in x/Q2

Wide kinematical coverage , multiple hadronic states

Correlations of transverse and longitudinal momenta (PT-dependences) in ALL

Collins asymmetry with longitudinally polarized (proton) target

Exclusive asymmetries as background

Sivers asymmetry

Collins asymmetry with transverse proton target

Shape of proton studies

Exclusive asymmetries as background

Sivers asymmetry

Collins asymmetry with transverse (neutron)

target

17

IWHSS09, Apr 1

E06-010:

Reaction on a Transversely Polarized 3He Target

- First measurement of the neutron Collins and Sivers asymmetries in SIDIS.
- High density polarized 3He target.
- Run in Hall A from 10/24/08-2/5/09.

110 shift workers, 7 Ph.D. students.

16o

g*

BigBite

30o

HRSL

p

pt ~ 65% (proposal 42%)

e’

Polarized

3He Target

e

Cell: Maureen

Cell: Astral

IWHSS09, Apr 1

Experimental Setup

50o

13o

Polarized target (NH3/ND3)

- Polarized NH3 with IC 60 days
- Polarized HD-Ice (no IC, 25 days)

IC

Inner Calorimeter (424 PbWO4 crystals) to detect high energy photons at forward lab angles.

IWHSS09, Apr 1

ALL PT-dependence in SIDIS

E05-113

M.Anselmino et al hep-ph/0608048

m02=0.25GeV2

mD2=0.2GeV2

0.4

- study the PT-dependence for different quark helicities and flavors for bins in x, m2 (x)
- flavor decomposition in PT-bins.

20

IWHSS09, Apr 1

Kotzinian-Mulders asymmetry

E05-113

Transversely polarized quarks in the longitudinally polarized nucleon

curves, cQSM from Efremov et al

60 days of CLAS

L=1.5.1034cm-2s-1

- Provide measurement of SSA for all 3 pions, extract the RSMT TMD (Ralston-Soper (1979), Mulders-Tangerman (1995)
- Study Collins fragmentation with longitudinally polarized target

21

IWHSS09, Apr 1

CLAS transversely polarized HD-Ice target

HD-Ice target vs std nuclear targets

Heat extraction is accomplished with thin aluminum wires running through the target (can operate at T~500-750mK)

- Pros
- Small field (∫Bdl~0.005-0.05Tm)
- Small dilution (fraction of events from polarized material)
- Less radiation length
- Less nuclear background (no nuclear attenuation)
- Wider acceptance
- much better FOM, especially for deuteron
- Cons
- HD target is highly complex and there is a need for redundancy due to the very long polarizing times (months).
- Need to demonstrate that the target can remain polarized for long periods with an electron beam with currents of order of 1-2 nA
- Additional shielding of Moller electrons necessary (use minitorus)

HD-Ice target at ~2nA ~ NH3 at 5 nA

IWHSS09, Apr 1

Collins SSAs

CLAS E08-015

Anselmino et al (2007)

Boffi et al (2009)

helicity-transversity=pretzelosity

CLAS with a transversely polarized target will allow measurements of transverse spin distributions and constrain Collins fragmentation function

23

IWHSS09, Apr 1

Measurement of Sivers function and GPD-E

CLAS E08-015

(DVCS)

(SIDIS)

GPD-E=0

DVCS Transverse asymmetry (function of momentum transfer to proton) is large and has strong sensitivity to GPD-E

CLAS will provide a measurements of Sivers asymmetry at large x, where the effect is large and models unconstrained by previous measurements.

Meissner, Metz & Goeke (2007)

24

IWHSS09, Apr 1

Summary

Significant azimuthal moments in pion production in SIDIS are measured using CLAS with longitudinally polarized target.

Measurements of azimuthal dependences of double and single spin asymmetries indicate that correlations between spin and transverse motion of quarks may be significant.

PT-dependences of the double and single-spin asymmetries provide important input for studies of flavor and helicity dependence of quark transverse momentum dependent distributions.

Upcoming CLAS SIDIS experiments at 6 GeV will significantly improve the statistical precision of longitudinally polarized target data, and will provide new data on transversely polarized target

IWHSS09, Apr 1

Support slides….

IWHSS09, Apr 1

Rpd-for any z, x!

Factorization studies

Simple LO picture in valence region:

Rpd+for any z, pt (if d and u have same pt dependence)!

IWHSS09, Apr 1

TheCLASDetector

~ 200 physicists

37 institutions

- large kinematical coverage
- high luminosity
- multi-particle final states
- charged particles:
- p>0.2 GeV/c
- 8o
- sp/p~0.5% (q<30o)
- sp/p~1-2%(q>30o)
- sq=1mrad
- sf=4mrad

IWHSS09, Apr 1

Sivers effect: proton

CLAS E08-015

Vogelsang & Yuan

Schweitzer et al

- CLAS will provide a superior measurements of Sivers asymmetry at large x, where the effect is large and models unconstrained by previous measurements.
- Measure also asymmetries in target fragmentation region and for exclusive r,r+,w,p,h channels (background)

30

IWHSS09, Apr 1

Collins fragmentation: Longitudinally polarized target

Kotzinian-Mulders Asymmetry

proton

deuteron

Pasquini et al.

- Study the Collins function of kaons
- Provides independent information on the RSMT TMD

IWHSS09, Apr 1

ST

fS

fS

fS’ = p-fS

sin(fh+fS)

spin of quark flips wrt y-axis

FUU∞h1 ┴H1┴

sT(p×kT)↔ h1┴

┴

(sTkT)(pSL)↔ h1L

┴

FUL∞h1L H1┴

Collins Effect: azimuthal modulation of the fragmentation functionFUT∞h1H1┴

sT(q×PT)↔H1┴

y

fC

PT

fC

sT

D(z,PT)=D1(z,PT)+H1┴(z,PT)sin(fh- fS’)

fh

fS’

x

sin(fh+fS)

y

y

PT

fS= p/2+fh

PT

fS=fh

fh

fh

cos(2fh)

sin(2fh)

fC

x

x

sin(2fh)

IWHSS09, Apr 1

Hall A E06-010: Neutron (3He) Transversity

- First JLab transverse SSA measurement: running now to 2/09
- First world neutron(3He) measurement

Sivers: Orbital Angular Momentum

Collins: transversity

33

IWHSS09, Apr 1

JLab, Nov 25

Spin densities in transverse proton from Lattice

G.Miller/”pretzelosity”

(QCDSF/UKQCD)

Boer-Mulders TMD

u-quark

Spin of quark

d-quark

IWHSS09, Apr 1

CLAS: Fraction from baryonic decays in SIDIS

Significant fraction from target fragmentation at pion momenta below 2 GeV

IWHSS09, Apr 1

Dilution factor in SIDIS

Fraction of events from polarized hydrogen in NH3

Nu,Np -total counts from NH3 and carbon normalized by lumi

ru, rp -total areal thickness of hydrogen (in NH3), and carbon target

Cn=Nitr/Carbon ratio (~0.98)

Diff. symbols for diff x-bins

p-

Multiple scattering and attenuation in nuclear environment introduces additional PT-dependence for hadrons

IWHSS09, Apr 1

Brodsky & Yuan (2006)Collins Effect: from asymmetries to distributions

need

CLAS12

Combined analysis of Collins fragmentation asymmetries from SIDIS and e+e- (BELLE) would allow separation of transverse spin distributions (Anselmino et al., arXiv:0707.1197 )

IWHSS09, Apr 1

BBS/LSS with OAM[email protected]: Inclusive DIS

BBS/LSS no OAM

PDF measurements at large x provide additional information on OAM

IWHSS09, Apr 1

Azimuthal Asymmetries in SIDIS

Chay,Ellis,Stirling-1991

Why

f=0

p

x

f=180

p

Due to color coherence the configuration with gluon inside the quark cone is more probable

IWHSS09, Apr 1

Fragmentationp+

p+

p0

HT and Semi-Exclusive Pion ProductionE. Berger, S. Brodsky 1979 (DY), E.Berger 1980,

A.Brandenburg, V. Khoze, D. Muller 1995

A.Afanasev, C.Carlson, C. Wahlquist Phys.Lett.B398:393-399,1997

- Azimuthal asymmetries with opposite sign from HT effects
- Effect may be suppressed for semi-exclusive p0 compared to p+/-

IWHSS09, Apr 1

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