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Neutron Transversity at Jefferson Lab

• Introduction• SIDIS measurements at JLab• JLab Hall-A neutron transversity experiment• Other transverse spin experiments• Other planned SIDIS experiments• Summary

Jian-ping Chen, Jefferson Lab

Transversity Workshop, Como, Italy, Sept. 7-10, 2005

Introduction/motivation

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Transversity• Three twist-2 quark distributions:

– Momentum distributions: q(x,Q2) = q↑(x) + q↓(x)– Longitudinal spin distributions: Δq(x,Q2) = q↑(x) - q↓(x)

– Transversity distributions: δq(x,Q2) = q┴(x) - q┬(x)

• Some characteristics of transversity:– δq(x) = Δq(x) for non-relativistic quarks– δq and gluons do not mix → Q2-evolution for δq and Δq are different– Chiral-odd → not accessible in inclusive DIS

• It takes two chiral-odd objects to measure transversity– Semi-inclusive DIS

Chiral-odd distributions function (transversity)

Chiral-odd fragmentation function (Collins function)

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Leading-Twist Quark Distributions

No K┴ dependence

K┴ - dependent, T-odd

K┴ - dependent, T-even

( A total of eight distributions)

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Eight Quark Distributions Probed in SIDIS

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26 4

Q

sxd

),()(])1(1{[ 211

,

22 h

qq

qqq PzDxfey

),()()sin()1(||

),()()2sin(4

)1(||

),()()2cos(4

)1(

2

,11

2

2

,1

)1(1

22

2

2

,1

)1(1

22

2

hqq

qqq

lS

lh

h

hT

hqq

qqLq

lh

hN

hL

hqq

qqq

lh

hN

h

PzHxhezM

PyS

PzHxheMMz

PyS

PzHxheMMz

Py

)},()()cos()2

11(||

),()()2

11(||

),()()3sin(6

)1(||

),()()sin()2

11(||

21

)1(1

,

2

21

,1

2

,

21

)2(1

223

3

21

)1(1

,

22

hqq

Tqq

qlS

lh

N

hTe

hq

qq

qqLe

qqh

qqTq

lS

lh

hN

hT

hqq

Tqq

qlS

lh

N

hT

PzDxgezM

PyyS

PzDxgeyyS

PzHxheMMz

PyS

PzDxfezM

PyyS

Unpolarized

Polarized target

Polarzied beam and

target

SL and ST: Target Polarizations; λe: Beam Polarization

Sivers

Transversity

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AUTsin() from transv. pol. H target

Simultaneous fit to sin( + s) and sin( - s)

`Collins‘ moments

• Non-zero Collins asymmetry

• Assume q(x) from model, then

H1_unfav ~ -H1_fav

• Need independent H1 (BELLE)

`Sivers‘ moments

•Sivers function nonzero (+) orbital angular momentum of quarks

•Regular flagmentation functions

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Collins asymmetry from COMPASS

COMPASS 2002-2004 data: ~ factor of 12 in statistics

hep-ex/0503002

• Transversely polarized 6LiD target

• Cover smaller x

• Consistent with 0

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Current Status

• Collins Asymmetries - sizable for proton

large at high x large for -

- consistent with 0 for deuteron - cancellation between p and n?

• Sivers Asymmetries - non-zero for p+ from proton - consistent with zero all other channels.

• Fit by Anselmino et al. and other groups

• Data on neutron at high x complementary and very helpful

SIDIS measurements at JLab

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Thomas Jefferson Accelerator Facility

6 GeV polarized CW electron beam

(P = 85%, I = 180 A)

3 halls for fixed target experiments

Hall A: 2 high resolution spectrometer

Polarized 3He, L=1036 cm-2s-1

Hall B: large acceptance spectrometer

Polarized p/d, L=1034 cm-2s-1

Hall C: 2 spectrometers

Polarized p/d, L=1035 cm-2s-1

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Jefferson Lab

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SIDIS at JLab

• Extensive SIDIS program with 12 GeV upgrade• Starting with 6 GeV running with optimized

kinematics• High luminosity compensates low rate at larger

scattering angle to reach large Q2

• Comparable Q2 range as HERMES• Access high x region• Factorization? experimental tests.

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Preliminary results of factorization test from JLab for semi-inclusive pion production

Data are well described by calculations assuming

factorization

Similar z-dependence for different x-bins

Hall-C E00-108 CLAS 5.7GeV data

Recent theory work on SIDIS factorization (hep-ph0404183)

ep e x ep e x

Planned neutron transversity experiment at JLab

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JLab Hall-A E03-004 Experiment

• High luminosity (1036 s-1)– 15 μA electron beam on 10-atm 40-cm 3He target

• Measure neutron transversity– Sensitive to δd, complementary to HERMES

• Disentangle Collins/Sivers effects

• Probe other K┴-dependent distribution functions

Single Target-Spin Asymmetry in Semi-Inclusive Electroproduction on a Transversely Polarized 3He Target

Argonne, CalState-LA, Duke, E. Kentucky, FIU, UIUC, JLab, Kentucky, Maryland, UMass, MIT, ODU, Rutgers, Temple, UVa, W&M, USTC-China, CIAE-China, Glasgow-UK, INFN-Italy, U. Ljubljana-Slovenia, St. Mary’s-

Canada, Tel Aviv-Israel, St. Petersburg-Russia

Spokespersons: J.-P. Chen (JLab), X. Jiang (Rutgers), J. C. Peng (UIUC)

Jefferson Lab Hall A Experimental Jefferson Lab Hall A Experimental Setup Setup

for polarized n (for polarized n (33He) ExperimentsHe) Experiments

BigBite

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Hall A

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Experimental Setup for 3He↑(e,e’π-)x

• Beam– 6 GeV electron, 15 μA

• Target– Optically pumped Rb spin-exchange 3He target, 50 mg/cm2, ~40%

polarization, transversely polarized with tunable direction• Electron detection

– BigBite spectrometer, Solid angle = 60 msr, θLab = 300

• Charged pion detection– HRS spectrometer, θLab = 160

Hall A polarized 3He target

Both longitudinal and transverse

Luminosity=1036 (1/s)

High in-beam polarization

Effective polarized neutron target

Caltech, Duke/MIT, JLab, Kentucky, Temple, UVA/Princeton, W&M

6 completed experiments 4 approved

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Transversely polarzied 3He target

Target polarization orientation can be rotated to increase the

coverage in ФSl

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Kinematic acceptance

Hall-A : x: 0.19 – 0.34, Q2: 1.8 – 2.7 GeV2, W: 2.5 – 2.9 GeV, z: 0.37 – 0.56

HERMES: <Q2> = 2.5 GeV2

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Disentangling Collins and Sivers Effects

Collins angle: ФC=Фhl + ФS

l

Sivers angle: ФS=Фhl - ФS

l

Coverage in ФSl is increased by rotating target polarization

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Model Predictions for δq and AUT

• AUT for favored quark fragmentation (dashed) and favored + unfavored (solid) at Q2 = 2.5 GeV2 and integrated over z

• AUT is large, increasing with x

• AUTπ+(p): dominated by δu

• AUTπ-(n): both δu and δd contribute

Quark – diquark model (solid) and pQCD-based model (dashed)B. –Q. Ma, I. Schmidt and J. –J. Yang, PRD 65, 034010 (2002)

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Expected Statistical Sensitivities

Comparison with HERMES projection

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Expected Statistical Sensitivities

JLab E03-004 Projection3He(e,e’-)

HERMESp(e,e’)

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Status and Schedule

• Polarized 3He: need to add a set of vertical coils fast polarization flip is being tested

• BigBite spectrometer used in SRC experiment new detectors will be used for GE

n experiment

• HSR is ready, excellent PID

- part is approved and scheduled to run in fall of 2007 + proposal is being developed K+/- got for free

Other transverse spin experiments

Proton transversityg2/d2: twist-3Target SSA: access GPD

29From X. Jiang

g2: twist-3, q-g correlations• experiments: transversely polarized target

SLAC E155x, JLab Hall A

• g2 leading twist related to g1 by Wandzura-Wilczek relation

• g2 - g2WW: a clean way to access twist-3 contribution

(q-g correlations)

h1 term suppressed by quark mass

1

21

21

22

22

22

22

),(),(),(

),(),(),(

x

WW

WW

y

dyQygQxgQxg

QxgQxgQxg

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Jefferson Lab Hall A E97-103

Precision Measurement of g2n(x,Q2): Search for Higher Twist Effects

T. Averett, W. Korsch (spokespersons) K. Kramer (Ph.D. student)

• Improve g2n precision by an order of magnitude.

• Measure higher twist quark-gluon correlations.• Accepted by PRL, K. Kramer et al., nucl-ex/0506005

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E97-103 results: g2n vs. Q2

• measured g2n consistently higher than g2

ww: positive twist-3• higher twist effects significant below Q2=1 GeV2

• Models (color curves) predict small or negative twist-3

Second Moment: d2n

• E99-117+SLAC (high Q2) E94-010 (low Q2)

• Twist-3 matrix element

• ChPT (low Q2) MAID model • Lattice QCD (high Q2) other models

GPD moment with target SSA with 2effect JLab E05-015: Spokespersons: T. Averett, J.P. Chen, X. Jiang

Other SIDIS experiments

Sea asymmetrySpin-flavor decomposition

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A Hall-A proposal PR-04-114

Semi-inclusive pion and kaon production using Bigbite and HRS spectrometers

Projected sensitivity for ud

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A Hall-C proposal PR-04-113

Spin asymmetries in ( , ) and ( , )p e e h X d e e h X

Large acceptance BETA detector and the HMS spectrometer

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Other planned experiments and outlook

• Approved SIDIS proposal in Hall B (H. Avakian)

• A new proposal with polarized 3He (n) for spin-flavor decomposition.

• Other measurements under consideration.

• SIDIS with JLab 12 GeV upgrade:

Transversity

Transverse momentum dependent parton distributions

Spin-flavor decomposition

Sea asymmetry

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Summary• With high luminosity and moderate energy,

factorization seems reasonable for JLab SIDIS.

• JLab experiment E03-004 will measure neutron SSA using transversely polarized 3He target.

Experimental preparation underway data taking in fall 2007.• Other transverse spin experiments.

• Other SIDIS experiments at JLab and 12 GeV.

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Collins Effect at 12 GeV Upgrade

UT ~Collins

Study the Collins fragmentation for all 3 pions with a transversely polarized target and measure the transversity distribution function. JLAB12 cover the valence region.

From H. Avakian

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Kaon fragmentation functions

KKP global fit:

This implies:

1 12 2, 0 00.05 0.05

( , ) 0.19, ( , ) 0.25K Ku s ddz z D z Q dz z D z Q

1 12 2

0 00.05 0.05( , ) 0.065, ( , ) 0.25K K

u ddz z D z Q dz z D z Q

( ) ( )?K Kud

D z D z

Connections between the parton distribution and fragmentation functions?