1. Neutron Transversity at Jefferson Lab
Jian-ping Chen, Jefferson Lab
Transversity Workshop, Como, Italy, Sept. 7-10, 2005
Introduction
SIDIS measurements at JLab
JLab Hall-A neutron transversity experiment
Other transverse spin experiments
Other planned SIDIS experiments
Summary

2. Introduction/motivation

3. 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)

4. Leading-Twist Quark Distributions
( A total of eight distributions)
No K┴ dependence
K┴ - dependent, T-even
K┴ - dependent, T-odd

5. Eight Quark Distributions Probed in SIDIS
Unpolarized
Transversity
Polarized target
Sivers
Polarzied beam and target
SL and ST: Target Polarizations; λe: Beam Polarization

6. AUTsin() from transv. pol. H target
Simultaneous fit to sin( + s) and sin( - s)
`Collins‘ moments
`Sivers‘ moments
Non-zero Collins asymmetry
Assume dq(x) from model, then
H1_unfav ~ -H1_fav
Need independent H1 (BELLE)
Sivers function nonzero (p+)
orbital angular momentum of quarks
Regular flagmentation functions

7. Collins asymmetry from COMPASS
Transversely polarized 6LiD target
Cover smaller x
Consistent with 0
hep-ex/
COMPASS data:
~ factor of 12 in statistics

8. Current Status Collins Asymmetries - sizable for proton
large at high x
large for p-
- 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

9. SIDIS measurements at JLab

10. Thomas Jefferson Accelerator Facility
6 GeV polarized CW electron beam
(P = 85%, I = 180 mA)
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

11. Jefferson Lab

13. 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.

14. Preliminary results of factorization test from JLab for semi-inclusive pion production
Hall-C E00-108
CLAS 5.7GeV data
Data are well described by calculations assuming factorization
Similar z-dependence for different x-bins
Recent theory work on SIDIS factorization (hep-ph )

15. Planned neutron transversity experiment at JLab

16. JLab Hall-A E03-004 Experiment
Single Target-Spin Asymmetry in Semi-Inclusive p 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)
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

17. Jefferson Lab Hall A Experimental Setup for polarized n (3He) Experiments
BigBite

18. Hall A

19. 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

20. 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

21. Transversely polarzied 3He target
Target polarization orientation can be rotated to increase the coverage in ФSl

22. HERMES: <Q2> = 2.5 GeV2
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

23. Disentangling Collins and Sivers Effects
Collins angle: ФC=Фhl + ФSl
Sivers angle: ФS=Фhl - ФSl
Coverage in ФSl is increased by rotating target polarization

24. Model Predictions for δq and AUT
Quark – diquark model (solid) and pQCD-based model (dashed)
B. –Q. Ma, I. Schmidt and J. –J. Yang, PRD 65, (2002)
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

25. Expected Statistical Sensitivities
Comparison with HERMES projection

26. Expected Statistical Sensitivities
HERMES
ph(e,e’p)
JLab E Projection
3Heh(e,e’p-)

27. 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 GEn experiment
HSR is ready, excellent PID
p- part is approved and scheduled to run in fall of 2007
p+ proposal is being developed
K+/- got for free

28. Other transverse spin experiments
Proton transversity
g2/d2: twist-3
Target SSA: access GPD

29. From X. Jiang

30. 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

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

32. E results: g2n vs. Q2
measured g2n consistently higher than g2ww: positive twist-3
higher twist effects significant below Q2=1 GeV2
Models (color curves) predict small or negative twist-3

33. 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

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

36. Other SIDIS experiments
Sea asymmetry
Spin-flavor decomposition

37. Projected sensitivity for
A Hall-A proposal PR
Semi-inclusive pion and kaon production using Bigbite and HRS spectrometers
Projected sensitivity for

38. Large acceptance BETA detector and the HMS spectrometer
A Hall-C proposal PR
Large acceptance BETA detector and the HMS spectrometer

39. 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

40. Summary
With high luminosity and moderate energy, factorization seems reasonable for JLab SIDIS.
JLab experiment E 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.

42. Collins Effect at 12 GeV Upgrade
clas12
Collins Effect at 12 GeV Upgrade
sUT ~
Collins
From H. Avakian
Study the Collins fragmentation for all 3 pions with a transversely polarized target and measure the transversity distribution function. JLAB12 cover the valence region.

43. Kaon fragmentation functions
KKP global fit:
This implies:
Connections between the parton distribution and fragmentation functions?