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Neutron Transversity at Jefferson Lab

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.

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Neutron Transversity at Jefferson Lab

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  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 • Sivers function nonzero (p+) orbital angular momentum ofquarks • Regular flagmentation functions • Non-zero Collins asymmetry • Assume dq(x) from model, then H1_unfav ~ -H1_fav • Need independent H1(BELLE)

  7. Collins asymmetryfromCOMPASS Transversely polarized 6LiD target Cover smaller x Consistent with 0 hep-ex/0503002 COMPASS 2002-2004 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

  12. 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.

  13. 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-ph0404183)

  14. Planned neutron transversity experiment at JLab

  15. Single Target-Spin Asymmetry in Semi-Inclusive p Electroproduction on a Transversely Polarized 3He Target JLab Hall-A E03-004 Experiment 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 • 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 Spokespersons: J.-P. Chen (JLab), X. Jiang (Rutgers), J. C. Peng (UIUC)

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

  17. Hall A

  18. 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

  19. 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

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

  21. 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

  22. Disentangling Collins and Sivers Effects Collins angle: ФC=Фhl+ ФSl Sivers angle: ФS=Фhl - ФSl Coverage inФSlis increased by rotating targetpolarization

  23. 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, 034010 (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

  24. Expected Statistical Sensitivities Comparison with HERMES projection

  25. Expected Statistical Sensitivities HERMES ph(e,e’p) JLab E03-004 Projection 3Heh(e,e’p-)

  26. 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

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

  28. From X. Jiang

  29. 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

  30. 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

  31. E97-103 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

  32. E99-117+SLAC (high Q2) E94-010 (low Q2) Twist-3 matrix element ChPT (low Q2) MAID model Lattice QCD (high Q2) other models Second Moment: d2n

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

  34. Other SIDIS experiments • Sea asymmetry • Spin-flavor decomposition

  35. A Hall-A proposal PR-04-114 Semi-inclusive pion and kaon production using Bigbite and HRS spectrometers Projected sensitivity for

  36. A Hall-C proposal PR-04-113 Large acceptance BETA detector and the HMS spectrometer

  37. 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

  38. 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.

  39. Collins sUT ~ clas12 Collins Effect at 12 GeV Upgrade 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.

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

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