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Neutron Transversity at Jefferson Lab

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Presentation on theme: "Neutron Transversity at Jefferson Lab"— Presentation transcript:

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

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?

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