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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 1 Introduction/motivation 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) 3 Leading-Twist Quark Distributions ( A total of eight distributions) No K┴ dependence K┴ - dependent, K┴ - dependent, T-even T-odd 4 Eight Quark Distributions Probed in SIDIS 4 2 sx d 6 Q4 {[1 (1 y) 2 ] eq f1q ( x) D1q ( z, Ph2 ) 2 q ,q Unpolarized Ph2 (1 y ) 2 cos(2 hl ) eq h1(1) q ( x) H 1 q ( z , Ph2 ) 2 4z M N M h q ,q Ph2 | S L | (1 y ) 2 sin(2 hl ) eq h1(1) q ( x) H 1 q ( z , Ph2 ) 2 L 4z M N M h q ,q Ph Transversity | S T | (1 y ) sin( hl S ) eq h1q ( x) H 1 q ( z , Ph2 ) l 2 zM h q ,q Polarized 1 P target Sivers | ST | (1 y y 2 ) h sin(hl S ) eq f1T (1) q ( x) D1q ( z, Ph2 ) l 2 2 zM N q ,q Ph3 | ST | (1 y ) 3 2 sin(3hl S ) eq h1( 2) q ( x) H1 q ( z, Ph2 ) l 2 T 6z M N M h q ,q 1 e | S L | y (1 y ) eq g1q ( x) D1q ( z , Ph2 ) 2 Polarzied 2 q ,q 1 P beam and e | ST | y (1 y ) h cos( hl S ) eq g1(T) q ( x) D1q ( z , Ph2 )} l 2 1 target 2 zM N q ,q SL and ST: Target Polarizations; λe: Beam Polarization 5 AUTsin() from transv. pol. H target Simultaneous fit to sin( + s) and sin( - s) `Collins‘ moments `Sivers‘ moments • Non-zero Collins asymmetry •Sivers function nonzero (+) orbital angular momentum of quarks • Assume dq(x) from model, then •Regular flagmentation functions H1_unfav ~ -H1_fav 6 • Need independent H1 (BELLE) Collins asymmetry from COMPASS • Transversely polarized 6LiD target • Cover smaller x • Consistent with 0 hep-ex/0503002 COMPASS 2002-2004 data: ~ factor of 12 in statistics 7 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 8 SIDIS measurements at JLab 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 10 Jefferson Lab 11 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 ep e x ep e x Data are well described by Similar z-dependence calculations assuming factorization for different x-bins Recent theory work on SIDIS factorization (hep-ph0404183) 14 Planned neutron transversity experiment at JLab JLab Hall-A E03-004 Experiment 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) • 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 16 Jefferson Lab Hall A Experimental Setup for polarized n (3He) Experiments BigBite 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 19 – 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 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 in ФSl is increased by rotating target polarization 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 JLab E03-004 Projection ph(e,e’) 3Heh(e,e’-) 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 - part is approved and scheduled to run in fall of 2007 + proposal is being developed K+/- got for free 27 Other transverse spin experiments Proton transversity g2/d2: twist-3 Target SSA: access GPD 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 g 2 ( x, Q ) g 2 ( x, Q ) g 2 ( x, Q ) 2 WW 2 2 1 dy ( x, Q ) g1 ( x, Q ) g1 ( y, Q ) WW 2 2 2 g2 x y • g2 - g2WW: a clean way to access twist-3 contribution (q-g correlations) h1 term suppressed by quark mass 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 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 2g effect JLab E05-015: Spokespersons: T. Averett, J.P. Chen, X. Jiang Other SIDIS experiments Sea asymmetry Spin-flavor decomposition A Hall-A proposal PR-04-114 Semi-inclusive pion and kaon production using Bigbite and HRS spectrometers Projected sensitivity for d u 37 A Hall-C proposal PR-04-113 Spin asymmetries in p (e, eh) X and d (e, eh) X Large acceptance BETA detector and the HMS spectrometer 38 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 39 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. 40 41 Collins Effect at 12 GeV Upgrade Collins UT ~ 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. 42 Kaon fragmentation functions 1 1 K KKP global fit: dz z D ( z , Q ) 0.19, u ,s 2 0 dz z DdK ( z , Q02 ) 0.25 0.05 0.05 1 1 K This implies: dz z D ( z , Q ) 0.065, u 2 0 dz z DdK ( z , Q02 ) 0.25 0.05 0.05 K K D ( z) D ( z)? d u Connections between the parton distribution and fragmentation functions? 43