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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

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**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**

( A total of eight distributions) No K┴ dependence K┴ - dependent, T-even K┴ - dependent, T-odd

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**Eight Quark Distributions Probed in SIDIS**

Unpolarized Transversity Polarized target Sivers Polarzied beam and target SL and ST: Target Polarizations; λe: Beam Polarization

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**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

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**Collins asymmetry from COMPASS**

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

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**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

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**SIDIS measurements at JLab**

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**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

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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**

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 )

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**Planned neutron transversity experiment at JLab**

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**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

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**Jefferson Lab Hall A Experimental Setup for polarized n (3He) 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

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**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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**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

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**Disentangling Collins and Sivers Effects**

Collins angle: ФC=Фhl + ФSl Sivers angle: ФS=Фhl - ФSl Coverage in ФSl is increased by rotating target polarization

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**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

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**Expected Statistical Sensitivities**

Comparison with HERMES projection

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**Expected Statistical Sensitivities**

HERMES ph(e,e’p) JLab E Projection 3Heh(e,e’p-)

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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 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

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**Other transverse spin experiments**

Proton transversity g2/d2: twist-3 Target SSA: access GPD

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From X. Jiang

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**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

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**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/

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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

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**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

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**GPD moment with target SSA with 2g effect**

JLab E05-015: Spokespersons: T. Averett, J.P. Chen, X. Jiang

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**Other SIDIS experiments**

Sea asymmetry Spin-flavor decomposition

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**Projected sensitivity for**

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

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**Large acceptance BETA detector and the HMS spectrometer**

A Hall-C proposal PR 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 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.

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**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.

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**Kaon fragmentation functions**

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

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