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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(3hl  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, eh) X and d (e, eh) 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

				
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