Transcript Document

Neutron Transversity at Jefferson Lab
Jian-ping Chen, Jefferson Lab
Transversity Workshop, Como, Italy, Sept. 7-10, 2005
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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
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-odd
K┴ - dependent,
T-even
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Eight Quark Distributions Probed in SIDIS
4 2 sx
d

Q4
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{[1  (1  y) 2 ] eq2 f1q ( x) D1q ( z, Ph2 )
q ,q
Ph2
 (1  y ) 2
cos(2 hl ) eq2 h1(1) q ( x) H 1 q ( z, Ph2 )
4z M N M h
q ,q
Unpolarized
Ph2
 | S L | (1  y ) 2
sin(2 hl ) eq2 h1L(1) q ( x) H 1 q ( z , Ph2 )
4z M N M h
q ,q
Transversity
Sivers
Ph 
sin( hl   Sl ) eq2 h1q ( x) H 1 q ( z, Ph2 )
zM h
q ,q
P
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 | ST | (1  y  y 2 ) h  sin(hl  Sl ) eq2 f1T(1) q ( x) D1q ( z , Ph2 )
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zM N
q ,q
 | S T | (1  y )
Polarized
target
Ph3
 | ST | (1  y ) 3 2
sin(3hl  Sl ) eq2 h1T( 2 ) q ( x) H1 q ( z , Ph2 )
6z M N M h
q ,q
 e | S L | y (1 
1
y ) eq2 g1q ( x) D1q ( z, Ph2 )
2 q ,q
 e | ST | y (1 
P
1
y ) h  cos(hl  Sl ) eq2 g1(T1) q ( x) D1q ( z , Ph2 )}
2 zM N
q ,q
Polarzied
beam and
target
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
• Non-zero
Collins asymmetry
• Assume dq(x) from model, then
H1_unfav ~ -H1_fav
• Need independent H1 (BELLE)
`Sivers‘ moments
•Sivers function nonzero (+)
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/0503002
COMPASS 2002-2004 data:
~ factor of 12 in statistics
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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
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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
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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
ep  e  x
Data are well described by
calculations assuming factorization
CLAS 5.7GeV data
ep  e  x
Similar z-dependence
for different x-bins
Recent theory work on SIDIS factorization (hep-ph0404183)
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Planned neutron transversity
experiment at JLab
JLab Hall-A E03-004 Experiment
Single Target-Spin Asymmetry in SemiInclusive  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’sCanada, 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
Hall A
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Experimental Setup for 3He↑(e,e’π-)x
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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
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– 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
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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, 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
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Expected Statistical Sensitivities
Comparison with
HERMES projection
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Expected Statistical Sensitivities
JLab E03-004 Projection
3Heh(e,e’-)
HERMES
ph(e,e’)
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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
- part is approved and scheduled to run in fall of 2007
+ 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
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
WW
2
2
2
g 2 ( x, Q )  g 2
( x, Q )  g 2 ( x, Q )
1
g2
WW
dy
( x, Q )   g1 ( x, Q )   g1 ( y, Q )
y
x
2
2
2
• 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
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E97-103 results: g2n vs. Q2
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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
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E99-117+SLAC (high Q2)
E94-010 (low Q2)
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Twist-3 matrix element
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ChPT (low Q2)
MAID model
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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
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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
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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 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.
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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.
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Kaon fragmentation functions

KKP global fit:
This implies:
K
d
1
0.05

1
0.05
K
u ,s
dz z D ( z, Q )  0.19,
K
u
2
0
dz z D ( z, Q )  0.065,
2
0

1

0.05

1
0.05
dz z DdK ( z, Q02 )  0.25

dz z DdK ( z, Q02 )  0.25
K
u
D ( z)  D ( z)?
Connections between the parton distribution
and fragmentation functions?
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