1 Measurement of Single Target-Spin Asymmetry in Semi-Inclusive n ↑ (e,e′πˉ) Reaction on a Transversely Polarized 3 He Target PR-06-010 (E-03-004) PAC-29, January 2006 Jen-Chieh Peng University of Illinois at Urbana- Champaign
Mar 27, 2015
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Measurement of Single Target-Spin Asymmetry in Semi-Inclusive n↑(e,e
′πˉ) Reaction on a Transversely Polarized 3He Target
PR-06-010 (E-03-004)
PAC-29, January 2006
Jen-Chieh Peng
University of Illinois at Urbana-Champaign
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Hall A Collaboration Experiment
The Institutions
California State Univ., Duke Univ., Florida International. Univ., Univ. Illinois, JLab, Univ. Kentucky, Univ. Maryland, Univ. Massachusetts, MIT, Old Dominion Univ., Rutgers Univ., Temple Univ., Penn State Univ., Univ. Virginia, College of William & Mary, Univ. Sciences & Tech, China Inst. Of Atomic Energy, Beijing Univ., Seoul National Univ., Univ. Glasgow,
INFN Roma and Univ. Bari, Univ. of Ljubljana, St. Mary’s Univ., Tel Aviv Univ.
A. Afanasev, K. Allada, J. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, F. Butaru, G. Cates, C. Chang, J.-P. Chen (Co-SP), W. Chen, S. Choi, C. Chudakov, E. Cisbani, E.
Cusanno, R. De Leo, A. Deur, C. Dutta, D. Dutta, R. Feuerbach, S. Frullani, L. Gamberg, H. Gao, F. Garibaldi, S. Gilad, R. Gilman, C. Glashausser, J. Gomez, M. Grosse-Perdekamp, D. Higinbotham, T. Holmstrom, D. Howell, M. Iodice, D. Ireland, J. Jansen, C. de Jager,
X. Jiang (Co-SP), Y. Jiang, M. Jones, R. Kaiser, A. Kalyan, A. Kelleher, J. Kellie, J. Kelly, A. Kolarkar, W. Korsch, K. Kramer, E. Kuchina, G. Kumbartzki, L. Lagamba, J. LeRose, R.
Lindgren, K. Livingston, N. Liyanage, H. Lu, B. Ma, M. Magliozzi, N. Makins, P. Markowitz, Y. Mao, S. Marrone, W. Melnitchouk, Z.-E. Meziani, R. Michaels, P. Monaghan, S. Nanda, E. Nappi, A. Nathan, V. Nelyubin, B. Norum, K. Paschke, J. C. Peng (Co-SP), E. Piasetzky, M. Potokar, D. Protopopescu, X. Qian, Y. Qiang, B. Reitz, R. Ransome, G. Rosner, A. Saha, A. Sarty, B. Sawatzky, E. Schulte, S. Sirca, K. Slifer, P. Solvignon, V. Sulkosky, P. Ulmer, G.
Urciuoli, K. Wang, D. Watts, L. Weinstein, B. Wojtsekhowski, H. Yao, H. Ye, Q. Ye, Y. Ye, J. Yuan, X. Zhan, X. Zheng, S. Zhou, X. Zong,
Collaboration members (103 members)
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• Remaining frontier of kT – independent structure functions
• Connections to many other kT – dependent distribution and fragmentation functions
• Major experimental efforts to measure transversity using lepton and hadron beams
Physics Motivation: Transversity
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Transversity• 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
Chiral-quark soliton model Quark – diquark model (solid) and pQCD-based model (dashed)
Similar to helicity distributionsB. –Q. Ma, I. Schmidt and J. –J. Yang,
PRD 65, 034010 (2002)hep-ph/0101300
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How to measure transversity?
• Transversely Polarized Drell-Yan
• Semi-Inclusive DIS– Single-hadron (Collins fragmentation function,
H1┴(z))
– Two hadrons (Interference fragmentation function)
– Vector meson polarization– Λ - polarization
• Chiral-odd → not accessible in DIS
• Require another chiral-odd object
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Leading-Twist Quark Distributions
Three have no kT
dependence
The other five are transverse momentum (kT)
dependent (TMD)
( A total of eight distributions)
Semi-inclusive DIS can access all leading-twist quark distributions
Transversity
Sivers function
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Observation of Single-Spin Azimuthal Asymmetry
Longitudinally polarized target
ep → e’πx HERMES
<ST> ~ 0.15
Collins effect: Correlation between the quark’s transverse spin with pion’s pT in the fragmentation process δq(x) • H1
┴(z).
Sivers effect: Correlation between the transverse spin of the proton with the quark’s transverse momentum f1T
┴(x) • D(z).
Other higher twist effects could also contribute.
Origins of the azimuthal asymmetry ?
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1
, , 1 1
1
Product of ( ) ( ) is non-zero
A surprising flavor dependence : / 1
Extraction of ( ) requires an independent measurement of
Collins function ( )
unfavored favored
q x H z
H H
q x
H z
AUTsin() from transv. pol. H target
Simultaneous fit to sin( + s) and sin( - s)
„Collins“ moments
hep-ex/0507013
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Collins functions from Belle
• Significant non-zero asymmetries
• Rising behaviour vs. z
• First direct measurement of the Collins functionz1
z2
hep-ex/0507063
(cos 2 correlation between pions)e e x
1 1 1 1 1 2 1 2Asymmetry ( ( ) / ( )) ( ( ) / ( ))H z D z H z D z
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Extraction of Collins functions from the Collins asymmetry measurements
Fits to the Hermes data “Prediction” of the Compass data
, ,1 1 1 1Assuming ( ) (1 ) ( ); ( ) (1 ) (
0.29 0.04, 0.33 0.
)
04
fav fav u
fav unfa
nfav favfav unfav
v
H z C z z D z H z C z z D
C C
z
( Vogelsang and Yuan, hep-ph/0507266 )
( , )p e e ( , )d h
, ,1 1/ 1unfavored favoredH H
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Sivers moments from transversity experiments
“Sivers“ moments
AUTsin(-s) from Hermes transv. pol. H target
First measurement of Sivers asymmetry
Sivers function nonzero orbital angular momentum of quarks
hep-ex/0507013
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Extraction of Sivers functions from the Sivers moment measurements
Fits to the Hermes data “Prediction” of the Compass data
, ,1 1Assuming ( ) (1 ) ( ); ( ) (1 ) ( )
0.81 0.07, 1.86 0.28
u dT u T d
u dS
f x S x x u x f x S x x u x
S
( Vogelsang and Yuan, hep-ph/0507266 )
Striking flavor dependence of the Sivers function
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Opportunities at JLab for transversity experiments
• High-intensity CW electron beam• High-density polarized 3He target which could be
polarized transversely• Probe valence-quark region similar to HERMES
kinematics, providing complimentary information on transversely polarized neutron
• An independent test of the striking flavor structures of Collins and Sivers functions observed at HERMES/COMPASS
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3He↑(e,e’π‾)x at Hall-A
• Beam– 6 GeV, 15 μA e- beam
• Target– Optically pumped Rb-K spin-exchange 3He target, 50 mg/cm2, ~42%
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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Kinematic coverage of the electron arm
• BigBite spectrometer set at θ=30° at beam-right detecting electrons with 0.5 < E’ < 2.2 GeV.
• The coverage in Bjorken-x is 0.135 < x < 0.405, corresponding to valence-quark region.
• For the four x bins, the range of mean-Q2 is 1.3 < <Q2> < 3.1 (GeV/c)2.
• The coverage in W, the invariant mass of the hadronic system, is 2.33 < W < 3.05 GeV, well above the resonances region.
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Kinematic coverage of the hadron arm
• HRSL situated at θ = -16° will measure charged hadrons with mean momentum p = 2.4 GeV/c.
• The fraction of the virtual photon energy carried by the hadron, z = Eh/ν, is z ≈ 0.5 to detect leading pion in the current fragmentation region.
• A cut of W ’ > 1.5 GeV is required to stay away from the delta resonance production region.
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Hall-A polarized 3He target
• 40-cm long Rb-K spin-exchange hybrid cell at 10 atm with beam current of 15 μA
• 42% target polarization with spin-flip frequency of 20 minutes
• A third set of Helmholtz coils will be added, together with the laser optics, to allow for vertical polarization of the 3He target
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Coverage of the Collins angle
90 (re0 (black 270 (pur), pl180 (blue )),d), e
l lColl
lS
l
ins h S
l lS SS
<x>=0.135
<x>=0.405
<x>=0.225
<x>=0.315
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Coverage of the Sivers angle
90 (red0 (black), 180 (blue), 270 (purpl )), e
l lSiver
llS
lS
s h S
lS S
<x>=0.135
<x>=0.405
<x>=0.225
<x>=0.315
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Beam time request and count rate estimate
Time (Hour)
Production on 3He 528
Reference cell runs 16
Target spin rotation and polarization measurement
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Total 576 (24 days)
<x> Rate (Hz) Nπ‾(103) δ AUT (n) %
0.135 0.17 317.5 1.47
0.225 0.12 231.1 1.82
0.315 0.07 139.7 2.46
0.405 0.05 95.8 3.03
Beam time request Count rate estimate
• Quark distribution function from CTEQ5M
• Pion fragmentation functions from KKP parameterization
• Gaussian pion PT distribution with <PT2> = 0.26 (GeV/c)2
• Effective neutron polarization of 86.5% in 3He and a dilution factor, f ≈ 0.3, are used to relate measured 3He asymmetry to deduced neutron asymmetry
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Projected sensitivities of Collins and Sivers asymmetries
2 (1)1 1
2 (1)1 1
2 21 1
21 1
( ) ( )(1 )
(1 / 2) (
( ) ( )
(
(
)
)
( )
)
q qqqCollin
q qq TqSivers
UT q qq
sUT
q
q
q q
q
e h x H zyA
y y e f x D
e f x D zA
e f x z
z
D
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Predictions of Collins asymmetry on neutron
1 14n unfav favUTA d H u H
1 1 1 1/ /unfav fav unfav favH H D D
1 1/ 1unfav favH H
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Predictions of Sivers asymmetry on neutron(1) (1)
1 1 1 14n d unfav u favUT T TA f D f D
(11 1
) (1)1 1/ 3
4
31/ n d uu
Unfav fav
T TA fD fD
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Progress since the approval of E-03-004• Improvement on the polarized 3He target (K-Rb hybrid,
new laser optical fiber system, etc.)• Commissioning of the BigBite spectrometer for the SRC
and GnE experiments. Background rate test run in April
2005• Operation of the Lumi detectors as luminosity monitor• Optimization of the experimental configuration and
detailed simulation of the background• First SSA SIDIS data on transversely polarized targets
from HERMES and COMPASS• Many theoretical progress including the proof of
factorization in SIDIS• First SIDIS data from Hall-C and CLAS
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Is SIDIS applicable at 6 GeV?
-
Preliminary results from Hall-C E00
( , ) and ( ,
-1
) at 0.3
08
p e e p e e x
Data are well described by SIDIS calculations for 0.4 < z < 0.7
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Summary• The physics of transversity and kT-dependent
quark distribution and fragmentation functions is an exciting frontier in nucleon structure.
• High-luminosity JLab beam together with the transversely polarized 3He target and the spectrometers at Hall-A provide a unique opportunity to test the intriguing flavor dependence observed in recent SSA experiments.
• Various recent progress both at JLab and around the world has further strengthened the physics case and shown the urgency of the proposed measurements.
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Backup Slides
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Is SIDIS applicable at 6 GeV?Preliminary results from Hall-C E00
( , ) and ( ,
-
) at 0.3
108
p e e d e e x
Data are well described by SIDIS calculations for 0.4 < z < 0.7
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Disentangling Collins from Sivers asymmetries
simulation taking into account of the finite acceptance of the spectrometer
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Disentangling Collins from Sivers asymmetries
simulation taking into account of the finite acceptance of the spectrometer, and the 3Φh-Φs term
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Systematic errors
• Nuclear effects in 3He– Proton carries ~ 2.8 % of the polarization and can be well
corrected for, using the asymmetry data from HERMES
• Target polarization drift– Only contributes to the relative uncertainty of the measured AUT at
a level of 4 %
• Decays from exclusive ρ-meson production– Negligible at z=0.5, based on the simulation of Hall-C E00-108
• Other terms in SSA– Monte-Carlo simulations indicate very small effect
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Why not wait for 12 GeV?
• The measurements can already be done at 6 GeV, and the impact of this first measurement on our current knowledge on SSA should be huge.
• It will provide extremely valuable inputs for optimizing a future program of transversity (and semi-inlcive DIS, in general) at 12 GeV.
• JLab will continue to play an important role in the global effort to understand the spin structure of the nucleons.
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π- versus π+, which do we prefer?
• If both π- and π+ data are obtained, one can make an independent extraction of the Sivers functions based on Jlab data alone (and compare them with Hermes data).
• π- and π+ data will provide two independent tests of the current results on Sivers and Collins function obtained at Hermes and Compass.
• If only one charged pion data will be measured, then one can make a single test of the results on Sivers and Collins function. In this case, there is no difference which charged state one selects.
• Under severe beam-time constraints, a measurement for both pions with somewhat reduced statistics might be considered.
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All Eight Quark Distributions Are Probed in Semi-Inclusive DIS
4
26 4
Q
sxd
),()(])1(1{[ 211
,
22 h
qqq PzDxfey
),()()sin()1(||
),()()2sin(4
)1(||
),()()2cos(4
)1(
2
,11
2
2
,1
)1(1
22
2
2
,1
)1(1
22
2
hqq
qqq
lS
lh
h
hT
hqq
qqLq
lh
hN
hL
hqq
qqq
lh
hN
h
PzHxhezM
PyS
PzHxheMMz
PyS
PzHxheMMz
Py
)},()()cos()2
11(||
),()()2
11(||
),()()3sin(6
)1(||
),()()sin()2
11(||
21
)1(1
,
2
21
,1
2
,
21
)2(1
223
3
21
)1(1
,
22
hqq
Tqq
qlS
lh
N
hTe
hq
qqLe
qqh
qqTq
lS
lh
hN
hT
hqq
Tqq
qlS
lh
N
hT
PzDxgezM
PyyS
PzDxgeyyS
PzHxheMMz
PyS
PzDxfezM
PyyS
Unpolarized
Polarized target
Polarized beam and
target
SL and ST: Target Polarizations; λe: Beam Polarization
Sivers
Transversity