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SPIN ASYMMETRIES IN ELECTRON SCATTERING USING
CLAS AT JEFFERSON LAB
Presented by Peter Bosted for the CLAS Collaboration
Photo shows my house on the south end of the Big Island of Hawaii where much of the anaysis was done
OUTLINE EXPERIMENTAL OVERVIEW
NEW VERY PRECISE RESULTS g1p and g1
d PRELIMINARY Pt DEPENDENCE SIDIS
EXCLUSIVE PION ELECTROPRODUCTION
CEBAF AT JEFFERSON LAB ELECTRON ENERGIES 1 TO 6 GEV
LONGITUDINAL POLARIZATION 70% TO 85%
CLAS DETECTOR In Hall B at Jefferson Lab
CLAS
drift chambers
beam
Cherenkov
calorimeter
e-
target
Time of flight scintillators
p(e, e’)X EVENT IN CLAS
long. pol. p, d target
LONGITUDINALLY POLARIZED PROTON, DEUTERON TARGETS
•5 TESLA MAGNETIC FIELD
•1 K LIQUID HELIUM
•AMMONIA TARGETS (NH3, ND3)
•POLARIZATION 70% (P) 30% (d)
Purple beads are ammonia (NH3);
only the protons are polarized, the
nitrogen makes for (big) background
Polarization of quarks Quarks have spin, which can be aligned or anti
aligned with proton spin
Anti-parallel
electron &
proton spins
Parallel
electron &
proton
spins
Experiment: compare:
5.9 GeV polarized electrons
EG1-DVCS experiment
Run in 2009: 4 months on NH3
1.5 months on ND3
Many improvements
compared to 2001: equivalent
to 30x more events
• Beam polarization PB about 0.8
• Target polarization 0.7 (p), 0.3 (d)
• Dilution factor f about 0.2
• Depolarization factor DLL(y) about 0.3
• Number cound N measured in billions
INCLUSIVE g1/F1 DETERMINATION
NN
NN
yfDPPF
g
LLTB )(
1
1
1
ADDITIONAL CORRECTIONS g1/F1
•
• RADIATIVE CORRECTIONS
• RADIATIVE DILUTION
• PAIR-SYMMETRIC BACKGROUND
• POLARIZATION OF NITROGEN
• CONTRIBUTION FROM g2
• ACCIDENTAL CONTAMINATION OF
ND3 TARGET WITH 10% NH3
EG1-DVCS PROTON g1/F1
Y. Prok, P. Bosted, N. Kvaltine et al (CLAS) Phys. Rev. C 90,025212 (2014).
LSS
RECENTLY PUBLISHED:
X=0.43
EG1-DVCS PROTON g1/F1
Y. Prok, P. Bosted, N. Kvaltine et al (CLAS) Phys. Rev. C 90,025212 (2014).
LSS
STASTICAL ERRORS VERY SMALL
RECENTLY PUBLISHED:
X=0.43
EG1-DVCS PROTON g1/F1
Y. Prok, P. Bosted, N. Kvaltine et al (CLAS) Phys. Rev. C 90,025212 (2014).
LSS
STASTICAL ERRORS VERY SMALL
SYST. ERROR MOSTLY INDEPENDENT Q2
RECENTLY PUBLISHED:
X=0.43
EG1-DVCS PROTON g1/F1
Y. Prok, P. Bosted, N. Kvaltine et al (CLAS) Phys. Rev. C 90,025212 (2014).
LSS
STASTICAL ERRORS VERY SMALL
SYST. ERROR MOSTLY INDEPENDENT Q2
RECENTLY PUBLISHED:
RESULTS SPAN RESONANCE TO DEEP INELASTIC REGIONS
X=0.43
EG1-DVCS PROTON g1/F1
0.15<X<0.6
1<Q2<5 GeV2
EG1-DVCS DEUTERON g1/F1
LSS FIT USING EG1-DVCS NEW RESULTS
Leader, Siderov, and Staminov 1410:1657 (October 2014)
Ds
DG
Dd
Du
LSS FIT USING EG1-DVCS NEW RESULTS
Leader, Siderov, and Staminov 1410:1657 (October 2014)
“We have stressed that, in principle, the inclusive DIS data
uniquely determine the strange quark polarization. Our new
analysis of the inclusive world data, including for the first time the
extremely accurate JLab CLAS data
on the proton and deuteron spin structure
functions and the recently published COMPASS proton data,
despite allowing, in the parametrization, for a possible sign
change, has confirmed the previous claim, namely, that the
inclusive data yield significantly negative values
for the strange quark polarization. The
fundamental difference between the SIDIS and DIS analysis is the
necessity in SIDIS to use information on the fragmentation
functions, which are largely determined from multiplicity
measurements.”
Moments of spin structure functions
ChPT
GDH sum rule
DIS pQCD
operator product expansion
quark models Lattice QCD?
Q2 (GeV2) 1
G1
dxQxgQ 2
1
0
1
2
1 ,G
Bjorken Sum Rule:
G1p
- G1n =
gA
6+ QCD corr.
GDH Sum Rule:
G1 Q2 ® 0( )®-Q2
2M 2
k 2
4
BJORKEN SUM RULE
A. Deur et al., 1405:7854 (July 2014
Scattering of 1 to 3 GeV polarized
electrons off polarized NH3, ND3
EG4 EXPERIMENT
Took data in 2004
Small scattering angles (6 to 20
degrees) to focus on low Q2
region
EG4 g1 PROTON
g1 AS FUNCTION OF
w IN 7 OF 20 Q2 BINS.
D(1232) PROMINENT
Preliminary EG4 DEUTERON INTEGRAL G1
One Level deeper: kT-dependent SIDIS
Assume Pt of observed pion is 3D vector sum of quark kt and a fragmentation that generates extra vector pt.
Does ratio g1/F1 depend pT?
Very preliminary results for p0 for g1/F1 versus pT from eg1-dvcs
Results consistent with no pT dependence
SIDIS STILL PRELIMINARY QED RADIATIVE CORRECTION CAN BE
LARGE AT HIGH PT.
NEED RELIABLE FITS TO CROSS SECTIONS AND ASYMMETRIES
FROM SGINLE PION AND DOUBLE PION
ELECTROPRODUCTION
EMBARK ON PROJECT TO ANALYZE LARGE BODY DATA FROM 00 AND 2009
ONE LEVEL DEEPER YET: EXCLUSIVE PION ELECTROPRODUCTION
NUCLEON NUCLEON
PION
ELECTRON
e p e n p+ e p e p p0 e n e p p-
NEW RESULTS EG1B (2000) AND EG1-DVCS (2009)
• 4 BEAM ENERGIES (1.6, 2.5, 4.2, 6 GEV) • 40 BINS IN W FROM 1.1 TO 3.0 GEV (OR 0.1<X<1) • 10 BINS IN Q2 FROM 0.05 TO 5 GEV2
• 10 BINS IN COS(q*) FROM -0.4 TO 1 (OR -1<t<0 GEV2) • 12 BINS IN f* FROM 0 TO 360 DEGREES
CAN’T SHOW ALL IN 2 MINUTES!
NN
NN
fPPA
TB
QWLL
1)
*),
*cos(,
2,( fq
BEAM-TARGET SPIN ASYMMETRY
•Leading term independent of f*
•Related to g1/F1
•Related to A1/2 – A3/2
ALL RESULTS ARE PRELIMINARY
RED CURVES ON PLOTS ARE UNITARY ISOBAR FIT TO PREVIOUS WORLD DATA: MAID 2007
ALL f-average E=1.6 GeV ep e n p+
ALL f-average E=2.5 GeV ep e n p+
ALL f-average E=4.2 GeV ep e n p+
ALL f-average E=1.6 GeV en e p p-
ALL f-average E=5.7 GeV ep e p p0
NN
NN
fPA
T
QWUL
1)
*),
*cos(,
2,( fq
TARGET SPIN ASYMMETRY
• Leading terms: sin(f*) and sin(2f*) • Related to L-T and T-T interference and higher twist contributions
AUL sin(f-moment E=1.6 GeV ep e n p+
AUL sin(f-moment E=1.6 GeV ep e n p+
AUL sin(f-moment E=2.5 GeV ep e n p+
AUL sin(f-moment E=4.2 GeV ep e n p+
AUL sin(f-moment E=1.6 GeV en e p p-
AUL sin(f-moment E=5.7 GeV ep e p p0
NN
NN
fPA
B
QWLU
1)
*),
*cos(,
2,( fq
BEAM SPIN ASYMMETRY
• Leading term: sin(f • Related to L-T interference and higher twist contributions
ALU sin(f-moment E=4.2 GeV ep e n p+
SUMMARY of EXCLUSIVE PION
• LOTS new data! (about 50,000 points) • Three reactions for flavor dependence • Three spin asymmetries • Should help determine Q2 dependece for resonant form factors and phases • Should help study of GPDs using W>2 GeV results
Acknowledgments: •Andrey Kim (p0 analysis 6 GeV) •Josh Pierce p+ analysis 4.2 GeV) •Sharon Creccia (p- analysis 1.6-4.2 GeV) •CLAS Collaboration
SUMMARY OF TALK •New very prcise g1
p g1d pusblished, shoing
very weak Q2-dependence g1/F1 •Preliminary low-Q2 g1
p g1d, agreement GDH
•Preliminary SIDIS: g1/F1 independent pT
•Huge body of new precise pion electro-production data spanning N* and DIS regions
Past : 6 GeV
Q2 = 1…6 GeV2
x = 0.1…0.6
W = 0.94…3 GeV
Future: 12 GeV
Q2 = 1…13 GeV2
x = 0.06…0.8
W = 0.94…4 GeV
Jefferson Lab in Perspective Q
2 [G
eV
2]
x
A1(d
)
Spin structure functions at large x H
all
A
SU(6)
LSS
A1(p
)
3He
LSS
BBS
BBS + Lq
Parno et al.,
arXiv:1406.120
7
BBS
BBS + Lq
2Q
-210 -110 1
0g
-7
-6
-5
-4
-3
-2
-1
0
Model used
MAID
PTcBernard et al
PTcKao et al HB
PTcLensky et al
Data-only
Data-Model
JLab (EG1b)
EG4 syst.
Spin Polarizabilities
Q2
Q2
(EG4)
Sensitive Test of Chiral Perturbation Theory calculations
g0
CLAS deuteron
G1
f 2p
-n
Sum rule (2)
Sum rule (1)
Bag model
Instanton(2002)
Instanton(2006)
Present study PRD 78 032001 (08) PRL 93 212001 (2004)-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
p
p-n
2Q
-210 -110 1
1G
-0.15
-0.1
-0.05
0
0.05
0.1
Model used
DIS
Burkert-Ioffe
Soffer et al
GDH slope
PTcJi et al
PTcBernard et al
PTcLensky et al
Data-only
Data+Model
JLab (EG1b)
SLAC
EG4 syst.d
n
EG4 g1 proton
EG4 g1 proton
(e,e’)
(e,e’m)
Mx2 = W2 = M2 + Q2 (1/x – 1)
Mx2 = W’2 = M2 + Q2 (1/x – 1)(1 - z)
z = Em/n
(For Mm small, pm collinear with g, and Q2/n2 << 1)
SIDIS – LO Picture
Leading-order Picture: hit one Quark
Want large Q2 to keep Mx big
ONE LEVEL DEEPER: SIDIS
z>0.3
P+ P0 P-
Very Preliminary results from eg1-dvcs
SIDIS kinematic plane and relevant variables
Ey /n
)/(sinEEQ ' 24 22 q
nMQx 2/2
'EE n
n/Ez h
Pt is transverse momentum relative to
virtual photon
Mx2=M2+Q2(1/x-1) is invariant mass of
total hadronic final state
pion
MX
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