Spin Study at JLab: from Longitudinal to Transverse J. P. Chen, Jefferson Lab Berkeley Summer Spin...
Transcript of Spin Study at JLab: from Longitudinal to Transverse J. P. Chen, Jefferson Lab Berkeley Summer Spin...
Spin Study at JLab: from Longitudinal to Transverse
J. P. Chen, Jefferson LabBerkeley Summer Spin Program, 2009, LBNL, California
Introduction
Longitudinal and transverse spin
Selected results from JLab
Recently completed and planned measurements
12 GeV plan
Strong Interaction and QCD• Strong interaction, running coupling ~1 -- QCD: accepted theory for strong interaction -- asymptotic freedom (2004 Nobel) perturbation calculation works at high energy -- interaction significant at intermediate energy quark-gluon correlations -- interaction strong at low energy (nucleon size)
confinement
theoretical tools: pQCD, OPE, Lattice QCD, ChPT, …
• A major challenge in fundamental physics: Understand QCD in strong interaction region Study and understand nucleon structure
E
s
Nucleon Structure and Sum Rules
• Global properties and structure
Mass: 99% of the visible mass in universe
~1 GeV, but u/d quark mass only a few MeV each!
Momentum: quarks carry ~ 50%
Spin: ½, quarks contribution ~30% Spin Sum Rule
Magnetic moment: large part anomalous, >150% GDH Sum Rule
Axial charge Bjorken Sum Rule
Angular momentum Ji’s Sum Rule
Polarizabilities (Spin, Color)
Tensor charge
Three Decades of Spin Structure Study• 1980s: EMC (CERN) + early SLAC quark contribution to proton spin is very small = (12+-9+-14)% ! ‘spin crisis’ (Ellis-Jaffe sum rule violated)
• 1990s: SLAC, SMC (CERN), HERMES (DESY) = 20-30% the rest: gluon and quark orbital angular momentum
A+=0 (light-cone) gauge (½) + Lq+ G + Lg=1/2 (Jaffe)
gauge invariant (½) + Lq + JG =1/2 (Ji) A new decomposition (X. Chen, et. al) Bjorken Sum Rule verified to <10% level
• 2000s: COMPASS (CERN), HERMES, RHIC-Spin, JLab, … : ~ 30%;G probably small, orbital angular momentum probably significant Transversity, Transverse-Momentum Dependent Distributions Generalized Parton Distributions
Unpolarized and Polarized Structure functions
Parton Distributions (CTEQ6 and DSSV)
DSSV, PRL101, 072001 (2008)
CTEQ6, JHEP 0207, 012 (2002)
Polarized PDFsUnpolarized PDFs
Jefferson Lab Experimental Halls
HallA: two HRS’ Hall B:CLAS Hall C: HMS+SOS
6 GeV polarized CW electron beam Pol=85%, 180A
Will be upgraded to 12 GeV by ~2014
Jefferson Lab Hall A Experimental Setup Jefferson Lab Hall A Experimental Setup for inclusive polarized n (for inclusive polarized n (33He) He)
ExperimentsExperiments
Hall A polarized 3He target
longitudinal, transverse and vertical
Luminosity=1036 (1/s) (highest in the world)
High in-beam polarization > 65%
Effective polarized neutron target
12 completed experiments 1 are currently running 6 approved with 12 GeV (A/C)
15 uA
Hall B/C Polarized proton/deuteron target
• Polarized NH3/ND3 targets
• Dynamical Nuclear Polarization
• In-beam average polarization
70-90% for p
30-40% for d• Luminosity up to ~ 1035 (Hall C)
~ 1034 (Hall B)
JLab Spin Experiments
• Results:• Moments: Spin Sum Rules and Polarizabilities• Higher twists: g2/d2
• Quark-Hadron duality• Spin in the valence (high-x) region
• Just completed: • d2
p (SANE) and d2n
• Transversity (n)
• Planned• g2
p at low Q2
• Future: 12 GeV• Inclusive: A1/d2,
• Semi-Inclusive: Transversity, TMDs, Flavor-decomposition
• Review: Sebastian, Chen, Leader, arXiv:0812.3535, PPNP 63 (2009) 1
Longitudinal Spin (I)
Spin in Valence (high-x) Region
Valence (high-x) A1p and A1
n results
Hall B CLAS, Phys.Lett. B641 (2006) 11 Hall A E99-117, PRL 92, 012004 (2004) PRC 70, 065207 (2004)
Inclusive Hall A and B and Semi-Inclusive Hermes
BBS
BBS+OAM
F. Yuan, H. Avakian, S. Brodsky, and A. Deur, arXiv:0705.1553
pQCD with Quark Orbital Angular Momentum
A1p at 11 GeV
Projections for JLab at 11 GeV
u and d at JLab 11 GeV
Flavor decomposition with SIDISFlavor decomposition with SIDIS
Polarized Sea
JLab @11 GeV
Longitudinal Spin (II)
Quark Hadron Duality in Spin Strcuture Function
Duality in Spin-Structure: Hall A E01-012 Results
• g1/g2 and A1/A2 (3He/n) in resonance region,
1 < Q2 < 4 GeV2
• Study quark-hadron duality in spin structure.
<Resonances> = <DIS> ?
• PRL 101, 1825 02 (2008)
A13He (resonance vs DIS)
Duality in Spin-Structure: Partial Moment Results
1 resonance comparison with pdfs
Spin Sum Rules: Zeroth Moments
Moments of Spin Structure Functions
Sum Rules
Global Property
Bjørken Sum Rule
1p (Q2) 1
n (Q2) {g1p (x,Q2) g1
n (x,Q2)}dx1
6gACNS
gA: axial vector coupling constant from neutron -decayCNS: Q2-dependent QCD corrections (for flavor non-singlet)
• A fundamental relation relating an integration of spin structure functions to axial-vector coupling constant
• Based on Operator Product Expansion within QCD or Current Algebra
• Valid at large Q2 (higher-twist effects negligible)
• Data are consistent with the Bjørken Sum Rule at 5-10 % level
Gerasimov-Drell-Hearn Sum RuleCircularly polarized photon on longitudinally polarized nucleon
• A fundamental relation between the nucleon spin structure and its anomalous
magnetic moment
• Based on general physics principles • Lorentz invariance, gauge invariance low energy theorem• unitarity optical theorem• casuality unsubtracted dispersion relation
applied to forward Compton amplitude
• First measurement on proton up to 800 MeV (Mainz) and up to 3 GeV (Bonn)
agree with GDH with assumptions for contributions from un-measured regions
New measurements from LEGS, MAMI(2), …
1 2 ( ) 3 2 () d
2 2EM
M 2 2
in
Generalized GDH Sum Rule
• Many approaches: Anselmino, Ioffe, Burkert, Drechsel, …
• Ji and Osborne (J. Phys. G27, 127, 2001):
Forward Virtual-Virtual Compton Scattering Amplitudes: S1(Q2,), S2(Q2, )
Same assumptions: no-subtraction dispersion relation
optical theorem
(low energy theorem)
• Generalized GDH Sum Rule
el v
dvvQGQS
),(4)(
212
1
Connecting GDH with Bjorken Sum Rules
• Q2-evolution of GDH Sum Rule provides a bridge linking strong QCD to pQCD• Bjorken and GDH sum rules are two limiting cases High Q2, Operator Product Expansion : S1(p-n) ~ gA Bjorken
Q2 0, Low Energy Theorem: S1 ~ 2 GDH
• High Q2 (> ~1 GeV2): Operator Product Expansion• Intermediate Q2 region: Lattice QCD calculations• Low Q2 region (< ~0.1 GeV2): Chiral Perturbation TheoryCalculations: HBPT: Ji, Kao, Osborne, Spitzenberg, Vanderhaeghen
RBPT: Bernard, Hemmert, Meissner
Reviews: Theory: Drechsel, Pasquini, Vanderhaeghen, Phys. Rep. 378,99 (2003)
Experiments: Chen, Deur, Meziani, Mod. Phy. Lett. A 20, 2745 (2005)
JLab E94-010 (Hall A)
Neutron spin structure moments and sum rules at Low Q2
• Q2 evolution of neutron spin structure moments
(sum rules) with pol. 3He
• transition from quark-gluon to hadron
• Test PT calculations
• Results published in several PRL/PLB’s
GDH integral on neutron
PRL 89 (2002) 242301 Q2
First Moment of g1p and g1
n :1p and 1
n
EG1b, arXiv:0802.2232 EG1a, PRL 91, 222002 (2003)
1p
Test fundamental understanding ChPT at low Q2, Twist expansion at high Q2, Future Lattice QCD
E94-010, from 3He, PRL 92 (2004) 022301 E97-110, from 3He, preliminaryEG1a, from d-p
1n
1 of p-n
EG1b, PRD 78, 032001 (2008)E94-010 + EG1a: PRL 93 (2004) 212001
Effective Strong Coupling
A new attempt at low Q2 Experimental Extraction from Bjorken Sum
s (Q) is well defined in pQCD
at large Q2. Can be extracted from data (e.g. Bjorken Sum Rule).
Not well defined at low Q2, diverges at QCD
The strong coupling constant from pQCD
...)58.3
1(6
)( 2)(111
ssAnpnp g
dxgg
Generalized Bjorken sum rule:
Definition of effective QCD couplings
G. Grunberg, PLB B95 70 (1980); PRD 29 2315 (1984); PRD 40 680(1989).
Prescription:Define effective couplings from a perturbative series truncated to the first term in
s.
tsHigherTwisg
dxgg ssAnpnp ...)
58.31(
6)( 2)(
111
)1(6
1)(
1 g
sAnp g
Use to define an effective s
g1.
Process dependent. But can be related through“Commensurate scale relations”
S.J. Brodsky & H.J Lu, PRD 51 3652 (1995)S.J. Brodsky, G.T. Gabadadze, A.L. Kataev, H.J Lu, PLB 372 133 (1996)
Extend it to low Q2 down to 0: include all higher twists.
Effective Coupling Extracted from Bjorken Sum
s/
A. Deur, V. Burkert, J. P. Chen and W. Korsch PLB 650, 244 (2007) and PLB 665, 349 (2008)
“Comparison” with theory
Furui & Nakajima
↔
Fisher et al.Bloch et al.Maris-TandyBhagwat et al. Cornwall
Godfrey-Isgur: Constituant Quark ModelFurui & Nakajima: Lattice
Schwinger
-Dyson
Transverse Spin (I): Inclusive
g2 Structure Function and Moments Burkhardt - Cottingham Sum Rule
g2: twist-3, q-g correlations• experiments: transversely polarized target
SLAC E155x, (p/d)
JLab Hall A (n), Hall C (p/d)
• g2 leading twist related to g1 by Wandzura-Wilczek relation
• g2 - g2WW: a clean way to access twist-3 contribution
quantify q-g correlations
1
21
21
22
22
22
22
),(),(),(
),(),(),(
x
WW
WW
y
dyQygQxgQxg
QxgQxgQxg
Precision Measurement of g2n(x,Q2): Search for Higher Twist Effects
• Measure higher twist quark-gluon correlations.• Hall A Collaboration, K. Kramer et al., PRL 95, 142002 (2005)
BC Sum Rule BC Sum Rule
P
N
3He
BC = Meas+low_x+Elastic
0<X<1 :Total Integral
very prelim
“low-x”: refers to unmeasured low x part of the integral. Assume Leading Twist Behaviour
Elastic: From well know FFs (<5%)
“Meas”: Measured x-range
Brawn: SLAC E155xRed: Hall C RSS Black: Hall A E94-010Green: Hall A E97-110 (preliminary)Blue: Hall A E01-012(very preliminary)
0)(1
0 22 dxxgΓ
BC Sum Rule BC Sum Rule
P
N
3He BC satisfied w/in errors for 3He
BC satisfied w/in errors for Neutron(But just barely in vicinity of Q2=1!)
BC satisfied w/in errors for JLab Proton2.8 violation seen in SLAC data
very prelim
BC Sum RuleBC Sum Rule
P
N
3He
Measured x 0<x<1
Unmeasured Low-X
“DIS” = -(RES+ELAS)
What can BC tell us about Low-X?
very prelim
Spin Polarizabilities
Higher Moments of Spin Structure Functions at Low Q2
Higher Moments: Generalized Spin Polarizabilities
• generalized forward spin polarizability 0
generalized L-T spin polarizability LT
dxxQgxQ
MxQgx
Q
M
dQQK
Q
x
TT
)],(4
),([16
),(),()
2
1()(
22
2
0 2
22
12
6
2
3
22
22
0
0
0
0
2
0
0
221
26
2
2
22
22
),(),([16
),(),()
2
1()(
x
LTLT
dxxQgxQgxQ
M
dQ
QQKQ
Neutron Spin Polarizabilities LT insensitive to resonance• RB ChPT calculation with resonance for 0 agree with data at Q2=0.1 GeV2 • Significant disagreement between data and both ChPT calculations for LT
• Good agreement with MAID model predictions
0 LT
Q2
Q2
E94-010, PRL 93 (2004) 152301
CLAS Proton Spin Polarizability
• EG1b, Prok et al. arXiv:0802.2232
Large discrepancies with ChPT!
Only longitudinal data, model for transverse (g2)
0 sensitive to
resonance
0p 0
p Q6
Summary of Comparison with PT
IAn 1
P 1n 1
p-n 0p 0
n LTn
Q2 (GeV2) 0.1 0.1 0.05 0.1 0.05 0.16 0.05 0.05 0.1 0.1
HBPT poor poor good poor good good good bad poor bad
RBPT/good fair fair fair good poor fair bad good bad
LT puzzle: LT not sensitive to , one of the best quantities to test PT,
it disagrees with neither calculations by several hundred %!
A challenge to PT theorists.
Very low Q2 data g1/g2 on n(3He) (E97-110)
g1 on p and d available soon (EG4)
Recently approved: g2 on proton E08-027
BC
Su
m R
ule
LT S
pin
Pola
riza
bili
ty
E08-027 : A- rating by PAC33K. Slifer, A. Camsonne, ,J. P. Chen
Septa Magnets for low Q2
Transverse bPolarized Proton Target
pg2 : central to knowledge of Nucleon Structure but remains unmeasured at low Q2
—Critical input to Hydrogen Hyperfine Calculations—Violation of BC Sum Rule suggested at large Q2
—State-of-Art PT calcs fail dramatically for LT
New Experiment: Proton g2 and LT
n
Color Polarizabilities
Higher Moments of Spin Structure Functions at High Q2
Color Polarizability (or Lorentz Force): d2
• 2nd moment of g2-g2WW
d2: twist-3 matrix element
d2 and g2-g2WW: clean access of higher twist (twist-3) effect: q-g correlations
Color polarizabilities are linear combination of d2 and f2
Provide a benchmark test of Lattice QCD at high Q2
Avoid issue of low-x extrapolation
Relation to Sivers and other TMDs?
1
0
22
21
2
1
0
22
22
222
)],(3),(2[
)],(),([3)(
dxQxgQxgx
dxQxgQxgxQd WW
Measurements on neutron: d2n (Hall A and SLAC)
d2(Q2) d2(Q2)
ProtonMAID Model
stat only
very prelim
GREEN: E97-110. (Hall A, 3He)
RED : RSS. (Hall C, NH3,ND3)
BLUE: E01-012. (Hall A, 3He)
BRAND NEW DATA!Very Preliminary
Neutron
d2(Q2) d2(Q2)
E08-027 “g2p”SANE
“d2n” just completed in Hall A
6 GeV Experiments
Sane: just completed in Hall C
“g2p” in Hall A, 2011
projected
Planned d2n with JLab 12 GeV
• Projections with 12 GeV experiments Improved Lattice Calculation (QCDSF, hep-lat/0506017)
Color “Polarizabilities”Color “Polarizabilities”
f2 Extraction and Color Polarizabilities• JLab + world n data, 4 = (0.019+-0.024)M2
• Twist-4 term 4 = (a2+4d2+4f2)M2/9
• extracted from 4 term f2 = 0.034+-0.005+-0.043
f2 can be measured from g3
• Color polarizabilities
= 0.033+-0.029 B = -0.001+-0.016
• Proton and p-n
f2= -0.160+-0.179 (p), -0.136+-0.109 (p-n)
PLB 93 (2004) 212001
Transverse Spin (II): Single Spin Asymmetries in SIDIS
Transversity and TMDs
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)
• It takes two chiral-odd objects to measure transversity• Semi-inclusive DIS
Chiral-odd distributions function (transversity) Chiral-odd fragmentation function (Collins function)
• TMDs: (without integrating over PT)
• Distribution functions depends on x, k┴ and Q2 : δq, f1T┴ (x,k┴ ,Q2), …
• Fragmentation functions depends on z, p┴ and Q2 : D, H1(x,p┴ ,Q2)• Measured asymmetries depends on x, z, P┴ and Q2 : Collins, Sivers, …
(k┴, p┴ and P┴ are related)
“Leading-Twist” TMD Quark Distributions
Quark
Nucleon
Unpol.
Long.
Trans.
Unpol. Long. Trans.
Current Status• Large single spin asymmetry in pp->X• Collins Asymmetries
- sizable for proton (HERMES and COMPASS) large at high x,- and has opposite sign unfavored Collins fragmentation as large as favored (opposite sign)? - consistent with 0 for deuteron (COMPASS)
• Sivers Asymmetries - non-zero for + from proton (HERMES), consistent with zero (COMPASS)? - consistent with zero for - from proton and for all channels from deuteron - large for K+ ?
• Very active theoretical and experimental study RHIC-spin, JLab (Hall A 6 GeV, CLAS12, HallA/C 12 GeV), Belle, FAIR (PAX)
• Global Fits/models by Anselmino et al., Yuan et al. and …
• First neutron measurement from Hall A 6 GeV (E06-010)
• Solenoid with polarized 3He at JLab 12 GeV Unprecedented precision with high luminosity and large acceptance
E06-010 Single Target-Spin Asymmetry in Semi-Inclusive n↑(e,e′π+/-) Reaction on a Transversely Polarized 3He Target
Collins
Sivers
First neutron measurement
7 PhD Students
Completed data taking in Feb.
Exceeded PAC approved goal
Hall-A Transversity: en→e’Xen→e’X
Polarized 3He: effective polarized neutron targetWorld highest polarized luminosity: 1036
New record in polarization: >70% without beam ~65% in beam and with spin-flip (proposal 42%)
HRSL for hadrons (p+- and K+-), new RICH commissioned
BigBite for electrons, 64 msr, detectors performing well
Cell: AstralCell: Astral Cell: MaureenCell: Maureen
Target PerformanceOnline preliminary
EPR/NMR analysis shows a stable 65% polarization with 15 A beam and 20 minute spin flip
Projections of g1T First Neutron (3He) MeasurementWith Fast Beam Helicity Flip (30Hz)Projected Uncertainties (Stat. Only):
2.3% at low x3.4% at high x
Precision Study of Transversity and TMDs
• From exploration to precision study• Transversity: fundamental PDFs, tensor charge• TMDs provide 3-d structure information of the nucleon• Learn about quark orbital angular momentum• Multi-dimensional mapping of TMDs
• 3-d (x,z,P┴ )
• Q2 dependence • Multi-facilities, global effort
• Precision high statistics• high luminosity and large acceptance
CHL-2CHL-2
Upgrade magnets Upgrade magnets and power suppliesand power supplies
Enhance equipment in Enhance equipment in existing hallsexisting halls
6 GeV CEBAF1112Add new hallAdd new hall
12 GeV Upgrade Kinematical Reach
• Reach a broad DIS region • Precision SIDIS for
transversity and TMDs• Experimental study/test of
factorization • Decisive inclusive DIS
measurements at high-x• Study GPDs
Solenoid detector for SIDIS at 11 GeV
GEMs
Proposed for PVDIS at 11 GeV
3-D Mapping of Collins/Siver Asymmetries at JLab 12 GeVWith A Large Acceptance Solenoid Detector
• Both + and -
• For one z bin
(0.5-0.6)
• Will obtain 4
z bins (0.3-0.7)
• Upgraded PID for K+ and K-
3-D Projections for Collins and Sivers Asymmetry (+)
Discussion• Unprecedented precision 3-d mapping of SSA
• Collins and Sivers• +, - and K+, K-
• Study factorization with x and z-dependences • Study PT dependence• Combining with CLAS12 proton and world data
• extract transversity and fragmentation functions for both u and d quarks• determine tensor charge• study TMDs for both valence and sea quarks • study quark orbital angular momentum
• Combining with world data, especially data from high energy facilities• study Q2 evolution
• Global efforts (experimentalists and theorists), global analysis• much better understanding of 3-d nucleon structure and QCD
Spin Structure with the Solenoid at JLab 12 GeV
• Program on neutron spin structure with polarized 3He and solenoid Polarized 3He target
effective polarized neutron highest polarized luminosity: 1036
A solenoid with detector package (GEM, EM calorimeter+ Cherenkov large acceptance: ~700 msr for polarized (without baffles) high luminosity and large acceptance
Inclusive DIS: improve by a factor of 10-100
A1 at high-x: high precision d2 at high Q2: very high precision parity violating spin structure g3/g5 : first significant measurement
SIDIS: improve by a factor of 100-1000 transversity and TMDs, spin-flavor decomposition (~2 orders improvement)• Unpolarized luminosity: 5x1038 , acceptance ~ 300 msr (with baffles)
Parity-Violating DIS Boer-Mulders function
Single Spin Asymmetries in (Qausi-)Ealstic
Two-photon Exchange and GPDs
E05-015: Target Single Spin Asymmetry Ay
• Inclusive quasi-elastic electron scattering on vertically polarized 3He target
•Target Single Spin Asymmetry Ay=0 in one-photon approximation, two-photon exchange gives non-zero Ay.
• Elastic contribution is well-known, inelastic response provides a new way to access the Generalized Parton Distributions.
E05-015 Projection
• Neutron data provide unique new constraints on GPDs.
• Measurements at Q2=0.5, 1.0 GeV2
(and 2 GeV2).
• GPD model prediction and expected uncertainty (~2x10-3) at Q2=1.0 GeV2.
• Data taken competed two weeks ago, exceeded approved goal.
•First clear non-zero asymmetry measurement @ 10level Established quantitatively the 2-photon-exchange mechanism. Established it as a tool to precisely probe hadron structure.
Blue curve = elastic contrib.Black curve = inelastic contrib.Red point = total contrib.
Summary
• Spin structure study full of surprises and puzzles• A decade of experiments from JLab: exciting results
• valence spin structure, quark-hadron duality • spin sum rules and polarizabilities• test PT calculations, ‘LT puzzle’• precision measurements of g2/d2: high-twist• first neutron transversity measurement• first quasi-elastic target SSA: 2-photon to probe GPDs
• JLab played a major role in recent experimental efforts • shed light on our understanding of STRONG QCD • lead to breakthrough?
• Bright future• complete a chapter in spin structure study with 6 GeV JLab• 12 GeV Upgrade will greatly enhance our capability • Goal: a full understanding of nucleon structure and strong interaction