QCD Evolution and TMD/Spin Experiments
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Transcript of QCD Evolution and TMD/Spin Experiments
QCD Evolution and TMD/Spin Experiments
J. P. Chen, Jefferson LabQCD Evolution Workshop, May 14-17, 2012
Introduction
SIDIS Transverse Experiments: Transversity and TMDs
Q2 Dependence of the Moments of Spin Structure Functions
Evolution and High-Twists
Experiments < -- > Theory (QCD)• Quarks/Gluons are fundamental degrees of freedom in QCD but they are confined in hadrons
experimental observables are on hadrons
• Hard process (factorization)example: DIS at high Q2
simplify situation to allow extraction of information on quarks/gluons • Observable depending on probing scale: Q2
power dependence (twists)logarithmic dependence (evolution)
• Initial exploration (discovery?) to precision study (full understanding?)
Unpolarized DIS: Discovery of Quarks (Partons)
J.T. Friedman R. Taylor H.W. Kendall
Nobel Prize 1990
Callan-Gross
relation:
Bjorken Scaling:
Point particles cannot be further resolved; their measurement
does not depend on wavelength, hence Q2,
Spin-1/2 quarks cannot absorb longitudinally polarized vector
bosons and, conversely, spin-0 (scalar) quarks cannot absorb
transversely polarized photons.
Unpolarized Structure Function F2
• Bjorken Scaling
• Scaling Violation
• Gluon radiation – QCD evolution
NLO: Next-to-Leading-Order
• One of the best experimental tests of QCD
Polarized DIS - Surprises with Spin
The sum of Quark Spins contribute little to the proton spin, and strange quarks are negatively polarized.
EMC: J.Ashman et al, Nucl. Phys. B328 (1989) 1
Polarized Structure functions
HERMES Collins/Sivers asymmetry data
Transverity2011 Franco Bradamante
COMPASS Sivers asymmetry 2010 datax > 0.032 region - comparison with HERMES results
NEW
NEW
JLab 12 GeV Projections: Map Collins and Sivers asymmetries in 4-D (x, z, Q2, PT):
Transverse Spin and TMDs
SIDIS Experiments with a Transversely Polarized Target
Leading-Twist TMD PDFs
f1 =
f 1T =
SiversSivers
HelicityHelicity
g1 =
h1 =TransversityTransversity
h1 =
Boer-MuldersBoer-Mulders
h1T =
PretzelosityPretzelosity
h1L =
Worm GearWorm Gear
: Survive trans. Momentum : Survive trans. Momentum integrationintegration
Nucleon Spin
Quark Spin
g1T =
Worm GearWorm Gear
Leading-Twist TMD PDFs
f1 =
f 1T =
SiversSivers
HelicityHelicityg1 =
h1 =TransversityTransversity
h1 =
Boer-MuldersBoer-Mulders
h1T =
PretzelosityPretzelosity
g1T =
Worm GearWorm Gear
h1L =
Worm GearWorm Gear
: Probed with transversely pol targetNucleon Spin
Quark Spin
Status of Transverse Spin Study • Large single spin asymmetry in pp->X (Fermi Lab, RHIC-spin)• Collins Asymmetries - sizable for the 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 the deuteron (COMPASS)• Sivers Asymmetries - non-zero for + from proton (HERMES), new COMPASS data - consistent with zero for - from proton and for all channels from deuteron - large for K+ ?• Collins Fragmentation from Belle• Global Fits/models: Anselmino, Prokudin et al., Vogelsang/Yuan et al.,
Pasquini et al., Ma et al., Gamberg et al.…• Very active theoretical and experimental efforts
Many workshops/conferences to discuss TMDs with QCD, evolution, … RHIC-spin, JLab (6 GeV and 12 GeV), Belle, FAIR, J-PARC, EIC, …• First neutron measurement from Hall A 6 GeV (E06-010)• SoLID (and CLAS12, …) with polarized 3He/p at JLab 12 GeV Unprecedented precision with high luminosity and large acceptance
Separation of Collins, Sivers and pretzelocity effects through angular dependence
1( , )
sin( ) sin( )
sin(3 )
l lUT h S
h SSiverCollins
Pretzelosi
UT
tyU
sUT h S
h ST
N NA
P N
A
A
N
A
1
1 1
1
1 1
sin( )
sin(3 )
sin( )Co
PretzelosityU
SiversUT
llins
T h S T
h S
UT
UT h S
TU
UT
TA
H
f
A
D
A h H
h
E06 010 Experiment‑Spokespersons: Chen/Evaristo/Gao/Jiang/Peng
• First measurement on n (3He)• Polarized 3He Target• Polarized Electron Beam, 5.9 GeV
– ~80% Polarization– Fast Flipping at 30Hz
• BigBite at 30º as Electron Arm– Pe = 0.7 ~ 2.2 GeV/c
• HRSL at 16º as Hadron Arm– Ph = 2.35 GeV/c – Excellent PID for /K/p
• 7 PhD Thesis Students (All graduated)
15
Beam Polarimetry(Møller + Compton)
LuminosityMonitor
XeeHe ),(3
E06-010 3He Target Single-Spin Asymmetry in SIDIS
3He Sivers SSA:negative for π+,
3He Collins SSA small Non-zero at highest x for +
Blue band: model (fitting) uncertainties Red band: other systematic uncertainties
X. Qian, et al. PRL (2011) 107:072003 (2011)
Neutron Results with Polarized 3He from JLab
Collinsasymmetries are not large, except at x=0.34
Sivers negative
Blue band: model (fitting) uncertainties Red band: other systematic uncertainties
X. Qian at al., PRL 107:072003(2011)
Asymmetry ALT Result
• 3He ALT : Positive for -
hq
qTLT DgFA shsh
11)cos()cos(
LT
To leading twist:
J. Huang et al., PRL. 108, 052001 (2012).
• – Corrected for proton dilution, fp
– Predicted proton asymmetry contribution < 1.5% (π+), 0.6% (π-)
•
– Dominated by L=0 (S) and L=1 (P) interference
• Consist w/ model in signs, suggest larger asymmetry
Neutron ALT Extraction
hq
qT
n DgA 11LT Trans-helictiy
JLab 12 GeV Era: Precision Study of TMDs
• From exploration to precision study with 12 GeV JLab• Transversity: fundamental PDFs, tensor charge• TMDs: 3-d momentum structure of the nucleon Quark orbital angular momentum• Multi-dimensional mapping of TMDs
• 4-d (x,z,P┴,Q2)
• Multi-facilities, global effort
• Precision high statistics• high luminosity and large acceptance
SIDIS with SoLID
12 GeV: Mapping of Collins/Siver Asymmetries with SoLID
• Both + and -
• For one z bin
(0.4-0.45)
• Will obtain many z bins (0.3-0.7)
• Tensor charge
E12-10-006 3He(n), Spokespersons: J. P. Chen, H. Gao, X. Jiang, J-C. Peng, X. QianE12-11-007(p) , Spokespersons: K. Allda, J. P. Chen, H. Gao, X. Li, Z-E. Mezinai
Map Collins and Sivers asymmetries in 4-D (x, z, Q2, PT)
Expected Improvement: Sivers Function
• Significant Improvement in the valence quark (high-x) region• Illustrated in a model fit (from A. Prokudin)
f 1T =
E12-11-107: Worm-gear functions (“A’ rating: )
Spokespersons: Chen/Huang/Qiang/Yan
• Dominated by real part of interference between L=0 (S) and L=1 (P) states
• No GPD correspondence• Lattice QCD -> Dipole Shift in mom. space.
• Model Calculations -> h1L =? -g1T
.
h1L =
g1T =
Longi-transversityTrans-helicity
Cent
er o
f poi
nts:
)()(~ 11 zDxgA TLT )()(~ 11 zHxhA LUL
Discussion• Unprecedented precision 4-d mapping of SSA
• Collins and Sivers• +, - and K+, K-
• New proposal polarized proton with SoLID• Study factorization with x and z-dependences • Study PT dependence• Combining with the 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• study Q2 evolution
• Global efforts (experimentalists and theorists), global analysis• much better understanding of multi-d nucleon structure and QCD
• Long-term future: EIC to map sea and gluon SSAs
Moments of Spin Structure Functions
Q2 Dependence, Evolution and Higher-Twists
Higher-Twist Extraction from Data
MRST, unpolarized PDF H-T coefficients
LSS, polarized PDF (NLO) H-T coefficients
First Moment of g1p/g1
n:1p /1
n
EG1b, arXiv:0802.2232 EG1a, PRL 91, 222002 (2003)
1p
Total quark contribution to nucleon spin (at high Q2)
Twist expansion at intermediate Q2, LQCD, ChPT at low Q2
E94-010, PRL 92 (2004) 022301 E97-110, preliminary, EG1a, from d-p
1n
Bjorken Sum: 1 of p-n
EG1b, PRD 78, 032001 (2008)E94-010 + EG1a: PRL 93 (2004) 212001
Higher Twist (Twist-4 f2) Extraction Color Polarizabilities/Lorentz Force
• JLab + world neutron 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
• Color polarizabilities/Lorentz force
= 0.033+-0.029 B = -0.001+-0.016
• Proton and p-n (A. Deur)
f2= -0.160+-0.028+-0.109 (p),
-0.101+-0.027+-0.067 (p-n)
PLB 93 (2004) 212001
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)
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)
1 resonance comparison with pdfspartial moments
Second Spin Structure Function g2
d2: Color Polarizability/Lorentz Force Burkhardt - Cottingham Sum Rule
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)
Color Polarizability /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
d2 on neutron
E01-012
d2(Q2)
E08-027 “g2p”SANE
“d2n” new in Hall A
6 GeV Experiments
Sane: new in Hall C
“g2p” in Hall A, running now
projected
Burkhardt - Cottingham 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 (preliminary)
0)(1
0 22 dxxgΓ
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
Results on 2n : E01-012 and E94-010
Higher-Twist Extraction and Comparison
Extract Higher-Twist part of 2DIS
Compare with higher-twist estimated from E97-103 data
E08-027 : Proton g2 Structure Function Fundamental spin observable has never been measured at low or moderate Q2
BC Sum Rule : violation suggested for proton at large Q2, but found satisfied for the neutron & 3He.
Spin Polarizability : Major failure (>8 of PT for neutron LT. Need g2 isospin separation to solve.
Hydrogen HyperFine Splitting : Lack of knowledge of g2 at low Q2 is one of the leading uncertainties.
Proton Charge Radius : also one of the leading uncertainties in extraction of <Rp> from H Lamb shift.
BC
Su
m R
ule
Spokespersons: Camsonne, Chen, Crabb, Slifer(contact), 6 PhD students, 3 postdocs
Running until 5/18/2012
Sp
in P
ola
riza
bili
ty
LT
Summary
• Study quark-gluon structure of nucleon depends on probing scale Q2 Q2 dependence provides valuable information on QCD dynamics
• TMD study from exploration to precision: Q2 evolution critical• Q2 dependence of moments of spin structure g1/g2:
• study higher-twists• precision measurements of g2 and d2: twist-3• Extraction of f2: twist-4
d2/f2 E, B : Color polarizabilities/Lorentz forces
Announcements
End-of-run (g2p experiment in Hall A) party this afternoon 3-5 pm at CEBAF Center Atrium
KITPC (Kavli Institute for Theoretical Physics China ) Program onNucleon structure (QCD and Hadron Physics)
July 2- 20, 2012, Beijing, China http://kitpc.itp.ac.cn/program.jsp?id=PF20120611 The last week (7/16-7/20) will be for The 4th Workshop on Hadron Physics in China and Opportunities in US
http://www.ciae.ac.cn/eng/hadron2012/index.htm
The 7th International Workshop on Chiral Dynamics August 6-10, 2012, JLab http://www.jlab.org/conferences/CD12/