Transcript Hadronic Physics at Jefferson Lab Volker D. Burkert Jefferson Lab GPDs with CLAS12 O In C P m D G S A B C Electromagnetic NN* Excitations, USC, August 13-15, 2012 Page 1

Hadronic Physics at Jefferson Lab
Volker D. Burkert
Jefferson Lab
GPDs with CLAS12
O
In
C
P
m
D
G
S
A
B
C
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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The hadron structure program at JLab
 The multi-dimensional structure of the nucleon –
from form factors and PDFs to GPDs and TMDs
 Quark confinement and the role of the glue in
meson and baryon spectroscopy.
 The strong interaction in nuclei – evolution of
quark hadronization, nuclear transparency of
hadrons.
 Search for science beyond the Standard Model.
Much of this program requires energies > 6 GeV
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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The CEBAF LargeHall
Acceptance
Spectrometer (CLAS)
B - CLAS12
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Hall B - CLAS12
• Show full installation
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Studying hadronic systems with em probes
energy &
resolution
of probe
π
N
low
q
Using electron beams with tunable resolution as
a clean probe allows us to address one of the
central questions of hadronic physics:
What are the relevant degrees of freedom at
varying distance scale and what do they reveal
about the nucleon structure?
→ Nucleon and mesons
→ Constituent quarks and q-qbar pairs
→ Elementary quarks and gluons
DIS experiments using e.m. probes at high
energies study the short distance behavior.
high
Today we know that a large portion of the
nucleon spin is not probed in DIS experiments
alone.
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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5
N* spectrum in LQCD
The physics encoded in the nucleon excitation spectrum spans degrees of freedom
from meson-baryon and dressed quarks to elementary quarks and gluons.
R. Edwards, J. Dudek,
D. Richards, S. Wallace,
PRD84 (2011) 074508
mπ=396MeV
LQCD predicts states with the same quantum numbers as
the CQM with underlying SU(6)xO(3) symmetry.
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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SU(6)xO(3) Classification of Baryons
Missing
states
P13
- Search for these states is major program at JLab involving large
amounts of x-section and polarization data.
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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CLAS results γp→K+Λ → K+pπBonn-Gatchina Coupled Channel Analysis, A.V. Anisovich et al, EPJ A48, 15 (2012)
(Includes nearly all new photoproduction data)
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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First new N* states in PDG 2012
BnGa energy-dependent coupled-channel PWA of CLAS K+Λ and other data.
S11(1895)
D13(1875)
D13(2080)
D15(2060)
P11(1880)
P13(1900)
F15(2000)
mπ=396MeV
Photoproduction allows us to identify new states but tells us little about their nature.
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Electrocouplings of resonances
nrQM
One example: The Roper resonance P11(1440)
LC QM
q3+Nσ
q3G
LCQM:
S. Capstick and B. Keister, Phys. Rev. D51, 3598 (1995)
I.G. Aznauryan, Phys.Rev.C76, 025212 (2007)
L.T. Obukhovsky et al., Phys.Rev. D84, 014004 (2011)
• A1/2 has zero-crossing near Q2=0.5, becomes dominant amplitude at high Q2.
• Eliminates gluonic excitation (q3G) as a dominant contribution.
• Consistent with radial excitation at high Q2 and large meson-baryon coupling at small Q2.
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Nucleon resonance transitions at 12 GeV
- Probe quark mass dependence on momentum transfer
- Transition form factors are sensitive to the running effective quark mass.
I. Aznauryan, V.Burkert, Phys.Rev. C85 (2012) 055202
quark mass (GeV)
accessible
at 6 GeV
LQCD
DSE
E12-09-003
accessible
at 12 GeV
CLAS12 projected
At 12 GeV we probe the transition from dressed quarks to elementary quarks.
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Figure 1: (From Fig. 9 of [1]) HERA combined NC e+ p reduced cross sectio
function of Q2 . The error bars indicate the total experimental uncertainty. The H
x = 0.0032, i=12
x = 0.005, i=11
posed.
The bands represent the total uncertainty of the fit. Dashed lines are show
x = 0.008, i=10
x = 0.013, i=9
in the
QCD
analysis.
x = 0.02, i=8
+
s
x = 0.0008, i=15
x = 0.0013, i=14
x = 0.0020, i=13
10
nctions
4
Gao
Deep-inelastic scattering and partonHaiyan
distributions
10 3
10 2
x = 0.032, i=7
x = 0.05, i=6
x = 0.08, i=5
10
x = 0.13, i=4
10
10 7
10
10 6
10
5
10 4
10
x = 0.65, i=0
1
10
10
2
10
3
10
4
10
x = 0.0032, i=12
x = 0.005, i=11
x = 0.008, i=10
3
10-4
H1 and ZEUS
x = 0.02, i=8
Q2 = 1.9 GeV 2
x = 0.032, i=7
10
-3
10-2
exp. uncert.
x = 0.08, i=5
model uncert.
x = 0.13, i=4
parametrization uncert.
0.6
-3
1
10
10
2
10-4
10
3
10
-3
10
4
10-2
10
5
2
xuv
xg (´ 0.05)
v
0.2
xg (´ 0.05)
xS ( ´ 0.05)
0.2
10
-3
3
10-1
Q / GeV
param
one third
0.4 of the total spin of the nucleon. Motivated by the EMC result, t
xd
experimental
and theoretical investigation
have resulted in a great deal of k
xS ( ´ 0.05)
x = 0.65,
xg (i=0
´ 0.05)
xS (´ 0.05)
parametrization uncert.
0.6
x = 0.40, i=1 xdv
0.2
-2
mode
0.4
PoS(ICH
10
0.4
2
exp. u
0.6
10-4
1
model uncert.
x = 0.25, i=2
-1
x
2
xuv
x = 0.18, i=3
1
10-1
H1 and ZEUS
1
HER
= 10 parton
GeV
Figure 2: (From Fig. 18 of [1]) QThe
distribution functions from HE
2
2
2
2x(Ũ + D̃),
xg, at Q = 1.9
GeV (left) and Q = 10 GeV2 (right). The gluon and
HERAPDF1.0
0.8
exp. uncert.
down by a factor 20. The experimental, model and parametrization uncertaintie
x = 0.05,
i=6
HERAPDF1.0
10
10
xf
2
1
0.8
10
xuv
parametrization uncert.
5
H1 an
1
0.8
exp. uncert.
model uncert.
-3
+
2
HERAPDF1.0
0.8
-2
x = 0.013, i=9
10
Q = 1.9 GeV
x = 0.40, i=1
xf
xf
2
0.6
HERA I NC e p
2
2
Q / GeV
Fixed Target
HERAPDF1.0
0.4
1: (From Fig. 9 of [1]) HERA combined NC e+ p reduced
cross section and fixed-target
data as a
xdv
2
function of Q . The error bars indicate the total experimental uncertainty. The HERAPDF1.0 fit is superimx = 0.0008, i=15
The bands represent the total uncertainty of the fit. Dashed
lines are shown for Q 2 values not included
0.2
x = posed.
0.0013, i=14
xg (´ 0.05)
xS
(´ 0.05)
x = the
0.0020,
i=13 analysis.
in
QCD
xf
+
x = 0.25, i=2
-1
x = 0.00005, i=21
x = 0.00008, i=20
x = 0.00013, i=19
x = 0.00020, i=18
Figure
x = 0.00032, i=17
x = 0.0005, i=16
2
sr,NC(x,Q ) x 2
i
H1 and ZEUS
1
PoS(ICHEP 2010)538
10
H1 and ZEUS
x = 0.18, i=3
1
x
2
1
10-4
10
-3
10-2
10-1
x
1
Valence quarks and gluon contributions to
proton momentum are well determined.
g. 9 of [1]) HERA combined NC e p reduced cross section and fixed-target data as a
Electromagnetic NN* Excitations, USC, August 13-15, 2012
Page 12
error bars indicate the total experimental uncertainty. The HERAPDF1.0 fit is superimFigure 2: (From Fig. 18 of [1]) The parton distribution functions from HERAPDF1.0, xu v , xdv , xS =
2x(Ũ + D̃), xg, at Q2 = 1.9 GeV2 (left) and Q2 = 10 GeV2 (right). The gluon and sea distributions are scaled
down by a+factor 20. The experimental, model and parametrization uncertainties are shown separately.
Polarized parton distribution functions
V. Darmawardane, et al., PLB641:11-17,2006
Y. Prok, et al., PLB672:12-16, 2009
JLab
domain
Similar data on the neutron (deuteron)
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Saturation of the effective αs
Γ1(p-n) = gA/6[1-αs(Q2)/π + ..]
A. Deur, et al., PLB 665, 2008, 349
Tests of χPT, pQCD + OPE, phenomenological models.
 The saturation of the strong coupling at large distances is a necessary condition
for the application of AdS/QCD correspondence in analytical calculation of nonperturbative processes.
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Photon asymmetry A1p & A1n in DIS
Proton
CLAS
Neutron
Hall A
Hyperfine
perturbed QM
World data parameterized
at Q2=10 GeV2
Need data extending to larger x
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Δu+Δu and Δd+Δd quark distribution functions
• Δu/u shows clear trend
towards +1(as expected
from pQCD)
• Δd/d remains negative
and shows no clear
trend towards +1
• Solid curves show
effect of orbital angular
momentum
H. Avakian, S. Brodsky, A. Deur, F.
Yuan, PRL 99 (2007) 082001
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Proton spin decomposition
Proton spin decomposition:
Jp = ½ΔΣ + Lq + ΔG + Lg
What do we know about the individual contributions?
• Quark helicity: ΔΣ~25-30%
• Gluon helicity contributions are small ΔG << ΔΣ ?
 Orbital angular momentum contribution to proton spin must
be large, i.e. Lq + Lg > 50%
 Need independent data on ΔG(x)
 Need first data on Lq (x)
Latest LQCD: ΔΣ~25%, ΔG+Lg ~ 25%, Lq ~50%
K.F. Liu et al., arXiv:1203.6388
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Parton spin structure functions at 12GeV
Precise information on g1(x,Q2) with SIDIS flavor tag strongly
reduces uncertainties in quark helicity distributions. The Q2
dependence and evolution provides model-independent xΔG(x).
Improved PDFs from NLO analyses
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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The neutron F2n(x) structure function
Previous DIS data taken on
hydrogen and deuterium
have large uncertainties at
high x due to uncertainties
in nuclear corrections.
d(x)/u(x) poorly constrained at x > 0.5 due to uncertainty in nuclear corrections
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Neutron structure and quark distributions
F2n/F2p ratio by tagging almost unbound neutrons using
detection of low momentum protons in a radial TPC.
N. Baille et al. (CLAS), Phys.Rev.Lett. 108 (2012) 199902
e-D→e-psX
n
Δ
N(1680)
N(1520)
ee-
n
p
ps >70MeV/c
BONUS Detector
5 Tesla
mag. field
First model-independent measurement of F2n/F2p and F2n
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Neutron structure function F2n(x) and d/u
Projected d /u Accuracy
!
Data taking of 35 days on D2
and 5 days on H 2
with L = 2 ! 10 34 cm-2 sec-1
!
Open squares represent data
points for W *> 1.8 GeV
F2n
1+4d/u
≈
4+ d/u
F2p
JLab@12GeV
Stephen Bü
Bültmann - ODU
BoNuS12, JLab PAC 36, August 2010
With 12 GeV d/u can be determined up to x~0.85.
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Wigner Function - GPDs and TMDs
(Quantum phase-space quark distribution in the nucleon)
A. Belitsky, X. Ji, F. Yuan,
PRD69 (2004) 074014
Integrate over
spatial dimensions
Transverse Momentum-dependent
Distributions (TMD)
3D imaging of the nucleon
in momentum space
Integrate over
momentum space
Generalized Parton
Distributions (GPD)
3D nucleon imaging in transverse
coordinate and longitudinal
momentum space.
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Accessing GPDs through DVCS
GPDs in leading twist depend on 3 variables, e.g. E(x, x, t).
They probe the quark structure at the amplitude level.
Deeply Virtual Compton Scattering (DVCS)
hard vertices
x+x
g
x-x
x
t
Electromagnetic NN* Excitations, USC, August 13-15, 2012
x – longitudinal quark
momentum fraction
2x – longitudinal
momentum transfer
xB
x ≈
2-xB
–t – Fourier conjugate
to transverse impact
parameter
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A path towards extracting GPDs
+ - 

A = +
=
2
 + -
ξ ~ xB/(2-xB)
k = t/4M2
Polarized beam, unpolarized target:
~
LU ~ sin {F1H + ξ(F1+F2)H +kF2E}d
H(ξ,t)
Unpolarized beam, longitudinal target:
~
UL ~ sin {F1H+ξ(F1+F2)(H +ξ/(1+ξ)E)}d
~
H(ξ,t)
Unpolarized beam, transverse target:
E(ξ,t)
UT ~ cossin(s-){k(F2H – F1E)}d
Unpolarized total cross section:
Separates h.t. contributions to DVCS
Electromagnetic NN* Excitations, USC, August 13-15, 2012
Re(TDVCS)
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~
First extraction of GPDs H, H at 6 GeV
Beam asymmetry
F.X. Girod et al. (CLAS), Phys.Rev.Lett100:162002,2008
Long. Target asymmetry
S. Chen et al. (CLAS), Phys.Rev.Lett97:072002,2006
Compton FF
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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ALU projections for JLab@12GeV
~
LU ~ sin {F1H + ξ(F1+F2)H +kF2E}d
ALU
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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ALU projections for protons
Ee = 11 GeV
0.3
0.2
epg
Q2=5.5GeV2
xB = 0.35
-t = 0.25 GeV2
sinφ
ep
0.1
0
-0.1
-0.2
-0.3
, GeV2
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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E(Q2,x,t) and H(Q2,x,t) from projected DVCS
Input: VGG model GPD parameterizations (Phys.Rev. D60 (1999) 094017)
Full CLAS12 acceptance simulation and event reconstruction for all 3
polarization observables and diff. cross section.
Output: Reconstructed CFF/GPDs in twist-2 approximation
t-dependence allows determination of quark densities in
transverse impact parameter space through Fourier transform
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Projected quark densities in impact parameter.
 Fourier transform of GPDs
give access to the quark
densities distribution in
impact parameter space.
 GPD E probes the quark
flavor separation in impact
parameter space.
 2nd x-moment of GPD E
probes quark orbital angular
momentum
 All other CFF/GPDs
extracted from same data.
Contribution of H+E
Contribution of E
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Transverse Momentum Dependent Distributions (TMDs)
• TMDs are complementary to GPDs in that they allow us
to construct 3-D images of the nucleon in momentum
space
• TMDs are connected to quark orbital motion – for a TMD
to be non-zero orbital angular momentum must be
present.
• TMDs can be studied in SIDIS experiments measuring
azimuthal asymmetries.
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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1.1
Spin and A zimut hal A symm et r ies in SI D I S
SIDIS and Transverse
Distribution
The SIDIS cross sect ionMomentum
at leading twist has eight contributions
related to differen
nations of the polarization st ate of t he incoming lept on and the target nucleon [35,
The lepton-hadron
sect ion
then be
paramet rized as [3]
SIDIS crosscross
section
in can
leading
twist:
dσ
α2
y
=
2
dx dy dz dφS dφh dPh⊥
xQ2 2(1 − ε)
×
h
FU U,T + ε cos(2φh ) FUcos2φ
+ SL ε sin(2φh ) FUsinL 2φh
U
√
sin(φ − φS )
+ SL λ e 1 − ε2 FL L + |ST | sin(φh − φS ) FU T,T h
sin(φh + φS )
+ ε sin(φh + φS ) FU T
+ |ST | λ e
√
cos(φh − φS )
1 − ε2 cos(φh − φS ) FL T
sin(3φh − φS )
+ ε sin(3φh − φS ) FU T
,
The 8 structure functions factorize
TMDfine
parton
distributions,
fragmentation
and hard parts:and transvers
where αinto
is the
st ruct
ure constant
and ε thefunctions,
ratio of longitudinal
flux,
Integrals over
1 − y transverse
ε=
.
momentum
and
1 − y +ofy2initial
/2
The kinematic variables x, y are scattered
defined as: parton
x = Q2/ 2(P1q), and y = (P1q)/ (P1
variable q = k1 − k2 is the momentum of t he virtual phot on, Q2 = − q2, φh is t he a
A full program to extract L.T. TMDs
measurements
separation
of the
function
using moment
polarization,
anglefrom
between
t he scat requires
tering plane
formed
bystructure
t he init ial
and final
a of t he
2
and coverage of a large range in x, z, PT along with sensitivity to Q , and the flavor separation in u, d, s quarks.
and t he production plane formed by the transverse momentum of t he observed ha
the virtual photon (see Fig. 1), and φS is the azimuthal angle of the transvers
NN* Excitations, USC, August 13-15, 2012
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the Electromagnetic
scattering plane.
The subscripts in FU L , FL L ,etc.,
specify t he beam (first in
TMD Program @ 12 GeV with CLAS12
e’
p,K
Leading twist TMD parton distributions:
information on correlations between
quark orbital motion and spin
e
E12-06-112: Pion SIDIS
E12-09-008: Kaon SIDIS
E12-07-107: Pion SIDIS
E12-09-009: Kaon SIDIS
E12-11-111: Pion SIDIS
Kaon SIDIS
Nucleon polarization
Quark spin polarization
Complete program of TMDs studies for pions and kaons
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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AUU for pions on proton target
E12-06-112
Measures momentum distribution of trans. pol. quarks in unpol. nucleon
4 <Q2< 5 GeV2
Wide x and PT range needed to map out phase space in longitudinal and transverse quark momentum
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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GPDs & TMDs: Spatial & orbital imaging
dX(x,b )
T
Eq(x, )
uX(x,b )
T
T
T
∫
Target polarization
TT
(x,b ) =
d2 i b
(2p)2 e
T
Cat scan of the
human brain
Flavor dipole
Electromagnetic NN* Excitations, USC, August 13-15, 2012
Shift
depends
on (x,b )
T
TMDs extend
the image to
include quarks
orbital motion.
Page 34
Summary
• JLab and the 12GeV energy upgrade address many open topics in hadronic
physics
– The nucleon resonance spectrum
– High Q2 studies that probe the transition from dressed quark d.o.f. to
elementary quarks
– Precision measurements of quark spin and gluon spin-dependent
distribution function to clarify proton spin decomposition
– Model-independent measurement of d(x)/u(x) at large x
– Study GPDs for spatial imaging in polarized DVCS and TMDs for orbital
imaging in polarized SIDIS
• Many more topics not discussed
– hybrid mesons
– precision measurements of the proton weak charge
– heavy photon search and dark matter
– QCD in nuclei
– ……
Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Electromagnetic NN* Excitations, USC, August 13-15, 2012
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Hybrid Baryons Spectrum in LQCD
J.J. Dudek, R.G. Edwards, arXiv:1201.2349
1.3GeV
N
regular states
Electromagnetic NN* Excitations, USC, August 13-15, 2012
hybrid states
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