Overview of Medium Energy Physics (“Cold QCD”):
Presentation to the Hadron Physics Town Meeting
(Presentation to the 2007 NSAC Long Range Plan Implementation Subcommittee)
Roy J. Holt
Newport Beach, CA
25 October 2012
Key questions in hadron physics

What is confinement and how is it connected with
dynamical chiral symmetry breaking, the origin of
more than 98% of visible mass in the Universe?
– What are the dynamics underlying elastic and transition
form factors and structure functions of hadrons? How
does valence quark structure affect the sea?
– Where is the missing spin in the nucleon? Are there
significant contributions from gluons or valence quark
orbital angular momentum?
– Can we reveal a novel landscape of nucleon substructure
through measurements of new multidimensional
distribution functions?
– Do gluonic excitations have a role in the spectroscopy of
light mesons and baryons?

How do nuclei emerge from QCD?
– What is the relation between short-range N-N
correlations and the partonic structure of nuclei?
Argonne National Laboratory
2
Elastic electron scattering from a nucleon
j=<e’||e>
J=<p’||p>
Deep inelastic
scattering
Nucleon vertex:
i  q ν
2
  p, p'    F (Q ) 
F (Q2)
1
2
2M
Dirac
1990 Nobel Prize
Pauli
Cross section for scattering
from a point-like object
Form factors describing
nucleon shape/structure
1961 Nobel Prize
Argonne National Laboratory
3
Tremendous advances in electron scattering
Unprecedented capabilities:
• High Intensity
• High Duty Factor
• High Polarization- M. Poelker
(2012 Lawrence Award)
• Large acceptance detectors
• State-of-the-art polarimetry,
polarized targets
Focal plane polarimeter
Polarized 3He target
– Jefferson Lab
Argonne National Laboratory
4
The proton form factor: Re-wrote the textbooks
Polarization measurements )
Revolutionized our knowledge

NP2010
Two-photon experiments: OLYMPUS (DESY), JLab, Novosibirsk
Argonne National Laboratory
proton
neutron
5
Flavor separation of proton form factors
Q4F2q/k
Cates, de Jager,
Riordan, Wojtsekhowski,
PRL 106 (2011) 252003
Q4 F1q
NSAC milestone HP4 (2010) completed

Very different behavior for u & d quarks

Evidence for diquark correlations – axial diquark -> soft f.f.
Thanks to Craig Roberts
6
Only JLab 12 GeV can access these form factors to ~10 GeV2
Locations of the zeroes depend on the relative probability of finding scalar & axial diquarks in proton
Plot credit: JLab whitepaper
Argonne National Laboratory
Requires SBS
Six 12-GeV experiments
7
Proton Radius Puzzle
7
PSAS 2012 Symposium
ECT* Workshop - Nov. 2012
rp≅0.8768(69)fm (ep atom)
rp≅0.8772(46)fm (ep scattering)
rp=0.84184(67)fm (μp atom)
X. Zhan et al, PLB 705 (2011) 59
Argonne National Laboratory
Future sub 1% measurements:
(1) ep elastic scattering at JLab
(2) μp elastic scattering at PSI - 16 U.S. institutions!
(~$2 M, no contingency)
Thanks to R. Gilman, H. Gao
8
Hadron polarizabilities – Compton scattering
“Faraday
effect”
HIS projection
D. Shukla, A. Nogga,
D. Phillips, PRL (2007)


High Intensity Gamma Source (HIS)
– Proton, neutron – polarized H target
– Polarized 3He target (9 U.S. institutions)
MAMI (3 U.S. institutions)
– Polarized hydrogen target + Crystal Ball
– Complete proton in 2014, begin neutron
 Lattice calculations
 Chiral perturbation theory
Interplay of “pion cloud” and
shorter distance effects

Thanks to H. Gao, H. Griesshammer, D. Phillips, W. Briscoe, R. Miskimen, B. Norum
Pion polarizability
– COMPASS –II (CERN)
(UIUC)
Argonne National Laboratory
9
Partonic structure of the nucleon
hadronic
leptonic
Structure function
Parton model
Three longitudinal structure functions:
Quark charge
Prob. of q in proton
Argonne National Laboratory
EIC whitepaper
10
The Neutron Structure Function
Parton model ->

Proton structure function:

Neutron structure function (isospin symmetry):
Upgraded JLab has
unique capability to
define the valence region
SU(6)
DSE

Ratio:

Focus on high x:

Three 12-GeV experiments
–
–
–
Proton : PVDIS and SoLID (K. Paschke)
Deuteron: radial TPC and CLAS12
3H/3He: 3H target and existing spectrometers
Argonne National Laboratory
Helicity
conservation
Scalar diquark
NSAC milestone HP14 (2018)
Thanks to C. Keppel, K. Kumar, G. Petratos
11
Spin Structure of the neutron – valence region
Polarized electron scattering from a polarized nucleon
NSAC milestone HP14 (2018)
Three 12-GeV experiments
(benefits from SoLID)
Thanks to N. Makins, Z.-E. Meziani
Courtesy of Z.-E. Meziani, K. Griffioen, S. Kuhn, G. Petratos
Tensor charge from transversity measurements at JLab
Distribution of
transversely polarized
quarks inside a
transversely polarized
proton
Tensor Charge
Collins fragmentation function
from KEK-B/Belle
- M. Grosse-Perdekamp (UIUC)
Two 12-GeV experiments
Argonne National Laboratory
dd benefits from SoLID
Thanks to A. Prokudin and Z.-E. Meziani
13
Drell-Yan is the best way to measure anti-quark distributions
What is the A dependence of antiquarks?
Experiment E906 FNAL:
3 national labs, 7 U. S.
universities, 3 off-shore
national labs, 4 off-shore
universities
Commissioning run
completed
No model predicts dbar/ubar <1.
Longer term: Polarized FNAL, J-PARC at 50 GeV (beyond 2017)?
Thanks to D. Geesaman, P. Reimer, J.-C. Peng
Argonne National Laboratory
14
HERMES Surprise!
Strange quark distribution
• Deep inelastic
scattering with
flavor tagging
• Serious
discrepancy with
decades of
neutrino data
Intrinsic sea?
Future: COMPASS-II at CERN (2015), JLab with12 GeV (RICH)
A. Airapetian et al, PLB 666 (2008) 446
Thanks to H. Jackson, J.-C. Peng
Strange sea and LHC
• Parton distribution
uncertainties at high x
feed into benchmark
LHC processes
rs = ½( s + sbar)/dbar
• Sea appears to be
flavor symmetric at
low x, consistent with
HERMES
ATLAS Collaboration,
ArXiV:1203.4051 [hep-ex]
Argonne National Laboratory
Thanks to T. LeCompte
16
Worldwide quest: spin structure of the nucleon
 From DIS measurements
What is the origin of the proton spin?
DS ≈ 0.3
DG = 1.0±1.2
 quark polarization Dq(x)
first 5-flavor separation from
HERMES: Dq ≈ 0
Spin budget of the proton
RHIC-spin: future chargecurrent measurements
 gluon polarizationΔG(x)
RHIC-spin, HERMES, COMPASS
 orbital angular momentum L
 GPD’s and TMD’s
70%
Jets,
ALLEIC
Farpions,
future:
30%
Measurement of the gluon polarization DG at RHIC
Dominates
at low pT
Dominates
at high pT
D. de Florian et al,
Prog. in Part. Nucl. Phys.
67 (2012) 251
0.2
ʃdxDg(x,Q2=10GeV2) = 0.13 (error?)
0.05
RHIC whitepaper
See E. Aschenauer’s talk for impact of 2013-14 experiments.
AL
W production expected from RHIC runs 12+13
®
p + p ® W ± + X ® e± + X
®
p + p ® W ± + X ® m± + X
0.6
0.4
25 GeV<E eT <50 GeV
m
15 GeV<E T
STAR PHENIX
0.2
W
-
See E. Aschenauer’s
talk for impact on
and
0
• Provides an important
check of SIDIS method
W+
-0.2
-0.4
-1
• No fragmentation
function
-0.6
L = 630 pb , P = 55%
e,m
W - W + CHE-DSSV (25 GeV<E )
T
Systematic Uncertainty
-2
-1
h
0
1
2
lepton
• Q2=MW2 (no high twist
effects)
B. Jacak, N. Xu, RHIC PAC 2012
http://www.bnl.gov/npp/pac0612.asp
Argonne National Laboratory
NSAC milestone HP8 (2013)
Thanks to E. Aschenaur
19
Is there a flavor asymmetry in the sea quark helicity distributions?



Sea quark polarization at
high x
JLab 12 GeV (Hall B)
Kaon detection - RICH
Plot credit: K. Hafidi
Argonne National Laboratory
20
Multidimensional parton distribution functions
Transverse momentum
distribution functions
Generalized parton
distribution functions
eg., Sivers distribution
eighteen 12-GeV experiments!
Separate talk: M. Guidal
JLab whitepaper
Argonne National Laboratory
21
Transverse Momentum Distributions: The Sivers effect
DIS
HERMES
Drell-Yan


NSAC Milestone HP13 (2015) “Test unique
QCD predictions for relations between singletransverse spin phenomena in p-p scattering
and those observed in deep-inelastic
scattering.”
COMPASS-II, RHIC-spin, polarized FNAL
Thanks to H. Jackson, M. Burkhardt
Polarized Drell-Yan and W production (2014+)
STAR
polarized
Delivered 500 pb-1
PHENIX
FNAL Polarized SeaQuest (>2017)
8 U.S. institutions, 4 off-shore institutions
~$10.5M including 50% contingency
Argonne National Laboratory
COMPASS-II (2014, if upgraded)
1 U. S. institution
~ $0.9M NSF (large area trackers)
Forward upgrades -> transverse spin asymmetries
Thanks to E. Aschenauer,
W. Lorenzon, M. Liu, M.
Grosse-Perdekamp
23
Generalized parton distributions and DVCS
e’
Vector: H (x,ξ,t)

t
e
Tensor: E (x,ξ,t)
*(Q2)
x+ξ
Forward limit (t →0, x→0)
~q
q
x-ξ
H (x,0,0) = Dq(x)
H (x,0,0) = q(x)
~
~
H, H, E, E (x,ξ,t)
p’
p
~
Axial-Vector: H (x,ξ,t)
~
Pseudoscalar: E (x,ξ,t)
Sum rules
1
1
1
1
 dx Hq(x,x,t) = Fq1 (t)
Quark angular momentum (Ji’s sum rule)
1
( H(x,x,t=0) + E(x,x,t=0) ) x dx = Jquark =1/2 DS  D Lz
-1

X. Ji, Phy.Rev.Lett.78,610(1997)
q
q
dx
E
(x,x,t)
=
F
2 (t)

A. Radyushkin,
PRD 56 (1996) 5524
C. Munoz Comacho et al,
PRL 97 (2006) 262002 ;
F. X. Girod et al,
PRL 100 (2008)162002.
Extraction of quark total angular momentum
•
NSAC milestones HP11 (2012), HP9 (2014)
Plot credit: JLab whitepaper
•
•
DVCS is the “golden channel”:
* + N ->  + N’
“Lattice + experiment provides a much greater constraint on
GPDs than from either alone.” - J. Negele
Major program for JLab 12 GeV, COMPASS-II, EIC
DVCS measurements and imaging
Argonne National Laboratory
Thanks to Z.-E. Meziani, JLab whitepaper
26
A new form of matter: Matter formed from the force field (gluons):
“Valence” gluon can add one unit of angular momentum.
Conventional mesons:
• meson
spin
• intrinsic parity
• charge conjugation
K. Juge et al, nucl-th:030711
separate talk: J. Dudek
Thanks to C. Meyer, C. D. Roberts
Search for exotic hybrid mesons at the 12-GeV JLab
R
M
Two 12-GeV JLab experiments
Hybrids are predicted by modern QCD treatments: DSE, lattice
NSAC milestone HP15 (2018)
Complementary work:
GSI (PANDA) : antiproton-proton
annihilation in charmonium
region (2017-) (Northwestern U.)
BES-III: electron-positron
annihilation in charmonium
region – also decays to light
quark bound states
(Indiana U.)
Plot credit: NP2010
Argonne National Laboratory
Thanks to K. Seth, M. Shepherd, J. Dudek
28
Baryon resonances – JLab Physics Analysis Center
Future: J-PARC, Mainz
6 U. S. institutions
Baryon spectrum from EBAC & Bonn-Ga (PDG12)
•
•
Kamano, Nakamura, Lee et al., 2012
NSAC milestones HP3 (2009) completed, HP7 (2012)
Previous (p,2p) data in the N* mass range
are all from 1970’s bubble chambers!
New Lattice calculations: arXiv:1201.2349
N* resonances and exotic baryons.
Coupled channels dynamics are essential!
Thanks to K. Hicks, W. Briscoe, M. Pennington, T.-S. H. Lee
Argonne National Laboratory
29
A look at quarks in the nucleus: the EMC effect


EMC effect discovered 1982 (H. Montgomery et al.),
remains a mystery today
Scattering from quarks in a nucleus is not just a
superposition of scattering from quarks in nucleons
– Dependence on nuclear density, short range
correlations, flavor, spin, isospin?
J. Seeley et al, PRL 103 (2009)
SLAC E-139, 1984, J. Gomez et al.
Argonne National Laboratory
30
EMC effect and short range N-N interaction
EMC effect is correlated with short
range N-N interaction – L. Weinstein et al,
SRC Scaling factors xB ≥ 1.5
PRL 106, 052301 (2011) , J. Arrington et al,
arXiv:1206.6343
N. Fomin et al, PRL 108, 092502 (2012)
Flavor, isospin and spin dependence of
EMC effect? JLab@12, Drell-Yan,
MINERvA
Four JLab 12 GeV experiments
Plot credit: JLab whitepaper
31
MINERA
Main Injector ExpeRiment ν-A
MINERvA is studying A dependence of neutrino
interactions in unprecedented detail, with He, C,
Scintillator (CH), H2O, Fe, Pb targets.
Uses high intensity NuMI Beamline at FNAL with
MINOS near detector as muon spectrometer
Nuclear physics goals
High precision measurement of the axial form factor to high Q2 and search for A
dependence of form factor
Studies of quark-hadron duality in neutrino interactions, complementing Jlab
Studying partonic nuclear effects with neutrino interactions
Precision cross section measurements and studies of final states
Schedule
Low E ν and anti-ν (average E ~4 GeV) 11/09-4/12
~1.7 Million ν CC interactions and 250 K anti-ν CC interactions on scintillator, ~300 K ν
CC interactions on Fe and Pb
Medium E ν (avg E ~8 GeV) spring 2013 to about 2019
MEP Participation
Hampton, Rutgers – PMT detector construction and testing, scintillator plane construction.
He target funded by MEP
Slide credit: R. Ransome
32
Hadronization and quark propagation in nuclear matter
 What governs the transition of quarks and gluons
into pions and nucleons? NSAC 2007






Production length
Parton energy loss
Formation length
Color transparency
Hadron multiplicity
pT broadening
CEBAF @ 12 GeV + CLAS12: ideal
facility to study light quark
hadronization:
h
 DIS
( A)
R( z, , p , Q )  h
 DIS ( D)
2
T
12 GeV Anticipated Data: 1035 cm-2s-1
2
W. Brooks, K. Hafidi, K. Joo et al.
The EIC (>2020)
Source: EIC whitepaper
Gluon imaging
Gluon saturation
Quark propagation
Gluon and sea quark polarization
Sea quark imaging
Argonne National Laboratory
34
2020 and beyond: Electron Ion Collider
Brookhaven National Lab
Jefferson Lab
Warm large
booster
(up to 20 GeV)
Prebooster
Transfer
beam
line
Medium
energy IP
SRF
linac
Ion
source
Electron
collider ring
(3 to 11 GeV)
Cold ion
collider ring
(up to 100
GeV)
Injecto
r
12 GeV CEBAF
“We recommend the allocation of resources to develop accelerator and detector technology
necessary to lay the foundation for a polarized Electron-Ion Collider.” NSAC LRP 2007
Unique: high-luminosity with polarized electrons, nuclear and polarized ion beams
Non-JLab, non-RHIC cold-QCD experiments
Education – # U.S.
MEP postdocs, grad.
students, undergrads
Contact
Status
Lab
# U.S. MEP
Institutions
H. Gao
Ongoing
HIS
9
2, 5, 3
D. Geesaman,
P. Reimer
Ongoing
FNAL
8
7, 7, 4
M. GrossePerdekamp
Ongoing
CERN
1
1, 2, 4
R. Miskimen
Ongoing
Mainz
3
2, 3, 1
Baryon resonances
W. Briscoe
Ongoing
Mainz
6
1, 3, 6
MINERvA
R. Ransome
Ongoing
FNAL
2
2, 2, 2
N polarizability,
GDH, few-body,
Bethe-Heitler
B. Norum
Ongoing
HiS
4
2, 1, 2
OLYMPUS
R. Milner
Ongoing
DESY
4
3, 6, 6
HERMES
H. Jackson
Ongoing
DESY
3
1, 4, 1
M. Shepherd
Ongoing
BES
1
1 ,2, 0
Ongoing
Mainz
3
1, 0, 0
Program
n polarizability,
GDH, few-body
Drell-Yan
COMPASS-II
N polarizability
BES-III
Threshold pion
photoproduction
A. Bernstein
Radiative pion
production
B. Norum
New
Mainz
2
0.2, 0, 0
Polarized DrellYan
W. Lorenzon
New
FNAL
8
0.5, 0.5, 3
N polarizability
R. Miskimen
New
HIS
4
0, 0, 1
Proton radius
R. Gilman
New
PSI
16
1, 0, 0
Baryon resonances
K. Hicks
New
J-PARC
6
2, 5, 0*
Charmed mesons
K. Seth
New
GSI
1
1, 2, 0
Argonne National Laboratory
*Expected
Hadron program at HIGS (next 3 years)
 Static- Electromagnetic-Polarizabilities
of the proton and neutron
 Spin Polarizabilities of the proton
 Spin Structure and the Gerasimov-DrellHearn (GDH) Sum Rule Measurements
Future program at HIGS (beyond 3 years)
 Chiral Dynamics using photopion production
 Spin Polarizabilities of the neutron
Thanks to C. Howell
36
Concluding statement
 Understanding hadrons will be one of nuclear physics’
greatest contributions to science
 New 21st century tools have positioned us well for the
next decade:
– JLab 12 GeV, RHIC - Major U.S. facilities lead the world
– FNAL – MI, CERN COMPASS-II, HIS, Mainz, J-PARC, FAIR provide
targeted experiments that complement the central program
– Far future: EIC
 We are camped on one of the most interesting frontiers
in science
Argonne National Laboratory
37
Many thanks to
M. Ahmed
E. Aschenauer
J. Arrington
T. Barnes
D. Beck
W. Briscoe
M. Burkhardt
G. Cates
A. Desphande
C. Djalali
E. Downie
R. Ent
C. Gagliardi
H. Gao
D. Geesaman
R. Gilman
H. Griesshammer
M. Grosse-Perdekamp
K. Hafidi
K. Hicks
C. Howell
B. Jacak
H. Jackson
K. Joo
B. Keister
C. Keppel
W. Korsch
K. Kumar
T.-S. H. Lee
M. Liu
W. Lorenzon
T. LeCompte
N. Makins
C. Meyer
Z.-E. Meziani
R. McKeown
R. Milner
R. Miskimen
H. Montgomery
J. Nagle
B. Norum
K. Orginos
K. Paschke
J.-C. Peng
M. Pennington
D. Phillips
G. Petratos
J. Qiu
R. Ransome
P. Reimer
C. Roberts
J. Rubin
K. Seth
M. Shepherd
M. Stratmann
B. Surrow
S. Vigdor
W. Vogelsang
H. Weller
R. Wiringa
B. Wojtsekhowski
N. Xu
Helpful documents:
• NP2010 Report
• NSAC 2007 Long Range Plan
• Whitepaper drafts:
JLab 12 GeV
The Case for Continuing RHIC
Operations
Electron Ion Collider
• JLab12, RHIC, COMPASS-II proposals
• STAR and PHENIX decadal plans
• NSAC Performance Measures 2008
Argonne National Laboratory
38