Transcript QCD and the origin of proton

Future Directions in
studying QCD aspects
of Nuclear Physics
+(1540)
Gerard van der Steenhoven
(NIKHEF/KVI)
International Nuclear Physics Conference,
Götenburg, Sweden, July 2nd, 2004
What remains to be discovered ?
• WMAP satellite:
– 70% dark energy
– 25% dark matter
– 5% visible matter
• The task of LHC:
– Unravel the Higgs Mechanism
~ 2% of the visible universe
• The task of QCD nuclear physics:
→ Unravel the origin of 98% of
the mass of the visible universe
(*) After: J. Maddox, What Remains to be Discovered?, XXXX Press, 2000
(*)
The QCD structure of the nucleon
• Lattice QCD calculations:
(From: G. Bali, Glasgow)
• Deep-Inelastic Scattering:
The nucleon contains a large
amount of quark-antiquark
pairs and gluons.
gluon
Quark-antiquark pair
The challenges of QCD
• Extrapolate s to the size
of the proton, 10-15 m:
• For s > 1 perturbative
expansions fail………
 Non-perturbative QCD:
– Proton structure & spin
– Confinement
– Nucleon-Nucleon forces
– Hadron spectroscopy…..
l  rproton   s  1
Lattice QCD
simulations…
Future directions
1. Hadronic form factors
–
Transition to pQCD, strangeness
2. Hadron spectroscopy
–
Pentaquarks, hybrids, glueballs,...
3. Spin structure
–
Gluons, transversity
4. Generalized parton distributions
–
Partonic correlations, orbital motion
5. Future facilities
MAMI-C
1. Hadronic Form Factors
• Physics issues:
– Proton: new data on GEp(Q2)/GMp(Q2)
– Pion: transition to pQCD?
– Axial form factors: role strangeness in proton
– Kaon and hyperon form factors: hadron size
• Relevant new facilities:
– MAMI-C…………………… 2005
– 12 GeV @ JLab …………. 2010
– PAX @ GSI ……………… 2012 (Letter of Intend)
Proton Form Factors
Time-Like Form Factors
 
p
p

e
e:
• Measure single-spin asymmetry in
sin(2 )  Im(GE*  GM ) / 
Ay 
(1  cos2  ) | GM |2  sin 2  | GE |2 / 
→ Relative phase of GM and GE
• Entirely new concept:
Polarized anti-protons in
the HESR ring @ FAIR:
- The PAX project (F. Rathmann et al., LOI – 2004)
MAMI facility
MAMI-C:
• Emax →1500 MeV
• Starting in 2005
2. Hadron spectroscopy
• Allowed multi-q states in QCD:
states  mesons
–
qq
–
qqq
–
qqqq q states 
states  baryons
pentaquarks?

θ
(1540)
Discovery
Harvest in 2003:
Discovery
D*
sJ (2317)

Discovery Ξcc (3520)
CLAS
New Narrow DsJ-states
• BaBar studied decay
D*sJ  D*s (2112)  0
with D*s (2112)  K  K  
• Two new s c mesons ?
• The K+K-+-spectrum:
0+ @ 2.32 GeV
1+ @ 2.46 GeV
New charmed baryons
• SELEX experiment at
FermiLab (E781)
– 600 GeV/c π/Σ beam
– Decay schematic:
– Discoveries:


Ξcc
(3460), Ξcc
(3520)
New narrow S=+1 states
θ  (1540)
Spring-8
H1
  (1860)
NA49
0cc (3095)
Chiral-Soliton mod.
prediction in 1997
by Diakonov, Petrov
and Polyakov (97):
Accumulating experimental evidence
• Results of three more experiments:
CLAS
SAPHIR
HERMES
• In all cases: a narrow peak near 1535 MeV/c2
Overview of +(1535) data
• Averaged mass value:
– 1536.2 ± 2.6 MeV
– /dof = 12.4/6
– Conf. level = 0.053
• Measured FHWMs:
– in most cases consistent
with exp. resolution
– HERMES data:
  12  9  3 MeV
HERMES paper:A. Airapetian et al, Physics Letters B 585 (2004) 213
Glueballs and Hybrids
• Partonic systems
predicted in QCD:
• “What remains to
be discovered”:
– Tetraquarks
– Glueballs
– Hybrids
– ……….?
Glueball searches
• Lattice QCD: flux tubes
• Normal mesons:
JPC = 0-+ 1+- 2-+
• Flux tubes (J=1, S=1):
JPC = 0-+ 0+- 1+- 1-+ 2-+ 2+exotic (mass ~ 1.7 – 2.3 GeV)
• Real photons couple to exotics via -VM transition
Hall D: the GlueX detector
• At JLab 12 GeV beam:
– coherent  beam
– new exp. Hall (D)
– GlueX detector
CH
L-2
Photon Flux
Charged Particles
coverage
momentum reso
position reso
vertex reso
Photons
energy measured
Pb glass reso
barrel reso
Trigger level 1 rate
108 /s
1° - 170°
1 - 2%
150 µm
500 µm
1° - 120°
2 + 5%/√E
4.4%/√E
20 kHz
Hybrid searches
• Antiproton annihiliation: gluon rich
• Production mechanism:
– Charmonium production
– Clear signature/tag
– Not so many states
What is to be expected?
• First glimpse ??
PANDA @
*
FAIR
: pellet target, particle ID, ~4
(*) Facility for Anti-proton and Ion Research
3. Search the carriers of proton spin
• Three possible sources:
– quarks:
o valence quarks
o sea quarks (qq )
– gluons
– orbital momentum
• Mathematically:
½ = ½ Sq + DG + Lq
~ 20  10 %
?
EMC: Sq ~ 10%
?
How to probe the quark polarization?
Polarized
deep
inelastic
electron
scattering
Parallel electron & proton spins
Anti-parallel electron & proton spins
Measure yield asymmetry:
1 N  N
A1 
DPT PB N  N
In the Quark-Parton Model:
A1 
g1 ( x)
1
2

e

f Dq f ( x)
F1 ( x) F1 ( x) f
Spin-dependent Structure Function
QCD analysis of world data (’03)
• Next-to-Leading-Order analysis of g1 ( x) -data
Excellent data for x > 0.01
Polarized Parton Densities
• First moments:
– input scale
Q02  4.0 GeV2
– pol. singlet density:
DSq  0.167 0.169(stat)
 0.133(exp) 0.070(th)
– pol. gluon density:
DG  0.616 0.388(stat)
 0.175(exp) 0.424(th)
There must be other sources of angular momentum in the proton
p
1
n
1
Future data on g ( x) and g ( x)
• Assume 400 pb-1 collected at e-RHIC:
g1p ( x)
n
1
g ( x)
Domains of existing precision data
Flavour decomposition of spin
• Semi-inclusive deep
inelastic lepton
scattering
• Hadron tags flavour of
struck quark
• Derive purity of tag
from unpolarized data
Key issue: role of sea quarks in nucleon spin
Sea quark polarization
• Up and down quarks
have opposite spins
• Sea is unpolarized...
• First data on xDu  Dd  :
[HERMES, hep-ex/0307064]
Chiral Quark Soliton Model
Future data on Ds and Dqvalence
Gluon polarization
• High-pT pion
pair production:
A *p   X
DG

G
f PGF aˆ PGF D * Pt arg et Pbeam
’99: First direct evidence for
non-zero gluon polarization
Curves consistent with DG   G ( x)dx  1.0
New experiments
• Photon-gluon fusion:
– COMPASS:
• Open charm production:
D 0 ( D 0 )  K   ( K   )
D*  D 0 s
• High pT –pairs (> 1 GeV)
• Prompt photons (RHIC):
 or 
q g  q
photon
 or 
 g  cc
The COMPASS experiment
Beam: 160 GeV µ+
2 . 108 µ/spill (4.8s/16.2s)
Muon filter 2
MWPCs
ECal2 & Hcal2
~50m
SM2
Muon
filter 1
ECal1 & Hcal1
RICH
GEM &
MWPCs
SciFi
SM1
GEM & MWPCs
Silicon
SciFi
Scintillating
fibers
GEM & Straws
Micromegas &Drift chambers
Polarized
target
Polarization:
• Beam: ~80%
• Target:<50%>
First COMPASS data
• Tagging of D*→D0:
– y-axis: MK - MK - m 
– x-axis: MK - mD0
80% 2002 data
317 D0
MK -mD0 [MeV/c2]
Gluon Polarization at RHIC

• Longitudinal double spin asymmetry in pp :
ALL 
d   d  direct photon
  

d   d 
 A1p ( xq )  aˆ LL
DG ( xg )
G ( xg )
• Dominant processes:
 or 
 or 
photon
 or 
Direct photon production
(heavy flavor)
 or 
Di-jet production
Polarized Protons at RHIC
Absolute Polarimeter (H jet)
RHIC pC CNI Polarimeters
BRAHMS
PHOBOS
RHIC
s = 50 - 500 GeV
PHENIX
STAR
Siberian Snakes
Spin Rotators



y








y
y








y
y




y




y
1
0
0
1
0
E
x
p
e
r
i
m
e
n
td
a
t
a
(
1
9
9
7
)
S
i
m
u
l
a
t
i
o
n
(
1
9
9
7
)
9
0
Partial Solenoid Snake
Pol. Source
500 mA, 300 ms
Partial Helical Snake
AGS
8
0
E
x
p
e
r
i
m
e
n
td
a
t
a
(
2
0
0
2
)
S
i
m
u
l
a
t
i
o
n
(
2
0
0
2
)
7
0
 Vertical Polarization 
LINAC
BOOSTER
9
0
E
x
p
e
r
i
m
e
n
td
a
t
a
(
2
0
0
0
)
S
i
m
u
l
a
t
i
o
n
(
2
0
0
0
)
AGS pC CNI Polarimeter
S
i
m
u
l
a
t
i
o
n
(
2
0
0
3
)
8
0
7
0
6
0
6
0
5
0
5
0
4
0
4
0
3
0
3
0
2
0
2
0
1
0
1
0
AGS Quasi-Elastic Polarimeter
200 MeV Polarimeter
Rf Dipoles
0
5
1
0
1
5
2
0
2
5
3
0
G

3
5
4
0
4
5
0
5
0
Anticipated improvement in xDG(x)
• Present QCD analysis
• Expected STAR data
M. Hirai, H.Kobayashi, M. Miyama et al.- preliminary
What is transversity?
• Three leading order quark distributions:
momentum carried by quarks
longitudinal quark spin, DS
transverse quark spin, dS
• Gluons don’t contribute to h1(x) - dominant in g1(x):
 Study nucleon spin while switching off the gluons
• New QCD tests: Q2 evolution h1(x); dS  DS (lattice)
Measuring transversity
• The relevant diagram:
– helicity flip of quark & target
quark flip
target flip
– chirally odd process
• Consequences:
+
+
-
D  2
– no gluon contributions….
D  1
… & measure single-spin asymmetries:
1 N h ( , s )  N h ( , s )
A ( , s ) 
PT N h ( , s )  N h ( , s )
h
UT
Single – Spin Asymmetries
• Sivers effect:
AUT driven by
orbital motion
struck quark:
measure L
• Collins effect:
AUT driven by
fragmentation
process: measure
transversity
First data on transversity
‘Collins’:
P 
zM 
sin(  s ) ~ h1 ( x)  H1(1) ( z )
‘Sivers’:
P 
zM p
sin(  s ) ~ f1T(1) ( x)  D1 ( z )
First evidence for non-zero Collins and Sivers effects
Future options - COMPASS
• First results based on 2002 data
• Future:
– Particle ID, more statistics, data on AUT for Collins/Sivers
– Comparison HERMES data: measure Q2 evolution
Future options - PAX
• Polarized antiproton beam x polarized target:
l+
q
p
l-
q2=M2
FAIR@GSI
qT
p
qL
• Double transverse spin asymmetry:
ATT  aˆ TT
h1u (x1 , M 2 )h1u (x1 , M 2 )
u(x1 , M 2 )u(x1 , M 2 )
Panda
• Key issue: amount of
p
-polar.:
– Concept proven in FILTEX exp.
– Separate
p -ring being studied
anti-P
4. Generalized Parton Distributions
• Consider exclusive processes:
– Deeply virtual Compton scatt.
– Exclusive vector meson prod.
initial
final
 quark
  quark
GPD
• Collins et al. proved factorization theorem (1997):
2
 excl. prod . 
 
*
m
( , z ) c mf ( x,  , Q 2 ) H fp ( x,  , t ) d
f
Distribution amplitude
(meson) final state
Hard scattering
coefficient (QCD)
Generalized Parton
Distribution (GPD)
(Nasty: x = xBj for quarks and x = -xBj for antiquarks → x  [-1,1])
The remarkable properties of GPDs
• Integration over x gives Proton Form Factors:
1
1
~
dx
H
 ( x,  , t )  GA (t )
 dxH ( x,  , t )  F1 (t ),
Dirac
1
-1
1
 dxE ( x,  , t )  F2 (t )
1
• The forward limit:
Axial vector
1
~
dx
E
 ( x,  , t )  GP (t )
Pauli
-1
Pseudoscalar
~
, 0
H q ( x,  , t )  q( x); H q ( x,  , t ) t
 Dq( x)
t , 0
• Second moment (X. Ji, PRL 1997):
1
1
2


t 0
1
x
H
(
x
,

,
t
)

E
(
x
,

,
t
)
dx



J

q
q
2 S q  Lq
 q
1
GPDs give access to Orbital Angular Momentum of Quarks
Applying the GPD framework
• GPDs enter description of different processes:
As Jq = ½Sq + Lq
information on Jq
gives data on Lq.
GPDs
• Take Fourier transform of leading GPD:
q ( x, b )  2 2  H ( x,  ,t )e
f

1
f
 ib t
dt
Spatial distribution of quarks in the perpendicular direction
A 3D-view of partons in the proton
Form Factor
Parton Density
Gen. Parton Distribution
A.V. Belitsky, D. Muller, NP A711 (2002) 118c
Experimental access to GPDs
• Exclusive meson electroproduction:
– Vector mesons (0): H ( x,  , t ) and E ( x,  , t )
~
~
– Pseudoscalar mesons (): H
( x,  , t ) and E ( x,  , t )
• Deeply virtual Compton scattering:
– Beam charge asymmetry:
– Beam spin asymmetry:
– Longitudinal target spin asymmetry:
Key
differences
Selected DVCS results
• Azimuthal dependence
beam-spin asymmetry:
1 N  ( )  N  ( )
ALU ( ) 
PT N  ( )  N  ( )
• Beam-charge and target
spin asymmetries……..
Future data on DVCS at JLab
• 2000 hr data taking in upgraded CLAS detector
Prospects: short-term future ’04-’09
• The spin structure of the proton:
– Gluon polarization DG: COMPASS (& HERMES & RHIC)
– Exploring transversity h1(x): HERMES, COMPASS (& RHIC)
– GPDs: HERMES & JLab
• Hadron spectroscopy
– Pentaquarks: JLab
– Heavier hadrons: COMPASS
• RHIC spin:
– Optimizing polarization
– First double-spin asymm.
• Mainz:
– starting MAMI-C
Prospects: long-term future ( 2010)
• Design, construction and commissioning of various
new QCD facilities in Europe and/or the US:

– JLab 12 GeV upgrade (glueballs, high-x physics, GPDs)

– PANDA (hybrids, GPDs)
– PAX (transversity, FFs)
– COMPASS-X10
EIC @ BNL
ELIC @ JLab with e-A coll
at 4 x 65 GeV2 & 1034 cm2/s
– eRHIC/ELIC
– ………
e-p coll at 10 x 250 GeV2 &1033 cm2/s
Conclusion
• Major progress in understanding the
QCD structure of nucleons
• Many new results anticipated in the
coming years
• Many new facilities in construction
or under design (in EU and US)
QCD develops into a key area
of research for nuclear, particle
and astrophysics alike.
ELIC @ JLab with e-A coll
at 4 x 65 GeV2 & 1034 cm2/s
Key QCD successes
• Data on the DIS structure
function F2(x,Q2):
• The energy (or distance)
dependence of s:
Pion Form Factor
• Pion Form Factor:
– simple quark structure
– pQCD prediction:
2
2
12
f

C

(Q
)
2

F s
f  (Q ) 
Q2

Search transition to pQCD regime !
Add new hall
116 GeV CEBAF
12
Upgrade magnets
and power
supplies
CHL-2
Enhance equipment in
existing halls
u
Pentaquark models….....
u
d
d
uu
d
d
s
s
a) Five quarks in a sstate configuration.
u
d
d
u
b) Five quarks in a K+ -n
molecular configuration.
d
u
s
c) Five quarks in a strong
diquark correlation state.
u
ss
d
u
d) Collective excitation of
a multiquark configuration.
Why is transversity important?
• Third leading order quark distribution:
– required for complete knowledge of the nucleon
• Helicity conservation:
– gluons don’t contribute to h1(x), while they dominate g1(x):
 study nucleon spin while switching off the gluons
• Novel testable QCD predictions:
– Tensor charge (dS much larger than axial charge (DS):
 Lattice QCD: dS = 0.56 (9), while DS = 0.18 (10)
– Q2 evolution of h1(x) is much weaker than that of g1(x)
 Novel test of DGLAP equations
What is the diagram?
• Label the quark helicities:
+
+
+
-
-
+
+
-
-
+
+
+
-
+
+
+
+
+
+
quark flip
target flip
-
+
Transversity: helicity flip of quark and target
-
Frequently asked questions
rator structure:

Dq ~ axial charges~ q  5 q (chiraleven)
dq ~ tensorcharges~ q  0 j 5 q (chiralodd)
at happens in the non-relativistic limit?


q  5 q  q  q

q   5q  q  q
0j

j
 dq  Dq or h1 ( x)  g1 ( x)
D  2
y no gluon contribution?
uon helicity flip:
ucleon helicity flip:
D  2
D  1
+
+
-
D  1
-
How to measure h1(x)?
• Drell-Yan & related reactions:
+
+
 
p  p  m m   X
-
• Semi-inclusive deep-inelastic scattering:
Chiral-odd fragmentation process
+
+
-
e  p  e'  X
Measuring transverse asymmetries
• Semi-inclusive DIS
with a transversely
polarized H target:
Transverse Target Magnet at HERMES
• Evaluate the azimuthal
asymmetry wrt Starget:
1 N h ( , s )  N h ( , s )
A ( , s ) 
PT N h ( , s )  N h ( , s )
h
UT
sin( )
UT
Extraction of sin() moments: A
• Define azimuthal angles:
- azimuthal spin orientation s
- azimuthal hadron angle h
• Amplitude of sin(+x) dependence
 A
sin(   x )
UT
 contains relevant physics:
“Collins”
“Sivers”
• Longitudinal polarized target: s = 0 → no distinction
First RHIC results
• Forward 0 prod. at STAR:
• Single spin-asymmetry in
p  p   X

0
• Relevance: transverse spin
• Red curve: Collins effect
(~ transversity)
• Blue curve: Sivers effect
(~ pT-dependence of PDF)
• Green curve: Twist-3 eff.
Generalized Parton Distributions
• Four independent Generalized Parton Distributions:
Pseudovector GPDs
Pseudoscalar GPDs
~
~
H ( x,  , t ), H ( x,  , t ), E( x,  , t ), and E( x,  , t )
Spin independent GPDs
Spin dependent GPDs
• Some GPD properties:
– Non-pQCD object
– Not calculable from first principles
GPDs are a probe
of correlations
between partons
– Unifies description of ALL reactions with hadrons
– Gives access to spatial distribution of quarks
Orbital angular momentum
• The origin of proton spin:
½ = ½ Sq + DG + Lq
Inclusive data: 0.2
High pT pairs: 1.0
Orb. ang. mom.: -0.6 ?
• A new idea: azimuthal asymmetry in 0 production
Ju = S u + L u