future directions in studying qcd aspects of nuclear physics
DESCRIPTION
Future Directions in studying QCD aspects of Nuclear Physics. + (1540). Gerard van der Steenhoven (NIKHEF/KVI). International Nuclear Physics Conference, Götenburg, Sweden, July 2 nd , 2004. What remains to be discovered ? (*). WMAP satellite: 70% dark energy 25% dark matter - PowerPoint PPT PresentationTRANSCRIPT
Future Directions in studying QCD aspects
of Nuclear Physics
International Nuclear Physics Conference,
Götenburg, Sweden, July 2nd, 2004
Gerard van der Steenhoven(NIKHEF/KVI)
+(1540)
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
• Lattice QCD calculations:
• Deep-Inelastic Scattering:
The nucleon contains a largeamount of quark-antiquark
pairs and gluons.
gluon
Quark-antiquark pair
The QCD structure of the nucleon
(From: G. Bali, Glasgow)
The challenges of QCD
• For s > 1 perturbative expansions fail………
• Extrapolate s to the size
of the proton, 10-15 m:
1 sprotonrl
Non-perturbative QCD:– Proton structure & spin
– Confinement
– Nucleon-Nucleon forces
– Hadron spectroscopy…..
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 facilitiesMAMI-C
1. Hadronic Form Factors
• Physics issues: – Proton: new data on GE
p(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• Measure single-spin asymmetry in :
→ Relative phase of GM and GE
• Entirely new concept:
(F. Rathmann et al., LOI – 2004)
/||sin ||)cos1(
/)Im()2sin(2222
*
EM
MEy GG
GGA
Polarized anti-protons inthe HESR ring @ FAIR: - The PAX project -
eepp
MAMI facility
MAMI-C:• Emax →1500 MeV• Starting in 2005
2. Hadron spectroscopy
• Allowed multi-q states in QCD:
– states mesons
– states baryons
– states pentaquarks?
qqq
qqqqq
)2317(D*sJ
)3520(Ξcc
)1540(θ
Harvest in 2003:
Discovery
Discovery
Discovery
CLAS
New Narrow DsJ-states
• BaBar studied decay
• Two new mesons ? • The K+K-+-spectrum:
KK(2112)Dwith
(2112)DD*s
0*s
*sJ
cs
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:
)3520(Ξ ),3460(Ξ cccc
New narrow S=+1 states
)1540(θ)3095(0
cc
)1860(
Spring-8 H1
NA49
Chiral-Soliton mod.prediction in 1997by Diakonov, Petrovand Polyakov (97):
HERMESSAPHIRCLAS
Accumulating experimental evidence• Results of three more experiments:
• 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:
MeV 3912
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
exotic (mass ~ 1.7 – 2.3 GeV)
LS
S
1
2
S = S + S1 2
J = L + S
C = (-1)L + S
P = (-1)L + 1
• Normal mesons: JPC = 0-+ 1+- 2-+
• Lattice QCD: flux tubes
• Flux tubes (J=1, S=1): JPC = 0-+ 0+- 1+- 1-+ 2-+ 2+-
• Real photons couple to exotics via -VM transition
Hall D: the GlueX detector
Photon Flux 108 /sCharged Particles
coverage1° - 170°
momentum reso 1 - 2%position reso 150 µmvertex reso 500 µm
Photonsenergy measured 1° - 120°Pb glass reso 2 +
5%/√Ebarrel reso 4.4%/√E
Trigger level 1 rate 20 kHz
CHCHL-2L-2
• At JLab 12 GeV beam:– coherent beam– new exp. Hall (D)– GlueX detector
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*
(*) Facility for Anti-proton and Ion Research
: pellet target, particle ID, ~4
3. Search the carriers of proton spin
½ = ½ q + G + Lq
• Three possible sources:– quarks:
o valence quarks
o sea quarks
– gluons– orbital momentum
• Mathematically:
~ 20 10 % ? ?
EMC: q ~ 10%
How to probe the quark polarization?
Measure yield asymmetry:
Polarizeddeep inelasticelectronscattering
1
1
NN
NN
PDPA
BT
Parallel electron & proton spins
Spin-dependent Structure Function
Anti-parallel electron & proton spins
In the Quark-Parton Model:
)()(
1
)(
)( 2
11
11
fff xqe
xFxF
xgA
QCD analysis of world data (’03)• Next-to-Leading-Order analysis of -data
Excellent data for x > 0.01
)(1 xg
Polarized Parton Densities• First moments:
– input scale
– pol. singlet density:
– pol. gluon density:
(th) 0.070 (exp) 0.133
(stat) 0.169 0.167
q
There must be other sources of angular momentum in the proton
220 GeV 0.4Q
(th) 0.424 (exp) 0.175
(stat) 0.388 0.616
G
Future data on and )(1 xg p )(1 xg n
• Assume 400 pb-1 collected at e-RHIC:
)(1 xg p
)(1 xg n
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 : dux
Chiral Quark Soliton Model[HERMES, hep-ex/0307064]
Future data on s and qvalence
Gluon polarization
• High-pT pion pair production:
ˆ arg
p
*
*
beamettPGFPGF
X
PPDaf
A
G
G
’99: First direct evidence for non-zero gluon polarization
1.0 )( dxxGGCurves consistent with
New experiments
ccg
qgq
sDD
KKDD
0*
00 )()(
or
or photon
• Photon-gluon fusion:– COMPASS:
• Open charm production:
• High pT –pairs (> 1 GeV)
• Prompt photons (RHIC):
The COMPASS experiment
Polarization:• Beam: ~80%• Target:<50%>
Beam: 160 GeV µ+
2 . 108 µ/spill (4.8s/16.2s)
Polarizedtarget
SM1RICH
ECal1 & Hcal1
Muon filter 1
SM2
MWPCs
Micromegas &Drift chambers
ECal2 & Hcal2
Muon filter 2
GEM & MWPCs
SciFi
GEM & MWPCs
GEM & Straws
SiliconSciFi Scintillating
fibers
~50m
First COMPASS data
• Tagging of D*→D0:– y-axis: MK - MK - m
– x-axis: MK - mD0
MK -mD0 [MeV/c2]
317 D0
80% 2002 data
Gluon Polarization at RHIC• Longitudinal double spin asymmetry in :
• Dominant processes:
or
or photon
or
or
(heavy flavor)
Direct photon production Di-jet production
)(
)(ˆ)(1
g
gLLq
p
photondirectLL
xG
xGaxA
dd
ddA
pp
Polarized Protons at RHIC
BRAHMS
STAR
PHENIX
AGS
LINACBOOSTER
Pol. Source 500 A, 300 s
Spin RotatorsSiberian Snakes
200 MeV Polarimeter AGS Quasi-Elastic Polarimeter
Rf Dipoles
RHIC pC CNI PolarimetersAbsolute Polarimeter (H jet)
PHOBOS
AGS pC CNI Polarimeter
Partial Helical Snake
RHICs = 50 - 500 GeV
Partial Solenoid Snake
Anticipated improvement in xG(x)
• Present QCD analysis
M. Hirai, H.Kobayashi, M. Miyama et al.- preliminary
• Expected STAR data
• Three leading order quark distributions:
momentum carried by quarks
longitudinal quark spin,
What is transversity?
transverse quark spin,
• 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); (lattice)
• The relevant diagram:– helicity flip of quark & target
– chirally odd process
• Consequences:
– no gluon contributions….
Measuring transversity
+
+ -
-quark flip
target flip
2
1
… & measure single-spin asymmetries:
),(),(
),(),(1),(
shsh
shsh
Ts
hUT
NN
NN
PA
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)()(~)sin( )1(
11 zHxhzM
Ps
‘Sivers’:‘Collins’: )()(~)sin( 1)1(
1 zDxfzM
PTs
p
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:
• Double transverse spin asymmetry:
• Key issue: amount of -polar.:– Concept proven in FILTEX exp.
– Separate -ring being studied
)M,x(u)M,x(u
)M,x(h)M,x(haA
21
21
21
u1
21
u1
TTTT
q
l+
p pqL
l-q2=M2
qT
Panda
anti-P
FAIR@GSI
p
p
4. Generalized Parton Distributions
• Consider exclusive processes:– Deeply virtual Compton scatt.– Exclusive vector meson prod.
• Collins et al. proved factorization theorem (1997):
Distribution amplitude(meson) final state
finalquark
initialquark
2
2*.. ),,( ),,( ),(
f
pf
mfmprodexcl dtxHQxcz
Hard scatteringcoefficient (QCD)
Generalized PartonDistribution (GPD)
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:
)(),,(~
);(),,( 0,0, xqtxHxqtxH tq
tq
• The forward limit:
• Second moment (X. Ji, PRL 1997):
)(),,(~
)(),,(
)(),,(~
),(),,(
1
1-
2
1
1
1
1-
1
1
1
tGtxEdxtFtxEdx
tGtxHdxtFtxHdx
P
A
qqqt
qq LJdxtxEtxHx ),,(),,( 210
1
121
Dirac
Pauli
Axial vector
Pseudoscalar
GPDs give access to Orbital Angular Momentum of Quarks
Applying the GPD framework• GPDs enter description of different processes:
• Take Fourier transform of leading GPD:
dtetxHbxq tibff ),,(),( 22
1
GPDsAs Jq = ½q + Lq
information on Jq gives data on Lq.
Spatial distribution of quarks in the perpendicular direction
A 3D-view of partons in the proton
A.V. Belitsky, D. Muller, NP A711 (2002) 118c
Form Factor Parton Density Gen. Parton Distribution
Experimental access to GPDs• Exclusive meson electroproduction:
– Vector mesons (0):
– Pseudoscalar mesons ():
• Deeply virtual Compton scattering:
– Beam charge asymmetry:
– Beam spin asymmetry:
– Longitudinal target spin asymmetry:
),,( and ),,( txEtxH
),,(~
and ),,(~
txEtxH Key
differences
Selected DVCS results
• Azimuthal dependence
beam-spin asymmetry:
• Beam-charge and target
spin asymmetries……..
)()(
)()(1)(
NN
NN
PA
TLU
Future data on DVCS at JLab• 2000 hr data taking in upgraded CLAS detector
• The spin structure of the proton:– Gluon polarization G: 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: short-term future ’04-’09
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
– eRHIC/ELIC
– ………
e-p coll at 10 x 250 GeV2 &1033 cm2/s
EIC @ BNLELIC @ JLab with e-A collat 4 x 65 GeV2 & 1034 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 collat 4 x 65 GeV2 & 1034 cm2/s
Key QCD successes
• The energy (or distance) dependence of s:
• Data on the DIS structure function F2(x,Q2):
Pion Form Factor
f (Q2)12 f
2CF s(Q2)
Q2
Search transition to pQCD regime !
• Pion Form Factor:– simple quark structure
– pQCD prediction:
CHL-2CHL-2
Upgrade magnets Upgrade magnets and power and power suppliessupplies
Enhance equipment in Enhance equipment in existing hallsexisting halls
6 GeV CEBAF1112Add new hallAdd new hall
u
u
d
d
s
u
d
d
us
uss
uu
d
d
sd
u
d
u
a) Five quarks in a s-state configuration.
b) Five quarks in a K+ -n molecular configuration.
c) Five quarks in a strong diquark correlation state.
d) Collective excitation ofa multiquark configuration.
Pen
taqu
ark
mod
els…
.....
u
d
d
• 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 ( much larger than axial charge (): Lattice QCD: = 0.56 (9), while = 0.18 (10)
– Q2 evolution of h1(x) is much weaker than that of g1(x)
Novel test of DGLAP equations
Why is transversity important?
• Label the quark helicities:
What is the diagram?
+
++
+ ++
+- -
+
+ ---
++
+
+
Transversity: helicity flip of quark and target
+
+ -
-quark flip
target flip
• Operator structure:
• What happens in the non-relativistic limit?
• Why no gluon contribution?
– gluon helicity flip:
– nucleon helicity flip:
Frequently asked questions
odd) (chiral ~ charges tensor ~
even) (chiral ~ charges axial ~
50
5
qqq
qqqj
qqqq
qqqqjj
50
5
)()(or 11 xgxhqq
+
+
-
-
2
1
2
1
How to measure h1(x)?
Xpp
-
• Drell-Yan & related reactions:
• Semi-inclusive deep-inelastic scattering:
+Xepe '+
++
-
-
-
Chiral-odd fragmentation process
Measuring transverse asymmetries
• Semi-inclusive DIS with a transversely polarized H target:
• Evaluate the azimuthal asymmetry wrt Starget:
),(),(
),(),(1),(
shsh
shsh
Ts
hUT
NN
NN
PA
Transverse Target Magnet at HERMES
Extraction of sin() moments:
• Define azimuthal angles:
- azimuthal spin orientation s
- azimuthal hadron angle h
• Amplitude of sin(+x) dependence
contains relevant physics:
• Longitudinal polarized target: s= 0 → no distinction
)sin(UTA
)sin( xUTA
“Collins”
“Sivers”
First RHIC results
• Forward 0 prod. at STAR:
• Single spin-asymmetry in
• Relevance: transverse spin
• Red curve: Collins effect
(~ transversity)
• Blue curve: Sivers effect
(~ pT-dependence of PDF)
• Green curve: Twist-3 eff.
X0 pp
Generalized Parton Distributions
• Four independent Generalized Parton Distributions:
• Some GPD properties:– Non-pQCD object
– Not calculable from first principles
– Unifies description of ALL reactions with hadrons
– Gives access to spatial distribution of quarks
),,(~
and ),,,( ),,,(~
),,,( txEtxEtxHtxH
GPDs are a probe of correlations
between partons
Pseudovector GPDs Pseudoscalar GPDs
Spin dependent GPDsSpin independent GPDs
Orbital angular momentum• The origin of proton spin:
• A new idea: azimuthal asymmetry in 0 production
½ = ½ q + G + Lq
Inclusive data: 0.2 High pT pairs: 1.0 Orb. ang. mom.: -0.6 ?
Ju = Su + Lu