Future Directions in studying QCD aspects of Nuclear Physics
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Transcript of Future Directions in studying QCD aspects of Nuclear Physics
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