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?

qq

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%

)( qq

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