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?

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