Delia Hasch

Delia HaschDelia Hasch

Spinstruktur des NukleonsSpinstruktur des Nukleons-elektromagnetische Sonden bei hohen -elektromagnetische Sonden bei hohen

Energien-Energien-

KHuK - Perspektivtagung, KHuK - Perspektivtagung, GSI, 25/26. Oktober 2007GSI, 25/26. Oktober 2007

outline:outline:• prerequisites

• polarisation of quarks:

• polarisation of gluons: G

• hunting for the OAM Lq,g

gz

qz

Nz LL

2

1

2

1s G

the spin of the nucleonthe spin of the nucleon

svv qdu

• transverse spin phenomena: transversity&friends

newdevelopments

)()(ˆ hgq,h zfragxpdfpartfDIS

how to study the nucleon structure how to study the nucleon structure ??… deep-inelastic scattering (DIS) :

)cos(12EE'qQlab

22 -

,2Mν

Qx

2lab

E'Eνlab

[0,1] x

Q2

,ν

Ez h

lab

factorisation:

universal, parametrises the structure of the nucleon

experimental prerequisitesexperimental prerequisites-the 2-the 2ndnd generation- generation-

HERMES: 27 GeV e, e

COMPASS @CERN: 160 GeV

Compass: d , p

HERMES: p , d, 3He unpol. H, D, 4He, N, Ne, Kr, Xe Nf

1

PP

1

tb

f: target dilution factor f=1 gas targets, f~0.02 solid targets

f=1

1995-2007

2002-2010-?

@DESY

experimental prerequisitesexperimental prerequisites-the 2-the 2ndnd generation- generation-

HERMES: 27 GeV e, e

COMPASS: 160 GeV

Compass: d , p

HERMES: p , d unpol. H, D, 4He, 14N, 20Ne, Kr, Xe

f=1

hadron ID:

SMC

E155HERMESE142

experimental prerequisitesexperimental prerequisites-the 2-the 2ndnd generation- generation-

HERMES: 27 GeV e, e

COMPASS: 160 GeV

Compass: d , p

HERMES: p , d unpol. H, D, 4He, 14N, 20Ne, Kr, Xe

f=1

hadron ID

DIS

polarisedpolarised structure function g structure function g11

q

2q1 )qq(e

2

1(x)g

)(q)(qq(x) xx

)(xq )(xq

polarisedpolarised structure function g structure function g11

q

2q1 )qq(e

2

1(x)g

assume saturation of 1d :

a0=

= 0.35 ± 0.03(stat) ± 0.05(sys+evol)

MS

polarisation of quarkspolarisation of quarks

a0=

MS

from theoryfrom hyperon beta decay

NS

s

CaC

a 8d

10 4

19

1

(exp) (theory) (evol)

= 0.330 ± 0.025 ± 0.011 ± 0.028a0=

MS

QCD-fit:

qq and and GG from inclusive datafrom inclusive data

• valence quarks are well determined: uv >0, dv <0

• gluons and sea quarks are poorly constraint by data SU(3)f symmetry

implicitly assumed

])Q,(g)Qq(x,[e2

1)Qx,( g

2qq

22q

2LO1

2NLO1 CxCegg

flavour separation: flavour separation: semi-inclusivesemi-inclusive DIS DIS

s=0

up

down

strange

u

d

HERMES: only direct 5-flavour separation of polarised pdfs

in short:

• u(x) is large and positive

• d(x) is smaller and negative

• u, d, s are approx. zero !

awaiting results from lower values of x

-0.1

0

0.1

0.2

0.3

0.001 0.01 0.1 1

AAC06

GRSV

BB

LSS

-0.6-0.4-0.2

00.20.40.60.8

11.21.4

0.001 0.01 0.1 1

x

xg(x)

Q2 = 1 GeV2

x(x)

AACBB

GRSV

LSS

…reminder: from scaling violation

how to measure the gluon how to measure the gluon polarisation polarisation G G

[hep-ph/0603213]

-0.1

0

0.1

0.2

0.3

0.001 0.01 0.1 1

AAC06

GRSV

BB

LSS

-0.6-0.4-0.2

00.20.40.60.8

11.21.4

0.001 0.01 0.1 1

x

xg(x)

Q2 = 1 GeV2

x(x)

AACBB

GRSV

LSS

…reminder: from scaling violation

how to measure the gluon how to measure the gluon polarisation polarisation G G

[hep-ph/0603213]

need more direct probes

unpolarised DIS

0.0350.054 d -

0.0340.028 s

direct measurement of direct measurement of GG • golden channel: charm productiongolden channel: charm production

theoretically very cleantheoretically very clean experimentally very challengingexperimentally very challenging

• hadron production at high Phadron production at high PTT (hard scale)

experimentally very cleanexperimentally very clean

highly model dependenthighly model dependent

due to variety of background processes

Photon-Gluon Fusion (PGF)

0.0350.054 d -

0.0340.028 s

‘‘direct’ measurement of direct’ measurement of GG

• hadron production at high Phadron production at high PTT (hard scale)

PGF

experimentally very cleanexperimentally very clean

highly model dependenthighly model dependent

+ + + ..q

g

q

g qg

other sub-processes make life hard:

extraction relies on Monte Carlo description of subprocesses (pythia)

• golden channel: charm productiongolden channel: charm production

direct measurement of direct measurement of GG

• hadron production at high Phadron production at high PTT

HERMES Preliminary

x

g/g

@x[0.06,0.3]

g/g ~ zero!

Q2

t

)(ˆ),,(

),,( 2Q|fixed

amplpart

excl

MxtGPD

xt

hunting for Lhunting for Lqq

Ji’s sum rule:

Generalised Parton Distributions (GPDs) appear in the factorisation scheme for hard exclusive processes

gz

qzgq

Nz LL

2

1JJ

2

1s G

)),,(E),,(H(2

1J gq,gq,

1

10

gq, txtxxdxlimt

≈30% ≈zero

GPDsonly known framework to gain information on 3D picture of hadrons

3D picture of the nucleon3D picture of the nucleon

form factorslocation of partons in nucleon

parton distributionslongitudinal momentum fraction x

generalised parton distributionslongitudinal momentum fraction x at transverse location b

T

very ambitious

measurements

• high beam energy (hard process)• very high luminosity (small cross sections)• complete event reconstruction (ensure exclusivity)

Deeply Virtual Compton ScatteringDeeply Virtual Compton Scattering

Ju=0

Ju=0.2

Ju=0.4GPD model by: [Goeke et al. (2001), code:VGG] [Ellinghaus et al. (2005)]

γpe pe ''

sensitive to Jq

DVCS transverse target-spin asymmetry:

different beam charges polarised beams polarised targets

only @HERA

hunting for Lhunting for Lqq

model dependent constraint of Ju vs Jd

hep-ex/0606061

0709.0450[nucl-ex]

arXiv:0705.4295[hep-lat]

Ju +

Jd /2

.9=

0.4

2±

0.2

1(e

xp)±

0.0

6(th

)

dedicated measurements of exclusive

processes:

@HERMES with recoil detector (2006/07)

JLab Hall-A and Hall-B experiments (2007++)

transverse spin phenomenatransverse spin phenomena

beyond collinear approximationbeyond collinear approximation

[courtesy of A. Bacchetta, DESY]

q

longitudinally polarisedquarks and nucleons

q(x): helicity difference

transversely polarisedquarks and nucleons

q(x): helicity flip

transversity

unpolarised quarksand nucleons

q(x) spin averaged

well known

q q

the nucleon quark structure the nucleon quark structure

nxqxqxqx T1

55LTw2Corr Sγγ)(γ)(S)(

2

1)(

q

longitudinally polarisedquarks and nucleons

q(x): helicity difference

transversely polarisedquarks and nucleons

q(x): helicity flip

transversity

unpolarised quarksand nucleons

q(x) spin averaged

well known

q q

the nucleon quark structure the nucleon quark structure

nxqxqxqx T1

55LTw2Corr Sγγ)(γ)(S)(

2

1)(

• probes relativistic nature of quarks

otherwise q q

• no gluon analog for spin-1/2 nucleon different Q2 evolution than q

• sensitive to valence quark polarisation

• only known way to obtain tensor charge

Peculiarities ofPeculiarities of qq

peculiarity of transversitypeculiarity of transversity• transversity flips helicity of both quark and nucleon

chiral-odd

chiral-odd

partnerXpp ll

Drell-Yan:

... X,'N hll

Chiral-odd fragmenation

funtion Collins FF : )(H1 z

hadron production:hadron production:

parthDIS zHxq ˆ)()( 1

needs

DIS: XlN l(PAX@FAIR)

Collins fragmentation functionCollins fragmentation function

Collins FF H1(z,kT

2) correlates transverse spin of fragmenting

quark and transverse momentum Ph of produced hadron h

h

h

q q

chiral–odd & naïve T–odd

produces left-right asymmetry in the direction of the outgoing hadron

leads to single-spin asymmetries

q

qq zHxqeS )()()sin(||2),( 12

STSUT

)()()sin(||2 112

ST zDxfeSq

qqTq

single-spin asymmetriessingle-spin asymmetries Unpolarised lepton beam (U) Transversely polarised target (T)

• describes correlation between intrinsic quark pT and transverse nucleon

spin• non-zero Sivers DF requires non-vanishing orbital angular momentum • Chiral – even & naïve T – odd

Sivers distribution function:

distinct signature!

Sivers asymmetriesSivers asymmetriesep X

)()( 1T1 zDxf qq )()( 1T1 zDxf qq

are substantial and positive: • first unambiguous evidence for a non-zero T-odd distribution function in DIS

• requires non-zero quark orbital angular momentum ! crucial test of pQCD:

DYT1DIST1 )()( qq ff DYT1DIST1 )()( qq ff

Collins asymmetriesCollins asymmetries

)()(δ 1 zHxq q )()(δ 1 zHxq qep X

first time: transversity & Collins FF are non-zero!

• asymmetries positive –

no surprise: u-quark

dominance and expect q>0

sinceq>0• large negative

asymmetries – ARE a

surprise: suggests the disfavoured CollinsFF being large and with oposite sign:

)()( fav,1

disfav,1 zHzH )()( fav,

1disfav,

1 zHzH

Collins asymmetriesCollins asymmetries

)()(δ 1 zHxq q )()(δ 1 zHxq qep X

• deuteron target:

)(δ)(δ xdxu )(δ)(δ xdxu

)()(δ 1 zHxq q )()(δ 1 zHxq q

Xπe'pe

Xhe'de

Xππee jet2jet1

global fit

xd

(x)

xu

(x)

up

down

q

first glimpsefirst glimpse of transversity of transversity

[Anselmino et al. PRD75(2007)]

structure of the nucleonstructure of the nucleonfrom unpolarised

DISfirst glimpse

direct flavourdecomposition

from polarised DIS :

a0==0.330±0.025(exp)

first extraction of q

first signals of GPDs: Ju +Jd

new concepts:

GPDs 3D picture of the nucleon

TMDs beyond collinear approximation

structure of the nucleonstructure of the nucleon

firstglimpse

first extraction of q

first signals of GPDs: Ju +Jd

extrapolation x0, x1

-the open tasks--the open tasks- detailed measurement

of x-dependence

detailed measurement

in 3 kine

variables detailed measurement

in 2 kine

variables

structure of the nucleonstructure of the nucleon

firstglimpse

first extraction of q

first signals of GPDs: Ju +Jd

-the future facilities--the future facilities-

polarised collider:EIC EIC,

PAX@FAIR

RHIC,EIC,(JPARC)

JLab@12GeVCompass-DVCS

EIC

future facilitiesfuture facilities high CM energies wide kinematic range in x and Q2

high luminosities mapping out observables differential in 2D and 3D

polarised beams and targets

@12 GeV

1 10 100 CM energy (GeV)

10

102

Lu

min

osit

y(*

103

0/c

m2

/s)

103

104

105

109

106

108

107

107

JLab

JLab@12GeV

HERMES

COMPASS

HERA

ELIC

eRHIC

EIC EIC (eRHIC, ELIC)(eRHIC, ELIC)

mapping out GPDs by measuring exclusive process

e p

‘dream machine’ for polarised DIS`: would address all open questions

future facilitiesfuture facilities high CM energies wide kinematic range in x and Q2

high luminosities mapping out observables differential in 2D and 3D

polarised beams and targets

1 10 100 CM energy (GeV)

10

102

Lu

min

osit

y(*

103

0/c

m2

/s)

103

104

105

109

106

108

107

107

JLab

JLab@12GeV

HERMES

COMPASS

HERA

ELIC

eRHIC

EIC EIC (eRHIC)(eRHIC)

Zusammenfassung Zusammenfassung

neue, komplementäre Konzepte/Entwicklungen:

neue Entwicklungen in der Spinphysik:

gz

qzgq

Nz LL

2

1JJ

2

1s G

≈30% ≈Null

Wege zur Messung aller Komponenten der Spin-SR sind aufgezeichnet;

wir müssen sie gehen ! neue Anlagen (EIC)

GPDs : Korrelation von longitudinalem Impuls + transvesaler

Position 3D Abbild des Nukleons

TMDs : Korrelation von transversalem Impuls + Spin

jenseits kollinearer Näherung

Backup slidesBackup slides

templatetemplate-GPDs correlation of longitudinal

momentum and transverse location

-TMDs correlation of transverse momentum and spin explore spin-orbit structure beyond collinear approximation

EIC: Lumi:• eRHIC: ~2*1032 /cm2/s(~1033 /cm2/s with R&D)• ELIC: ~1034 /cm2/s

)Q(x,Fν

pp)Q(x,FW 2

2

νμ2

1μν

μν g

...),(b(...)6

1),(b 2

22

1 QxQxr

polarised polarised inclusiveinclusive DIS DIS

μνμν'

2

WLdEd

d

)Xe'pe(

)Q(x,gqpSqSp

ν

1)Q(x,gS

ν

qiε 2

2σσ2

1σλμνλσ

spin1: often neglected… but:

polarisedpolarised structure function g structure function g11

q

2q1 )qq(e

2

1(x)g

)(F

)(g(x)A

1

11 x

x

)Xe'pe( h

polarised polarised semi semi -inclusive DIS-inclusive DIS

f

fff zDdxqz )()()(d hqh

distributionfunction

fragmentationfunction

‘purities’ (based on MC tuned to HERMES multiplicities)

0

s

s,

s

s,

d

d,

u

u,

d

d,

u

uQ

//

/,1/,1/,1 ,,A Kdpdpdp AAA

QPA

how to further proceed ?how to further proceed ?• q and q and G from inclusive G from inclusive

DIS data viaDIS data via evolution evolution

equations :equations : requires wide kinematic range in Q2 and x

unpolarised DIS

only fixed target spin experiments so far …

need polarised collider

to

extend kinematic

coverage

need polarised collider

to

extend kinematic

coverage need more direct probes

OR:

0.0350.054 d -

0.0340.028 s

direct measurement of direct measurement of GG • golden channel: charm productiongolden channel: charm production theoretically very cleantheoretically very clean experimentally very challengingexperimentally very challenging

• @HERMES (√s=7 GeV): hadron production at high Phadron production at high PTT

ALL

g/g = 1g/g = 0g/g = 1

PythiaMC:

direct measurement of direct measurement of GG • golden channel: charm productiongolden channel: charm production

• @HERMES: hadron production at high PT

: direct, resolved, soft processesXhed

PGF

QCD 22(g)

signal processes:

||A bg||

bgAr sig||

sigAr

[Pythia MC]

direct measurement of direct measurement of GG • golden channel: charm productiongolden channel: charm production

• @HERMES: hadron production at high PT

Xhed

hunting for Lhunting for Lqq Generalised Parton Distributions (GPDs)

hard exclusive processes are difficult to measure: • high beam energy (hard process)• very high luminosity (small cross sections)• complete event reconstruction (ensure exclusivity)

• no complete event reconstruction missing mass (MX) technique:

CLAS MC

associated BHBethe-Heitler

+ data

HERMES

MN

Deeply Virtual Compton Deeply Virtual Compton ScatteringScattering

Bethe-Heitler

DVCS-BH interference leads to non-zero azimuthal asymmetry

γpepe ''

)τττ(τ |τ||τ|dσ BH*DVCSDVCS

*BH

2DVCS

2BH

DVCS

Bethe-Heitler

BH

II

d

dd

)(d)(d

)(d)(d)(A

= xB/(2-xB ),k = t/4M2

UT ~ sin∙Im{k(H - E) + … }

C ~ cos∙Re{ H + H +… }~

LU ~ sin∙Im{H + H + kE}~

DVCS asymmetries DVCS asymmetries )τττ(τ |τ||τ|dσ BH

*DVCSDVCS

*BH

2DVCS

2BH

UL ~ sin∙Im{H + H + …}~

polarisation observables:

UT

beam target

kinematically suppressed

H

H

H, E

~

different charges: e e (only @HERA!):

H

DVCS: beam charge DVCS: beam charge asymmetryasymmetry

- VanderhaeghenVanderhaeghen (1999/02)(1999/02) ––

HERA: 2005/06 e beam (10x)

e+/- p → e+/- p X<1.7 GeVin HERMES acceptance

Regge, D-term

Regge, no D-term

fac., D-termfac., no D-term

γpepe ''/-

AC sensitive to GPD-models

GPD calculations:

different parametrisations for H

tiny e-p sample (L=10pb-1) simultanous fit of charge and polarisation observables provide pure interference term

e+/e-

27.5 GeV

2006-07:2006-07:

dedicated measurements of hard exclusive processes with recoil

prospects for exclusive prospects for exclusive processesprocesses

Bg ~10% Bg ~1%

detection of recoiling proton