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
