delia hasch
DESCRIPTION
Spinstruktur des Nukleons -elektromagnetische Sonden bei hohen Energien-. Delia Hasch. KHuK - Perspektivtagung, GSI, 25/26. Oktober 2007. the spin of the nucleon. outline:. prerequisites. polarisation of quarks:. polarisation of gluons: D G. hunting for the OAM L q,g. new - PowerPoint PPT PresentationTRANSCRIPT
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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
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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
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)()(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
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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
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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:
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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
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polarisedpolarised structure function g structure function g11
q
2q1 )qq(e
2
1(x)g
)(q)(qq(x) xx
)(xq )(xq
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polarisedpolarised structure function g structure function g11
q
2q1 )qq(e
2
1(x)g
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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:
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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
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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
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-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]
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-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
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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)
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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)
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• 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!
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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
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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)
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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
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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++)
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transverse spin phenomenatransverse spin phenomena
beyond collinear approximationbeyond collinear approximation
[courtesy of A. Bacchetta, DESY]
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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)(
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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
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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)
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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
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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!
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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
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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
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Collins asymmetriesCollins asymmetries
)()(δ 1 zHxq q )()(δ 1 zHxq qep X
• deuteron target:
)(δ)(δ xdxu )(δ)(δ xdxu
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)()(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)]
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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
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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
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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
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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
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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)
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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
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Backup slidesBackup slides
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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
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)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:
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polarisedpolarised structure function g structure function g11
q
2q1 )qq(e
2
1(x)g
)(F
)(g(x)A
1
11 x
x
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)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
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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:
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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:
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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]
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direct measurement of direct measurement of GG • golden channel: charm productiongolden channel: charm production
• @HERMES: hadron production at high PT
Xhed
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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
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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
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= 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
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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
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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