1 e.c. aschenauer recent results from lepton proton scattering on the spin structure of the nucleon
TRANSCRIPT
11EE.C. Aschenauer.C. Aschenauer
Recent results from lepton proton Recent results from lepton proton scattering on the spin structure scattering on the spin structure
of the nucleonof the nucleon
22EE.C. Aschenauer.C. Aschenauer
The The contemporarycontemporary experiments experiments
Beam: 27.5 GeV eBeam: 27.5 GeV e±±; <50>% polarization; <50>% polarizationTarget: (un)-polarized gas targets; <85%> polarizationTarget: (un)-polarized gas targets; <85%> polarization
Beam: 160 GeV Beam: 160 GeV ; 75% polarization; 75% polarizationTarget: Target: 66LiD; 50% polarizationLiD; 50% polarization
Two high-resolution Two high-resolution 4 GeV spectrometers4 GeV spectrometers
Hall A
Large acceptance spect. Large acceptance spect. electron/photon beamselectron/photon beams
Hall B
7 GeV spectrometer, 7 GeV spectrometer, 1.8 GeV spectrometer, 1.8 GeV spectrometer,
large installation large installation experimentsexperiments
Hall CBeam: ≤6 GeV eBeam: ≤6 GeV e--; 85% polarization; 85% polarizationTarget: polarized targets Target: polarized targets 33He, He, 66LiD, NHLiD, NH3 3
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1 1( )
2 2 v vu d 1 1( )
2 2 v gsv qLd LGqu
1 1( )
2 2 v svu q Gd
( ) s su d u d s s
News on the spin structure of the News on the spin structure of the nucleonnucleon
Naïve parton modelNaïve parton model
43 vu 1
3 vdBUTBUT
1989 EMC measured1989 EMC measured = 0.120 0.094 0.138= 0.120 0.094 0.138± ±
Spin PuzzleSpin Puzzle
Unpolarised structure fct.Unpolarised structure fct.
Gluons are important !Gluons are important !
Sea quarksSea quarks qqss
GG Full description of JFull description of Jqq and J and Jgg
needsneedsorbital angular momentumorbital angular momentum
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Deep Inelastic ScatteringDeep Inelastic Scattering
( , )E k( ', ')E k
qq22 2( ')qQ k k
'E E 2
2
Qx
Mv hEz
Important kinematic variables:Important kinematic variables:
cross section:cross section:
DFDF FFFF2
~'
Ld
d dEW
1 2 1 22( )
p p i ig q s q p qsF gs pF gW q
1 2 3 4
1 1 1( ) ( ) ( )
6 2 2r s t u s u s tb b b b
Spin 1Spin 1
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How to measure Quark How to measure Quark PolarizationsPolarizations
3/ 2 (~ )q x
* 3 / 2NSS
N qSS
1/ 2 (~ )q x
* 1/ 2NSS
N qSS
Virtual photon Virtual photon ** can only couple to quarks of opposite helicity can only couple to quarks of opposite helicity Select Select qq++(x)(x) or or qq--(x)(x) by changing the orientation of by changing the orientation of
target nucleon spin or helicity of incident lepton beamtarget nucleon spin or helicity of incident lepton beam
', ','||
', '
1 e h e he h
B Te h e h
N L N LA
P P N L N L
', ',', 1 / 2 3 / 2
|| ', ',1 / 2 3 / 2
~e h e h
e he h e hA
Asymmetry definition:Asymmetry definition:qq q
inclusiveinclusive DIS: only DIS: only e’e’ info used info used semi-inclusivesemi-inclusive DIS: DIS: e’+he’+h info used info used
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World data on inclusive DISWorld data on inclusive DIS
New data from COMPASS, New data from COMPASS, HERMES & JLab very preciseHERMES & JLab very precise
high x-behaviour consistent withhigh x-behaviour consistent with AA1 with x1 with x1 1
AA11d d consistent with zero consistent with zero
for x < 0.05for x < 0.05ProtonProton DeuteriumDeuterium
CLAS PLB 641, 11 (2006) AA11nn from from 33HeHe
(Hall-A)(Hall-A)
COMPASS PRD75(2007)012007COMPASS PRD75(2007)012007
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World data on inclusive DISWorld data on inclusive DIS
1 1 1
1 3( )(1 )
2 2d p n
Dg g g w Combine p and d to get n:Combine p and d to get n:
or or 33HeHe3
1 1 12He np
pnP Pg g g
What can we learn on the PDFsWhat can we learn on the PDFs
21 ~ [ Ge C GCg
LO-QCD2 ,1
2p nNSe q
, ]p nNS NSC q
Compass: hep-ex/0609038Compass: hep-ex/0609038Hermes: hep-ex/0609039Hermes: hep-ex/0609039
41 22 2 21 / 2 ( )
22 2( , ) (( , ) , )1
2
2/ 4 8 2
dunpolQ y
y yg x Q g x Qx
dA Q
y dx Q
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HERMES: IntegralsHERMES: Integrals
QQ22=5 GeV=5 GeV22, NNLO in MS scheme, NNLO in MS scheme
Saturation in deuteron integral is assumedSaturation in deuteron integral is assumed use only deuteriumuse only deuterium
80191 1
[ ]3 4(1 )2
d
NSS
D
CC w
a a
From hyperon beta decayFrom hyperon beta decay aa88=0.586=0.586±0.031±0.031From neutron beta decayFrom neutron beta decay
aa33=1.269±0.003=1.269±0.003
80 3
1[2 3 ]
6au u aa
80 3
1[2 3 ]
6ad d aa
80
1[ ]
3as s a
0.9
10.0210.0436 0.0012( ) 0.0018( ) 0.0008( ) 0.0026( )ddxg stat syst par evol
COMPASS: COMPASS:
0.08 0.01 0.02s s 0 0.33 0.03 0.05a
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CLAS: CLAS: qq
Using:Using:
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Polarised quark distributionsPolarised quark distributions
Correlation between detected hadron and struck Correlation between detected hadron and struck qqff
““Flavor – Separation”Flavor – Separation”Inclusive DIS:Inclusive DIS:
Semi-inclusive DIS:Semi-inclusive DIS:
( )u d u d s s
( , , , , , )u d u d s s
In LO-QCD:In LO-QCD:2 2
2 1/ 2 3 / 21 2 2
1/ 2 3 /
2
2'
22 ''
2( , )( , , ) ~
'( , )
( , )
( , )
( , )
( , )
hh hqh
h
q
qh
q qh q
e q x QA x Q z C
e
D z Q
D
q x Q
q Qq Q xzx Q
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COMPASS: Valence PDFsCOMPASS: Valence PDFs
/( ) ( )
( ) ( )
h h h h
h h h h
A
( ) ( )( )
( ) ( )K K v v
d dv v
u x d xA x A
u x d x
1 0 8
1 1( )
9 4N a a
1
0( ( ) ( ))v v vu x d x dx
1 8
8
1 13
2 121
( ) ( )2
Nv
v
u d a
s s a
For LO:For LO:
Assuming:Assuming:
vv is 2.5 is 2.5statstat away from flavour away from flavour symmetric sea scenariosymmetric sea scenario
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Polarised quark distributionsPolarised quark distributions
Correlation between detected hadron and struck Correlation between detected hadron and struck qqff
““Flavor – Separation”Flavor – Separation”Inclusive DIS:Inclusive DIS:
Semi-inclusive DIS:Semi-inclusive DIS:
( )u d u d s s
( , , , , , )u d u d s s
A PQTTTTTTTTTTTTTTTTTTTTTTTTTTTT
Extract Extract qq by solving:by solving:
1, 1, 1, 1, 1,( ( ), ( ), ( ), ( ), ( ))Kp p d d dA A x A x A x A x A x
TTTTTTTTTTTTTT( , , , , , )u d u d s s
Qu d su d s
TTTTTTTTTTTTTT
In LO-QCD:In LO-QCD:2 2
2 1/ 2 3 / 21 2 2
1/ 2 3 /
2
2'
22 ''
2( , )( , , ) ~
'( , )
( , )
( , )
( , )
( , )
hh hqh
h
q
qh
q qh q
e q x QA x Q z C
e
D z Q
D
q x Q
q Qq Q xzx Q
2( , , )hqP x Q z MCMC
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good agreement with NLO-QCDgood agreement with NLO-QCDPolarised opposite to proton spinPolarised opposite to proton spin
Polarized Quark DensitiesPolarized Quark Densities
u(x) > 0
First complete separation of First complete separation of pol. PDFs without assumption on pol. PDFs without assumption on sea polarizationsea polarization
Polarised parallel to proton spinPolarised parallel to proton spin
d(x) < 0
u(x), d(x) ~ 0~ 0
No indication forNo indication fors(x) << 00
In measured range (0.023 – 0.6)In measured range (0.023 – 0.6)
0.002 0.043u 0.054 0.035d 0.028 0.034s
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SIDIS data improves description of allSIDIS data improves description of all qq, especially light sea, especially light sea Kretzer FF favor SU(3) symmetric sea, not so for KKPKretzer FF favor SU(3) symmetric sea, not so for KKP~30%~30% in all casesin all cases
D. De Florian et al. hep-ph/0504155D. De Florian et al. hep-ph/0504155NLO @ Q2=10 GeV2
KretzerKretzer
KKPKKP
DIS SIDIS uv udv d s g
NLO FIT to DIS & SIDIS DataNLO FIT to DIS & SIDIS Data
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Several more fitsSeveral more fits
using mainly only inclusive data or a combination of inclusive and using mainly only inclusive data or a combination of inclusive and some semi-inclusive datasome semi-inclusive data
Results for Results for G still completely all over the placeG still completely all over the place Need a consistent approach for fit and uncertainty determinationNeed a consistent approach for fit and uncertainty determination
with all world data taken into accountwith all world data taken into account
G<0
G>0
G<0
G>0Lets measure Lets measure G more directlyG more directly
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The golden channelsThe golden channelsIdea: Direct measurementIdea: Direct measurement ofof GG
Isolate the photon gluon fusion process (PGF)Isolate the photon gluon fusion process (PGF) Open Charm productionOpen Charm production
Reaction:Reaction:
* 0 0p D D X * 0reconstruct Dc ,Dcˆ ˆ( , )
ˆ ˆ( , )
PGF
gPGF
N PGF
g
ds G x sA
ds G x s
PGF
LLa
G
G
(stat.)0.57 0.41 0.17G
G
2 20.15 13Gx GeV
LO-MC: AromaLO-MC: Aroma
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The golden channelsThe golden channelsIdea: Direct measurement ofIdea: Direct measurement of GG
Isolate the photon gluon fusion processIsolate the photon gluon fusion process
detection of hadronic final states with high pdetection of hadronic final states with high pTT
high phigh pTT pairs of hadrons pairs of hadrons
single high psingle high pTT hadrons hadrons
hh±±hh±±
hh±±
2 1Q 2 0.1Q
2 0.1Q 2 0.1Q
less sub-processes contributing less sub-processes contributing
more sub-processes contributing more sub-processes contributing higher statistics higher statistics
less sub-processes contributing less sub-processes contributing
more sub-processes contributing more sub-processes contributing higher statistics higher statistics
+ + + ..
|||| ||| |( ) ;B SigSig
gmeas i it i i
i tB
tog f AA p f A ff A
|| ||ˆ]
1[ meas
Sig
BgBgfG
Aa
AG
f
Several possible contributions to the measured Several possible contributions to the measured asymmetryasymmetry
MC needed to determine R and aMC needed to determine R and aLLLL
q
g
q
g qg
Important Important at Q2<0.1at Q2<0.1
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COMPASS ResultsCOMPASS Results
1 2, 0.7T Tp p GeV 2 2 2,1 ,2 2.5T Tp p GeV
Channel:Channel:hh±±hh±±
xxFF > 0.1 z > 0.1 > 0.1 z > 0.1m(hm(h11,h,h22) > 1.5 GeV) > 1.5 GeV
10% ofstatistics
RRPGFPGF = 0.34 +/- 0.07 = 0.34 +/- 0.07
22(scale) ~ 3 GeV(scale) ~ 3 GeV22 <x<xGG> > ~~ 0.130.13
|| 0.015 0.080( ) 0.013( )A
stat systD
0.06 0.31( ) 0.06( )stg
gat syst
QQ22 > 1 GeV > 1 GeV22 Cuts:Cuts:
QQ22 < 1 GeV < 1 GeV22
used for used for g/g extractiong/g extraction
&&
g/g=g/g=0.016±0.058(stat.)±0.055(syst.)0.016±0.058(stat.)±0.055(syst.)0.070.0350.085gx 22=3.0GeV=3.0GeV22
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HERMES ResultsHERMES Results Channels:Channels:hh±±hh±±, h, h±±
Subprocess AsymmetriesSubprocess Asymmetries(using GRSV std.)(using GRSV std.)
Subprocess FractionsSubprocess Fractions
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World Data on World Data on G/GG/G
Long way to go till Long way to go till g(x)g(x)
xx
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The Hunt for LThe Hunt for Lqq
Study of hard Study of hard exclusive processesexclusive processes leads to leads toa new class of PDFsa new class of PDFs
GGeneralized eneralized PParton arton DDistributionsistributions
, , ,q qq qH H EE
possible access topossible access toorbital angular momentumorbital angular momentum
1
1 0
1
2q
t
HJ Exdx
1
2q qLJ
exclusive:exclusive: all products of the reaction are detected all products of the reaction are detected missing energymissing energy ( (E) and missing Mass (ME) and missing Mass (Mxx) = 0) = 0 from DIS: ~0.3from DIS: ~0.3
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GPDs IntroductionGPDs Introduction
What does GPDs charaterize?What does GPDs charaterize?
unpolarized unpolarized polarizedpolarized
, ,qH x t , ,qH x t
, ,qE x t , ,qE x t
conserve nucleon helicityconserve nucleon helicity( ,0,0) , ( ,0,0)q qH x q H x q
flip nucleon helicityflip nucleon helicitynot accessible in DISnot accessible in DIS
DDVVCCSS
quantum numbers of final state select different GPDquantum numbers of final state select different GPD
,q qH Epseudo-scaler mesonspseudo-scaler mesons
,q qH Evector mesonsvector mesons
AACC,A,ALULU,, AAUTUT, A, AULUL
qEqHqEqHAAUTUT,,++ AAUTUT,,
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HERMES / JLAB HERMES / JLAB kinematics: BH >> DVCSkinematics: BH >> DVCS
DVCSDVCStwo experimentally undistinguishable processes:two experimentally undistinguishable processes:
DVCSDVCS Bethe-Heitler (BH)Bethe-Heitler (BH)
p + p +
* 2 2*~ | | | |BH DVCS DVC BS HB DVCSHd
isolate isolate BH-DVCS interferenceBH-DVCS interference term non-zero azimuthal asymmetries term non-zero azimuthal asymmetries
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UT ~ sin∙Im{k(H - E) + … }
C ~ cos∙Re{ H + H +… }~
LU ~ sin∙Im{H + H + kE}~
UL ~ sin∙Im{H + H + …}~
polarization observables:polarization observables:
UT
beam target
kinematically suppressedkinematically suppressed
H
H
H, E
~
different charges: edifferent charges: e++ e e-- (only (only @HERA!):@HERA!):
H
DVCS ASYMMETRIESDVCS ASYMMETRIES
= xB/(2-xB ),k = t/4M2
* 2 2*~ | | | |BH DVCS DVC BS HB DVCSHd
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CLAS: DVCS - BSACLAS: DVCS - BSA
Integrated over tIntegrated over t
<-t> = 0.18 GeV2 <-t> = 0.30 GeV2 <-t> = 0.49 GeV2 <-t> = 0.76 GeV2
Accurate data in a Accurate data in a large kinematical large kinematical domaindomain
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AA way to E and Jway to E and Juu-J-Jdd
2 1Im( )F H F E
sin( )cos( ) ~sUTA
Hermes DVCS-TTSA:Hermes DVCS-TTSA:
Hall A nDVCS-BSA:Hall A nDVCS-BSA:
x=0.36 and Qx=0.36 and Q22=1.9GeV=1.9GeV22
Neutron obtained combining Neutron obtained combining deuterium and protondeuterium and proton
FF11 small u & d cancel in small u & d cancel in H1 1 2 22~ ( )
4LU
tF H x F F H F E
MA
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Can we constrain (JCan we constrain (Juu - J - Jdd))
first model dependent extraction of first model dependent extraction of JJuu - - JJdd possible possible
VGG-Code: GPD-model: LO/Regge/D-term=0VGG-Code: GPD-model: LO/Regge/D-term=0
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Access to LAccess to Lqq in semi-inclusive in semi-inclusive scatteringscattering
New structure function accessible with SSANew structure function accessible with SSA
2
11
sin( )
, ( , , )h s
TT
UU T h
h pF Dfx z P
MC[
std. FFstd. FFSivers Sivers DFFDFF
Side viewSide view Front viewFront view
right
left
photon
NOTE: QCD tells us that the FSI has to be attractive, NOTE: QCD tells us that the FSI has to be attractive, since quark and remnants form a color antisymmetric since quark and remnants form a color antisymmetric statestate
right
left
photon
right
left
proton
quarks
A distortion in the distribution of quarks in A distortion in the distribution of quarks in transverse space can give rise to a nonzero Sivers transverse space can give rise to a nonzero Sivers functionfunction
The presence of spin can distort the distribution of The presence of spin can distort the distribution of quarks in transverse space (orbital angular momentum quarks in transverse space (orbital angular momentum of quarks is required)of quarks is required)
2929EE.C. Aschenauer.C. Aschenauer
HERMES & COMPASS MeasuremnetsHERMES & COMPASS Measuremnets
1 1( ) ( )Sivers TA f x D z ^1 1( ) ( )Sivers TA f x D z ^
DeuteriumDeuteriumProtonProton
Proton:Proton: Sivers moment:Sivers moment:
++ > 0 > 0 - - ~ 0~ 0 KK+ + > 0 K> 0 K- - ~ 0~ 0
KK++ > >++
sea quarks importantsea quarks important Deuterium ~ 0 Deuterium ~ 0
u and d quark cancelu and d quark cancel
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Results from theoryResults from theory
QCDSF/UKQCD Collab. (hep-ph/05110032) QCDSF/UKQCD Collab. (hep-ph/05110032)
Lattice QCD: SiversLattice QCD: Sivers
negative negative for up quarksfor up quarks
positive positive for down quarksfor down quarks
Anselmino et al., hep-ph/0511017Anselmino et al., hep-ph/0511017
[20] Anselmino et al., PRD72 (05)[20] Anselmino et al., PRD72 (05)
[21] Vogelsang, Yuan, PRD72 (05)[21] Vogelsang, Yuan, PRD72 (05)
[23] Collins et al., hep-ph/0510342[23] Collins et al., hep-ph/0510342
Pheno. analysis from data:Pheno. analysis from data:
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SummarySummary
GG
LLgg
LLqq
qq1Tf
GGLLgg
LLqq
qq1Tf
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Spin is fascinatingSpin is fascinating
Thank you for your attentionThank you for your attention
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BACKUP SLIDESBACKUP SLIDES
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)( S angle of hadron relative to angle of hadron relative to initialinitial quark spin (Sivers) quark spin (Sivers)
)( S angle of hadron relative to angle of hadron relative to finalfinal quark spin (Collins) quark spin (Collins)
1T1 Df (Sivers)(Sivers)
11 Hh (Collins)(Collins)
Azimuthal angles and asymmetriesAzimuthal angles and asymmetries
chiral-even naïve T-odd DFchiral-even naïve T-odd DF
related to parton orbital related to parton orbital momentummomentum
violates naïve universality of PDFviolates naïve universality of PDF
peculiarity of fpeculiarity of f1T1T
different sign of fdifferent sign of f1T1T in DY in DY