1 PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer The Quest for the spin of the proton ! or...
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Transcript of 1 PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer The Quest for the spin of the proton ! or...
1PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
The Quest for the spin of the proton !or
“You think you understand something?Now add spin…” - R. Jaffe
2PheniX- FoCal - Workshop, May 2009
How do the partons contribute
E.C. Aschenauer
SqDq
DG
Lg
SqLq
dq1Tf
SqDq
DG
Lg
SqLq dq1Tf
Is the proton looking like this?
“Helicity sum rule”
12h= P, 12 |J QCD
z |P, 12 = 12q
∑ Sqz+Sg
z+ Lqz
q∑ +Lg
z
total u+d+squark spin
angular momentum
gluonspin Where do we stand
solving the “spin puzzle” ?
Dq & DG contributions to the proton spin
E.C. Aschenauer
3PheniX- FoCal - Workshop, May 2009
γ*
u,d,s,gpolarized DIS
SqDq, DG
γ*
u,d,s
p,K
polarized SIDISDqf
polarized pp scattering
Dqf, DG
u,d,s,g
u,d,s,g
u,d,s,g
p,Kjet
Existing data from:
to extract polarized PDFs! a “global QCD analysis” is required !
all processes tied together: universality of pdfs & Q2 – evolution
each reaction provides insights into different aspects and kinematics
in NLO
DSSV PRL101:072001,2008
Inclusive World data
4PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
not in DNS
: input to the old GRSV-analysis
: input to the DIS & SIDIS – analysis by DNS
Inclusive DIS-Data:
Semi-Inclusive World Data
5PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
not in DNS Semi-inclusive DIS-Data:
6PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
includes all world data from DIS, SIDIS and pp Kretzer FF favor SU(3) symmetric sea, not so for KKP, DSS DS ~25-30% in all cases
D. De Florian et al. arXiv:0804.0422 NLO @ Q2=10 GeV2
NLO FIT to World Data
KretzerKKP
c2DIS c2
SIDIS Duv DuDdv Dd Ds Dg DS
206206
225231
0.940.70 -0.26
-0.340.087-0.049
-0.11-0.055
-0.045-0.051
0.310.28
DSS 0.813 -0.458 0.036 -0.115 -0.057 0.242
New semi-inclusive data
7PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
Compass: Deuterium-Data:
x
large x-range 0.005 < x < 0.2Proton data still to come
Will the RHIC W-data really be competitive ??x-range and statistics (300 pb-1 polarization: 0.7)
but no FF-knowledge required
Polarized Strangeness
8PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
Driven by SIDISK-AsymmetriesK-FFdominated by
Driven bySU(3); (3F-D)
New Results from
isoscaler method AK++K- & Aincl
“Purity” Method using FF
Input : A1,d , A1,dπ +
, A1,dπ−
, A1,dK+
, A1,dK−
Results are completely consistent with Hermessea quark polarizations ~ 0
Big question: What will happen to DSSV-Ds
9PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
More on Strangeness PDF Kaon multiplicities from Deuterium target
strange quark sea in proton and neutron identical fragmentation simplifies
Only assumptions used: isospin symmetry between proton and neutron charge-conjugation invariance in fragmentation
.( ) 4 ( ) ( )K K K K Kds un trD z dz D z dz D z dz
( ) 2 ( )strangK K K
seD z dz D z dz
.( ) ( ) ( ) ( )( ) /
( ) / 5 ( ) 2 ( )nK
str strangKK
Dis
eQ x D z dz S x D z dzdN x dx
dN x dx Q x S x
Fit x-dependence of multiplicitiesusing PDFs from CTEQ-6
dotted:CTEQ-6L & fit ( )K
SD z dz( )K
QD z dzdashed:
solid:S(x)=Q(x): CTEQ-6L & DSS
1 2/ (1 )a x ax e x
s(x) + sbar(x)
dashed-dotted:
€
DsK (z )dz
The Gluon Polarization
10PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
unpolarised cross sections nicely reproduced in NLO pQCD
in NLO
RHIC: many sub-processes with a dominant gluon contribution high-pT jet, pion, heavy quark, …
RHIC Data
11PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
STAR
GRSV curves with cone radius 0.7 and -0.7 < < 0.9
2005 jet data: PRL 100, 232003 (2008)
2005: PRD 76, 051106
2006: arXiv:0810.0694
p0 @ 200 GeV
The Gluon Polarization
12PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
x
RHIC range0.05· x · 0.2
small-x0.001· x · 0.05
large-xx ¸ 0.2
Dg(x) very small at medium x best fit has a node at x ~ 0.1 huge uncertainties at small x
small-x behavior completely unconstrained
Dg(x) small !?
Δg(x) dx0.
1
∫ = −0.084@10GeV 2
δ g = Δg(x,10GeV 2 ) dx0.05
0.2
∫
Need to enlarge x-range
13PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
Compass & Hermes: The golden channels for Dg
Idea: Direct measurement of DGIsolate the photon gluon fusion process
detection of hadronic final states charmed mesons
high pT pairs of hadrons
single high pT hadronsh±h±
h±
2 1Q 2 0.1Q
2 0.1Q 2 0.1Q
less sub-processes contributing
more sub-processes contributing higher statistics
less sub-processes contributing
more sub-processes contributing higher statistics
+ + + ..
|||| ||| |( ) ;B SigSig
gmeas i it i i
i tB
tog f AA p f A ff A
|| ||ˆ]
1[ meas
Sig
BgBgf
GA
aA
G
f
Δ
Several possible contributions to the measured asymmetryMC needed to determine R and aLL
q
g
q
g qg
Important at Q2<0.1
h±h± vs. h±: h± more inclusive → pQCD NLO calculations (easier) possible
Dg from electro production
14PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
DSSV gluon agrees well with model-dependent “LO” extractions of Dg/g
not in global fit[NLO not available]
a future global NLO fit will use measured ALL not derived Dg/gneed first to check unpolarized cross section
15PheniX- FoCal - Workshop, May 2009
Beyond form factors and quark distributions
E.C. Aschenauer
Generalized Parton Distributions
Proton form factors, transverse charge & current densities
Structure functions,quark longitudinalmomentum & helicity distributions
X. Ji, D. Mueller, A. Radyushkin (1994-1997)
Correlated quark momentum and helicity distributions in transverse space - GPDs
How to access GPDs?
quantum number of final state selects different GPDs: theoretically very clean DVCS (g): H, E, H, E VM ( , , ):r w f H E info on quark flavors
PS mesons ( , )p h : H E ~
~ ~
~
ρ0 2u+d, 9g/4
ω 2u-d, 3g/4f s, g
ρ+ u-d
J/ψ g
p0 2Du+Ddh 2Du-Dd
J
qz =
12
xdx H q + E q( )−1
1
⎛⎝
⎞⎠t→ 0
J q
z =12
Δqq∑ + Lq
z
q∑
12=J q
z + J gz =
12
Δqq∑ + Lq
z
q∑ + J g
z
E.C. Aschenauer
16PheniX- FoCal - Workshop, May 2009
W & t dependences: probe transition from soft hard regime
VM production @ small x
r fJ/Y
U
s ~ Wd
steep energy dependence of s in presence of the hard scale
s ~ e-b|t|
universality of b-slope
parameter: point-like
configurations dominate
E.C. Aschenauer
17PheniX- FoCal - Workshop, May 2009
18PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
HERMES / JLAB kinematics: BH >> DVCS
Deeply Virtual Compton Scattering DVCS
two experimentally undistinguishable processes:
DVCS Bethe-Heitler (BH)
p + D
* 2 2*~ | | | |BH DVCS DVC BS HB DVCSHd
isolate BH-DVCS interference term non-zero azimuthal asymmetries
€
d / dpedΩedΩγ(pb / GeVsr 2 )
H, %H, E, %E
most clean channel for interpretation in terms of GPDs
can measure DVCS – cross section and I
19PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
HERMES: combined analysis of charge & polarization dependent data separation of interference term + DVCS2
DVCS
Beam Charge Asymmetry
~ Ac(n=0)cosΦ
~ Re[F1H]
higher twist
higher twist
LU (Φ, Pl ,el ) = σ UU (Φ){1 + Pl ALUDVCS (Φ) + el Pl ALU
I + el AC (Φ)}
snI sin(nΦ)
n=1
2
∑ cnI cos(nΦ)
n=1
3
∑Beam Spin Asymmetry
~ Im[F1H]
DVCS
DVCS from &
20PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
Archiv: 0812.2517
only some appetizers on existing data lets see what theory says
Hermes BCA CLAS BSA
Hall A Hall A
different GPD parametrisations
Results from Theory
21PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
con
trib
uti
on
to n
ucle
on
sp
in
mp2 GeV2
LHPC Collab. hep-lat/0705.4295
Lattice:K. Kumericki & D. MuellerarXiv: 0904.0458
t=0
t=-0.3
First hints for a small Jq Lq
More insights to the proton - TMDs
22PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
Unpolarized distribution function q(x), G(x)
Helicity distribution function Dq(x), DG(x)
Transversity distribution function dq(x)
kr⊥q
Correlation between and rs⊥
q
kr⊥q
Correlation between and rS⊥
N
Correlation between and rs⊥
q rS⊥
N
Sivers distribution functionf1T⊥
Boer-Mulders distribution functionh1⊥
Single Spin Asymmetries
Explore spin orbit correlations
peculiarities of f^1T
chiral even naïve T-odd DFrelated to parton orbital
angular momentumviolates naïve universality of
PDFsQCD-prediction:
f^1T,DY = -f^1T,DIS
also valid for BM-fct h^1
Transverse Polarization Effects @ RHIC
23PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
Left
-Right
Naive pQCD (in a collinear picture) predicts AN ~ mq/sqrt(s) ~ 0
However, large AN observed in forward pions / Kaons.
Proposed mechanisms - Sivers - Collins - twist-3 process - ...need correlations between particles ( -g jet)to disentangle underlying process
K+ > 0 K- ~ 0 K+ > p+
importance of sea quarks? Deuterium ~ 0
u and d quark cancel
24PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
HERMES & COMPASS Measurements
ASivers ∝ f1T^ (x)D1(z)
Proton
Proton: Sivers moment:
p+ > 0 p- ~ 0
hep-ex/0802.2160Deuterium
25PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
COMPASS p-data M. Anselmino et al.
combine Hermes Proton and Compass Deuterium add adhoc pt dependence to std. unpol. FF extract flavor dependent f^1T
How does this compare with Compass p-data
Bummer, Hermes and Compass Sivers p-data disagree
What about Transversity?
Bummer, Hermes and Compass Sivers p-data disagree
What about Transversity?Perfect agreement !
The Boer-Mulders fct.
26PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
ddxdydzdΦdPh⊥
2 =2π a2
xyQ2y2
2(1−ε)(1+ γ2
2x)[FUU ,T + 2ε(1+ε)cosΦFUU
cosΦ +ε cos(2Φ)Fuucos(2Φ)]
Unpol. SIDIS cross section:
Boer-Mulders x Collins FF
remember Collins FF:H1fav⊥ (z)=−H1unfav
⊥ (z)
Boer-Mulders fct. for u and d quark seem to have same sign What do we know from DY-experiments???
h1,u⊥ =h1d
⊥ < 0
L.P. Gamber & G.R. Goldstein PRD 77, 094016, 2008
27PheniX- FoCal - Workshop, May 2009
Boer-Mulders fct. in Drell-Yan
Results from DY experiments at Fermi=Lab. and CERNLam-Tung relation (PRD 21 2712, 1980)
unpolarized DY:
E.C. Aschenauer
ddΩ
~1+λ cos2θ + μ sin2θ cosΦ+ν2
sin2θ cos2Φ 1- l = 2nd DY ~h1
⊥h1⊥ cos(2Φ)
p-W-DY: valence x valencepd-DY: valence x seapQCD
first BM- fct extractions very first hints h1,DY⊥ =−h1,DIS
⊥
New Fermi-Lab DY-Experiment E906What can we do at RHIC
Conclusions
28PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
What are the avenues for further important
measurements and theoretical developments?
we have just explored the tip of the iceberg
you are here
Lq,g
DsDg
Dutot, Ddtot
Du, Dd
spin sum ruleThank you for your attention
TMDs
29PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
BACKUP SLIDES
30PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
good agreement with NLO-QCDPolarised opposite to proton spin
Polarized Quark Densities
Du(x) > 0
First complete separation of pol. PDFs without assumption on sea polarization
Polarised parallel to proton spin
Dd(x) < 0
Du(x), Dd(x) ~ 0
No indication for Ds(x) < 0
In measured range (0.023 – 0.6)
0.002 0.043uΔ 0.054 0.035dΔ 0.028 0.034sΔ
DSS: good global fit of all e+e-, ep, and pp hadron data
31PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
de Florian, Sassot, MSmain results:
• results for p±, K±, chg. hadrons
• full flavor separation for DiH(z) and Dg
H
• uncertainties (L.M.) well under control• fits all LEP, HERMES, SMC, RHIC, … data • supersede old fits based only on e+e- data
apart from cross-over trajectory ( =x x) GPDs not
directly accessible: deconvolution needed ! (model dependent)
but only x and t accessible experimentally ),,( txH
x is mute variable (integrated over):
GPD moments cannot be directly revealed,
extrapolations t 0 are model
dependent
1
1
),,(~ dx
ix
txHT DVCS
ε
1
1
),,(),,(
~ tHidxx
txHP π
e.g.
cross sections & beam-charge asymmetry ~ Re(T
DVCS )
beam or target-spin asymmetries ~ Im(T DVCS )
accessing GPDs: some caveats
t=0q(x)
x=0 q(x)
E.C. Aschenauer
32PheniX- FoCal - Workshop, May 2009
detour: DSS kaon FF’s DiK(z)
33PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
RHIC pp data (BRAHMS,
STAR) explain different Dg
smaller u & larger s-frag. required by SIDIS
note: some issues with K- data (slope!)await eagerly final HERMES data
34PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
DsUT ~ sinf∙Im{k(H - E) + … }
DsC ~ cosf ∙Re{ H + xH +… }~
DsLU ~ sinf∙Im{H + xH + kE}~
DsUL ~ sinf∙Im{H + xH + …}~
polarization observables:
DsUT
beam target
kinematically suppressed
H
H
H, E
~
different charges: e+ e- (only @HERA!):
H
DVCS ASYMMETRIES
x = xB/(2-xB ),k = t/4M2
* 2 2*~ | | | |BH DVCS DVC BS HB DVCSHd
35PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
[M. Burkardt, M. Diehl 2002]
FT (GPD) : momentum space impact parameter space:probing partons with specified long. momentum @transverse position b
T
polarized nucleon:
[x=0]
from lattice
What does theory tell
d-quarku-quark
Sivers function and OAM
36PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
Anselmino et al. arXiv:0809.2677
Model dependent statement:
(1−x) f1T⊥q(x)=−3
2MCFαsEq(x,0,0)
dx0
1
(1−x) f1T⊥q(x)=−32MCFαsκ q
anomalous magnetic moment:
ku = 1.67kd = -2.03
x
Sivers fct. from fit to M. Burkardt et al.
Lattice: P. Haegler et al.lowest moment of distribution of unpol. q in transverse pol. protonand of transverse pol. quarks in unpol. proton
37PheniX- FoCal - Workshop, May 2009 E.C. Aschenauer
Hermes: Charge and Beam Spin Asymmetry Heavy Targets
Beam Charge Asymmetry
Beam Spin Asymmetry
Why nuclear DVCS: constrain nuclear GPDs constrain models attempting
to describe nuclear matter neutron and proton matter distribution in nuclei
Beam: 27.5 GeV e±; <50>% polarizationTarget: (un)-polarized gas targets; <85%> polarizationLumi: pol: 5x1031 cm-2/s-1; unpol: 3x1032-33 cm-2/s-1
Data taking finished June 2007
38
The contemporary experiments
E.C. Aschenauer
PheniX- FoCal - Workshop, May 2009
SM1
SM2
6LiD Target
160 GeV μ
RICH
ECal & HCalμ Filter
Trigger-hodoscopes
SiliconMicromegas
SciFi
Gems
Drift chambers
Straws
MWPC
50 m
Beam: 160 GeV m: 80% polarizationTarget: 6LiD: 50% polarization (2002-2006) NH3: 80% polarisation (2007)Lumi: 5x1032 cm-2s-1
STAR Detector
Beams: √s=200 GeV pp; 50% polarizationLumi: 50 pb-1