Polarized Structure Functions - Jefferson Lab · Polarized Structure Functions Gerard van der...
Transcript of Polarized Structure Functions - Jefferson Lab · Polarized Structure Functions Gerard van der...
Polarized Structure Functions
Gerard van der Steenhoven (NIKHEF)
JLab, Newport News, 4 March 2002
u u
d
9th Int. Conference on the Structure of Baryons
Introduction
� The origin of spin in the baryon octet:
��� �
���q ��G� Lz
� Developing insight:
– EMC (SLAC, SMC and HERMES): ��q � ���� ���– The quark model: ��q � ���� � ���– Relativistic MIT bag model: ��q � ���� ����
� Experimental questions:
– What about flavour dependence?�u�x, �d�x, �s�x
– What about gluons?�G�x
– What about orbital angular momentum?Deeply Virtual Compton Scattering: Lz?
– What about other baryons?n, �,..
– What about lattice QCD?longitudinal spin: ��q � ����� ����
transverse spin: ��q � ���� ����
Outline
� Introduction
� Longitudinal spin:
– Inclusive experiments: gn�p� �x� gn�p� �x– Semi-inclusive experiments: �qf�x– Photo-production of high pT -pairs: �G�x– Deeply-virtual Compton scattering: Lz�x– Hyperon production: -spin
� Transverse spin:
– Single-spin asymmetries in �-production: h��x
1h = -
� Future perspectives:
– HERMES Run-II– COMPASS– RHIC-spin– SLAC– TESLA-N, EIC,...
Introduction
� Polarized Deep Inelastic Lepton Scattering:
θ
E
E'+1
-1/2
+1/2
photon
quark
quark
� Asymmetry w.r.t. to target spin orientation:
A� ��
DPTPB
N�� �N��
N�� �N��
� The spin-dependent structure function g��x :
A� � g��x
F��x� �
F��x
Xf
e�f�qf�x
with the quark polarization:
�qf�x � q�f �x � q�f �x
� General objective:
Spin structure of the nucleon
The HERMES experiment
� The HERMES spectrometer at DESY:
1
0
2
-1
-2
m
LUMINOSITY
CHAMBERSDRIFT
VC 1/2
FC 1/2
VERTEX CHAMBERS
TARGETCELL
DVC
MC 1-3
HODOSCOPE H0
MONITOR
BC 1/2
BC 3/4 TRD
MAGNET
PROP.CHAMBERS
FIELD CLAMPS
PRESHOWER (H2)
STEEL PLATE CALORIMETER
DRIFT CHAMBERS
TRIGGER HODOSCOPE H1
0 1 2 3 4 5 6 7 8 9
IRON
WIDE ANGLEMUON HODOSCOPE
FRONTMUONHODO
RICH
� Internal Target (���H , �
��H , �
��He, �He, ��N, ��Ne, ��Kr) :
gas injection
storage cell
fixed collimator
e-beam
spectrometer
exit window
pumps
suppressors
wake field
target
vacuum chamber
thin walled
beam pipe
Data collected in Run I
� Accumulated polarized DIS events per year:
Hermes Running 1996-2000
0
1000
2000
3000
4000
5000
6000
7000
8000
0 50 100 150 200 250 300Days of Running
Acc
umul
ated
DIS
[·10
3 ]
1996 (e++ p→
)
1997 (e++ p→
)
1998/99 (e-+ d→
)1999 (e++ d
→)
2000 (e++ d→
)
T. L
inde
man
n H
erm
es C
olla
bora
tion
onl
ine
anal
ysis
� Data taking in 2000:
– cell size reduced to 21 X 8.9 mm�
– lower cell temperature: 96 � 62 K
Luminosity increased by factor 2.5 !!
Unpolarized data taking
� End-of-Fill running:
– Last hour of every fill: high-density targets– Loss of normal data taking: few �– Targets used: �H, �H, �He, ��Ne– Positron beam life time: 0.5 – 2 hours– Data collected: 13.6 Million DIS events
0
20
40
60
80
100
120
12 14 16 18 20 22 0 2 4 6 8 10 12 14 16 18 20 22 24 2 4 6 8 10 12 0
10
20
30
40
50
60
HERA
Current-p [mA] Lifetime-e [h] Current-e [mA]
Time [h]
Fri Jul 14 12:00 2000 Sun Jul 16 12:00 2000
p: 103.6 [mA] -1.0 [h] 920 [GeV/c] e+: 41.0 [mA] 6.9 [h] 27.6 [GeV/c]
luminosity run
Tau(e)ProtonsLeptons
Maximum luminosity: 4 10�� N/cm�/s
� Dedicated HERA run at E = 12 GeV:
– HERMES spectrometer operated well– Collected: 1 Million DIS ev. on �H, �H, ��N, ��Kr.
Inclusive measurements - 1
� New deuterium data on gd��x�Fd� �x:
gd�F d�
��
� � �
�Ad��
D� �� � �Ad
�
�
0
0.1
0.2
0.3
0.4
10-2
10-1
x
g1d
F1d
HERMES PRELIMINARY(’00 data, no smearing correction)
exp. systematic uncertainty
uncertainty due to R
� Observation:
HERMES probes down to x � � ����
Inclusive measurements - 2
� Compare to existing data:
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
10-4
10-3
10-2
10-1
g1d
F1d
HERMES PRELIMINARY
SMC
E143
E155(averaged by HERMES)
(’00 data, no smearing correction)
10-2
10-1
1
10
10-4
10-3
10-2
10-1
x
<Q2>
GeV2
� Conclusion:
gd��x: no strong Q� dependence
Polarized Structure Functions
� Overview of existing xg��x data:
0
0.02
0.04
0.06xg1
proton
HERMESHERMES prel.HERMES prel. rev.
E143E155
SMC
0
0.02
0.04 deuteron
-0.04
-0.02
0
0.02
E142E154
x
neutron (3He)
0.0001 0.001 0.01 0.1 1
The structure function g��x
� Preliminary data from SLAC E143 and E155x:
[g��x� is sensitive to qg-correlations and higher twist]
gWW�
�x� exp.:� solid;M. Stratmann (93):
� dot-dash;Gamberg-Weigel (97):
� short-dash;Song (96):
� dotted;Wakamatsu (96):
� long-dash;
� Wandzura - Wilczek interpretation:
gWW� �x�Q� � �g��x�Q� �
Z �
x
g��y�Q�
ydy
g��x�Q� dominated by twist-2 part
Semi-Inclusive Asymmetries
� Asymmetry for semi-inclusive hadron (h) production:
Ah��x �
RdzP
f e�f �qf�xD
hf �zR
dzP
f e�f qf�xD
hf �z
Nh�� �Nh
��
Nh�� �Nh
��
� Define purity Phf �x:
Phf �x �
e�fqf�xRDhf �zdzP
f e�fqf�x
RDhf �zdz
[probability that hadron h is produced when quark f is hit]
� Measure asymmetries on various targets:
�A�x � P�x �Q�x
with �A�x� = (A�p,Ah�
�p , Ah�
�p , A�d, ...)and �Q�x� = (�u�x�, �d�x�, ��u�x�, ...)
� Polarized quark distributions: �u�x, �d�x, ...
Polarized quark distributions - 1
� Measured semi-inclusive asymmetries Ah��x:
-0.2
0
0.2
0.4
0.6
0.8
1
0.02 0.1
A1,d
HERMES prelim.(spring '99 data)
E143
0.02 0.1
A1,d
h+
HERMES prelim.(spring '99 data)
SMC
x0.02 0.1 0.7
A1,d
h−
� Extracted quarkspin distributions:
0
0.25
0.5
0.75 HERMES preliminary (1995 - Spring 1999)
(∆u+∆u–)/(u+u
–)
-1
-0.5
0
0.5(∆d+∆d
–)/(d+d
–)
-2
-1
0
∆qs/qs
0.02 0.1 0.6x
Spin - flavourseparation.
Polarized quark distributions - 2
� Expected data quality with ’00 data included:
HERMES ∆q extraction MC projection
0
0.25
0.5
x (∆
u +
∆u–
)
MC: 96/97 H→
+ 98-00 D→
HERMES publ. PLB 464 (1999) 123
-0.25
0
0.25
x (∆
d +
∆d–
)
CTEQ4LQ / (1+R)GRSV 2000 / (1+R)
0
0.05
x ∆u
–
0
0.05
x ∆d
–
-0.05
0
0.05
x ∆s
= x
∆s–
0.02 0.1 0.7x
M. B
eckm
ann,
J. W
endl
and,
H
ER
ME
S 2
001
High-pT hadron pairs from �H
� pQCD Compton graph and Photon-Gluon Fusion:
������
��
��
�
����
���
�� �� ��
�����
q
��
g
q
����
���
������
��
��
��
g
��
q
�q
� Asymmetry for high-pT pions (R � PGF�Com) :
AeN�h�h�LL � �aQCDC
�q
q
�
� �R� �aPGF
�G
G
R
� �R
� Target spin-asymmetry on long. polarized �H:
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.6 0.8 1 1.2 1.4 1.6 1.8 2
GSA (<∆G/G> ~ 0.4)GSB (<∆G/G> ~ 0.3)GSC (<∆G/G> ~ -0.1)
pTh2 (GeV/c)
A||(
pTh
1 ,pTh
2 )
pTh1>1.5 GeV/c ∆G/G=-1
∆G/G=0
∆G/G=+1
∆G/G=0.41
HERMES CollaborationPRL 84 (2000) 2584
High-pT hadron pairs on �H
� Require oppositely charged hadron pairs:
– PGF produces only (+ –) pairs: favored– pQCD on �H � more + hadrons: disfavored
� Preliminary results on �H:
pTh+ (GeV/c)
A||(
p Th-
,pT
h+)
pTh- (GeV/c)
A||(
p Th+
,pT
h-)
pTh2 (GeV/c)
A||(
p Th1
,pT
h2)
pTπ2 (GeV/c)
A||(
p Tπ1
,pT
π2)
-1-0.8-0.6-0.4-0.2
00.20.40.60.8
1
0.5 1 1.5 2-1
-0.8-0.6-0.4-0.2
00.20.40.60.8
1
0.5 1 1.5 2
-1-0.8-0.6-0.4-0.2
00.20.40.60.8
1
0.5 1 1.5 2-1
-0.8-0.6-0.4-0.2
00.20.40.60.8
1
0.5 1 1.5 2
High-pT kaon pairs
� Strangeness production suppressed in pQCD....
� High-pT kaon pairs on �H and �H:
pTK2 (GeV/c)
A||(
p TK
1 ,p T
K2 )
pTK2 (GeV/c)
A||(
p TK
1 ,p T
K2 )
pTK2 (GeV/c)
A||(
p TK
1 ,p T
K2 )
-1-0.8-0.6-0.4-0.2
00.20.40.60.8
1
0.5 1 1.5 2-1
-0.8-0.6-0.4-0.2
00.20.40.60.8
1
0.5 1 1.5 2
-1-0.8-0.6-0.4-0.2
00.20.40.60.8
1
0.5 1 1.5 2
� More statistics needed (+ MC studies)
Deep Virtual Compton Scattering
� Off-shell photon�-quark scattering:
– Detect e� and �, and require: Emiss = 0
� Ji’s sumrule [Phys. Rev. Lett. 78 (1997) 610]:Zxdx�H�x���� �E�x���� � � Aq��
� �Bq���
with �� � �t and
lim����
�Aq��� �Bq��
�� � �Jquark � �q � �Lq
� DVCS: total quark angular momentum
� Experimental considerations:
– Interference with Bethe-Heitler process:
DVCSN
BH makes DVCS measurable
– Detect scattered photon, but suppress � �’s– Observe azim. asymmetry: A BetheHeitler
LU � �
First observations of DVCS
� Missing mass spectrum and Asin�LU � �N
PNi�
sin�iPl�i
:
0
1000
2000
3000
4000
5000
-5 0 5 10 15 20 25 30 35 40 45
Co
un
ts
0
200
400
600
800
1000
-4 -2 0 2 4 6 8
Mx2 (GeV2)
Co
un
ts
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-1 0 1 2 3 4 5 6 7
e→+p → e+γ X
Mx (GeV)
AL
Usi
n φ
� Azimuthal (�) distributions from HERMES & JLab:
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-3 -2 -1 0 1 2 3
φ (rad)
AL
U
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0 50 100 150 200 250 300 350φ (deg)
A
HERMES, PRL 87(’01)182001 CLAS Collab., PRL 87(’01)182002
DVCS: helicity dependence
� Exclusive leptoproduction of photon:
d�
d�dtdQ�dx�
xy�
�� ����Q�
j�BH� �DVCSj��� � �x�m��Q�
���
� Leading order interference term:
���BH�DVCS � ��DVCS�BHpol ��p� me�
tQx� �p
�� x
el Pl
�� sin� �r� �
Im �M���
�� Extract sin��-moment, Asin��
LU � �N�
PN�
i�sin�ijPlji
:
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-1 0 1 2 3 4 5 6 7
λBeam = +1
λBeam = -1
Average
Mx (GeV)
AL
Usi
n φ±
e→+p → e+γ X
Data showexpectedhelicitydependence!
DVCS: formalism
� Beam-charge asymmetry with unpolarised leptons:
d��e�p� � d��e
�p� � cos�� �
Re
�F�H� �
xB
�� xB�F� � F�� eH� �
��
�M�F�E�
�
� Beam-spin asymmetry with polarised positrons:
d����e�p� � d��
��e�p� � sin�� �
Im
�F�H� �
xB
�� xB�F� � F�� eH� �
��
�M�F�E�
�
� Relate DVCS amplitudes H�� eH�,.. to GPDs:
ImH� � ��Xq
e�
q�H��� ������H���� ������
Im eH� � ��Xq
e�
q�eH��� ���
�� � eH���� ���
���
ReH� �Xq
e�
qP
Z ��
��
H�x� ����� �
x� ��
x � ��dx �
Re eH� �Xq
e�
qP
Z ��
��
eH�x� ����� �
x� ��
x � ��dx �
New DVCS results
� Dependence of Asin�LU on x and �t:
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.05 0.1 0.15 0.2 0.25 0.3
xBj
AL
Usi
n φ
e→+p → e+γ X Mx < 1.7 GeV
⟨-t⟩ = 0.25 GeV2 ⟨Q2⟩ = 2.46 GeV2
HERMES 96/97 PRELIMINARY
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-0.2 0 0.2 0.4 0.6 0.8 1
-t (GeV2)
AL
Usi
n φ
e→+p → e+γ X Mx < 1.7 GeV
⟨xBj⟩ = 0.11 ⟨Q2⟩ = 2.46 GeV2
HERMES 96/97 PRELIMINARY
� Q�-dependence and new 2000 data for Asin�LU :
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
1 2 3 4 5 6 7 8 9 10
Q2 (GeV2)
AL
Usi
n φ
e→+p → e+γ X Mx < 1.7 GeV
⟨xBj⟩ = 0.11 ⟨-t⟩ = 0.25 GeV2
HERMES 96/97 PRELIMINARY
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
-3 -2 -1 0 1 2 3
φ (rad)
AL
U
e→ + p → e+γ X (Mx< 1.7 GeV)
HERMES 2000PRELIMINARY
P1 + P2 sin φ
P1 = -0.01 ± 0.03 (stat)
P2 = -0.21 ± 0.04 (stat)
No Q�-dependence: hard scattering regime!
DVCS: beam-charge asymmetry
� First data for AC � Ne��Ne�
Ne��Ne�on �H:
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-3 -2 -1 0 1 2 3
φ (rad)
AC
e± p → e±γ X (Mx< 1.7 GeV)
HERMES PRELIMINARY
P1 + P2 cos φ
P1 = -0.05 ± 0.03 (stat)
P2 = 0.11 ± 0.04 (stat) -0.2
-0.1
0
0.1
0.2
0.3
0.4
-1 0 1 2 3 4 5 6
M x (GeV)
AC
co
s φ
e± p → e±γ X
HERMES PRELIMINARY
AC cos φ |M < 1.7 GeV = 0.11 ± 0.04 (stat) ± 0.03 (sys)
x
� Calculation by Kivel et al. [hep-ph/0012136]:
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0 20 40 60 80 100 120 140 160 180
e-/e+ + p → e-/e+ + p + γEe = 27 GeV, Q2 = 2.5 GeV2, xB = 0.3, t = -0.25 GeV2
d
σ e- /
(dQ
2 dx B
dt d
Φ)
(nb
/GeV
4 )
Φ (deg)
(σe+
- σ
e-)
/ (σ e+
+ σ
e-)
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0 20 40 60 80 100 120 140 160 180
BH + twist 2 + D-termBH + tw 2 + tw 3 + D-termBH onlyBH + twist 2 - D-term
The spin structure - 1
� Two schemes for the spin content:
– Quark parton model: �s = 1.00– SU(3) flavour symm.: �s = 0.6, �u = �d = -0.2
� Measure the polarization from � p��:
�
N
dN
d��
�
���� � ��� �P � �p
� Determine u� spin transfer D LL�:
D LL� �
�P � �L�PBD�y
�
Pf e
�f q
Nf �x �D
f �zP
f e�f q
Nf �xD
f �z
� �D u �z
D u �z
� Electroproduction of hyperons at HERMES:
0
100
200
300
400
500
600
700
1.08 1.1 1.12 1.14 1.16 1.18 1.2
Invariant mass (GeV/c2)Invariant mass (GeV/c2)Invariant mass (GeV/c2)
EV
EN
TS
DΛu ≈ nΛ(z), no Monte-Carlo correction
HERMES PRELIMINARY
z*=(EΛ-mΛ)/ν
DΛ u
Kaidalov, Piskunovade Florian, Stratmann, Vogelsang (LO)de Florian, Stratmann, Vogelsang (NLO)
10-5
10-4
10-3
10-2
10-1
1
0 0.2 0.4 0.6 0.8
The spin structure - 2
� Data for u� spin transfer:
Diquark, u+d (Boros)
Diquark (Ma)pQCD (Ma)
z
Lo
ng
itu
din
al s
pin
fra
nsf
er D
Λ
SU(3)f( BJ)
u+d+s
naive CQM
HERMES 1996-2000 PRELIMINARY
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
� D�
LL�� = 0.04(9)
consistent with�u� � 0(CQM prediction).
� Negative polarisation for xF (= �pLW � 0:
xF
Lo
ng
idu
din
al s
pin
tra
nsf
er D
LΛ a
lon
g W
/γ
HERMES PRELIMINARY Ee=27.5 GeVNOMAD <Eν> =43.8 GeVWA59 <Eν
_> =44.2 GeVE665 Eµ =470 GeV
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
NOMAD Collab.NPB 588 (2000) 3
Contributions from:��� �
���
��� ��
Transverse polarization
� Three leading order distribution functions:
1f = momentum carried by quarks
g1 -= longitudinal quark spin, ��
1h = - transverse quark spin, ��
� Importance of h��x measurements:
– HERMES data: �� = 0.30 � 0.04 � 0.09– �� is so small because of axial anomaly:
� Redistribution of angular momentum in nucleon:
�
��� � ���, �G � ��, Lz � ����
� Redistribution is less in transverse case:
�� � �� � 1 (Quark Parton Model)
� Lattice QCD calculation (Phys. Rev. D 56 (1997) 433):
�� = 0.18(10) and �� = 0.56(9)
Measurements of h��x
� The structure function h��x is chirally odd :
– Not accessible in inclusive DIS– Use semi-inclusive DIS with chirally-oddH
���u� �z
– Assume u-quark dominance– Asymmetry for Collins process:
A��
T �x� y� z � PT �Dnn � �u�xu�x
� H���u� �z
Du��z
�
– H���u� depends on �c � �h � �s � �
� Evidence for transversity from HERMES �H data:
0.2 0.4 0.6
-0.05
0
0.05
0.1 0.2
z
AU
L
sin
φ
π0
π+
π-
x P⊥ (GeV)
0.25 0.5 0.75 1
[HERMES, PRL 84 (2000) 4047 and PRD 64 (2001) 097101]
Single-Spin Asymmetries on �H
� z, x, p�-dependences of Asin�UL for ���� and K�:
-0.1
-0.05
0
0.05
0.1
0.15
0.2 0.4 0.6 0.8 1
z
AU
L
sin
φ
HERMES PRELIMINARY
deuteron
π+
π-
-0.1
-0.05
0
0.05
0.2 0.4 0.6 0.8 1
z
AU
L
sin
φ
HERMES PRELIMINARY
deuteron
K+
-0.02
0
0.02
0.04
0 0.1 0.2 0.3
xB
AU
L
sin
φ
HERMES PRELIMINARY
deuteron
π+
0.2<z<0.7
π-
0
0.025
0.05
0.075
0.1
0 0.1 0.2 0.3
xB
AU
L
sin
φ
HERMES PRELIMINARY
deuteron
K+
0.2<z<0.7
-0.02
0
0.02
0.04
0 0.25 0.5 0.75 1
pt / GeV
AU
L
sin
φ
HERMES PRELIMINARY
deuteron
π+
0.2<z<0.7
π-
-0.02
0
0.02
0.04
0.06
0 0.25 0.5 0.75 1
pt / GeV
AU
L
sin
φ
HERMES PRELIMINARY
deuteron
K+
0.2<z<0.7
Future: HERMES
� HERMES - Run II: 2001 – 2006
– Transverse spin 2001 - 2003– Longitudinal spin 2003 - 2004– Excl. react. w. Recoil Detector : 2004 - 2006– Unpolarized end-of-fill runs 2001 - 2006
Simulated DVCS data with Recoil Detector (1 yr run):
φγ, rad
Ach
e p → e p γ
-0.1
-0.05
0
0.05
0.1
-3 -2 -1 0 1 2 3φγ, rad
AL
U
e p → e p γ
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-3 -2 -1 0 1 2 3
� HERMES - Run III(beyond 2006 ?)
detectorphoton
boardssilicon &
LambdaWheels pumping cross
flange tochamber1mm alu
space forconnectors
magnet
C2 collimator
C2 flangefibers
Future: COMPASS
� The Compass experiment at CERN:
� Successful commissioning in 2001:
– Most detectors commissioned at 2 10� �/s.– Tracking: half of the channels– �LiD target hosted in SMC magnet: P � ����– 2 weeks smooth data taking
� Prospects for 2002:
– Complete tracking and finish commissioning– First measurement of �G�G in 3 month run– Other objectives: �q�x, h��x, �D , spectroscopy
Future: RHIC
� RHIC at BNL as seen by LANDSAT:
� Experimental break-through at RHIC:
Colliding polarized protons atps = 200 GeV
– Pproton = 70� at injection and 25 � at 100 GeV– Luminosity: 1.5 10�� cm��s��
– Physics: transverse spin asymmetries AN
� Longitudinal polarization: spin rotators in 2002
– Measure �G�G from jets, c�c, ...– Measure �qf from W� production
� The PHENIX experiment:
Outlook
� End-station A at SLAC:
– E160: single spin-asymm. for inelastic J��– E161: open charm photoproduction � �G�G
� What to expect in coming years?
– Polarized quark distributions– Polarized gluon distribution
� The big challenges in spin physics:
– The role of orbital angular momentum:
Analysis and interpretation of DVCS � Jq?
– The role of transverse spin:
Measure the (x�Q�)-dependence of h��x
� The more distant future (� 2010):
– Electron-Ion Collider at BNL: 10 250 GeV�
– TESLA-N at DESY: 250 GeV e� on fixed target