CURRNET STUDIES OF THE SPIN
STRUCTURE OF THE NUCLEON
NuFACT’02
July 1-6, 2002, Imperial College, London
Naohito Saito
Kyoto University/ RIKEN / RBRC
Proton and its Properties
Proton is the most fundamental
building block of all matter as well
as a complex mixture of quarks
and gluons
up quark + up quark + down quark
glued together with gluon, with
infinite number of quark-anti-quark
pairs
Spin is one of the fundamental
properties of the Proton
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Why Spin Physics?
“Spin” is a fundamental observable.
  0.1 ~ 0.3
Total fraction of the proton
spin carried by the quark
spin; Scheme dependent.
1
J
2
Axial vector nature is useful in
symmetry tests
Parity
Time
Reversal
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Quark and Gluon Distributions
Quark Distributions q  u, d , s,..., u , d , s ,...
unpolarized distribution
q(x,Q2)=
=
helicity distribution
q(x,Q2)=
transversity distribution
dq(x,Q2)=
Gluon Distributions
g(x,Q2)=
g(x,Q2)=
No Transverse Gluon Distribution
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Current Experimental Data
DIS is the Major Source
1 4
1
1

2
2
g ( x, Q )   U ( x, Q )  D( x, Q )  S ( x, Q 2 ); Q( x)  q( x)  q ( x)
2 9
9
9

p
1
2
F2
Q2 (GeV2)
g1
Q2 (GeV2)
Major Source of Uncertainties:
1. No Gluon Measurement
2. No Separation of Anti-Quark
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Spin Structure Functions and PDFs
Precision Data from Inclusive pol-DIS
Only two independent observables: g1p(x) and g1n(x)
 p
1 4
1
1
2
2
2
2 
g
(
x
,
Q
)


U
(
x
,
Q
)


D
(
x
,
Q
)


S
(
x
,
Q
)

1

2 9
9
9



 g n ( x, Q 2 )  1  1 U ( x, Q 2 )  4 D( x, Q 2 )  1 S ( x, Q 2 )


 1
2 9
9
9

U  u  u , D  d  d
S  s  s
Often three independent quark distributions
are extracted:
    U  D  S 

 a3
a
 8
 

   U  D 
  U  D  2S 
 

• (x), qNSp(x), qNSn(x)
• (x), a3(x), a8(x)
• U(x), D(x), S(x) (with SU(3) symmetric sea assumption)
More Independent Observables should be measured
• Semi-Inclusive DIS
• W production in polarized pp
Naohito Saito (Kyoto University/RIKEN/ RBRC)
How Pol-PDFs are Separated?
The Case of the
1st Moment
Inclusive DIS:
G1p and G1n
G
p
1
1
G   g ( x)dx
0
n
G1
p
1
p
1
4
1
1
G  U  D  S
18
18
18
1
4
1
n
G1  U  D  S
18
18
18 a
p
1
Neutron and Hyperon
Decay Constants
3
a3  U  D
a8  U  D  2S
Naohito Saito (Kyoto University/RIKEN/ RBRC)
a8
Separation of (x) and qNS(x)
Q2 evolution of (x) couples with g(x)
  ( x, t )   S (t )  Pqq ( x) Pqg ( x)   ( x, t ) 

  

 



t  g ( x, t ) 
2  Pgq ( x) Pgg ( x)   g ( x, t ) 
While qNS(x) does not
 S (t )

q NS ( x, t ) 
Pq  , NS ( x)  q NS ( x, t )
t
2
Better Determination of g(x) will provide a better
separation of (x) and qNS(x)
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Polarized Quark and Gluon Distributions
Detailed analysis of lepton scattering experiments revealed…
up quark
sea quark
x
x
down quark
gluon
x
Naohito Saito (Kyoto University/RIKEN/ RBRC)
x
Where are we?
Inclusive DIS provided precision
information
U, D, S can be extracted with the help
of beta decay constants
• Separation of  and qNS utilizes g
• Q should be separated into Quark and Antiquark
Handful Measurements of g and q
Photon-gluon fusion
COMPASS – g(x) from Charm production
RHIC Spin – g(x) from Prompt Photon etc
q(x) from W, Drell-Yan
HERMES – q(x) from Semi-Inclusive DIS
g(x) from high-pT Hadron pair
Gluon Compton
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Prompt Photon Production
Gluon Compton Dominates
Small Contamination from Annihilation
No fragmentation contribution in LO
e q ( x )

g ( x )


a
g(x )
 e q (x )
2
i
ALL
1
2
i
i
2
i i
1
LL
2
i
0.001
1
Naohito Saito (Kyoto University/RIKEN/ RBRC)
( gq  qg )
Prompt Photon Production and g(x)
Gold Plated mode for both PHENIX & STAR
Comparison at cross section level
x-reconstructed using jet
= direct observable
L. Bland
x
W. Vogelsang et al.
Naohito Saito (Kyoto University/RIKEN/ RBRC)
World Competition on g/g(x)
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Impact of RHIC Spin g Measurement
If we include PHENIX Prompt Photon Data in
Global QCD Analysis…
M. Hirai et al.
Naohito Saito (Kyoto University/RIKEN/ RBRC)
W Production in polarized pp
W is produced through pure V-A
Chirality is fixed  ideal for spin structure studies
W couples to weak charge ~ flavor
Flavor is (almost) fixed  ideal for flavor structure
studies
Parity Violating Asymmetry AL :
J. Soffer et al.
u ( xa )d ( xb )  d ( xa )u ( xb )
A 
u ( xa )d ( xb )  d ( xa )u ( xb )
W
L
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Sea-quark measurement with W
W production is the best
tool to pin down spinflavor structure of the
nucleon
V-A process fixes spin of
quarks
Charged current ~flavor
Comparison with DESYHERMES; Semi-inclusive
DIS
W has no fragmentation
ambiguity
Naohito Saito (Kyoto University/RIKEN/ RBRC)
How we can Improve s Determination?
Charm Associated W Production
At RHIC, s will contribute to W
cross section by 5% (W+) and 25%
(W-) respectively, but should be
multiplied by charm detection
efficiency <10%
Possible at Luminosity Upgraded
RHIC Spin
Neutrino-Nucleon Elastic
Scattering
Extrapolation axial form factor
down to Q2
Polarized Target with Neutrino
Beam
Naohito Saito (Kyoto University/RIKEN/ RBRC)
BNL E734
Spin Physics at RHIC
Measure Spin Asymmetries in pp collision to pin
down
Spin Structure of the Nucleon
• Proton Spin Sum Rule
• Transversity Distributions
Spin Dependence of Fundamental Interactions
• Parity Violating Interaction
• T Violation  CP Violation ( CPT = 1 )
Spin Dependence of Fragmentation
• e.g. Lambda fragmentation function
Spin Dependence in pp elastic scattering
Naohito Saito (Kyoto University/RIKEN/ RBRC)
RHIC’s Experiments
Pp2pp &
STA
R
Naohito Saito (Kyoto University/RIKEN/ RBRC)
PHENIX Detector System
Inner Detectors:
BBC
MVD
NTC
Central Arms
EMCal
Tracking
PID
• RICH
• TOF
Muon Arms
South Completed
North to be ready
for next run
Naohito Saito (Kyoto University/RIKEN/ RBRC)
PHENIX Run2 Configuration
Fully equipped
Central Arms
EMCal
Trk Chambers
RICH
Newly installed Muon
Arm
Muon Tracker
Muon Identifier
New Counter
NTC
EMC-RICH Trigger
Naohito Saito (Kyoto University/RIKEN/ RBRC)
PHENIX Central Spectrometer
East Carriage
Ring Imaging Cerenkov
Drift Chamber
Pad Chamber
Beam-Beam Counter
Central Magnet
West Carriage
Naohito Saito (Kyoto University/RIKEN/ RBRC)
PHENIX Run-2 Installation
Naohito Saito (Kyoto University/RIKEN/ RBRC)
RHIC Achievements
Run-1
First Collision of Gold beams at 56 and
130 GeV/A last year
10% of Designed Luminosity achieved
Successful Physics Run
Successful Spin Commissioning!
Run-2
First Collision of Gold beams at 200
GeV/A !!!
• 42 mb-1 delivered & 24 mb-1 recorded
• 170 M events processed
First Collision of Polarized Proton
Beams at 200 GeV!!!
• 3.7 G events processed
• 0.15 pb-1 recorded
Naohito Saito (Kyoto University/RIKEN/ RBRC)
PHENIX Run2 pp
Delivered peak
luminosity at PHENIX
~ 1x1030cm-2 s-1
Data Band Width
~ 60 MB/s = 6 CD’s/min
Naohito Saito (Kyoto University/RIKEN/ RBRC)
PHENIX Run-2 Projection For AN(0)
Will Reach Highest pT
Statistical Significance
= E704 x 10 !!
Complementary to STAR
Measurement at Forward
region
0
FNAL E704
s  20GeV
Local Polarimeter @
12 o’clock or
STAR Forward Pion
Detector
Naohito Saito (Kyoto University/RIKEN/ RBRC)
PHENIX Spin Goal for Next Run
Hi Statistics Pion Data! Sensitive to g(x)!

gg  gg
G G
G G
gq  gq
Fractional Contribution
q G

q G
q q

q q
qq  qq
5 pb-1 and 50% polarization
Model II
qq
Model I
gq
gg
W. Vogelsang and M. Stratmann
Naohito Saito (Kyoto University/RIKEN/ RBRC)
RHIC Spin Plan (under discussion)
Year CM Energy Weeks
Int. Lum.
Remarks
2002 200 GeV
5
7 pb-1
Gluon pol. with pions / TT*
2003 200 GeV
500 GeV
8
2
160 pb-1
90 pb-1
Gluon pol. with direct g , jets/ TT
PV W production, u-quark pol.
2004 200 GeV
500 GeV
8
2
160 pb-1
120 pb-1
Gluon pol. with g + jet/ TT
First ubar,dbar pol. meas..
2005 500 GeV
8
480 pb-1
200 GeV
2
48 pb-1
Gluon pol. with g+jet, g,jet+jet,
heavy flavor, ubar, dbar pol.
Gluon pol. with g, g+jet, heavy flavor/TT
2006 500 GeV
200 GeV
5
5
300 pb-1
120 pb-1
2007 200 GeV
10
210 pb-1
More statistics
* TT Transverse Spin Physics
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Summary
Spin Structure Studies Definitely Needs
Gluon polarization measurements
Flavor sensitive measurements
First RHIC Spin Physics Run was SUCCESSFUL
COMPASS is starting
HERMES is making a progress
But Still Neutrino Factory will provide a
significant Impact on Polarized PDF !
Naohito Saito (Kyoto University/RIKEN/ RBRC)
PHENIX Run 2 Spin
Beam Polarized
Transversely
Yellow > Blue
<Pyellow>=17%
<Pblue>=14%
• Assumption:
Analyzing Power
is E-indep.
Enough Statistics
for first AN physics
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Single Transverse Spin Asymmetry AN
Large LEFT-RIGHT asymmetries have been observed up to
maximum energies available
Possible origins are:
Transverse spin dependence in initial state  Transversity
Transverse spin dependence in final state  CollinsHeppelman Effect
However always suppressed by pT-1 according to pQCD :
Higher-twist Effect
Forward Production
Hi pT data is crucial in understanding
this effect
Left
Right
“Right”
=
“Left”
Central Production
Naohito Saito (Kyoto University/RIKEN/ RBRC)
PHENIX EMCal Performance in Run-2
Excellent g reconstruction!
Both 0 and h are clearly seen
Statistics extend to > 10 GeV/c
pT(gg) > 3.5 GeV/c
Naohito Saito (Kyoto University/RIKEN/ RBRC)
Minimum bias
High pt trigger