measurements with polarized hadrons t.-a. shibata tokyo institute of technology aug 15, 2003...
TRANSCRIPT
Measurements with Polarized Hadrons
T.-A. Shibata
Tokyo Institute of Technology
Aug 15, 2003Lepton-Photon 2003
T.-A. Shibata 2
Introduction: Spin of Proton
Polarized Deep Inelastic Lepton-Nucleon Scattering
1. Flavor Separation of Quark Helicity Distributions
2. Deeply Virtual Compton Scattering
3. Single-Spin Azimuthal Asymmetries
in Semi-Inclusive Deep Inelastic Scattering
Polarized Proton-Proton Collisions
Contents:
T.-A. Shibata 3
Introduction:
Measurements with Polarized Hadrons
‘Explore spin structure of hadrons and further develop QCD using Spin’
QCD was successful, both in perturbative and
non-perturbative regions, but spin of the nucleon still needs
to be studied in many aspects to be fully explained with QC
D.
T.-A. Shibata 4
Introduction : Spin of Proton
Sum of Spins of u u d Quarks = Spin of Proton
2
1
2
1
2
1
2
1
+ +
SU(6) Quark Wave Functions of Baryons1 / 2
1 / 2- 1 / 2
1 / 2
2
106800470060
2
1 ...)( sdu
)%( 14912
EMC Experiment (1988)
20 – 30 % of Nucleon Spin
Gqq
JLsdu )(2
1
2
1
=
‘Nucleon Spin Problem’
T.-A. Shibata 5
Introduction:
Fixed Target Experiments :
Polarized Targets + (Polarized) Beams
Nucleon (p, n) + e+/e- HERMES
e- SLAC, JLab
COMPASS Collider Experiments :
Polarized Proton - Proton Collisions RHIC
Measurements with Polarized Hadrons
Experimental Methods: Lepton-Hadron Scattering, Hadron-Hadron Collision
/
T.-A. Shibata 6
Deep Inelastic Scattering, Semi-inclusive Measurements
Semi-inclusive measurement,
e’ and
... pp,K,,
)()(),( zDxqezx hq
qqh 2
( quark distribution ) x ( fragmentation function )
e
e’
Flavor tagging
Inclusive measurement, e’
)()( xqexq
q 2
/hEz
T.-A. Shibata 7
Detectors
Target
HERMES @DESY- HERA1995 --
27.6 GeV
Polarized Internal gas targets
(3He, H, D)
e
T.-A. Shibata 8
Compass Set-up
2002-2003
polarized target
magnets
RICH
muon filter
GeV160
@ CERN
Gluon Spin ContributionD’s identified in 2002.
)(xGc
c
Photon Gluon Fusion
N
T.-A. Shibata 9
1. Flavor Separation of Quark Helicity Distributions
)(),(),(),(),( xsxdxuxdxu
T.-A. Shibata 10
Quark Helicity Distributions, Flavor Separation
Double-spin asymmetry
)()(
)()(),(
xx
xxzxA
1
XeNe
Beam and target, both polarized
....
.... ....
....NucleonVirtual photon
T.-A. Shibata 11
Quark Helicity Distributions, Flavor Separation
x
Ah1(x)
K+
K-
asymmetries similar to inclusive asymmetry,except asymmetry.
Double-spin asymmetries Ah1 (d) from semi-inclusive DIS
K,-K
Hadron identification for the first time
HERMES
x
T.-A. Shibata 12
Quark Helicity Distributions , Flavor Separation
)()(),( zDxqezx hq
qqh 2
Semi-inclusive DIS cross section
Double-spin asymmetry
/hEz
q
hqq
q
hqq
hh
hhh
zDxqe
zDxqe
zxzx
zxzxzxA
)()(
)()(
),(),(
),(),(),( 2
2
1
)()()( xQxPxA
1 ),,,,()(s
s
d
d
u
u
d
d
u
uxQ
XmeNe
)()()( xqxqxq )()()( xqxqxq Quark Helicity Distributions
Quark Density Distributions
)(K),( susu unconstraineds
N = p, d m =
unpol. PDF and FF from data of unpol. semi-inclusive DIS
T.-A. Shibata 13
Flavor Separation, Quark Helicity Distributions
Result:
x
ux
dx
ux
dx
sx QCD fits to inclusive measurements
etc.11
xasd
d
• X bin by bin analysis except
for smearing correction.
• No functional forms are
assumed.
• No first moments are assume
d.
• Helicity conservation not
assumed
0u0d0q
HERMES
x
Error band – systematic error
T.-A. Shibata 14
2. Deeply Virtual Compton Scattering -- Generalized (Off-forward) Parton Distributions
T.-A. Shibata 15
Deeply Virtual Compton Scattering (DVCS) -- Exclusive production of a real photon
Deeply Virtual Compton Scattering
GPD
p
p
x x
Im
Coss section for inclusive deep inelasticscattering
:Light cone momentum fraction
:Exchanged longitudinal momentum fraction
:Momentum transfertBJ
BJ
x
x
2
x
T.-A. Shibata 16
Generalized (Off-Forward) Parton Distributions
Generalized Parton Distributions (GPD)
Deep InelasticScattering
Deeply Virtual Compton Scattering
Electromagnetic Form Factors( Elastic Scattering )
Total Angular Momentum Jq
qqqq EHEH~
,~
,,
Exclusive Meson Production ,,,
21 FF ,
qq ,
Orbital Angular Momentum Lq
T.-A. Shibata 17
Generalized Parton Distributions
),,(~
),,,(~
),,,(),,,( txEtxHtxEtxH qqqq
),()( xq,x,Hq 00 )()(~
xq,x,Hq 00
Sum rules, x – integral, sum over q
),(),,( tFtxHq1 )(),,( tFtxE q
2
),(),,(~
A tgtxHq )(),,(~
A thtxE q
Dirac and Pauli Nucleon Form Factors
Axial-vector and Pseudo- scalar Form Factors
qqq
t
JtxEtxHxdx
1
10 2
1)],,(),,([lim
qz
q LqJ 2
1
Ordinary QuarkDistributions
Forward limit ,0t
Total angular momentum
Orbital angular momentum
2nd moment
T.-A. Shibata 18
Deeply Virtual Compton Scattering
Beam-spin asymmetry by HERMES and CLASBeam-charge asymmetry by HERMES -- DVCS-BH Interference, Real and Imaginary
Deeply Virtual Compton Scattering Bethe-Heitler Process, known calculable
DVCS Cross Section by ZEUS and H1
IAAAAxQt
2222
4
||||||dddd
dBHDVCSBHDVCS
Ipe Imsinp)e(-)(LU �
Ipepech Recos)(-)(
How to measure DVCS
T.-A. Shibata 19
HERMES (2001) CLAS (2001)
Deeply Virtual Compton Scattering
LUA
First observation of beam-spin asymmetry of DVCS
~ 30% effect
T.-A. Shibata 20
Beam-Spin Asymmetry
Deeply Virtual Compton Scattering, Generalized Parton Distributions
Momentsin HERMES
XM
Missing Mass Resolution 0.8 GeV
T.-A. Shibata 21
Deeply Virtual Compton Scattering, Generalized Parton Distributions
Missing Mass Resolution 0.8 GeV
Momentcos Beam-Charge AsymmetryHERMES
XM
T.-A. Shibata 22
How to extend
GPD
GPD
Quantum number of final state Select different GPD
,,
Pseudo scalar meson Vector meson
Exclusive Meson Productions
),,(~
),,,(~
txEtxH qq ),,(),,,( txEtxH qq HERMES’s data
T.-A. Shibata 23
3. Single-Spin Azimuthal Asymmetry in Semi-inclusive Deep Inelastic Scattering ‘Quark Transversity Distributions ’)(xq
T.-A. Shibata 24
Last unmeasured leading twist distribution:q
3 leading twist quark distributions
Quark Density Distributions
Quark Helicity Distributions
Quark Transversity Distributions
Single-Spin Azimuthal Asymmetries in Semi-Inclusive DIS, Transversity
is Chiral Odd. Not accessible with inclusive DIS It is accessible with semi-inclusive DIS,accompanied with a Chiral Odd Fragmentation Function does not couple with gluon. ( Collins FF ) Q2 evolution is different from
)(xq
)(xq)(),( xqxq
)()( , zHxqeAh
qh 1
2
)(xq
)(xq
)(xq
Spin averaged, vector charge
Helicity difference, axial charge
Helicity flip, tensor charge
)(zH 1
|)()(||)(| xqxqxq 2
1
Soffer bound
T.-A. Shibata 26
Single-Spin Azimuthal Asymmetries in Semi-Inclusive DIS
LongitudinallyPolarized Target
TransverselyPolarizedTarget
XmeNe
150
12
.sin
yQ
xMS
T
Azimuthal Angle
sAzimuthal Angle
NN HERMES, JLab
HERMES, COMPASS, JLab
dependence
s s
dependence
dependence
with respect to
T.-A. Shibata 27
Xmede
Single-Spin Azimuthal Asymmetries in Semi-Inclusive DIS
Longitudinally polarized target ,Target Spin Asymmetry AUL
LNLN
LNLN
pA
L /)(/)(
/)(/)(
||)(UL
1
sin1P
221 sinsin PP
ULA
π
0π
π
K
HERMES
sinULA positive for
Increases with x nearly zero for
K,, 0
2sin moment ~ 0
T.-A. Shibata 28
(Quark transversity distribution) x (Chiral odd FF )
HERMES (2002--) focused on it. 700K D.I.S. events recorded.
Further data taking 2003-- . COMPASS data at higher Q2, JLab
UTs )(sin UTs )(sin moment: Collins Effect
moment: Sivers Effect
Transversely polarized target data can distinguish between the two. becomes dominant.
UTTULLUL SSA sinsin~sin
sinOrigins of moment, Longitudinally polarized target0S
)()(~ , zHxqe q
q q 1
2
)()(~ T zDxfe q
q q 112
TS
))(~
)()()((~sin ,, zHxhz
zHxheQ
qL
qqL
qqUL
112 11
UT sin
Q2 evolution of ),( 2Qxq
Sivers Effect:
Collins Effect:
( see also polarized pp collisions )
T.-A. Shibata 29
Polarized Proton-Proton Collisions
T.-A. Shibata 30
g
jet
q
Polarized Proton-Proton Collision
Gluon spin contribution to the nucleon spin
Gluon Compton scattering
LLLL axq
xq
xG
xGA ˆ
)(
)(
)(
)(
2
2
1
1
qqg 2 jet production
qg
jetjetgg
)(
Inclusivemeasurement
p
p
q
Polarized Parton-Parton Collision
Polarized pp Collisions at RHIC
100 GeV + 100 GeV
2001/2002 P = ~0.2, Int L ~ 0.3 pb-1, transverse
- May 2003 P = ~0.3, Int L ~ 0.8 pb-1, transverse + longitudinal
Physics Goal P = 0.7, Int L = 320 pb-1 , at 100 + 100 GeV
800 pb-1 , at 250 + 250 GeV
T.-A. Shibata 32
STAR
p + p + X ,
s = 200 GeV
Single-Spin Asymmetry, Transversely Polarized Beam
PHENIX and STAR collected data of inclusive production
Polarized pp Collisions at RHIC
Similar to the earlier Fermilab data at s=20 GeV, pT = 0.5-2.0 GeV/c
Forward , small pT
Double spin asymmetry, ALL,at large pT will becomeavailable soon
T.-A. Shibata 33
Conclusions 1
To understand hadrons in terms of QCD, Spin Structure of the
Nucleon is an important subject.
Many experiments are currently running with beams
at different labs in the world.
Flavor separation of quark helicity distributions has been mad
e.
Deeply Virtual Compton Scattering provides access to Generalized
Parton Distributions.
Single-spin azimuthal asymmetries in semi-inclusive DIS have bee
n
observed. Quark Transversity Distributions is a new subject
which is being investigated. Results from transversely polarized
targets will become available soon.
... p,,,e
q
q
T.-A. Shibata 34
Conclusions 2
Polarized proton-proton collider has now longitudinally as well as
transversely polarized beams. Single-spin asymmetries in
productions at small angles from transversely polarized
beam have been obtained. The asymmetries at large pT are being
analyzed.
Spin physics with the nucleon is a rapidly expanding field. Many
new ideas of measurements are being proposed. High precision
data as well as new surprises are expected.
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