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Transcript of Spin of the proton and its transverse spin structure at RHIC HERMES seminar at Tokyo Tech November...
Spin of the protonand its transverse spin structure
at RHIC
HERMES seminar at Tokyo Tech
November 9, 2005
Yuji Goto (RIKEN)
November 9, 2005 Yuji Goto (RIKEN) 2
RHIC – QCD collider
November 9, 2005 Yuji Goto (RIKEN) 3
RHIC polarized-proton collision
• Luminosity 11031 cm-2sec-1 at s = 200 GeV achieved– 81031 cm-2sec-1 at 200 GeV and 21032 cm-2sec-1 at 500 Ge
V in the future• Polarization 50% achieved – 70% in the future
BRAHMS & PP2PP
STAR
PHENIX
AGS
LINAC BOOSTERPol. H- Source
Spin Rotators(longitudinal polarization)
Solenoid Partial Siberian Snake
Siberian Snakes
200 MeV Polarimeter AGS Internal Polarimeter
Rf Dipole
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
AGS pC PolarimetersStrong AGS Snake
Helical Partial Siberian Snake
PHOBOS
Spin Rotators(longitudinal polarization)
Spin flipper
Siberian Snakes
installed and commissioned during in 2004 runinstalled in 2005 and to be commissionedto be commissioned
November 9, 2005 Yuji Goto (RIKEN) 4
STAR and PHENIX
• STAR detector• 2 coverage for
jet measurement• barrel TPC and EMC• endcap EMC
• PHENIX detector• limited acceptance• high resolution central EMCal• high-rate trigger and DAQ• forward muon detectors
November 9, 2005 Yuji Goto (RIKEN) 5
RHIC/PHENIX polarized-proton runs
s = 200 GeV P recorded L recorded LP4 data volume2001-2002 transverse-spin run 15% 0.15 pb-1 20 TB first polarized proton collisions2003 longitudinal-spin run 27% 0.35 pb-1 1.5 nb-1 35 TB spin rotators commissioned, AGS p-C CNI polarimeter2004 commissioning run (longitudinal spin) 40% 0.12 pb-1 3.3 nb-1 35 TB AGS warm snake commissioned, gas-jet absolute polarimeter2005 longitudinal-spin run 49.5/44.5% 3.8 pb-1 205 nb-1 262 TB AGS cold snake installed
2005 – First long longitudinal-spin polarized-proton runFigure of merit (LP4) more than 40 times larger thanthat of previous runs
November 9, 2005 Yuji Goto (RIKEN) 6
Where is the proton spin ?
• Origin of the nucleon spin 1/2– polarized DIS experiments showed the quark contribution is only 10-30%– gluon contribution ?
• Scaling violation in polarized DIS
• Semi-inclusive DIS– high-pT hadron pairs– open charm production
(th)(syst)(stat)99.0)GeV 1( :SMC 43.145.0
42.022.0
17.131.0
22
Qg
1.1(syst)(stat)8.06.1)GeV 5( :E155 22 QgB. Adeva et al., PRD 58, 112002 (1998).
P.L. Anthony et al., PLB 493, 19 (2000).
lepton beam or
or nucleon target
*
gluon
heavy flavor
November 9, 2005 Yuji Goto (RIKEN) 7
Gluon contribution ?
• Polarized hadron collision– leading-order gluon measurement
• ALL of 0
][][][ qqgqgg
dd
ddA
qqgqgg
LL
proton beam
proton beam
or
or
gluon
photon
proton beam
proton beam
or
or gluon
gluonheavy flavor
direct photon production heavy-flavor production
gg + qg dominantsensitive to the gluon reaction
November 9, 2005 Yuji Goto (RIKEN) 8
PHENIX ALL of 0
Theory model C.L. (%)
GRSV-std 17.1-21.7
*GRSV-max (g=g) 0.0-0.0
*GRSV g=0 16.7-18.4
*GRSV g=−g 0.0-0.7
* at input scale Q2 = 0.4 GeV
- Run5 conclusively excludes GRSV maximal scenarios.- Data consistent with GRSV standard and GRSV G = 0.
GRSV-max: g = 1.84
GRSV-std: g = 0.42at Q2=1(GeV/c)2
best fit to DIS data
November 9, 2005 Yuji Goto (RIKEN) 9
Single transverse-spin asymmetry
• Left-right asymmetry
• Forward-rapidity– Fermilab-E704
• fixed-target experiment at s = 19.4 GeV
left
rightRightLeft
RightLeftN dd
ddA
November 9, 2005 Yuji Goto (RIKEN) 10
STAR forward pion
• Run2 results– In agreement with several model
s including different dynamics:
Sivers: spin and k correlation in initial state (related to orbital angular momentum?)
Collins: Transversity distribution function & spin-dependent fragmentation function
suppressed? (hep-ph/0408356)
Qiu and Sterman (initial-state) / Koike (final-state) twist-3 pQCD calculations
STAR collaboration, hep-ex/0310058, Phys. Rev. Lett. 92 (2004) 171801
STARSTAR
November 9, 2005 Yuji Goto (RIKEN) 11
STAR forward pion
• Run3 results– Positive AN at large positive x
F has been confirmed
• Larger significance to be non-zero & positive than published data
– The first measurement of negative xF AN has been done, and is consistent with zero
• Sensitive to twist-3 gluon-gluon correlation
Statistical error only for <>=4.1
November 9, 2005 Yuji Goto (RIKEN) 12
STAR outlook
• Disentangling the dynamics of AN via
– Higher precision AN measurement vs xF and pT
– AN with mid rapidity correlation
– Forward jet
• Proposal for forward calorimeter upgrade– Heavy mesons and direct photons – Low x gluons in nuclei
• Mid rapidity jets– Di-jet kT balance gluon Sivers function
– Inside jet particle correlation Collins function * Transversity
~2.4m square~1500 cells
=4.2
=3.2
=2.5
Current FPD
November 9, 2005 Yuji Goto (RIKEN) 13
Mid-rapidity at PHENIX
• Different kinematic region– forward-rapidity at STAR (xF > 0.3)
• quark-gluon reaction dominant
• large contribution from x ~ 0.6 quark polarization/transversity
– mid-rapidity at PHENIX (xF ~ 0)
• contribution from both gluon-gluon and quark-gluon reactions
• x = 0.03 – 0.1
• small quark polarization/transversity
• no gluon transversity in leading twist
• negligible transversity & Collins effect contribution
November 9, 2005 Yuji Goto (RIKEN) 14
Mid-rapidity at PHENIX
• Run2 results– AN for both 0 and charged hadrons consistent with zero at mid-
rapidity– ~5 times smaller asymmetry than STAR forward-rapidity data
(~10%)– comparable data with Fermilab-E704 for 0 and charged hadrons
Fermilab-E704
November 9, 2005 Yuji Goto (RIKEN) 15
Forward neutron asymmetry
• PHENIX local polarimeter R&D at IP12
EM Cal Base
PbWO4
Charge Veto
Neutron VetoHadron Cal Base
Pb
Scintillator
W+Fiber Cal
Post-shower
November 9, 2005 Yuji Goto (RIKEN) 16
Forward neutron asymmetry
Hadron Cal EM Cal
AN = 0.1260.0080.041AN = 0.1160.0180.020
preliminary preliminary
preliminaryvery forward neutronAN ~ -12%xF > 0.2pT < 0.3 GeV/c
November 9, 2005 Yuji Goto (RIKEN) 17
Local polarimeter at PHENIX
• Longitudinal component of the proton polarization at PHENIX
• 410 GeV run in 2005– analyzing power of local polarime
ter roughly the same despite doubling of energy
2005 run
%04.021.094.98/
%02.012.048.99 /
YellowL
BlueL
pp
pp
November 9, 2005 Yuji Goto (RIKEN) 18
Back-to-back jet at PHENIX
• Boer and Vogelsang find that this parton asymmetry will lead to an asymmetry in the distribution of back-to-back jets
• Should also be able to see this effect with fragments of jets, and not just with fully reconstructed jets
ST
j1
j2
0
2
h
Boer and Vogelsang, Phys.Rev.D69:094025,2004
Ng = Nd (E704)
November 9, 2005 Yuji Goto (RIKEN) 19
Back-to-back jet at PHENIX
• Measurement of the gluon Sivers function via AN for di-hadron angular correlations– Sivers distribution is a transverse parton momentum
distribution correlated with the nucleon’s spin axis, which could arise from orbital angular momentum
– Error bars: Expected sensitivity with P=60% and 7 pb-1
November 9, 2005 Yuji Goto (RIKEN) 20
Back-to-back jet at STAR
November 9, 2005 Yuji Goto (RIKEN) 21
Spin dependence of kT of jets
• Possible helicity effect– We may observe net effec
t (after averaging over impact factor)
kT larger kT smaller
Same helicity
Opposite helicity
November 9, 2005 Yuji Goto (RIKEN) 22
Spin dependence of kT of jets
• Run3 result: hint of helicity dependence ?– not yet sure
• Run5 data should yield a definite answer.
November 9, 2005 Yuji Goto (RIKEN) 23
Summary
• RHIC data began to provide restriction to the gluon-spin contribution to the proton spin– We need to know contribution of the orbital angular moment
um as the final piece
• RHIC has potential measurements of the orbital angular momentum and/or transverse spin structure of the proton– single transverse-spin asymmetries– Sivers effect/function measurements– …
• We will have some transverse-spin run in 2006
Backup slides
November 9, 2005 Yuji Goto (RIKEN) 25
Naohito’s analysis
November 9, 2005 Yuji Goto (RIKEN) 26
Vertical vs radial run in 2006
Boer and Vogelsang, PRD69:094025,2004
STST
1 = 01 = /2
)sin(||)sin(|| 22,1, TTN ppA
1 = 0 : )sin(|| 2, TN pA 1 = /2 : )cos(|||| 2,1, TTN ppA
21 ~
)(
TT pp
sin(
cos(1~
private communication, Boer and Vogelsang
November 9, 2005 Yuji Goto (RIKEN) 27
Spin dependence of kT of jets
• Back-to-back nature of jets is broken by initial/final state transverse momentum kT ( e.g., intrinsic kT, soft gluon radiation )
• Orbital angular momentum: kT× rintroduces intrinsic kT in the initial state
measurement of jet kT gives an access to parton orbital angular momentum
November 9, 2005 Yuji Goto (RIKEN) 28
Transversity at PHENIX
• Transversity throught +- interference FF– non-vanishing “support” only in
the mass region
2P
)( 1xqi
)( 2xqi
11Px
22Pxij
1ps ,
Jet
Jet
Proton Structure
Hard Scattering Process
InterferenceFragmentation
)(ˆsin)(ˆsin...ˆ)()(
...ˆ)(ˆ)()()cos()sin(sinsin
4
61
112
002
21
211010 zqzqxGxG
zqxGxq
NN
NN
PA
qqgg
qgqgI
beam
,
200 GeV
500 GeV
][GeVp jetT
qqqqqq
m
I
2,3/ˆˆ4ˆ
1cos83.0,0
102
,
GeV,
Maximum Asymmetry
November 9, 2005 Yuji Goto (RIKEN) 29
Transversity throught +- interference FF
• Projected asymmetrypair vs TT pXpA )(
GeV) Tang 85.0,1(cos mA
)1010Tang sin(sinsincos A
Small aymmetry below5% but good rate!
MeV MeV
GeV
GeV
950800
4
4
32
22
21
,
1
21
m
pp
E
pbLdt
TT
For 32pb-1 (1 week of running)
5.2 Million events in 32 pb-1
15% with pair after cuts