spin physics with star at rhic
DESCRIPTION
STAR. Spin Physics with STAR at RHIC. 徐庆华 , 山东大学 威海, 2009.8.11. Introduction STAR longitudinal spin program: results and future STAR transverse spin program: results and future Summary. Spin structure of nucleon. Spin sum rule (longitudinal case) :. Gluon spin , Poorly known. - PowerPoint PPT PresentationTRANSCRIPT
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Spin Physics with STAR at RHIC
徐庆华 , 山东大学威海, 2009.8.11
• Introduction
• STAR longitudinal spin program: results and future
• STAR transverse spin program: results and future
• Summary
STARSTAR
2
€
1
2=
1
2ΔΣ + ΔG+ < Lq, g >
Quark spin, (~30%)-DIS
Gluon spin,Poorly known
Orbital Angular MomentaLittle known
• Spin sum rule (longitudinal case):
Spin structure of nucleon
€
Δq(x,Q2) = q + (x,Q2) − q− (x,Q2)
€
δq(x,Q2) = q↑ (x,Q2) + q↓ (x,Q2)
• Little known in the transverse case:
Proton spin
Proton spin
€
1
2∝
1
2δΣ + < Lq, g >
Helicity distribution:
Transversity:
3
Detailed knowledge on ∆q(x), ∆g(x) (before RHIC)
x
4
RHIC- the first polarized pp collider in the world
BRAHMS
PHENIX
AGS
BOOSTER
Spin Rotators(longitudinal polarization)
Solenoid Partial Siberian Snake
Siberian Snakes
200 MeV PolarimeterAGS Internal Polarimeter
Rf Dipole
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
AGS pC Polarimeters
Strong Helical AGS Snake
Helical Partial Siberian Snake
Spin Rotators(longitudinal polarization)
Spin flipper
Siberian Snakes
STAR
PHOBOS
Pol. H- SourceLINAC
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RHIC- the first polarized pp collider in the world
pp Run Year 2002 2003 20042005
2006 2008 2009(200/500)
< Polarization> % 15 30 40-45 45-50 60 45 55 / 35*Lmax [ 1030 s-1cm-2 ] 2 6 6 16 30 35 40 / 85*
Lint [pb-1 ] at STAR
(Long./Transverse)0 / 0.3 0.3 / 0.25 0.4 / 0 3.1 / 0.1 8.5 / 3.4 0 /3.1 22 /10.5*
*first 500 GeV run
BRAHMS
PHENIX
AGS
BOOSTER
Spin Rotators(longitudinal polarization)
Solenoid Partial Siberian Snake
Siberian Snakes
200 MeV PolarimeterAGS Internal Polarimeter
Rf Dipole
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
AGS pC Polarimeters
Strong Helical AGS Snake
Helical Partial Siberian Snake
Spin Rotators(longitudinal polarization)
Spin flipper
Siberian Snakes
STAR
PHOBOS
Pol. H- SourceLINAC
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The STAR spin program
Longitudinal spin program: determination of the helicity distributions:
• Gluon polarization ∆g(x) in the nucleon
-- results & status (inclusive jet, hadrons)
-- status & future plan (di-jets, +jet, heavy flavor)
• Flavor separation: quark & anti-quark polarization
-- RHIC 500 GeV program (W prodction)
-- (anti-)hyperons spin transfer
Transverse spin program:
• Single spin asymmetry AN (SSA) on 0,
• QCD mechanisms (Sivers, Collins, high-twist)
-- forward +jet production on Sivers effects
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MRPC ToF barrelMRPC ToF barrel100% ready for run 10100% ready for run 10
PMD
FPD
FMS
EMC barrel
EMC End Cap
DAQ1000DAQ1000
Complete
Ongoing
TPC
FTPC
BBC
STAR Detector (current)
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COMPASS, PLB676,31(2009)
Δg determination from DIS
• Recent measurements from DIS:
€
q
€
q
9
Δf2Δf1
€
ALL =σ + + − σ +−
σ + + + σ +−
• Longitudinal spin asymmetry:
Accessing ∆g(x) in pp collision
€
challenging pion background
€
10
STARSTAR PRL 97, 252001 STARSTAR PRL 97, 152302
pQCD works at RHIC energies-unpolarized cross sections
• Mid-rapidity jet cross section is consistent with NLO pQCD over 7 orders of magnitude
• Forward rapidity π0 cross section also consistent with NLO pQCD
• Many other examples
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STAR inclusive π0 ALL at various rapidities
• During Run 6, STAR measured ALL for inclusive π0 for three different rapidity regions
• Mid-rapidity result excludes large gluon polarization scenarios• Larger rapidity correlates to stronger dominance of qg scattering
with larger x quarks and smaller x gluons
• Expect ALL to decrease as increases
|| < 0.95 1 < < 2 = 3.2, 3.7
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STAR inclusive π0 ALL at various rapidities
• During Run 6, STAR measured ALL for inclusive π0 for three different rapidity regions
• Mid-rapidity result excludes large gluon polarization scenarios• Larger rapidity correlates to stronger dominance of qg scattering
with larger x quarks and smaller x gluons
• Expect ALL to decrease as increases
|| < 0.95 1 < < 2 = 3.2, 3.7
PHENIX, arXiv:0810.0694|| < 0.35
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PRL 97, 252002 (2006)
Results on jet X-section and spin asymmetry
QuickTime™ and a decompressor
are needed to see this picture.
PRL 97, 252001 (2006)
Experimental cross section agrees withNLO pQCD over 7 orders of magnitude
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Experimental cross section agrees withNLO pQCD over 7 orders of magnitude
PRL 97, 252002 (2006)
PRL 100, 232003 (2008)
Results on jet X-section and spin asymmetry
2005
2006
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RHIC constraints
Impact of RHIC early results on Δg(x)
de Florian et al., PRL101(2008)
• Early RHIC data (2005, 2006) included in a global analysis along with DIS
and SIDIS data.• Evidence for a small gluon polarization over a limited region of momentum
fraction (0.05<x<0.2).
STAR
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Future inclusive jet measurements: Increasing Precision
• Precision will be significantly improved in future runs.
• 500 GeV data will reach low x-range for Δg with high statistics.
Projected improvement in xΔg from Run 9
Projected sensitivities:Run 9 & 500 GeV running
xT=2pT/s
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- Inclusive measurement cover integration of x-gluon.
- High pT measurement begin to separate large x, but still suffer from mixture of subprocesses.
- Need correlation measurements to constrain the shape of Δg(x)
10 20
frac
tio
n
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Inclusive Jets: LO (W. Vogelsang)
pT/GeV
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First correlation study: charged pions opposite jets
• Trigger and reconstruct a jet, then look for charged pion on the opposite side
• Correlation measurement significantly increases the sensitivity of ALL(π+)
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Probing Δg(x) with di-jets production
• Upcoming Correlation Measurements :
access to partonic kinematics
through di-jet production,
direct photon+jet production
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Sensitivity of di-jets measurements
• Projections with 50 pb-1 provide high sensitity to gluon polarization:
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Direct Photon - Jet Correlations
• Direct +jet dominated by qg-Compton process: 90% from qg
€
ALL ≈Δg(x1 )
g(x1 )⋅
eq2[Δq(x2)
q∑ + Δq (x2)]
eq2[q(x2)
q∑ + q (x2)]
⋅ ) a LL
qg →qγ + (1 → 2)
Reconstruction of partonic kinematics --> x-dependence of Δg !
x2
x1
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Anti-quark helicity distribution
D. de Florian et al, PRL101(2008)
• From global fit with DIS data:
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PRD71,2005
Extrating Δq(x) in Semi-inclusive DIS
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Flavor separation of proton spin
€
(Δu,Δd,Δu ,Δd through W ± production)
€
ALW +
=σ + −σ −
σ + + σ −
=−Δu( x1 )d ( x2) + Δd (x1 )u(x2)
u( x1 )d (x2) + d ( x1 )u( x2)=
€
−Δu(x1 )
u( x1 ), y
W + >> 0
Δd ( x1 )
d ( x1 ), y
W + << 0
• Quark polarimetry with W-bosons:
• Spin measurements:
€
−Δd(x1 )
d( x1 ), y
W − >> 0
Δu ( x1 )
u (x1 ), y
W − << 0
€
ALW −
=
€
where x1 = τ ey , x2 = τ e−y and τ = Mw2 / s.
W-detection throughhigh energy lepton
-
€
∝Δd (x)u(x)
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Sensitivity of W measurements
• Strong impact on constraining the sea quark polarizations with
300 pb-1 :
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• Clear need to measure. • Can we do it with hyperons at RHIC?
- hyperons contain at least one strange quark and their polarization can be determined via their weak decay.
€
ΔS = Δs + Δs , Δs = Δs( x)0
1
∫ dx
D. de Florian et al, PRL101(2008)• ΔS~ -0.08 from inclusive DIS under SU(3)_f symmetry
Strange quark polarization
• SDIS results at HERMES:
€
x[Δs(x) + Δs (x)] PLB666(2008)
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GeV 8
GeV 200
>=
Tps
Q. X, E. Sichtermann, Z. Liang, PRD 73(2006)077503
models sΔ
• Expectations at LO show sensitivity of DLL for anti-Lambda to :
GRSV00-M.Gluck et al, Phys.Rev.D63(2001)094005
Typ. range at RHIC
DLL-Longitudinal spin transfer at RHIC
- DLL of is less sensitive to Δs, due to larger u and d quark frag. contributions.
Pol. frag. func. models
- Promising measurements---effects potentially large enough to be observed.
sΔ
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Spin transfer for Lambda hyperons
€
DLLΛ ≡
σp + p →Λ+X
−σp + p →Λ−X
σp + p →Λ+X
+ σp + p →Λ−X
• (anti-)Lambda reconstruction using TPC tracks:
p
V0_vertex
V0_DCA
rr
−
• First proof-of-principle measurement;
~10% precision with pT up to 4 GeV.
- not yet to discriminate pol. pdfs,
- extend pT with specific trigger
• DLL extraction:
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Transverse spin program
• Single transverse-spin asymmetry
STAR, Phys. Rev. Lett. 92 (2004)171801
• Basic QCD calculations (leading-
twist, zero quark mass) predict AN~0
---AN~0.4 for + in pp at E704 (1991)
• Understanding transverse spin
effect: Qiu and Sterman (initial-state) / Koike (final-state) twist-3 pQCD calculations
Sivers: spin and k correlation in initial state (related to orbital angular momentum)
Collins: spin and k correlation in fragmentation process (related to transversity)
€
AN =NL − NR
NL + NR
€
xF = 2p// / sTwist-3 correlation and the k dependent
distribution/fragmentation in intermediate pT generate the same physics.
Ji-Qiu-Vogelsang-Yuan,PRL97,2006
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Recent results on SSA
• AN increase with xF, in agreement
with pQCD model calculation.
• X-section reproduced with pQCD
STAR, PRL97,152302(2006)
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• pQCD based models predicted
decreasing AN with pT , which
Is not consistent with data.
• AN increase with xF, in agreement
with pQCD model calculation.
Recent results on SSA
STAR, PRL97,152302(2006)
• X-section reproduced with pQCD
STAR, Phys. Rev. Lett. 101 (2008)222001
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• AN for the η mass region is much larger at high xF>0.55
STAR 2006 PRELIMINARY
η ~ 3.66
Run 6 inclusive AN at large xF
<AN> = 0.36 +/- 0.06 <A> = 0.08 +/- 0.02
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19.4s GeV=
~ 1 /Tp GeV c
E704 Nucl. Phys. B 510 (1998) 3
+
-
200 GeV
62.4 GeV
BRAHMS,PRL101(2008)
Large SSA of different hadrons in different experiments
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Separating Sivers and Collins effect in pp
collisions Collins effect:
spin and k correlation in fragmentation process (related to transversity)
• For hadron SSA, both Sivers and Collins effects can contribute.
• Forward jets and photon may provide separation of them.
SPk,q
p
p
Sivers effect:
spin and k correlation in initial state (related to orbital angular momentum)
SP
p
p
Sq k,πSensitive to transversity
Sensitive to orbital angular momentum
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• Mid-rapidity jet AN~0, different as the conventional calculations with
Sivers function fitted from SDIS.
Sivers distribution, is process dependent (not universal),
AAN N of jet production - Sivers effect of jet production - Sivers effect
€
Sivers|Drell-Yan=−Sivers|DIS
STAR, PRL99,142003(2007)
• AN of mid-rapidity consistent with zero:
An example:
attractive color interactionrepulsive color interaction
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Probing Sivers effect with + mid-rapidity jet
Bacchetta et al., PRL 99, 212002
• Conventional calculations predict the asymmetry to have the same sign in SIDIS and γ+jet
• Calculations that account for the repulsive interactions between like color charges predict opposite sign
• Critical test of our basic theoretical understanding
€
Sivers|+ jet~ −Sivers |DIS
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STAR Detector - futureMRPC ToF barrelMRPC ToF barrel
100% ready for run 10100% ready for run 10
FMS
FGT Ongoing
MTD
R&DHFT
TPC
FHC
Forward jet reconstruction with FMS+FHC
=2.8FPD
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SSA with forward jets and photons
Projected precision of AN for p+pjet + X :Jet energy profile from FHC+FMS:
• Collins effects(spin and k correlation in fragmentation process ):
Accessed via spin-dependent correlations of hadrons within forward jet
• Sivers effect(spin and k correlation in initial state):
Accessed by symmetric azimuthal integration of hadrons from forward jet
Accessed by forward direct photons
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Transverse spin transfer of hyperons and δq(x)
€
PTH =
dσ ( p↑ p→ H↑ X ) − dσ ( p↑ p→ H↓ X )
dσ ( p↑ p→ H↑ X ) + dσ ( p↑ p→ H↓ X ) =dΔTσ
dσ
• Transverse spin transfer of hyperons transverse spin can provide
access to transversity, via channel ->n+ :
transversity distribution :
δf(x) = f (x) - f(x)pQCD Transversely polarized
fragmentation function :
Measurement at BELLE ?
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
€
dΔTσ (r p ⊥ p→
r H ⊥X ) ∝ dxadxbdzδfa (∫
abcd
∑ xa ) fb (xb )ΔT DcH (z)dΔT
) σ (
r a ⊥b →
r c ⊥d )
- Transverse spin transfer can provide access to transversity, which is still poorly known so far.
40
• Large polarization with unpolarized beam p + p + X , observed in different experiments.
Still not fully understood.
target
produced
production plane
€
rN :
€
rN =
r p b ×
r p Λ /(|
r p b ×
r p Λ |)
bpr
Transverse hyperons polarization in unpolarized pp
How about at RHIC energy?
( = 2pL/s)
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Longitudinal spin physics at STAR:
Determination of gluon polarization ΔG :
Currently inclusive probes with jets, are providing important constraints on ΔG. Early results have been included in global analysis.
Near future probes:
Increased statistics and higher energy for inclusive jets will provides additional constraints with better precision and wider x-range.
Correlation measurements (di-jet, photon-jet) with access to partonic kinematics will provide better resolution in x and direct probe to ΔG.
Determination of sea quark polarization:
With 500 GeV collisions, W-production provide unique tool to study the anti-quark polarization.
Spin transfer of hyperons provides sensitivity to strange quark polarization.
Summary & Outlook - I
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Transverse spin physics at STAR:
STAR has observed large transverse single-spin asymmetries for forward particle production.
Study Collins and Sivers effects in pp reaction with Single-spin asymmetry with forward jet .
STAR transverse γ+jet measurements will provide a direct illustration of attractive vs. repulsive color-charge interactions
Transverse hyperon polarization at forward region at STAR
Summary & Outlook -II
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FMS: expanding STAR’s forward acceptance
• Expanded pT range for inclusive π0 AN during Run 8
STAR Forward Meson Spectrometer2.5 < η < 4.0 STARSTAR
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What is the FHC?
• Two identical 9x12 enclosures of E864 hadron calorimeter detectors
---100X100X117 cm3
• Refurbished and used by PHOBOS collaboration as forward hadron multiplicity detectors for run-3 d+Au
Recycle
45
PHENIX, arXiv:0810.0694
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World efforts for spin physics
• Current running– Lepton-nucleon
scattering: COMPASS, JLAB
– Polarized proton-proton scattering, RHIC
• Future facilities– EIC (BNL)
– JPARC (Japan)
– GSI-FAIR (Germany)
HERMES@ DESY e+-p @27GeV
COMPASS@CERN p@160GeV
Jefferson Labe-
p@6,12GeV
RHIC@BNLpp@200&500Ge
VSLAC
E142-155 EMC@CERN
Finished experiments: SLAC, EMC, SMC, HERMES
All these experiments have their unique coverage on Δq, Δg, Lq,g, and they are complementary as well
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Hyperon spin transfer at forward region
Forward hyperons, reconstructed via n+ channel, and polarization can
be determined through decay product, i.e, dN/dcos * = N0(1+Pcos *)
€
Δσ ∝ Δfa (x1 ) ⋅∫ fb (x2) ⊗Δ√ σ ⊗ΔDΛ (z)
Provide access to pol.p.d.f. and fragmentation functions
• Longitudinal spin transfer DLL:
Model evaluation shows
DLL provide sensitivity to
pol. parton distributions.
€
s = 200 GeV
p T(Λ) > 2 GeVΔs(x) models
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Jet Finding in STAR
Jet reconstructed with TPC tracks and EMC energy deposits, using midpoint Cone Algorithm:
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The STAR Detector
Magnet• 0.5 T Solenoid
Triggering & Luminosity Monitor• Beam-Beam Counters
– 3.4 < || < 5.0• Zero Degree Calorimeters
Central Tracking• Large-volume TPC
– || < 1.3
Calorimetry• Barrel EMC (Pb/Scintilator)
– || < 1.0– Shower-Maximum Detector
• Endcap EMC (Pb/Scintillator)– 1.0 < < 2.0
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Transverse spin asymmetry- spin structure of nucleon
• Large single transverse-spin asymmetry observed at RHIC:
STAR, Phys. Rev. Lett. 92 (2004)171801
€
AN =NL − NR
NL + NR
€
xF = 2p// / s
STAR, Phys. Rev. Lett. 97 (2006)152302
• Basic QCD calculations (leading- twist, zero quark mass) predict
AN~0,
while cross sections are found to be in agreement with pQCD
evaluations.