STAR
10-th Workshop on High Energy Spin PhysicsSeptember 16-21, 2003, Dubna, Russia
The STAR Spin Physics Program
Sandibek B. NurushevInstitute for High Energy Physics, Protvino,
Russia
(On behalf of the STAR Collaboration)
STAR
Introduction
The polarized RHIC Complex
STAR detector
Lessons of the first polarized beam runs
Main goals of the STAR Spin Physics Program
Hyperon polarizations
Summary
Contents
STARPoland:Warsaw Univ. of Tech.Russia:MEPHI - MoscowLPP/LHE JINR - DubnaIHEP - ProtvinoU.S. Laboratories:ArgonneBerkeleyBrookhavenU.S. Universities: Arkansas UniversityUC BerkeleyUC DavisUC Los AngelesCarnegie Mellon UniversityCreighton UniversityIndiana UniversityKent State UniversityMichigan State UniversityCity College of New YorkOhio State UniversityPenn. State UniversityPurdue UniversityRice UniversityTexas A&MUT AustinValparasio UniversityWashington UniversityWayne State UniversityYale University
Brazil: Universidade de Sao PauloChina: IHEP - BeijingIMP - LanzhouIPP - WuhanUSTCINR - ShanghaiTsinghua UniversityGrotia:University of ZagrebCzech Republic:NPI - AS CR RezGreat Britain: University of BirminghamFrance:IReS StrasbourgSUBATECH - NantesGermany: MPI – MunichUniversity of FrankfurtIndia:IOP - BhubaneswarPanjab UniversityUniversity of RajasthanJammu UniversityIIT - BombayVECC - KolcataNetherlands:NIKHEF
The STAR Collaboration
~ 500 Collaborators12 Countries
48 Institutions
STAR
Equipment to be
installed after FY03
Polarized RHIC Complex
STARSTAR – Solenoid Tracker At RHIC
Run0 Run1 Run2 and beyondSpin
Magnet Coils
B=0.25T
0.5T
Endcap EMC1< <2 = 2
Barrel EMC0< < 1 =2
|| < 1 = 2
Forward Pion Detector
(FPD) 3.1 < < 4.4+ upgrade
θ/2)] ln[tan(η
Time Projection
Chamber |<1.5
Silicon VertexTracker
Forward TPCs2.4 < || < 4.0
Beam-Beam Counters2 .4< || < 5.0
RICH: ||<0.3, =
Central Trigger Barrel |h| < 1
2 m
4.2 m
18 papers in NIM A499 (2003)
STAR
Left Right
Top
Bottom*BBC West
BBC East
InteractionVertex
3.3<||< 5.0
STAR uses observed asymmetry (AN ~0.006) in inclusive forward charged particle production in Beam-Beam Counters:
BBC - luminosity monitoring detector at STAR
Fast, highly-segmented scintillation counter serves many purposes in STAR:• Minimum Bias Trigger• Absolute Luminosity• Relative Luminosity• Measurement of Transverse Asymmetries
STAR upgrades for SpinSTAR
EndCapEMC (1/3)
EMC (Half) Barrel
Forward Pion Dets. (L,R,U,D on E; L,D on W)
STAR adding lots of EM calori-metry to detect high-energy , e, 0 plus Beam-Beam Counters for relative luminosity and polarization monitoring. EMC’s and FPD’s partially implemented for 2003 run, will be completed before 2005.
BBCWest
BBC EastTPC
See L. Bland talk
STARLessons of the first polarized beam runs
at s=200 GeV
1. BBC detector. It revealed the asymmetry of charged particles on the level AN(1±0.2)10-3 for each run. This is comparable to AN(CNI) (3±0.3)10-3 .
2. TPC. The asymmetry of the Leading Charged Particles (LCP) is close to zero on the level AN(1±1)10-2 up to pT 4 GeV/c for charged particles of both signs.
3. FPD. It detected inclusive 0 asymmetry on the level AN(0.2±0.07) at xF0.5.
STARThe Leading Charged Particle Asymmetry
Among the many complicated theoretical formulae the pQCDprediction for asymptotic quark asymmetry (polarization) is verysimple, namely
22T
TqsN mp
pmαA
Here mq is the quark mass, m is the final hadronic mass,
pT is the transverse momentum and
GeV 0.234Λ ,n3
211β ,
) /Λμ ln(β
4π)μ (α f022
0
2s
where nf is the number of flavors.
The asymptotic quark asymmetry
STARThe spin-orbital interaction
The soft scattering regime. It is well known from the dawn of the Spin Physics, that the spin orbital interaction (much smaller than the central potential) leads to the shift of the angular distribution of the scattered particles, so
θ Δ )) θ ( σ(ln dθ
d
) θ (σ) θ (σ
) θ (σ) θ (σAN
F.Halzen, Phys.Rev. 1962
STAR
This above expression was modified by M.G. Ryskin (Sov. Jour. Nucl. Phys. 48 (1988) 1114).
He assumed that two quarks in the colored string interact through the potential
The model of the quark polarization
GeV 0.1Hμδp
))(p (lnσdp
dδp) ) θ ( (lnσ
dθ
d
) θ (σ) θ (σ
) θ (σ) θ (σA
T
TT
TqN
,HμVμH
STAR
The inclusive pion versus quark asymmetry
onpolarizatiquark initial thex,q
P
2GeV60
s ,
0s3x)s(1
0sR
RAPA qNq
πN
3N
1/2qTT
108A
GeV 200s MeV, 100m 0.04, xGeV/c, 4p
The prediction can be verified at STAR
STAR
0.43 0.80 ΔG
0.03 0.09 - Δs
0.04 0.43- Δd
0.03 0.84 Δu
0.06 0.32 ΔΣ
0.01 0.1 1
0.0
0.1
0.2
0.3
0.4
PD(g1
NLO/F1
NLO)
x
xG(x)
0.01 0.1 1
-0.4
-0.3
-0.2
-0.1
0.0
x
-x(d+d)
0.01 0.1 1
-0.2
-0.1
0.0
x
-x(s+s)
0.01 0.1 10.0
0.1
0.2
0.3
0.4
x
PD (g1
NLO + HT)
-x(u+u)
Global NLO QCD analysis of DIS data SLAC (E142, E143, E154, E155)CERN (EMC, SMC)DESY (HERMES)
185 exp. points
E. Leader, A. Sidorov, D. Stamenov Phys. Rev. D67 (2003) 074017
22 GeV 1Q (JET), QCD NLO
G not well constrained not extracted
dΔ ,uΔ
Spin-dependent PDFs
dp,1
dp,1
dn,p,1 /Fg ,A
First moments at Q2 = 1 GeV2
STARSpin Physics Program at STAR
Gluon Polarization Direct Photon + jet Jet and DiJets Heavy flavor production (?)
Quark / Anti-Quark Polarization & Flavor Decomposition W production
Transversity & Transverse Spin Effects Single transverse spin asymmetries Transversity via Jet fragmentation Transversity via Dijet or Drell-Yan pairs
New Physics ? Parity violating asymmetries
qg q QCD Compton scattering
qg Jet Jet or gg Jet Jet
eWqq_
QQgg
STAR
Where is the spin
of the proton?
At present, the gluon contribution to the proton spin (G) is known only poorly from scaling violation in polarized deep inelastic scattering
STAR Spin goals: determine the gluon contribution to the proton’s spin determine the flavor decomposition of the quark (antiquark)
polarization probe transversity: the unknown, remaining leading-twist
structure function
STAR Parton distributions in proton
Helicity probes quark-gluon mixing qGq & G Probability to find longitudinal (z direction) polarized quarks & gluons in longitudinal polarized nucleon moving in the z direction.
Transversity probes dynamical chiral symmetry breakingq Probability to find transversely (x direction) polarized quarks in transversely
polarized nucleon moving in the z direction.
qqδq
GGΔG qqΔq
x
y
z
GGG qqq
Helicity average probes quark-gluon mixing q & G
q & G Probability density to find quarks in nucleon moving in the z direction
helicity difference
helicity flip
Quark chirality is conserved at all QCD and electroweak vertices, however quark chirality can flip in distribution function because they probe the soft regime where chiral symmetry is dynamically broken in QCD.
helicity average
STARALL(π0) Measurements at E704
The two-spin parameter ALL in inclusive π0 production by longitudinally-polarizedprotons and antiprotons on a longitudinally-polarized proton target has been measured
at 200 GeV Fermilab spin physics facility, for π0‘s at xF =0 with 1 ≤ pt ≤ 3 GeV/c. The
results exclude, at 95% confidence level, values of ALL(pp)>0.1 and < − 0.1, for π0‘s
produced by protons, and values of ALL(pp)>0.1 and < − 0.2 for incident antiprotons.The data are in good agreement with “conventional”, small or zero, gluon polarization.
A.Bazilevsky
π0 ALL from pp at s 1/2 =20 GeV
E704
STARALL(nγ) Measurements at E704
The double-spin asymmetry, ALL, for inclusive multi-γ pair production was measured with a 200 GeV/c longitudinally-polarized proton beam and a longitudinally-polarized proton target. The ALL values were found to be consistent with zero. The ALL values have been compared with theoretical predictions of gluon polarization, ΔG/G. The results put restrictions on the size of ΔG/G in the region of 0.05<x<0.35.
STAR STAR spin goals
Gluon spin-dependent distribution
function
Gluon contribution to proton spin
Sign of G
Jet, di-jet production
Measure of double-spin asymmetry ALL
with longitudinally polarized protons
L
LR
RNN
RNN
PP
1A
21LL
Xjetpp
Xjetjetpp
gq)(gqa)(xqe
)(xΔqe
)G(x
)ΔG(x
σσ
σσA LL
2i2i
2i2i
1
1LL
“ ..A priori not even the sign of Г is known, and it may be negative.” R.L.Jaffe
N – spin dep.yields of processL – yields of luminosity monitoring processR – relative luminosityP – beam polarization
STAR
gz
qz LLΔGΔΣ
2
1
2
1
STAR spin goals
Gluon spin-dependent distribution
function
Gluon contribution to proton spin
Sign of G
ΔsΔdΔuΔΣ
Direct productionjet correlation
Measure of double-spin asymmetry ALL
with longitudinally polarized protons
L
LR
RNN
RNN
PP
1A
21LL
Xjetγpp
Xγpp
1ΔΣ
0Δs γq)(gqa)(xqe
)(xΔqe
)G(x
)ΔG(x
σσ
σσA LL
2i2i
2i2i
1
1LL
N – spin dep.yields of processL – yields of luminosity monitoring processR – relative luminosityP – beam polarization
STARSTAR Spin Goals
))u(x(xd)(xd)u(x
))u(x(xdΔ)(xd)Δu(xA
2121
2121WL
XWpp
Separate quark - u, d , antiquark u, d helicity distribution functions
flavour andspin selects W
)u(x
)Δu(x
1
1
)(xd
)(xdΔ
1
1
21 xx
21 xx
Measure of parity violating asymmetry AL
with longitudinally polarized protons
L
LR
RNN
RNN
P
1AL
))d(x(xu)(xu)d(x
))d(x(xuΔ)(xu)Δd(xA
2121
2121WL
)d(x
)Δd(x
1
1
)(xu
)(xuΔ
1
1
21 xx
21 xx
N – spin dep.yelds of processL – yields of luminosity monitoring processR – relative luminosityP – beam polarization
¯ ¯
STAR STAR Spin Goals
GeV 20s
p
●0 - D.L. Adams, et al., Phys. Lett. B261(1991)201.●+/- - D.L. Adams, et al., Phys. Lett. B264(1991)462.
GeV/c 2.0p0.5 T
Transverse single pion asymmetry AN
from E704 to STAR
FNAL
AN increases with xF and reaches 40%
AN ≈ 0 at xF ≈ 0
sign(AN) – charge(correlation
AN (pp) ≈ – AN (pp)
RL
RLN σσ
σσA
LRLR
LRLR
P
1A
BN
Xπpp ,0
p_
STAR STAR Spin Goals Measure of double-spin
longitudinal ALL and transverse ATT
asymmetry for Drell-Yan pair production
LL22i
21i
2i
22i
21i
2i
LL a2)](1)Q,(xq)Q,(x[qe
2)](1)Q,(xq)Q,(xΔq [e
σσ
σσA
TT22i
21i
2i
22i
21i
2i
TT a2)](1)Q,(xq)Q,(x[qe
2)](1)Q,(xq)δQ,(xδq [e
σσ
σσA
Longitudinally polarized density q
Transverse polarized density q
Transversity distributions can not be measured in conventional DIS, semi-inclusive DIS is required. Transversity distributions are prime candidates for experiments at polarized proton collider.
Xllpp
Xllpp
STARSTAR Spin Goals
Measure of spin-transfer asymmetry
Spin-dependent fragmentation function
XΛpp ΛA
describes the transformation of a longitudinal polarized parton into
a longitudinal polarized (z)D(z)D(z)ΔD )Λ(
)i()Λ(
)i(Λi
hadronisation polarization transfer
)σ(σ)σ(σ
)σ(σ)σ(σA
)Λ()Λ()Λ()Λ(
)Λ()Λ()Λ()Λ(Λ
D. de Florian, M.Stratmann, W.VogelsangPRL 81 (1998) 530; PR D57 (1998) 5811
Sensitivity to flavour polarization transfer. Negative s (1), (u+d) (2), (s+u+d)(3) transmission of polarization to .
Phenomena exist but are not understandable
expected errors for STAR
STAR
Hyperon Polarization at STAR
STAR will be able after some upgrades to study a full set of the hyperon polarization parameters: I-diff. cross-section, P-polarization, AN-asymmetry, R, R’ -spin rotation parameters, A, A’ -longitudinal spin parameters, DNN -normal spin transfer parameters and Aij (i,j=n,s,l)-double spin parameters.
Hyperon polarization as a probe of the QGP.
STARSTAR Spin Goals
Measure of parity-violating spin asymmetry for one jet production
Standard Model test
)σ(σ)σ(σ
)σ(σ)σ(σAPV
LL
Xjetpp
New parity-violating interactions could lead to large modifications of the SM predictions
Asymmetry is nonzero due to electroweak QCD interference (g & Z0)
quark compositeness new short-range interactionSearch for
STARXjetγpp
BEMC
BEMC+EEMC
Compton
annihilation
N+(-) : Spin dependent event yield
R: Relative luminosity
P: Beam polarization
Double spin asymmetry:
RNN
RNN
PP
1A
21LL
RNN
)AP(P1
PP
1δA
2LL21
21LL
0ΔG
0ΔG
G.Skoro, M.T., hep-ph/0009028; E2-2001-40,JINR
G (x) determination via ALL
in p + p + jet + X
ALL
is sensitive to G
STAR
Simulation based on Pythia including trigger and and jet reconstruction efficiencies
Coverage of EMC (barrel) + EEMC (endcap) 0 < Φ < 2π and -1 < η < 2
Jet reconstruction: Cone algorithm
(seed = 1.5 GeV, R = 0.7) Luminosity: 320 pb-1
Polarization: 0.7 s = 200GeV
Sensitivity to Gluon Polarization at RHIC
xg , xq reconstruction G reconstruction
Comparison with other Comparison with other experimentsexperiments
STAR scans a wide range of xg=0.01-0.3
STAR
Xjetpp
Double spin asymmetry ALL: Inclusive jet production
Xdijetpp Simulation based on Pythia including jet
reconstruction efficiencies Coverage of EMC(barrel)+EMC(endcap)
0 < Φ < 2π and -1 < η < 2
Jet reconstruction: Cone algorithm (seed = 1.5 GeV, R = 0.7)
Luminosity: 8.1031 cm-2 s-1 s = 200 GeV Polarization: 0.7
Sign of ? ΔG
gz
qz LLΔGΔΣ
2
1
2
1
G.Skoro, M.T., M.ZupanNuovo Cim. A111(1998)353Nuovo Cim. A112(1999)809
0ΔG
0ΔG
0ΔG
0ΔG
G (x) determination via ALL in p + p jet+ jet + X
ALL
is sensitive to sign of G
STAR Flavor Decomposition of the proton’s spin
ALe(p p) d /d
ALe( p
p ) u /u
ALe (p p) u /u
ALe ( p
p ) d /d
Forward (backward) lepton measurement
p ( p)
p (p )
Blue beamtoward endcap
Yellow beamaway from endcap
Spin parity-violated asymmetry
Detect W ± in STAR via isolated high-pT daughter lepton, without away-side jet
u , d determination via AL
PV in p + p W ± + X @ s = 500 GeV
– –
STARSummary
Single spin asymmetry AN is measured by BBC. Precision is <10-3 allowing to control the transversal components of the beam polarization.
Significant single spin asymmetry in the inclusive 0 production is revealed by FPD in the polarized proton beam large xF region at s1/2 =200 GeV.
First single and double spin measurements in inclusive LCP production are made at STAR with transversally polarized protons. Measurements were done in the level of precision <10-2. Asymmetries are compatible with zero.
New measurements were done in this year with longitudinally polarized protons.
STAR at RHIC started a new generation of proton spin structure studies gluon contribution to the proton’s spin spin/flavor decomposition of the sea
double-spin asymmetries polarization transfer
transversity
STAR
• Measured cross sections consistent with pQCD calculations.
• Large spin effects observed for s = 200 GeV pp collisions, qualitatively
consistent with models extrapolating from FNAL E704 data at s = 20 GeV.
• Large normalization uncertainty on measured AN is reduced when Pbeam
calibration exp’t is done.
p + p “”+ X , s = 200 GeV
STAR Spin Results:STAR Spin Results:
Forward Pion Asymmetry and Cross SectionForward Pion Asymmetry and Cross Section
STAR PRELIMINARY