star william christie, bnl mini-symposium on orbital motion of quarks in hard scattering i 2005 2nd...
TRANSCRIPT
STARSTAR William Christie, BNL
Mini-symposium on Orbital Motion of Quarks in Hard Scattering I
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and the Physical Society of Japan
September 21, 2005.
Transverse Spin Results from STAR
Outline
• Physics motivation
• Brief introduction to the STAR Detector
• STAR Transverse polarization Data sets
• Cross section measurements
• Forward 0 asymmetry
• Future measurements
• Summary
STARSTAR
500+ collaborators52 institutions14 countries
Austria: Bern Brazil: Sao Paolo
China: IHEP-Beijing, IMP-Lanzhou, Shanghai INR, Tsinghua, USTC, IPP-Wuhan Croatia: Zagreb
Czech Republic: Nuclear Physics Institute-AS-CR
England: Birmingham France: IReS - Strasbourg, SUBATECH-Nantes
Germany: Frankfurt, MPI-Munich India: Bhubaneswar, Jammu, IIT, Panjab, Rajasthan, VECC-Kolkata Netherlands: NIKHEF Poland: Warsaw U. of Technology Russia: JINR - Dubna, IHEP – Protvino, MEPHI - Moscow S. Korea: Pusan
U.S.: Argonne, Berkeley, Brookhaven National Laboratories UC Berkeley, UC Davis, UCLA, CalTech, Creighton, Carnegie-Mellon, Indiana, Kent State,
Michigan State, CCNY, Ohio State, Penn State, Purdue, Rice, Texas, Texas A&M, Valparaiso, Washington, Wayne State, Yale Universities
The STAR Collaboration
STARSTARPhysics Motivation
It has been determined, through polarized deep inelastic scattering experiments, that the quarks alone can not account for the spin of the proton (i.e.
To account for the spin of the proton, either the gluons are polarized and/or there are significant contributions to the protons spin from the orbital motion of its constituents.
Would like to unravel the contributions to transverse spin asymmetries (an area of intense recent theoretical development) from:
a) quark transverse spin preferences in a transversely polarized proton (p)
“transversity” quark property decoupled from gluons
b) quark and gluon transverse motion preferences in p
spin-kT correlation related to quark/gluon orbital ang. mom.
1
2
1
2G + L
Quark spin Gluon Spin Angular momentumProton Spin:
STARSTARBarrel EM Calorimeter
-1<η< 1
STAR Detector
=0
Forward Pion Detector
Endcap EM Calorimeter
Beam-Beam Counters
Time Projection Chamber
-1<η< 1
1<η< 2-4.1<η< -3.3
2<|η|< 5
Solenoidal MagneticField (5 kG) analyzestransverse momentumpT of charged particles
=2= -1
Tracking 200320042005
Triggering
Triggering
- ln(tan(/2) Lum. Monitor Local Polarim.
ForwardTPC
2.8 < < 3.8
Central TriggerBarrel
SiliconVertex
Tracker
STARSTARTransverse Polarization Data sets and FPD Configurations
2002 Run: <Pb> ~ 15%, Lint = 0.3 pb-1
2003 Run: <Pb> ~ 30%, Lint = 0.5 pb-1
Upgraded Forward Detector (FPD)
• Pb-glass EM calorimeter
(from IHEP Protovino, used in E704)
• Shower-Maximum Detector (SMD)
• Preshower
Forward Detector (FPD, aka pEEMC)
- 24 layer Pb-scintillator sampling calorimeter
- 2 orthogonal planes of finely segmented triangular scintillator strips (Shower-Maximum Detector, or SMD)
- 2 Preshower layers
East of STAR
Top
Bottom
North
South
STARSTAR
Polarization Pattern at STAR: Spin Up Spin Down Unpolarized
Spin asymmetries in proton-proton collider
Double Spin Asymmetries (F.o.M = P4L)
A 1P
N RN
N RN R L
L
=1P
NL NR
NR NL
NL NR
NR NL
Single Spin Asymmetries (F.o.M = P2L)
A 1P1P2
N RN
N RN R =L
L
N = spin dependent yields of process interestN = spin dependent yields of process interestL = yield of luminosity monitoring process L = yield of luminosity monitoring process R = relative luminosity between different spin configuration R = relative luminosity between different spin configuration P = beam polarization(s) from polarimeter at RHICP = beam polarization(s) from polarimeter at RHICAlso need direction of polarization vector at IRAlso need direction of polarization vector at IR
AN with left-right symmetric detectors
Requires 3 different process/measurements “Bunch/Spin sorting” Up to 120 bunches in RHICBunch Spacing 107nsec (9MHz)Alternating spin patternBunch/Spin sorted scaler system
bunch crossing number at STAR IR
inte
ract
ions
(kH
z)/c
ross
ing
STARSTAR
Left Right
Top
Bottom*BBC West
BBC East
InteractionVertex
3.3<||< 5.0 (inner tiles)
BBC’s register hits for ~50% of tot (pp); EW coinc. discriminates against beam-gas bkgd. for good L monitoring; segmentation local polarimeter with AN
obs.~0.006.
1
L
LR
Example of R
• Statistical uncertainty: dRstat ~10-4 -10-3
• Systematic uncertainty ( beam-gas background ) < 10-3
BBC gives triggering, (Rel.) Luminosity, and local polarimetry.
Negative xFPositive xF
• = BBC L/R asym.
= BBC T/B asym.
Time [Run Number]
2.1 <||< 5.0
R 1 and time dependent!
05/16/03 05/30/03
BB
C
YCNI B
CNI
STARSTAR
<z>
<xq>
<xg>
NLO pQCDJaeger,Stratmann,Vogelsang,Kretzer
p p 0, 3.8, s 200GeV
Forward 0 production in a hadron collider
• Large rapidity production ~4 probes asymmetric partonic collisions
• Mostly high-x valence quark + low-x gluon
• 0.3 < xq< 0.7
• 0.001< xg < 0.1
• <z> nearly constant and high 0.7 ~ 0.8
• Large-x quark polarization is known to be large from DIS
• Directly couple to gluons = A probe of low x gluons
pd
pAu
q
g
Q2 ~ pT2
s 2EN
ln(tan(2
))
xq xF / zEN
xqpxgp
xF 2E
s
z E
Eq
xg pT
se g
EN
(collinear approx.)
STARSTAR2002 STAR Forward Detector (aka pEEMC)
M
reconstruction atE=20~80GeV, 1 <pT < 4 GeV 3<<4
EventDisplay
SMD
EMC
o Cluster separation in shower maximum detector and measured calorimeter energy serves as input to the 0 mass determination.
STARSTARRun 2 Results: Forward Inclusive Cross Section
STAR data consistent with Next-to-Leading Order pQCD calculations
in contrast to data at lower s (Bourrely and Soffer, Eur.Phys.J. C36 (2004) 371-374)
• STAR data at
= 3.8 (hep-ex/0310058, Phys. Rev. Lett. 92 (2004) 171801)
• = 3.3 (hep-ex/0403012, Preliminary)
• NLO pQCD calculations at fixed with equal factorization and renormalization scales = pT
• Solid and dashed curves differ primarily in the g fragmentation function
STARSTARRun 2 Results: Large Analyzing Powers at RHIC
First measurement of AN for forward π0 production at s=200GeV
Similar to FNAL E704 result at s = 20 GeV
In agreement with several models 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
First shown at spin2002
• pT dependence?
• xF<0?
•AN with mid-rapidity correlation?
• Spin dependence in jet?
STARSTARRun 3 Results: AN for forward & backward 0 production at s=200GeV
Positive AN at large positive xF 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
STAR Preliminary
Statistical error only for <>=4.1
STARSTAR
Different position for FPD relative to the beam, relative to already accumulated 2002 data, allows mapping of AN in xF and pT plane to begin
xF and pT range of the data
Run 3 Results: Add 0 cross sections at = 4.0
STARSTAROutlook
• 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
STARSTARSummary
• Forward hadron production at hadron-hadron collider selects high-x (thus high polarization) quark + low-x gluon scatterings
• Inclusive cross section is consistent with NLO pQCD calculations and PYTHIA(LO pQCD + parton showers)
• Analyzing power for forward 0 mesons at large positive xF was found to be large and positive
• The first measurement of negative xF AN has been done, and is consistent with zero
• Accumulation of significant (O 10 pb-1, P 50%) transverse polarization data set expected in upcoming FY06 RHIC run. Expect to start extracting information on dynamics responsible for transverse spin asymmetries.
STARSTAR
Backup
STARSTARCoincidence Transverse Spin Measurements Should Unravel Coincidence Transverse Spin Measurements Should Unravel
Transversity, Collins, Sivers EffectsTransversity, Collins, Sivers Effects
p
p
q
g
Jets with 2 hadrons detected
+
+ …
p
p q
q
Study transversity by exploiting chiral-odd fragment’n “analyzing powers” (Collins or interference frag. fcns.) calibrated at BELLE
Search for spin-dependent transverse motion preferences inside proton (related to parton Lorbit ) via predicted leading-twist spin-dependent deviation from back-to-back alignment of di-jet axes study unique to RHIC spin
STAR projections for 30 pb1, Pbeam=70%
parton kT
AN
pp dijet + X s = 200 GeV 8 pT(1,2) 12 GeV |(1,2)| 1.0
D. Boer & W. Vogelsang predictions
p spin
STARSTAR
kPS
)k(PS)k(x,ƒΔ
21
)k(x,ƒ)s,k(x,ƒPP
pPq
NqqPq
s
2EX
0πF
D. Boer and W. Vogelsang,Phys.Rev. D 69 (2004) 094025
Analyzing Powers at Mid-RapidityDo processes invoked in forward scattering show up at large angles?
Sivers Function – correlation between kT and spin
For given parton at some x kT
L=kTR
Jet
Jet
DijetDijet
DijetDijetN
YY
YY
Pol1
A
Measure
STARSTAR
STAR Collab. Phys. Rev. Lett. 92 (2004) 171801
STARSTAR4.1 x 10 -4
Partonic kT from Dijet Analysis
kT = <kT>2 = ET sin (σ)
ET = 13.0 ± 0.7sys → Trigger Jet
0.030.05
σ =0.23 ± 0.02±
AN8 < pT1,2 < 12 GeV
|η1,2 | < 1
Sivers Effect Prediction
STAR agrees well with World
Data on Partonic kT
D. Boer and W. Vogelsang,Phys.Rev. D 69 (2004) 094025
• Curves are for various gluonic Sivers functions
• Connection to partonic orbital angular momentum
• Suppressed by Sudakov effect
kT distribution
STARSTAR
T. Henry