3D parton structure, INT 1
Overview of Transverse Single Spin Asymmetry Measurements at RHIC
L.C. Bland
Brookhaven National Laboratory
INT Workshop on 3D parton structure of the nucleon
Seattle, September 2009
OutlineReview of Findings on Transverse SSA at RHIC
• Motivations/goals and methods
• Findings from the first polarized proton collisions at RHIC (medieval times)
• Findings from the renaissance
• First findings from the modern age
• Possible paths forward (more on Friday)
3D parton structure, INT 2
In QCD: proton is not just 3 quarks !
Rich structure of quarksanti-quarks, gluons
Recall: simple quark model
RHIC Spin Goals - IHow is the proton built from its known quark and gluon constituents?
As with atomic and nuclear structure, this is an evolving understanding
3D parton structure, INT 3
RHIC Spin Goals - IIUnderstanding the Origin of Proton Spin
Spin Sum Rules
Longitudinal Spin
Transverse Spin PRD 70 (2004) 114001
Understanding the origin of proton spin helps to understand its structure
3D parton structure, INT 4
RHIC Spin Goals - III Objectives
• Determination of polarized gluon distribution (G) using multiple probes
• Determination of flavor identified anti-quark polarization using parity violating production of W
• Transverse spin: connections to partonic orbital angular momentum (Ly) and transversity ()
gluon
quark pion or jet
quark
RHIC Spin Probes - IPolarized proton collisions / hard scattering probes of G
Describe p+p particle production at RHIC energies (s 62 GeV) using perturbative QCD at Next to Leading Order,
relying on universal parton distribution functions and fragmentation functions
cabccbb
cbaaacba dzDxfxfdzdxdxd
ˆ)()()( ,,
3D parton structure, INT 6
p + p, s = 200 GeV
jets direct
PRL 97 (2006) 252001
PRL 98 (2007) 012002
p + p + X, s = 200 GeV PRD 76 (2007) 051106 PRL 92 (2004) 171801
Large rapidity ,K,p cross sections for p+p, s=200 GeV
PRL 98 (2007) 252001
Good agreement between experiment and theory calibrated hard scattering probes of proton spin
RHIC Spin Probes - IIUnpolarized cross sections as benchmarks and heavy-ion references
3D parton structure, INT 7
Longitudinal Two-Spin (ALL)
Status of probing for gluon polarization viameasurements of ALLfor midrapidity jet,production
3D parton structure, INT 8
ALL: 0
PRL 103 (2009) 012003
0.1(scale)(shape)0.1(sys)(stat)1.02.0 0.00.4-
]3.0,02.0[ GRSVG
3D parton structure, INT 9
Inclusive ALLjets Results
STARSTARB. Jager et.al, Phys.Rev.D70, 034010
The inclusive measurements give sensitivity to gluon polarization over a broad momentum range
Data are compared to predictions within the GRSV framework with several input values of G.
GRSV-std
arXiv:0805.3004
3D parton structure, INT 10
Global AnalysisDetermining g from Existing World Data
PRL 101 (2008) 072001
g(x,Q2) is small in the accessible range of momentum fraction [presently measured]
3D parton structure, INT 11
RHIC as a Polarized Proton Collider
BRAHMS & PP2PP
STAR
PHENIX
AGS
LINACBOOSTER
Pol. H- Source
Spin Rotators(longitudinal polarization)
Siberian Snakes
200 MeV Polarimeter
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
AGS pC PolarimeterStrong AGS Snake
Helical Partial Siberian Snake
PHOBOS
Spin Rotators(longitudinal polarization)
Siberian Snakes
3D parton structure, INT 12 AN measurements initially motivated by search for local polarimeter
3D parton structure, INT 13
Transverse Single-Spin Asymmetries (AN)
Probing for (1) orbital motion within transversely polarized protons;
(2) Evidence of transversely polarized quarks in polarized protons.
Analyzing power is a tool to measure polarization and is one example of transverse single spin asymmetries (SSA) with origins yet to be fully understood
3D parton structure, INT 14
Expectations from Theory
What would we see from this gedanken experiment?
F0 as mq0 in vector gauge theories, so AN ~ mq/pT
or,AN ~ 0.001 for pT ~ 2 GeV/cKane, Pumplin and Repko PRL 41 (1978) 1689
3D parton structure, INT 15
s=20 GeV, pT=0.5-2.0 GeV/c
�0 – E704, PLB261 (1991) 201.�+/- - E704, PLB264 (1991) 462.
Xpp
• QCD theory expects very small (AN~10-3) transverse SSA for particles produced by hard scattering.
A Brief History…
• The FermiLab E-704 experiment found strikingly large transverse single-spin effects in p+p fixed-target collisions with 200 GeV polarized proton beam (s = 20 GeV).
3D parton structure, INT 16
STAR
• Large acceptance near midrapidity
• Windows to large rapidity
3D parton structure, INT 17
PHENIX Detector
BBC
ZDCZDC
EMCal detection• Electromagnetic Calorimeter (PbSc/PbGl):
• High pT photon trigger to collect 0's, ’s, ’s
• Acceptance: ||x • High granularity (~10*10mrad2)
• Drift Chamber (DC) for Charged Tracks• Ring Imaging Cherenkov Detector (RICH)
• High pT charged pions (pT>4.7 GeV).Relative Luminosity• Beam Beam Counter (BBC)
• Acceptance: 3.0< 3.9• Zero Degree Calorimeter (ZDC)
• Acceptance: ±2 mradLocal Polarimetry• ZDC• Shower Maximum Detector (SMD)
3D parton structure, INT 18
BRAHMS
3D parton structure, INT 19
Brahms
•Transvers beam pol•Particle ID
BRAHMS measured AN s=62.4 GeV and 200 GeV•Large xF dependent SSAs seen for pions and kaons•Collinear factorization and (NLO) pQCD describe unpolarized
cross-section at RHIC in wide kinematic region
3D parton structure, INT 20
Medieval TimesFirst polarized p+p collisions at RHIC
3D parton structure, INT 21
Transverse Spin Asymmetries at Midrapidity
p+p /h± + X, s = 200 GeV
Transverse single spin asymmetries are consistent with zero at midrapidity
PRL 95 (2005) 202001
3D parton structure, INT 22
Measuring AN: Inclusive 0 Production
PRL 92, 171801 (2004)PRL 97, 152302 (2006)
Cross-section is consistent with NLO pQCD calculations
Transverse spin asymmetries found at lower √s persist to √s=200 GeV
p+p+X, √s=200 GeV, <η> = 3.8
RHIC Runs 2-3 with Forward Pion Detector (FPD)
STARSTAR
3D parton structure, INT 23
STAR-Forward STAR-Forward Cross SectionsCross Sections
Similar to ISR analysisJ. Singh, et al Nucl. Phys. B140 (1978) 189.
6
5
13
3
B
C
pxdp
dE B
TC
F
Expect QCD scaling of form:
anBpxspxxdp
dE an
TC
F
anT
CF
aT 12/1
3
3
Require s dependence (e.g., measure cross sections at s = 500 GeV) to disentangle pT and xT dependence
3D parton structure, INT 24
The Renaissance
3D parton structure, INT 25
Idea: directly measure kT by observing momentum imbalance of a pair of jets produced in p+p collision and attempt to measure if kT is correlated with incoming proton spin
Boer & Vogelsang, PRD 69 (2004) 094025
jet
jet
AN pbeam (kT ST)
pbeam into page
STAR Results vs. Di-Jet Pseudorapidity SumSTAR Results vs. Di-Jet Pseudorapidity SumRun-6 ResultRun-6 Result
STARSTAR PRL 99 (2007) 142003
Emphasizes (50%+ ) quark Sivers
AN consistent with zero
~order of magnitude smaller in pp di-jets than in semi-inclusive DIS quark Sivers asymmetry!
VY 1, VY 2 are calculations by Vogelsang & Yuan, PRD 72 (2005) 054028
3D parton structure, INT 26
xF Dependence of Inclusive 0 ANRHIC Run 6 with FPD++
Fits to SIDIS (HERMES) is consistent with data
AN at positive xF
grows with increasing xF
PRL 101, 222001 (2008)arXiv:0801.2990v1 [hep-ex]
U. D’Alesio, F. MurgiaPhys. Rev. D 70, 074009 (2004)arXiv:hep-ph/0712.4240
C. Kouvaris, J. Qiu, W. Vogelsang, F. Yuan, Phys. Rev. D 74, 114013 (2006).
STARSTAR
3D parton structure, INT 27
• xF dependence is consistent with Sivers model
• Rising pT dependence is not explained
6/1/2009 27Chris Perkins
STAR, PRL 101 (2008) 222001
RHIC Runs 3,5,6 with FPDpT Dependence of Inclusive 0 AN
B.I. Abelev et al. (STAR) PRL 101 (2008) 222001
STARSTAR
3D parton structure, INT 28
xF and pT dependence of AN for p+p±+X, s=62 GeV
• AN(+) ~ -AN(-), consistent with results at lower s and u,d valence differences
• At fixed xF, evidence that AN grows with pT
I. Arsene, et al. PRL101 (2008) 042001
3D parton structure, INT 29
Transverse Spin Effects for Kaons
I. Arsene, et al. PRL101 (2008) 042001
p+pK±+X, s=62 GeV
• Large transverse single spin asymmetries are observed for kaons
3D parton structure, INT 30
PHENIX Muon Piston Calorimeter
SOUTH
• 192 PbWO4 crystals with APD readout
• Better than 80% of the acceptance is okay
2.22.2 18 cm3
3D parton structure, INT 31
PHENIX Goes ForwardFirst results with muon piston calorimeter from run 6
p+p+X, s = 62 GeV
Transverse SSA persists with similar characteristics over a broad range of collision energy (20 < s < 200 GeV)
3D parton structure, INT 32
p p M X M 200s GeV
STAR 2006 PRELIMINARY
Heavier mesons also accessible at high XF
Di-photons in FPD with E(pair)>40 GeV
No “center cut” (requirement that two-photon system point at middle of an FPD module)
With center cut and Z<0.85
Average Yellow Beam Polarization=56%
arXiv:0905.2840 (S. Heppelmann, PANIC 2008)
3D parton structure, INT 33
Towards Modern Times
• To separate Sivers and Collins effects need to move beyond inclusive production
• To isolate Sivers effect, need to either avoid fragmentation or integrate azimuthally• Full Jets, Di-Jets (away side), Direct photons, Drell-Yan
• To isolate Collins effect, need to look azimuthally within a jet.
3D parton structure, INT 34
Guzey, Strikman and Vogelsang Guzey, Strikman and Vogelsang Phys. Lett. B603 (2004) 173Phys. Lett. B603 (2004) 173
PYTHIA Simulation PYTHIA Simulation
• constrain x value of gluon probed by high-x quark by detection of second hadron serving as jet surrogate.
• span broad pseudorapidity range (-1<<+4) for second hadron span broad range of xgluon
• provide sensitivity to higher pT for forward reduce 23 (inelastic) parton process contributions thereby reducing uncorrelated background in correlation.
1Brookhaven National Laboratory2University of California- Berkeley3Pennsylvania State University4IHEP, Protvino5Stony Brook University6Texas A&M University7Utrecht, the Netherlands
8Zagreb University
STAR Forward Calorimeter ProjectsF.Bieser2, L.Bland1, E. Braidot7, R.Brown1, H.Crawford2, A.Derevshchikov4, J.Drachenberg6, J.Engelage2, L.Eun3, M.Evans3, D.Fein3, C.Gagliardi6, A. Gordon1, S.Hepplemann3, E.Judd2, V.Kravtsov4, J. Langdon5, Yu.Matulenko4, A.Meschanin4, C.Miller5, N. Mineav4, A. Mischke7, D.Morozov4, M.Ng2, L.Nogach4, S.Nurushev4, A.Ogawa1, H. Okada1, J. Palmatier3, T.Peitzmann7, S. Perez5, C.Perkins2, M.Planinic8, N.Poljak8, G.Rakness1,3, J. Tatarowicz3, A.Vasiliev4, N.Zachariou5
These people built the Forward Meson Spectrometer (FMS) and/or its components
3D parton structure, INT 36
STAR Forward Meson Spectrometer
PRL 101 (2008) 222001
• 50 larger acceptance than the run-3 forward pion detector (FPD).
• azimuth for 2.5<<4.0
• Discriminate single from up to ~60 GeV
Runs 3-6
FPD
Run8
FMSNorth half of FMS
before closing
3D parton structure, INT 37
Run-8 Results from STAR Forward Meson Spectrometer
(FMS)
Full azimuth spanned with nearly contiguous electromagnetic calorimetry from -1<<4
approaching full acceptance detector
3D parton structure, INT 38
Run 8 FMS Inclusive 0 Results
Octant subdivision of FMS for inclusive spin sorting. arXiv:0901.2828
Nikola Poljak – SPIN08
• Azimuthal dependence as expected• AN comparable to prior
measurements
x
y
P
3D parton structure, INT 39
Negative xF
arXiv:0901.2763 (J. Drachenberg– SPIN08)Akio Ogawa – CIPANP 09
Positive xF
RHIC Run 8 with East FPD/FMSpT Dependence
Indication of Positive AN persists up to pT ~5 GeVNeeds more transverse spin running
Negative xF consistent with zero
3D parton structure, INT 40
First Look at “Jet-like” Events in the FMSEvent selection:
• “Jet shape” in data matches simulation well• Reconstructed Mass doesn’t match as well• High-Tower Trigger used in Run 8 biases Jets
• >15 detectors with energy > 0.4GeV in the event (no single pions in the event)• cone radius = 0.5 (eta-phi space)• “Jet-like” pT > 1 GeV/c ; xF > 0.2• 2 perimeter fiducial volume cut (small/large cells)
“Jet-shape” distribution of energy within jet-like objects in the FMS as a function of distance from the jet axis.
arXiv:0901.2828 (Nikola Poljak – SPIN08)
3D parton structure, INT 41
•Comparison to dAu •Spin-1 meson AN
High xF Vector MesonsRHIC Run 8 with FMS
Background only MCRun8 FMS dataFit is gaussian + P3
μ=0.784±0.008 GeV σ=0.087±0.009 GeV Scale=1339±135 Events
3 photon events to look for0BR
•PT(triplet)>2.5 GeV/c •E(triplet)>30 GeV•PT(photon cluster)>1.5 GeV/c •PT(π0)>1 GeV/c
Significant (10) 0 signal seen in the data.
arXiv:0906.2332
A Gordon– Moriond09
Triple Photons : 0
Next :
3D parton structure, INT 42
STAR Detector• Large rapidity coverage for electromagnetic calorimetry (-
1<<+4) spanning full azimuth azimuthal correlations
• Run-8 was the first run for the Forward Meson Spectrometer (FMS)
3D parton structure, INT 43
Azimuthal Correlations with Large E. Braidot (for STAR), Quark Matter 2009
Unc
orre
cted
Coi
ncid
ence
P
roba
bilit
y (r
adia
n-1)
p+p+h±+X, s=200 GeV
requirements:
pT,>2.5 GeV/c
2.8<<3.8
h± requirements:
1.5<pT,h<pT,
h<0.9
• clear back-to-back peak observed, as expected for partonic 22 processes
• fixed and large trigger, with variable h map out Bjorken-x dependence
• of greatest interest for forward direct- trigger
3D parton structure, INT 44
Forward 0 – Forward 0 Azimuthal Correlations
• Possible back-to-back di-jet/di-hadron Sivers measurement• Possible near-side hadron correlation for Collins fragmentation function/Interference fragmentation function + Transversity • Low-x / gluon saturation study – accessing lowest xBj
gluon
Akio Ogawa- CIPANP 09
3D parton structure, INT 45
Proposals for the FutureSSA beyond inclusive meson production
• Forward jets
• Forward photons
• Forward virtual photons
(Just mentioned here… much more about future prospects on Friday)
3D parton structure, INT 46
Conclusions and Summary• Transverse spin asymmetries are present at RHIC
energies
• Transverse spin asymmetries are present at large
• Particle production cross sections and correlations are consistent with pQCD expectations at large where transverse spin effects are observed
• Essential to go beyond inclusive production to disentangle dynamical origins
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