Title: Spin%20at%20RHIC%20Present%20Status%20and%20Future%20Plans
1Spin at RHICPresent Status and Future Plans
- OUTLINE
- Spin at RHIC how its done, why its done, and
who does it - Status of ALL measurements at RHIC sensitivity
to DG - Status of transverse single-spin asymmetries at
RHIC - Future plans
L.C. Bland, BNL IWHSS08, Torino 2 April 2008
2RHIC Spin CollaborationConfederation of Groups
Involved in the Effort
- Accelerator Physicists
- Primarily BNL Collider-Accelerator Department
- RHIC spin is a successful accelerator physics
experiment - Essential contributions from RIKEN for spin at
RHIC - RHIC Experiments (PHENIX,STAR,BRAHMS)
- RIKEN / RBRC, University and National Laboratory
groups - RHIC spin planning fully integrated in experiment
collaborations - Polarimetry
- Primarily BNL effort, with detailees from RHIC
experiments - Essential measurements required for RHIC spin
results - Theory
- RIKEN / RBRC, University and National Laboratory
groups - RHIC spin results require QCD global analyses to
extract physics
3RHIC Spin Goals - I
How is the proton built from its known quark and
gluon constituents? As with atomic and nuclear
structure, this is an evolving understanding
4RHIC Spin Goals - IIUnderstanding the Origin of
Proton Spin
Understanding the origin of proton spin helps to
understand its structure
5RHIC Spin Goals - III Milestones and Other
Objectives
- Direct measurement of polarized gluon
distribution (DG) using multiple probes - Direct measurement of flavor identified
anti-quark polarization using parity violating
production of W? - Transverse spin connections to partonic orbital
angular momentum (Ly) and transversity (dS)
6RHIC Spin Probes - IPolarized proton collisions
/ hard scattering probes of DG
Describe pp 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
7RHIC Spin Probes - IIUnpolarized cross sections
as benchmarks and heavy-ion references
Good agreement between experiment and theory ?
calibrated hard scattering probes of proton spin
8RHIC As a Polarized Collider
2005 Pblue 49.3 /- 1.5 /- 1.4
Pyellow 44.3 /- 1.3 /- 1.3
DP/P 4.2 (goal5) 2006 1 MHz collision
rate Polarization0.6 (online)
9RHIC Run-6
Plot by Phil Pile
An extraordinary Run-6!
Average Polarization 60!
Outstanding luminosity and polarization
performance from RHIC for polarized proton
collisions at ?s 200 GeV
10PHENIX Detector
- p0/g/h detection
- Electromagnetic Calorimeter (PbSc/PbGl)
- High pT photon trigger to collect p0's, hs, gs
- Acceptance hlt0.35, f 2 x p/2
- High granularity (1010mrad2)
- p/ p-
- Drift Chamber (DC) for Charged Tracks
- Ring Imaging Cherenkov Detector (RICH)
- High pT charged pions (pTgt4.7 GeV).
- Relative Luminosity
- Beam Beam Counter (BBC)
- Acceptance 3.0lt hlt3.9
- Zero Degree Calorimeter (ZDC)
- Acceptance 2 mrad
- Local Polarimetry
- ZDC
- Shower Maximum Detector (SMD)
EMCal
11Run-6 STAR detector layout
- Detectors used for jets
- Time Projection Chamber, ?lt1.4 Tracking
- Barrel EM Calorimeter, ?lt1 Triggering
Calorimetry - Endcap EM Calorimeter, 1.09lt?lt2 Triggering
Calorimetry - Beam-Beam Counters, 3.4lt?lt5 Triggering,
Luminosity, local Polarimetry
12Longitudinal Two-Spin (ALL)
Status of probing for gluon polarization
via measurements of ALLfor midrapidity jet,p0
production
13ALL ?0
5
10
pT(GeV)
GRSV model ?G 0 ?G(Q21GeV2)0.1 ?G
std ?G(Q21GeV2)0.4
Statistical uncertainties now to the point of
distinguishing std and 0 scenarios?
Run3,4,5 PRL 93, 202002 PRD 73, 091102
hep-ex-0704.3599
14From pT to xgluonmidrapidity neutral pion ALL
- Each pT bin corresponds to a wide range in
xgluon, heavily overlapping with other pT bins - Data are not sensitive to variation of ?G(xgluon)
within our x range - Quantitative analysis needs to assume some
?G(xgluon) shape
log10(xgluon)
- NLO pQCD for ?0, 2lt pT lt 9 GeV/c ? 0.02 lt xgluon
lt 0.3 - GRSV model ?G(0.02 lt xgluonlt 0.3) 0.6?G(0 lt
xgluon lt 1 )
15Constraining ?G from p0 ALLSimilar approach as
used for jets
Calculations by W.Vogelsang and M.Stratmann
?
- GRSV-std scenario, ?G(Q21GeV2)0.4, is
excluded by data on gt3s level - Only exp. stat. uncertainties are included (the
effect of syst. uncertainties is expected to be
small in the final results) - Theoretical uncertainties are not included
16Jet reconstruction in STAR
- Midpoint cone algorithm (Adapted from
Tevatron II - hep-ex/0005012 ) - Seed energy 0.5 GeV
- Cone radius in ?-?
- R0.4 (2005)
- R0.7 (2006)
- Splitting/merging fraction f0.5
Data jets MC
jets
Geant
Detector
Pythia
Particle
Use PythiaGEANT to quantify detector response
17Final 2005 Inclusive ALLjets Results
hep-ex arXiv0710.2048
0.2 lt ? lt 0.8
- Data are compared to predictions within the GRSV
framework with several input values of ?G.
B. Jager et.al, Phys.Rev.D70, 034010
GRSV-std
- The inclusive measurements give sensitivity to
gluon polarization over a broad momentum range
18Constraining DG from jet production ALLBefore
global analyses
- Compute ALL in NLO pQCD varying integral DG, but
maintaining GRSV shape - Perform ?2 analysis between calculations and
measured jet ALL
19Run 2006 Data
- Improved FOM
- Luminosity 2 ? 4.7 pb-1
- Polarization 50 ? 60 (online polarization)
- Barrel EMC ? coverage 0,1 ? -1,1
- In addition
- Jet Cone Radius 0.4 ? 0.7
- -0.7 lt ?jet axis lt 0.9
- Neutral Energy Fraction lt 0.85
- Increased trigger thresholds
- Inclusion of Endcap EMC towers
- Improved tracking at large ?
STAR Preliminary
202006 Inclusive ALLjets
-0.7 lt ? lt 0.9
GRSV curves with cone radius 0.7 and -0.7 lt ? lt
0.9
ALL systematics (x 10 -3)
Reconstruction Trigger Bias -1,3 (pT dep)
Non-longitudinal Polarization 0.03 (pT dep)
Relative Luminosity 0.94
Backgrounds 1st bin 0.5 Else 0.1
pT systematic ?6.7
- Using jet patch trigger (??x?? 1x1 patch of
towers) only - Statistical uncertainties are 3-4 times smaller
than 2005 in high pT region (pTgt13 GeV/c)
212006 Inclusive ALLjets
Theoretical uncertainties not included
GRSV DIS best fit0.24 1? -0.45 to 0.7 PRD 63,
094005 (2001)
- Within GRSV framework
- ?g_std excluded with 99 CL
- ?glt-0.7 excluded with 90 CL
22Summary of ALL Measurements
- Data accumulated through RHIC run 6 for inclusive
?0 and jet ALL has reached high statistical
significance to constrain ?G in the limited x
range (0.02?0.3) - ?G is found to be consistent with zero, to date
- Theoretical uncertainties (x dependence) are
significant
- Future Plans for Probing DG
- Improve statistical precision of midrapidity
p0,jet ALL measurements and extend measurements
to higher pT - Determine x-dependence of DG via correlation
measurements jet1jet2 and gjet - Extend gluon-x range probed to lower x via
measurements of ALL at larger rapidity and higher
?s - Global analysis in NLO pQCD of RHIC data and
HERMES,COMPASS data
23Transverse Single-Spin Asymmetries (AN)
Probing for orbital motion within transversely
polarized protons
24Expectations from Theory
What would we see from this gedanken experiment?
F?0 as mq?0 in vector gauge theories, so AN
mq/pT or,AN 0.001 for pT 2 GeV/c Kane,
Pumplin and Repko PRL 41 (1978) 1689
25A Brief History
?s20 GeV, pT0.5-2.0 GeV/c
- QCD theory expects very small (AN10-3)
transverse SSA for particles produced by hard
scattering.
- 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).
- ??0 E704, PLB261 (1991) 201.
- ??/- - E704, PLB264 (1991) 462.
26Two of the Explanations for Large Transverse
SSASpin-correlated kT
initial state
final state
Require experimental separation of Collins and
Sivers contributions
27Transverse Single-Spin AsymmetriesWorld-wide
experimental and theoretical efforts
- Transverse single-spin asymmetries are observed
in semi-inclusive deep inelastic scattering with
transversely polarized proton targets - ? HERMES (e) COMPASS (m) and planned at JLab
- Collins fragmentation function is observed in
hadron-pair production in ee- collisions (BELLE) - Intense theory activity underway
SPIRES-HEP search title including
Transverse spin, Transversity,
single spin
Total number 625 (19682006) Experimental
results 14
28Spin Effects in the Forward DirectionStatus
prior to RHIC run 6
J. Adams et al. (STAR), PRL 92 (2004) 171801 and
PRL 97 (2006) 152302
- Transverse SSA persist at large xF at RHIC
energies where unpolarized cross sections are
calculable
29STAR Results vs. Di-Jet Pseudorapidity Sum Run-6
Result
30High Precision Analyzing Powers
(2003 ? 2006)
B.I. Abelev, et al, hep-ex/0801.2990
? Precision measurements at ?s 200 GeV provide
stringent contraints on the models
31High Precision Analyzing Powers
(2003 ? 2006)
B.I. Abelev, et al, hep-ex/0801.2990
? No model fully describes the precision
data More experimental (and theoretical) work
needed
32(No Transcript)
33PHENIX Goes ForwardFirst results with muon
piston calorimeter from run 6p?p?p0X, ?s 62
GeV
Transverse SSA persists with similar
characteristics over a broad range of collision
energy (20 lt ?s lt 200 GeV)
34Summary Transverse Single Spin Asymmetry (SSA)
Measurements
- Feynman-x dependence of large-rapidity pion
production shows large transverse SSA at RHIC
energies, where cross sections are described by
NLO pQCD - Feynman-x dependence of large-rapidity transverse
SSA are consistent with theoretical models
(Sivers effect ? orbital motion / twist-3
calculations) - The pT dependence of large-rapidity p0 transverse
SSA does not follow theoretical expectations - Direct measurement of spin-correlated kT (Sivers
effect) via midrapidity di-jet spin asymmetries
completed in RHIC run 6 and found consistent with
zero. - Cancellations found in theory calculations
subsequent to measurements also expect small
di-jet spin asymmetries at midrapidity.
35Future RHIC Spin Plans
- Measure parity violation for W? production to
determine flavor dependence of quark and
antiquark polarization. - Requires completion of PHENIX muon trigger
upgrade and STAR forward tracking for charge sign
discrimination.
36Plans for Transverse Polarization
MeasurementsRHIC run 8 and beyond
- Experimental separation of Collins and Sivers
effects via transverse single-spin asymmetry
measurements for large rapidity p-p production - Extend measurements of transverse single spin
asymmetries from hadron production to prompt
photon production, including away-side
correlations - Develop RHIC experiments for a future measurement
of transverse single spin asymmetries for
Drell-Yan production of dilepton pairs
Transverse-Spin Drell-Yan Physics at RHIC L.
Bland, S.J. Brodsky, G. Bunce, M. Liu, M.
Grosse-Perdekamp, A. Ogawa, W. Vogelsang, F.
Yuan http//spin.riken.bnl.gov/rsc/write-up/dy_fin
al.pdf
37Forward Meson SpectrometerQuantifying possible
color glass condensate viaforward p0 and
correlations in dAu versus pp at ?sNN200 GeV
North FMS half before sealing
pp data at ?s 200 GeV also acquired Recorded
8 pb-1 in run 8
38Sivers in SIDIS vs Drell Yan
Transverse-Spin Drell-Yan Physics at RHIC L.
Bland, S.J. Brodsky, G. Bunce, M. Liu, M.
Grosse-Perdekamp, A. Ogawa, W. Vogelsang, F.
Yuan http//spin.riken.bnl.gov/rsc/write-up/dy_fin
al.pdf
- Important test at RHIC of the fundamental QCD
prediction of the non-universality of the Sivers
effect! - requires very high luminosity ( 250pb-1)
39Non-universality of Sivers Asymmetries Unique
Prediction of Gauge Theory !
Simple QED example
Drell-Yan repulsive
DIS attractive
Same in QCD
As a result
40 Experiment SIDIS vs Drell Yan SiversDIS -
SiversDY Test QCD Prediction of
Non-Universality
HERMES Sivers Results
RHIC Drell Yan Projections
0
Sivers Amplitude
Markus Diefenthaler DIS Workshop Munchen, April
2007
0
0.1 0.2 0.3 x
41Rapidity and Collision Energy
Large rapidity acceptance required to probe
valence quark Sivers function
42Backup
43Benchmarking Simulations
pp ? J/?X ? ll-X, ?s200 GeV
PHENIX, hep-ex/0611020
mm- 1.2lthlt2.2
ee- hlt0.35
J/? is a critical benchmark that must be
understood before Drell-Yan
44Dilepton Backgrounds
Drell-Yan
J/?
?
?
Isolation needed to discriminate open heavy
flavor from DY