1. Transverse Spin and RHIC Probing Transverse Spin in p+p Collisions
OUTLINE
Features of RHIC for polarized p+p collisions
Transverse single spin effects in p+p collisions at s=200 GeV
Towards understanding forward p0 cross sections
Plans for the future
L.C. Bland
Brookhaven National Laboratory
Transverse Polarization in Hard Processes
Como 7 September 2005

2. Developments for runs 2 (1/02), 3 (3/03  5/03) and 4 (4/04  5/03)
Installed and commissioned during run 4
To be commissioned
Installed/commissioned in run 5
Developments for runs 2 (1/02), 3 (3/03  5/03) and 4 (4/04  5/03)
Helical dipole snake magnets
CNI polarimeters in RHIC,AGS
 fast feedback
b*=1m operataion
spin rotators  longitudinal polarization
polarized atomic hydrogen jet target
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3. RHIC Spin Physics Program
Direct measurement of polarized gluon distribution using
multiple probes
Direct measurement of anti-quark polarization using
parity violating production of W
Transverse spin: Transversity & transverse spin effects:
possible connections to orbital angular momentum?
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4. Calendar Summary for RHICRun-5 p+p Run
pp commissioning started on March 24, 2005
pp Physics running, for longitudinal polarization, started on April 19, 2005
410 GeV Collider dev. & data, was May 31st to June 3rd
Transverse polarization was June 13th to June 16th
Run ended on June 24, 2005
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5. RHIC Run-5 Performance (nb-1) (nb-1) Total for run
~ 9.2 pb-1 delivered
~ 3.1 pb-1 smpled
(nb-1)
(nb-1)
Delivered
STAR 2005 Longitudinal Goal
Sampled
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6. PHENIX Detector Philosophy: 0 reconstruction and
High rate capability & granularity
Good mass resolution and particle ID
0 reconstruction and
high pT photon trigger:
EMCal: ||<0.38, =
Granularity  = 0.010.01
Minimum Bias trigger and Relative Luminosity:
Beam-Beam Counter (BBC):
3.0<||<3.9, =2
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8. STAR detector layout TPC: -1.0 <  < 1.0
FTPC: 2.8 <  < 3.8
BBC : 2.2 <  < 5.0
EEMC:1 <  < 2
BEMC:0 <  < 1
FPD: || ~ 4.0 & ~3.7
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9. First AN Measurement at STAR prototype FPD results
STAR collaboration
Phys. Rev. Lett. 92 (2004)
Similar to result from E704 experiment (√s=20 GeV, 0.5 < pT < 2.0 GeV/c)
Can be described by several models available as predictions:
Sivers: spin and k correlation in parton distribution functions (initial state)
Collins: spin and k correlation in fragmentation function (final state)
Qiu and Sterman (initial state) / Koike (final state): twist-3 pQCD calculations, multi-parton correlations
√s=200 GeV, <η> = 3.8
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10. Why Consider Forward Physics at a Collider? Kinematics
Deep inelastic scattering
Hard scattering hadroproduction
Can Bjorken x values be selected in hard scattering?
Assume:
Initial partons are collinear
Partonic interaction is elastic  pT,1  pT,2 
Studying pseudorapidity, h=-ln(tanq/2), dependence of particle production probes parton distributions at different Bjorken x values and involves different admixtures of gg, qg and qq’ subprocesses.
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11. Simple Kinematic Limits
Mid-rapidity particle detection:
h10 and <h2>0
 xq  xg  xT = 2 pT / s
Large-rapidity particle detection:
h1>>h2
xq  xT eh1  xF (Feynman x), and
xg  xF e-(h1+h2)
NLO pQCD (Vogelsang)
1.0
0.8
0.6
0.4
0.2
0.0
p+p  p0+X, s = 200 GeV, h=0 qq
fraction qg gg
pT,p (GeV/c)
 Large rapidity particle production and correlations involving large rapidity particle probes low-x parton distributions using valence quarks
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12. Do they work for forward rapidity?
How can one infer the dynamics of particle production? Particle production and correlations near h0 in p+p collisions at s = 200 GeV
Inclusive p0 cross section
Two particle correlations (h)
STAR
STAR, Phys. Rev. Lett. 90 (2003), nucl-ex/
At √s = 200GeV and mid-rapidity, both NLO pQCD and PYTHIA explains p+p data well, down to pT~1GeV/c, consistent with partonic origin
Do they work for forward rapidity?
Phys. Rev. Lett. 91, (2003)
hep-ex/
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13. Forward p0 production in hadron colliderEp p0 p d EN qq qp p Au
xgp
xqp qg EN
(collinear approx.)
Large rapidity p production (hp~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
<z>
<xq>
<xg>
NLO pQCD
Jaeger,Stratmann,Vogelsang,Kretzer
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14. xF and pT range of FPD data
STAR
xF and pT range of FPD data
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15. ppp0X cross sections at 200 GeV
The error bars are point-to-point systematic and statistical errors added in quadrature
The inclusive differential cross section for p0 production is consistent with NLO pQCD calculations at 3.3 < η < 4.0
The data at low pT are more consistent with the Kretzer set of fragmentation functions, similar to what was observed by PHENIX for p0 production at midrapidity.
D. Morozov (IHEP),
XXXXth Rencontres de Moriond - QCD,
March , 2005
NLO pQCD calculations by Vogelsang, et al.
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16. STAR -FPD Preliminary Cross Sections Similar to ISR analysis
J. Singh, et al Nucl. Phys.
B140 (1978) 189.
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17. PYTHIA: a guide to the physics
Forward Inclusive  Cross-Section:
Subprocesses involved:
q+g
g+g and
q+g  q+g+g
STAR FPD
Soft processes
PYTHIA prediction agrees well with the inclusive 0 cross section at 3-4
Dominant sources of large xF  production from:
q + g  q + g (22)   + X
q + g  q + g + g (23)   + X q g  q  g
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18. Single Spin Asymmetry Definitions
dσ↑(↓) – differential cross section of p0 then incoming proton has spin up(down)
Two measurements:
Single arm calorimeter:
R – relative luminosity (by BBC)
Pbeam – beam polarization
Two arms (left-right) calorimeter:
No relative luminosity needed
π0, xF<0
π0, xF>0
Left
Right
p  p
positive AN: more p0 going
left to polarized beam
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19. Run 3 Preliminary Result. -More Forward angles. -FPD Detectors.
Caveats:
-RHIC CNI Absolute polarization still preliminary.
-Result Averaged over azimuthal
acceptance of detectors.
-Positive XF (small angle
scattering of the polarized proton).
Run 2 Published Result.
Run 3 Preliminary Result.
-More Forward angles.
-FPD Detectors.
- ~0.25 pb-1 with Pbeam~27%
Run 3 Preliminary
Backward Angle Data.
-No significant Asymmetry
seen.
(Presented at Spin 2004: hep-ex/ )
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20. New Physics at high gluon density
Figure 3 Diagram showing the boundary between possible “phase” regions in the t=ln(1/x) vs ln Q2 plane .
New Physics at high gluon density
Shadowing. Gluons hiding behind other gluons. Modification of g(x) in nuclei. Modified distributions needed by codes that hope to calculate energy density after heavy ion collision.
Saturation Physics. New phenomena associated with large gluon density.
Coherent gluon contributions.
Macroscopic gluon fields.
Higher twist effects.
“Color Glass Condensate”
Edmond Iancu and Raju Venugopalan, review for Quark Gluon Plasma 3,
R.C. Hwa and X.-N. Wang (eds.), World Scientific, 2003 [hep-ph/ ].
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21.  Dependence of RdAu y=0 As y grows
Kharzeev, Kovchegov, and Tuchin, Phys. Rev. D 68 , (2003)
G. Rakness (Penn State/BNL),
XXXXth Rencontres de Moriond - QCD,
March , 2005
See also J. Jalilian-Marian, Nucl. Phys. A739, 319 (2004)
From isospin considerations, p + p  h is expected to be suppressed relative to d + nucleon  h at large  [Guzey, Strikman and Vogelsang, Phys. Lett. B 603, 173 (2004)]
Observe significant rapidity dependence similar to expectations from a “toy model” of RpA within the Color Glass Condensate framework.
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22. Constraining the x-values probed in hadronic scattering
Log10(xGluon)
Gluon
TPC
Barrel EMC
FTPC
FPD
For 22 processes
Guzey, Strikman, and Vogelsang, Phys. Lett. B 603, 173 (2004).
Log10(xGluon)
Collinear partons:
x+ = pT/s (e+h1 + e+h2)
x = pT/s (eh1 + eh2)
FPD: ||  4.0
TPC and Barrel EMC: || < 1.0
Endcap EMC: 1.0 <  < 2.0
FTPC: 2.8 <  < 3.8
CONCLUSION: Measure two particles in the final state to constrain the x-values probed
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23. Back-to-back Azimuthal Correlations with large 
Beam View
Top View
Fit LCP normalized distributions and with Gaussian+constant
Trigger by forward   ]
E > 25 GeV
  4 ]
Coicidence Probability
[1/radian]
Midrapidity h tracks in TPC
-0.75 < < +0.75
Leading Charged Particle(LCP)
pT > 0.5 GeV/c
LCP
S = Probability of “correlated” event under Gaussian
B = Probability of “un-correlated” event under constant
s = Width of Gaussian
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24. Statistical errors only
STAR
PYTHIA (with detector effects) predicts
“S” grows with <xF> and <pT,>
“s” decrease with <xF> and <pT,>
PYTHIA prediction agrees with p+p data
Larger intrinsic kT required to fit data
STAR Preliminary
25<E<35GeV
45<E<55GeV
STAR Preliminary
Statistical errors only
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25. Plans for the Future
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26. STAR Forward Meson Spectrometer
NSF Major Research Initiative (MRI) Proposal
submitted January 2005
[hep-ex/ ]
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27. STAR detector layout with FMS
TPC: -1.0 <  < 1.0
FTPC: 2.8 <  < 3.8
BBC : 2.2 <  < 5.0
EEMC:1 <  < 2
BEMC:-1 <  < 1
FPD: || ~ 4.0 & ~3.7
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28. Three Highlighted Objectives In FMS Proposal (not exclusive)
A d(p)+Aup0p0+X measurement of the parton model gluon density distributions xg(x) in gold nuclei for 0.001< x <0.1. For 0.01<x<0.1, this measurement tests the universality of the gluon distribution.
Characterization of correlated pion cross sections as a function of Q2 (pT2) to search for the onset of gluon saturation effects associated with macroscopic gluon fields. (again d-Au)
Measurements with transversely polarized protons that are expected to resolve the origin of the large transverse spin asymmetries in reactions for forward  production. (polarized pp)
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29. Frankfurt, Guzey and Strikman,
J. Phys. G27 (2001) R23 [hep-ph/ ].
constrain x value of gluon probed by high-x quark by detection of second hadron serving as jet surrogate.
span broad pseudorapidity range (-1<h<+4) for second hadron  span broad range of xgluon
provide sensitivity to higher pT for forward p0  reduce 23 (inelastic) parton process contributions thereby reducing uncorrelated background in Df correlation.
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Pythia Simulation

30. Sivers mechanism asymmetry is present for forward jet or g
Disentangling Dynamics of Single Spin Asymmetries Spin-dependent particle correlations
Collins/Hepplemann mechanism requires transversity and spin-dependent fragmentation
Sivers mechanism asymmetry is present for forward jet or g
Large acceptance of FMS will enable disentangling dynamics of spin asymmetries
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31. Loaded On a Rental Truck for Trip To BNL
New FMS Calorimeter
Lead Glass From FNAL E831
804 cells of 5.8cm5.8cm60cm
Schott F2 lead glass
Loaded On a Rental Truck for Trip To BNL
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32. FPD++ Physics for Run6
Run-7 FMS
Run-6 FPD++
Run-5 FPD
We intend to stage a large version of the FPD to prove our ability to detect direct photons.
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33. How do we detect direct photons?
Isolate photons by having sensitivity to partner in decay of known particles:
π0 M=0.135 GeV BR=98.8%
K0  π0π0   %
  %
 π0    %
Detailed simulations underway
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34. Where do decay partners go?
m = p0(h) di-photon parameters
zgg = |E1-E2|/(E1+E2)
fgg = opening angle
Mm = GeV/c2 (p0)
Mm=0.548 GeV/c2 (h)
Gain sensitivity to direct photons by making sure we have high probability to catch decay partners
This means we need dynamic range, because photon energies get low (~0.25 GeV), and sufficient area (typical opening angles few degrees at our h ranges).
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35. Sample decays on FPD++
With FPD++ module size and electronic dynamic range, have >95% probability of detecting second photon from p0 decay.
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36. Ongoing progress on developing luminosity and polarization
Timeline for the Baseline RHIC Spin Program
Ongoing progress on developing luminosity and polarization
Research Plan for Spin Physics at RHIC (2/05)
Program divides into 2 phases:
s=200 GeV with present detectors for gluon polarization (g) at higher x & transverse asymmetries;
s=500 GeV with detector upgrades for g at lower x & W production
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37. Summary / Outlook
Large transverse single spin asymmetries are observed for large rapidity p0 production for polarized p+p collisions at s = 200 GeV
AN grows with increasing xF for xF>0.35
AN is zero for negative xF
Large rapidity p0 cross sections for p+p collisions at s = 200 GeV is in agreement with NLO pQCD, unlike at lower s. Particle correlations are consistent with expectations of LO pQCD (+ parton showers).
Large rapidity p0 cross sections and particle correlations are suppressed in d+Au collisions at sNN=200 GeV, qualitatively consistent with parton saturation models.
Plan partial mapping of AN in xF-pT plane in RHIC run-5
Propose increase in forward calorimetry in STAR to probe low-x gluon densities and establish dynamical origin of AN (complete upgrade by 10/06).
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38. Backups
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39. Towards establishing consistency between FPD (p0)/BRAHMS(h-)
Extrapolate xF dependence at pT=2.5 GeV/c to compare with BRAHMS h- data. Issues to consider:
<h> of BRAHMS data for 2.3<pT<2.9 GeV/c bin. From Fig. 1 of PRL 94 (2005) take <h>=3.07  <xF>=0.27
p-/h- ratio?
Results appear consistent but have insufficient accuracy to establish p+pp-/p0 isospin effects
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40. Systematics
Measurements utilizing independent calorimeters consistent within uncertainties
Systematics:
Normalization uncertainty = 16%:
position uncertainty (dominant)
Energy dependent uncertainty = 13% - 27%:
energy calibration to 1% (dominant)
background/bin migration correction
kinematical constraints
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41. FPD Detector and º reconstruction
robust di-photon reconstructions with FPD in d+Au collisions on deuteron beam side.
average number of photons reconstructed increases by 0.5 compared to p+p data.
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42. d+Au  p0+p0+X, pseudorapidity correlations with forward p0
HIJIING Simulations
increased pT for forward p0 over run-3 results is expected to reduce the background in Df correlation
detection of p0 in interval -1<h<+1 correlated with forward p0 (3<h<4) is expected to probe 0.01<xgluon<0.1  provides a universality test of nuclear gluon distribution determined from DIS
detection of p0 in interval 1<h<4 correlated with forward p0 (3<h<4) is expected to probe 0.001<xgluon<0.01  smallest x range until eRHIC
at d+Au interaction rates achieved at the end of run-3 (Rint~30 kHz), expect 9,700200 (5,600140) p0-p0 coincident events that probe 0.001<xgluon<0.01 for “no shadowing” (“shadowing”) scenarios.
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43. STAR Forward Calorimetry Recent History and Plans
Prototype FPD proposal Dec 2000
Approved March 2001
Run 2 polarized proton data (published spin asymmetry and cross section)
FPD proposal June 2002
Review July 2002
Run 3 data pp dAu (Preliminary An Results)
FMS Proposal: Complete Forward EM Coverage (hep-ex/ ).
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44. Students prepare cells at test Lab at BNL
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