Transcript Slide 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
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
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• b*=1m operataion
• spin rotators  longitudinal polarization
• polarized atomic hydrogen jet target
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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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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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RHIC Run-5 Performance
14000
Sum Integrated Luminosity
12000
Total for run
10000
(nb-1)
8000
~ 9.2 pb-1 delivered
6000
~ 3.1 pb-1 smpled
4000
6/21/2005
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PHENIX Detector
Philosophy:
 High rate capability & granularity
 Good mass resolution and particle ID
p0 reconstruction and
high pT photon trigger:
EMCal: ||<0.38, =p
Granularity  = 0.010.01
Minimum Bias trigger and
Relative Luminosity:
Beam-Beam Counter (BBC):
3.0<||<3.9, =2p
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STAR detector layout
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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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First AN Measurement at STAR
prototype FPD results
STAR collaboration
Phys. Rev. Lett. 92 (2004) 171801
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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Why Consider Forward Physics at a Collider?
Deep inelastic scattering
Kinematics
Hard scattering hadroproduction
Can Bjorken x values be selected in hard scattering?
Assume:
1. Initial partons are collinear
2. Partonic interaction is elastic


pT,1  pT,2
Studying pseudorapidity, =-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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Simple Kinematic Limits
NLO pQCD (Vogelsang)
Mid-rapidity particle detection:
1.0
p+p  p0+X, s = 200 GeV, =0
10 and <2>0
 xq  xg  xT = 2 pT / s
fraction
0.8
Large-rapidity particle detection:
qq
0.6
qg
0.4
0.2
gg
0.0
1>>2
0
 xq  xT e1  xF (Feynman x), and
10
20
30
pT,p (GeV/c)
xg  xF e-(1+2)
 Large rapidity particle production and correlations involving large
rapidity particle probes low-x parton distributions using valence quarks
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How can one infer the dynamics of particle production?
Particle production and correlations near 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/0210033
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
Phys. Rev. Lett. 91, 241803 (2003)
hep-ex/0304038
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Do they work for
forward rapidity?
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Forward p0 production in hadron collider
p0
Ep
p
E
d N
qq
xqp
qp
xgp
EN
qg
2E p
s
s  2E N
E
q
z p
  -ln(t an( ))
Eq
2
p -
xq  xF / z
xg  T e g
(collinear approx.) s
Q 2 ~ pT2
p
Au
xF 
• Large rapidity p production (p~4) probes asymmetric partonic collisions

p + p  p 0,p 3.8, s  200GeV
• Mostly high-x valence quark + low-x gluon
• 0.3 < xq< 0.7
<z>

• 0.001< xg < 0.1
<xq> NLO pQCD
Jaeger,Stratmann,Vogelsang,Kretzer
• <z> nearly constant and high 0.7 ~ 0.8
<xg>
• Large-x quark polarization is known to be large from DIS
• Directly couple to gluons = A probe of low x gluons
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STAR
xF and pT range of FPD data
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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 12 - 19, 2005
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NLO pQCD calculations by Vogelsang, et al.
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STAR -FPD
Preliminary
Cross Sections
Similar to ISR analysis
J. Singh, et al Nucl. Phys.
B140 (1978) 189.
d 3
N
-B
E 3  (1 - xF ) pT
dp
N 5
B6
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PYTHIA: a guide to the physics
Forward Inclusive p0 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 p0 cross section at 3-4
• Dominant sources of large xF p0 production from:
●
q + g  q + g (22)  p0 + X
●
q + g  q + g + g (23)  p0 + X
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q
p0
g
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p0
g
g
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Single Spin Asymmetry
Definitions
• Definition:
d  - d 
AN 
d  + d 
• dσ↑(↓) – differential cross
section of p0 then incoming
proton has spin up(down)
Left
π0, xF<0
π0, xF>0
p
Two measurements:
• Single arm calorimeter:
1  N  - RN  
L

AN 
  
R 
 
PBeam  N + RN 
L
R – relative luminosity (by BBC)
Pbeam – beam polarization
• Two arms (left-right) calorimeter:




1  N L  N R - N R  N L 
AN 

PBeam  N   N  + N   N  
L
R
R
L 
p

No relative luminosity needed
Right
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positive AN: more p0 going
left to polarized beam
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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/0502040)
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New Physics at high gluon density
1. 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.
2. Saturation Physics. New phenomena
associated with large gluon density.
• Coherent gluon contributions.
• Macroscopic gluon fields.
• Higher twist effects.
• “Color Glass Condensate”
Figure 3 Diagram showing the boundary
between possible “phase” regions in the
t=ln(1/x) vs ln Q2 plane
Edmond Iancu and Raju Venugopalan, review for Quark Gluon Plasma 3,
.
R.C. Hwa and X.-N. Wang (eds.), World Scientific, 2003 [hep-ph/0303204].
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 Dependence of RdAu
Ed 3
 inelastic
dp 3 dAu
1  dAu
pp
RdAu 

inelastic
2  197  pp
N binary  dAu
Ed 3 3
dp pp
y=0
As y grows
G. Rakness (Penn1 State/BNL),
 dAu
RdAu 
XXXXth Rencontres
2 197de
 ppMoriond - QCD,
March 12 - 19, 2005
Kharzeev, Kovchegov, and Tuchin,
Phys. Rev. D 68 , 094013 (2003)
See also J. Jalilian-Marian,
Nucl. Phys. A739, 319 (2004)
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)]
• From
• Observe significant rapidity dependence similar to expectations from a “toy
model” of RpA within the Color Glass Condensate framework.
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Constraining the x-values probed in hadronic scattering
Guzey, Strikman, and Vogelsang,
Phys. Lett. B 603, 173 (2004).
Log10(xGluon)
For 22 processes
TPC
FTPC
FPD
FTPC
Barrel EMC
FPD
Log10(xGluon)
Collinear partons:
+
+1 + e+2)
● x = p /s (e
T
-1 + e-2)
● x = p /s (e
T
Gluon
• FPD: ||  4.0
CONCLUSION: Measure two
particles in the final state to constrain
the x-values probed
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• TPC and Barrel EMC: || < 1.0
• Endcap EMC: 1.0 <  < 2.0
• FTPC: 2.8 <  < 3.8
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Back-to-back Azimuthal Correlations
with large 
Top View
Trigger by
] forward p0

• Ep > 25 GeV
• p  4
]
Midrapidity h tracks in TPC
• -0.75 < < +0.75
Leading Charged Particle(LCP)
Fit p-LCP normalized
distributions and with
Gaussian+constant
Coicidence Probability
[1/radian]
Beam View
p-LCP
• pT > 0.5 GeV/c
S = Probability of “correlated” event under Gaussian
B = Probability of “un-correlated” event under constant
s = Width of Gaussian
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STAR
PYTHIA (with detector
effects) predicts
• “S” grows with <xF>
and <pT,p>
• “s” decrease with
<xF> and <pT,p>
25<Ep<35GeV
PYTHIA
prediction agrees
with p+p data
Larger intrinsic kT
required to fit data
45<Ep<55GeV
Statistical errors only
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Plans for the Future
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STAR Forward Meson Spectrometer
NSF Major Research Initiative (MRI) Proposal
-submitted January 2005
[hep-ex/0502040]
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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:
~ 4.04.0
& ~3.7
FMS: ||
2.5<<
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Three Highlighted Objectives In FMS Proposal
(not exclusive)
1.
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.
2.
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)
3.
Measurements with transversely polarized
protons that are expected to resolve the origin of
the large transverse spin asymmetries in
reactions for forward p0 production.
(polarized pp)
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Frankfurt, Guzey and Strikman,
J. Phys. G27 (2001) R23 [hep-ph/0010248].
• 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 p0 
reduce 23 (inelastic) parton process contributions
thereby reducing uncorrelated background in 
correlation.
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Pythia Simulation
Disentangling Dynamics of Single Spin
Asymmetries
Spin-dependent particle correlations
Collins/Hepplemann mechanism
requires transversity and spindependent 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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New FMS Calorimeter
Lead Glass From FNAL E831
804 cells of 5.8cm5.8cm60cm
Schott F2 lead glass
7/7/2015
Loaded On a Rental Truck for Trip To BNL
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FPD++ Physics for Run6
We intend to stage a
large version of the FPD
to prove our ability to
detect direct photons.
Run-5
FPD
Run-6
FPD++
Run-7
FMS
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How do we detect direct
photons?
Isolate photons by having sensitivity to partner in decay of known particles:
π0gg
M=0.135 GeV BR=98.8%
K0  π0π0 gg gg 0.497
31%
 gg
0.547
39%
 π0 g gg g
0.782
8.9%
Detailed simulations underway
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Where do decay partners go?
m = p0() di-photon parameters
zgg = |E1-E2|/(E1+E2)
gg = opening angle
Mm = 0.135 GeV/c2 (p0)
Mm=0.548 GeV/c2 ()
for candidatephoton with E1  Eg ,
1 - zgg
E2 
Eg , gives energyof secondphoton
1 + zgg
ggmax M m c 2 1 + zgg
sin

, gives maximumopeningangle with probability  zgg
2
2 Eg 1 - zgg
ggmin M m c 2
1
sin


, gives minimumopeningangle in termsof Lorentzfactorfor meson
2
E1 + E2 g m
• 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  ranges).
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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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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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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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Backups
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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:
• <> of BRAHMS data for 2.3<pT<2.9 GeV/c
bin. From Fig. 1 of PRL 94 (2005) 032301
take <>=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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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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FPD Detector and pº 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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d+Au  p0+p0+X, pseudorapidity correlations with forward p0
HIJIING 1.381 Simulations
• increased pT for forward p0 over run-3 results is
expected to reduce the background in  correlation
• detection of p0 in interval -1<<+1 correlated with
forward p0 (3<<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<<4 correlated with
forward p0 (3<<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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STAR Forward Calorimetry
Recent History and Plans
•
Prototype FPD proposal Dec 2000
–
–
•
Approved March 2001
Run 2 polarized proton data (published
2004 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/0502040).
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Students prepare cells at test Lab at BNL
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