Title: Transverse Spin and RHIC Probing Transverse Spin in p p Collisions
1Transverse Spin and RHICProbing Transverse Spin
in pp Collisions
- OUTLINE
- Features of RHIC for polarized pp collisions
- Transverse single spin effects in pp
collisions at ?s200 GeV - Towards understanding forward p0 cross sections
- Plans for the future
L.C. Bland Brookhaven National Laboratory Transver
se Polarization in Hard Processes Como 7
September 2005
2Installed 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
- b1m operataion
- spin rotators ? longitudinal polarization
- polarized atomic hydrogen jet target
3RHIC 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?
4- Calendar Summary for RHICRun-5 pp 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
5RHIC Run-5 Performance
Total for run 9.2 pb-1 delivered 3.1 pb-1
smpled
(nb-1)
Delivered
STAR 2005 Longitudinal Goal
Sampled
6PHENIX Detector
- Philosophy
- High rate capability granularity
- Good mass resolution and particle ID
?0 reconstruction and high pT photon
trigger EMCal ?lt0.38, ??? Granularity ?????
0.01?0.01 Minimum Bias trigger and Relative
Luminosity Beam-Beam Counter (BBC)
3.0lt?lt3.9, ??2?
7(No Transcript)
8STAR detector layout
- TPC -1.0 lt ? lt 1.0
- FTPC 2.8 lt ??? lt 3.8
- BBC 2.2 lt ??? lt 5.0
- EEMC1 lt ? lt 2
- BEMC0 lt ? lt 1
- FPD ? 4.0 3.7
9First AN Measurement at STARprototype FPD results
STAR collaboration Phys. Rev. Lett. 92 (2004)
171801
Similar to result from E704 experiment (vs20
GeV, 0.5 lt pT lt 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
vs200 GeV, lt?gt 3.8
10Why Consider Forward Physics at a Collider?
Kinematics
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.
11Simple Kinematic Limits
- Mid-rapidity particle detection
- h1?0 and lth2gt?0
- ? xq ? xg ? xT 2 pT / ?s
- Large-rapidity particle detection
- h1gtgth2
- xq ? xT eh1 ? xF (Feynman x), and
- xg ? xF e-(h1h2)
NLO pQCD (Vogelsang)
1.0 0.8 0.6 0.4 0.2 0.0
qq
fraction
qg
gg
0 10 20 30
pT,p (GeV/c)
? Large rapidity particle production and
correlations involving large rapidity particle
probes low-x parton distributions using valence
quarks
12How can one infer the dynamics of particle
production?Particle production and correlations
near h?0 in pp collisions at ?s 200 GeV
Inclusive p0 cross section
Two particle correlations (h?)
STAR, Phys. Rev. Lett. 90 (2003), nucl-ex/0210033
At vs 200GeV and mid-rapidity, both NLO pQCD
and PYTHIA explains pp data well, down to
pT1GeV/c, consistent with partonic origin
Do they work for forward rapidity?
Phys. Rev. Lett. 91, 241803 (2003) hep-ex/0304038
13Forward p0 production in hadron collider
p0
Ep
p d
qq
EN
qp
p Au
xgp
xqp
qg
EN
(collinear approx.)
- Large rapidity p production (hp4) probes
asymmetric partonic collisions - Mostly high-x valence quark low-x gluon
- 0.3 lt xqlt 0.7
- 0.001lt xg lt 0.1
- ltzgt 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
NLO pQCD Jaeger,Stratmann,Vogels
ang,Kretzer
14xF and pT range of FPD data
15pp?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 lt ? lt 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
NLO pQCD calculations by Vogelsang, et al.
16STAR -FPD Preliminary Cross Sections
Similar to ISR analysis J. Singh, et al Nucl.
Phys. B140 (1978) 189.
17PYTHIA a guide to the physics
Forward Inclusive ?? Cross-Section
Subprocesses involved
qg
gg and qg ? qgg
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
18Single Spin AsymmetryDefinitions
- Definition
- ds?(?) 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
positive AN more p0 going left to polarized beam
19Caveats -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
Pbeam27
Run 3 Preliminary Backward Angle Data. -No
significant Asymmetry seen. (Presented at
Spin 2004 hep-ex/0502040)
20New Physics at high gluon density
- Shadowing. Gluons hidingbehind other gluons.
Modificationof g(x) in nuclei. Modified
distributionsneeded by codes that hope to
calculateenergy 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/0303204.
21? Dependence of RdAu
G. Rakness (Penn State/BNL), XXXXth Rencontres
de Moriond - QCD, March 12 - 19, 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.
22Constraining the x-values probed in hadronic
scattering
Guzey, Strikman, and Vogelsang, Phys. Lett. B
603, 173 (2004).
Log10(xGluon)
- Collinear partons
- x pT/?s (eh1 eh2)
- x? pT/?s (e?h1 e?h2)
- FPD ? ? 4.0
- TPC and Barrel EMC ? lt 1.0
- Endcap EMC 1.0 lt ? lt 2.0
- FTPC 2.8 lt ??? lt 3.8
CONCLUSION Measure two particles in the final
state to constrain the x-values probed
23Back-to-back Azimuthal Correlationswith large ??
Fit ???????????LCP normalized distributions and
with Gaussianconstant
Beam View
Top View
Trigger by forward ??
??
Coicidence Probability 1/radian
- Midrapidity h? tracks in TPC
- -0.75 lt ??lt 0.75
- Leading Charged Particle(LCP)
- pT gt 0.5 GeV/c
???????????LCP
S Probability of correlated event under
Gaussian B Probability of un-correlated event
under constant ?s Width of Gaussian
24- PYTHIA (with detector effects) predicts
- S grows with ltxFgt and ltpT,?gt
- ?s decrease with ltxFgt and ltpT,?gt
- PYTHIA prediction agrees with pp data
- Larger intrinsic kT required to fit data
25ltE?lt35GeV
45ltE?lt55GeV
Statistical errors only
25Plans for the Future
26STAR Forward Meson Spectrometer
- NSF Major Research Initiative (MRI) Proposal
- submitted January 2005
- hep-ex/0502040
27STAR detector layout with FMS
- TPC -1.0 lt ? lt 1.0
- FTPC 2.8 lt ??? lt 3.8
- BBC 2.2 lt ??? lt 5.0
- EEMC1 lt ? lt 2
- BEMC-1 lt ? lt 1
- FPD ? 4.0 3.7
28Three Highlighted Objectives In FMS
Proposal(not exclusive)
- A d(p)Au?p0p0X measurement of the parton model
gluon density distributions xg(x) in gold nuclei
for 0.001lt x lt0.1. For 0.01ltxlt0.1, 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)
29Frankfurt, 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 (-1lthlt4) 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.
Pythia Simulation
30Disentangling Dynamics of Single Spin
AsymmetriesSpin-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
31New 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
32FPD Physics for Run6
We intend to stage a large version of the FPD to
prove our ability to detect direct photons.
33How do we detect direct photons?
- Isolate photons by having sensitivity to partner
in decay of known particles - p0??? M0.135 GeV BR98.8
- K0 ? p0p0 ??? ?? 0.497 31
- ?? ?? 0.547
39 - ?? p0 ? ??? ? 0.782
8.9 - Detailed simulations underway
34Where do decay partners go?
m p0(h) di-photon parameters zgg
E1-E2/(E1E2) fgg opening angle Mm 0.135
GeV/c2 (p0) Mm0.548 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).
35Sample decays on FPD
With FPD module size and electronic dynamic
range, have gt95 probability of detecting second
photon from p0 decay.
36Timeline 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
- s200 GeV with present detectors for gluon
polarization (?g) at higher x transverse
asymmetries - ?s500 GeV with detector upgrades for ?g at lower
x W production
37Summary / Outlook
- Large transverse single spin asymmetries are
observed for large rapidity p0 production for
polarized pp collisions at ?s 200 GeV - AN grows with increasing xF for xFgt0.35
- AN is zero for negative xF
- Large rapidity p0 cross sections for pp
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 dAu collisions at
?sNN200 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).
38Backups
39Towards establishing consistency between FPD
(p0)/BRAHMS(h-)
- Extrapolate xF dependence at pT2.5 GeV/c to
compare with BRAHMS h- data. Issues to consider - lthgt of BRAHMS data for 2.3ltpTlt2.9 GeV/c bin.
From Fig. 1 of PRL 94 (2005) 032301 take lthgt3.07
? ltxFgt0.27 - p-/h- ratio?
- Results appear consistent but have insufficient
accuracy to establish pp?p-/p0 isospin effects
40Systematics
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
41FPD Detector and ?º reconstruction
- robust di-photon reconstructions with FPD in
dAu collisions on deuteron beam side. - average number of photons reconstructed
increases by 0.5 compared to pp data.
42dAu ? p0p0X, 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 Df
correlation - detection of p0 in interval -1lthlt1 correlated
with forward p0 (3lthlt4) is expected to probe
0.01ltxgluonlt0.1 ? provides a universality test of
nuclear gluon distribution determined from DIS - detection of p0 in interval 1lthlt4 correlated
with forward p0 (3lthlt4) is expected to probe
0.001ltxgluonlt0.01 ? smallest x range until eRHIC - at dAu interaction rates achieved at the end of
run-3 (Rint30 kHz), expect 9,700?200 (5,600?140)
p0-p0 coincident events that probe
0.001ltxgluonlt0.01 for no shadowing
(shadowing) scenarios.
43STAR 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).
44Students prepare cells at test Lab at BNL