RHIC SPIN: Experimental Issues

1
RHIC SPIN Experimental Issues
Matthias Grosse Perdekamp, UIUC and RBRC

• Physics Goals
• PDFs from hadron collisions?
• A new experimental technique Polarized
• proton-proton collisions at high energies!
• First Results from RHIC
• Upgrades
• Summary

2
Nucleon Structure
Quark and Gluon (parton) Distribution Functions
(well known)
(moderately well known)
(unknown)
(moderately well known)
What is the origin of the Proton Spin?
(unknown)
3
Proton Spin Structure at Hard Scales
Physics Channels Inclusive jets, hadrons,
heavy flavor, direct photons, in STAR and
PHENIX Single lepton asymmetries AL(e,µ) in
W-production in STAR and PHENIX AN in STAR,
PHENIX and BRAHMS back to back correlations, AT
in Collins- and interference fragmentation and
ATT in Drell Yan in STAR and PHENIX.
What is unique at RHIC? o Robust extraction
of spin dep. pdfs from pQCD analysis o Broad
x-range 0.001ltxlt0.3 o Multiple channels good
control of of sys. and theor.
uncertainties ? determine G(x) and ??G(x)dx ! o
direct and theoretically clean flavor
separation of spin dependent pdfs o sufficient
statistical resolution ? sea quark spin vs gluon
spin o high precision measurements of
multiple single and double spin asymmetries
at hard scales aim at a separation of Sivers
and Transversity contributions
Gluon polarization Flavor separation of
quark polarizations Transverse spin struc-
ture of the Nucleon
4
Can Gluon Distributions be Extractedfrom Hadron
Collisions?

1. Lets take a look at G(x,Q2)
2. NLO pQCD vs RHIC data

5
Global QCD Analysis for G(x,Q2) and q(x,Q2)
J. Pumplin et.al JEHP 0207012 (2002)
CTEQ6 use DGLAP Q2-evolution of quark and
gluon distributions to extract q(x,Q2) and
G(x,Q2) from global fit to data sets at different
scales Q2.
2.0
error on G(x,Q2)
/- 10
Quark and Gluon Distributions
1.0
Ratio to CTEQ6
H1 Zeus F2
CTEQ6M
up-quarks
CDF D0 Jets
gluon
0.5
CTEQ5M1
10-410-3 10-2 10-1
0.5 x
2.0
2.0
error for d(x,Q2)
error for u(x,Q2)
down
1.0
1.0
Ratio to CTEQ6
anti-down
Ratio to CTEQ6
/- 5
/- 5
10-410-3 10-2 10-1
0.5 x
0.5
0.5

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G(x,Q2) and q(x,Q2) pQCD beautifully agree
with HERA Tevatron!
J. Pumplin et.al JEHP 0207012 (2002)
ZEUS F2
D0 Jet Cross Section
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and RHIC ? q(x,Q2), G(x,Q2) and D(z,Q2) pQCD
nicely consistent with
experiment!
PHENIX p0 cross section a ?lt0.35
Phys.Rev.Lett.91241803,2003
STAR p0 cross section a 3.4lt?lt4.0
Phys.Rev.Lett.92171801,2004
gluon fragmentation !?
o Good agreement between NLO pQCD
calculations and experiment ? can use a NLO pQCD
analysis to extract spin dependent quark
and gluon distributions from RHIC data!
8
Direct Photons NLO pQCD vs RHIC data

• NLO-pQCD calculation
• Private communication with W.Vogelsang
• CTEQ6M PDF.
• direct photon fragmentation photon
• Set Renormalization scale
• and factorization scale pT/2,pT,2pT

The theory calculation shows good agreement with
our result.
Kensuke Okadas SPIN 2004 talk
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30 years of spin dependent DIS
Field started with polarized electron sources
and targets Yale/SLAC mid 70s SLAC, CERN,
DESY

• J. Ashman et al., Phys.Lett.B206364,1988
• Proton Spin Crisis
• gt 1200 citations on
  SPIRES

Current Experiments on Nucleon Structure (as
reported at DIS 2004)
Helicity difference distribution quarks
?q(x) moderately well known gluons ?G(x)
unknown Helicity flip (transversity)
distribution quarks dq(x) unknown

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A New Experimental Tool for Proton Spin
Structure High Energy Polarized Proton Beams
and Collisions
RHIC pC Polarimeters
Absolute Polarimeter (H jet)
Siberian Snakes
BRAHMS PP2PP
PHOBOS
Spin 2004 M. Bai, H. Huang, V. Ptitsyn, T.
Roser A. Bravar, P. Cameron, D. Sviridia, A.
Zelenski, T. Wise, W. McKay
Siberian Snakes
Spin Flipper
PHENIX
STAR
Run 04 achieved
Spin Rotators
Partial Snake
Helical Partial Snake
Strong Snake
Polarized Source
Pb45 , 55 bunches New working point with long
beam and polarization lifetimes
LINAC
AGS
BOOSTER
Run 05 planned
200 MeV Polarimeter
Time to tune accelerator complex Measure
ALL(jets), ALL(p0) Commission strong
supercon-ducting AGS snake
Rf Dipole
AGS Internal Polarimeter
AGS pC Polarimeter
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An Example High Energy Proton Polarimeters for
p20-250 GeV/c

• High Energy Polarimeter Requirement for RHIC Spin
• Absolute RHIC polarimeter
• Fast relative RHIC and AGS polarimeters for
  monitoring and tuning
• Local Polarimeters to confirm spin orientation
  at collision point

• RHIC polarimetery relies on newly observed spin
  asymmetries
• o Sizeable elastic proton-Carbon spin
  asymmetries at high energies
• ? J. Tojo et al. Phys. Rev. Lett.
  89052302, 2002
• o Very forward neutron asymmetries
• ? A. Bazilevsky et al. AIP Conf.
  Proc. 675 584-588, 2003
• o Spin asymmetries in forward
  multiplicity production as seen by
• beam-beam counters in STAR
• ? J. Kiryluk, AIP Conf. Proc. 675,
  424 (2003)

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Run 04 The Polarized Jet Target for RHIC
Courtesy Sandro Bravar, STAR and Yousef Makdisi,
CAD

• Polarized Hydrogen Gas Jet Target
• thickness of gt 1012 p/cm2
• polarization gt 93 (1 -2)!
• no depolarization from beam wake fields
• Silicon recoil spectrometer to measure
• The left-right asymmetry AN in pp elastic
  scattering in the CNI region to ?AN lt 10-3
  accuracy.
• Transfer this to the beam polarization
• Calibrate the p-Carbon polarimeters
• For 2004 we expect to measure PB to 10

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Recoil protons elastic pp ?pp scattering
Jet profile FWHM 6 mm As designed
Number of elastic pp events
TDC 1 ct 1.2 ns
ADC 1 ct 40 keV
Hor. pos. of Jet 10000 cts. 2.5 mm
CNI peak AN 1 lt E REC lt 2 MeV
? source calibration
prompt events and beam gas

• Data collected in this run
• 100 GeV 700,000 events at the peak of the
  analyzing power ( 3 x 106 total useful pp
  elastic events)
• 24 GeV 120,000 events at the peak of the
  analyzing power ( 5 x 105 total useful pp
  elastic events)

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Local Polarimetry in PHENIX Transverse Neutron
Asymmetry in ZDC
Rotators on--gt radial polarization
Rotators on --gt vertical polarization
Yellow
Blue
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First Results AN
Run 02, ?Ldt 0.2pb-1, P0.15
STAR AN(p0) at 3.4lt?lt4.0 Phys.Rev.Lett.921718
01,2004
PHENIX AN(p0) and AN(p0) at ?lt0.35 C.
Aidala, DIS 2004, to be published

• o Experiments are ready for spin
• measurements at low luminosity
• ? relative luminosity 5x10-4
• ? trigger
• ? polarization analysis
• ? data analysis

o First spin results from RHIC ? AN sizeable
in forward XF ? AN compatible with 0 at ?0
(as expected from pQCD)
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First Results ALL
Run 3 and 4 combined
B.Jager et al., PRD67, 054005 (2003)
Run34

• First results on longitudinal double
• spin asymmetries from RHIC
• ?consistent with DIS sample
• ?result disfavors large ?G
• ?if ?Ldt 3pb-1 and P-0.4 (2005)
• errors will reduce by factor 8
• Experiments are ready for spin
• measurements at low to moderate
• luminosities!
• ? relative luminosity 5x10-4
• ? trigger
• ? polarization analysis
• ? data analysis

?G(x)G(x)
GRSV ?G(x)
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Schedule for RHIC Spin
example STAR 32 week scenario ? all schedules
subject to further advances
in RHIC
operations and/or funding!
L 6x1030cm-2s-1

8x1031cm-2s-1
P 0.45 0.5 0.7
.
vs .. 200 GeV .........
2004 2005 2006
2007 2008 2009 .
pp 51 510 511
0 59 ? 156pb-1
Inclusive hadrons Jets
Transverse Physics
Charm Physics

direct photons

Bottom physics

W-physics
ALL(hadrons, Jets)
ALL(charm)
AL(W)
ALL(?)
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Gluon Polarization at Low LuminosityInclusive
Jets and Hadrons (1pb-1lt ?Ldt lt 30pb-1,
0.4ltPlt0.6)
ALL in inclusive p0 production (PHENIX)
Vogelsang hep-ph/0405069
ALL(p0) ?Ldt3pb-1 P0.4
Input ?G(x)G(x)
GRSV standard ?G(x)
?G(x) -G(x)
?G(x)0
pT GeV/c

• GRSV standard ?G(x)
• Gluon distribution from NLO pQCD fit to DIS data
  on A1, Gluck
• Reya, Stratmann, Vogelsang Phys. Rev.
  D63094005, 2001

Expected in run 05 ?Ldt 5pb-1 P 0.5 All
required instrumentation in STAR and PHENIX is
in place!
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Gluon Polarization at Moderate LuminosityCharm
Production ( ?Ldt gt 30pb-1, Pgt0.6)
from Wei Xie, PHENIX
ALL for single electrons in PHENIX
Silicon Vertex Detector Upgrade!
--- ?Ldt32pb-1 --- ?Ldt320pb-1
GS-A/B/C ?G(xg) parametrization from Gehrmann
and Stirling Phys.Rev. D53 6100-6109,1996
?GA(x)dx 1.8 ?GB(x)dx 1.6 ?GC(x)dx 0.2
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Sensitivity to Gluon Polarization at RHIC
from Les Bland, STAR
GS-A/B/C ?G(xg) parametrization from Gehrmann
and Stirling Phys.Rev. D53 6100-6109,1996
?GA(x)dx 1.8 ?GB(x)dx 1.6 ?GC(x)dx 0.2
xgluon

• PHENIX and STAR are sensitive to ?G through
  several independent channels
• Inclusive photons, inclusive jets, jet-photon,
  J/? production, heavy flavor production

Good control of experimental and theoretical
uncertainties!
21
Sensitivity to Gluon Polarization at RHIC
from F.-H. Heinsius, DIS 2004
RHIC data at hard scale ? pQCD applicable for the
extraction of polarized pdfs.
(I)
HERMES Phys. Rev.Lett.842584- 2588,2000
(II) RHIC spans a broad range of xgluon ?
Determine first moment ??G(x)dx gluon
contribution to the proton spin!
(III)
Assumes data sample of 320pb-1 at vs200 GeV and
800pb-1 at vs500 GeV P0.7. (This is baseline
spin!)
(IV)
Upgrades extending kinematic coverage to low x
decrease error on ??G(x)dx (low x behavior has
been critical in proton spin structure in the
past SLAC E80/E130 vs EMC ? spin crisis)
SMC, B. Adeva et al. hep-ex/0402010
22
W Production in Polarized pp Collisions
Single Spin Asymmetry in the naive Quark Parton
Model
Parity violation of the weak interaction in
combination with control over the proton spin
orientation gives access to the flavor spin
structure in the proton!
Experimental Requirements ? tracking at high
pT ?event selection for muons difficult
due to hadron decays and beam backgrounds.

W
Z
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Can We Connect Observables inclusive AL(lepton)
with quark polarizations?

• Machine and detector requirements
• ?Ldt800pb-1, P0.7 at vs500 GeV
• Upgrades o Muon trigger in PHENIX
• o Forward tracking in STAR

pTmGeV
24
Quark Polarization RHIC vs HERMES
from Naohito Saito, PHENIX

• W-production at RHIC
• No fragmentation ambiguity
• x-range limited
• Semi-inclusive DIS
• Wide x-range
• Limited sensitivity to sea flavors
• Fragmentation functions poorly known at low
  scales (HERMES)

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Transverse Spin at RHIC
(A) Physics Channels for Low Luminosity
STAR, PHENIX and BRAHMS
STAR and PHENIX
(I)
(II)
Boer and Vogelsang (hep-ph/0312320) azimuthal
back to back correlation between hadrons in
opposite hemisphere jets
STAR Phys. Rev. Lett. 92171801, 2004
Clean channel for Sivers effect!
Separation of intrinsic transverse quark spin
(transversity) from trans- verse momentum effects
(Sivers)?
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Transverse Spin at RHIC
Transverse Spin Physics Elsewhere
HERMES, COMPASS and Jefferson Lab
(B) Physics Channels for high L
STAR and PHENIX
Separate transverse quark spin (transversity) and
transverse momentum contributions (Sivers) in
semi- inclusive deep Inelastic scattering
o low scale leads to significant theoretical
ambiguities o Final data set from
HERMES available in mid 2005
J.C. Collins, Nucl. Phys. B396, 161(1993)
J. Collins, S. Heppelmann, G. Ladinsky,
Nucl.Phys. B420 (1994)565
Brahms AN measurements from 2004 and 2005
polarized proton runs! Brief PHENIX and STAR
runs on AN and back-to-back correlations as ?
Ldt/weekgt1pb-1/week (2006?) Brief PHENIX and
STAR runs on AT as ? Ldt/weekgt10pb-1/week
R. Jaffe, X.Jin, J. Tang Phys. Rev. D57 (1999)5920
Statistical sensitivity for AT with 32pb-1
Spin Rotators Give flexibility!
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Upgrades and RHIC Spin

• Upgrades required for core spin program
• flavor separation of spin dependent quark
  distribution
• in W-production
• STAR integrated forward
  tracking
• PHENIX muon trigger
• Upgrades aimed at a precision measurement of
• the first moment ??G(x)dx ? constrain
  orbital angular mometum?
• STAR micro vertex detector
• PHENIX Silicon Vertex Detector,
  nose cone calorimeter

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Measurement of the first moment ??G(x)dx ? DG at
low x ? 0.001
Upgrades extends the range of xG for the prompt-g
measurement down to XG0.001 at Ös 200
GeV Measurement of ??G(x)dx over a wide x
range will be essential in constraining spin sum
1/2?S ?GLz Sensitivity to shape of polarized
gluon distribution over a large x range
(important input in fixing the shape and
extrapolation to low x in global QCD analysis
aimed at extracting ?G)
GS95
prompt photon
Silicon Tracker NCC
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Summary Polarized Proton Collisions
o A new experimental method has been
successfully developed and we are beginning
to exploit a truly novel experimental tool on
proton spin structure. o Fixed target DIS
experiments are carried out at comparably soft
scales and are subject to various theoretical
uncertainties. Leader- ship in the field will
shift from DIS experiments to RHIC spin. o First
physics results are available from exploratory
runs. 2005 promises to be the first spin
physics run at RHIC. o Integrated forward
tracking (STAR) and muon trigger upgrades
(PHENIX) are necessary for W-physics. o
Measurement of gluon spin (first moment)
contribution to the proton spin requires
larger kinematic range ? eg. nose-cone
calorimeter in PHENIX