Columbia UniversityChristine Aidala
September 2005
Transverse Spin at
Results and Prospects
Transversity 2005, Como
C. Aidala, Transversity 2005, September 2005
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RHIC’s Experiments
Transverse spin only (No rotators)
Longitudinal or transverse spin
Longitudinal or transverse spin
Also pp2pp, pC, and polarized H jet polarimeters studying polarized elastic
scattering
C. Aidala, Transversity 2005, September 2005
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AGSLINACBOOSTER
Polarized Source
Spin Rotators
200 MeV Polarimeter
AGS Internal Polarimeter
Rf Dipole
RHIC pC Polarimeters Absolute Polarimeter (H jet)
PHENIX
PHOBOS BRAHMS & PP2PP
STAR
AGS pC Polarimeter
Partial Snake
Siberian Snakes
Siberian Snakes
Helical Partial SnakeStrong Snake
Spin Flipper
RHIC as a Polarized p-p Collider
Various equipment to maintain and measure beam polarization through acceleration and storage
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The PHENIX Collaboration 13 Countries; 62 Institutions; 550 Participants as of 3/05
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The PHENIX Detector2 central spectrometers- Track charged particles and detect electromagnetic processes
2 forward spectrometers- Identify and track muons
2 global detectors- Determine when there’s a collision
Philosophy: High rate capability & granularity Good mass resolution and particle ID Sacrifice acceptance
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PHENIX Detector (cont.) Central arms
Photons, electrons, identified charged hadrons
|| < 0.35 = 180 degrees
Forward muon armsTrack and identify muons
1.2 < || < 2.4
Beam-beam counters Charged particles
3.0 < || < 3.9
Zero-degree calorimetersNeutrons
4.7 < || < 5.6
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Spin Running at PHENIX So Far
• 2001-2– Transversely polarized p+p
collisions– Average polarization of ~15%– Integrated luminosity 150 nb-1
– Figure of merit (P2L) 3.38 nb-1
• 2003– Longitudinally polarized p+p
collisions achieved– Average polarization of ~27%– Integrated luminosity 220 nb-1
– Figure of merit (P4L) 1.17 nb-1
• 2004– 5 weeks commissioning, 4 days
data-taking– Average polarization ~40%– Integrated luminosity 75 nb-1
– Figure of merit (P4L) 1.92 nb-1
• 2005– Average polarization ~48%– Integrated longitudinal lumi
3.59 pb-1
– Figure of merit (P4L) ~1.9 pb-1
– Integ. transverse lumi 0.163 pb-1
– Figure of merit (P2L) 0.038 pb-1
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ATT
Proton Spin Structure at PHENIX
Prompt Photon LLA (gq X)
Transverse Spinu u d d , , ,
u u d d
Flavor decomposition
L lA (u d W ) T
,
A p p ( , ) X
I nterference fragmentation:
NSingle Asymmetries A
GGluon Polarization
Production LLA (gg,gq X) W Production
L lA (u d W )
Heavy Flavors LLA (gg cc,bb X)
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Current Context for Transverse Measurements at PHENIX
• STAR and BRAHMS measurements at 200 GeV– Non-zero asymmetries for forward pions
• Coverage: STAR xF > 0.2, BRAHMS xF > 0.15
– Potential contributions from multiple mechanisms
– AN consistent with zero for backward pions and forward protons
• HERMES and COMPASS Sivers and Collins results• BELLE measurement of non-zero Collins FF for pions
– Input for further interpretation of observed and future asymmetries!
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AN
xF*100
Transverse single-spin asymmetries for +, -, and proton production at BRAHMS
Preliminary
xF < 0
Raw asym
PreliminaryRaw asym
pT (GeV/c)
protons
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AN of Mid-rapidity Neutral Pions and Charged Hadrons: Final Results
hep-ex/0507073Submitted to PRL
|| < 0.35
AN for both charged hadrons and neutral pions at mid-rapidity consistent with zero to within a few percent.
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• NLO pQCD consistent with data within theoretical uncertainties.
• PDF: CTEQ5M
• Fragmentation functions:• Kniehl-Kramer-Potter (KKP)Kniehl-Kramer-Potter (KKP)
• Kretzer
• Spectrum constrains D(gluon ) fragmentation function
• Factorization applicable, with small scale dependence
hep-ex/0507073
|| < 0.35
Mid-rapidity Cross Section Measurements
9.6% normalization error not shown
PRL 91, 241803 (2003)
|| < 0.35
0
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Mid-rapidity Partonic Processes
• Particle production at mid-rapidity at these transverse momentum values mostly from gluon scattering– AN results should constrain
gluon Sivers (U. d’Alesio’s discussion)
• Future measurements reaching higher pT dominated by quark scattering, thus more sensitive to transversity + Collins
0
Fraction
's producedLarge asymmetries observed due to
valence quarks?
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Other (So Far Unpolarized) Mid-rapidity Measurements
Direct ’s
(Published for pT < 7 GeV/cas Phys. Rev.
D71:071102, 2005)
PHENIX Preliminary
— Fit to data
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Mid-rapidity Cross Sections (cont.)
Non-photonic electrons
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Forward-Backward Neutrons and Charged Particles
• Zero-degree calorimeters (ZDC)– Hadronic calorimeters– Neutrons, 4.7 < || < 5.6
• Beam-beam counters (BBC)– Quartz Cherenkov detectors– Charged particles, 3.0 < || < 3.9
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Forward neutrons (ZDC) at 200 and 410 GeV: AN ~ -11%
Backward neutrons (ZDC): AN consistent with zero
Neutron Asymmetry vs.
(Raw
Asy
mm
etry
) / (
bea
m
pol
.)
Vertical polarization
Radial polarization
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• Inclusive forward charged particles (BBC): AN consistent with zero
• Forward charged (BBC) in forward-neutron-tagged (ZDC) events:
• Backward charged (BBC) in forward-neutron-tagged (ZDC) events: 210)10.055.028.2(
210)22.050.050.4(
Forward-Backward Neutrons and Charged Particles (cont.)
p
N*(*) n+X
Y
Diffractive-like process?
AN(X) < 0, AN(Y) > 0
p
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Upcoming Transverse Spin Measurements at PHENIX
• 2005 data– Similar transverse statistics to 2001-02, but ~3x
higher polarization
– Improved mid-rapidity measurements of 0, h+/- AN
– More detailed study of forward and backward neutrons at 200 and 410 GeV
– Forward and backward stopped hadrons (mostly pi and K)
– AN of forward and backward muons
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2005 Expected Muon Measurements
• Single inclusive muons from 2005 data– Mostly pion and kaon decays
– pT 0.5-5.0 GeV/c
– xF 0.02-0.11 GeV/c• More data in the future will allow access to higher xF
– 1.2 < || < 2.4– Eventually separate into prompt muons (heavy flavor)
and muons from light meson decays• Decay muons have enhanced K/ ratio, K/ ~ 1
C. Aidala, Transversity 2005, September 2005
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Upcoming Transverse Spin Measurements at PHENIX (cont.)
• 2006 or 2007: Expect long spin run at RHIC– PHENIX anticipates 5-20(?) pb-1 transverse data, 60-70% polarization
• Depends on machine performance • 2006 Beam-Use Proposal under development this month
• studies• AN of mid-rapidity single electrons—open charm• Forward-backward single muon studies to higher xF
• Forward-backward J/ AN (note forward cross section already published)
• ATT measurements possible (but not yet for DY)
• Back-to-back jets to probe Sivers– Because of PHENIX central arm acceptance, better to run with radial than
vertical polarization
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Jet Asymmetry Due to Sivers
• Non-zero Sivers function implies spin-dependence in kT distributions of partons within proton
• Would lead to an asymmetry in of back-to-back jets
• Trigger doesn’t have to be a jet or leading particle, but does have to be a good jet proxy– Studies being done for high-pT photon + away-
side charged hadron
0
2
h
Boer and Vogelsang, Phys.Rev.D69:094025,2004
anti-alignedaligned
Run03 -charged dn/d
(Schematic)
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Di-Hadrons vs. Di-Jets
updownunpolarized
away side parton AN
di-hadrondi-jet
• Don’t reconstruct jets fully—use di-hadron correlations to measure jet . • Smears out di-hadron AN relative to the di-jet AN, with smearing function g (assumed here to be a gaussian, with jT=0.35).
'))('()'())()((
'))('()'()())()(()(
dxdxxxxgxNxN
dxdxxxxgxAxNxNA
dijetdijet
dijetNdijetdijetdihad
N
Broadens and slightly lowers asymmetry, but still measurable
C. Aidala, Transversity 2005, September 2005
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PHENIX Detector Upgrades(longitudinal)
Also: silicon endcaps covering muon arm acceptance (1.2 < || < 2.4) - forward-backward charm and B physics hadron-blind detector for 2 electron coverage at mid-rapidity - open charm, electronic decays of J/, , . . .
Transverse spin possibilities with planned upgrades not yet fully explored!
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Summary• Final 2002 PHENIX results for mid-rapidity 0
and charged hadron asymmetries now available (hep-ex/0507073)– consistent with zero within a few percent
• PHENIX forward neutron asymmetry of -11% observed at 200 and 400 GeV– Backward neutron asymmetry consistent with zero
• Significant non-zero results for forward and backward charged particles in events with a forward neutron
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Summary (cont.)• Muon arm results expected from 2005 data• Di-jet Sivers measurement expected 2006 or 2007• Forward upgrades will improve access to kinematic
region where large asymmetries have been observed • Mid-rapidity upgrades will improve jet measurements
• Present RHIC results at forward, backward, and mid-rapidity suggest large SSA’s a valence quark effect?– Significance of BRAHMS zero proton asymmetries?
• Some overlapping, some complementary coverage and capabilities of PHENIX with other experiments should allow upcoming measurements to gradually put together a cohesive picture of proton transverse spin structure
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Extra Slides
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Single Transverse Collision
Hard Scattering Process
2 2x P
1 1x P
s
qgqg
)(0
zDq
X
q(x1)
g(x2)
1P
2P
left
right
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Unpolarized Results from Run03 p+p
anti-alignedaligned
•Asymmetry
•numerator is difference between aligned and anti-aligned dist’s, where aligned means trigger jet and spin in same direction•denominator is simply unpolarized distribution
•On left are some theoretical guesses on expected magnitude of AN from Siver’s•On right are gamma-charged hadron dist’s from Run03 p+p
•2.25 GeV gamma’s as jet trigger, 0.6-4.0 GeV charged hadrons to map out jet shape•Dotted lines are schematic effect on away side dist due to Siver’s Fn (not to scale)
NA
Run03 -charged dn/dBoer and Vogelsang, PRD69:094025,2004
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Obtaining the (Spin-Dependent) 0 Yields• 18M events used • Central spectrometer
arms || < 0.35– 0 via 0 – Electromagnetic
calorimeter (EMCal)• Lead scintillator calorimeter
(PbSc)
• Lead glass calorimeter (PbGl)
0 width ~10-15 MeV/c2
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EMCal-RICH Trigger• 2x2 tower non-overlapping energy sum
• Threshold ~ 0.8 GeV
• Also used in conjunction with RICH to form an electron trigger
2x2 Trigger in 2001-2002 run.
Min. Bias range
~14 GeV/c
0 trigger efficiency
0 5 10PT (GeV/c)
0.78 0.03+_
Min. Bias range
~14 GeV/c
0 trigger efficiency
0 5 10PT (GeV/c)
0.78 0.03+_
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Handling Background in the 0 Asymmetry
Invariant mass (GeV/c2)
- 50-MeV/c2 windows around the 0 peak (60-110 and 170-220 MeV/c2)- 250-450 MeV/c2 (between 0 and )
• Eliminate as much background as possible using EMCal cluster shower shape cut and charged veto• Calculate asymmetry of (signal + background) in the 0 mass window• Calculate the asymmetry of two different background regions as an estimate of the asymmetry of the background under the peak• Subtract the asymmetries
r
rAAA
bkgN
bkgN
N
1
0
0
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Obtaining Charged Hadron Yields
• 13M events used• Event vertex from
BBC’s• Track reconstruction
from – vertex
– drift chamber
– pad chambers
BBC
PC1 PC1
PC3PC3
DCDC
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Background in h+/h- Sample• Note that tracking detectors in
PHENIX are outside the magnetic field
• Assume track originates at event vertex, then measure momentum based on deflection angle observed at drift chamber
• Low-momentum tracks that don’t originate from the vertex may be misreconstructed with higher momentum – Conversion electrons– Decay products from long-lived
particles (K+-, K0L)
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Background in h+/h- Sample (cont.)
• RICH veto to eliminate electrons– Electron threshold 0.017 GeV/c– Pion threshold 4.7 GeV/c– < 1% electron contamination in final sample
• Estimate decay background from long-lived particles from tracks with reconstructed pT > 9 GeV/c but that didn’t produce a hit in the RICH– < 5% in final sample
C. Aidala, Transversity 2005, September 2005
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AN of Neutral Pions and Charged Hadrons: Systematic Checks
• Independent results from two polarized beams
• Independent results from two detector arms (luminosity formula)
• Comparison of square-root and luminosity formulas
• Fill-by-fill stability of asymmetry
• Effects of background on 0 asymmetry– Integrate over different ranges of photon-pair invariant
mass
– Measure and subtract asymmetry of two different background invariant-mass regions
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Forward Neutron Asymmetry at RHIC
• Large and negative (-11%)
• Observed at 200 and 410 GeV
• ~Zero for backward neutrons
• Why large asymmetry for forward neutrons but not forward protons?? (But admittedly not same kinematics)
AN = 0.110±0.015
preliminary
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BBC Asymmetry• Forward neutron, forward BBC, left-right
- 9!• Forward neutron, backward BBC, left-right
- No significant asymmetry in backward ZDC
tagged data or in top-bottom asymmetry. Systematic error doesn’t include AN
CNI error.
210)22.050.050.4(
210)10.055.028.2(
K.Tanida
p
N*(*) n+X
Y
• Diffractive-like process
AN(X) < 0, AN(Y) > 0
pp
n
X
p
• kick-out/recoil picture
AN(X) > 0, AN(Y)??
C. Aidala, Transversity 2005, September 2005
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Converter subtraction methodWe defined as • P : the yield of the photonic component• N : the yield of the non-photonic component• A : All electron yield in the non-converter data set• C : All electron yield in the converter data set• Rsim : the ratio of the photonic electron in converter to non-converter data set
• The following relation holds between those variables C = Rsim * P + N A = P + N
• Therefore P and N can be determined as P = ( C – A ) / ( Rsim – 1) N = ( Rsim * A – C ) / ( Rsim – 1)
** All parameter have pt dependence.