Longitudinal Spin Program: Results and Plans
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Longitudinal Spin Program: Results and Plans
A.BazilevskyBrookhaven National Laboratory
For the PHENIX Collaboration
SPIN-Dubna-2011, Sep 20-24
Gluon helicity distribution G from ALL
(Anti-)quark helicity distribution from AL of W
+ STAR
For RHIC-Spin Collaboration
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From DIS to pp: pp(semi)DIS
Probes G:
Q2 dependence of quark PDFs
Photon-gluon fusion
(Anti-)quark flavor separation:
Through fragmentation processes
Probes G:
Directly from gg and qg scattering
(Anti-)quark flavor separation:
Through and Wdu Wdu
Complimentary approaches2
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RHIC as polarized proton collider
BRAHMS & now ANDY
STAR
PHENIX
AGS
LINACBOOSTER
Pol. Proton Source500 mA, 300 ms
GeVs
L
50050
onPolarizati%70
cms102 2132max
Spin Rotators
Partial Siberian Snake
Siberian Snakes
200 MeV Polarimeter AGS Internal PolarimeterRf Dipoles
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
2 1011 Pol. Protons / Bunche = 20 p mm mrad
Year s [GeV]L [pb-1]
(recorded) Pol. [%]
2003 200 0.35 / 0.3 27
2004 200 0.12 / 0.3 40
2005 200 3.4 / 3.1 49
2006 200 7.5 / 8.5 57
2006 62.4 0.08 / - 48
2009 200 16 / 25 57
2009 500 14 / 12 39
2011 500 ~17 / ~12 ~52
Longitudinal Spin Running in PHENIX/STAR
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Measuring Asymmetries in a Collider
L
LR
RNN
RNN
PPdd
ddALL ;
||
1
21
(N) Yield 0, , ±, h±, , e, etc.
(R) Relative Luminosity
(P) Polarization RHIC Polarimeters (at 12 o’clock) Local Polarimeters (in experiments)
Bunch spin configuration alternates every 106 ns, at RHIC Data for all bunch spin configurations are collected at the same time
Possibility for false asymmetries are greatly reduced4
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PHENIX and STAR
STAR
STAR:Large acceptance with azimuthal symmetryGood tracking and PIDCentral and forward calorimetryUpgrades to higher rate capabilities, inner and forward tracking
PHENIX:High rate capabilityHigh granularityGood mass resolution and PIDLimited acceptanceUpgrades to wider acceptance, forward capabilities, inner tracking
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Local PolarimetryZero Degree Calorimeter:
<2.5 mrad Utilizes spin dependence of very forward neutron production discovered in RHIC Run-2002 (PLB650, 325)
neutronchargedparticles
Before Run11, STAR also used BBCs (3.3<|h|< 5.0) utilizing spin dependence of hadron production at high xF
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Local Polarimeter
Vertical f ~ ±p/2Radial f ~ 0Longitudinal no asymmetry
Measures transverse polarization PT , Separately PX and PY
Longitudinal component:P – from CNI polarimeters
22TL PPP
Vertical
Radial
Longitudinal
-/2 0 /2
Asymmetry vs
Longitudinal spin runs: 99.0PPL 7
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Relative Luminosity (PHENIX) Two arrays of 64 elements, each a
quartz Cherenkov radiator with PMT Δη = ±(3.1 to 3.9), Δφ = 2π
144 cm
Beam-Beam Counters (BBC)
Cross checked with ZDC:
<2.5 mrad (>6)
Different physics signal, different kinematic region
ALL of BBC relative to ZDC is ~0
Results:
R ~ (25)10-4 ALL ~ (37)10-4 (for P~0.6)
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GPolarized Gluon Distribution Measurements :
Use a variety of probes with variety of kinematicsAccess to different gluon momentum fraction xDifferent systematics
Use different beam energies Access to different gluon momentum fraction x
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Unpol. Cross Section and pQCD in pp
PHENIX pp 0 XPRD76, 051106
Good agreement between NLO pQCD calculations and data pQCD can be used to extract spin dependent pdf’s from RHIC data.
PHENIX pp XPRL 98, 012002
s=200 GeVSTAR: ppjet XPRL 97, 252001
||<0.35||<0.35
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Probing G in pol. pp collisionspp hX
hf
fXff
baba
hf
fXffLL
fXff
baba
LL Ddff
Dadff
dd
ddA
ba
baba
ˆ
ˆˆ
,
,
Double longitudinal spin asymmetry ALL is sensitive to G
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ALL: jets
STAR Preliminary Run6 (s=200 GeV)10 20 pT(GeV)
Good discriminative power between calculations with different assumption for G
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0 ALL
PHENIX Run5+6: PRL103, 012003
0 pT wBG 2 GeV/c 20%5 8%10 5%
pT(GeV)5 10
The most abundant probe in PHENIX(triggering + identification capability)
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From ALL(pT) to G
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2(G)
binsp stat
theoryLL
dataLL
T
AA2
2
2
)3(2.0and)1(1.02.04:errorStat. 2.08.0
22]3.0,02.0[
GeVG xGRSV
1.0:error.expSyst.
Compare ALL(pT) data with calculated ALL(pT) for a variety of 1
0)( dxxgG
From pQCD:
pT = 212 GeV/c
xgluon = 0.02 0.3
Only weakly model dependent
PRL103, 012003 (2009)
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G: Global FitDSSV:Daniel de FlorianRodolfo SassotMarco StratmannWerner Vogelsang
• Phys. Rev. Lett. 101, 072001(2008)• First truly global analysis of all available polarized data including
RHIC results
Uncertainty estimation:2=1 (optimistic)
2/2=2% (conservative)
… Truth is in between2/2=2%
A node?...
RHIC data
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+ Run9 0 ALL : PHENIX Preliminary
Run5Run6Run9
Dataset <PB> (%) <PY> (%) Lanalyzed (pb-1) FOM (P4L)
Run5 50 49 2.5 0.15
Run6 56 57 6.5 0.66
Run9 57 57 14 1.5
Tendency to positive G? 16
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Global Fit for +PHENIX Run9 0 ALL By S.Taneja et al (DIS2011)
ala DSSV with slightly different uncertainty evaluation approach
DSSV DSSV + PHENIX Run9 0 ALL
No node …Uncertainties decreased
A node at x~0.1 ? 17
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+ Run9 0 ALL : STAR Preliminary
Run9:
3-4 smaller stat. uncertainties than in Run6: Trigger upgrade
(improved eff.)
DAQ upgrade (increased rate, lower ET threshold)
Run9 data will definitely have considerable impact on G global fit and its uncertainty
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Other probes
±• Preferred fragmentation
u+ and d- ; u>0 and d<0 different
qg contributions for +, 0, -
access sign of G
• Analysis similar to 0
• Different flavor structure• Independent probe of G
PRD83,032001(2011)
PHENIX
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Other probes
Heavy Flavor• Production dominated by gluon
gluon fusion• Measured via e+e-, +-, e, eX, X• Need more P4L
Direct Photon• Quark gluon scattering dominates• Direct sensitivity to size and sign
of G• Need more P4L
~80%
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Extend x-range different s
2-2.5 GeV/c4-5 GeV/c9-12 GeV/c
2-2.5 GeV/c4-5 GeV/c9-12 GeV/c
0 at ||<0.35: xg distribution vs pT bin
s=500 GeV
s=62 GeV
s=200 GeV
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0 at s=62 and 500 GeV:Unpolarized cross section
s=500 GeV: PHENIX Preliminary
May need inclusion of NLL to NLO
s=62 GeV: PHENIX, PRD79, 012003
Data below NLO at =pT by (3015)%22
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s=62 GeV
Charged hadrons
Very limited data sample (0.04 pb-1, compared 2.5 pb-1 from Run2005 s=200 GeV)
Clear statistical improvement at larger x; extends the range to higher x (0.06<x< 0.4)
Overlap with 200 GeV ALL provides measurements at the same x but different scale (pT)
s=500 ALL results will be available soon (from Run2009 with L~10 pb-
1 and P~0.4)
0: PHENIX, PRD79, 012003
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G: Path Forward
Improve precision of current measurements
Get more data
Extend xg-range
Move to forward rapidities
Constrain kinematics: map G vs xg
More exclusive channels: pp + jet and pp jet + jet
Limitations in current data: Limited x-range covered Weak sensitivity to the shape of G(x)
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Get more data
STAR pp jet X : projections PHENIX pp 0 X : projections
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Forward Calorimetry: PHENIX MPCMuon Piston Calorimeter (MPC): PbWO4
3.1 < || < 3.9
2 azimuth
Gives access to lower: x10-3
Fully available from 2008
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MPC 0 500 GeV300 pb-1 P=0.55
STAR: 0 forward rapidityPRL 97, 152302
pQCD looks working even in forward rapidities
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STAR: di-jet ALLConstrains kinematics shape of G(x)
2exp, 43
21
s
Mxx
Run9 data !
Projections for s=500 GeV
The same trend as from inclusive jets: Slightly positive G? …
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PHENIX Silicon Vertex tracker (VTX & FVTX)
FVTX endcaps1.2<|h|<2.7 mini strips
VTX barrel |h|<1.2VTX: available from 2011FVTX: available from 2012
432
ees
px T
431
ees
px T
EMC and MPC: pT and photon VTX: jet
May be luminosity (and polarization) hungry
Rejects hadronic backgroundc/b separated measurements
g
g Q
QQ = c or b
q
g
g
q jet
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(Anti)quark flavor separationDSSV: PRL 101, 072001 (2008)
Mainly from SIDIS:
Fragmentation functions to tag (anti)quark flavor
l+
p+p W (e/) +
Parity violating W production:
Fixes quark helicity and flavor
No fragmentation involved High Q2 (set by W mass)
)()()()(
)()()()(
baba
babaWL xuxdxdxu
xuxdxdxuA
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W: AL vs l
STAR
Central (barrel) region (We , ||<1)
First data from 2009: PRL106, 062002 (2011)
Forward (endcup) region (We , 1<||<2) :
Forward tracker upgrade, first data in 2012
PHENIX
Central Arms (We , ||<0.35)
First data from 2009: PRL106, 062001 (2011)
Forward Arms (W , 1.2<||<2.4) :
Trigger upgraded, first data from 2011
u
uAW
L
u
uAW
L
d
dAW
L
d
dAW
L
u
u
d
dAW
L 2
1
d
d
u
uAW
L 2
1
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Central region: W e from Run9 Triggered by energy in EMCal Momentum from energy in EMCal Charge from tracking in B field
e+
e+ e-
e-
PHENIX: |e|<0.35STAR: |e|<1
L=8.6 pb-1L=12 pb-1
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Central region: W e from Run9
PHENIX: PRL106, 062001 (2011)STAR: PRL106, 062002 (2011)
P=0.39 L=8.6/12 pb-1 in PHENIX/STAR
Run11: larger sample with P~0.52
PHENIX AL
Cross section
STAR AL
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e-
e+
e+ e-
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PHENIX Forward Arm: W
First data collected in 2011: L~15 pb-1 P~0.52Data being analyzed
trigger rejection
trigger eff.
PHENIX 2kHz Bandwidth
Raw yields with different triggers and cuts
More challenging than We at ~0
Expected W yield
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W l : ProjectionsPHENIX: We STAR: WePHENIX: W
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Longer term upgradesp+p: s=500 GeV 650 GeV
Will increase W production cross section twice
p+3He: s=432 GeVWill allow full flavor separation for light quarks
Workshop “Opportunities for polarized He-3 in RHIC and EIC” at BNL, Sep 28-30, 2011
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Summary RHIC is the world’s first and the only facility which provides collisions of high
energy polarized protons Allows to directly use strongly interacting probes (parton collisions) High s NLO pQCD is applicable
PHENIX&STAR continues producing results for different spin observables
Significant constraint on G for xg~0.02-0.03 from inclusive 0 and jet ALL at s=200 GeV
Other ALL measurements to be included in G global fit with different systematics and x-coverage
First AL results from We in central rapidity at s=500 GeV from 2009
First AL results from W in forward rapidity at s=500 GeV from 2011 coming soon
A major machine, PHENIX and STAR upgrades are under discussion Machine: Polarized source upgrade and electron lenses in RHIC to increase L and P;
s=500 GeV 650 GeV; polarized 3He
Experiments: considerably extended acceptance and improved capabilities in forward rapidity
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Backup
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Proton Spin
zLG 2
1
2
1Proton
Spin
1988 EMC (CERN): is small Proton Spin Crisis
From recent fits: ~1/4 (PRL101:072001,2008)
sdusdu
Determination of G is the main goal of longitudinal spin program at RHIC
(anti)quarkspin
Parton OrbitalMomentum
Gluonspin
Gluons carry ~1/2 of the proton momentum Natural candidate to carry proton spin
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From DIS …
Semi-inclusive polarized DIS Probe gluon through photon-gluon fusion process. Record heavy mesons (fragmented from heavy quarks)
+ Theoretically clean (high energy scale established by quark heavy mass)
– Background, low statistics Record light mesons (fragmented from light quarks)
+ High statistics – Large background and low energy scale
(problematic theoretical interpretation)
Inclusive polarized DIS Only information about input and scattered
lepton (e, ) is recorded x and Q2 reconstructed from kinematics
Do not have direct access to gluon Probe it through scaling violation (Q2 dependence of quark PDFs) - with poor precision currently
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… To polarized pp collider
Utilizes strongly interacting probes
Probes gluon directly Higher energies clean pQCD interpretation
Polarized Gluon Distribution Measurements (G): Use a variety of probes with variety of kinematics
Access to different gluon momentum fraction xDifferent systematics
Use different beam energies Access to different gluon momentum fraction x
g
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PHENIX Detector in 2011
p0, , g hElectromagnetic Calorimeter: ||<0.35Muon Piston Calorimeter: 3.1<||<3.9
p±, e, J/ye+e- : ||<0.35Drift, Pad Chambers, VTX (||<1)Ring Imaging Cherenkov Counter, ToFElectromagnetic Calorimeter
, J/y+- : 1.2<||<2.4Muon Id/Muon Tracker
Relative LuminosityBeam Beam Counter (BBC) Zero Degree Calorimeter (ZDC)
Local Polarimetry – ZDCSpin direction control
Philosophy (initial design): High rate capability & granularity Good resolutions & particle ID Sacrifice acceptance
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From soft to hard
exponential fit
Exponent (e-pT) describes our pion cross section data perfectly well at pT<1 GeV/c (dominated by soft physics):
=5.560.02 (GeV/c)-1
2/NDF=6.2/3
Assume that exponent describes soft physics contribution also at higher pTs soft physics contribution at pT>2 GeV/c is <10%
PRD76, 051106 (2007)
pT>2 GeV/c – hard scale?
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From soft to hard
xT scaling:
)(1
3
3
Tn xGsdp
dE
Running (Q2)Evolution of PDF and FFHigher order effectsEtc.
n=n(xT,Ös)
Soft region: n(xT) increase with xT If ~exp(-pT)
Hard region: n(xT) decrease with xT
Stronger scale breaking at lower pT
2 GeV/c at Ös=62 GeV pT~2 GeV/c – transition from soft to hard scale?
2004.62log
log 4.62200 n
PRD76, 051106 (2007)
xT10-2 10-1
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xT scalings=500/200 GeVs=200/62 GeV
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RHIC Spin Measurements
gq pp
Jet
Other exp.
Check theory (pQCD) works
q yieldJet g
This exp. Theory
Extract polarized PDF from spin asymmetries using pQCD
This exp. Theory
Jet Yield Spin Asymmetry
q g
Other exp.
Extract! 46
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From pT to xgluon
NLO pQCD: 0 pT=212 GeV/c xgluon=0.020.3 GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 )
Each pT bin corresponds to a wide range in xgluon, heavily overlapping with other pT bins
These data is not much sensitive to variation of G(xgluon) within our x range
Any quantitative analysis should assume some G(xgluon) shape
10-210-3 10-1 x
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From ALL to G (with GRSV)Generate g(x) curves for different (with DIS refit)
Calculate ALL for each G
Compare ALL data to curves (produce 2 vs G)
1
0)( dxxgG
1.0:error.expSyst. )3(2.0and)1(1.02.04:errorStat. 2.0
8.022]3.0,02.0[
GeVG x
GRSV
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G: theoretical uncertaintiesParameterization (g(x) shape) choice
• Vary g’(x) =g(x) for best fit, and generate many ALL
• Get 2 profile• At 2=9 (~3), consistent constraint:
-0.7 < G[0.02,0.3] < 0.5 Our data are primarily sensitive to the
size of G[0.02,0.3].
Theoretical Scale Dependence:
Vary theoretical scale : =2pT, pT, pT/2
0.1 shift for positive constraint Larger shift for negative constraint
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MPC: 0 cross section
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Forward Arm: W Momentum and charge: from tracking in B field
W
W is dominant(pT>20 [GeV/c])
Muon Tracking Chambers (Tr) 3 stations of Cathode strip chambers
Muon Identifier (ID) 5 layers of Iarocci tubes in x and y 80 cm of steel plate absorber (total) Provides trigger p >2 GeV (Rej ~100)
New Muon trigger (Rej ~100)Tr fast front end electronics
Provides momentum sensitive info for level1 trigger (p >7 GeV )
Two trigger RPC stations Another tracking point Precise timing to reject the
background
RPC3RPC1(to be in 2012)
ID
Tr
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W cross section
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sPHENIX
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