PHENIX G Program: Results and Plans
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PHENIX G Program: Results and Plans
A.BazilevskyBrookhaven National Laboratory
For the PHENIX Collaboration
SPIN-Praha-2010, Jul 18-24
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Proton Spin
zLG 21
21Proton
Spin
1988 EMC (CERN): is small Proton Spin CrisisFrom 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 colliderUtilizes 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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Polarized PDF
q(x,Q2) =
q(x,Q2)=
helicity (longitudinal spin) distribution
unpolarised distribution
unpolarised distribution
g(x,Q2) =
g(x,Q2)=helicity (longitudinal spin) distribution
Gluo
nsQ
uark
sQuark
spinProton
spinq = u,d,s …
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Probing G in pol. pp collisionspp hX
hf
fXff
baba
hf
fXffLL
fXff
baba
LL Ddff
Dadff
ddddA
ba
baba
ˆ
ˆˆ
,
,
Double longitudinal spin asymmetry ALL is sensitive to G
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RHIC as polarized proton collider
BRAHMS & PP2PP (p)
STAR (p)PHENIX (p)
AGS
LINAC BOOSTER
Pol. Proton Source500 A, 300 s
GeVs
L
50050
onPolarizati%70cms102 2132
max
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 mradYear s [GeV]
L [pb-1] (recorded) Pol. [%]
FOM (P4L)
2003 200 0.35 27 0.0019
2004 200 0.12 40 0.0031
2005 200 3.4 49 0.20
2006 200 7.5 57 0.79
2006 62.4 0.08 48 0.00422009 200 ~15 57 ~1.5
2009 500 ~15 39 ~0.35
Longitudinal Spin Running in PHENIX
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Measuring ALL
LLR
RNNRNN
PPddddALL ;
||1
21
(N) Yield p0, , p±, h±, , e, etc.
(R) Relative Luminosity
(P) Polarization RHIC Polarimeter (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 reduced
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PHENIX Detector
azimuth 24.2||2.1
p
azimuth 9090
35.0||
p0, ,
Electromagnetic Calorimeter
p±, e, J/ye+e-
Drift ChamberRing Imaging Cherenkov CounterElectromagnetic Calorimeter
, J/y+-
Muon 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 mass resolution & particle ID Sacrifice acceptance
azimuth 9090
35.0||
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PHENIX Local PolarimeterZero Degree Calorimeter:
<2.5 mrad Utilizes spin dependence of very forward neutron production discovered in RHIC Run-2002 (PLB650, 325)
neutronchargedparticles
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PHENIX 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
-p/2 0 p/2
Asymmetry vs f
Longitudinal spin runs: 99.0PPL
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Relative Luminosity 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 regionALL of BBC relative to ZDC is ~0
Results: R ~ (25)10-4 ALL ~ (37)10-4 (for P~0.6)
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Unpol. Cross Section and pQCD in ppp0: PRD76, 051106 (2007)
Good agreement between NLO pQCD calculations and data pQCD can be used to extract spin dependent pdf’s from RHIC data.
pp X: PRL 98, 012002s=200 GeV
||<0.35
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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):
=5.56±0.02 (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:
)(13
3
Tn xGsdp
dE
Running (Q2)Evolution of PDF and FFHigher order effectsEtc.
n=n(xT,s)
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 s=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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p0 ALL
PRL103, 012003 (2009)
p0 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 pT to xgluon
NLO pQCD: p0 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 xGRSV
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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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Other probes
• Analysis similar to p0
• Different flavor structure• Independent probe of G
p p
p±
• Preferred fragmentation up+ and dp- ;
u>0 and d<0 different qg contributions for p+, p0, p-
access sign of G
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Other probes
Heavy Flavor• Production dominated by gluon
gluon fusion• Measured via e+e-, -, e, eX,
X• Need more P2L
Direct Photon• Quark gluon scattering dominates• Direct sensitivity to size and sign
of G• Need more P2L
~80%
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Extend x-range different s
present (p0)x-ranges = 200 GeV
Extend to lower x at s = 500 GeV
Extend to higher x at s = 62.4 GeV
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p0 at s=62 and 500 GeV:Unpolarized cross section
s=500 GeV: PHENIX Preliminary
May need inclusion of NLL to NLO
s=62 GeV: PRD79, 012003 (2009)
Data below NLO at =pT by (30±15)%
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s=62 GeVp0
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)
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G: Global FitDaniel de FlorianRodolfo SassotMarco StratmannWerner Vogelsang
• PRL101, 072001(2008)• First truly global analysis of polarized DIS, SIDIS and pp results• PHENIX s = 200 and 62 GeV p0 data used• RHIC data significantly constrain G in range 0.05<x<0.2• Other data will be incorporated into the fit
G~0 in the probed x-rangeVery large uncertainty at lower x
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G: Path Forward
Improve precision of current measurementsGet more data
Extend xg-range
Move to forward rapidities
Constrain kinematics: map G vs xg
More exclusive channels: pp + jet and pp jet + jet
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Get more data
PHENIX p0: projections
A factor of 3-4 reduction in stat. errors expected in next s=200 GeV RHIC Run (2013?)
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Forward Calorimetry
FOCAL: Tungsten absorber with silicon pad readout
1< <32p azimuth24 X0 deep
Available by 2013 (?)
Muon Piston Calorimeter (MPC): PbWO4
3.1 < || < 3.72p azimuthFully available from 20082009 ALL data being analyzed
28
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Silicon Vertex tracker (VTX & FVTX)
FVTX endcaps1.2<||<2.7 mini strips
VTX barrel ||<1.2Available in 2011/12
432
eespx T
431
eespx T
FOCAL: 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
q jet
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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 inclusive p0 ALL data offer a significance constraint on G in the xg range ~0.020.3 G ~ 0 in this xg range
Other PHENIX ALL data are available , p±, h± - will be included in the G constraint (and global fit) , e, , J/y - need more P4L
Extending xg coverage is crucial Other channels from high luminosity and polarization Different s
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Backup
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xT scalings=500/200 GeVs=200/62 GeV
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x pT
UpDown Glue
pT=4-5 GeV/c
pT=9-12 GeV/c
pT=2-2.5 GeV/c
ggqg
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