1Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Recent Results from the PHENIX Detector at RHIC
Kieran Boyle (Stony Brook U.)
Outline:• Motivation• RHIC and the PHENIX Detector• ALL measurements (g) from
Longitudinal Polarization − Requirements− Results
• Transverse Spin Physics Results
2Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Various channels can be used to probe g:– – direct photon– jets– Heavy flavor
Double Helicity Spin Asymmetry
g2 gq q2
Hard Scattering Process
2P2 2x P
1P
1 1x P
0
0
LLA
+- =
+++
+=
= agg * g2 + bgq * g q + cqq q2
P2
N++ - RN+-
N++ + RN+-
1 , R=L++
L+-P=polarizationN = particle yieldL = Luminosity
with ~25%, g not well constrained L ?
3Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
RHIC
BRAHMS & PP2PP (p)
STAR (p)PHENIX (p)
AGS
LINAC BOOSTER
Pol. Proton Source
Spin RotatorsPartial Siberian Snake
Siberian Snakes
200 MeV Polarimeter AGS Internal PolarimeterRf Dipoles
RHIC CNI (pC) PolarimetersAbsolute Polarimeter (H jet)
Year s [GeV] Luminosity [pb-1] (recorded) Polarization [%] Figure of Merit (P4L)
2005 * 200 3.4 46 0.15
2006 * 200 7.5 62 1.11
2006 * 62.4 0.08** 48 0.0053**
* Longitudinal ** Not yet finalized
4Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
PHENIX Detector
BBC
ZDCZDC
EMCaldetection• Electromagnetic Calorimeter (PbSc/PbGl):
• High pT photon trigger to collect 0's, ’s, ’s • Acceptance: ||x • High granularity (~10*10mrad2)
• Drift Chamber (DC) for Charged Tracks• Ring Imaging Cherenkov Detector (RICH)
• High pT charged pions (pT>4.7 GeV).Relative Luminosity• Beam Beam Counter (BBC)
• Acceptance: 3.0< 3.9• Zero Degree Calorimeter (ZDC)
• Acceptance: ±2 mradLocal Polarimetry• ZDCLvL2 data filter• Filters “rare” events for fast analysis
• pT>2.5 GeV photon for 0
5Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Relative Luminosity• Number of BBC triggered events used to determine Relative Luminosity.• For estimate of Uncertainty, fit
where
• Limited by ZDC statistics.Year [GeV] R ALL
2005 * 200 1.0e-4 2.3e-4
2006 * 200 1.1e-4 1.5e-4
2006 * 62.4 1.3e-3 2.8e-3* Longitudinal
6Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Local Polarimetry at PHENIX• Use Zero Degree Calorimeter
(ZDC) to measure a L-R and U-D asymmetry in forward neutrons (Acceptance: ±2 mrad).
• When transversely polarized, we see clear asymmetry.
• When longitudinally polarized, there should be no asymmetry.
BLUE YELLOW
Raw
as
ymm
etry
Raw
as
ymm
etry
Idea: Use neutron asymmetry to study transversely polarized component.
BLUE YELLOW
Raw
as
ymm
etry
Raw
as
ymm
etry
7Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Measured Asymmetry During Longitudinal Running
(2005)
<PT/P>=10.25±2.05(%)
<PL/P> =99.48±0.12±0.02(
%)
LR 2/NDF = 88.1/97p0 = -0.00323±0.00059
LR
UD 2/NDF = 82.5/97p0 = 0.00423±0.00057
XF>0 XF>0
XF<0 XF<0
2/NDF = 119.3/97p0 = 0.00056±0.00063
UD 2/NDF = 81.7/97p0 = -0.00026±0.00056
Fill NumberFill Number
<PT/P>=14.47±2.20(%)
<PL/P> =98.94±0.21±0.04(%
)
8Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
0 Cross Section
• Consistent with previous PHENIX results.
• Extends previous results to pT of 20 GeV/c.
• NLO pQCD Theory is consistent with data over nine orders of magnitude.
• As theory agrees well with our data, we can use it to interpret our results in terms of g
9Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Calculating ALL
1. Calculate ALL(+BG) and ALL(BG) separately.
2. Get background ratio (wBG) from fit of all data.
3. Subtract ALL(BG) from ALL(+BG):
ALL(+BG) = w· ALL() + wBG · ALL(BG)+BG region :
±25 MeV around peakBG region :
two 50 MeV regions around peak
Invariant Mass Spectrum
10Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
0 ALL (s=200 GeV)• Run6 Data set from 2.0-
2.7 times improvement on statistical uncertainties from Run5.
• Variation due to LvL2 “turn on.”
• Due to unreleased absolute polarizations, which scale ALL and which contain correlated and uncorrelated parts, we have not combined the two data sets.
GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 63 (2001) 094005.
Theory model Run5 Run6 Run5&Run6
GRSV-std 18-22 0.5-7 1-9
*GRSV-max (g=g) 0-0 0-0 0-0
*GRSV g=0 17-19 14-17 11-12
*GRSV g=−g 0-1 0-1 0-0
Confidence Levels •Theoretical uncertainties are not taken into account (for now).•Run 6 rules out maximal gluon scenarios.•Expect clearer statement when lower pT data from Run6 is available
11Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
0 ALL (s=62 GeV)
GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 53 (1996) 4775.
• ALL|R = 2.8x10-3.
• 0 unpolarized cross section at s=62 GeV is not yet finished.
– Not clear how well NLO pQCD describes our data.
– Validity of comparison with expected ALL theory curves calculated from NLO pQCD is NOT clear.
– Cross section result expected soon
• Converting to xT, we can get a better impression of the significance of the s=62 GeV data set, when compared with the Run5 preliminary data set.
12Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
High pT Charged Pion
g2 gq q2
Hard Scattering Process
2P 2 2x P
1P
1 1x P
+, -• First “Proof of concept” measurement
• Charged pions begin firing the RICH at pT~4.7 GeV, which is used for particle ID.
• Expect g>0, then: ALL(+)>ALL(0)>ALL(-)
Fraction of pion production
13Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
ALL
• Independent measure for gluon polarization.
• Analysis similar to 0
• fragmentation function not available, so no expected ALL curves have been calculated.
g2 gq q22P 2 2x P
1P
1 1x P
14Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Run6 Projections
0 +—
15Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Transverse Physics
• Large Asymmetries at large xF at s~20 GeV from E704.
• Large asymmetries remain at s=200 GeV for large xF .
• Cause?– Sivers effect
• left-right asymmetry in transverse momentum distribution of partons (“kT”) inside the transversely polarized nucleon
– Transversity• transverse polarization of partons
inside the transversely polarized nucleon
– Higher Twist
s = 19.4 GeV
left
rightRightLeft
RightLeftN dd
ddA
Phys.Rev.Lett. 92 (2004) 171801
s = 200 GeV
16Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
AN of 0 and h for ~0 at s=200GeV
π0 (2001/02)
pt (GeV/c) pt (GeV/c)
•P=15%, ~0.15pb-1 in Run2, P=47% in Run5PRL 95(2005)202001
|| < 0.35 Run 2
May provide information on gluon-Sivers effect• gg and qg processes are dominant (with small xB)
17Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Forward 0 at s=62 GeV• New calorimeter added in
Run6.• 3.1 < || < 3.65• Only south arm in Run6, north
just installed.
• Asymmetry seen in yellow beam (positive xF), but not in blue (negative xF)
• Only 10% of total statistics from 62 GeV Transverse Run
XF>0 XF<0
RLRL
RLRLNN
NNNN
NNNNRawA
R
aw A
sym
.
Raw
Asy
m.
18Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Conclusions
• At PHENIX, we are exploring proton spin through both transversely and longitudinally polarized proton collisions.
• Longitudinal– 0 ALL at s=200 GeV excludes maximal gluon scenarios.– 0 ALL at s=62 GeV will allow us to probe a higher xT region– Many complementary analyses are on the way.
• Transverse– Midrapidity 0 and charged hadron data may provide information
on the gluon Sivers effect.– Significant Run6 transverse data.
• L = 2.7 pb-1• P = 57 %• FoM = LP2 =880nb-1
– Results expected soon.
19Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Backups
20Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Photon Trigger Efficiency
Detector 1<pT<2 GeV/c 2<pT<3 GeV/c 3<pT<4 GeV/c pT> 4GeV
PbSc 6% 50% 81% 88%
PbGl 21% 72% 87% 90%
21Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
• Minimum Bias (BBC |z|<30)
• Minimum Bias in coincidence with High Energy Photon trigger (Cluster Energy>1.4GeV)
22Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
200 GeV 0 ATT
• Here
• ATT
– azimuthally independent double transverse spin asymmetry.
– ALL background.– expected to be small,
but previously unmeasured.
• In Run5, PHENIX took a short transverse run specifically to measure ATT.
• Consistent with zero.
23Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
62 GeV: Local Polarimetry
• Forward Neutron asymmetry reduced at 62 GeV, but still measurable.
xpos
xpos
xpos
xpos
Red : transverse dataBlue : longitudinal data
Blue Forward Blue Backward
Yellow BackwardYellow Forward
<PLR/AN>
BLUE 0.065 ± 0.143
YELLOW 0.132 ± 0.100
<PUD/AN>
BLUE -0.025 ± 0.119
YELLOW -0.020 ± 0.093
PLBLUE 100% – 2.3%
PLYELLOW 100% – 2.2%
24Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Direct photon
• First step, direct photon cross section using isolation cut.
• Isolation cut:– ETot<0.1Ecandidate within 0.5 rad.
• Background from merged 0 removed by shower shape (calibrated with test beam).
• Background from isolated 0 photon <15% above 10 GeV.
gq2P 2 2x P
1P
1 1x P
Gluon-photon compton dominant
hep-ex/
0609031
RUN5
isolated pi0 photon
signal
Asymmetry analysis underway. Results expected soon.
25Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
AN of J/ at s=200GeV
• Transverse running in Run6:• L = 2.7 pb-1• P = 57 %• FoM = LP2 =880nb-1
• J/ may be sensitive to gluon Sivers as produced through g-g fusion
• Charm theory prediction is available– Open Question:
How does J/production affect prediction?
26Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Charged Pion pT spectrum
27Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Charged pion—Background
• Use Power law fit. Conservative estimate of backgrounds.
28Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
January 2006 MPC South Installation
May 11, 1st 0 peak
•Muon Piston Calorimeter (MPC) Run06 Summary•Only South Side Installed, 192 PbWO4 crystals with APD readout•About 12 crystals did not function•Some problems with noisy crystals and electronics•Cannot fix since they are in an inaccessible region of the detector•Better than 80% of the acceptance is good.
29Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Forward neutrons• Discussed
previously in terms of local polarimetry.
• Forward neutron cross section in good agreement with ISR data.
• Forward asymmetry calculated as a function of XF
AN
-8.3 ±0.4 %
neutronchargedparticles
Run 5
30Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Uncertainty of ALL
0
LLA =
+- =
+++
+=
N++ - RN+-
N++ + RN+-
• For ALL, detector efficiencies and acceptance cancel out.• Relative luminosity:
• Polarization:– 20% relative uncertainty per beam—scales ALL and ALL similarly– Remaining transverse component can contribute to ALL as
– From transverse asymmetry in forward neutron production, estimate Run5, both beams were ~99% longitudinally polarized2<0.03
– ATT consistent with zero—Possible systematic contribution to ALL<0.05ATT.
P2
1 P=polarizationN = particle yieldL = Luminosity
Year [GeV] R ALL
2005 * 200 1.0e-4 2.3e-4
2006 * 200 1.1e-4 1.5e-4
2006 * 62.4 1.3e-3 2.8e-3 * Longitudinal
31Group on Hadronic Physics—Oct. 23, 2006Kieran Boyle
Di-Hadron Azimuthal Correlations
Possible helicitydependence– We may observe net
effect (after averaging over impact factor)
Spin-correlated transverse momentum (orbital angular momentum) may contribute to jet kT.
Run 5
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