recent results from the phenix detector at rhic

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


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 ?


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


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


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


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


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(%

)


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


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


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


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.


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


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


Run6 Projections

0 +—


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


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)


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.


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.


Backups


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%


• Minimum Bias (BBC |z|<30)

• Minimum Bias in coincidence with High Energy Photon trigger (Cluster Energy>1.4GeV)


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.


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%


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

qq

Gluon-photon compton dominant

hep-ex/

0609031

RUN5

isolated pi0 photon

signal

Asymmetry analysis underway. Results expected soon.


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?


Charged Pion pT spectrum


Charged pion—Background

• Use Power law fit. Conservative estimate of backgrounds.


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.


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


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


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

recent results from the phenix detector at rhic

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