K. Barish

Kenneth N. Barish (for Kinichi Nakano)for the PHENIX Collaboration

CIPANP 2009 San Diego, CA 26-31 May 2009

Measurement of Measurement of G at RHIC G at RHIC PHENIXPHENIX

Drawings by Àstrid Morreale

K. Barish

RHIC is sensitive to RHIC is sensitive to G via strongly interacting probesG via strongly interacting probes

Probes gluon at leading order High enough s for clean pQCD interpretation

Gluon contribution to proton spinGluon contribution to proton spin

ˆ

Hard Scattering Process

2P2 2x P

j 2f x

i 1f x1P

1 1x P

zhqD

s

1ps

2ps

1 1 2 2LL LL

1 1 2 2

f (x ) f (x )ˆA a

f (x ) f (x )

What is the gluon contribution to the proton spin (What is the gluon contribution to the proton spin (G)?G)?

q g

1 1L L

2 2G ~ .25 q gG,L ,L ?

K. Barish

Leading hadrons as jet tagsLeading hadrons as jet tags

ˆ

Hard Scattering Process

2P2 2x P

j 2f x

i 1f x1P

1 1x P

zhqD

s

1ps

2ps

gggg

G

G

G

G

gqgq

G

G

q

q

qqqq

q

q

q

q

qg+gq

qq

gg

Tp

0

Fraction

's produced

Double longitudinal spin asymmetry ALL is sensitive to G

K. Barish

Philosophy (initial Philosophy (initial

design):design): High rate capability & granularityHigh rate capability & granularity Good mass resolution & particle IDGood mass resolution & particle ID limited acceptancelimited acceptance

The PHENIX Detector for Spin The PHENIX Detector for Spin PhysicsPhysics

detectionElectromagnetic Calorimeter

eDrift ChamberRing Imaging Cherenkov CounterElectromagnetic Calorimeter

, JMuon Id/Muon Tracker

Relative LuminosityBeam Beam Counter (BBC) Zero Degree Calorimeter (ZDC)

Local Polarimetry - ZDCFilters for “rare” events

azimuth 2

4.2||2.1

azimuth 9090

35.0||

azimuth 9090

35.0||

K. Barish

Longitudinally Polarized Runs Longitudinally Polarized Runs @PHENIX@PHENIX

Year s [GeV] Recorded L Pol [%] FOM (P4L)

2003 (Run 3) 200 .35 pb-1 27 1.9 nb-1

2004 (Run 4) 200 .12 pb-1 40 3.1 nb-1

2005 (Run 5) 200 3.4 pb-1 49 200 nb-1

2006 (Run 6) 200 7.5 pb-1 57 790 nb-1

2006 (Run 6) 62.4 .08 pb-1 48 4.2 nb-1

2009 (Run 9) 500 ~10 pb-1 ~35 ~150 nb-1

2009 (Run 9) 200 in progress

BRAHMS & PP2PP (p)

STAR (p)PHENIX (p)

AGS

LINAC BOOSTER

Pol. Proton Source

Spin RotatorsPartial Siberian Snake

Siberian Snakes

200 MeV PolarimeterAGS Internal Polarimeter

Rf Dipoles

RHIC CNI (pC) PolarimetersAbsolute Polarimeter (H jet)

K. Barish

prompt photon

cceX

bbeXJ/

GS95

xG

(x)

Robust measurement covering wide Robust measurement covering wide xxgg region through region through multiple channels:multiple channels:

AALLLL Measurements Measurements

MeasurementsMeasurementsπ0 200GeV – Run 3, 4, 5, 6

64GeV – Run 6

πRun 5, 6 (prelim)

Photon Run 5, 6 (prelim)

Run 5, 6 (prelim)

Heavy FlavorRun 5, 6 (prelim)

gggg

G

G

G

G

gqgq

G

G

q

q

qqqq

q

q

q

q

gg QQ

G

G

G

G

gq g

G

G

q

q

K. Barish

(N) Helicity dependent yields (R) Relative Luminosity

BBC vs ZDC

(P) PolarizationRHIC Polarimeter (at 12 o’clock)Local Polarimeters (SMD&ZDC)

Bunch spin configuration alternates every 106 ns Data for all bunch spin configurations are collected at the same

time Possibility for false asymmetries are greatly reduced

Measuring AMeasuring ALL LL at RHIC-PHENIXat RHIC-PHENIX

+ - =

++ =

+

+

K. Barish

00 cross section at 200GeV cross section at 200GeV

NLO pQCD calculations are consistent with cross-section measurements

G2 Gq q2

2P2 2x P

1P

1 1x P

Phys.Rev.D 76, 051106 (2007)

K. Barish

00 A ALLLL

PHENIX Run6 (s=200 GeV)

arXiv:0810.0694

GRSV model:“G = 0”: G(Q2=1GeV2)=0.1“G = std”: G(Q2=1GeV2)=0.4

Statatistical uncertainties are on level to distinguish “std” and “0” scenarios

K. Barish

Relationship between pRelationship between pTT and and xxgluongluon

Log10(xgluon)

arXiv:0810.0694

NLO pQCD: NLO pQCD: 00 p pTT=2=212 GeV/c12 GeV/cGRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 )Note: the relationship between pT and xgluon is model dependent

Each pEach pTT bin corresponds to a wide range in x bin corresponds to a wide range in xgluongluon, heavily , heavily overlapping with other poverlapping with other pTT bins bins

Data is not very sensitive to variation of G(xgluon) within measured range

Any quantitative analysis assumes some G(xgluon) shape

arXiv:0810.0694

K. Barish

arXiv:0810.0694

Sensitivity of Sensitivity of 00 A ALLLL to to G (with G (with GRSV)GRSV)

1

0)( dxxgG

)3(2.0and)1(1.02.04:errorStat. 2.08.0

22]3.0,02.0[

GeVG xGRSV

Generate g(x) curves for different

Calculate ALL for each G

Compare ALL data to curves (produce 2 vs G)

K. Barish

Systematic uncertaintySystematic uncertainty Primary systematic

uncertainties are from polarization (ΔP) and relative luminosity (ΔR).

Polarization uncertainty is insignificant when extracting ΔG.

Uncertainty in relative luminosity while small cannot be neglected when extracting ΔG.

Systematic uncertainty gives an additional +/- 0.1

G: experimental uncertaintiesG: experimental uncertaintiesarXiv:0810.0694

1.0:error.expSyst.

K. Barish

G: theoretical uncertaintiesG: theoretical uncertainties

g(x) Parameterizationg(x) Parameterization

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

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

arXiv:0810.0694

arXiv:0810.0694

arXiv:0810.0694

K. Barish

x

xG

(x)

ΔΔG(x) C from Gehrmann StirlingG(x) C from Gehrmann Stirling

present x-range

Much of the first momentΔG = ∫ΔG(x)dx might emerge from low x!

GSC-NLO: ΔG = ∫ΔG(x)dx ~ 1.0

GSC-NLO

GSC-NLO: ΔG = ∫0.02ΔG(x)dx ~ small0.3

Extending x-range is crucialExtending x-range is crucial

K. Barish

Extend x RangeExtend x Range

Extend to lower x at s = 500 GeV

Extend to higher x at s = 62.4 GeV

To measure To measure G, need as wide an G, need as wide an xxgg range as range as possible.possible.

By measuring at different center of mass energies, we can reach different xg ranges. We can extend our xg coverage towards higher x at s = 62.4 GeV.

Run6 We can extend our xg coverage towards lower x at s = 500 GeV. test:

Run9 Upgrades in the forward/backward direction (FVTX, FOCAL) have

the potential to enable sensitivity to xg~10-3.

present (0)x-ranges = 200 GeV

K. Barish

00 A ALLLL @ @ s=s=62.4 GeV62.4 GeV Short run with longitudinal

polarized protonsALL

probes x range from .06 to 0.4 » Better statistical precision at

higher x than previous measurements at 200GeV

PRD79,012003 (2009)

NLL may be important @ s=62 GeV

PRD79,012003 (2009)

K. Barish

Other Probes IOther Probes I

Analysis similar to 0

Different flavor structure

Independent probe of G

±±

Preferred fragmentation u+ and d- ;

u>0 and d<0 different qg contributions for +, 0, -

access sign of G

+ 0 -

u u uD D >D

G 0 + 0 -

LL LL LLA A A

K. Barish

Other Probes IIOther Probes II

Heavy Flavor• Production dominated by

gluon gluon fusion• Measured via e+e-, +-, e,

eX, X• Future luminosity and

detector upgrades will significantly improve.

Direct @ 200 GeV

Direct Photon

• Quark gluon scattering dominates

• Direct sensitivity to size and sign of G

• Need more P4L

~80%

K. Barish

Recent Global Fit: DSSVRecent Global Fit: DSSV» First truly global analysis of polarized DIS, SIDIS and pp results» PHENIX s = 200 and 62 GeV data used» RHIC data significantly constrain G in range 0.05<x<0.3

PRL 101, 072001(2008)

g(x) small is current RHIC measured range Best fit has a node at x~0.1 Low-x unconstrained

RH

ICra

ng

e

K. Barish

SummarySummaryRHIC is a novel accelerator which provides collisions of RHIC is a novel accelerator which provides collisions of high energy polarized protonshigh energy polarized protons» Allows to directly use strongly interacting probes (parton collisions)» High s NLO pQCD is applicable

PHENIX inclusive PHENIX inclusive 00 A ALLLL data provide a significance data provide a significance constraint on constraint on G in the xG in the xgg range range ~[0.02;0.3]~[0.02;0.3]» The effect of stat. as well as experimental and theoretical syst.

uncertainties are evaluated

» At 3 level a constraint -0.7<Gx=[0.02;0.3] <0.5 is nearly shape independent

Other PHENIX AOther PHENIX ALLLL data are available data are available , ± - will be included in the G constraint , e, - need more P4L

Extending x coverage is crucialExtending x coverage is crucial» Other channels from high luminosity and polarization» Different s» Upgrades

)scale(1.0)shape(

)systexp.(1.0)stat(1.02.0)4(0.04.0

22]3.0;02.0[

GeVG x

K. Barish

Extra slides…Extra slides…

K. Barish

USA Abilene Christian University, Abilene, TX Brookhaven National Laboratory, Upton, NY University of California - Riverside, Riverside, CA University of Colorado, Boulder, CO Columbia University, Nevis Laboratories, Irvington, NY Florida Institute of Technology, FL Florida State University, Tallahassee, FL Georgia State University, Atlanta, GA University of Illinois Urbana Champaign, IL Iowa State University and Ames Laboratory, Ames, IA Los Alamos National Laboratory, Los Alamos, NM Lawrence Livermore National Laboratory, Livermore, CA University of Maryland, College Park, MD University of Massachusetts, Amherst, MA Muhlenberg College, Allentown, PA University of New Mexico, Albuquerque, NM New Mexico State University, Las Cruces, NM Dept. of Chemistry, Stony Brook Univ., Stony Brook, NY Dept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY Oak Ridge National Laboratory, Oak Ridge, TN University of Tennessee, Knoxville, TN Vanderbilt University, Nashville, TN

Brazil University of São Paulo, São PauloChina Academia Sinica, Taipei, Taiwan China Institute of Atomic Energy, Beijing Peking University, BeijingCzech Charles University, Prague, Republic Czech Technical University, Prague, Czech Republic Academy of Sciences of the Czech Republic, PragueFinland University of Jyvaskyla, JyvaskylaFrance LPC, University de Clermont-Ferrand, Clermont-Ferrand Dapnia, CEA Saclay, Gif-sur-Yvette IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, Orsay LLR, Ecòle Polytechnique, CNRS-IN2P3, Palaiseau SUBATECH, Ecòle des Mines at Nantes, NantesGermany University of Münster, MünsterHungary Central Research Institute for Physics (KFKI), Budapest Debrecen University, Debrecen Eötvös Loránd University (ELTE), Budapest India Banaras Hindu University, Banaras Bhabha Atomic Research Centre, BombayIsrael Weizmann Institute, RehovotJapan Center for Nuclear Study, University of Tokyo, Tokyo Hiroshima University, Higashi-Hiroshima KEK, Institute for High Energy Physics, Tsukuba Kyoto University, Kyoto Nagasaki Institute of Applied Science, Nagasaki RIKEN, Institute for Physical and Chemical Research, Wako RIKEN-BNL Research Center, Upton, NY Rikkyo University, Toshima, Tokyo Tokyo Institute of Technology, Tokyo University of Tsukuba, Tsukuba Waseda University, Tokyo S. Korea Cyclotron Application Laboratory, KAERI, Seoul Ewha Womans University, Seoul, Korea Kangnung National University, Kangnung Korea University, Seoul Myong Ji University, Yongin City System Electronics Laboratory, Seoul Nat. University, Seoul Yonsei University, SeoulRussia Institute of High Energy Physics, Protovino Joint Institute for Nuclear Research, Dubna Kurchatov Institute, Moscow PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg Lomonosoy Moscow State University, Moscow St. Petersburg State Technical University, St. PetersburgSweden Lund University, Lund

14 Countries; 68 Institutions; 550 Participants

K. Barish

)(

)2/(

0

0

HERMES

(hadron pairs)

COMPASS(hadron pairs)

E708(direct photon)

RHIC(direct photon)

CDF(direct photon)

pQCD partonic level asymmetriespQCD partonic level asymmetries

NLO corrections are now known for all relevant reactions NLO corrections are now known for all relevant reactions

LOLLaHigh s and pT make the NLO pQCD analysis reliable

» dependence of the calculated cross section on represents an uncertainty in the theoretical predictions

M. S

trat

man

n an

d W

. Vog

elsa

ng

)(GeV/ cpT

K. Barish

• 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

Use neutron asymmetry to study transversely polarized component.

BLUE YELLOW

Raw

as

ymm

etry

Raw

as

ymm

etry

Local Polarimety at PHENIXLocal Polarimety at PHENIX

K. Barish

Measured Asymmetry During Longitudinal Measured Asymmetry During Longitudinal RunningRunning

<PT/P>=10±2(%)

<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±2(%)

<PL/P>=98.94±0.21±0.04(%)

Also confirmed in Run6 analysis

Measurement of remaining transverse component spin pattern is correct

(2005)

K. Barish

Relative LuminosityRelative Luminosity

Number of BBC triggered events (NBBC) used to calculate Relative Luminosity.

For estimate of Uncertainty, fit

for all bunches in a fill with

Year [GeV] R ALL

2005 * 200 1.0e-4 2.3e-4

2006 * 200 3.9e-4 5.4e-4

2006 * 62.4 1.3e-3 2.8e-3* Longitudinal

K. Barish

Possible contamination from soft Possible contamination from soft physicsphysics

• By comparing 0 data with charged pion data, which has very good statistics at low pT, can estimate soft physics contribution

• Fitting an exponential to the low pT charged pion data (pT<1 GeV/c) gives an estimate on the soft physics contribution.

• Fit result: = 5.56±0.02 (GeV/c)−1

2/NDF = 6.2/3• From this, we see that for

pT>2 GeV, the soft physics component is down by more than a factor of 10.

exponential fit

PHENIX: hep-ex-0704.3599

For G constrain use 0 ALL data at pT>2 GeV/c

K. Barish

AALLLL of jet-like cluster at of jet-like cluster at s=200GeVs=200GeV

Run 5

2P 2 2x P

1P

1 1x P

» “Jet” detection: tag one high energy photon and sum energy of nearby photons and charged particles

» Definition of pT cone: sum of pT measured by EMCal and tracker with R = (||2+||2)

» Real pT of jet is evaluated by tuned PYTHIA

K. Barish

Forward Neutron asymmetry reduced at 62 GeV, but still measurable.

xpos

xpos

xpos

xpos

Red : transverse data, Blue : 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%

62 GeV: Local Polarimetry62 GeV: Local Polarimetry

K. Barish

Calculate ALL(+BG) and ALL(BG) separately.

Get background ratio (wBG) from fit of all data.

Subtract ALL(BG) from ALL(+BG):

ALL(+BG) = w· ALL() + wBG · ALL(BG)

This method is also used for other probes with two particle decay mode:

• , J/

+BG region :±25 MeV around

peakBG region :

two 50 MeV regions around peak

Calculating Calculating 00 A ALLLL