PHENIX G Program: Results and Plans

A.BazilevskyBrookhaven National Laboratory

For the PHENIX Collaboration

SPIN-Praha-2010, Jul 18-24

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

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

… 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

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 …

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

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

Measuring ALL

LLR

RNNRNN

PPddddALL ;

||1

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(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

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||

PHENIX Local PolarimeterZero Degree Calorimeter:

<2.5 mrad Utilizes spin dependence of very forward neutron production discovered in RHIC Run-2002 (PLB650, 325)

neutronchargedparticles

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

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)

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

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?

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

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)

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

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

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

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

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%

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

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)%

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)

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

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

Get more data

PHENIX p0: projections

A factor of 3-4 reduction in stat. errors expected in next s=200 GeV RHIC Run (2013?)

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

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

29

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

Backup

xT scalings=500/200 GeVs=200/62 GeV

x pT

UpDown Glue

pT=4-5 GeV/c

pT=9-12 GeV/c

pT=2-2.5 GeV/c

ggqg