J. Seele (RBRC) 1

The PHENIX W Program

Joe Seele RIKEN BNL Research Center

Brookhaven National Laboratory New York, USA

ISSP2013 (Erice)

Polarized PDFs

J. Seele (RBRC) 2

Mom

entu

m

cont

ribu

tion

Spin

contribution

Unpolarized Polarized

Don’t care about the helicity of the parton

Care about the helicity of the parton in polarized proton

PDF = parton distribution function

Number distribution of partons inside the proton (or other hadron)

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The Spin Puzzle

!

12

=12"#+ Lq

z + "G + Lgz

Fairly well measured only ~30% of spin

The proton is viewed as being a “bag” of bound quarks and gluons interacting via QCD

Spins + orbital angular momentum need to give the observed spin 1/2 of proton

Being measured at RHIC

!

"# = ("u + "d + "s + "u + "d + "s +!)dx$

Its decomposition is not well understood, especially the sea (low-x)… needs data

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Flavor Asymmetry in Parton Sea

•  Pauli blocking should contribute to the observed signal, but how much is currently debated •  Non-perturbative processes may be needed in generating the sea  

•  E866 results are qualitatively consistent with pion cloud models, instanton models, chiral quark soliton models, etc.  

Phys.Rev.D80:034030

Q2=54 GeV2

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Probing the Sea through Ws

•  Detect Ws through e+ and e- (and u+ and u-) decay channels •  V-A coupling leads to perfect spin separation •  Neutrino helicity gives preferred direction in decay  

Measure parity violating single helicity asymmetry AL (Helicity flip in one beam while averaging over the other)

     

       

u+ d !W + ! l+ +!

u + d!W " ! l" +!

!

ALW +

"#$u(x1)d (x2) + $d (x1)u(x2)

!

ALW " #"$d(x1)u (x2) + $u (x1)d(x2)

RHIC The world’s first polarized proton collider

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PHENIX Central Arms: •  γ/π0/η detection

–  Electromagnetic Calorimeter (-0.35 < η < 0.35)

–  PC3 - Charge Veto Muon Arms: (1.2<|η|<2.4 + 2π) •  Large aborber in front •  Separate magnet (radial field) •  Tracking and high-p triggering MPC •  Electromagnetic Calorimeter (3.1<|η|<3.9 +

2π) Global Detectors: •  Relative Luminosity

–  Beam-Beam Counter (BBC) (+- 3.1 < η < 4.0)

–  Zero-Degree Calorimeter (ZDC) (+- 6.9 < η < infinity)

•  Local Polarimetry - ZDC

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J. Seele (RBRC) 8

The Mid-Rapidity Analysis Idea

ET

~MW/2 Yi

eld

Yiel

d

Expect a Jacobian peak in the ET distribution

Expect a steeply falling, but large background

ET Yi

eld ~MW/2

ET

W Signal QCD Background

We expect to see a bump in the ET spectrum at MW/2

Jacobian Peaks + Cross Section

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Positrons

Electrons

Forward Rapidity is Difficult

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• At forward rapidity there is either NO Jacobian peak or our p resolution isn’t good enough, so we can’t use shape to separate signal and background

Forward Rapidity Analysis Idea

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•  Currently we rely heavily on simulation for the estimation of the background size and shape

•  There are ideas to extract

background shapes from sqrt(s)=200GeV data where there should be less W signal (less simulation dependent)

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A Spin Experiment

!

AL =! " #" "

! " +" "

=1PN + # RN#

N + + RN#

•  P - polarization of beam •  R - relative luminosity •  N - physics process

PHENIX Run12 AL Results

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Future Projections

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Conclusions •  RHIC has a vibrant program measuring W

production in polarized p+p collisions to get the flavor separated pdfs (polarized and unpolarized)

•  The first proof of principle measurements have been done and the analysis of larger datasets is ongoing

•  We have just recorded a large sqrt(s)=510 p+p dataset (run13, 150pb-1) and are in the process of analyzing it.

•  Stay tuned for more results!

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Backup Slides

Expectations for W AL

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W Cross Sections

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J. Seele (RBRC) 19

Polarized Protons at RHIC

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Control of Helicity of Beams

Blue beam helicity: - - + + Yellow beam helicity:

+ - + - spin

rotator

+ helicity - helicity

spin rotator

(mostly) longitudinal polarization

Both experiments sees 4 helicity configurations

Experiment

Future Projections

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STAR PHENIX

STAR Run12 AL Results

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Jacobian Peaks

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E+ E-

RHIC Performance

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STAR

BBC

BEMC

EEMC

TPC

BBC

BEMC

EEMC

TPC

•  BEMC + EEMC: EM Calorimetry (-1 < h < 2 + 2pi)

•  TPC: Tracking and particle ID (-1 < h < 1)

•  FMS: Forward EM Calorimetry (2.3 < h < 4)

•  ZDC: Relative luminosity and local polarimetry

•  BBC: Relative luminosity and Minimum bias trigger

FMS

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J. Seele (RBRC) 26

Motivation What we want to accept What we want to reject

Look for the electron-type events with no energy/momentum on the away side

PHENIX Run9 AL Results

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Sea Quark Pol. PDFs

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DSSV Polarized PDFs

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PHENIX Forward Likelihoods

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PHENIX Forward dw23 Dists

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PHENIX Forward Rap Dists

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PHENIX For. Extraction - 2009

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Run12 Muon Trigger Hardware

34

FVTX Upgrade +Adds tracking RPC1 +Adds acceptance +Adds trigger rejection Additional Absorber +Shields detector from in-time backgrounds

J. Seele (RBRC)

J. Seele (RBRC) 35

W Algo: Motivation What we want to accept What we want to reject

Look for the electron-type events with no energy/momentum on the away side

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W Algo: Lepton Isolation

TPC track extrapolated to BTOW tower grid

4x4!2x2!

Lepton Isolation Cuts: • Require TPC track with pT > 10 GeV • Extrapolate track to Barrel Calorimeter • Require highest 2x2 cluster around pointed tower sum ET > 15 GeV • Require excess ET in 4x4 cluster < 5% • Match track to 2x2 cluster position • Get charge sign of lepton  

Signal region Jets

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W Algo: Suppress QCD Background Suppress jets with leading hadron

• Near side jet-cone veto Suppress di-jets and multi-jet events

• Away side pT sum veto • Require an imbalance in pT of the lepton cluster and any jets reconstructed outside the near side jet cone  

Cluster  ET  /  0.7  Cone  ET  

Signal region Jets

Signal

Dijets

nearCone delR=0.7

ptBalance 4pi - nearCone

sum only jets

Transverse plane view

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The Raw Signal

STAR recorded 13.7pb-1 in the run9 500 GeV running period

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Extracting the W Signal

eeW

!!"

!"

"

"

++#

+#

MC Normalized to L=13.7 pb-1  PYTHIA+GEANT MC

50

Run 9 Data Missing Endcap Vetoed QCD Background

1.  Run analysis with EEMC in veto cuts

2.  Run analysis without EEMC in veto cuts

3.  Subtract two raw signals

50

Normalized at ET<19 GeV Data Driven QCD Bkgd.

Signal

Dijets

50

EMC Cluster ET (GeV)

Total Background

EMC Cluster ET (GeV)

70

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STAR W Signals

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Data/MC Shape Comparison

Monte-Carlo is full PYTHIA+GEANT simulation of W→e+ν events at 500 GeV

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2009 500 GeV Data Set

STAR recorded 13.7pb-1 in the 500 GeV running period

Required a high tower trigger (ET > 7.3 GeV) and a high ET 2x2 clusters (ET > 13 GeV)

leptons from Ws should appear here

7.3

GeV

13 G

eV

EMC tower ADC

J. Seele (RBRC) 43 LO interpretation for x1=x2

STAR Barrel EMC

Predictions for AL

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Charge Separation at High pT

+/- distance D ~ 1/PT PT=5 GeV/c : D~15 cm

PT=40 GeV/c : D ~2 cm

shown electron & positron

PT= 5 GeV/c

infinite PT

vertex  

200  cm  of  tracking  

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Event Rejection

Run  9  Data   Pythia+Geant  W+  MC  

Track  pT  >  10  GeV  Lepton  IsolaEon  

Cut    Near  Side  pT  Veto  Away  Side  pT  &  ptBalance  Veto  

 

Ws  

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Example Lego Plots

W event

Dijet event

π π

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Cross Section Formula

( )

GeV 25 and 1 : Acceptance Kinematic

11112

><

!== " " #

eTe

backobsW

recovertextrigeT

eeWee

TW

E

NNLdEd

dddE

$

%%%$&

$& '

Efficiencies  Calculated  from  full  PYTHIA  +  GEANT  simulaBons    

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Cross Section Uncertainties •  W Reconstruction Systematic

–  Track Reconstruction: 15-20% –  Vertex Reconstruction: 4% –  Energy Scale: < 1%

•  Normalization/Luminosity Systematic –  Vernier scan absolute cross section: 23%

•  Background Systematic –  Vary data driven QCD background shape

and normalization region

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+ helicity - helicity STAR sees 4 helicity states STAR runs 4 parallel measurements

Helicity of beams at STAR

RHIC measured polarization Run 9 @ 2x250 GeV Pol yellow 0.40 Pol blue 0.38 syst. pol (blue+yellow)=9.2%

Blue helicity: - - + + ... Yellow helicity: + - + - ...

R

R

R

R

spin rotator

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Monitor spin dependent luminosity

2x2!4x4!

relative luminosities of 4 states monitored to ~1%

TPC track extrapolated

to BTOW tower grid

B -

Y

-

B -

Y

+

B +

Y

-

B +

Y

+

helicities of beams colliding at STAR

Cou

nts

Ws pi0’s jets

relative luminosity monitor C

ount

s

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negative helicity

unpolarized

negative ALP statistically significant

W+ yield integrated over |eta|<1

Null test passed

Co

un

ts

B -

Y

-

B -

Y

+

B +

Y

-

B +

Y

+

Up quark pol. seen by “naked eye”

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Spin dependent xsec for long. Pol.

P-V AL ( the goal ) ALL

AN x residual transverse pol Q

neglected because STAR is phi-symmetric

yields integrated over |eta|<1

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Long. spin asymmetries for Ws

AL

ALL

Null test

STAR has measured 4 independent yields for the physics process selected 3 asymmetries are independent ( 6 were investigated)

yields integrated over |eta|<1

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6 measured spin asymmetries for Ws

P-V AL

Null test

W+

P-V AL

ALL

Null test

W-

ALL

Physics asymmetries corrected for unpolarized background

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Systematic errors for AL Full list of accounted systematic errors in Run 9

W+ W - high low high low

0.092 0.092 0.092 0.092 CNI average polarization of both beams (P1+P2)

0.070 0.020 0.130 0.030 QCD unpolarized background

0.065 0.065 0.135 0.135 QCD pol. bckg. ~0: use 1/2 stat error of this test

0.004 0.000 0.004 0.000 decay of pol. within fill

0.13 0.11 0.21 0.17 total syst. in fraction of measured AL

Following effects were considered and their contribution set to zero * dilution of AL due to swap of W+/W- charge - the Q/PT cut prevents it * *