Exploring Gluon Polarization in the Proton with STAR Carl Gagliardi - - PowerPoint PPT Presentation

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Exploring Gluon Polarization in the Proton with STAR Carl Gagliardi - - PowerPoint PPT Presentation

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Exploring Gluon Polarization in the Proton with STAR Carl Gagliardi Texas A&M University for the Collaboration STAR STAR Outline Introduction Inclusive measurements Correlation measurements Partonic origin of the proton

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SLIDE 1

Exploring Gluon Polarization in the Proton with STAR

Carl Gagliardi Texas A&M University

for the

Collaboration Outline

  • Introduction
  • Inclusive measurements
  • Correlation measurements

STAR STAR

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SLIDE 2

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 2

Partonic origin of the proton spin?

  • Measuring the gluon polarization distribution

is a primary goal of the RHIC spin program

〉 〈 + Δ + ΔΣ = =

z z

L G S 2 1 2 1

Three 2006 fits of equal quality: – ΔG = 0.13 ± 0.16 – ΔG ~ 0.006 – ΔG = -0.20 ± 0.41 all at Q2 = 1 GeV2

Leader et al, PRD 75, 074027

Polarized DIS: ~0.3 Poorly Constrained

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SLIDE 3

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 3

LL b a b a LL

a f f f f A ˆ Δ Δ ∝ + − =

− + + + − + + +

σ σ σ σ

Δf: polarized parton distribution functions

∗

θ cos

For most RHIC kinematics, gg and qg dominate, making ALL for hadrons, photons, and jets sensitive to gluon polarization.

10 20 30 pT(GeV)

Partonic fractions in jet production at 200 GeV

Exploring gluon polarization at RHIC

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SLIDE 4

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 4

STAR detector in two views

BEMC EEMC FMS FPD TPC BBC

  • High precision tracking with the TPC
  • Electromagnetic calorimetry with the BEMC, EEMC, and FMS
  • Additional detectors for relative luminosity, local polarimetry, and

minbias triggering

ZDC ZDC

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SLIDE 5

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 5

Gluon polarization measurements at STAR

Inclusive measurements – Features

  • High precision measurements
  • Average over partonic

kinematics

  • Powerful for determining the

scale of ΔG

– Channels

  • Neutral pions
  • Direct photons
  • Jets

Correlation measurements – Features

  • Less abundant
  • Resolve partonic kinematics
  • n event-by-event basis
  • Provide information about the

shape of Δg(x)

– Channels

  • Charged pions opposite jets
  • γ+jet
  • Di-jets
  • Both types of measurements provide important information

for global analyses

  • Large acceptance of STAR makes jet and di-jet measurements

particularly attractive

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SLIDE 6

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 6

STAR inclusive π0 ALL at various rapidities

  • During 2006, STAR measured ALL for inclusive π0 for three different

rapidity regions

  • Larger rapidity correlates to stronger dominance of qg scattering

with larger x quarks and smaller x gluons

  • Expect ALL to decrease as η increases

|η| < 0.95 1 < η < 2 η = 3.2, 3.7

STAR STAR

Status of ’09 data analysis: See poster by W. Leight

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SLIDE 7

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 7

Jet cross section from 2006 data

  • Good agreement between data and simulation
  • Good agreement with NLO pQCD calculation after hadronization

and underlying event correction is applied

  • Jet production is well understood at RHIC energies

STAR STAR

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SLIDE 8

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 8

Jet cross section from 2006 data

  • Good agreement between data and simulation
  • Good agreement with NLO pQCD calculation after hadronization

and underlying event correction is applied

  • Jet production is well understood at RHIC energies

STAR STAR

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SLIDE 9

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 9

STAR inclusive jet ALL from 2006

200 GeV

  • 0.7 < η < 0.9

STAR STAR

  • STAR inclusive jet ALL excludes those scenarios that have a

large gluon polarization within the accessible x region

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SLIDE 10

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 10

STAR inclusive jet ALL from 2006

200 GeV

  • 0.7 < η < 0.9

STAR STAR

  • STAR inclusive jet ALL excludes those scenarios that have a

large gluon polarization within the accessible x region

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SLIDE 11

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 11

DSSV – first global analysis with polarized jets

  • The first global NLO analysis to include inclusive DIS, SIDIS, and

RHIC pp data on an equal footing

de Florian et al., PRL 101, 072001

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SLIDE 12

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 12

DSSV – first global analysis with polarized jets

  • The first global NLO analysis to include inclusive DIS, SIDIS, and

RHIC pp data on an equal footing

de Florian et al., PRL 101, 072001

STAR

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SLIDE 13

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 13

2009 upgrades

  • 2009 jet patch trigger upgrades

– Overlapping jet patches and lower ET threshold improve efficiency and reduce trigger bias

  • Net increase of 37% in jet acceptance

– Remove beam-beam counter trigger requirement:

  • Trigger more efficiently at high jet pT
  • Measure non-collision background
  • Improvements in jet reconstruction

– Subtract 100% of track momentum from struck tower energy (2009) instead of MIP (2006) – Overall jet energy resolution improved from 23% to 18%

  • Increased trigger rate and reduced thresholds enabled by

DAQ1000

  • Sampled ~ 4 times the figure-of-merit relative to 2006

Jet specific Enhance all channels

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SLIDE 14

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 14

Direct photon cross section and ALL from 2009

For details: See poster by

  • M. Betancourt
  • Cross section at 200 GeV is consistent

with NLO pQCD calculations

  • ALL for direct photons has very clean

theoretical interpretation, but

– Cross section is very small – Background is very large – Very difficult measurement!

  • Need far more statistics
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SLIDE 15

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 15

ALL for inclusive jets: 2006 to 2009

  • 2009 STAR inclusive jet ALL measurements are a factor of 3

(high-pT) to >4 (low-pT) more precise than 2006

  • Results fall between predictions from DSSV and GRSV-STD
  • Precision sufficient to merit finer binning in pseudorapidity

STAR STAR

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SLIDE 16

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 16

2009 STAR inclusive jet ALL

STAR STAR

  • ALL separated into two pseudorapidity ranges
  • Forward jets involve:

– A larger fraction of quark-gluon scattering with:

  • Higher x quarks that are more polarized
  • Lower x gluons that are less polarized

– Larger |cos(θ*)|, which reduces aLL

  • ALL falls between the predictions from DSSV and GRSV-STD

∧ Mid rapidity Forward rapidity

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SLIDE 17

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 17

Expected future inclusive jet ALL precision

  • STAR will measure inclusive jet ALL in 500 GeV collisions

during the 2012 and 2013 RHIC runs – Higher beam energy provides sensitivity to smaller xg – Expect ~ 90 pb-1 during 2012; much more during 2013

Inclusive Jet A_LL for |eta|<1

  • 0.005

0.000 0.005 0.010 0.015 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 x_T A_LL Run 9 Preliminary Run 12 Proj Stat GRSV-Std (500) DSSV (500) GRSV-Std (200) DSSV (200) Assumes 190 pb-1 with 50% polarization

200 GeV Run 9 500 GeV projection

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SLIDE 18

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 18

Inclusive Jet A_LL for |eta|<1

  • 0.005

0.000 0.005 0.010 0.015 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 x_T A_LL Run 9 Preliminary Run 12 Proj Stat GRSV-Std (500) DSSV (500) GRSV-Std (200) DSSV (200) Fut 200 GeV

Expected future inclusive jet ALL precision

  • STAR will measure inclusive jet ALL in 500 GeV collisions

during the 2012 and 2013 RHIC runs – Higher beam energy provides sensitivity to smaller xg – Expect ~ 90 pb-1 during 2012; much more during 2013

  • STAR also anticipates significant future reductions in the

uncertainties for 200 GeV collisions relative to the 2009 results

200 GeV future 200 GeV Run 9 500 GeV projection

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Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 19

Beyond inclusive ALL measurements

  • Inclusive ALL measurements at fixed pT average over a broad x range.
  • Can hide considerable structure if Δg(x) has a node
  • Correlation measurements can constrain the shape of Δg(x)

STAR STAR PRL 100, 232003

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Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 20

Charged pions opposite jets

STAR STAR

  • Trigger and reconstruct a jet, then look for a

charged pion on the opposite side

  • Events with high-z π+ emphasize gluon scattering
  • ff highly-polarized u quarks
  • Significantly increases the sensitivity of ALL(π+)

ALL ALL Status of ’09 data analysis: See poster by J. Hays-Wehle

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Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 21

2006 di-jet cross section

  • Di-jets permit event-by-event calculations of x1 and x2 at LO
  • Di-jet cross section is well-described by NLO pQCD with corrections

for hadronization and underlying event STAR STAR

( ) ( )

2 tanh cos 2 ln 2 1 | η η | | θ | η η x x y s x x M e p e p s 1 x e p e p s 1 x

4 3 * 4 3 2 1 2 1 η T,4 η T,3 2 η T,4 η T,3 1

4 3 4 3

− = + = = = + = + =

− −

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SLIDE 22

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 22

2006 di-jet ALL

  • 2006 di-jet ALL provides a start at constraining the

shape of Δg(x) STAR STAR

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SLIDE 23

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 23

2009 STAR di-jet partonic coverage

STAR STAR

For more details: See poster by

  • M. Walker

( ) ( )

2 tanh cos 2 ln 2 1 | η η | | θ | η η x x y s x x M e p e p s 1 x e p e p s 1 x

4 3 * 4 3 2 1 2 1 η T,4 η T,3 2 η T,4 η T,3 1

4 3 4 3

− = + = = = + = + =

− −

x x

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SLIDE 24

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 24

2009 STAR di-jet partonic coverage

STAR STAR

For more details: See poster by

  • M. Walker

( ) ( )

2 tanh cos 2 ln 2 1 | η η | | θ | η η x x y s x x M e p e p s 1 x e p e p s 1 x

4 3 * 4 3 2 1 2 1 η T,4 η T,3 2 η T,4 η T,3 1

4 3 4 3

− = + = = = + = + =

− −

x x

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SLIDE 25

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 25

2009 STAR di-jet partonic coverage

Larger aLL Smaller σ

STAR STAR

For more details: See poster by

  • M. Walker

( ) ( )

2 tanh cos 2 ln 2 1 | η η | | θ | η η x x y s x x M e p e p s 1 x e p e p s 1 x

4 3 * 4 3 2 1 2 1 η T,4 η T,3 2 η T,4 η T,3 1

4 3 4 3

− = + = = = + = + =

− −

∧ Smaller aLL Larger σ ∧

x x

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Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 26

2009 STAR di-jet ALL

  • For fixed M, different kinematic regions sample different x ranges
  • ALL falls between DSSV and GRSV-STD

STAR STAR

For more details: See poster by

  • M. Walker
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Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 27

Projected sensitivity for di-jets at 500 GeV

  • Higher energy accesses

lower xg

  • Expect smaller ALL
  • Uncertainties shown are

purely statistical

  • Maybe add EEMC-EEMC

di-jets to reach lowest x values after FGT is installed (?)

Assumes 600 pb-1 delivered @ P = 50%

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ± = 2 exp

4 3 2 1

η η s M x , x

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Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 28

Conclusions

  • STAR 2006 results play a significant role in recent global analysis
  • STAR 2009 results will have a strong impact on the determination
  • f gluon polarization
  • We will reduce the uncertainties even further in the near future
  • Stay tuned!

STAR STAR

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Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 29

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Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 30

Midpoint cone algorithm

(Adapted from Tevatron II - hep-ex/0005012)

Jet reconstruction in STAR

Detector

etc p e , , , π γ ν , ,

g q,

GEANT PYTHIA Data jets MC jets Particle

  • Seed energy = 0.5 GeV
  • Cone radius R = 0.7 in η-φ space
  • Split/merge fraction f = 0.5

Use PYTHIA + GEANT to quantify detector response

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SLIDE 31

Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 31

Jet+hadron correlations at NLO

from de Florian, PRD 79, 114014

  • NLO calculations show strong correlation between the real x and z

values and LO estimates

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Carl Gagliardi – Exploring Gluon Polarization in the Proton with STAR 32

Gluon polarization with gamma+jet

  • Sensitivity estimates including realistic photon efficiencies and

purities, benchmarked with real data – Maybe higher purity with future isolation cuts using FGT