How to measure jet properties using two particle correlation method (In PHENIX)?

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Jets in PHENIX
Jiangyong Jia, Columbia Univerisity
Hot Quark Matter, Taos Valley, NM
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Hard-scattering and Jet fragmentation

• Partons scatters with large Q2 hard-scattering
• Outgoing partons fragment into sprays of hadrons
  Jets
• Properties that we want to measure
• The spread of the hadrons around the jet axis and
  
• relative orientation of the two jets jT, kT.
• The multiplicity of hadrons fragmentation
  function Dq?h(z)

Leading hadron
Q2
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jT and kT

• jT Momentum perpendicular to jet axis jT pT
  sinDf
• ltjTgt is related to the non-perturbative QCD.
• Typical value is 500 MeV/c, very weakly depends
  on pT and ?s.

• Jets are not exactly back-to-back in transverse
  direction
• kT Intrinsic radiative transverse momentum of
  the initial partons.

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Same jet correlation
Projected to azimuth plane
ftq trigger-parton faq associated-parton fta
trigger-associated
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Far side jet correlation

• ,fqq is the angle between the jets.

Projected to azimuth plane
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jT, kT RMS values

• Pout is directly related to the angular width

(for Gauss statistics)

• 1D RMS value

• Comparing with Jans formula

(QM2004)
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Comparison using Pythia simulation

• Trigger ptgt5 GeV/c, change associated pT

Jans formula
This formula
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kT Broadening in dAu

• Presence of cold medium can broaden the jet kT

pp
pA
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Is kT in dAu sensitive to broadening?

• Seems radiation contribution dominate over the
  broadening

I.Vitev
hep-ph/0310274
10 difference between dAu and pp for 4.5 GeV
trigger
the sensitivity on broadening decreases as pT
increases.
sfar not very sensitive to additional broadening
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Fragmentation function ? Conditional yield

• Direct jet reconstruction.

ee-
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Two particle azimuth correlation method

• In ideal acceptance, real pair distribution is

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Pair acceptance function ACC in PHENIX
Triangle results from convoluting two flat
distribution

• Shape from overlapping four triangles
• west1-west2, east1-east2, west1-east2, east1-west2

effi is 100 at Df0, Dh0 Average is 25
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Normalization for 2D and 1D CY

• 2D CY

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Test the correction with Pythia simulation

• Generate 1 M triggered events and 1 M minimum
  bias events.
• Mixed distribution is obtained by mixing trigger
  with minbias event.
• Requiring trigger always has hlt0.35.
• If we dont constrain associated particle, we
  would get full yield.

• Compare three correlations.
• No cut on associated particle ? full jet yield
  (near side)
• Near side jet has a gauss shape in Dh the
  integral of the gauss.
• Cut Dhlt0.7 on associated particle ? full yield
  in Dhlt0.7(away side)
• Far side jet has a very broad shape in Dh.
• PHENIX acceptance cut ? measured yield in near
  and away side.

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CY, with no constrain on associated particle

• Trigger pt gt 5 GeV/c, associated 1ltpT lt1.5 GeV/c
• Trigger hlt0.35, associated no eta cut.
• This gives the true conditional yield for the
  near side 0.717

True conditional yield
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CY, with associated particle in Dhlt0.7

• Trigger pt gt 5 GeV/c, 1ltpTasso lt1.5 GeV/c
• Trigger hlt0.35, and associated particle
  Dhlt0.7
• This gives the true conditional yield with in
  Dhlt0.7 for the far side 0.92

True conditional yield
Because the away side correlation is very wide in
Dh. We just want the yield in Dhlt0.7, which is
the range sampled by PHENIX.
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Conditional yield in PHENIX acceptance

• Trigger pt gt 5 GeV/c, 1ltpTasso lt1.5 GeV/c
• Trigger hlt0.35, and associated hlt0.35.
• Azimuth acceptance cut on both particles..
• This gives the Measured conditional yield for
  same side and way side
• 0.279(near), 0.233(far).

Raw conditional yield
FG
MIX
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Corrected CY compared with true CY
Far side
Near side
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The ratio between true and corrected

• The agreement is good.
• This implies that our correction and
  extrapolation is valid.

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Summary

• Discuss the general formula for and
• Some difference from previously used formula,
  especially for kTz and low associated pT region.
• The sensitivity on kT dies out as the trigger pT
  increases.
• Discuss the how to extract the conditional yield
  using two particle correlation method and event
  mixing. The correction factor is derived for
  limited detector acceptance(can be trivially
  generalized to other detectors).
• Verified with Pythia simulation