Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Azimuthal correlations between non-photonic electrons and charged hadrons in p+p collisions from STAR

Xiaoyan Lin

IOPP/UCLA

For the STAR Collaboration

MotivationElectron identificationPhotonic electron backgroundElectron-hadron correlationComparison to PYTHIA Summary

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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STARSTAR

Features in H-Q Measurements at RHIC

Heavy Quark RAA = Light Quark RAA

Curves: S. Wicks, et al, nucl-th/0512076

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Features in H-Q Measurements at RHIC

•Heavy Meson Flows !

•Note the decay kinematics of D and B mesons are different!

•Electrons from B decays cannot follow the B meson momentum direction as good as electrons from D decays!

Non-photonic electron V2

Curves: Greco, Ko, Rapp, PLB 595 (2004) 202

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Charm versus b quark contribution

Quantitative understanding of features in heavy quark measurements requires Charm versus b quark contributions to non-photonic electrons !

Such information should be best obtained from direct measurement of hadronic decays of charm and bottom mesons. This motivates the STAR and PHENIX vertex detector upgrade!

See Dr. Nu Xu’s talk.

Non-photonic electron and hadron correlations can help to estimate the C and B contribution !

X. Lin hep-ph/0602067

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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• Significant difference between D decays and B decays in the near-side correlations.

• The difference is largely due to decay kinematics, not the production dynamics.

• The large difference in the near-side Δφ between D and B mesons can help us to estimate relative B and D contributions to non-photonic electrons.

PYTHIA Simulation2.5<PT(trig)<3.5 GeV/c 3.5<PT(trig)<4.5 GeV/c 4.5<PT(trig)<5.5 GeV/c

Associated PT > 0.1 GeV/c

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Signal: Non-photonic electron

Background: HadronPhotonic electron

Major Detectors Used

•Time Projection Chamber (TPC)

•Electro-Magnetic Calorimeter (EMC)

•Shower Maximum Detector (SMD)

Charm decay

Bottom decay

Photon conversionπ0 Dalitz decayη Dalitz decaykaon decayvector meson decays

Data Sample:

About 20M p+p collisions at ssNN NN = 200 = 200

GeVGeV in year 5 run.in year 5 run.

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Electron Identification: dE/dx

• TPC can identify charged particles to some extent

• Two orders of magnitude more hadrons than electrons

• Additional information needed to identify electrons

(-0.4σ, 3.0σ)

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Electron Identification: P/E

• P is measured by TPC. E is the sum of the associated BEMC points’ energy measured by BEMC.

• Electrons will deposit almost all of their energy in the BEMC towers. 0.3 < P/E <1.5 was used to keep electrons and reject hadrons.

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Electron Identification: Shower Size

• Number of SMD hits per shower indicates shower size.

• Electrons have larger number of BSMD hits than those for hadrons.

• Electron candidates have to satisfy Number of BSMD hits > 1.

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Electron Identification: Projection Distance

• -3σ < ZDist < 3σ and -3σ < PhiDist < 3σ were set to remove lots of random associations between TPC tracks and BEMC points.

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Purity of Inclusive Electron Sample

electron pT purity

2.5-3.5 GeV/c 99.99%

3.5-4.5 GeV/c 99.34%

4.5-5.5 GeV/c 99.14%

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Photonic Background

• The combinatorial background is small.

• Reconstructed photonic electron is the subtraction.

• Photonic electron is the reconstructed-photonic/eff

• eff ~ 60-70% from simulation for pp year 4. Still working on progress for pp year 5.

M<100 MeV/c2

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Method to Extract the Signal of E-H Correlation • Start with Semi-Inclusive electron sample.

If tracks pass the electron identification cuts, then they are inclusive electrons. In this inclusive electron sample we throw away those electrons which satisfy the photon conversion condition. The sample remaining is called semi-inclusive electrons.

Semi-Inclusive = non-phtonic + not reconstructed-photonic - combinatorics

• Combinatorics can be estimated by Same-Sign.

• Not reco-photonic = photonic – reco-photonic = (1/eff – 1) (reco-photonic). For the e-h correlation analysis, we have to remove the photonic partner of the reco-photonic.

• Δφnon-pho = Δφsemi-inc + Δφcombinatorics - (1/ε -1) (Δφopp-sign-NoPartner -

Δφsame-sign-NoPartner)

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Δφ Distributions2.5<PT(trig)<3.5 GeV/c 3.5<PT(trig)<4.5 GeV/c 4.5<PT(trig)<5.5 GeV/c

Associated PT > 0.1 GeV/c

Semi-incSemi-inc

Combinatorics Combinatorics

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Δφ Distributions2.5<PT(trig)<3.5 GeV/c 3.5<PT(trig)<4.5 GeV/c 4.5<PT(trig)<5.5 GeV/c

Opposite-Sign Opposite-Sign

Same-Sign Same-Sign

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Comparison to PYTHIA SimulationAssume the photonic b.g. reconstruction efficiency is 70%

• At low pT 2.5 - 3.5 GeV/c, the preliminary data indicates D contribution is dominate.

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Comparison to PYTHIA SimulationAssume the photonic b.g. reconstruction efficiency is 70%

• At high pT 4.5-5.5 GeV/c , the preliminary data indicates D contribution is larger than B.

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Summary

We find that non-photonic electron and hadron correlations are sensitive to D and B contributions.

The preliminary data indicates D contribution is larger than B contribution up to PT ~ 5.5 GeV/c.

To quantitatively estimate B contribution, we need more study on the background, photonic electron reconstruction efficiency…

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Back up slides

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Photonic b.g. reco. efficiency uncertainty

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Photonic b.g. reco. efficiency uncertainty

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Photonic b.g. reco. efficiency uncertainty

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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Width of near-side peak in PYTHIA simulation

electron Pt (GeV/c) 2.5-3.5 3.5-4.5 4.5-4.5

All hadrons

e from D decays

0.359±

0.003 0.29 ± 0.003

0.2532 ± 0.0042

Hadrons from D decays

e from D decays

0.3792 ± 0.0096

0.2992 ± 0.0098

0.2457 ± 0.0106

Xiaoyan Lin Hard Probes 2006, Asilomar, June 9-16

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