Study B and D Contributions to Nonphotonic Electrons via Azimuthal
Correlations between NonPhotonic Electrons and
Charged Hadrons
Xiaoyan Lin
林晓燕
(for the STAR Collaboration)
Central China Normal University
Wuhan, P.R. China
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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Outline
 Motivation
 Data analysis
---- Electron identification
---- Photonic electron background
---- Electron-hadron correlations
 Preliminary results of B/(B+D)
 Summary
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
2
Features in Heavy Quark Measurements at RHIC
----Non-Photonic Electron RAA
Heavy quark RAA has
the similar magnitude
as light quark RAA.

The high pT region
non-photonic electron
RAA is surprising !

Where is the bottom
contribution?

Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
3
Features in Heavy Quark Measurements at RHIC
----Non-Photonic Electron v2

Reduction of v2 at
pT > 2 GeV/c.
Bottom contribution??
The decay kinematics of
D and B mesons are
different!

Y. Zhang, hep-ph/0611182
PYTHIA
The same D and B v2 can
lead to very different nonphotonic electron v2 !

Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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B and D Contributions to Electrons
Quantitative understanding of features in heavy quark
measurements requires experimental measurement of B
and D 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 vertex detector upgrade!
See Talk by Andrew Rose (1.4)

Poor (wo)man’s approach to measure B/D
contributions to non-photonic electrons
---- e-h correlations
X.Y. Lin, hep-ph/0602067
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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PYTHIA Simulation of e-h Correlations
 Associated
pT >
0.3 GeV/c.
 Significant
difference in the
near-side
correlations.
 Width of nearside correlations
largely due to
decay kinematics.
B
D
X.Y. Lin, hep-ph/0602067
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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Major Detectors Used
Signal:
Non-photonic
electron
Charm decay
Bottom decay
Background:
Photon conversion
Hadron
π0 Dalitz decay
Photonic electron η Dalitz decay
kaon decay
vector meson decays
Data Sample:
p+p collisions at sNN = 200 GeV in
year 5 run.

Time Projection Chamber (TPC)
2.37 million EMC HT1 triggered
events with threshold 2.6 GeV; 1.68
 Electro-Magnetic Calorimeter (EMC)
million EMC HT2 triggered events
 Shower Maximum Detector (SMD)
with threshold 3.5 GeV.
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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Electron ID Using TPC and EMC
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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Electron ID Using TPC and EMC

The purity of electron sample is above 98% up to pT ~ 6.5 GeV/c.
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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Photonic Background
m<100 MeV/c2
Electron candidates are combined with tracks passing a loose cut on dE/dx
around the electron band.
 The invariant mass for a pair of photonic electrons is small.

The combinatorial background is small in p+p collisions.
 Reconstructed photonic = Opposite sign – Same sign.
 Photonic electron = reconstructed-photonic/ ε. ε is the background
reconstruction efficiency calculated from simulations.

Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
10
Procedure to Extract the Signal of e-h Correlations
All Tracks
Pass EID cuts
Inclusive electron
Non-photonic electron
Photonic electron
Reco-photonic electron
=OppSign - combinatorics
Not-reco-photonic electron
=(1/eff-1)*(reco-photonic)
Semi-inclusive electron
Signal:
non-photonic = semi-inclusive +combinatorics-(1/eff-1)*reco-photonic
 Each item has its own corresponding Δφ histogram.

Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
11
e-h Azimuthal Correlations after Bkgd. Subtraction
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
12
Use PYTHIA Curves to Fit Data Points
B
D
Fit function: R*PYTHIA_B+(1-R)*PYTHIA_D
 R is B contribution, i.e. B/(B+D), as a parameter in fit function.

Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
13
Use PYTHIA Curves to Fit Data Points

B/(B+D) consistent varying fit range.
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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Preliminary Results: B Contribution .VS. pT
Error bars are statistical only!
 Data uncertainty includes statistic
errors and systematic uncertainties
from:
---- photonic background
reconstruction efficiency (dominant).
---- difference introduced by
different fit functions.
 Preliminary data is within the
range that FONLL calculation
predicts.
 Non-zero B contribution is
observed.

Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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Summary
 Non-photonic electron and charged hadron
correlations are sensitive to D and B contributions to
non-photonic electrons.
 We have measured e-h correlations in 200 GeV p+p
collisions.
 The preliminary data indicates at pT ~ 4-6 GeV/c the
measured B contribution to non-photonic electrons is
comparable to D contribution based on PYTHIA model.
 Our measurement of B/(B+D) provides a constraint to
the FONLL prediction.
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
16
Backup slides
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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Method to Extract the Signal of e-h Correlations
non-pho. e = semi-incl. e +combinatorics - not-reco-pho.
= semi-incl. e +combinatorics - (1/eff-1)*reco-pho.
Δφnon-pho = Δφsemi-inc + Δφcombinatorics - Δφnot-reco-pho
= Δφsemi-inc + Δφcombinatorics - (1/eff -1) *Δφreco-pho-no-partner
Note Δφnot-reco-pho = (1/eff -1) *Δφreco-pho-no-partner! Δφreco-pho-no-partner is the reco-pho
after removing the conversion partner.
 The photonic background has two parts: reco-pho and not-reco-pho. In electron
yield or v2 analysis, the not-reco-pho part can just be calculated by reco-photonic
part after an efficiency correction, i.e. not-reco-photonic = (1/eff-1)*reco-pho.
 However, in e-h correlation analysis, that is different. The reco-pho electron means
we find the conversion partner, while the not-reco-pho electron means we miss the
conversion partner. The resulting e-h correlations for these two parts are different. If
we use reco-pho part to calculate the not-reco-pho part, we have to remove the
conversion partner of reco-pho part.

Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
18
The distributions of ChiSquare .VS. ratio_B
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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The distributions of ChiSquare .VS. ratio_B
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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Preliminary Results: B Contribution .VS. pT
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
21
Electron Identification: Projection Distance
-3σ < z distance < 3σ and -3σ < φdistance < 3σ were set to
remove lots of random associations between TPC tracks and
BEMC points.
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
22
PYTHIA Simulation: e pT .VS. parent pT
 C-quark needs to have larger momentum than b-quark
to boost the decayed electron to high pT.
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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PYTHIA Simulation: e pT .VS. hadron pT
 The efficiency of associated pT cut is different between D
decay and B decay. Therefore, it is better to use lower pT cut
on the associated particles in order to avoid analysis bias!
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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PYTHIA Simulation: e pT .VS. hadron pT
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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PYTHIA parameters used in this analysis
PYTHIA version: v6.22
δ fragmentation function used for both charm and bottom.
Parameters for charm:
PARP(67) = 4 (factor multiplied to Q2)
<kt> = 1.5 GeV/c
mc = 1.25 GeV/c2
Kfactor = 3.5
MSTP(33) =1 (inclusion of K factor)
MSTP(32) = 4 (Q2 scale)
CTEQ5L PDF
Parameters for bottom are the same as for charm except
mb = 4.8 GeV/c2.
X.Y. Lin, hep-ph/0602067
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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Near-side width due to decay kinematics
All hadrons
with δ
fragmentation
function
Xiaoyan Lin
Hadrons
from D
Background
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
27
Near-side width does not strongly depend on FF
2.5-3.5 GeV/c
4.5-5.5 GeV/c

3.5-4.5 GeV/c
5.5-6.5 GeV/c
Will be included in the systematic uncertainties in the future.
Xiaoyan Lin
Quark Matter 2006, Shanghai, Nov. 14-20, 2006
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