Transcript PowerPoint 演示文稿 - Wayne State University

The Study of D and B Meson Semileptonic Decay Contributions to the
Non-photonic Electrons
Xiaoyan Lin
CCNU, China/UCLA
for the STAR Collaboration
22nd Winter Workshop on Nuclear Dynamics 11-19 Mar. 2006
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Outline
 Motivation
Why study this?
 Simulation
PYTHIA p+p Collisions at sNN = 200 GeV
 Real Data Analysis
Electron Identification
Photonic Electron Removal
Electron-Hadron Correlation
 Outlook
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Motivation
• The present non-photonic
electron RAA data is a challenge
to the existing theoretical
calculations of heavy quark
energy loss in the medium
produced at RHIC.
• The separation of B and D
meson decay contributions to
the non-photonic electrons will
help to fully understand the
energy loss mechanism for
heavy quarks.
Armesto et al. hep-th/0511257, van Hess et al. nucl-th/0508055
DVGL theory from nucl-th/0507019 nucl-th/0512076
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PYTHIA Simulation: Parameter Setup
Charm quark pt distributions
Start with the parameter set (refer it as
set I) --- <kt> = 1.5, mc = 1.25, K factor
= 3.5, PDF = CTEQ5L, PARP(67) = 1.
( from PHENIX Collaboration, Phys.
Rev. Lett. 88, 192303(2002))
Further tune PARP(67) to 4 (refer it as
set II). In PYTHIA it is to account for
higher order pQCD effect. It allows for
gluon splitting and can effectively
reproduce NLO calculation.
The existent measurements have no
constraint on the D meson production
at high pt. The c-quark spectra from
both of these two sets of parameters
match the measured data.
NLO pQCD predictions from R. Vogt, Int. J. Mod. Phys. E12 (2003) 211
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PYTHIA Simulation: Parameter Setup
Charmed hadron pt distributions
The default Peterson
fragmentation function (ε =
0.05) is too soft to reproduce
the measured spectrum.
• Modified Peterson function
to make the fragmentation
function harder. ε = 10-5 is
used.
• PYTHIA calculation with
modified Peterson function
using both of these sets of
parameters can reasonably
depict the measured open
charm data.
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PYTHIA Simulation: Parameter Setup
Non-photonic electron pt distribution
(STAR Prelim.)
(STAR Prelim.)
• Electron spectra from PYTHIA
calculation with modified
fragmentation using both of these
two parameter sets are consistent
with the STAR measured data.
• In PYTHIA calculation with
parameter set II, b quark decays are
not dominant for pt up to 8 GeV/c
while in the calculation with
parameter set I b contribution is not
dominant for pt up to 6 GeV/c.
• The STAR open charm data and
non-photonic electron data are
consistent within our PYTHIA
calculation.
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PYTHIA Simulation: e-h correlation
Δφ Distribution
D
B
• Trigger: electron
Association: charged hadron
• The Δφ distributions change
slightly from PYTHIA
calculations with parameter set II
to parameter set I.
• When the electron pt range
goes higher, the peaks centered
at zero become narrower and
higher.
• The peaks centered at zero
from D decay are much narrower
than those from B decay.
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PYTHIA Simulation: e-h correlation
Summed pt of charged hadrons distribution
• The summed pt is the sum of charged hadron pt within a cone of triggered
high pt electrons.
• The cone is defined by |ηh - ηe| < 0.35 and |φh - φe| < 0.35.
• The summed pt distributions do not
change significantly between the
parameter set II and the parameter set
I.
• The distributions from D decay are
much wider than those from B decay.
• When electron pt range goes higher,
the distributions become broader.
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PYTHIA Simulation: B contribution
The B contribution to the non-photonic electrons can be determined
directly from the electron spectra.
• B contribution = (B decay electron yield)/(B+D decay electron yield)
• Remove those electrons which have no hadrons in the cone around them.
• This method is not experimentally feasible.
Electron pt (GeV/c)
parameter set II
parameter set I
2.5-3.5 3.5-4.5 4.5-5.5
8.33% 15.07% 23.23%
9.23% 16.58% 24.17%
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PYTHIA Simulation: B contribution
An experimental way to determine
the B contribution fraction.
• Use the summed pt histograms
from B decay and D decay to fit the
summed pt histogram from PYTHIA
inclusive , and let B contribution
fraction as a parameter.
• The contribution fraction is
determined by the minimum value of
χ2.
• The fitting error is determined by
one σ shift of χ2/ndf from the
minimum value.
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PYTHIA Simulation: B contribution
Electron pt (GeV/c)
2.5-3.5
3.5-4.5
4.5-5.5
parameter set II
8.33±2.17%
15.07±3.72%
23.23±5.89%
parameter set I
14.49±2.32%
17.74±4.02%
28.46±6.49%
8.33 %
9.23 %
15.07 %
16.58 %
23.23 %
24.17 %
• The results for PYTHIA calculation with parameter set II are consistent with those
directly from the electron spectra. This indicates the method we propose is selfconsistent.
• Use summed pt histograms of B and D decays from PYTHIA calculation with
parameter set II to fit the summed pt histogram of the inclusive case from
PYTHIA calculation with parameter set I.
• Comparing the results of PYTHIA calculation with parameter set I with those from
electron spectra, the results are consistent for the high pt ranges within fitting errors,
while for the pt range 2.5-3.5 GeV/c, the results are inconsistent.
• The inconsistency is due to the window size of Δφ. The low pt range is more
sensitive than the high pt range to the choice of window size of Δφ.
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Summary for Simulation
 We find that the charm quark fragmentation function
has to be harder than default Peterson function. A delta
fragmentation function scheme yields consistent result
with the STAR measurements.
 An experimental method using e-h correlation is
proposed based on PYTHIA calculation to
quantitatively determine the contributions from D and
B semi-leptonic decays.
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Real Data Analysis: Solenoidal Tracker At RHIC
• Signal: non-photonic electrons
Three detectors used in this analysis:
• Background: hadrons and
photonic electrons (photon
conversion and π0 Dalitz decays, • Time Projection Charmber (TPC)
etc.)
• Barrel Electro-Magnetic Calorimeter (BEMC)
• Barrel Shower Maximum Detector (BSMD)
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Real Data Analysis: BEMC
• 0 <φ< 2π
• -1<η<1
• 120 calorimeter modules
• 40 towers for each module
• Energy resolution~16%/E
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Real Data Analysis: BSMD
• Provide high
spatial resolution
• Measure the
position of the
shower
• Measure the size
of the shower
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Real Data Analysis: Data Set
200 GeV pp year 5 data
Event cut: |Z| < 30 cm
About 9M events were used
1.3M HT One events
0.87M HT Two events
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Electron Identification
In this part of analysis, about 2.9M pp events were analyzed.
dEdx
NFitPts [20,50)
NdEdxPts [15,100)
Chi square [0,3.0)
NFitPts/NMaxPts
[0.52, 1.2)
Eta [-0.7, 0.7)
dEdx cut:
(0σ, 3σ)
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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.
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Electron Identification
Distance between Projection point and EMC Point
< ZDist < 3σ and -3σ < PhiDist < 3σ were set to remove lots
of random associations between TPC tracks and BEMC points.
• -3σ
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Electron Identification
Number of BSMD hits
• Electrons have larger number of BSMD hits than those for hadrons.
• Electron candidates have to satisfy Number of BSMD hits > 1.
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The purity of Electron sample
The electron purity > 99%!
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Photonic Background
• Global info. is used.
• The invariant mass for a pair
• The cut for the partner only is dEdx within 3σ
on electron band.
of photonic electrons is small.
• Dca between two tracks less than 1cm.
• Angle between two tracks less than 0.1. Angle
in eta plane less than 0.02 and angle in phi plane
less than 0.1
• A cut less than 100MeV is
chosen.
• No worry about the
combinatorial background!
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Electron-hadron Correlation
Cuts for hadron selection
NFitPts: [15,50)
NFitPts/NMaxPts: [0.52,1.2)
Pt > 0.1 GeV/c
-0.75 < η < 0.75
Track Id different from electron track Id
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Electron-hadron Correlation
Δφ Distribution
Inc. E
Pho. E
2.5-3.5
GeV/c
2.5-3.5
GeV/c
Very preliminary!
Inc. E
Pho. E
3.5-4.5
GeV/c
3.5-4.5
GeV/c
Inc. E
Pho. E
4.5-5.5
GeV/c
4.5-5.5
GeV/c
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Electron-hadron Correlation
Summed pt of charged hadron Distribution
2.5-3.5 GeV/c
Inc. E
2.5-3.5 GeV/c
Pho. E
3.5-4.5 GeV/c
Inc. E
3.5-4.5 GeV/c
Pho. E
Very preliminary!
4.5-5.5 GeV/c
Inc. E
4.5-5.5 GeV/c
Pho. E
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Outlook
 The largest uncertainty in STAR is the background
from photon conversion in materials before the TPC.
 To calculate the photonic background removal
efficiency.
 To get the results for the non-photonic electrons
 Compare to PYTHIA simulation.
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