single electron measurements at rhic-phenix t. hachiya hiroshima university for the phenix...
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Single Electron Measurements at RHIC-PHENIX
T. HachiyaHiroshima University
For the PHENIX Collaboration
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Motivation
• Charm is produced through mainly gluon-gluon fusion in heavy ion collisions
• Sensitive to gluon density in initial stage of the collisions
• Charm is propagated through hot and dense medium created in the collisions
• Energy loss of charms via gluon radiation can be seen. (PHENIX observed high pT suppressions in hadron measurements)
• Charm can be produced thermally at very high temperature
• Sensitive to state of the matter
• Charm measurements bring us an important baseline of J/ measurement
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Charm Measurement
Direct method:Reconstruction of D-meson(e.g. D0K).Very challenging withoutmeasurement of displaced
vertex
Indirect method:Measure leptons from semi-leptonic decay of charm.
This method is used by PHENIX at RHIC
c c
0DK
0D
K
+
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Electron Measurement
All charged tracks
BG
Net e±
e± real.
Electrons are measured by DC→PC1→RICH→EMCal
Electron Identification : Cherenkov light in RICH
Number of Hit PMT Ring shape
Energy – Momentum matching
e+
EM Calorimeter
PC2
Mirror
PC3
RICH
PC1
DC
X
Cherenkov light in RICH
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Photon conversions :
Dalitz decays of 0,,’,,0ee, ee, etc) Kaon decays Conversion of direct photons Di-electron decays of ,, Thermal di-leptons
Most of the background are PHOTONIC
Source of Electrons
Background
Charm decays Beauty decays
Those are Non-PHOTONIC signal
Signal
0 e+e-
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PHENIX Run 2
Amount of data • 20 times larger statistics
All detectors work in Central arm spectrometers• Acceptance is 4 times as large
Special run with a photon converter 1.7 % radiation length of brass and placed around beam pipe The converter can increase electrons only from photonic source by a fixed factor By comparing the data with and without the converter, We can separate electron from non-photonic and photonic source
Complementary to cocktail method
Photon Converter
e+
e-
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Photon Converter Method
Single electron spectra : • data with the converter• data w/o the converter
If all electrons are from photonic source, the ratio is constant.But the data shows that electron yield approach at high pT each other.
It is an evidence for non-photonic electrons
Ne
0
1.1% 1.7%
Dalitz : 0.8% X0 equivalent
0
With converter Conversion in converter
W/O converter Conversion from pipe and MVD
0.8%
Non-photonic
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Electrons from Non-photonic Source
• Back ground subtracted single electron spectra at sNN=200GeV
• 200GeV data is higher than 130GeV data.• Spectral shape at 200GeV is similar to that at 130GeV• The data is in good agreement with PYTHIA calculation
cc(130GeV)=330 b
cc(200GeV)=650 b
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Centrality Dependence
Single electrons in each centrality class are in reasonable agreement with PYTHIA calculation scaled by binary collision
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Observations• Our data is consistent with binary scaling within our current statistical and systematic uncertainties. • NA50 at SPS has inferred a factor of ~3 charm enhancement from intermediate mass di-muon measurement. We do not see this large effect at RHIC.• PHENIX observes a factor of ~3-5 suppression in high pT 0 relative to binary scali
ng. We do not see this large effect in the single electrons. • Initial state high pt suppression excluded?• smaller energy loss for heavy quark ? (dead cone effect)
NA50 - Eur. Phys. Jour. C14, 443 (2000).
N part
En
ha
nce
me n
t o
f O
pe
n C
har
m Y
ield Binary Scaling
PHENIX Preliminary
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Summary & Outlook
PHENIX measured single electrons from non-photonic source at sNN=130GeV and 200GeV The single electrons are in good agreement with PYTHIA charm calculation using number of binary collision scaling within current statistic and systematic uncertainties
Refine the converter method and cross-check by the cocktail calculation Finalize single electron spectra from non-photonic source Comparison to single electron in p+p and d+Au at sNN=200GeV (RHIC Run2 and Run3)
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Inclusive Electrons at s=130GeV
1.5M M.B. events are analyzed.
The back ground from random association is estimated by event mixing method
Spectra are fully corrected with acceptance and efficiency loss
Back ground electrons fromphotonic source are included
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conversion
0 ee
ee, 30
ee, 0ee
ee, ee
ee
’ ee
Cocktail Calculation
pT distribution of 0 are constrained with PHENIX 0 and measurement
• pT spectra of , ’ and are
estimated with mT scaling pT = sqrt(pT
2 + Mhad2 – M2)
• Hadrons are relatively normalized by 0 at high pT from the other measurement at SPS, FNAL, ISR, RHIC
• Material in acceptance are studied for photon conversion
Signal above cocktail calculation can be seen at high pT
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Data / Background Ratio of Electrons
• conversions and 0 dalitz are ~ 80% of photonic source• is ~ 20%• Contribution from the other hadrons are very small
Top figure shows data/background ratio in M.B event sample.
The data shows excess above background in pT > 0.6[GeV/c].
Most of the systematic uncertainty comes from single electron measurementand cocktail calculation.-> need reference point in run2
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Single Electron Spectra at sNN=130GeV
PYTHIA
direct (J. Alam et al. PRC 63(2001)021901)
b
c
PHENIX: PRL 88(2002)192303• Single electron spectra after background (photonic source) is subtracted for central and M.B collisions at sNN=130GeV
• Electrons from charm and beauty decays calculated by PYTHIA are overlaid -- PYTHIA parameter is tuned to fit low energy data -- scaled to Au+Au using number of binary collision.
• Charm in PYTHIA are in reasonably agreement with data (within relatively large uncertainty)
• The contribution from thermal dileptons and direct is neglected -- We may over-estimate the charm yield.
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Charm Cross Section
• Single electron cross section is compared with ISR data• Charm cross section is compared with fixed target charm data.
• Solid curve : PYTHIA• shaded Band : NLO pQCD
Assuming binary scaling, PHENIX data are consistent with s systematics (within large uncertainties)
By fitting the PYTHIA electron spectrum to the data for pt>0.8[GeV/c], we obtained charm yield Ncc per event. The charm cross section per binary NN collision is obtained as
TAA is nuclear overlap integral ~ NN integrated luminosity per eventTAA(0-10%)=22.6±1.6/mb TAA(0-92%)=6.2±0.4/mb
Charm cross section derived from the single electron
ccAA
ccN
T
1
0 10%cc 380 60 200 b and 0 92%
cc 420 33 250 b
PHENIX
PYTHIA ISR
NLO pQCD (M. Mangano et al., NPB405(1993)507)
PHENIX: PRL 88(2002)192303
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Cocktail Calculation
pT distribution of 0 are constrained with PHENIX 0 and measurement
• pT spectra of , ’ and are
estimated with mT scaling pT = sqrt(pT
2 + Mhad2 – M2)
Systematic uncertainty in cocktail calculation is assigned 50 % in each ratio
PHENIX DATA
Data Systematic errorsRun1 11%Run2 12%
Meson Meson/ pi0 at high pT0.550.251.001.000.40
ηη'ρωφ
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Photon conversions :
Dalitz decays of 0,,’,,0ee, ee, etc) Kaon decays Conversion of direct photons Di-electron decays of ,, Thermal di-leptons
Most of the background are PHOTONIC Charm decays Beauty decays
Those are Non-PHOTONIC signal
Source of Electrons
Background
Signal
0 e+e-
conversion
0 ee
ee, 30
ee, 0ee
ee, ee
ee
’ ee
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Outline
Motivation Charm and electron measurements PHENIX experiment: how to measure electrons Run-1: Au + Au @ sNN = 130 GeV
single electrons from charm decays (c D e + X) Run-2: Au + Au @ sNN = 200 GeV
single electrons refined Summary and outlook
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PHENIX Experiment
Two central spectrometers , e and hadrons Coverage:
• || < 0.35• = /2 2
M.B. Trigger and Centrality • Beam Beam Counter• Zero Degree Calorimeter
Collision vertex• Beam Beam Counter
BBC
DC&PC
RICH
EMCAL