open heavy flavor measurements at phenix y. akiba (riken) for phenix nov. 2, 2007 lbnl heavy quark...
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Open heavy flavor measurements at PHENIX
Y. Akiba (RIKEN)for PHENIX
Nov. 2, 2007LBNL Heavy Quark Workshop
Outline• Single electron measurements
– Details of the analysis– Cross section in pp– Spectra in AuAu and RAA– v2
• Single muon (New)– Method– result
• b/c ratio from e-h charge correlation (New)– Method– result
• D0 K- + 0 (New)• Summary
3
c c
0D
Indirect Measurement via Semileptonic decays
0DK
+
K
Heavy Quark Measurement
Direct Measurement:DK, DK
PHENIX single e measurementsPublished• Au+Au 130 GeV
– PRL88,192303(2002) First charm measurement at RHIC
• Au+Au 200 GeV– PRL94,082301(2005) Ncoll scaling of total charm yield– PRL96,032301(2006) Observation of suppression at high pT– PRC72,024901(2005) First measurement of v2(e)– PRL98,172301(2007) High statistic RAA and v2; /s
• p+p 200 GeV– PRL96,032001(2006) First pp baseline measurement– PRL97,252002(2006) High statistic pp baseline
Preliminary• d+Au 200 GeV
– QM2004 Ncoll scaling
• Au+Au 62 GeV
Inclusive e± measurement: roadmap• PHENIX central arm coverage:
– || < 0.35
– = 2 x /2
– p > 0.2 GeV/c
– typical vertex selection: |zvtx| < 20 cm
• charged particle tracking analysis using DC and PC1
• electron identification based on– Ring Imaging Cherenkov detector
(RICH)
– Electro-Magnetic Calorimeter (EMC)
e-
Electron identification
• Electron identificaition is very easy for pT<5 GeV/c
• After RICH hit is required, basically all tracks are electrons
• Electron signal is clearly visible in E/p ratio distribution (the peak ~ 1 is electron)
• The tail part is due to off vertex conversion and Ke3 decay.
• MC reproduces the distribution very well.
• In the plots, the data and the MC are absolutely normalized
Ke3 decay BG(MC)
0 Dalitz and Conversion (MC)
MC (0+Ke3)
Data
MC (0+Ke3)
Data
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Electron Signal and Background
Photon conversions → → e+ e- in materialMain backgroundDalitz decays→ e+ e- Direct PhotonSmall but significant at high pT
Measured by PHENIX
Heavy flavor electronsD → e± + X
Weak Kaon decaysKe3: K± → e± e < 3% of non-photonic in pT > 1.0 GeV/c
Vector Meson DecaysJ → e+e-< 2-3% of non-photonic in all pT
Photonic electron Non-photonic electron
Background is subtracted by two independent techniques:
• Cockail Method
• Converter method
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Most sources of backgroundhave been measured in PHENIX
Decay kinematics and photon conversions can be reconstructed by detector simulation
Then, subtract “cocktail” of all background electrons from the inclusive spectrum
Advantage is small statistical error.
Background Subtraction: Cocktail Method
Inclusive vs cocktail
pT (GeV/c)
Cocktail calculation
Inclusive electrons
Inclusive – cocktail = heavy flavor signal
Converter subtraction: idea • introduce additional
converter in PHENIX acceptance for a limited time– 1.68 % X0 brass foil close
to beam pipe– increases yield of photonic
electrons by a fixed factor– comparison of spectra
with and without converter installed allows to separate electrons from photonic and non-photonic sources
e+
e-
γ
p
p e+
e-Converter
Photon Converter
Reality
Converter subtraction: the calculation• electron yields:
• useful definitions:
• then:
nonee
outConve NNN
non
eeinConv
e NNRN )1(
outConve
inConveCN NNR /
e
noneNP NNR /
NP
NPCN R
RRR
1
)1(
measured
simulated
calculated from
this equation!
PRL 94(2005)082301 (run2 AuAu)
RCN in p+p Run-5
• RCN is ratio of “raw” electron spectra!
• signal/background is LARGE (see next slide) and increases as function of pT!
RExpected forPure photonic
Measured RCN
Non-photonic signal
Cross-check: Cocktail vs Photonic (measured)
pT(GeV/c)
Red:Measured photonic electron spectrum using the converter method
Curve:Cocktail calculation
Photonic electronMeasured/Cocktail=0.94±0.04
Consistent within cocktail systematic error Used to re-normalize cocktail
Singnal/Backgroud of Heavy Flavor electrons
• S/B = 0.1 to ~3 • Large S/B is due to small conversion material in PHENIX
acceptance
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Run-5 p+p Result at s = 200 GeVHeavy flavor electroncompared to FONLL
Data/FONLL = 1.71 +/- 0.019 (stat) +/- 0.18 (sys)
FONLL agrees with datawithin errors
All Run-2, 3, 5 p+p data areconsistent within errors
Total cross section of charmproduction: 567 b+/- 57 (stat) +/- 224 (sys)
PRL97,25
Upper limit of FONLL
Total Charm Crossection
)(224)(57567 systbstatCC New charm total crossection:
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Run-4 Au+Au Result at sNN = 200 GeV
Heavy flavor electroncompared to binary scaledp+p data (FONLL*1.71)
Clear high pT suppression in central collisions
S/B > 1 for pT > 2 GeV/c
(according to inside figure)
Submitted to PRL (nucl-ex/0611018)
MB
p+p
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Nuclear Modification Factor: RAA
Suppression level is the almost same as 0 and in high pT region
Total error from p+p
Binary scaling works well for p’T>0.3 GeV/c integration (Total charm yield is not changed)
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Elliptic Flow: v2
Non-zero elliptic flow for heavy-flavor electron → indicates non-zero D v2
Kaon contribution is subtracted
Elliptic flow: dN/dφ N∝ 0(1+2 v2 cos(2φ)) Collective motion in the medium
v2 forms in the partonic phase before hadrons are made of light quarks (u/d/s)
→ partonic level v2
If charm quarks flow, - partonic level thermalization - high density at the early stage of heavy ion collisions
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RAA and v2 of Heavy Flavor Electrons
PRL, 98, 172301 (2007) Only radiative energy loss model can not explain RAA and v2 simultaneously.
Rapp and Van HeesPhys.Rev.C71:034907,2005
Simultaneously describes RAA and v2 with diffusion coefficient in range: DHQ × 2πT ~ 4 – 6
Assumption: elastic scattering is mediated by resonance of D and B mesons. They suggest that small thermalization time τ(~ a few fm/c) and/or DHQ.Comparable to QGP life time.
Heavy flavor measurement by single muons
• PHENIX can measure open heavy flavor in forward rapidity via single muons
• So far, results from RUN2 pp at 200 GeV is published.– Relatively large systematic
unceratinties– Limited statistics
• new analysis of RUN5pp data is on going with better systematic uncertainties and higher statistics
hep/ex0609032 PRD in proof
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Dominant sources of tracks in the muon arm0 1 2 3 4Gap:Muon from heavy flavor
(the signal)
A low energy muon that ranges out due to ionization energy loss (primarily hadron decay muons)
Hadron (does not interact and punches through the entire detector)
A muon from hadron decay
An interacting hadron (nuclear interaction)
PHENIX Detector
Analysis by D. Hornback (U. Tennessee)
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Methodology of this single muon analysis0 1 2 3 4Gap:
Simultaneous matching of background hadron cocktail and data:
1. of measured stopped hadrons in gaps 2 and 3
2. and of z-vertex distributions for gap 4 muons from hadron decay
The ~10λ of steel is a problem however.
PHENIX Detector
Momentum (GeV/c)
Momentum (GeV/c)
2 3 4 5 6
2 3 4 5 6
Raw
Cou
ntR
aw C
ount
Muons above 2.7 GeV/c punchthrough the entire detector.
hadrons
“stopping” muons and hadrons
Tracks stopping in Gap 3
Tracks stopping in Gap 2
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matching hadrons for simulation and data
≡1 by definition
≈1 for a a good hadron shower code
A cocktail of hadrons are fully simulated in the muon arm.This background estimate is normalized to match data at gap 3.
Gap 3 stopped hadron yield
Gap 2 stopped hadron yield
25
matching z-vertex distributions at gap 4in
varia
nt y
ield
inva
riant
yie
ld
Z (cm)Z (cm)
ppTT=1.0-1.25=1.0-1.25 ppTT=1.25-1.5=1.25-1.5
ppTT=1.5-1.75=1.5-1.75 ppTT=1.75-2.0=1.75-2.0
ppTT=2.0-2.25=2.0-2.25 ppTT=2.25-2.5=2.25-2.5
ppTT=2.5-2.75=2.5-2.75 ppTT=2.75-3.0=2.75-3.0
Black: data
Red and green:pion/kaon components
Matching z-vertex distribution slopes → proper hadron decay muon determination
Blue:total cocktail
Heavy flavor muon invariant cross section• p+p at 200 GeV. Run5 prelimianry result
Comparison with RUN2 results
• The new RUN5 muon data is somewhat lower than the RUN2 results (nucl-ex/0609032; accepted in PRD)
run2
Comparison with electron data
• Observed cross sections are similar to that of electron at y~0• Data/FONLL ratio is ~ 2 for high pT
Measurement of b/c ratiovia
electron-hadron charge correlation
30
c c
0D
K
Using the charge correlation to measure ceSo far we do not separate ce and be components of heavy-flavor electrons.
Here we separate ce component using the charge correlation of K and e from D-meson decay.
If D-meson decays into charged kaon and electron, their charges are opposite:
Thus one can determine the fraction of ce component by measuring the fraction associated with opposite sign kaon, or opposite sign charged hadron
Charged kaon and lepton from D decayhas opposite charge
XeKD
XeKD
Actual analysis is done as e-h charge correlation (i.e. no kaon PID) for higher statistic
Details of the Analysis
Ntag = Nunlike - N like
unlike sign e-h pairs contain large background from photonic electrons.like sign pair subtraction (Ntag is from semi-leptonic decay)
From real data analysisNc(b)e is number of electronsfrom charm (bottom)Nc(b)tag is Ntag from charm (bottom)
From simulation (PYTHIA and EvtGen)
data can be written by only charm and bottom component
The tagging efficiency is determined only decay kinematics and the production ratio of D(B)hadrons to the first order(85%~).
Main uncertainty of c and b •production ratios (D+/D0, Ds/D0 etc)•contribution from NOT D(B) daughters
Analysis by Y. Moritno
charm productionbottom productioncharm c = 0.0364 +- 0.0034(sys)bottomb = 0.0145 +- 0.0014(sys)
Details of the Analysis(2)
unlike pairlike pair
From real data
Electron pt 2~5GeV/cHadron pt 0.4~5.0GeV/c
countX 1/Nnon-phot e
data
0.029 +- 0.003(stat) +- 0.002(sys)
From simulation (PYTHIA and EvtGen (B decay MC) )
Electron pt 2~5GeV/cHadron pt 0.4~5.0GeV/c
unlike pairlike pair
(unlike-like)/# of ele
After like-sign subtraction
Charge correlation in b-decay and/or for high mass are due to charge conservation
Resulttheoretical uncertaintyis NOT included.comparison of data with simulation
(0.5~5.0 GeV)
pt(e) 2~5GeV/c2 /ndf 58.4/45 @b/(b+c)=0.34
Yield of (unlike-like) in the data is between the expectation of ce and beExtract b/c ratio from the data/simulation comparison
Tagging efficiency as function of pT
• If electrons are purely from charm decay, tagging efficiency should increase with increasing electron pT.
• The tagging efficiency of pure b-decay is small and almost constant. The data is in between, indicating that the b fraction increase with pT.
Yie
ld o
f (u
nlik
e –
like)
had
ron
p
er le
adin
g e
lect
ron
Result: b/(b+c) ratio as function of pT(e)
(b max) and (c min)
(b min) and (c min)
(b min) and (c max)
(b max) and (c max)
FONLL: Fixed Order plus Next to Leading Log pQCD calculation
Summary of e-h correlation analysis• be/(ce + be) has been studied in p+p collisions at
√s =200GeV(RUN5)• Invariant mass distributions of simulation agree well with
the data.• Experimental result is somewhat higher than FONLL
calculation (almost consistent)
Outlook• Extension of the analysis for higher pT (pT(e)>5 GeV/c)• RUN6 analysis for more statistics(~X3).
Measurement of DK
• Reconstruct D0K+ - 0 decay in pp
• 0 identified via 0 decay
• No charged hadron pid.
• Advantages of D0K+ - 0
mode:– Relatively large BR (14.1%)– Can be triggered by 0
c
0DK
+
Direct Measurement:DK
0
Trigger EMCal Trigger
Invariant Mass Distribution• Year5 p+p s=200GeV data set is used• Observe 3 significant signal in pT D range 5 ÷ 15 GeV/c• No clear signal is seen for pT D < 5 GeV/c• The signal is undetectably small for pT D > 15 GeV/c
Analysis by S. Butyk (LANL)
Momentum Dependence
• Observe clear peak in all pT bins from 5 GeV/c to 10 GeV/c
• Fits are parabola + gaussian• Background is uniform within fitting
range• Mass is systematically lower then PDG
value Trying to resolve by improving momentum and energy calibration
Summary of DK analysis
• Clear peak of D0 meson observed in Run5 p+p data in D0K+ - 0 decay channel
• Signal statistic significantly enhanced by use of high momentum photon trigger
• Signal is measurable in 5 to 15 GeV/c pT bins• Analysis is under way to determine invariant cross
section for the production
Summary
• PHENIX has rich open heavy flavor measurement• Main work has done so far in single electron channel
– Observation of strong suppression of heavy flavor electrons– Observation of large v2 of heavy flavor electrons
• New analyses in pp– b/c measurement via e-h charge correlation– Single muon measurement– Direct observation of D K