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

7

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

8

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

15

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:

17

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

18

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)

19

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

20

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

22

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)

23

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

24

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