Open heavy flavor measurements at PHENIX Y. Akiba (RIKEN) for PHENIX Nov. 2, 2007 LBNL 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 D 0  K -  +  0 (New) Summary

3 Indirect Measurement via Semileptonic decays ++ Heavy Quark Measurement Direct Measurement: D  K , D  K 

PHENIX single e measurements Published 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 – QM2004Ncoll 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: |z vtx | < 20 cm charged particle tracking analysis using DC and PC1 electron identification based on –Ring Imaging Cherenkov detector (RICH) –Electro-Magnetic Calorimeter (EMC) e-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 material Main background Dalitz decays    →  e + e - Direct Photon Small but significant at high p T Measured by PHENIX Heavy flavor electrons D → e ± + X Weak Kaon decays K e3 : K ± →   e ± e 1.0 GeV/c Vector Meson Decays  J  → e + e - < 2-3% of non-photonic in all p T Photonic electron Non-photonic electron Background is subtracted by two independent techniques: Cockail Method Converter method

8 Most sources of background have 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 p T (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 % X 0 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+ e-e- γ p p e+ e- Converter Photon Converter Reality

Converter subtraction: the calculation electron yields: useful definitions: then: measured simulated calculated from this equation! PRL 94(2005) (run2 AuAu)

R CN in p+p Run-5 R CN is ratio of “raw” electron spectra! signal/background is LARGE (see next slide) and increases as function of p T ! R  Expected for Pure photonic Measured R CN Non-photonic signal

Cross-check: Cocktail vs Photonic (measured) p T (GeV/c) Red: Measured photonic electron spectrum using the converter method Curve: Cocktail calculation Photonic electron Measured/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 GeV Heavy flavor electron compared to FONLL Data/FONLL = / (stat) +/ (sys) FONLL agrees with data within errors All Run-2, 3, 5 p+p data are consistent within errors Total cross section of charm production: 567  b+/- 57 (stat) +/- 224 (sys) PRL97,25 Upper limit of FONLL

Total Charm Crossection New charm total crossection:

17 Run-4 Au+Au Result at  s NN = 200 GeV Heavy flavor electron compared to binary scaled p+p data (FONLL*1.71) Clear high p T suppression in central collisions S/B > 1 for pT > 2 GeV/c (according to inside figure) Submitted to PRL (nucl-ex/ ) MB p+p

18 Nuclear Modification Factor: R AA Suppression level is the almost same as  0 and  in high p T 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: v 2 Non-zero elliptic flow for heavy-flavor electron → indicates non-zero D v 2 Kaon contribution is subtracted Elliptic flow: dN/dφ ∝ N 0 (1+2 v 2 cos(2φ)) Collective motion in the medium v 2 forms in the partonic phase before hadrons are made of light quarks (u/d/s) → partonic level v 2 If charm quarks flow, - partonic level thermalization - high density at the early stage of heavy ion collisions

20 R AA and v 2 of Heavy Flavor Electrons PRL, 98, (2007) Only radiative energy loss model can not explain R AA and v 2 simultaneously. Rapp and Van Hees Phys.Rev.C71:034907,2005 Simultaneously describes R AA and v 2 with diffusion coefficient in range: D HQ × 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 D HQ. 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/ex PRD in proof

22 Dominant sources of tracks in the muon arm Gap: 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 analysis Gap: 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

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 yieldGap 2 stopped hadron yield

25 matching z-vertex distributions at gap 4 invariant yield Z (cm) p T = p T = p T = p T = p T = p T = p T = p T = 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/ ; 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 ratio via electron-hadron charge correlation

30 Using the charge correlation to measure c  e So far we do not separate c  e and b  e components of heavy-flavor electrons. Here we separate c  e 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 c  e component by measuring the fraction associated with opposite sign kaon, or opposite sign charged hadron Charged kaon and lepton from D decay has opposite charge Actual analysis is done as e-h charge correlation (i.e. no kaon PID) for higher statistic

Details of the Analysis N tag = N unlike - N like unlike sign e-h pairs contain large background from photonic electrons.  like sign pair subtraction (N tag is from semi-leptonic decay) From real data analysis N c(b)  e is number of electrons from charm (bottom) N c(b)  tag is N tag 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 + /D 0, D s /D 0 etc) contribution from NOT D(B) daughters Analysis by Y. Moritno

charm production bottom production charm  c = (sys) bottom  b = (sys) Details of the Analysis(2) unlike pair like pair From real data Electron pt 2~5GeV/c Hadron pt 0.4~5.0GeV/c count X 1/N non-phot e  data (stat) (sys) From simulation (PYTHIA and EvtGen (B decay MC) ) Electron pt 2~5GeV/c Hadron pt 0.4~5.0GeV/c unlike pair like pair (unlike-like) /# of ele After like-sign subtraction Charge correlation in b-decay and/or for high mass are due to charge conservation

Result theoretical uncertainty is NOT included. comparison of data with simulation (0.5~5.0 GeV) pt(e) 2~5GeV/c  2 /ndf Yield of (unlike-like) in the data is between the expectation of c  e and b  e Extract 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. Yield of (unlike – like) hadron per leading electron

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 b  e/(c  e + b  e) 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 D  K  Reconstruct D 0  K +  -  0 decay in pp  0 identified via  0   decay No charged hadron pid. Advantages of D 0  K +  -  0 mode: – Relatively large BR (14.1%) – Can be triggered by  0 ++ Direct Measurement: D  K  00 Trigger EMCal Trigger

Invariant Mass Distribution Year5 p+p  s=200GeV data set is used Observe 3  significant signal in p T D range 5 ÷ 15 GeV/c No clear signal is seen for p T D < 5 GeV/c The signal is undetectably small for p T D > 15 GeV/c Analysis by S. Butyk (LANL)

Momentum Dependence Observe clear peak in all p T 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 D  K  analysis Clear peak of D 0 meson observed in Run5 p+p data in D 0  K +  -  0 decay channel Signal statistic significantly enhanced by use of high momentum photon trigger Signal is measurable in 5 to 15 GeV/c p T 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 