H eavy quark production in p+p and d+Au collisions at √s NN = 200 GeV

Heavy quark production in p+p and d+Au collisions at √sNN = 200 GeV

Youngil Kwon Univ. of Tennessee

For the collaboration

Quark Matter 2005 Budapest, Hungary, 4-9 August, 2005

Physics Dept.

This is Youngil Kwon on behalf of the PHENIX collaboration. We will talk about "how" and "what" PHENIX has learned about heavy flavor production with a focus on the light ion collisions.

Aug. 8th, 2005 Y. Kwon for PHENIX @ QM2005, Budapest 2

Outline

Physics Motivations (pQCD & parton model)

PHENIX (with some emphasis on aspect)

Open heavy-flavor (charm) measurements– Method (semi-leptonic decays and single leptons)

– Selected results for non-photonic e (y ~ 0) & prompt (y ~ 1.65) production from

• p+p collisions at √s = 200 GeV

• d+Au collisions at √sNN = 200 GeV as a function of centrality

Near term prospect (leptons over wide rapidity)

Summary & Outlook

Physics Dept.

Outline of this talk is shown here.What makes this talk different from others are stressed as pink.pQCD & parton model is the heart of this talk.New results are coming from the muon analysis and we describe PHENIX with some emphasis on the muon aspect.PHENIX measures leptons resulting from semileptonic decay of heavy quarks,and present selected results from p+p and d+Au collisions.With time, we will see further measurement of hard leptons over wide rapidity range, an important piece to our current study.


Physics Motivations

Fundamental quest of our field: Exploration of QCD in various limits. Scenarios in discussion : For the p - p collisions Is mass of charm quark heavy enough? Can pQCD be applied to

charm production? J.C.Collins, D.E.Soper, G.Sterman, Nucl. Phys. B263, 37(1986)

For the d - Au collisions Does “binary scaling” work?

If charm producing process is point-like and there’s no modification of the

initial parton distribution or the final fragmentation, there will be scaling

with the number of binary nucleon collisions Ncoll.

CGC ( Color Glass Condensate ) There will be modification of the initial parton distribution, and the scaling

will be modified as a function of rapidity. D. Kharzeev et al, Phys. Lett. B599 (2004) 23-31

Physics Dept.

Fundaemental question of our field is to explore Quantum ChromoDynamics in its limit.For the current efforts, heavy flavor production is used as the probe.We will study how good description of perturbative QCD is for charm production in p+p collision.For d+Au collision, we will check the point-like scaling of the production process and study possible features such as CGC.


J.C.Collins,D.E.Soper and G.Sterman, Nucl. Phys. B263, 37(1986)

d[A+BX] = ij f

i/Af

j/B d [ijcc+X] D

cH

+ ...

Factorization

fi/A, fj/B : distribution function for point-like parton i,j

Dc/H : fragmentation function for c

d [ijcc+X] : calculable parton cross section

+ ... : higher twist (power suppressed by QCD/mc, or QCD/pt if pt ≫mc ) :e.g. "recombination" E.Braaten, Y.Jia, T. Mehen, PRL, 89 122002 (2002)

Hard processes and factorization

Point-like, Process independent

Power-suppressed

Physics Dept.

Let's review what is general assumption behind parton model.The cross section for a specific hard process can be factorized into pieces, namely process-independent distribution and fragmentation functions for point-like partons, cross section between partons calculable by pQCDOf course, there are power-suppressed correction.Let me emphasize two important features with animation.


measurement

PHENIX, How to measure heavy flavor?Semi-leptonic decays contribute to single lepton spectra!

c c

K

Semileptonic decay 0D

Fragmentation

Spectator model?

Peterson function?

S. Frixione et al, J. Phys. G 27(2001)1111

b fragmentation function (HERWIG)

Larger uncertainty in fragmentation function!

1 2 3 4 1 2 3 4

pb < 5 GeV/c 0.87 0.78 0.71 0.66 0.95 0.94 0.94 0.96

e+e-, √s = 91.2 GeV ppbar, √s = 1.8 TeV

Physics Dept.

How deoes PHENIX measure the heavy quark production? This cartoon shows how...Produced heavy quarks become heavy flavored hadrons through fragmentation process, for which a few theory motivated model exists. Subsequently, produced hadrons undergoes semileptonic decay.Rough scheme of the decay can be described by the spectator modelwhich assumes heavy quarks inside charmed hadron decay freely. The spectator model was tested by the various e+e- experiment. Uncertainty for the fragmentation function seems to be bigger, however.Even for bottom production, Melin moments of the fragmentation function estimated from e+e- results and ppbar results differ significantly.Note large moment is important in hadron collisions due to the steeply falling pT spectra. For low pT bottom, fragmentation function from ppbaris harder than e+e- case.Indeed, ppbar bottom measurement generally lies at upper limit of NLO prediction.


PHENIX Optimized for

lepton measurements

two central electron/photon/hadron spectrometers

Electrons : central armsmeasurement range:

0.35 p 0.2 GeV/c

two forward muon spectrometers

Muons : forward armsmeasurement range:

1.2 < || < 2.4 p 2 GeV/c

Physics Dept.

PHENIX is optimized for the lepton measurements. At midrapidity, two central arms measure electrons down to low pT. At forward and backward rapidities,two forward arms measure muons over wide rapidity range. Acceptance for the detector is displayed here. Two central arm and two forward arm is displayed here.


Inclusive e± , p+p at √s = 200 GeV

Inclusive electrons = photonic + non-photonic electron

Direct measurement :converter method

Estimation based on other(PHENIX) measurement :

Cocktail method

Dominant background : 0 Dalitz decay, conversion

Mostly from heavy quark

Physics Dept.

This page describes how we extract the non-photonic electrons. 1st, we produce inclusive electron spectra at top pannel and subtract the photonic background to get the non-photonic electrons.Background displayed as solid black line is determined through the direct measurement called converter method, or measurement driven estimation called cocktail methos.Signal to background ratio is about 1 around 2 (GeV/c) in pT, and improves better at higher pT.Largest source of background is pi0 dalitz and gamma conversion.


TrackerIdentifier Absorber

Collision vertex range

Collision

Muon HadronAbsorber

Symbols

Detector

-measurement, Sources

1

1 : Hadrons, interacting and absorbed (98%),

2

2 : Charged /K's, “decaying into ” before absorber (≤1%),

3

3 : Hadrons, penetrating and interacting (“stopped”)

4

4 : Hadrons, “punch-through”, 5 : Prompt , ”desired signal”

5

zcoll zcollzcoll

Physics Dept.

This is the simplified scheme of the muon spectrometer. Bulk of the hadrons displayed as 1 are absorbed in the front absorber.Small fraction of them decay into muon before absorption and still are the largest source of muons, which are called decay muons.Some hadrons penetrateall absorber layers and we call them punch-through,which is another source of backgroundto the measurement.Some hadrons penetrate front absorberbutare absorbed in the muon identifier.They are observable, used for the light hadron analysis, and used to estimate the punch-through's.Muons from semi-leptonic decay are produced instantly and we call them prompt muons.Depending on the location of collision, average distance for decay change linearly.So, actual yield of muon will depend on collision point. We use this characteristics to extract decay muons.


PRELIMINARY

Generator 1. Light hadron measurement by

PHENIX central arm (y = 0)2. Gaussian extrapolation in

rapidity to muon arm acceptance ( = 2.5)

3. Simplified spectrometer geometry.

-measurement, Signal extraction and level

Sources of candidates1. Decay is important at all pT.2. Punch-through is small, but

important due to large uncertainty.3. Prompt signal comparable to decay

when pT ~ 2(GeV/c).

decay muons + punch-through

Physics Dept.

Left bottom plot shows the invariant multiplicity of inclusive muons as a function of collision vertex. As explained, we see linear rise in yieldas the collision vertex gets farther away from the front absorber.Prediction of decay muons and punch-through is possible based on light hadron measurement and displayed in black. The excess in data is due to the prompt muons.The slope corresponds to the amount of lighthadrons, and is physical quantity.The slope can be converted to decay muon production per unit length.Right plot shows the level of signal and background.Decay muon fraction reduces with pT and cross prompt muon production at around pT = 2(GeV/c).Punch-through is small fraction of data at all pTbut carries large uncertainties and hence important.


Decay spectrap + p @√s = 200 GeV, = 1.65

PRELIMINARY PRELIMINARY

10 data points for + and for - correspond to the slopes for 10 pT bin( 1 < pT < 1.2, 1.2 < pT < 1.4, … , 2.8 < pT < 3.0 GeV/c ). Each slope representsamount of decaying light hadrons, and good match occurs between the generator prediction and the measurement up to absolute normalization (5%). Hence we can determine decay component precisely.

Physics Dept.

This page compares the decay muon spectra with the generator prediction. Without any adjustment, the prediction matches with data.We get 5% difference in normalizationwhen we fit data with the generator predicted shape.


Final Non-photonic e & Preliminary Prompt Invariant Cross section

For details of prompt muons analysis, please go to D. Hornback’s poster.

PRELIMINARYPRELIMINARY

p+p at √s = 200 GeV

Muon spectra and electron spectra are similar over the observed pT range…

Physics Dept.

This page shows the non-photonic electron and the prompt muon spectra, both of which are dominated by the semileptonic decay of heavy flavor.A notable observation is non-photonic electron and prompt muon spectra are quite similar.


Comparison to Theory, Cross section

PYTHIA 6.205 parameters, tuned to describe existing s < 63 GeV p+N world data

( PDF – CTEQ5L, mC = 1.25 GeV, mB = 4.1 GeV, <kT> = 1.5 GeV, K = 3.5 )

Total cross section for PYTHIA 6.205CC = 0.658 mb, BB = 3.77 b

PRELIMINARY

FONLL: Fixed Order next-to-leading order terms and Next-to-Leading-Log large pT resummation.

We see excess over NLO calculation.The excess gets even stronger at forward, possibly due to the rapiditydependence of cross section.

Physics Dept.

According to the theoretical calculations, non-photonic and prompt muon lepton spectra below 3 (GeV/c) in pT are dominated by the semileptonic decays of charm.Let's look at electron spectra first. The spectra is harder than the prediction of pythia 6.205 tuned to the world data.%We note recent pythia version produce %significantly harder pT spectra %largely due to the change in initial radiation. Comparison to the NLO prediction indicates there are possible excess.Now let's add the prompt muon measurement. Prompt muon spectra is also harder than pythia prediction. The measurement also indicates even stronger excess over the NLO prediction. While the absolute yield is more than NLO prediction at all rapidity, the narrow rapidity distribution of theory makes the difference larger. An interesting note isNLO predicts the rapidity distribution tightly, but the width is significantly different from the one in pythia. The difference will be due to the higher twist effects. We are making efforts to improve uncertainties in the electron and prompt muon measurement.


d+Au,centrality definition & Glauber model

NBBC

coun

t coun

t

Ncoll

BBC

-4 < < -3

Physics Dept.

In this page, we briefly show how we define the centrality classes andthe Glauber model variable Ncoll.We categorize events according to the number of hits in our beam-beam counter.


Non-photonic e± , d+Au at √sNN = 200 GeV

PHENIX PRELIMINARY

1/T

ABE

dN

/dp

3 [m

b G

eV

-2]

PHENIX PRELIMINARY

PHENIX PRELIMINARYPHENIX PRELIMINARY

PHENIX PRELIMINARY

1/T A

B1/

T AB

1/T A

B1/

T AB

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

Physics Dept.

Midrapidity non-photonic electrons for minimum bias events scales with the number of binary collision Ncoll. Further we studied the scaling in 4 centrality bins.Withing the uncertainty, we see approximate binary scaling.


± & NMF, d+Au at √sNN = 200 GeVSouth : Au-going direction, North : d-going direction

Decay ’s ( from light hadrons )

From M. K. Lee’s poster

PRELIMINARY

Au-goingd-going

Direction

pT(GeV/c)

Au-goingd-going

Direction

Prompt ’s ( from heavy quarks )

PRELIMINARY

pT(GeV/c)

From X. R. Wang’s poster

Physics Dept.

These are the 1st d+Au results from the forward muon arm.Error bars are large, and we will work to improve error bars.To 1st order, we see consistencies with BRAHMS for the light hadrons.Note the systematic error bar for the prompt muons is 1 sigma.For prompt muons, we see difference between deuteron going and Au going side. When we improve analysis procedure,backward RdAu for the prompt muons will be probably reduced with smaller error bars.

Physics Dept.

Here are results from the forward spectrometer.Rcp for the light hadrons was presented at last QM, and was published recently.We show RdAu from the light hadrons and from the prompt muons. For both cases,we observe difference between d-going and Au-going directiondifferent from naive binary scaling. The systematic error band represent 1 sigma-like uncertainty.We will get back with the improved resultswith smaller error bars.


Summary & Outlook

1. PHENIX measured production of non-photonic e at mid-rapidity and prompt at forward/backward rapidities in p+p at √s = 200 GeV and d+Au at √sNN = 200 GeV.

2. We demonstrated single analysis is possible and presented the 1st results of the prompt analysis.

3. Non-photonic e pT spectra at y = 0 and prompt pT spectra at y = 1.65 are similar.

4. Non-photonic e pT spectra at y = 0 shows excess over the prediction by FONLL or PYTHIA 6.205 tuned to world data. The prompt pT

spectra at y = 1.65 shows even stronger excess.5. We observe “binary scaling” in non-photonic e production at

midrapidity for d+Au collisions at √sNN = 200 GeV, which is consistent with the point-like interaction for charm production.

6. For the decay and the prompt , there seem to be differences in production between the deuteron-going and the Au-going directions. Further Efforts will reduce measurement uncertainty.

7. PHENIX started to explore lepton production over wide rapidity range. Many new results will follow in the near future.


Prospect

From D. J. Kim’s poster

Prospect

Cu+Cu at √sNN = 200 GeV

Physics Dept.

This page shows near future prospectfor muon arm result.We got the PRELIMINARY decay muon spectra and the RAA for the CuCu collisions at 200 GeV/c.Obtained RAA is consistent to the central arm measurement.The challenge in the large multiplicity environment such as AuAu collisions is the combinatorial background.You can find those background can be controled from Irakli's poster.

Physics Dept.

Slow speaking...


USA Abilene Christian University, Abilene, TX Brookhaven National Laboratory, Upton, NY University of California - Riverside, Riverside, CA University of Colorado, Boulder, CO Columbia University, Nevis Laboratories, Irvington, NY Florida State University, Tallahassee, FL Florida Technical University, Melbourne, FL Georgia State University, Atlanta, GA University of Illinois Urbana Champaign, Urbana-Champaign, IL Iowa State University and Ames Laboratory, Ames, IA Los Alamos National Laboratory, Los Alamos, NM Lawrence Livermore National Laboratory, Livermore, CA University of New Mexico, Albuquerque, NM New Mexico State University, Las Cruces, NM Dept. of Chemistry, Stony Brook Univ., Stony Brook, NY Dept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY Oak Ridge National Laboratory, Oak Ridge, TN University of Tennessee, Knoxville, TN Vanderbilt University, Nashville, TN

Brazil University of São Paulo, São PauloChina Academia Sinica, Taipei, Taiwan China Institute of Atomic Energy, Beijing Peking University, BeijingFrance LPC, University de Clermont-Ferrand, Clermont-Ferrand Dapnia, CEA Saclay, Gif-sur-Yvette IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, Orsay LLR, Ecòle Polytechnique, CNRS-IN2P3, Palaiseau SUBATECH, Ecòle des Mines at Nantes, NantesGermany University of Münster, MünsterHungary Central Research Institute for Physics (KFKI), Budapest Debrecen University, Debrecen Eötvös Loránd University (ELTE), Budapest India Banaras Hindu University, Banaras Bhabha Atomic Research Centre, BombayIsrael Weizmann Institute, RehovotJapan Center for Nuclear Study, University of Tokyo, Tokyo Hiroshima University, Higashi-Hiroshima KEK, Institute for High Energy Physics, Tsukuba Kyoto University, Kyoto Nagasaki Institute of Applied Science, Nagasaki RIKEN, Institute for Physical and Chemical Research, Wako RIKEN-BNL Research Center, Upton, NY

Rikkyo University, Tokyo, Japan Tokyo Institute of Technology, Tokyo University of Tsukuba, Tsukuba Waseda University, Tokyo S. Korea Cyclotron Application Laboratory, KAERI, Seoul Kangnung National University, Kangnung Korea University, Seoul Myong Ji University, Yongin City System Electronics Laboratory, Seoul Nat. University, Seoul Yonsei University, SeoulRussia Institute of High Energy Physics, Protovino Joint Institute for Nuclear Research, Dubna Kurchatov Institute, Moscow PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg St. Petersburg State Technical University, St. PetersburgSweden Lund University, Lund

*as of January 2004

12 Countries; 58 Institutions; 480 Participants*


RHIC• RHIC (Relativistic Heavy Ion Collider)

– Dedicated to heavy ion physics & spin studies– 4 experiments– 100+100 GeV/A for various combinations of nuclei– p+p up to 500 GeV– Variable incident

energy


BBC

PHENIX, Detectors for centrality


Application to nuclei

fi/Au

79 fi/p

+ 118 fi/n

197 fi/N

fi/d

fi/p

+ fi/n

2 fi/N

Parton distribution for Au and d :

d+Au

Au+Au

This scaling does not work for high pt particles in central Au+Au collisions! PHENIX, PRL, 91, 072303 (2003)

For the interaction between point-like particles,

Cross section number of colliding nucleon pairs, Ex) 197 * 2 for the d+Au collisions!


e-measurement, Signal Extraction (I)Mininum Bias Au+Au in sNN=200GeV

Inclusive e/photonic eNe

0

1.1% 1.7%

Dalitz : 0.8% X0 equivalent

0

With converter Conversion in converter

W/O converter Conversion from detector

0.8%

Non-photonic

• Non-photonic signal relative to photonic electrons depends on pT & collision system .


e-measurement, Sources

Charm decays Beauty decays

Non-PHOTONIC Signal

Photon conversions :

Dalitz decays of 0,,’,,0ee, ee, etc) Kaon decays Conversion of direct photons Di-electron decays of ,, Thermal di-leptons

Most background is PHOTONIC

Background

0 e+e-


“Non-photonic” Electron Invariant Cross section from Converter Subtraction

Good agreement between two independent methods


• excess above cocktail–increasing with pT

–expected from charm decays

• attribute excess to semileptonic decays of open charm

e-measurement, Signal Extraction (II)

PHENIX: PRL 88(2002)192303

conversion

0 ee

ee, 30

ee, 0ee

ee, ee

ee

’ ee

H eavy quark production in p+p and d+Au collisions at √s NN = 200 GeV

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