comprehensive study of heavy quark production by phenix at rhic youngil kwon univ. of tennessee for...

Comprehensive study of heavy quark production by PHENIX at RHIC

Youngil KwonUniv. of Tennessee

For the collaboration

21st Winter Workshop on Nuclear Dynamics Breckenridge, Colorado , 5-12 February, 2005

ykwon

This is Youngil Kwon on behalf of PHENIX collaboration.We will discuss how and what PHENIX has learned about heavy flavor productionwith a special focus on p+p and d+Au collisions.Later today, Sergey Butsyk will talk about other part of comprehensive study.

Feb. 10th, 2005 WWND@Breckenridge, Y.Kwon for PHENIX 2

Outline

• Physics Motivations• RHIC & PHENIX• Open heavy-flavor charm measurements

– method– selected results for non-photonic e± production from

• p+p collisions at √s = 200 GeV

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

• Summary & Outlook

ykwon

This presentation is made up ofMotivations Available experimental facility and apparatus with a focus on what they can do.Description of methodSelected resultsSummary & Outlook


Physics Motivations

Fundamental quest : Test prediction of the parton model and pQCD, and address limitations of them. Scenarios in discussion For the collisions of 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 collisions of d+Au collisions Does “binary scaling” work?

If charm producing process is point-like and there’s no modification of initial parton distribution, they will scale.

ykwon

The fundamental question of current efforts is"How good is the parton model and pQCD?".They say paton model works in very hard processes. Then question is "what does the phrase very hard mean?". Forthermore the understanding, if fundaemental, has to quantitatively describe "how the measurement approaches the limit".Our basic scope is to test this feature.

ykwon

Here are specifics of questions we can ask...Charm and bottom poduction are often quoted as "hard process". For p+p collisions, we will test if they are really hard.Hard processes predict so called "scaling with the number of binary collisions".For d+Au collisions, we will test this scaling.

ykwon

Other interesting subjects are ... binary scaling in AuAu reactions as in R(AuAu),in R(CP), excitation over collision energy, and flow...Most of which will be covered by Sergey Butsyk this evening.


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

DcH

: fragmentation function for c

d [ijcc+X] : parton cross section

+ ... : higher twist (power suppressed by

QCD/m

c, or

QCD/p

t if p

t ≫m

c ) :

e.g. "recombination" E.Braaten, Y.Jia, T. Mehen, PRL, 89 122002 (2002)

Hard processes and factorization

Process independentProcess independent

ykwon

General contents of factorization theorem are as follows.The cross section for a given hard process is made up of "process indepdent" parton distribution function and parton fragmentation function and parton cross section.The remaining terms are "power suppressed" by the scale of process.

ykwon

The reminder terms appears as a series of power-suppressed terms, i.e., by 1/Q^{n}. Break down of pQCD will happen when these reminder terms become important than the 1st term.When collision energy increases, the 1st term getsbigger, and partonic chracteristics of interaction gets stronger.

ykwon

The reminder of conventional pQCD predictionFor charm, Excess over pQCD production Flow of charmed hadron Charge asymmetry Non-Scaling with the number of binary nucleon collisions


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!

ykwon

Let's make two assumptions!1. parton model dominates,2. nucleus is a bundle of nucleons.Production by hard process will scale with the number of colliding nucleon pairs.

ykwon

Does pQCD and parton model work? We see wild violation in some of the processes...and note the scale Q we talk about is substancially bigger.


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

ykwon

Next few pages we discuss experimental facility and apparatus.This page shows conventional picture of collider.Few things of note for the current scope!


PHENIX

Optimized for

lepton measurements

two central electron/photon/hadron spectrometers

electrons: central arms measurement range:

0.35 p 0.2 GeV/c

two forward muon spectrometers

muons: forward arms muon measurement

in range: 1.2 < || < 2.4 p 2 GeV/c

ykwon

This is conventional picture of PHENIX. Detector is optimized for leptons.Electrons are measured at mid-rapidity, and muons are measured at forward rapidity.


BBC

PHENIX, Detectors for centrality

ykwon

Frequently centrality and glauber model is used to probe so called binary scaling. This page displays centrality detectors PHENIX use.


PHENIX, Acceptance for Particles

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This page shows acceptance of various particles.


measurement

How to measure open charm and bottom

Semi-leptonic decays contribute to single lepton spectra.

c c

K

Semileptonic decay0D

Fragmentation

ykwon

Next few pages will describe how PHENIX measures heavy flavor.Key words are semi-leptonic decay.


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-

ykwon

Next three pages are for electrons.This page shows varous sources of leptons.One key observation can be "photons" are major source of background.


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 .

ykwon

How do we deal with "photon contribution"?One way is to induce additional photon conversion with the converter.The study is often reported as "inclusive electrons"/"photonic electron".Signal to background ratio depends on pt and collision system.


• 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

ykwon

Another approach will be to include conventional sources of leptons, and establish estimated background. Each source comes partially from measurementand partially from reasonable guess.Sergey Butsyk will discuss further detail later today.


1 : Hadrons, interacting and absorbed (98%), 3 : Hadrons, penetrating and interacting (“stopped”)4 : Hadrons, “punch-through”, 2 : Charged /K's, “decaying” before absorber (≤1%), 5 : Prompt muons, desired signal

TrackerIdentifier Absorber

Collision range

Collision

Muon HadronAbsorber

Symbols

Detector

1

-measurement, Sources

23

4

5

ykwon

Next three pages are for muons, where most of my efforts were spent.This page displays major sources of muon candidate tracks.Decay muons becomes dominant source of backgrounds, and the amount of decay muons depends on collision location.


-measurement, Signal level3

[arb

. u

nit

]

An illustration of strength,Major background vs signal

ykwon

This page shows multiplicity distribution of major sources.The plot is to demonstrate significance of signal we have.


-measurement, Signal Extraction (

arb

. U

nit

)

Generator

1. Hadron measurement. by central arm,

2. Extrapolation to muon arm acceptance.

3. Simplified spectrometer geometry.

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This page shows yields of muon candidate tracks for various collision locations.

ykwon

Above three pages are all for muons. One of my responsibility today is to advocate single muon analysis. A result was there quite a while, but generating enough force to mobilze a big collaboration is alsoa tough task.Recently I moved to Tennessee, heart land of muon efforts, and PHENIX are being mobilized quickly for this analysis.


Inclusive e±, p+p at √s = 200 GeV

Following plots for p+p results from S. Butsyk’s dissertation.

ykwon

From now, we will discuss selected results.

ykwon

First we go to proton on proton collisions at sqrt{s} = 200 (GeV).As a side note, let me note key plots are from Sergey Butsyk's dessertation.Interesting discussions on electron results can be there between STAR and PHENIX.If STAR electron group offers him good job, a lot of useful information exchange will be there I guess.

ykwon

This page shows the inclusive electron spectra with the estimated conventional background.Sergey can answer details better than me.What I'd like to point out is that dominant sources are pi0 dalitz and gamma conversion, which is accurately determined.Also signal to background improves as we go to higher pt.


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

Good agreement between two independent methods

ykwon

As described, we have two methods to determine conventional background. This page shows consistency between two method.


Final “Non-photonic” Electron Invariant Cross section

ykwon

This page shows background subtracked non-photonic electron spectra.Systematic error is about 30% at low pt and about 20% at high pt in upward direction. Electron group used significant hours on analysis and I'm confident that 1 sigma means 1 sigma.


Comparison, PYTHIA

• PYTHIA parameters, tuned to describe the 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 from PYTHIA CC = 0.658 mb BB = 3.77 b

ykwon

This page shows comparison to the pythis prdiction tuned to the existing world data.Value for K factor and <kT> are less intuitive, but are needed for tuning.According to this study, leptons from bottom gets improtant when pt > 3(GeV/c) or so.


Comparison, FONLL

• Mateo Cacciari, private communication.

FONLL : Fixed Order next-to-leading order terms and Next-to-Leading-Log

large pT resummation.

• Central theory curve underpredict data by

a factor of 2-3 when pT > 1.5 (GeV/c).

ykwon

This page shows comparison to FONLL. Naming come from ... . At Ferimi lab, the prediction works reasonably well for charm and bottom production.At low pt, model uncertainty gets large due to the charm mass and scale uncertainty. However the prediction is significantly below data at high pt. This raise question on "Is charm really heavy enough?".


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

PHENIX PRELIMINARY

1/T

ABE

dN

/dp

3 [m

b G

eV

-2]

ykwon

Now we go to d+Au collisions at sqrt{s} = 200 AGeV.This plot is as it was at QM. One thing I still want to note is non-photonic electron scales with the number of binary collisions "within the given error range". Since we don't sample full interaction, there's correction due to glauber model TAB, but model uncertainty will be minimal.


Centrality & Glauber Model

NBBC

coun

t coun

t

Ncoll

ykwon

We frequently use N_{coll} deduced from Glauber model to further test scaling with the number of binary collisions. We use negative binomial distribution to link N_{part} in glauber model and the measured charge in BBC. In doing so, we can link selected centrality and N_{coll} distribution. Furthermore, we get trigger efficiency.


Centrality (in)dependence in d+Au collisions

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]

ykwon

This page shows comparison of pp spectra and scaled d+Au spectra.


Summary & Outlook

Near future :– + Single muons at forward rapidity.– + Significant increase in statistics. Significant

improvements in systematic and statistical uncertainty.

PHENIX measured non-photonic electron production at mid-rapidity in p+p at √s = 200 GeV and d+Au at √sNN = 200 GeV. NLO pQCD underpredicts production in p+p when pT > 1.5 (GeV/c). This suggests limitation of pQCD-based approach for charm production. Observed “binary scaling” in d+Au is consistent with the point-like interaction for charm production. Improvements of error bars and measurement at the extended kinematic region, i.e. forward measurement, are highly desired.

ykwon

Here's the summary. Two things we want to note as near future.Forward muon spectra.Significant imprvement in systematics ans statistics in AuAu single electron analysis.


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*

comprehensive study of heavy quark production by phenix at rhic youngil kwon univ. of tennessee for...

Documents

collisions of p p collisions

collisions of d au collisions

parton model

gevd au collisions

hard processes

parton fragmentation

number of binary collisions

given hard process