measurement of single muons with the phenix experiment at rhic

Single muon measurements at RHIC(PHENIX) , D.J Kim, Yonsei University 1/19

Measurement of single muons with the PHENIX experiment at RHIC

D.J Kim D.J Kim

Yonsei UniversityYonsei University

For the PHENIX CollaborationFor the PHENIX Collaboration

Hot Quarks 2006, May 20


Outline

Introduction How can we measure HF ? Background measurements to the cocktails

( 1.Free Decay[K,π], 2.Punch-through ) Prompt muon results in pp. dAu Light meson bg measurement in CuCu Summary and Outlook


Physics Motivations

Why do we measure heavy quarks (charm/bottom)?

In p+p collisions:Important test of pQCD. Can pQCD predict charm

production( LO, NLO )? Base line analysis for d+Au and Au+Au

In d+Au collisions:Study of “cold” nuclear matter effect (Gluon

Saturation/CGC,[shadowing] , Cronin effect) In A+A collisions:

Medium modification effects (energy loss, collective flow)

Important baseline of J/ analysis


Even heavy quark (charm) suffers substantial energy loss in the matter

The data provides a strong constraint on the energy loss models.

Charm/Bottom contribution ?

Radiative energy loss + Elastic energy loss with Different αs = .3 or .43

(M. G. Mustafa, Phys.Rev.C72:014905,2005)

Teaney and Moore (hep-ph/0412346)

K.J Eskola (Nucl.Phys.A747(2005) 511)

Systematics

Large in low pT because of low S/B

At higher pT, systematic error

~ statistical error

Uncertainty in pp is large

preparing the high pT RAA (up to pT = 10 GeV/c).

Run5 pp ( ~ x 10 stat )

(3) q_hat = 14 GeV2/fm



(4) dNg / dy = 1000

Charm energy loss in Au+Au 200GeV at y~0

(1-3) from N. Armesto, et al., hep-ph/0501225(4) from M. Djordjevic, M. Gyulassy, S.Wicks, Phys. Rev. Lett. 94, 112301

Run04: X=0.4%, Radiation length

Run02: X=1.3%

Signal/Background


• PHENIX– Single electron measurements

in p+p, d+Au, Au+Au , y~0sNN = 130,200,62.4 GeV

– Single muon measurements in p+p, d+Au ,1<|y|<2 sNN = 200 GeV

• STAR– Direct D mesons

hadronic decay channels in d+Au

• D0Kπ• D±Kππ• D*±D0 π

– Single electron measurements in p+p, d+AuPhys. Rev. Lett. 88, 192303 (2002)

How to measure Heavy Flavor ? Experimentally observe the decay products of Heavy Flavor

particles (e.g. D-mesons)

– Hadronic decay channels DKD00

– Semi-leptonic decays De() Ke

Meson D±,D0

Mass 1869(1865) GeV

BR D0 --> K+- (3.85 ± 0.10) %

BR D --> e+ +X 17.2(6.7) %

BR D --> ++X 6.6 %

PHENIX Preliminary

(η = 0)


What have we measured

Open heavy flavor (HF)

@ y, pT dependence (y=0,pp,dAu,AuAu, y=1.65,pp,dAu)

@ Centrality dependence (y=0,dAu,AuAu)

@ Reaction plane dependence (y=0, AuAu)

RHIC provided Cu+Cu 200GeV(~3.0 nb^-1), 62.4GeV(~0.19 nb^-1) Collisions during 2005@ Better systematic studies are possible with

different √s, collision species. @ better precision on the centrality

measurement in the lower Npart region

Species : pp, dAu, CuCu, AuAu√s : 200 GeV, 62.4GeV, 130GeV

Statistics : More is always better (allows reduction in statistical and systematic errors)


PHENIX detector at RHIC

Electron measurements ||<0.35 Two separate arms

2x = 900

p/p ~ 1% p Electron ID

RICH (thr=35)

e/ separation up to pT ~ 4.8 GeV/c

Muon measurements 1.2 < || < 2.4 Two separate arms in forward

and backward rapidity


Muon Production ; origin of muons

• Origins of muons– PYTHIA p+p @

√s=200GeV– low PT:

• light hadron decays

– high PT: • Heavy quark decays

Muon PT distribution%63)(

%99.99)(

%10)(

%10)(

vKBR

vBR

XbBR

XcBR


Candidate Muon Tracks in the Muon SpectrometerCandidate Muon Tracks in the Muon Spectrometer

Punch-through hadrons

The muon arms covered rapidities 1.2 < || < 2.4

Stopped hadrons

Decay muons

Prompt Muons

Candidate Tracks:

throughpunchdecayprompttotal NNNN


Decay muon Contribution(N_decay)

The yield of decay muons depends on the collision location linearly, which also constrains the hadron production, I I hadron , at the collision point.

Average flight Distance (blue

arrows)

Absorbers are in Red

TrackerIdentifier Absorber

Collision range

Positive z →

Decay muons (green tracks)

Prompt muons

Punch-through hadronsDecay muons


Punch-Through hadrons ( N_punch)

Extract decay component from z-vertex slope of normalized muon yield. Calculate punch-through component with simplified absorption model:

Momentum (GeV/c)

Momentum (GeV/c)

2 3 4 5 6

2 3 4 5 6

Raw

Cou

ntR

aw C

ount

hadrons

“stopping” muons and hadrons

Tracks stopping in Gap 3

Tracks stopping in Gap 2

Muons above 2.7 GeV/c punch through the entire detector.

Nuclear interaction cross section~ not well-known • can be resolved with large statistics run5pp, CuCu with this method!!

Nuclear interaction length λ


Cocktails

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).

Prompt muons

Punch-through hadrons

Decay muons


Comparison to Theory ; p+p 200GeV

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 6.205

CC = 0.658 mb, BB = 3.77 b

PRELIMINARY

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

Excess over NLO calculation.The excess gets even stronger at forward, 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.


PHENIX muon arms “x” coverage

From Eskola, Kolhinen, VogtNucl. Phys. A696 (2001) 729-746.

gluons in Pb / gluons in p

X

PYTHIA open charm simulation

Particle production in the d direction (north) is sensitive to the small-x parton distribution in the Au nuclei; whereas in the gold (south) is sensitive to the large-x in Au


Prompt ’s pT spectra in dAu collisions and RdAu

North Arm: d going direction;

South Arm: Au going direction

• For muons from open heavy flavor decay, a suppression in forward rapidity is observed. It is consistent with CGC. Results are statistically limited.• The mechanism of the observed enhancement at backward rapidity needs more theoretical investigation. Anti-shadowing and recombination could lead to such enhancement ?


Decay muons ( pT) in Cu+Cu 200GeV

• consistent with run2 p+p• MinBias pT spectra in Cu+Cu 200GeV only at this moment(Online production)• Limited statistics now, Full data set will be available in the near future• CuCu 200GeV : ~ statistics x10 more

200GeV p+p 200GeV Cu+Cu

PHENIX preliminary


Nuclear Modification Factor CuCu 200GeV

• shows enhancement in higher pT in the forward rapidity• it is consistent with the mid-rapidity measurement within the errors• One of main physical background to Inclusive muons is under control


Rapidity

•Modest Gaussian Shape is observed•pT>1GeV/c in MinBias collisions


FONLL and PYTHIA 6.205 under predicted prompt at forward rapidity in pp collisions at 200 GeV.

For muons from open heavy flavor decay, a suppression in forward rapidity is observed. It is consistent with CGC. Results are statistically limited.

The mechanism of the observed enhancement at backward rapidity needs more theoretical investigation. Anti-shadowing and recombination could lead to such enhancement.

Summary ; p+p, d+Au


Perspective

Non-photonic Single electron RAA in Au+Au 200GeV collisions suggests that Even heavy quark suffers substantial energy loss in the matter Still systematical errors and statistical error is not sufficient to constraint energy loss models Can be improved with better pp reference and

more high pT data points AND…. More systematic studies can be possible via different collision

species, energies (Cu+Cu 200GeV, 62.4GeV), and rapidities.@ stage is set, background analysis are underway@ Light meson pT and RAA in Cu+Cu MB 200GeV collisions are measured at

this moment in the forward rapidity.@ punch-through hadrons can be calibrated with large set of tracks

( run5pp,CuCu ) with great precision Perspectives on Cu+Cu 200GeV , 62.4GeV

@ Light mesons : centrality dependency can be studied with good statistics @ Prompt muon signal ( charm, bottom )@ Flow


RHIC History

X 25


Comparison Prompt - pt spectrum with theory

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

FONLL and PYTHIA calculation under predicted PHENIX Data at forward rapidity,

Run2pp -

FONLL: Solid line and bandWithout scaling the charm contribution: dotted line


Theory Comparison

Disagreement with PHENIX preliminary data!

1000gdN

dy

dNg/dy=1000

M. Djordjevic, M. Gyulassy, S.Wicks, Phys. Rev. Lett. 94, 112301M. Djordjevic, M. Gyulassy, S.Wicks, Phys. Rev. Lett. 94, 112301


How can we solve the problem?

Reasonable agreement, but the dNg/dy=3500 is not physical!

3500gdN

dy

dNg/dy=3500N. Armesto et al.,

Phys. Rev. D 71, 054027 (2005)


• Electrons • Pionss = .3

+ Elastic Energy loss ?+ Elastic Energy loss ?

First results indicate that the elastic energy loss may be importantM. G. Mustafa, Phys.Rev.C72:014905,2005

First results indicate that the elastic energy loss may be importantM. G. Mustafa, Phys.Rev.C72:014905,2005


With Different αs

s = .3 s = .4


Rapidity dependency

measurement of single muons with the phenix experiment at rhic

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