SQM06, Zhangbu Xu (BNL) 1

Overview of charm production at RHIC

Zhangbu Xu (BNL)

Presentions:Xiaorong Wang, PHENIX (Forward muon)Yifei Zhang, STAR (mid-rapidity, muon, electron)Haibin Zhang, STAR (STAR overview)Adrew Glenn, PHENIX (PHENIX overview)Posters: Chen Zhong, STAR (Low-pt muon)H.D. Liu et al., nucl-ex/0601030X. Dong, thesis, nucl-ex/0509011

All nice talks on data are Over I am offering my own view

Thank the organizers

SQM06, Zhangbu Xu (BNL) 2

Outline

• Charm Total Cross Sections• Are we alone?• What’s right and what’s wrong?

• Are lepton spectra sensitive to flow?• Form Factors • What scale? (30%, x3)

• Does it make senses?• Color, flavor (dE/dx)?• Is pp/FONLL off by 3—6 serious?

• Wild Speculations and Outlook

Mc1.5 GeV>>Tc, QCD, Muds

M/E>>0

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Are we alone?

Can we confirm or rule out Cosmic Ray experiments (Pamir, Muon, Tian Shan) under similar conditions?

Data provide reference for Au+Au data and J/psi from charm coalescence

STAR >3x PYTHIA,pQCDEnergy dependence R and F?

Need smaller errors to constrain pQCD and determine the effects in Cosmic Ray Showers

Pamir, Nuovo Cim 24c (2001) 557; NPB 122(2003) 353c

X. Dong USTC

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Pamir EM shower depth

With charm

Without charm

XREC upgrade

Pamir, Nuovo Cim 24c (2001) 557

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Muons on the Side

Two techniques, Two SpectraFluorescence vs Muon/scintillator

What is the problem?

Incorrect Model of Detector?Incorrect Model of Showers?Heavy Primaries?New Physics?

A. Olinto, PANIC05

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Can we get rid of data points we don’t like?if the data points shouldn’t be there in the first place?

R. Vogt

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What’s right and what’s wrong

X. Dong (USTC) PH.D. Thesis

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CDF/ISR ce SpectraCDF directy D measurement -- high pT

hep-ex/0307080

X. Dong, Thesis, nucl-ex/0509011

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Discrepancy at RHIC?

PHENIX, PRL 94, 082301(2005)

dNe/dy[0.8<pT<4.0]/Ncoll

Y.F. Zhang, H.B.Zhang, C. Zhong, SQM06

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Which part of the lepton spectrum is sensitive to cc ?

90%

15%

σcc = 1.1 0.1 0.3 mb

Change (n, <pT>), Left: 0.16<pT () <0.26, ±10%Right: pT(e)>1.0 GeV/c, x8

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Measure cc vs sqrt(s)

Propose to measure total cross sections with low-pt muons: CDF, ALICE, Energy Scans at STARH.D. Liu et al.,nucl-ex/0601030

1) Constrains pQCD2) Baseline for charm Coalescence Model 3) Test PBM thermal model

x4 below STAR measurements

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Are they talking about the same thing?

H.B. Zhang, Y.F. Zhang, C. Zhong SQM06

PHENIX, PRL 94, 082301(2005)

•consistent with Nbin scaling!•Produced at initial impact!•Large values:

•pQCD•J/psi coalescenceNo sensitive to FSI Dynamics

FSI Dynamics

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Are lepton spectra sensitive to flow?

Electron spectra cannot disentangle different charm hadron shapes at low pT

S. Batsouli, et al, Phys.Lett.B 557 (2003) 26 Electrons: Smearing in pT axis

X. Dong QM05

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Preserve the Orientation for v2?

B. Zhang nu-th/0502056

H. Va Hees hep-ph/0601166

v2 and other calculations shows sensitivity?Is it by accident?

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Charm Decay Form Factors

PDG

Form factor is different between PYTHIA and PDG

Electron spectrum depends strongly on charm spectrum shape at pT~1—2 GeV/c H.D. Liu, nucl-ex/0601030

e

c

s

u,d,ud

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Charm flows, but not quite as large

S. Esumi: (Next session)Overview of non-photonic electron v2

BlastWave model-dependent fit shows sensitivity of electron spectrum to charm spectrum shape

Likely, Freeze-out early with less flow

H.B. Zhang, Y.F. Zhang

AuAu Central , K, p

AuAu Central charm hadron

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RAA of non-photonic electrons

Evidence of large heavy quark energy loss!

STAR Highlight talk PHENIX, PRL96

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Flavor or Color factor?• Radiative dE/dx and

Radiation+Elasitic The bigger difference is gluon vs quarks charm vs u/d is quite small

• The biggest difference between and charm RAA is due to gluon

The ten thousand things rise and fall without cease– 道德经 http://www.actus.org/laotzu.html

S. Wicks, nucl-th/0512076

• dE/dx(g) ~=9/4 dE/dx(uds)pbar, p vs

• dE/dx(c/b)<dE/dx(uds)

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Gluon vs light quarks

• dE/dx(g) ~=9/4 dE/dx(uds)pbar, p vs

• dE/dx(c/b)<dE/dx(uds)

STAR nucl-ex/0601033

from quarks, pbar (p) from gluonsat pT~=10 GeV/c

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Pbar(p), same suppression

STAR Preliminary

L.J. Ruan, WWND06

Same suppression

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First thing first!

p+p (PHENIX,STAR)/FONLL=(3,5.7)Are we worried? What if charm is off, but bottom is correct

Cacciari, PRL95

STAR |y|<1

PHENIX, X.R. Wang, SQM06

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Speculations

• Gluon and light quark have similar dE/dx– color-factor 9/4 doesn’t work for large dE/dx?

But, I. Vitev hep-ph/0601010: dE/E(g)=50%, (q)=25%

• NLO underpredicts charm but predicts bottom correctly– Mc~ 1.5 GeV/c too small– Other processes?

• These will explain:pbar(p), pion,electron RAA

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Outlook

• Measurecc by low-pt muonsLHC, Tevetron and energy scan at RHIC

• Measure D, c, and B separately and cleanly

• Explain why gluons and light quarks have same dE/dx

• Does pQCD dE/dx work all the way to pT(e)~=1 GeV/c?

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A same ending of charm production at RHIC??

Thanks to PBMWhatever the truth,Triumph over mistrust!

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Effects related to Open Charm• Radiation Energy Loss• Collision Energy Loss

• Dead Cone Effect• Ter-Mikayelian Effect• Transition Radiation

• Flow (radial & elliptic)• (quark) Coalescence• Death of “dead cone”

• Charm Resonance • CGC

All these happen at intermediate pT

Emphasize on experimental measurements

DownDownUpUpDownUpUpDownDownUp?

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Challenges to theory

Current energy loss mechanisms can only account for part of strong suppression of RAA for electrons.

N. Armesto et. al. private comm.M. Djordjevic, et. al. nucl-th/0507019

any beauty?

X. Dong QM05

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