Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Suppression of Non-photonic Electrons at High Pt John W. Harris Yale University.

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)

Suppression of Non-photonic Electrons at High Pt

John W. Harris

Yale University

for the Collaboration


High pT Suppression - Energy Loss of Partons

• Parton energy loss

due to gluon radiation

• Depends on properties of medium (gluon density and volume)• Depends on properties of the “probe” (color charge and mass)

– dE/dx (gluons) > dE/dx (quarks) (due to stronger color coupling with medium)

– dE/dx (heavy quarks (c,b)) < dE/dx (light quarks)

mass dep. suppression of small angle radiation –

(“dead cone”)

ref – Dokshitzer, Kharzeev PLB 519(2001)199

– dE/dx due to heavy quark elastic scattering?

ref - M.G.Mustafa Phys. Rev C 72 (2005)

• Must consider dynamics!ref – Wicks, Gyulassy et al, nucl-th/0512076

hadronsq g

productionparton energy

loss in medium

fragmentation

light

M.Djordjevic PRL 94 (2004)

E-lo

ss


Suppression of Light Quarks

• High pT suppression / quenching of away-side jet for light quark hadrons

Pedestal&flow subtracted


Why Investigate Non-photonic Electrons?• Non-photonic electrons come from semi-leptonic decays of heavy quarks

– c e+ + anything (B.R. = 9.6%)• Do e+ + anything (B.R. = 6.87%) • D± e ± + anything (B.R. = 17.2%)

– b e+ + anything (B.R. = 10.9%)• B± e ± + anything (B.R. = 10.2%)

– plus small contribution from Drell-Yan for pT < 10 GeV/c

• Hadronic decays channels are– Do K– D* Do– D± K

• Must understand background from photonic electrons– conversions (o , e+e- )– Dalitz decays of o, , ’– Decays of , small– Ke3 decays (small)


Predictions for Heavy Quark Electron

Non-photonic electron suppression

Single e- RAA

Large electron suppression ~ 5 for c

Modest suppression ~ 2.5 for c+b

Single e- from NLO/FONLLM. Cacciari et al., PRL 95:122001 (2005)

Above which pT does beauty dominate?

Single e- from NLO/FONLL


Directly Reconstructed Open Charm Decays• Measure Do (Do) Kin d + Au and Au + Au for pT < 3 GeV/c

• InvestigatingD± K

• Non-photonic electrons push heavy quark studies to higherpT (~ 10 GeV/c)

D0

STAR, Phys. Rev. Lett. 94 (2005) 062301 H.Zhang (STAR) QM2005

STAR

STARSTAR


First Must Understand Production of Heavy Quarks• Heavy quarks produced via gg fusion in initial scattering

– Predicted by pQCD (should follow binary scaling)

• Total charm cross section per NN interaction

200 GeV minimum bias

AuAu

1.11 0.08(stat.) 0.42(sys.) mb

dAu

1.4 0.2(stat.) 0.4(sys.) mb

• Binary scaling dAu to AuAu Charm produced in initial collisions!

STAR Preliminary

NLO pQCD from R. Vogt

H. Zhang, X. Dong (STAR) QM05


Experimental Setup

Detectors used for electron ID: TPC tracking, dE/dx ||<1.3, =2 EMC towers, Shower Max 0 < < 1, =2 ToF patch

STARSTAR

EMC Barrel High Tower Trigger: Events with ET > 3 GeV in an EMC tower Enhanced high pT particles

hadrons electrons

Electron ID Using TPC and EMC

• TPC: dE/dx for p > 1.5 GeV/c• Tracks from primary vertex only

(intent – eliminate conversions,

i.e. reduce effective radiation length)

• Electrons discriminated from hadrons

for pT ≤ 8 GeV/c

• EMC:

a) Tower E p/E

b) Shower Max Detector (SMD)

• Hadron/electron showers develop

different shapes

• Use cuts on # hits

• Hadron Discrimination ~103-104

electrons

K p d

hadrons

electrons

Jaro Bielcik (STAR) QM05

STARSTAR


Determining the Electron Background

Inclusive Electron Spectra

Signal– Heavy quark semi-leptonic decays

Background– conversion

– Dalitz decays (primarily 0, )

Background rejection efficiency for central Au+Au

M e+e-<0.14 GeV/c2

Red - like-signBlack/gray - unlike-sign

Strategy for Photonic Electron Rejection

Combine all TPC electron candidates– Me+e-< 0.14 GeV photonic e’s

Subtract all non-primary vertex electrons

Correct for background rejection efficiency

STARSTAR


High pT Electron ID and Background SubtractionSTARSTAR


Inclusive Electron Spectra for sNN = 200 GeV AuAu

3 centrality bins0-5%, 10-40%, 40-80%

High tower trigger extendse spectra to pT ~ 10 GeV

Hadron contaminationcorrection (inc.) ~ 10 – 15 %

Remaining issue under studycharge exchange in EMC

(at high pT )

± 0

STARSTAR


Non-photonic electron spectra for pp, dAu and AuAu

• Photonic electrons subtracted• Excess of non-photonic

electrons observed• Consistent with STAR ToF

spectra

Beauty contribution expected above ~ 5 GeV/c

ToF data - H.Zhang (STAR) QM05

STARSTAR


pp

AA

AAAA

dpd

T

dpNd

R

3

3

3

3

Non-photonic Electron RAA

Suppression observed

~ 0.4-0.6 in 40-80% centrality

~ 0.3 -0.4 in 10-40%

~ 0.2 in 0-5%

Max suppression at pT ~ 5-6 GeV

STARSTAR

Theories currently cannot describe the data! Only c contribution describes RAA but not p+p spectra


Emphasis – Closer Look at Present Theory

Djordjevic et al, nucl-th/0507019

Observed suppression of heavy quarks is not understood!

Requires excessive gluon densities or dE/dx- incompatible with light quark RAA!


Contributions to Charm vs Beauty E-loss and Yields

• Radiative and collisional dE/dx differs for charm and beauty

S. Wicks, M. Gyulassy et al, nucl-th/0512076


Further Considerations for Suppression of Heavy Flavor

• Significant charm suppression due to 3-body elastic scattering (cqq cqq) in a QGP!

• Charm quark drag-coefficient 3-body ~ 2-body elastic and radiative scatterings.

• Large charm suppression at high pT described when both 2- & 3-body scatterings included.

• Only charm included here

– beauty expected to increase RAA!

W. Liu and C.M. Ko, nucl-th/0603004 (March 2006)


Present Uncertainties in Non-photonic Electrons

• R. Vogt uncertainty analysis when does beauty overtake charm?

The low end of c-b overlap

The high end of c-b overlap


Summary and Conclusions

• Non-photonic electrons measured in pp, dAu, Au up to pT ~ 10 GeV/c

– Can be used to determine charm + beauty spectra (RAA) at RHIC

• Strong suppression of non-photonic electrons (heavy flavors) in AuAu– Suppression similar to light quark suppression in AuAu

– Large energy loss for heavy quarks also (similar to light quarks)?

• Observed suppression not explained by present theory– Unless little to no beauty contribution

– However, this is incompatible with p + p spectrum

• Need further consideration of production/propagation of charm & beauty– Theory – collisional (3-body) & radiative E-loss, dynamical evolution,…

– Experiment – measure displaced vertices

• directly measure and separate charm/beauty secondary vertices


Special thanks for contributions to presentation

Jaro Bielcik

Alex Suaide

Zhangbu Xu

Thomas Ullrich

Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale) Suppression of Non-photonic Electrons at High Pt John W. Harris Yale University.

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