Non-photonic electron production in STAR

A. G. Knospe

Yale University

9 April 2008

Heavy Flavor and the QGP• Heavy quarks produced in

initial hard scattering of partons– Dominant: gg QQ– Production rates from pQCD– Sensitive to initial gluon

distributions

• Heavy quark energy loss– Prediction: less than light quark

energy loss (dead cone effect)

– Sensitive to gluon densities in medium

light

M.Djordjevic PRL 94 (2004)

ENERGY LOSS

bottom

parton

medium

slide 1

_

A. G. Knospe

Heavy Flavor Decays• Must study heavy-flavor decay products• Some studies reconstruct hadronic decays: i.e. D0K,

D*D0, D±K, Ds± (S. Baumgart, A. Shabetai)

• I look at semileptonic decay modes:– c e+ + anything (B.R.: 9.6%)

• D0 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%)

– decay modes• Heavy flavor decays expected to dominate

non-photonic (single) e± spectrum; b decays should dominate at high pT

• Photonic e± background:– conversions (, e+e-)– Dalitz decays of 0, , ’– , , Ke3 decays (small contributions)

non-photonic e±

slide 2 A. G. Knospe

Previous Results• Combine e± with oppositely

charged tracks in same event; e± is background if Minv < 150 MeV/c2

• Simulate background e± from “cocktail” of measured sources (,0,, etc.)

• Measure e± with converter, extrapolate to 0 background

To Remove Photonic e± Background:

Au+Au:0-5%

40-80%

p+p

d+Au

Au+Au:0-92%

0-10%

10-20%

20-40%

40-60%

60-92%

p+p

10-40%

STAR: Non-photonic e±, √sNN=200 GeV

STAR: B. I. Abelev et al, Phys. Rev. Lett. 98 (2007) 192301PHENIX: A. Adare et al, Phys. Rev. Lett. 98, 172301 (2007)

PHENIX: Non-photonic e±, √sNN=200 GeV

slide 3 A. G. Knospe

Nuclear Modification FactorPHENIX and STAR: RAA for Non-photonic e±

central Au+Au, √sNN=200 GeV

Light Hadron RAA

PHENIX: PRL 98 (2007) 172301STAR: PRL 98 (2007) 192301DVGL: Djordjevic, Phys. Lett. B 632 (2006) 81BDMPS: Armesto, Phys. Lett. B 637 (2006) 362

slide 4

• RAA for non-photonic e±: PHENIX consistent with STAR

• Similar to light hadron RAA

• Kinematics: pT(e±) < pT(D)• Use light hadron RAA to

constrain parameters dNg/dy, q • Models tend to under-predict

suppression• Models still being refined

^

A. G. Knospe

Nuclear Modification FactorPHENIX and STAR: RAA for Non-photonic e±

central Au+Au, √sNN=200 GeV

Light Hadron RAA

PHENIX: PRL 98 (2007) 172301STAR: PRL 98 (2007) 192301DVGL: Wicks, nucl-th/0512076 (2005)van Hees, Phys. Rev. C 73 034913 (2006)

slide 4

• RAA for non-photonic e±: PHENIX consistent with STAR

• Similar to light hadron RAA

• Kinematics: pT(e±) < pT(D)• Use light hadron RAA to

constrain parameters dNg/dy, q • Models tend to under-predict

suppression• Models still being refined

A. G. Knospe

^

Nuclear Modification FactorPHENIX and STAR: RAA for Non-photonic e±

central Au+Au, √sNN=200 GeV

Light Hadron RAA

PHENIX: PRL 98 (2007) 172301STAR: PRL 98 (2007) 192301DVGL: Djordjevic, Phys. Lett. B 632 (2006) 81

slide 4

• RAA for non-photonic e±: PHENIX consistent with STAR

• Similar to light hadron RAA

• Kinematics: pT(e±) < pT(D)• Use light hadron RAA to

constrain parameters dNg/dy, q • Models tend to under-predict

suppression• Models still being refined• Do only c decays contribute?

A. G. Knospe

^

B-decay Contribution

• STAR measures angular correlations of non-photonic e+ with hadrons– sensitive to relative

contributions of D and B decays

• Measured B/(B+D) ratio consistent with FONLL– ~ 40% at pT=5 GeV/c

• b-quarks should be considered in RAA calculation (cf. previous slide)

Fractional Contribution of B

slide 5

X. Lin, SQM 2007

A. G. Knospe

Non-photonic electrons in Cu + Cu, 200 GeV events

Cu+Cu: Event Selection• Analyze STAR data from 2005

Cu+Cu 200 GeV run• EMC High Tower Trigger:

– At least one tower with E > 3.75 GeV – Enhances yields at high pT

• Start with: 34M minimum bias events and 3.7M high tower events

• Event Selection Cuts:– centrality 0-54%– primary vertex |z| < 20 cm– Normal e+ yield

• Analyzed 10M min. bias events and 1.9M high tower events

slide 6

preliminary

preliminary

A. G. Knospe

e± Identification• BEMC:

– EMC = Towers + Shower Maximum Detector (SMD)

– e± in STAR EMC: p/E ≈ 1– Use a loose cut: 0 < p/E < 2– SMD used to identify e±: showers

better developed than h±

– Require hits (> 2 strips) in both the and planes of SMD

– Mean BEMC Acceptance ~78%

• TPC:– 3.5 < dE/dx < 5 keV/cm– Good dE/dx separation

between e± and ± for p > 1.5 GeV/c

– distance to primary vertex < 1.5 cm

– 0 < < 0.7– quality cuts

EMC

slide 7

preliminary

A. G. Knospe

e± Identification• BEMC:

– EMC = Towers + Shower Maximum Detector (SMD)

– e± in STAR EMC: p/E ≈ 1– Use a loose cut: 0 < p/E < 2– SMD used to identify e±: showers

better developed than h±

– Require hits (> 2 strips) in both the and planes of SMD

– Mean BEMC Acceptance ~78%

• TPC:– 3.5 < dE/dx < 5 keV/cm– Good dE/dx separation

between e± and ± for p > 1.5 GeV/c

– distance to primary vertex < 1.5 cm

– 0 < < 0.7– quality cuts

slide 7 A. G. Knospe

hadrons e±

preliminary

preliminary

e± Identification• BEMC:

– EMC = Towers + Shower Maximum Detector (SMD)

– e± in STAR EMC: p/E ≈ 1– Use a loose cut: 0 < p/E < 2– SMD used to identify e±: showers

better developed than h±

– Require hits (> 2 strips) in both the and planes of SMD

– Mean BEMC Acceptance ~78%

• TPC:– 3.5 < dE/dx < 5 keV/cm– Good dE/dx separation

between e± and ± for p > 1.5 GeV/c

– distance to primary vertex < 1.5 cm

– 0 < < 0.7– quality cuts

slide 7 A. G. Knospe

hadrons e±

SMD Clusters:

preliminary preliminary

Corrections• Embed simulated e± tracks into

real Cu+Cu events• = Reconstruction Efficiency:

fraction of simulated e± reconstructed and identified by cuts

• Correct for TPC energy loss separately

• Fit ln(dE/dx) projections in p slices

• purity (P): fraction of particles within dE/dx cut that are e±

– 90-100%, decreasing w/ pT

• efficiency (E): fraction of e± that fall within dE/dx cut– 70-80%

slide 8

preliminary

from embedding

Cu+Cu 200 GeV, MinBias, 0-54%

A. G. Knospe

preliminary

e±

±

h±

from real data

2 GeV/c < p < 3 GeV/c

Photonic e± Background• Dominant sources of

photonic e±:– Conversion ( e+e-)– Dalitz decays (0, e+e-)

• Photonic e± from invariant mass cut:– e± is paired with oppositely-

charged tracks in same event• Same-charge pairs give

combinatorial background– Find pairs with dca < 1.5cm

and M(e+e-) < 150 MeV/c2

– Photonic e± yield:

slide 9

back. comb.pairs charge-unlike

2 NNNNP

• Some ph. e± not rejected– Embed simulated 0 e+e-

decays + conversions into real Cu+Cu events

– Background rejection efficiency (B): eff. to find true conversion partner (70-80%)

preliminary

black: e+e- pairsblue: comb. back.red=photonic

invariant mass [GeV/c2]

1.2 GeV/c < pT < 1.6 GeV/c

A. G. Knospe

Spectra and RAA

inclusive rawinclusive corrected

E

P

A

photonic raw1

photonic correctedBE

P

A

• Apply corrections:

• Merge data sets• Nuclear Modification Factor:

– Nbinary = 82.2 for 0-54%– RAA ~ 0.6 - 0.7 for pT > 3 GeV/c

slide 10

ppdN

pRbinary

inelasticTAA

CuCuyield

preliminary

preliminary

A. G. Knospe

RAA Comparisons• Consistent with ± RAA

in Cu+Cu 200 GeV

Non-photonic e± Cu+Cu 200 GeV

0-54%

• Consistent with Au+Au 200 GeV data for similar Npart

RAA for ±, Cu+Cu 200 GeV RAA for non-photonic e±

slide 11

*

R. Hollis, WWND 2007 STAR: PRL 98 (2007) 192301PHENIX: PRL 98 (2007) 172301

A. G. Knospe

Summary

• Non-photonic e± are proxies for heavy quarks

• Found the non-photonic e± spectra in Cu+Cu 200 GeV data– Particle ID in TPC, BEMC,

BSMD– Remove photonic e± with

invariant mass cut: M(e+e-) < 150MeV/c2

• Nuclear Modification Factor 0.6 - 0.7 for pT > 3 GeV/c, centrality 0-54%– Consistent with ± RAA in

Cu+Cu 200 GeV– Consistent with non-

photonic e± RAA in Au+Au 200 GeV at similar Npart

slide 12 A. G. Knospe

The Future

• Coming soon: find yields and RAA in three centrality bins

• Paper on D-mesons and non-photonic e± in Cu+Cu 200 GeV: S. Baumgart, A. G. Knospe, and A. Shabetai

slide 13

Thank you! Are there any questions?

A. G. Knospe

Additional Material

Comparisons to PQCD• FONLL describes shape

of non-photonic e± spectra

• PHENIX spectrum < STAR by factor ~2

• FONLL predition < STAR by factor ~4-5

• differences constant in pT

Non-photonic e± in p+p, 200 GeV

• New PQCD calculations:– Error bars on total cc larger

than earlier calculations– STAR data consistent with

new upper limit (Prediction II)

Total Charm Cross-Section

A. G. Knospe