non-photonic electron production in star a. g. knospe yale university 9 april 2008
Post on 22-Dec-2015
218 Views
Preview:
TRANSCRIPT
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
top related