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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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
Suppression of Light Quarks
• High pT suppression / quenching of away-side jet for light quark hadrons
Pedestal&flow subtracted
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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)
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
High pT Electron ID and Background SubtractionSTARSTAR
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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!
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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)
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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
Winter Workshop on Nuclear Dynamics – San Diego, 16 Mar. 2006John Harris (Yale)
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