417 th WE-Heraeus-Seminar Characterization of the Quark Gluon Plasma with Heavy Quarks Physikzentrum...
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![Page 1: 417 th WE-Heraeus-Seminar Characterization of the Quark Gluon Plasma with Heavy Quarks Physikzentrum Bad Honnef June 25-28, 2008 Ralf Averbeck, Heavy-Flavor.](https://reader035.fdocuments.us/reader035/viewer/2022062515/56649cdb5503460f949a58d7/html5/thumbnails/1.jpg)
417th WE-Heraeus-Seminar
Characterization of the Quark Gluon Plasma with Heavy Quarks
Physikzentrum Bad Honnef
June 25-28, 2008
Ralf Averbeck,
Heavy-Flavor Cross Sections at RHIC
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R. Averbeck,2 June 26, 2008
charm and bottom from hadronic collisions mc~1.3 GeV, mb~4.5 GeV hard process (mq >> QCD),
even at low pT
open heavy flavor (D, c, B, b) quarkonia (J,
heavy-ion collisions heavy quarks are produced before the medium is formed
Introduction
D mesons
, ’,
investigating QCD matter with hard probes well calibrated in pp collisions slightly affected and well understood in hadronic
matter strongly affected in a partonic medium
today's focus: calibration at RHIC
vacuum
hadronicmatter
QGP
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R. Averbeck,3 June 26, 2008
hadronic decay channels D0 K (BR: ~4%) D0 K0 (BR: ~14%) D± K (BR: ~10%) c pK (BR: ~5%)
How to measure open heavy flavor
c c
0DK
0D
K+
-
advantage unambiguous identification,
i.e. a peak in invariant mass
disadvantagesdifficult to triggerhuge combinatorial
background improvement?
–resolve decay vertices–charm: c ~ 100-200 m–bottom: c ~ 400-500 m
silicon vertex detectors
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R. Averbeck,4 June 26, 2008
semileptonic decay channels D0 lX (BR: ~7%) D± lX (BR: ~17%) c lX (BR: ~5%) B0,± lX (BR: ~11%)
How to measure open heavy flavor
c c
0DK
0D
K+
-
advantages 'straight forward' trigger no combinatorial BG
disadvantagesneed to control/subtract
background from other lepton sources
loss of kinematic information
continuum can NOT disentangle c & b with single leptons only
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R. Averbeck,5 June 26, 2008
2 central electron/photon/hadron spectrometer arms: 0.35 p 0.2 GeV/c
PHENIX & STAR at RHIC
2 forward muon spectrometers:1.2 < || < 2.4 p 2 GeV/c
muons in forward arms tracking muon ID:“absorber”
electrons in central arms tracking electron ID:
RICH + EMC
large acceptance tracking detector: TPC hadrons:
TPC (dE/dx) Time-of-Flight detector
electron ID: EMC in addition
PHENIX
optimized fo
r leptons
but can do hadrons STAR
optimized fo
r hadrons
but can do leptons
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R. Averbeck,6 June 26, 2008
MANY electrons sources Dalitz decay of light neutral mesons
– most important → e+e-
– but also: ’ conversion of photons
– main photon source: → – in material: → e+e-
weak kaon decays– Ke3, e.g.: K± → e± e
dielectron decays of vector mesons– → e+e-
direct/thermal radiation– conversion of direct photons in material– virtual photons: * → e+e-
heavy flavor decays
need excellent BG subtraction!
e± from heavy flavor: difficulties
PHOTONIC e±
NON-PHOTONIC e±
electrons are rare: e±/± ~ 10-2
need excellent PID!
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R. Averbeck,7 June 26, 2008
Cocktail subtractionALL relevant background
sources are measured calculate e± BGBG subtraction e± from heavy-flavor decays
performance limited by signal/background ratio works well towards high pT
– good for measurement of e± spectra
difficult towards low pT
– limited use for measurement of total cross sections
PRL 96(2006)032001 p+p @ √s = 200 GeV
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R. Averbeck,8 June 26, 2008
PRL 97, 252002 (2006)
p+p @ √s = 200 GeV
Converter subtraction converter (known X/X0)
added for part of the run converter multiplies
photonic BG by KNOWN factor difference between converter in & out runs MEASURES photonic BG
performance limited by statistics in converter run works well towards low pT
– good for total cross section measurement
difficult towards high pT
excellent agreement between methods!
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R. Averbeck,9 June 26, 2008
PRL 97, 252002 (2006)
total cross section cc= 56757(stat)±224(sys) b
e± from heavy flavor in p+p (√s=200 GeV)non-photonic e± from c e± and b e±
comparison with FONLL calculation– Fixed Order
Next-to-Leading Log perturbative QCD (M. Cacciari, P. Nason, R. Vogt PRL95,122001 (2005))
– data ~ 2 x FONLL–seen also in charm yields at
» DESY (photoproduction)» FNAL (hadroproduction)
– consistent within large uncertainties
high pT: b is important!
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R. Averbeck,10 June 26, 2008
Background subtraction in STARphotonic e± BG in STAR
dominant source– photon conversions
– mainly in Si detectors near vertex
– conv. / Dalitz ~ 5– compare with PHENIX:
conv. / Dalitz ~ 0.5 subtraction
– large acceptance TPC – reconstruction and
subtraction of conversion and Dalitz pairs (efficiency: ~ 70-80% for pT > 4 GeV/c)
– remaining BG: cocktail
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R. Averbeck,11 June 26, 2008
ratio of heavy-flavor e± spectra to FONLLPHENIX
– spectral shape of e± agrees with FONLL
– total cross section above FONLL by a factor ~2
STAR– shape consistent with
PHENIX and FONLL– total cross section
above FONLL by a factor ~4
systematic uncertainties in pQCD are large, i.e. a factor ~2 (or even ~4: R. Vogt hep-ph/0709.2531)
PHENIX vs. STAR vs. FONLL
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R. Averbeck,12 June 26, 2008
PRL 98, 172301 (2007)
Hot matter: Au+Au at √sNN=200 GeV
ppinYieldN
AuAuinYieldR
binaryAA
PRL 98, 172301 (2007)
binary scaling of total e± yield from heavy-flavor decays hard process production and no destruction (as expected)
high pT e± suppression increasing with centrality footprint of medium effects; similar to 0 (a big surprise)
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R. Averbeck,13 June 26, 2008
Hot matter: Au+Au at √sNN=200 GeV
STAR & PHENIX: consistent in nucl. modification factor RAA normalization discrepancy does NOT depend on system size!
high pT e± suppression - a challenge for models what about bottom? need additional observables to address these issues!
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R. Averbeck,14 June 26, 2008
D0 K invariant mass analysismain problem: S/B ratio << 1/100
need huge stat. (yield uncertainty ~ 40-50%) currently limited to pT ≤ ~3 GeV/c
– reasonable for total cross section– insufficient to address high pT suppression
D-meson reconstruction in STAR
PRL 94(2005)062301A. Shabetai, QM'08 arXiv:0805.0364
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R. Averbeck,15 June 26, 2008
muon identification at low pT (~0.2 GeV/c)Time-of-Flight and
dE/dx in the TPC
Low pT muons in STAR
subtraction of BG from and K decaydistance of closest
approach of tracks to primary vertex
low pT muon yield sensitive to total charm
cross section insensitive to spectral shape
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R. Averbeck,16 June 26, 2008
combined fit to e±, ±, D0
data are consistent
Total charm cross section in STAR
binary scaling of charm yield total charm cross section ~ 1 mb
~ 4x pQCD value (still within huge uncertainties)
~ 2x PHENIX value
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R. Averbeck,17 June 26, 2008
Charm and bottom from e+e- pairs e+e- inv. mass after
background subtraction compared to cocktail
absolutely normalized excellent agreement charm & bottom
accessible after subtracting the cocktail
charm: integration after cocktail subtraction cc= 544 ± 39 (stat) ± 142 (sys) ± 200 (model) b from single e±: cc= 56757(stat)±224(sys) b
simultaneous fit of charm and bottom: cc= 518 ± 47 (stat) ± 135 (sys) ± 190 (model) b bb= 3.9 ± 2.4 (stat) +3/-2 (sys) b
bottom irrelevant for total e± yield, but crucial at high pT!
arXiv: 0802.0050
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R. Averbeck,18 June 26, 2008
electron – kaon charge correlation D decay
unlike-sign eK pairs B decay
mostly like sign eK pairs (with small (1/6) admixture of unlike-sign pairs)
approach– eh (for higher statistics)
invariant mass– subtract like-sign pairs from
unlike-sign pairs– disentangle charm and
remaining bottom contribution via (PYTHIA) simulation of charm and bottom decay kinematics
Separating ce from be (I) the key: electron-hadron correlations
charm and bottom are differentc c
0DK
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R. Averbeck,19 June 26, 2008
electron-hadron azimuthal angle correlations small angle (near side)
electron and hadron are from the same decay
width of near side correlation: largely due to decay kinematics
B decay has larger "Q value" than D decay
approach– eh azimuthal angle correlation
for B and D decays from PYTHIA– fit measured correlation with
B/(B+D) as parameter
Separating ce from be (II) the key: electron-hadron correlations
charm and bottom are differentc c
0DK
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R. Averbeck,20 June 26, 2008
electron-D0 correlations trigger on e from heavy-flavor decay use D meson (reconstructed in
hadronic decay) as a probe investigate eD correlation in azimuth
Separating ce from be (III) the key: electron-hadron correlations
charm and bottom are different
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R. Averbeck,21 June 26, 2008
e from b / e from c ≥ 1 for pT ≥ 6 GeV/cPHENIX & STAR: consistent with FONLL
B contribution to e± spectra
not precise enough to extract b suppressionneed vertex detectors to measure charm and bottom hadrons!
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R. Averbeck,22 June 26, 2008
high pT muons in PHENIX: 1.2<||<2.2 again, background subtraction is difficult
Rapidity dependence of charm production
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R. Averbeck,23 June 26, 2008
charm yield similar at mid and forward rapidity large uncertainties everywhere
better data are needed measurement of displaced vertices
Rapidity dependence of charm production
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R. Averbeck,24 June 26, 2008
charm (& bottom) are crucial probes for the medium produced in HI collisions @ RHIC
even calibration measurements are difficult large uncertainties
charm cross section / binary collisionbinary scaling is observed in STAR
& PHENIXbut the cross sections differ
by a factor ~2
Summary
from e, , D
from e, e+e-
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R. Averbeck,25 June 26, 2008
complete systematics of existing observablesPHENIX
– e± from d+Au & Cu+Cu
– D reconstruction in p+p (D0 K+-0)
– heavy flavor from e- pairs
Outlook: near future
photonic backgroundreduced by factor ~10
STAR– improved e± data from
running without inner silicon detectors
X. Dong, Hard Probes '08
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R. Averbeck,26 June 26, 2008
silicon vertex trackers for unambiguous resolution of displaced vertices direct D- and B-meson measurements
Outlook: longer term future
PHENIX STAR