Transcript Document

Heavy-Flavour Production in
Nucleus-Nucleus Collisions:
From RHIC to LHC
André Mischke
ERC-Starting Independent Research Group
QGP - Utrecht
Hirschegg 2010
Strongly Interacting Matter under Extreme Conditions
38nd International Workshop on Gross Properties of Nuclei and Nuclear Excitations
Hirschegg, Kleinwalsertal, Austria, January 17 - 23, 2010
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Outline
• Introduction
- heavy-flavour production and energy loss
in QCD matter
• Total charm production cross section
• Nuclear modification factor
• Heavy-flavour azimuthal correlations
• Summary
I will not talk about collectivity and Quarkonia
Andre Mischke (UU)
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Probing hot and dense QCD matter
• Simplest way to establish the
properties of a system
- calibrated probe
- calibrated interaction
- suppression pattern tells about
density profile
Quark-Gluon
Plasma
• Heavy-ion collisions
p+p collision
collision
Au+Au
- hard processes serve as
calibrated probe (pQCD)
after the collision
Nuclear modification factor:
Yield ( A  A)
RAA ( pT ) 
Yield ( p  p )  N coll
Andre Mischke (UU)
- traversing through the medium
and interact strongly
- suppression provides density
measure
- General picture: energy loss via
medium induced gluon radiation
(Bremsstrahlung)
Hirschegg - 22. Jan. 2010
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Light hadron spectra at RHIC
• Strong suppression in central
Au+Au collisions
• Suppression well described by
energy loss models
• Medium density 30-50 times
normal nuclear matter
• Surface bias effectively leads
to saturation of RAA with density
photons
light charged hadrons,
neutral pions
K.J. Eskola et al., Nucl. Phys. A747 (2005) 511
• Limited sensitivity to the
region of highest energy density
central RAA data
increasing density
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Heavy quark production
“Thermalization
Hadronisation
of QGP”
Quarkonia melts
and flow develops
~0.1
~1
Parton energy loss
~10
1015
time scale (fm)
Heavy-flavour production
 ~ h/2mQ
• Primarily produced by gluon fusion in early stage
of collision: production rates calculable in pQCD
• Sensitivity to initial state gluon distribution
Charm,
PYTHIA 6.208
M. Gyulassy and Z. Lin, Phys. Rev. C51, 2177 (1995)
• Heavy quarks provide information about the
hottest initial phase of the collision
• Higher penetrating power: mQ>> Tc, QCD
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Energy loss of heavy quarks
• Probe deeper into the medium
hot and dense medium
parton
Dead-cone effect:
gluon radiation suppressed at
small angles (q < mQ/EQ)
Wicks et al, NPA784, 426 (2007)
Dokshitzer & Kharzeev, PLB 519, 199 (2001), hep-ph/0106202
• Less energy loss:
Eg > ELQ > EHQ
Gluon radiation probability:

dI
d


HEAVY
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dI
d

1   mQ
E

 Q

LIGHT




2
1 
q2 

2
Hirschegg - 22. Jan. 2010
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Detection of heavy-flavour particles
 Semileptonic decay of charm and bottom
mesons
single or nonphotonic electron
- first evidence for heavy-flavour particles
F.W. Buesser et al. (CCRS), Nucl. Phys. B113, 189 (1976)
- robust electron trigger
- needs handle on photonic background
 Full reconstruction of open charmed
mesons
- direct clean probe: signal in invariant mass
distribution
- difficulty: large combinatorial background;
especially in a high multiplicity environment
- event-mixing and/or vertex tracker needed
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Single electron spectra
Phys. Rev. Lett. 98 (2007) 192301
Phys. Rev. Lett. 98, 172301 (2007)
Au+Au
Au+Au
0-5%
10-40%
40-80%
d+Au
p+p
p+p
• Spectra measured up to 10 GeV/c
• Integrated yield follows binary collision scaling
• Yield strongly suppressed at high pT for central Au+Au
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0
D
reconstruction in STAR
d+Au 200 GeV
PRL 94 (2005) 062301
Au+Au 200 GeV
arXiv:0805.0364 [nucl-ex]
Cu+Cu 200 GeV
A. Shabetai, QM 2008
• First identified open charmed mesons in heavy-ion collisions
• Current measurements limited to low-pT
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Charm cross section in STAR
• Use all possible signals
- D0 mesons
- electrons
- muons
D0
• Charm cross section is well
constrained
muon
- 90% of total cross section
- direct measurement
- D0 mesons and muons
constrain the low-pT region
electron
 ccNN  1.40  0.11(stat.)  0.39(syst.) mb
in 0-12% central Au+Au
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Di-electron measurement in PHENIX
Phys. Lett. B670, 313 (2009)
after subtraction of cocktail
c dominant
b dominant
• “Cocktail” of backgrounds constructed from measured
background sources
• Comparison to charm, bottom and Drell-Yan from PYTHIA
•
cc= 518 ± 47(stat) ± 135(sys) ± 190(model)
mb
± 2.4(stat) +3/-2(sys)
mb electrons (PRL 103, 082002 (2009))
bb= 3.9agreement
In good
with single
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Inclusive charm production cross section
x4.5
x2
R. Vogt, Eur. Phys. J. Spec.
Topic 155, 213 (2008)
• Factor ~2 difference between STAR and PHENIX; but consistency with
NLO pQCD (large uncertainties; primarily from scale choice and parton density functions)
• Checks
- removal of silicon vertex detectors (STAR)
- better control over background contributions (PHENIX): 1/3 of single electrons are
from J/ decays for pT > 5 GeV/c up to 16% decrease in open heavy
• Cross section follows binary collision scaling
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Open-charmed meson spectra from CDF
pp¯ @ 1.96 TeV
5.8 pb-1
• Deviation of 50-100% at moderate and high-pT, but
consistent within errors
• Theoretically not fully understood …even in pp collisions
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Charm production cross section (cont’d)
NLO pQCD, CTEQ6M parton densities
R. Vogt, private communication, 2009
LHC: 7-10 TeV
• Large uncertainties  more data needed to constrain
model parameters
• Parton spectra from pQCD input for energy loss models
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Charm cross section in ALICE
• First promising decay
channels
- D*  D0s, D0  K, D+  K-++
- D,B  e + X
• ALICE has the capability
to measure open charm
down to pT = 0 in pp and
p-Pb (1 GeV/c in Pb-Pb)
• ITS: impact parameter
resolution better than 50 mm
for pT > 1.5 GeV/c
cc
cc
 LHC
 25  RHIC
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bb
bb
 LHC
 100  RHIC
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NLO processes: gluon splitting
c
cbar
g
g
c

cbar
flavor creation (LO)
g
g
g
0
g
A. M., PLB 671, 361 (2009)
MC@NLO
LO PYTHIA
like-sign e-K pairs
3 < pT < 7 GeV/c
gluon splitting (NLO)
• e-D0 correlations at 200 GeV
- away-side peak: Good agreement
of peak shape between LO PYTHIA
and MC@NLO
- near-side: small gluon splitting
contribution (6.5%)
• Gluon splitting rate at RHIC
consistent with MC@NLO
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LHC ?
MC@NLO
Gluon jet energy (GeV)
D* - jet azimuthal correlations at LHC
Full Pythia simulation, pp@10 TeV
candidates
 background
☐ signal

gluon splitting +
flavour creation
300k jets, <Ejet> ~ 30 GeV
gluon splitting
(z < ~0.5)
• Different fragmentation characteristic:
soft charm FF for gluon jets
• Results promising; more statistic needed
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Nuclear modification factor
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Single electron RAA
One of the most surprising results from RHIC
light hadrons
STAR
PHENIX
• Electron yield at high-pT stronger suppressed than expected
• Models implying D and B energy loss are inconclusive yet
• Large suppression requires extreme conditions;
DGLV: dNg/dy = 3500
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Hope? – AdS/CFT
• Heavy quarks lose
momentum according to
dp/dt = −p/Q + stochastic
• Equilibration times Q
are roughly consistent
with single electron RAA
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Open heavy-flavour in Pb+Pb in ALICE
D0  K
Open bottom reconstruction
through displaced electrons
S/B ≈ 10 %
S/(S+B) ≈ 40
1 year @ nominal luminosity
107(109) central Pb+Pb(p+p) events
D0  K
B  e+X
mb = 4.8 GeV
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Hirschegg - 22. Jan. 2010
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Heavy-flavour energy loss at LHC
Colour charge dependence
Mass hierarchy
D
h
RD / h ( pt )  RAA
( pt ) RAA
( pt )
e from B
e from D
RB / D ( pt )  RAA
( pt ) RAA
( pt )
• More details on heavy-flavour quenching mechanism
• RcAA/RbAA ratio different for pQCD and AdS/CFT
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Single electron – D0 correlations
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D and B contribution to single electrons
• FONLL has large
uncertainty around the Be
/ De crossing point (RHIC:
3 < pT < 10 GeV/c)
• Crossing point at LHC
similar to that at RHIC
• Separate De and Be
contribution experimentally
−c
-- b
e± + X (BR = 9.6%)
e± + X (BR = 10.86%)
compilation by A.M. 2009
M. Cacciari et al., PRL 95, 122001 (2005)
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Single electron-tagged correlations
trigge
r
NLO pQCD: D/B meson crossing
point is largely unknown
Near side: study D/B
decay contribution to
single electrons?
M. Cacciari et al., PRL 95, 122001 (2005)
A. M., PLB 671, 361 (2009)
PYTHIA, pp@200 GeV
bottom dominant
charm dominant
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Away side: study in-medium D/B
lose energy? conical emission?
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Electron-hadron correlations in STAR
• B and D contributions
comparable at pT > 5 GeV/c
and consistent with FONLL
• Similar result from
PHENIX (PRL 103, 082002)
• Bottom stronger
suppressed than expected?
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Single electron RAA at LHC
Pyquen: Pb+Pb(5%)@5.5 TeV
T0 = 1 GeV
0 = 0.15 fm/c
# quark flavours: 2
H. van Hees and R. Rapp, 2007
I. Vitev, A. Adil & H. van Hees, 2007
Pyquen
• Pythia afterburner
• Radiative (generalisation of BDMPS)
and collisional energy loss (high-pT
approximation)
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Single electron –
0
D angular
correlations
2 < pTtrigger ele < 4 GeV/c
Pythia
Pyquen
• Near side: B decays + gluon splitting charm
• Away side: charm flavour creation
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900M events
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NLO processes
bottom
Andre Mischke (UU)
E. Norrbin and T. Sjostrand, Eur. Phys. J. C17, 137 (2000)
charm
GS charm + B decays
GS charm only
NLO processes (such as
gluon splitting) become
important at LHC
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(e, D0): Near-side width and IAA
2 < pTtrigger ele < 4 GeV/c
IAA of near-side yield
• Broader peak for Pyquen than Pythia
• Suppression of D0 yield for Pyquen
• Next: fragmentation function
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Summary
• Heavy quarks are particularly good probes to study the properties
of hot QCD matter (especially transport properties)
• RHIC (200 GeV)
- energy loss of heavy quarks in the medium larger than expected
energy loss mechanism not fully understood yet (bottom stronger
suppressed as expected ?)
• LHC (14 and 5.5 TeV)
- pp data are important baseline measurements
- inclusive charm production cross section & spectral shape: test pQCD
- relevant for suppression measurements of Quarkonia states
- NLO processes (like gluon splitting) become important:
accessible by “charm content in jets” measurements
Pythia  pp
Pyquen  PbPb
- Jet-like heavy-flavour particle correlations:
modification of the fragmentation function
- First heavy-ion collisions anticipate in fall 2010
• Exciting time ahead of us…
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Backup
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Electron identification
Data
PHENIX
MC (0+Ke3)
0 Dalitz and
g conversion (MC)
• Electromagnetic calorimeter
and RICH at mid rapidity
Ke3 decays (MC)
 pT < 5 GeV/c
E/p
STAR
• ToF + TPC
 pT < 4 GeV/c
• EMCal + TPC
 pT > 1.5 GeV/c
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Electron background sources
• Photonic electron background
Phenix
- g  e+ + e- (small for Phenix)
- 0  g + e+ + e- h, , , etc.
• Phenix is almost material free
 their background is highly
reduced compared to STAR
• Background is subtracted by two
independent techniques - very
good consistency between them
e+
STAR
e-
- converter method (1.68% X0)
dca
- cocktail method
• STAR determines photonic
background using invariant mass
e-
g
mass (GeV/c2)
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Electron-hadron correlations in PHENIX
p+p
• Use e-K invariant mass
• Statistics limited
arXiv:0903.4851
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• Mid-rapidity electron and forwardrapidity muon -> promissing…
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Charmonium contribution to single electrons
• New study takes J/ e±+X
contribution into account
• 1/3 of single electrons are from
J/ decays for pT > 5 GeV/c
 up to 16% decrease in open
heavy
• But what is RAA of high-pT J/ ?
1/3 of e from J/ decays
Andre Mischke (UU)
• Background contribution from
K0s decays may also play a role
(especially at low-pT)  under
investigation
Hirschegg - 22. Jan. 2010
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Charm and bottom RAA
pT > 5 GeV/c
• Knowing RAA of single
electrons and relative B
contribution rB in p+p
collisions, one can study
RAA(b) as a function of RAA(c):
RAA = rB RAA(b) + (1-rB) RAA(c)
• Exclude original radiative
calculation
• D and B measurements in
A+A necessary
I: Djordjevic, Gyulassy, Vogt and Wicks, PLB 632 (2006) 81; dNg/dy = 1000
II: Adil and Vitev, PLB 649 (2007) 139
III: Hees, Mannarelli, Greco and Rapp, PRL 100 (2008) 192301
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Single electron-hadron correlations in Au+Au
STAR preliminary
• Away-side modification?
• Improved statistics and better background rejection needed
• Similar analysis in PHENIX
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D* in jets
UA1 jet reconstruction
- cone size 0.4
- Ethr = 10 GeV/c2
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Heavy-flavour production at LHC
• Heavy flavour copiously
produced
• Charm and bottom yields
(NLO pQCD predictions using MNR PDF)
system,
sNN
pp @ 14 TeV
Pb+Pb (0-5%)
@ 5.5 TeV
QQ
 NN
[mb]
11.2 / 0.5
4.3 / 0.2
NtotQQ
0.16 / 0.006
115 / 4.6
cc
cc
 LHC
 25  RHIC
bb
bb
 LHC
 100  RHIC
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Kinematics for c-cbar pairs
ALICE (central barrel) acceptance
Δϕ
Δη
Gluon splitting
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(e,D0) correlations for like-sign pairs
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Near-side width and yield
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Near-side IAA
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Relevant heavy-flavour decay modes
• Charm
charmed meson modes
c  D0 + X (BR = 56.5%)
Based on e+e- data from
c  D+ + X (BR = 23.2%)
CLEO/ARGUS and LEP
c  D*+ + X (BR = 23.5%)
experiments
semileptonic channel
c  e+ + X (BR = 9.6%)
 single (non-photonic) electron continuum
• Bottom
charmed meson modes
b  D0 + X (BR = 59.6%)
b  D- + X (BR = 23.5%)
b  D*+ + X (BR = 17.3%)
semileptonic channel
b  e+ + X (BR = 10.86%)
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Hirschegg - 22. Jan. 2010
Review of Particle Physics,
C. Amstler et al. (Particle Data
Group), Physics Letters B667,
1 (2008).
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LHC running conditions
pp nominal run
Pb-Pb nominal run
Ldt = 5.1026 cm-2 s-1 x 106 s
Ldt dt = 3.1030 cm-2 s-1 x 107 s
5.1032 cm-2 PbPb run, 5.5 TeV
5.1037 cm-2 for pp run, 14 TeV
NPbPb collisions = 2 .109 collisions
Npp collisions = 2 .1012 collisions
Muon triggers:
~ 100% efficiency, ~ 1kHz
Electron triggers:
Bandwidth limitation
NPbPb central = 2 .108 collisions
Hadron triggers:
NPbPb central = 2 .107 collisions
Muon triggers:
~ 100% efficiency, < 1kHz
Electron triggers:
~ 50% efficiency of TRD L1
20 physics events per event
Hadron triggers:
Npp minb = 2 .109 collisions



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Hirschegg - 22. Jan. 2010

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