Transcript Heavy-flavour production in p-p and Pb-Pb collisions at ALICE André Mischke for the ALICE Collaboration Rencontres de Moriond - QCD and High Energy Interactions La.

Heavy-flavour production
in p-p and Pb-Pb collisions
at ALICE
André Mischke for the ALICE Collaboration
Rencontres de Moriond - QCD and High Energy Interactions
La Thuile, Italy – 20-27 March 2011
Outline
• Motivation
• ALICE detector setup
• Trigger and data sample
• Production cross sections in 7 TeV p-p collisions
- D mesons at mid-rapidity
- single electrons at mid-rapidity
- single muons at forward rapidity
• First open charm signals in Pb-Pb at √sNN = 2.76 TeV
• Summary
Andre Mischke (ERC-UU)
Moriond-QCD 2011
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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 collision
p+pcollision
collision
Pb-Pb
after the collision
- hard processes serve as calibrated
probe (pQCD)
- traversing through the medium and
interact strongly
Quantify medium effects with
nuclear modification factor
- suppression provides density
measurement
Yield ( A  A)
RAA ( pT ) 
Yield ( p  p )  N coll
- General picture: energy loss via
medium induced gluon radiation and
collisional energy loss
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Energy loss of heavy quarks
• Higher penetrating power
 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., Nucl. Phys. A784, 426 (2007)
Y. Dokshitzer, D. Kharzeev, PLB 519, 199 (2001), hep-ph/0106202
• Less energy loss:
Eg > ELQ > EHQ
Gluon radiation probability:

dI
d


HEAVY
Andre Mischke (ERC-UU)
dI
d

1   mQ
E

 Q

LIGHT




2
1 
q2 

2
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A Large Ion Collider Experiment
L3 magnet
B = 0.5 T
Size: 16x26 meters
Weight: 10.000 tons
Complete
ITS, TPC, TOF, HMPID,
FMD, T0, V0, ZDC,
PMD, EMCAL (approved 2009),
Muon arm, Acorde, DAQ,
HLT (High Level Trigger)
Partial installation
10/18 TRD (approved 2002)
3/5 PHOS (funding)
Short status:
All systems
fully
operational
• PID from ~100 MeV/c to above 30 GeV/c
• Large acceptance in azimuth
• Mid-rapidity coverage (|| < 0.9) and -4 <  < -2.5 in forward region
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Trigger and data sample
• Minimum bias (MB) trigger:
coincidences between
SPD
- SPD or V0 A-side or V0 C-side
- at least one charged particle in
8 η units
V0-A
- 95% efficient on sinel
V0-C
• single-muon trigger
- forward muon in coincidence
with MB
L ~ 1025 cm-2s-1
rate ~ 100 Hz
Lint ~ 9 μb-1
Pb-Pb
Andre Mischke (ERC-UU)
Year
Collision
system
Energy
(TeV)
# of MB
events
2009
p-p
0.9
3.x105
2009
p-p
2.36
4.x104
2010
p-p
0.9
8.x106
2010
p-p
7
8x108
2010
208Pb-208Pb
2.76x208
~30x106
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Heavy-flavour measurements
Impact parameter resolution
SSD
SDD
SPD
87.2 cm
• Radius inner
pixel layer: 3.9 cm
• ≈1 cm from the
vacuum
Inner Tracking System (ITS)
6 layers of silicon detectors
- aligned using cosmics
and first p-p data
- current resolution for pixels:
14 μm (nominal ≈11 μm)
- X/X0 = 7.18% for radial tracks
Andre Mischke (ERC-UU)
• Capabilities to measure open
charm down to pT=0 in p-p and
p-Pb (1 GeV/c in Pb-Pb)
• High precision tracking, better
than 75 mm for pT > 1 GeV/c
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Reconstruction of D mesons
D0  K-p+
D0  K-2p+pD*+  D0(Kp)p+s
D+  K-p+p+
Ds+  K+K-p+
Lc+  pK-p+
BR: 3.89%
BR: 8.09%
BR: 67.7%
BR: 9.22%
BR: 5.5%
BR: 5.%
D0  K-p+
• Analysis based on decay topology and invariant mass technique
• Essential selection cuts
- impact parameter
- distance of closest approach
- pointing angle
• High precision tracking (ITS+TPC)
• K and p identification (TPC+TOF)  reducing background at low pT
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Open charm signals in 7 TeV p-p
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D meson cross sections at |η| < 0.5
7 TeV p-p, 1.4 nb-1
• Current pT range: 2-12 GeV/c with 20% of the 2010 statistics
• B feed-down calculated from theory (10-15%)
data driven method will be used with full 2010 statistics
• Results agree with pQCD calculation (FONLL and GM-VFNS)
• Ongoing: extension to low and high pT
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Single electrons at mid-rapidity
• High quality tracks in TPC and ITS
- hit in innermost pixel layer to reduce conversions
• Electron identification using TPC and TOF
- TOF to reject Kaons (<1.5 GeV/c) and protons (<3 GeV/c)
- TPC: asymmetric cut around the electron Bethe-Bloch curve
- measure contamination by fitting dE/dx with a double Gaussian distributions
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Inclusive electron spectrum
• Efficiency correction and corrections for electron
Bremsstrahlung
• Cocktail based on neutral pion cross section measured in PHOS
and from double conversion reconstruction in TPC
• Excess of inclusive/cocktail ratio at high-pT, arising from D and B
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Single electron cross section
• Total systematic uncertainty is
16-20% pT dependent plus
7% on normalization
• Single electrons in agreement
with expectations from D mesons
• Results agree with FONLL
calculation within errors
• Extend pT range with EMCal
and TRD
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Single muons at -4< <-2.5: analysis strategy
charm, bottom
Muon sources
from Pythia
p, K primaries
p, K secondaries
punch-through
• Remove hadrons and low-pT muons (secondary p, K) by requiring
muon tracking-trigger
• Remove decay muons (primary p, K) by subtracting MC dN/dpT
normalized to data at low pT (< 2 GeV/c)
• Remaining contribution are muons from charm and bottom
• Corrections on acceptance x efficiency (~80% for pT > 2 GeV/c)
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Single muon cross section
1.3 108 events
• Good agreement with FONLL within (large) errors
• 20-25% systematic uncertainties
• Will be extended to 15 GeV/c with more statistics and
improved spectrometer alignment
• Reference for single muon RAA
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Pb-Pb collision at 0.57 PeV
Jump in collision energy
by a factor of ~15
compared to RHIC
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D meson signals in 0.57 PeV Pb-Pb
• First open charm signals in
heavy-ion collisions
• Next
- RAA (energy rescaling for p-p reference,…)
Andre Mischke (ERC-UU)
elliptic flow (event plane definition,…)
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Open charm in Pb-Pb: Perspectives
MC simulations: 1 year at nominal luminosity
107 central Pb-Pb and 109 p-p events
Curves: Armesto et al, 2005
D0  Kp
B  e+X
mb = 4.8 GeV
• Initial energy density (from meas. dNch/dy): at least 3x higher than at RHIC
• Relatively long-lived QGP phase; thermal equilibrium reached much faster(?)
• Most of the in-medium effects should be enhanced
• Bottom energy loss expected to be lower due to dead-cone effect
• Elliptic flow of charmed particles sensitive to thermalisation in the medium
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Explore energy loss mechanisms in more detail
E medium   SCR qˆL2
MC simulations

Colour charge dependence
D
h
( pt ) RAA
( pt )
RD / h ( pt )  RAA
dI
d


HEAVY
dI
d

1   mQ
E

 Q

LIGHT
2
 1 

 q2 


2
Mass dependence (dead cone effect)
CR is 4/3 for quarks
and 3 for gluons
e from B
e from D
RB / D ( pt )  RAA
( pt ) RAA
( pt )
RcAA/RbAA ratio different for pQCD and AdS/CFT
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Summary
• Heavy quarks (charm and bottom)
- particularly good probes to study the properties of hot quark matter
(especially the transport properties)
- abundantly produced at LHC energies
• Open charm in heavy-ion collisions
- detailed understanding of energy loss mechanisms
- flow: thermalisation and hydrodynamic expansion in QGP
• Charm production in 7 TeV p-p collisions
- cross-section of single muons, electrons and D mesons measured
up to pT = 6.5, 4 and 12 GeV/c, respectively
- data described by pQCD predictions
• Many more to come
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Thank you
Andre Mischke (ERC-UU)
Moriond-QCD 2011
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Backup
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Charm production cross section in p-p
CDF, PRL, 91, 241804 (2003)
NLO pQCD, CTEQ6M parton densities
R. Vogt, private communication, 2009
– FONLL
pp¯ @ 1.96 TeV
5.8 pb-1
LHC: 7-14 TeV
• Test pQCD (theoretically not fully understood?)
• Baseline for Quarkonia measurements in Pb-Pb
• Parton spectra from pQCD input for energy loss models
 prompt charm production cross section from D spectra in pp (advantage: low pT capabilities of ALICE)
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PID using ITS
Vertex detector
pT(min) < 100 MeV/c
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Particle Identification
Specific ionisation
energy loss; PID based
on comparison with
Bethe-Bloch curves
TPC
sdE/dx/dEdx ≈ 5-6%
p/p = 5% at 100 GeV/c
PID based on comparison
of time of flight with
particle mass hypothesis
Andre Mischke (ERC-UU)
TOF (150k
channels)
s ≈ 90 ps
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D0 signal in different pT bins
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D+ signal in different pT bins
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D*± signal in different pT bins
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Data – Monte-Carlo comparison
Detector response well
described in Monte-Carlo
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Efficiencies for D mesons
• PID strategy developed to retain almost 100% of the signal
for pT > 2 GeV/c
• 1-10% efficiency from low to high pT
• Factor 2 larger for D mesons from B decays
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Feed-down from B decays
• FONLL calculations used for
B feed-down: contribution
about 10-15%
• Final results will be corrected
based on data with full 2010
statistics; displaced-D meson
analysis
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Systematic uncertainties
• Total systematic is 20-40% pT
dependent + 10% on normalization
(Van der Meer-scans)
• Main systematic error: B feeddown from FONLL+MC
to be reduced using data-driven method with
full 2010 statistics
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Comparison with world data
D0/D+ and D0/D* ratios in line
with previous measurements
at lower energies
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