heavy-flavour production in p-p and pb-pb collisions at alice andré mischke for the alice...
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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
Moriond-QCD 2011 2Andre Mischke (ERC-UU)
• 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
• “Simplest way” to establish the properties of a system- calibrated probe- calibrated interaction- suppression pattern tells about
density profile
• Heavy-ion collision- hard processes serve as calibrated
probe (pQCD)- traversing through the medium and
interact strongly - suppression provides density
measurement- General picture: energy loss via
medium induced gluon radiation and collisional energy loss
p+p collisionPb-Pb collision
Quark-GluonPlasma
after the collision
Probing hot and dense QCD matter
collTAA NppYield
AAYieldpR
)(
)()(
Quantify medium effects with nuclear modification factor
Moriond-QCD 2011 3Andre Mischke (ERC-UU)
Wicks et al., Nucl. Phys. A784, 426 (2007)
Energy loss of heavy quarks
BottomCharm
Gluon radiation probability:
parton
hot and dense medium• Higher penetrating power probe deeper into the medium
• Dead-cone effectgluon radiation suppressed at small angles (q < mQ/EQ)Y. Dokshitzer, D. Kharzeev, PLB 519, 199 (2001), hep-ph/0106202
• Less energy loss: Eg > ELQ > EHQ
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dd
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d2
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LIGHT
HEAVY
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Moriond-QCD 2011 4Andre Mischke (ERC-UU)
• 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
CompleteITS, 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)
A Large Ion Collider Experiment
Short status:All systems fully
operational
L3 magnetB = 0.5 T
Size: 16x26 metersWeight: 10.000 tons
Andre Mischke (ERC-UU) 5Moriond-QCD 2011
SPD
V0-C
V0-A
Trigger and data sample• Minimum bias (MB)
trigger: coincidences between
- SPD or V0 A-side or V0 C-side
- at least one charged particle in 8 η units
- 95% efficient on sinel
• single-muon trigger - forward muon in coincidence with MB
L ~ 1025 cm-2s-1
rate ~ 100 HzLint ~ 9 μb-1
Year Collisionsystem
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
Andre Mischke (ERC-UU) 6Moriond-QCD 2011
Pb-Pb
• 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
Heavy-flavour measurementsImpact parameter resolution
SSD
SDD
SPD
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) 7Moriond-QCD 2011
• Radius inner pixel layer: 3.9 cm
• ≈1 cm from the vacuum
87.2 cm
Reconstruction of D mesons
• 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
D0 K-+
D0 K-+ BR: 3.89%
D0 K-2+- BR: 8.09%
D*+ D0(K)+s BR: 67.7%
D+ K-++ BR: 9.22%
Ds+ K+K-+ BR: 5.5%
Lc+ pK-+ BR: 5.%
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Open charm signals in 7 TeV p-p
Andre Mischke (ERC-UU) 9Moriond-QCD 2011
D meson cross sections at |η| < 0.5
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• 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
7 TeV p-p, 1.4 nb-1
Single electrons at mid-rapidity
• High quality tracks in TPC and ITS- hit in innermost pixel layer to reduce γ 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
Andre Mischke (ERC-UU) 11Moriond-QCD 2011
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 decay electronsAndre Mischke (ERC-UU) 12Moriond-QCD 2011
Single electron cross section
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• 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
• 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)
charm, bottom
, K primaries
, K secondaries
punch-through
Muon sources from Pythia
Single muons at -4<<-2.5: analysis strategy
Moriond-QCD 2011 14Andre Mischke (ERC-UU)
• 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
Single muon cross section
1.3 108 events
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Jump in collision energy by a factor of ~15 compared to RHIC
Pb-Pb collision at 0.57 PeV
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D meson signals in 0.57 PeV Pb-Pb
Andre Mischke (ERC-UU) 17Moriond-QCD 2011
• First open charm signals in heavy-ion collisions
• Next
- RAA (energy rescaling for p-p reference,…)
- elliptic flow (event plane definition,…)
mb = 4.8 GeV
D0 Kp B e+X
MC simulations: 1 year at nominal luminosity107 central Pb-Pb and 109 p-p events
Andre Mischke (ERC-UU)
Open charm in Pb-Pb: Perspectives
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• 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 mediumMoriond-QCD 2011
Curves: Armesto et al, 2005
)()()(/ thAAt
DAAthD pRpRpR
Mass dependence (dead cone effect)Colour charge dependence
RcAA/Rb
AA ratio different for pQCD and AdS/CFTAndre Mischke (ERC-UU) 19
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)()()( D from eB from e/ tAAtAAtDB pRpRpR
Emedium SCRˆ q L2
Explore energy loss mechanisms in more detail
Moriond-QCD 2011
MC simulations
CR is 4/3 for quarksand 3 for gluons
• 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
Summary
Andre Mischke (ERC-UU) 20Moriond-QCD 2011
Moriond-QCD 2011 21Andre Mischke (ERC-UU)
Thank you
Backup
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LHC: 7-14 TeV
NLO pQCD, CTEQ6M parton densitiesR. Vogt, private communication, 2009
Andre Mischke (ERC-UU) 23
Charm production cross section in p-p
– FONLL
CDF, PRL, 91, 241804 (2003)
• 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 p-p (advantage: low pT capabilities of ALICE)
Moriond-QCD 2011
pp @ 1.96 TeV5.8 pb-1
¯
Vertex detectorpT(min) < 100 MeV/c
PID using ITS
Moriond-QCD 2011 24Andre Mischke (ERC-UU)
Particle Identification
TOF (150k channels)s ≈ 90 ps
Specific ionisation energy loss; PID based on comparison with Bethe-Bloch curves
PID based on comparison of time of flight with particle mass hypothesis
TPC dE/dx/dEdx ≈ 5-6%
p/p = 5% at 100 GeV/c
Andre Mischke (ERC-UU) 25Moriond-QCD 2011
D0 signal in different pT bins
Moriond-QCD 2011 26Andre Mischke (ERC-UU)
D+ signal in different pT bins
Moriond-QCD 2011 27Andre Mischke (ERC-UU)
D*± signal in different pT bins
Moriond-QCD 2011 28Andre Mischke (ERC-UU)
Data – Monte-Carlo comparison
Moriond-QCD 2011 29Andre Mischke (ERC-UU)
Detector response well described in Monte-Carlo
Efficiencies for D mesons
Moriond-QCD 2011 30Andre Mischke (ERC-UU)
• 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
• 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
Feed-down from B decays
Moriond-QCD 2011 31Andre Mischke (ERC-UU)
Systematic uncertainties
Moriond-QCD 2011 32Andre Mischke (ERC-UU)
• Total systematic is 20-40% pT dependent + 10% on normalization (Van der Meer-scans)
• Main systematic error: B feed-down from FONLL+MCto be reduced using data-driven method with full 2010 statistics
Comparison with world data
D0/D+ and D0/D* ratios in line with previous measurements at lower energies
Moriond-QCD 2011 33Andre Mischke (ERC-UU)