Heavy- flavour production in p-p and Pb-Pb collisions at ALICE

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


Wicks et al., Nucl. Phys. A784, 426 (2007)

Energy loss of heavy quarks

BottomCharm

Gluon radiation probability:

partonhot 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

11

dd

dd

2

2

2

q

Q

Q

LIGHT

HEAVY

Em

II


• 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


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


• 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-p+

D0 K-p+ BR: 3.89%D0 K-2p+p- BR: 8.09%D*+ D0(Kp)p+

s BR: 67.7%D+ K-p+p+ BR: 9.22%Ds

+ K+K-p+ BR: 5.5%Lc

+ pK-p+ BR: 5.%


Open charm signals in 7 TeV p-p


D meson cross sections at |η| < 0.5


• 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


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


• 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

p, K primaries

p, K secondaries

punch-through

Muon sources from Pythia

Single muons at -4<<-2.5: analysis strategy


• 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


Jump in collision energy by a factor of ~15 compared to RHIC

Pb-Pb collision at 0.57 PeV


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,…)

- 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

18

• 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

11

dd

dd

2

2

2

q

Q

Q

LIGHT

HEAVY

Em

II

)()()( D from eB from e/ tAAtAAtDB pRpRpR

Emedium SCR ˆ 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



Thank you

Backup


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


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 sdE/dx/dEdx ≈ 5-6%p/p = 5% at 100 GeV/c


D0 signal in different pT bins


D+ signal in different pT bins


D*± signal in different pT bins


Data – Monte-Carlo comparison


Detector response well described in Monte-Carlo

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

• 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


Systematic uncertainties


• 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


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Heavy- flavour production in p-p and Pb-Pb collisions at ALICE

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