Harald Appelshäuser Goethe-Universität Frankfurt for the ALICE Collaboration

Harald Appelshäuser, Quark Matter 2011, Annecy, France 1

Harald Appelshäuser

Goethe-Universität Frankfurt

for the ALICE Collaboration

Particle Production at

Large Transverse Momentum

with ALICE


Introduction

X.N. Wang and M. Gyulassy, PRL 68 (1992).

J. D. Bjorken, FERMILAB-PUB-82-059-THY (1982)


Introduction

STAR, Quark Matter 2001 PHENIX, Quark Matter 2001


RAA at RHIC - data

very detailed experimentalinformation available by now:

• pT reach 20 GeV/c

• identified hadrons, leptons, photons

• reaction plane dependence

• pp and d-Au reference data


RAA at RHIC - models

Bass et al, PRC79, 024901

• good description by theory

• but extraction of medium parameters still ambiguous


8,6 km

The Large Hadron Collider

• pp up to √s=14 TeV

• Pb-Pb up to √sNN=5.5 TeV

abundant production of hard probes


The Large Hadron Collider

ALICE Collaboration, Phys. Lett. B696 (2011)

day-1 physics!


ALICE

Central Detectors:Inner Tracking SystemTime Projection ChamberTime-of-FlightTransition Radiation Detector

Spectrometers:High Momentum PID (RICH)Photon MultiplicityForward MultiplicityMuon Spectrometer

Calorimeters:EM CalorimeterPhoton Spectrometer (PHOS)Zero Degree Calorimeter

Trigger:Trigger Detectorspp High-Level-Trigger


momentum resolution

• combined TPC-ITS momentum resolution:

σ(pT)/pT = 20% at pT = 100 GeV/c


Pb-Pb: charged particle spectra

• charged particle spectra in Pb-Pb at √sNN = 2.76 TeV out to pT = 100 GeV/c

• strong modification of the spectral shape in central collisions

Talk: J. Otwinowski


Pb-Pb: charged particle spectra

• charged particle spectra in Pb-Pb at √sNN = 2.76 TeV out to pT = 100 GeV/c

• strong modification of the spectral shape in central collisions

INELppAAcoll

Tpp

coll

TAA

AA

TN

ddpNdN

ddpNdR

/

/2

2

Talk: J. Otwinowski


pp: charged particle spectra

• charged particle spectra in pp at √s = 0.9, 2.76, 7 TeV

• 2.76 TeV: reference measurement for pp baseline

Poster: M. Knichel


pp reference

pp reference spectrum derived from:

• measured data points for pT ≤ 5 GeV/c

• extrapolation of Hagedorn fit for pT > 5 GeV/c

CMS: 1104.3547


RAA with new pp reference

• good agreement with published results

• significant improvement of systematic uncertainties


charged particle RAA

• pronounced centrality dependence below pT = 50 GeV/c

• minimum at pT ≈ 6-7 GeV/c

• strong rise in 6 < pT < 50 GeV/c

• no significant centrality and pT dependence at pT > 50 GeV/c


charged particle RAA – centrality dependence

low pT: • approximate scaling with multiplicity density,• matching also RHIC results


low pT: • approximate scaling with multiplicity density,• matching also RHIC results

high pT:• weak suppression, no significant centrality dependence

charged particle RAA – centrality dependence


charged particle RAA - models

• pronounced pT dependence of RAA at LHC

sensitivity to details of the energy loss distribution


reaction plane dependent RAA

)cos()( 221 2vRR AAAA

Talk: A Dobrin


particle identification: dE/dx

• almost constant separation of pions to K, p above p = 3 GeV/c

Talk: A Kalweit

π


pion identification at high pT

chchT

ch

T N

N

dpd

Nd

p

E

dydp

Nd

22

from TPC dE/dx

Poster: P. Christiansen


charged pion fraction

• no centrality dependence of pion-to-charged ratio for pT > 6 GeV/c


charged pion spectra

• charged pion spectra out to pT = 20 GeV/c


charged pion RAA

• agrees with charged particle RAA - in peripheral events - for pT > 6 GeV/c

• is smaller than charged particle RAA for pT < 6 GeV/c


secondary vertex reconstruction

π0 γγ e+e-e+e-

Λ π- p

K0s π+ π-

e+

e+e-

e-


photon conversions

• ALICE material budget (11.4% X0 up to middle of TPC) agrees within +3.4%/-6% with its implementation in GEANT

Talk: K. Reygers


π0 spectra in pp and Pb-Pb

Talk: G. Balbastre


π0 - RAA: comparison to π++ π-- RAA

• good agreement between charged pion and π0 - RAA


π0 - RAA: comparison to charged particle RAA

• compatible with charged particle RAA in peripheral events

• is lower in central events at 2 < pT < 5 GeV/c

• good agreement between charged pion and π0 - RAA


Λ and K0s - RCP

• K0s - RAA very similar to that of

charged particles: strong suppression of K0

s at high pT

• Λ - RAA significantly larger than charged at intermediate pT: enhanced hyperon production counteracting suppression

• for pT > 8 GeV/c, Λ and K0s - RAA

similar to charged particle RAA: strong high-pT suppression also of Λ

Talk: S. Schuchmann


Λ - RCP: comparison to RHIC

• Λ enhancement reaches out to higher pT than at RHIC

• magnitude of RCP compatible

• K0s - RAA very similar to that of

charged particles: strong suppression of K0

s at high pT

• Λ - RAA significantly larger than charged at intermediate pT: enhanced hyperon production counteracting suppression

• above 8 GeV/c, Λ and K0s - RAA

are similar to charged: strong high-pT suppression also of Λ


Λ and K0s - RAA

• high-pT: suppression of Λ and K0s similar to charged particles

• intermediate pT: moderate enhancement in peripheral collisions central RAA similar to RCP


Λ and K0s - RAA: comparison to RHIC

• strong nuclear enhancement of Λ observed at RHIC not seen at the LHC


summary

• charged particle pT spectra in Pb-Pb at √sNN = 2.76 TeV measured with ALICE at the LHC

• new reference pT spectrum derived from pp collisions at √s = 2.76 TeV

• strong suppression charged particle production observed at pT < 50 GeV/c

• comparison to RHIC data suggests that suppression scales with the charged particle density

• at pT > 50 GeV/c, no strong centrality dependence of charged particle production is observed

• results on identified particles will allow to disentangle the interplay between quark and gluon energy loss, and recombination mechanisms at intermediate pT



comparison ALICE-CMS

Harald Appelshäuser Goethe-Universität Frankfurt for the ALICE Collaboration

Documents

pt dependence of raa

particle spectra

rhic resultslow pt

rhic resultshigh pt

tev pbpb

pk0s e e ee

gevccharged pion raa

centrality dependence