Performance of the ALICE Experiment at the CERN LHC

TL;DR

ALICE demonstrates strong, end-to-end capability for studying QCD matter created in high-energy collisions, detailing running conditions, data handling, calibration, and detector performance across central-barrel, forward, and muon systems. The paper outlines precise luminosity calibration via van der Meer scans, robust background rejection, and a comprehensive calibration/alignment program that enabled high-efficiency tracking and PID (ITS/TPC/TOF/HMPID) essential for diverse observables. It also covers advanced photon, jet, and muon analyses in pp and heavy-ion contexts, highlighting how online compression and offline processing supported large data volumes. The findings validate that ALICE operated close to design expectations during Run 1 and establish a solid baseline for future upgrades aimed at higher-rate, continuous-readout physics to further illuminate the properties of hot QCD matter.

Abstract

ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.

Figures (85)

• Figure 1: The ALICE experiment at the CERN LHC. The central-barrel detectors (ITS, TPC, TRD, TOF, PHOS, EMCal, and HMPID) are embedded in a solenoid with magnetic field $B=0.5$ T and address particle production at midrapidity. The cosmic-ray trigger detector ACORDE is positioned on top of the magnet. Forward detectors (PMD, FMD, V0, T0, and ZDC) are used for triggering, event characterization, and multiplicity studies. The MUON spectrometer covers $-4.0<\eta<-2.5$, $\eta=-\ln\tan(\theta\!/2)$.
• Figure 2: Background rate observed during several fills as a function of the product of the intensity of Beam 1, N$_1$, and the sum of the measured pressures from three vacuum gauges on the left LSS2.
• Figure 3: Beam pipe pressure and background rate in fill 2181. The expected background rate has been estimated using the linear parameterization shown in Fig. \ref{['fig:bkgVSvacuum']}. VGPB.120.4L2, VGPB.231.4L2, and VGI.514.4L2 are the pressure gauges located in front of the Inner triplet (at 69.7 m from IP2), on the TDI beam stopper (at 80 m from IP2), and on the large recombination chamber (at 109 m from IP2), respectively.
• Figure 4: Top: minimum bias, centrality, and muon triggers as a function of time during Pb--Pb data taking (run 169721). The B mask selects the LHC bunch slots where collisions between bunches of Beam 1 and Beam 2 are expected at IP2, while the ACE mask selects slots where no beam--beam collision is expected. Bottom: ZDC-A trigger rate as a function of time in the same run.
• Figure 5: Correlation between the sum and difference of signal times in V0A and V0C. Three classes of events -- collisions at (8.3 ns, 14.3 ns), background from Beam 1 at (-14.3 ns, -8.3 ns), and background from Beam 2 at (14.3 ns, 8.3 ns) -- can be clearly distinguished.