Abstract
Charged-particle spectra obtained in 0.15 nb${}^{-1}$ of Pb+Pb interactions at $\sqrt{{s}_\mathsf{{NN}}}=2.76$TeV and 4.2 pb${}^{-1}$ of pp interactions at $\sqrt{s}=2.76$ TeV with the ATLAS detector at the LHC are presented in a wide transverse momentum ($0.5 < p_{\mathrm{T}} < 150$ GeV) and pseudorapidity ($|\eta|<2$) range. For Pb+Pb collisions, the spectra are presented as a function of collision centrality, which is determined by the response of the forward calorimeter located on both sides of the interaction point. The nuclear modification factors $R_{\mathrm{AA}}$ and $R_{\mathrm{CP}}$ are presented in detail as function of centrality, $p_{\mathrm{T}}$ and $\eta$. They show a distinct $p_{\mathrm{T}}$-dependence with a pronounced minimum at about 7 GeV. Above 60 GeV, $R_{\mathrm{AA}}$ is consistent with a plateau at a centrality-dependent value, within the uncertainties. The value is $0.55\pm0.01(stat.)\pm0.04(syst.)$ in the most central collisions. The $R_{\mathrm{AA}}$ distribution is consistent with flat $|\eta|$ dependence over the whole transverse momentum range in all centrality classes.
Highlights
Collisions with respect to the yield in pp collisions by factor of two to four [9, 10]
The pixel detectors (Pixel) detector occupancy is below 1% even in the most central collisions
A precise measurement of inclusive charged-hadron production in Pb+Pb collisions at sNN = 2.76 TeV and in pp collisions at s = 2.76 TeV is presented in the pT interval from 0.5 to 150 GeV
Summary
The measurements presented in this paper were performed using the ATLAS inner detector (ID), calorimeter, muon spectrometer, and the high-level trigger and data acquisition systems [19]. Charged particles in the barrel region with pT 0.5 GeV and |η| < 1.0 typically traverse 3 layers of silicon pixel detectors, 4 layers of double-sided microstrip modules, and 36 straws. It has a ∆η × ∆φ granularity of 0.1 × 0.1 for |η| < 2.5 and 0.2 × 0.2 for 2.5 < |η| < 4.9.2 The EM calorimeter is segmented longitudinally in shower depth into three compartments with an additional pre-sampler layer. The L1 trigger selects events with energy deposition in the calorimeters above a preset level, or events with signals from the ZDC. Such events are further processed by software-based high-level triggers (HLT)
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