Search results for "COLLISION"

Performance of the ALICE experiment at the CERN LHC

2014

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.

Collision Avoidance with Potential Fields Based on Parallel Processing of 3D-Point Cloud Data on the GPU

2014

In this paper we present an experimental study on real-time collision avoidance with potential fields that are based on 3D point cloud data and processed on the Graphics Processing Unit (GPU). The virtual forces from the potential fields serve two purposes. First, they are used for changing the reference trajectory. Second they are projected to and applied on torque control level for generating according nullspace behavior together with a Cartesian impedance main control loop. The GPU algorithm creates a map representation that is quickly accessible. In addition, outliers and the robot structure are efficiently removed from the data, and the resolution of the representation can be easily ad…

ϕ-Meson production at forward rapidity in p–Pb collisions at √sNN = 5.02 TeV and in pp collisions at √s = 2.76 TeV

2017

The first study of φ-meson production in p–Pb collisions at forward and backward rapidity, at a nucleon– nucleon centre-of-mass energy √sNN = 5.02 TeV, has been performed with the ALICE apparatus at the LHC. The φ-mesons have been identified in the dimuon decay channel in the transverse momentum (pT) range 1 < pT < 7 GeV/c, both in the p-going (2.03 < y < 3.53) and the Pb-going (−4.46 < y < −2.96) directions — where y stands for the rapidity in the nucleon–nucleon centre-of-mass — the integrated luminosity amounting to 5.01 ± 0.19 nb−1 and 5.81 ± 0.20 nb−1, respectively, for the two data samples. Differential cross sections as a function of transverse momentum and rapidity are presented. Th…

Production of K∗ (892) 0 and ϕ(1020) in p–Pb collisions at √sNN = 5.02 TeV

2016

The production of K∗(892)0 and ϕ(1020) mesons has been measured in p–Pb collisions at √sNN = 5.02 TeV. K∗0 and ϕ are reconstructed via their decay into charged hadrons with the ALICE detector in the rapidity range −0.5<y<0. The transverse momentum spectra, measured as a function of the multiplicity, have a pT range from 0 to 15 GeV/c for K∗0 and from 0.3 to 21 GeV/c for ϕ. Integrated yields, mean transverse momenta and particle ratios are reported and compared with results in pp collisions at s√ = 7 TeV and Pb–Pb collisions at √sNN = 2.76 TeV. In Pb–Pb and p–Pb collisions, K∗0 and ϕ probe the hadronic phase of the system and contribute to the study of particle formation mechanisms by compar…

Direct photon elliptic flow in Pb–Pb collisions √sNN = 2.76 TeV

2019

The elliptic flow of inclusive and direct photons was measured at mid-rapidity in two centrality classes 0–20% and 20–40% in Pb–Pb collisions at √sNN = 2.76 TeV by ALICE. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the detector material with the e+e− pairs reconstructed in the central tracking system. The results of the two methods were combined and the direct-photon elliptic flow was extracted in the transverse momentum range 0.9 < pT < 6.2 GeV/c. A comparison to RHIC data shows a similar magnitude of the measured directphoton elliptic flow. Hydrodynamic and transport model calculations are systematically lower than the data, but …

Nucleon dissociation and incoherent J/ψ photoproduction on nuclei in ion ultraperipheral collisions at the CERN Large Hadron Collider

2019

Using the general notion of cross section fluctuations in hadron-nucleus scattering at high energies, we derive an expression for the cross section of incoherent J / ψ photoproduction on heavy nuclei d σ γ A → J / ψ Y / d t , which includes both elastic d σ γ p → J / ψ p / d t and proton-dissociation d σ γ p → J / ψ Y / d t photoproduction on target nucleons. We find that, with good accuracy, d σ γ A → J / ψ Y / d t can be expressed as a product of the sum of the d σ γ p → J / ψ p / d t and d σ γ p → J / ψ Y / d t cross sections, which have been measured at HERA, and the common nuclear shadowing factor, which is calculated using the leading twist nuclear shadowing model. Our prediction for …

Exclusive J=ψ Photoproduction off Protons in Ultraperipheral p-Pb Collisions at √sNN = 5.02 TeV

2014

Azimuthal correlations of prompt D mesons with charged particles in pp and p–Pb collisions at √sNN = 5.02 TeV

2020

The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in pp collisions at √s = 5.02 TeV and p–Pb collisions at √sNN = 5.02 TeV with the ALICE detector at the LHC is reported. The D0D0, D+D+, and D∗+D∗+ mesons, together with their charge conjugates, were reconstructed at midrapidity in the transverse momentum interval 30.3 GeV/c and pseudorapidity |η|<0.8. The properties of the correlation peaks appearing in the near- and away-side regions (for Δφ≈0 and Δφ≈π, respectively) were extracted via a fit to the azimuthal correlation functions. The shape of the correlation functions and the near- and away-side peak features are found to be consistent in pp a…

Measurement of an Excess in the Yield of J/ψ at Very Low pT in Pb-Pb Collisions at √sNN = 2.76 TeV

2016

We report on the first measurement of an excess in the yield of J=ψ at very low transverse momentum (pT < 0.3 GeV=c) in peripheral hadronic Pb-Pb collisions at √sNN=2.76  TeV, performed by ALICE at the CERN LHC. Remarkably, the measured nuclear modification factor of J=ψ in the rapidity range 2.5 <y< 4 reaches about 7 (2) in the pT range 0–0.3 GeV=c in the 70%–90% (50%–70%) centrality class. The J=ψ production cross section associated with the observed excess is obtained under the hypothesis that coherent photoproduction of J=ψ is the underlying physics mechanism. If confirmed, the observation of J=ψ coherent photoproduction in Pb-Pb collisions at impact parameters smaller than twice the nu…

Measurement of ϕ-meson production at forward rapidity in p+p collisions at √s = 510 GeV and its energy dependence from √s = 200 GeV to 7 TeV

2018

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section of ϕ ( 1020 ) -meson production at forward rapidity in p + p collisions at √ s = 510     GeV via the dimuon decay channel. The partial cross section in the rapidity and p T ranges 1.2 < | y | < 2.2 and 2 < p T < 7     GeV / c is σ ϕ = [ 2.28 ± 0.09 ( stat ) ± 0.14 ( syst ) ± 0.27 ( norm ) ] × 10 − 2     mb . The energy dependence of σ ϕ ( 1.2 < | y | < 2.2 , 2 < p T < 5     GeV / c ) is studied using the PHENIX measurements at √ s = 200 and 510 GeV and the Large Hadron Collider measurements at √ s = 2.76 and 7 TeV. The experimental results are compared to various event generator predicti…