Search results for "Collisions"

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…

Centrality Dependence of the Charged-Particle Multiplicity Density at Midrapidity in Pb-Pb Collisions at √sNN = 5.02 TeV

2016

The pseudorapidity density of charged particles, dNch=dη, at midrapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of √sNN=5.02 TeV. For the 5% most central collisions, we measure a value of 1943±54. The rise in dNch=dη as a function of √sNN is steeper than that observed in proton-proton collisions and follows the trend established by measurements at lower energy. The increase of dNch=dη as a function of the average number of participant nucleons, hNparti, calculated in a Glauber model, is compared with the previous measurement at √sNN=2.76 TeV. A constant factor of about 1.2 describes the increase in dNch=dη from √sNN=2,76 to 5.02 TeV for all central…

Azimuthal Anisotropy of Heavy-Flavor Decay Electrons in p-Pb Collisions at √sNN = 5.02 TeV

2019

Angular correlations between heavy-flavor decay electrons and charged particles at midrapidity (|η|<0.8) are measured in p-Pb collisions at √sNN=5.02  TeV. The analysis is carried out for the 0%–20% (high) and 60%–100% (low) multiplicity ranges. The jet contribution in the correlation distribution from high-multiplicity events is removed by subtracting the distribution from low-multiplicity events. An azimuthal modulation remains after removing the jet contribution, similar to previous observations in two-particle angular correlation measurements for light-flavor hadrons. A Fourier decomposition of the modulation results in a positive second-order coefficient (v2) for heavy-flavor decay ele…

Charged-particle multiplicity distributions over a wide pseudorapidity range in proton-proton collisions at s√= 0.9, 7, and 8 TeV

2017

We present the charged-particle multiplicity distributions over a wide pseudorapidity range (−3.4<η<5.0) for pp collisions at s√=0.9,7, and 8 TeV at the LHC. Results are based on information from the Silicon Pixel Detector and the Forward Multiplicity Detector of ALICE, extending the pseudorapidity coverage of the earlier publications and the high-multiplicity reach. The measurements are compared to results from the CMS experiment and to PYTHIA, PHOJET and EPOS LHC event generators, as well as IP-Glasma calculations. peerReviewed

Study of xT scaling in proton-proton collisions measured by the ALICE experiment

2012

In this Master's Thesis an analysis of proton proton data measured by the ALICE (A Large Ion Collider Experiment) Collaboration at center-of-mass energies 7 TeV and 2.76 TeV is presented. The ALICE detector is located at the LHC (Large Hadron Collider) at CERN, Switzerland. The goal of this thesis was to study whether the isolation requirement can increase the sensitivity of the xT spectra (xT=2pT/sqrt(s)) to higher-twist (HT) processes. In HT processes the outgoing hadron is produced directly in the hard subprocess, rather than in the fragmentation process described by the leading-twist (LT) processes in the perturbative QCD picture. Higher-twist processes are mainly low pT phenomena, caus…