Azimuthally-differential pion femtoscopy relative to the third harmonic event plane in Pb–Pb collisions at s NN = 2.76 TeV
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Engineering topics
Arnaldi, R.
Publications and source records attributed to Arnaldi, R..
Dielectron production in proton-proton collisions at $ \sqrt{s}=7 $ TeV
The first measurement of e + e - pair production at mid-rapidity (|η e | < 0.8) in pp collisions at s√=7 TeV with ALICE at the LHC is presented. The dielectron production is studied as a function of the invariant mass (m ee < 3.3 GeV/c 2 ), the pair transverse momentum (pT, ee < 8 GeV/c), and the pair transverse impact parameter (DCA ee ), i.e., the average distance of closest approach of the reconstructed electron and positron tracks to the collision vertex, normalised to its resolution. The results are compared with the expectations from a cocktail of known hadronic sources and are well described when PYTHIA is used to generate the heavy-flavour contributions. In the low-mass region (0.14 < m ee < 1.1 GeV/c2), prompt and non-prompt e + e - sources can be separated via the DCA ee . In the intermediate-mass region (1.1 < m ee < 2.7 GeV/c 2 ), a double-differential fit to the data in m ee and pT, ee and a fit of the DCA ee distribution allow the total $c\overline{c}$ and $b\overline{b}$ cross sections to be extracted. Two different event generators, PYTHIA and POWHEG, can reproduce the shape of the two-dimensional mee and pT,ee spectra, as well as the shape of the DCA ee distribution, reasonably well. However, differences in the cc and bb cross sections are observed when using the generators to extrapolate to full phase space. Finally, the ratio of inclusive to decay photons is studied via the measurement of virtual direct photons in the transverse-momentum range 1 < pT < 8 GeV/c. This is found to be unity within the statistical and systematic uncertainties and consistent with expectations from next-to-leading order perturbative quantum chromodynamic calculations.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Anisotropic flow of identified particles in Pb-Pb collisions at $ {\sqrt{s}}_{\mathrm{NN}}=5.02 $ TeV
The elliptic (v 2 ), triangular (v 3 ), and quadrangular (v 4 ) flow coefficients of π ± , K ± , p+$ \overline{p}\ $,Λ+$ \overline{Λ}\ $,K S 0 , and the Φ-meson are measured in Pb-Pb collisions at $ {\sqrt{s}}_{\mathrm{NN}}=5.02 $ TeV. Results obtained with the scalar product method are reported for the rapidity range |y| < 0.5 as a function of transverse momentum, p T , at different collision centrality intervals between 0–70%, including ultra-central (0–1%) collisions for π ± , K ± , and p + $ \overline{p}\ $. For p T < 3 GeV/c, the flow coefficients exhibit a particle mass dependence. At intermediate transverse momenta (3 < p T < 8–10 GeV/c), particles show an approximate grouping according to their type (i.e., mesons and baryons). The Φ-meson v 2 , which tests both particle mass dependence and type scaling, follows p + $ \overline{p}\ $ v 2 at low p T and π ± v 2 at intermediate p T . The evolution of the shape of v n (p T ) as a function of centrality and harmonic number n is studied for the various particle species. Flow coefficients of π ± , K ± , and p + $ \overline{p}\ $ for p T < 3 GeV/c are compared to iEBE-VISHNU and MUSIC hydrodynamical calculations coupled to a hadronic cascade model (UrQMD). The iEBE-VISHNU calculations describe the results fairly well for p T < 2.5 GeV/c, while MUSIC calculations reproduce the measurements for p T < 1 GeV/c. A comparison to v n coefficients measured in Pb-Pb collisions at $ {\sqrt{s}}_{\mathrm{NN}}=2.76 $ TeV is also provided. [Figure not available: see fulltext.].
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Anisotropic flow in Xe–Xe collisions at s NN = 5.44 TeV
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74 ATOMIC AND MOLECULAR PHYSICS↗
Inclusive J/ψ production in Xe–Xe collisions at s NN = 5.44 TeV
J/ψ production is studied in Xe–Xe interactions at a centre-of-mass energy per nucleon pair of √ s NN=5.44 TeV, using the ALICE detector at the CERN LHC. The J/ψ meson is reconstructed via its decay into a muon pair, in the centre-of-mass rapidity interval 2.5 < y < 4 and down to zero transverse momentum. In this Letter, the nuclear modification factors R AA for inclusive J/ψ, measured in the centrality range 0–90% as well as in the centrality intervals 0–20% and 20–90% are presented. The R AA values are compared to previously published results for Pb–Pb collisions at √ s NN=5.02 TeV and to the calculation of a transport model. A good agreement is found between Xe–Xe and Pb–Pb results as well as between data and the model.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Neutral pion and $$\eta $$η meson production in p–Pb collisions at $$\sqrt{s_{\mathrm{NN}}}$$sNN = 5.02 TeV
Neutral pion and η meson invariant differential yields were measured in non-single diffractive p–Pb collisions at $ \sqrt{s}=5.02 $ TeV with the ALICE experiment at the CERN LHC. The analysis combines results from three complementary photon measurements, utilizing the PHOS and EMCal calorimeters and the Photon Conversion Method. The invariant differential yields of π0 and η meson inclusive production are measured near mid-rapidity in a broad transverse momentum range of 0.3 4 GeV / c at 0.483 ± 0. 015 stat± 0. 015 sys. A deviation from mT scaling is observed for pT< 2 GeV / c. The measured η/ π 0 ratio is consistent with previous measurements from proton-nucleus and pp collisions over the full pT range. The measured η/ π 0 ratio at high pT also agrees within uncertainties with measurements from nucleus–nucleus collisions. The π 0 and η yields in p–Pb relative to the scaled pp interpolated reference, RpPb, are presented for 0.3 < pT< 20 GeV / c and 0.7 < pT< 20 GeV / c, respectively. The results are compared with theoretical model calculations. The values of RpPb are consistent with unity for transverse momenta above 2 GeV / c. These results support the interpretation that the suppressed yield of neutral mesons measured in Pb–Pb collisions at LHC energies is due to parton energy loss in the hot QCD medium.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Constraints on jet quenching in p–Pb collisions at s NN = 5.02 TeV measured by the event-activity dependence of semi-inclusive hadron-jet distributions
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Inclusive J/ψ production at forward and backward rapidity in p-Pb collisions at s N N = 8.16 TeV
Inclusive J/ψ production is studied in p-Pb interactions at a centre-of-mass energy per nucleon-nucleon collision s N N = 8.16 TeV, using the ALICE detector at the CERN LHC. The J/ψ meson is reconstructed, via its decay to a muon pair, in the centre-of-mass rapidity intervals 2.03 < y cms < 3.53 and -4.46 < y cms < -2.96, where positive and negative y cms refer to the p-going and Pb-going direction, respectively. The transverse momentum coverage is p T < 20 GeV/c. In this paper, y cms - and p T -differential cross sections for inclusive J/ψ production are presented, and the corresponding nuclear modification factors R pPb are shown. Forward results show a suppression of the J/ψ yield with respect to pp collisions, concentrated in the region p T ≲ 5 GeV/c. At backward rapidity no significant suppression is observed. The results are compared to previous measurements by ALICE in p-Pb collisions at s N N = 5.02 TeV and to theoretical calculations. Finally, the ratios R FB between forward- and backward-y cms R pPb values are shown and discussed.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Energy dependence and fluctuations of anisotropic flow in Pb-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ and 2.76 TeV
Here, measurements of anisotropic flow coefficients with two- and multi-particle cumulants for inclusive charged particles in Pb-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ and 2.76 TeV are reported in the pseudorapidity range |η| < 0.8 and transverse momentum 0.2 < p T < 50 GeV/c. The full data sample collected by the ALICE detector in 2015 (2010), corresponding to an integrated luminosity of 12.7 (2.0) μb –1 in the centrality range 0-80%, is analysed.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the inclusive J/$\psi $ polarization at forward rapidity in pp collisions at $\mathbf {\sqrt{s} = 8}$ TeV
Here, we report on the measurement of the inclusive J/ψ polarization parameters in pp collisions at a center of mass energy $ \sqrt{s}=8 $ TeV with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.23 pb -1 . J/ψ resonances are reconstructed in their di-muon decay channel in the rapidity interval 2.5 < y< 4.0 and over the transverse-momentum interval 2 < p T < 15 GeV / c. The three polarization parameters (λ θ , λ φ , λ θφ ) are measured as a function of p T both in the helicity and Collins-Soper reference frames. The measured J/ψ polarization parameters are found to be compatible with zero within uncertainties, contrary to expectations from all available predictions. The results are compared with the measurement in pp collisions at $ \sqrt{s}=7 $ TeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
φ meson production at forward rapidity in Pb–Pb collisions at s N N = 2.76 TeV
φ meson measurements provide insight into strangeness production, which is one of the key observables for the hot medium formed in high-energy heavy-ion collisions. ALICE measured φ production through its decay in muon pairs in Pb–Pb collisions at s N N = 2.76 TeV in the intermediate transverse momentum range 2 < p T < 5 GeV/c and in the rapidity interval 2.5 < y < 4 . The φ yield was measured as a function of the transverse momentum and collision centrality. The nuclear modification factor was obtained as a function of the average number of participating nucleons. Results were compared with the ones obtained via the kaon decay channel in the same p T range at midrapidity. The values of the nuclear modification factor in the two rapidity regions are in agreement within uncertainties.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Prompt and non-prompt J/ψ production and nuclear modification at mid-rapidity in p–Pb collisions at $\mathbf{\sqrt{{ s}_{\text {NN}}}= 5.02}$ TeV
A measurement of beauty hadron production at mid-rapidity in proton-lead collisions at a nucleon–nucleon centre-of-mass energy $\mathbf{\sqrt{{ s}_{\text {NN}}}= 5.02}$ TeV is presented. The semi-inclusive decay channel of beauty hadrons into J / ψ is considered, where the J / ψ mesons are reconstructed in the dielectron decay channel at mid-rapidity down to transverse momenta of 1.3 GeV/c. The b b ¯ production cross section at mid-rapidity, d σbb ¯/ d y, and the total cross section extrapolated over full phase space, σbb ¯, are obtained. This measurement is combined with results on inclusive J / ψ production to determine the prompt J / ψ cross sections. The results in p–Pb collisions are then scaled to expectations from pp collisions at the same centre-of-mass energy to derive the nuclear modification factor RpPb, and compared to models to study possible nuclear modifications of the production induced by cold nuclear matter effects. RpPbis found to be smaller than unity at low pTfor both J / ψ coming from beauty hadron decays and prompt J / ψ.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Longitudinal asymmetry and its effect on pseudorapidity distributions in Pb–Pb collisions at s NN = 2.76 TeV
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
First measurement of Ξ c 0 production in pp collisions at s = 7 TeV
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Physics opportunities with a fixed target experiment at the LHC (AFTER@LHC)
By extracting the beam with a bent crystal or by using an internal gas target, the multi-TeV proton and lead LHC beams allow one to perform the most energetic fixed-target experiments (AFTER@LHC) and to study p+p and p+A collisions at \sqrt{s_NN}=115 GeV and Pb+p and Pb+A collisions at \sqrt{s_NN}=72 GeV. Such studies would address open questions in the domain of the nucleon and nucleus partonic structure at high-x, quark-gluon plasma and, by using longitudinally or transversally polarised targets, spin physics. In this paper, we discuss the physics opportunities of a fixed-target experiment at the LHC and we report on the possible technical implementations of a high-luminosity experiment. We finally present feasibility studies for Drell-Yan, open heavy-flavour and quarkonium production, with an emphasis on high-x and spin physics.
Hadjidakis, Cynthia↗
Measurement of Z0-boson production at large rapidities in Pb–Pb collisions at s NN = 5.02 TeV
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Λ c + production in pp collisions at $ \sqrt{s}=7 $ TeV and in p-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV
The p T -differential production cross section of prompt Λ c + charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at √s = 7 TeV and in p-Pb collisions at √ S NN = 5.02 TeV at midrapidity. The Λ c + and Λ¯ c¯ were reconstructed in the hadronic decay modes Λ c + → pK – π+, Λ c + → pK S 0 and in the semileptonic channel Λ c + → e+ν e Λ (and charge conjugates). The measured values of the Λ c + /D 0 ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and p T intervals, where the Λ c + production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Λ c + nuclear modification factor, R pPb , is also presented. Furthermore, the R pPb is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗