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Arnaldi, R.

Publications and source records attributed to Arnaldi, R..

At least 325 records · Page 18
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DOE OSTI2015

Forward-backward multiplicity correlations in pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV

The strength of forward-backward (FB) multiplicity correlations is measured by the ALICE detector in proton-proton (pp) collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV. The measurement is performed in the central pseudorapidity region (|η| < 0.8) for the transverse momentum p T > 0.3 GeV/c. Two separate pseudorapidity windows of width ($\delta$η) ranging from 0.2 to 0.8 are chosen symmetrically around η = 0. The multiplicity correlation strength (b corr ) is studied as a function of the pseudorapidity gap (η gap ) between the two windows as well as the width of these windows. The correlation strength is found to decrease with increasing η gap and shows a non-linear increase with $\delta$η. A sizable increase of the correlation strength with the collision energy, which cannot be explained exclusively by the increase of the mean multiplicity inside the windows, is observed. The correlation coefficient is also measured for multiplicities in different configurations of two azimuthal sectors selected within the symmetric FB η-windows. Two different contributions, the short-range (SR) and the long-range (LR), are observed. The energy dependence of b corr is found to be weak for the SR component while it is strong for the LR component. Moreover, the correlation coefficient is studied for particles belonging to various transverse momentum intervals chosen to have the same mean multiplicity. Both SR and LR contributions to b corr are found to increase with p T in this case. Results are compared to PYTHIA and PHOJET event generators and to a string-based phenomenological model. In conclusion, the observed dependencies of b corr add new constraints on phenomenological models.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Inclusive photon production at forward rapidities in proton–proton collisions at $\mathbf {\sqrt{s}}$ = 0.9, 2.76 and 7 TeV

The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities (2.3 < η < 3.9) in proton–proton collisions at three center-of-mass energies, √s = 0.9, 2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2 ± 0.3 % (stat) ± 8.8 % (sys) and 61.2 ± 0.3 % (stat) ± 7.6 % (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. As a result, limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Production of $\mathbf {\Sigma (1385)^{\pm }}$ and $\mathbf {\Xi (1530)^{0}}$ in proton–proton collisions at $\mathbf {\sqrt{s}=}7$ TeV

The production of the strange and double-strange baryon resonances (Σ(1385) ± , Ξ(1530) 0 ) has been measured at mid-rapidity (|y|<0.5) in proton–proton collisions at √s = 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. Lastly, a search for the Φ(1860) pentaquark, decaying in the Ξπ channel, has been carried out but no evidence is seen.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Measurement of electrons from semileptonic heavy-flavor hadron decays in p p collisions at s = 2.76 TeV

We measured the p T -differential production cross section of electrons from semileptonic decays of heavy-flavor hadrons at midrapidity in proton-proton collisions and at √s=2.76 TeV in the transverse momentum range 0.5 T <12 GeV/c with the ALICE detector at the LHC. Our analysis was performed using minimum bias events and events triggered by the electromagnetic calorimeter. Predictions from perturbative QCD calculations agree with the data within the theoretical and experimental uncertainties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Production of inclusive Υ{hooktop}(1S) and Υ{hooktop}(2S) in p–Pb collisions at √ s NN = 5.02 TeV

We report on the production of inclusive Y{hooktop}(1S) and Y{hooktop} (2S) in p–Pb collisions at √ s NN = 5.02 TeV at the LHC. The measurement is performed with the ALICE detector at backward (-4.46< ycms <-2.96) and forward (2.03< ycms <3.53) rapidity down to zero transverse momentum. The production cross sections of the Υ{hooktop}(1S) and Υ{hooktop}(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of Υ{hooktop}(1S). A suppression of the inclusive Υ{hooktop}(1S) yield in p–Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon–nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects.

Abelev, B.↗
DOE OSTI2014

Measurement of prompt D -meson production in p – Pb collisions at s N N = 5.02 TeV

The p T -differential production cross sections of the prompt charmed mesons D⁰, D⁺, D*⁺, and D⁺ s and their charge conjugate in the rapidity interval −0.96 < y cms < 0.04 were measured in p−Pb collisions at a center-of-mass energy √ s NN = 5.02 TeV with the ALICE detector at the LHC. The nuclear modification factor R pPb , quantifying the D-meson yield in p−Pb collisions relative to the yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15%–20% uncertainties with unity in the transverse momentum interval 1 < p T < 24 GeV/c. No significant difference among the R pPb of the four D-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. The measurement adds experimental evidence that the modification of the momentum spectrum of D mesons observed in Pb-Pb collisions with respect to pp collisions is due to strong final-state effects induced by hot partonic matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Event-by-event mean p T fluctuations in pp and Pb–Pb collisions at the LHC

Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at √s = 0.9, 2.76 and 7 TeV, and Pb–Pb collisions at √ s NN = 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emission are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb–Pb data exhibit a similar multiplicity dependence as that observed in pp. In central Pb–Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb–Pb are in qualitative agreement with previous measurements in Au–Au at lower collision energies and with expectations from models that incorporate collective phenomena.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Transverse momentum dependence of inclusive primary charged-particle production in p–Pb collisions at $\sqrt{s_\mathrm{{NN}}}=5.02~\text {TeV}$ = 5.02 TeV

The transverse momentum (p T ) distribution of primary charged particles is measured at midrapidity in minimum-bias p–Pb collisions at √s NN = 5.02 TeV with the ALICE detector at the LHC in the range. The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for p T larger than 2 GeV/c, with a weak indication of a Cronin-like enhancement for p T around 4 GeV/c. The measurement is compared to theoretical calculations and to data in Pb–Pb collisions at √s NN = 2.76 TeV.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Measurement of quarkonium production at forward rapidity in pp collisions at √s = 7 TeV

The inclusive production cross sections at forward rapidity of J/ψ, ψ(2S), Y(1S) and Y(2S) are measured in pp collisions at √s = 7 TeV with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.35 pb -1 . Quarkonia are reconstructed in the dimuon-decay channel and the signal yields are evaluated by fitting the μ + μ - invariant mass distributions. The differential production cross sections are measured as a function of the transverse momentum p T and rapidity y, over the ranges 0 < p T < 20 GeV/c for J/ψ, 0 < p T < 12 GeV/c for all other resonances and for 2.5 < y < 4. The measured cross sections integrated over p T and y, and assuming unpolarized quarkonia, are: σ J/ψ = 6.69 ± 0.04 ± 0.63 μb, σ ψ(2S) = 1.13 ± 0.07 ± 0.19 μb, σ Y(1S) = 54.2 ± 5.0 ± 6.7 nb and σ Y(2S) = 18.4 ± 3.7 ± 2.9 nb,where the first uncertainty is statistical and the second one is systematic. The results are compared to measurements performed by other LHC experiments and to theoretical models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗