16 Search Results

The measurements of the production of prompt D⁰, D⁺, D^*+, and D$$_s^+$$ mesons in proton–proton (pp) collisions at $$\sqrt{s}$$=5.02 TeV with the ALICE detector at the Large Hadron Collider (LHC) are reported. D mesons were reconstructed at mid-rapidity (|y| < 0.5) via their hadronic decay channels D⁰ → K^- $$π$$⁺, D⁺ → K^- $$π$$⁺ $$π$$⁺, D^*+ → D⁰$$π$$⁺ → K^- $$π$$ ⁺ $$π$$ ⁺, D$$_s^+$$ → Φ$$π$$⁺ → K⁺K^- $$π$$⁺, and their charge conjugates. The production cross sections were measured in the transverse momentum interval 0 < $$p$$T < 36 GeV/$$c$$ for D⁰, 1 < $$p$$T < 36 GeV/$$c$$ formore » D⁺ and D^*+, and in 2 < $$p$$T < 24 GeV/$$c$$ for D$$_s^+$$ mesons. Thanks to the higher integrated luminosity, an analysis in finer $$p$$T bins with respect to the previous measurements at $$\sqrt{s}$$ = 7 TeV was performed, allowing for a more detailed description of the cross-section $$p$$T shape. The measured $$p$$T differential production cross sections are compared to the results at √ s = 7 TeV and to four different perturbative QCD calculations. Its rapidity dependence is also tested combining the ALICE and LHCb measurements in pp collisions at $$\sqrt{s}$$ = 5.02 TeV. This measurement will allow for a more accurate determination of the nuclear modification factor in p–Pb and Pb–Pb collisions performed at the same nucleon– nucleon centre-of-mass energy.« less

The pseudorapidity density of charged particles, d$$N$$_ch/d$$η$$, in p–Pb collisions has been measured at a centre-of-mass energy per nucleon–nucleon pair of $$\sqrt{s_{NN}}$$ = 8.16 TeV at mid-pseudorapidity for non-single-diffractive events. The results cover 3.6 units of pseudorapidity, |$$η$$| < 1.8. The d$$N$$_ch/d$$η$$ value is 19.1 ± 0.7 at |$$η$$| < 0.5. This quantity divided by (N_part)/2 is 4.73 ± 0.20 , where (N_part) is the average number of participating nucleons, is 9.5% higher than the corresponding value for p–Pb collisions at $$\sqrt{s_{NN}}$$ = 5.02 TeV. Measurements are compared with models based on different mechanisms for particle production. All models agreemore » within uncertainties with data in the Pb-going side, while HIJING overestimates, showing a symmetric behaviour, and EPOS underestimates the p-going side of the d$$N$$_ch/d$$η$$ distribution. Saturation-based models reproduce the distributions well for < -1.3. The d$$N$$_ch/d$$η$$ is also measured for different centrality estimators, based both on the charged-particle multiplicity and on the energy deposited in the Zero-Degree Calorimeters. A study of the implications of the large multiplicity fluctuations due to the small number of participants for systems like p–Pb in the centrality calculation for multiplicity-based estimators is discussed, demonstrating the advantages of determining the centrality with energy deposited near beam rapidity.« less

First results on K/$$\pi$$, p/$$\pi$$ and K/p fluctuations are obtained with the ALICE detector at the CERN LHC as a function of centrality in Pb-Pb collisions at $$\sqrt{s_\mathrm{{NN}}} =2.76\hbox { TeV}$$. The observable ν_dyn, which is defined in terms of the moments of particle multiplicity distributions, is used to quantify the magnitude of dynamical fluctuations of relative particle yields and also provides insight into the correlation between particle pairs. This study is based on a novel experimental technique, called the Identity Method, which allows one to measure the moments of multiplicity distributions in case of incomplete particle identification. The resultsmore » for p/$$\pi$$ show a change of sign in ν_dyn from positive to negative towards more peripheral collisions. For central collisions, the results follow the smooth trend of the data at lower energies and ν_dyn exhibits a change in sign for p/$$\pi$$ and K/p.« less

The invariant differential cross sections for inclusive π 0 and η mesons at midrapidity were measured in pp collisions at √s=2.76 TeV for transverse momenta 0.4 < p _T < 40 GeV/c and 0.6 < p _T < 20 GeV/c, respectively, using the ALICE detector. This large range in p _T was achieved by combining various analysis techniques and different triggers involving the electromagnetic calorimeter (EMCal). Particularly, a new single-cluster, shower-shape based method was developed for the identification of high-p _T neutral pions, which exploits that the showers originating from their decay photons overlap in the EMCal. Above 4 GeV/c, the measured crossmore » sections are found to exhibit a similar power-law behavior with an exponent of about 6.3. Next-to-leading-order perturbative QCD calculations differ from the measured cross sections by about 30% for the π ⁰ , and between 30–50% for the η meson, while generator-level simulations with PYTHIA 8.2 describe the data to better than 10–30%, except at p _T < 1 GeV/c. The new data can therefore be used to further improve the theoretical description of π ⁰ and η meson production.« less

A detailed study of pseudorapidity densities and multiplicity distributions of primary charged particles produced in proton–proton collisions, at s= 0.9, 2.36, 2.76, 7 and 8 TeV, in the pseudorapidity range | η| < 2 , was carried out using the ALICE detector. Measurements were obtained for three event classes: inelastic, non-single diffractive and events with at least one charged particle in the pseudorapidity interval | η| < 1. The use of an improved track-counting algorithm combined with ALICE’s measurements of diffractive processes allows a higher precision compared to our previous publications. A KNO scaling study was performed in the pseudorapiditymore » intervals | η| < 0.5, 1.0 and 1.5. The data are compared to other experimental results and to models as implemented in Monte Carlo event generators PHOJET and recent tunes of PYTHIA6, PYTHIA8 and EPOS.« less

The measurement of primary π^±, K^±, p and $$\bar{p}$$ production at mid-rapidity (|y|< 0.5) in proton–proton collisions at $$\sqrt{s}$$ = 7 TeV performed with a large ion collider experiment at the large hadron collider (LHC) is reported. Particle identification is performed using the specific ionisation energy-loss and time-of-flight information, the ring-imaging Cherenkov technique and the kink-topology identification of weak decays of charged kaons. Transverse momentum spectra are measured from 0.1 up to 3 GeV/c for pions, from 0.2 up to 6 GeV/c for kaons and from 0.3 up to 6 GeV/c for protons. The measured spectra and particle ratios aremore » compared with quantum chromodynamics-inspired models, tuned to reproduce also the earlier measurements performed at the LHC. Lastly, the integrated particle yields and ratios as well as the average transverse momenta are compared with results at lower collision energies.« less