Calibration of the photon spectrometer PHOS of the ALICE experiment

The procedure for the energy calibration of the high granularity electromagnetic calorimeter PHOS of the ALICE experiment is presented. The methods used to perform the relative gain calibration, to evaluate the geometrical alignment and the corresponding correction of the absolute energy scale, to obtain the nonlinearity correction coefficients and finally, to calculate the time-dependent calibration corrections, are discussed and illustrated by the PHOS performance in proton-proton (pp) collisions at s=13 TeV. After applying all corrections, the achieved mass resolutions for π0 and η mesons for pT > 1.7 GeV/c are σm π0 = 4.56 ± 0.03 MeV/c2 and σm η = 15.3 ± 1.0 MeV/c2, respectively. © 2019 CERN for the benefit of the Alice collaboration.

Enhanced production of multi-strange hadrons in high-multiplicity proton-proton collisions

At sufficiently high temperature and energy density, nuclear matter undergoes a transition to a phase in which quarks and gluons are not confined: the quark-gluon plasma (QGP). Such an exotic state of strongly interacting quantum chromodynamics matter is produced in the laboratory in heavy nuclei high-energy collisions, where an enhanced production of strange hadrons is observed. Strangeness enhancement, originally proposed as a signature of QGP formation in nuclear collisions, is more pronounced for multi-strange baryons. Several effects typical of heavy-ion phenomenology have been observed in high-multiplicity proton-proton (pp) collisions, but the enhanced production of multi-strange particles has not been reported so far. Here we present the first observation of strangeness enhancement in high-multiplicity proton-proton collisions. We find that the integrated yields of strange and multi-strange particles, relative to pions, increases significantly with the event charged-particle multiplicity. The measurements are in remarkable agreement with the p-Pb collision results, indicating that the phenomenon is related to the final system created in the collision. In high-multiplicity events strangeness production reaches values similar to those observed in Pb-Pb collisions, where a QGP is formed. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved

Erratum to: Insight into particle production mechanisms via angular correlations of identified particles in pp collisions at s = 7 TeV (The European Physical Journal C, (2017), 77, 8, (569), 10.1140/epjc/s10052-017-5129-6)

We have identified a mistake in how Fig. 1 is referenced in the text of the article Eur. Phys. J. C 77 (2017) no. 8, 569 which affected three paragraphs of the results section. The corrected three paragraphs as well as the unmodified accompanying figure are reproduced in this document with the correct labeling. In addition, an editing issue led to a missing acknowledgements section. The missing section is reproduced at the end of this document in the manner in which it should have appeared in the published article. © 2019, CERN for the benefit of the ALICE collaboration

Measurement of D-0, D+, D+* and D-s(+) production in pp collisions at root s=5.02 TeV with ALICE

The measurements of the production of prompt D , D + , D 17 + , and Ds+ mesons in proton\u2013proton (pp) collisions at s=5.02TeV 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 D \u2192 K - \u3c0 + , D + \u2192 K - \u3c0 + \u3c0 + , D 17 + \u2192 D \u3c0 + \u2192 K - \u3c0 + \u3c0 + , Ds+\u2192\u3d5\u3c0+\u2192K+K-\u3c0+, and their charge conjugates. The production cross sections were measured in the transverse momentum interval 0<36GeV/c for D , 1<36GeV/c for D + and D 17 + , and in 2<24GeV/c for Ds+ mesons. Thanks to the higher integrated luminosity, an analysis in finer p T bins with respect to the previous measurements at s=7TeV 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 s=5.02TeV. This measurement will allow for a more accurate determination of the nuclear modification factor in p\u2013Pb and Pb\u2013Pb collisions performed at the same nucleon\u2013nucleon centre-of-mass energy

Calibration of the photon spectrometer PHOS of the ALICE experiment

The procedure for the energy calibration of the high granularity electromagnetic calorimeter PHOS of the ALICE experiment is presented. The methods used to perform the relative gain calibration, to evaluate the geometrical alignment and the corresponding correction of the absolute energy scale, to obtain the nonlinearity correction coefficients and finally, to calculate the time-dependent calibration corrections, are discussed and illustrated by the PHOS performance in proton-proton (pp) collisions at s=13 TeV. After applying all corrections, the achieved mass resolutions for \u3c00 and \u3b7 mesons for pT > 1.7 GeV/c are \u3c3m\u3c0javax.xml.bind.JAXBElement@533d1c3d = 4.56 \ub1 0.03 MeV/c2 and \u3c3m\u3b7 = 15.3 \ub1 1.0 MeV/c2, respectively

Relative particle yield fluctuations in Pb-Pb collisions at root s(NN)=2.76 TeV

First results on K / \u3c0, p / \u3c0 and K/p fluctuations are obtained with the ALICE detector at the CERN LHC as a function of centrality in Pb--Pb collisions at 1asNN=2.76TeV. The observable \u3bd 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 results for p / \u3c0 show a change of sign in \u3bd 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 \u3bd dyn exhibits a change in sign for p / \u3c0 and K/p

Charged-particle pseudorapidity density at mid-rapidity in p-Pb collisions at root S-NN=8.16 TeV

The pseudorapidity density of charged particles, d N ch / d \u3b7, in p\u2013Pb collisions has been measured at a centre-of-mass energy per nucleon\u2013nucleon pair of 1asNN = 8.16 TeV at mid-pseudorapidity for non-single-diffractive events. The results cover 3.6 units of pseudorapidity, | \u3b7| < 1.8. The d N ch / d \u3b7 value is 19.1 \ub1 0.7 at | \u3b7| < 0.5. This quantity divided by \u27e8 N part \u27e9 / 2 is 4.73 \ub1 0.20 , where \u27e8 N part \u27e9 is the average number of participating nucleons, is 9.5% higher than the corresponding value for p\u2013Pb collisions at 1asNN = 5.02 TeV. Measurements are compared with models based on different mechanisms for particle production. All models agree 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 \u3b7 distribution. Saturation-based models reproduce the distributions well for \u3b7> - 1.3. The d N ch / d \u3b7 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\u2013Pb in the centrality calculation for multiplicity-based estimators is discussed, demonstrating the advantages of determining the centrality with energy deposited near beam rapidity