Search for highly-ionizing particles in pp collisions at the LHC's Run-1 using the prototype MoEDAL detector

A search for highly electrically charged objects (HECOs) and magnetic monopoles is presented using 2.2 fb(-1) of p - p collision data taken at a centre of mass energy (E-CM) of 8 TeV by the MoEDAL detector during LHC's Run-1. The data were collected using MoEDAL's prototype Nuclear Track Detectord array and the Trapping Detector array. The results are interpreted in terms of Drell-Yan pair production of stable HECO and monopole pairs with three spin hypotheses (0, 1/2 and 1). The search provides constraints on the direct production of magnetic monopoles carrying one to four Dirac magnetic charges and with mass limits ranging from 590 GeV/c(2) to 1 TeV/c(2). Additionally, mass limits are placed on HECOs with charge in the range 10e to 180e, where e is the charge of an electron, for masses between 30 GeV/c(2) and 1 TeV/c(2).Peer reviewe

Inclusive J/psi production at mid-rapidity in pp collisions at root s=5.02 TeV

Inclusive J/psi production is studied in minimum-bias proton-proton collisions at a centre-of-mass energy of root s = 5.02 TeV by ALICE at the CERN LHC. The measurement is performed at mid-rapidity (vertical bar y vertical bar and are extracted and compared with results obtained at other collision energies.Peer reviewe

Anomalous Evolution of the Near-Side Jet Peak Shape in Pb-Pb Collisions at root S-NN=2.76 TeV

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Anisotropic Flow of Charged Particles in Pb-Pb Collisions at root S-NN=5.02 TeV

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Production of pi(0) and eta mesons up to high transverse momentum in pp collisions at 2.76 TeV

Correction: DOI:10.1140/epjc/s10052-017-5144-7The invariant differential cross sections for inclusive pi(0) and eta mesons at midrapidity were measured in pp collisions at root s = 2.76 TeV for transverse momenta 0.4 <pT <40 GeV/c and 0.6 <pT <20 GeV/c, respectively, using the ALICE detector. This large range in pT was achieved by combining various analysis techniques and different triggers involving the electromagnetic calorimeter (EMCal). In particular, a newsingle-cluster, shower-shape based method was developed for the identification of high-pT neutral pions, which exploits that the showers originating from their decay photons overlap in the EMCal. Above 4 GeV/c, the measured cross 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 pi(0), and between 30-50% for the. meson, while generator-level simulations with PYTHIA 8.2 describe the data to better than 10-30%, except at pT <1 GeV/c. The new data can therefore be used to further improve the theoretical description of pi(0) and eta meson production.Peer reviewe

Measurement of an Excess in the Yield of J/psi at Very Low p(T) in Pb-Pb Collisions at root s(NN)=2.76 TeV

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Measurement of electrons from beauty-hadron decays in p-Pb collisions at √sNN=5.02 TeV and Pb-Pb collisions at √sNN=2.76 TeV

The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval 1 <PT <8 GeV/c in minimum-bias p-Pb collisions at root(NN)-N-S = 5.02 TeV and in 1.3 <PT <8 GeV/c in the 20% most central Pb-Pb collisions at root(NN)-N-S = 2.76 TeV. The pp reference spectra at root s = 5.02 TeV and root s = 2.76 TeV, needed for the calculation of the nuclear modification factors RpPb and R-PbPb, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at root s = 7 TeV. In the PT interval 3 <PT <8 GeV/c, a suppression of the yield of electrons from beauty-hadron decays is observed in Pb-Pb compared to pp collisions. Towards lower PT, the R-PbPb values increase with large systematic uncertainties. The R-ppb is consistent with unity within systematic uncertainties and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured R-pPb and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb-Pb collisions. Therefore, the observed reduction of R-PbPb below unity at high PT may be ascribed to an effect of the hot and dense medium formed in Pb-Pb collisions.Peer reviewe

Evolution of the longitudinal and azimuthal structure of the near-side jet peak in Pb-Pb collisions at root s(NN)=2.76 TeV

In two-particle angular correlation measurements, jets give rise to a near-side peak, formed by particles associated to a higher-p(T) trigger particle. Measurements of these correlations as a function of pseudorapidity (Delta eta) and azimuthal (Delta phi) differences are used to extract the centrality and p(T) dependence of the shape of the near-side peak in the p(T) range 1 <p(T) <8 GeV/c in Pb-Pb and pp collisions at root s(NN) = 2.76 TeV. A combined fit of the near-side peak and long-range correlations is applied to the data and the peak shape is quantified by the variance of the distributions. While the width of the peak in the Delta phi direction is almost independent of centrality, a significant broadening in the Delta eta direction is found from peripheral to central collisions. This feature is prominent for the low-p(T) region and vanishes above 4 GeV/c. The widths measured in peripheral collisions are equal to those in pp collisions in the Delta phi direction and above 3 GeV/c in the Delta eta direction. Furthermore, for the 10% most central collisions and 1 <p(T, assoc) <2 GeV/c, 1 <p(T,trig) <3 GeV/c, a departure from a Gaussian shape is found: a depletion develops around the center of the peak. The results are compared to A Multi-Phase Transport (AMPT) model simulation as well as other theoretical calculations indicating that the broadening and the development of the depletion are connected to the strength of radial and longitudinal flow.Peer reviewe

W and Z boson production in p-Pb collisions at TeV root s(NN)=5.02 TeV

The W and Z boson production was measured via the muonic decay channel in proton-lead collisions at root s(NN) = 5.02 TeV at the Large Hadron Collider with the ALICE detector. The measurement covers backward (4.46 10 GeV/c are determined. The results are compared to theoretical calculations both with and without including the nuclear modification of the parton distribution functions. The W-boson production is also studied as a function of the collision centrality: the cross section of muons from W-boson decays is found to scale with the average number of binary nucleon-nucleon collisions within uncertainties.Peer reviewe

First measurement of jet mass in Pb-Pb and p-Pb collisions at the LHC

This letter presents the first measurement of jet mass in Pb-Pb and Pb-Pb collisions at root s(NN) = 2.76 TeV and root s(NN) = 5.02 TeV, respectively. Both the jet energy and the jet mass are expected to be sensitive to jet quenching in the hot Quantum Chromodynamics (QCD) matter created in nuclear collisions at collider energies. Jets are reconstructed from charged particles using the anti-k(T) jet algorithm and resolution parameter R = 0.4. The jets are measured in the pseudorapidity range |eta(jet)| <0.5 and in three intervals of transverse momentum between 60 GeV/c and 120 GeV/c. The measurement of the jet mass in central Pb-Pb collisions is compared to the jet mass as measured in p-Pb reference collisions, to vacuum event generators, and to models including jet quenching. It is observed that the jet mass in central Pb-Pb collisions is consistent within uncertainties with p-Pb reference measurements. Furthermore, the measured jet mass in Pb-Pb collisions is not reproduced by the quenching models considered in this letter and is found to be consistent with PYTHIA expectations within systematic uncertainties. (C) 2017 The Author. Published by Elsevier B.V.Peer reviewe