First experimental results are presented on event-by-event net-proton fluctuation measurements in Pb–Pb collisions at sNN=2.76 TeV, recorded by the ALICE detector at the CERN LHC. The ALICE detector ...is well suited for such studies due to its excellent particle identification capabilities and large acceptance, which is crucial for fluctuation analysis. The studies are focussed on second order cumulants, but the analysis technique used is more general and will be applied, in the near future, also to higher order cumulants.
Ultra-peripheral Pb-Pb collisions, in which the two nuclei pass close to each other, but at an impact parameter greater than the sum of their radii, provide information about the initial state of ...nuclei. In particular, heavy vector meson production, where the particle mass sets a hard scale, proceeds in such collisions by photon-gluon interactions, and gives access to nuclear PDFs. The ALICE collaboration has published measurements of J/ψ and ψ(2S) photoproduction in ultra-peripheral collisions in LHC Run 1 at forward (J/ψ) and mid-rapidity, and has obtained a substantially larger data set in 2015 from LHC Run 2, allowing much more detailed studies of the production mechanism to be performed. In particular, the increased energy and more detailed measurements in the forward region in Run 2 give access to significantly lower values of Bjorken-x than in previous studies. In this talk, the latest available results from Run 2 will be given.
The availability at the LHC of the largest collision energy in pp collisions allows a significant advance in the measurement of J/ψ production as function of event multiplicity. The interesting ...relative increase observed with data at the LHC at s=7 TeV and at RHIC at s=0.2 TeV is studied now at unprecedented multiplicities at s=13 TeV. The measurement at mid-rapidity in the dielectron channel with ALICE is presented and discussed in comparison to predictions from available theoretical models and to data at lower energies.
Two- and multi-particle azimuthal correlations have proven to be an excellent tool to probe the properties of the strongly interacting matter created in heavy-ion collisions. Recently, the results ...obtained for multi-particle cumulants have been interpreted as evidence for collectivity in the small collision systems (pp and p–Pb) providing new insights into the systems' fluctuating initial conditions. In this article, first ALICE results on two- and multi-particle cumulants as a function of charged hadron multiplicity produced at midrapidity (|η| < 1.0) in pp collisions at s=13 TeV are reported. The results are compared with measurements in p–Pb collisions at sNN=5.02 TeV and in Pb–Pb collisions at sNN=2.76 TeV. A new method for the 4-particle cumulant with an η gap denoted as cn{4,|Δη|} will be presented, which is capable of further suppressing non-flow effects in multi-particle cumulants. The results allow for further understanding of the origin of multi-particle correlations in pp collisions.
The aim of this work is to explore possible medium modifications to the substructure of inclusive charged jets in Pb-Pb relative to proton-proton collisions by measuring a set of jet shapes. The set ...of shapes includes the radial moment, g, and the momentum dispersion pTD. They provide complementary information on the fragmentation and can help to discriminate between two different scenarios: intra-jet broadening or collimation as a result of jet quenching. The shapes are measured in Pb–Pb collisions at sNN=2.76 TeV with a constituent cutoff of 0.15 GeV/c and jet resolution R=0.2. New techniques for background subtraction are applied and a two-dimensional unfolding is performed to correct the shapes to particle level. The corrected jet shapes for jet pT 40≤pT,jet≤60 GeV/c are presented and discussed. The observed jet shape modifications suggest that the in-medium fragmentation is harder and more collimated than vacuum fragmentation as obtained by a PYTHIA calculation. The PYTHIA calculation is validated with proton-proton data at 7 TeV.
PDF
