This week in Kobe, Japan, the CERN experiments ALICE, CMS, ATLAS and LHCb presented results at Quark Matter 2015 - the 25th international conference on ultrarelativistic heavy-ion collisions.
ALICE announced advances in the study of quark-gluon plasma including how the medium responds to fluctuations in the initial geometry of lead-lead collisions and how high-energy quarks and gluons are affected as they traverse the expanding, cooling medium. A further study showed that colliding lead nuclei generate electromagnetic fields so strong that new particles can be created out of the vacuum. New ALICE data suggest that such phenomena may be important even in short-range collisions.
CMS presented results showing “elliptic flow” in proton-proton collisions, from long-range correlations for charged hadrons, K0s and Lambda particles, where a mass ordering is observed. The collaboration also presented new data on the D meson nuclear modification factor for lead-lead collisions. CMS showed an indication of mass-dependent jet quenching when compared to its results of non-prompt J/Psi from B meson decay. Studies on the distribution of associated energy flow around a dijet axis were also presented by exploring wider angle of coverage, and with respect to leading and subleading jets individually.
ATLAS presented its first paper from Run 2, which expands the preliminary "ridge" analysis presented at the EPS2015 conference to fit for the modulation of the single-particle positions. The collaboration also presented results from papers on charged-particle measurements in proton-lead collisions; and Z-boson production in proton-lead collisions; as well as preliminary results on the dijet asymmetry in lead-lead and proton-proton collisions; the production of upsilon particles and W-bosons in heavy ion collisions (ATLAS-CONF-2015-050 and ATLAS-CONF-2015-051); nuclear modification factor and structure dependence measurements (ATLAS -CONF-2015-054 and ATLAS-CONF-055) and jet structure measurements in lead-lead collisions (ATLAS-CONF-2015-056).
Last but not least, LHCb presented a measurement on Psi(2S) production in proton-lead collisions at sqrt(s)=5 TeV, which suggests that Psi(2S) are more suppressed that J/psi in proton collisions.