First result at LHC from lead-lead collisions
The ALICE experiment at the Large Hadron Collider at CERN submits today on the electronic preprint server, ArXiv, the first paper from lead-lead collisions at center-of-mass energy 5TeV per nucleon pair from the entire LHC project. The paper is concurrently being submitted to Physical Review Letters.
“The experiments with lead-lead collisions started on November 25 and it is fantastic that the first results can be made public less than four weeks after data taking”, says Jens Jørgen Gaardhøje, professor and head of the ALICE group at the Niels Bohr Institute.
Postdoc Valentina Zaccolo form the HEHI-ALICE group at the Niels Bohr Institute has been responsible for the analysis together with a small and fast working analysis group.
This is the first publication from Pb+Pb collisions that is submitted by the LHC experiments. The article presents the first measurement of the number of charged particles that are produced around mid-rapidity, that is in a narrow angular range at right angles with respect to the beam direction.
“This angular range is particularly interesting to map out first, since particles here are mostly produced in the collisions. The measurement shows that over 2000 charged particles are produced per unit of rapidity for the 2.5% most central collisions”, Jens Jørgen Gaardhøje says.
He explains that this number makes it possible to estimate that the energy density in the collisions exceeds 20 GeV/fm^3 ( 1 fm^3 = 10^-45 m^3). This is more than 20 times the energy density necessary for forming the Quark-Gluon-Plasma and over 40 times the energy density of the proton.
The results were presented this morning in an open seminar at CERN.
The experiments are supported by the NICE center, The Discovery Center (DNRF) and by FNU (DFF).