A new world record for the energy of colliding heavy ions
After the restart of the LHC earlier this year at CERN with proton-proton collisions, it is the turn of heavy-ion physics to take center stage. The lead ions collide now at a new world record of a petaelectronvolt (1015 eV), an energy almost doubled with respect to Run 1 of the LHC.
The LHC receives the beam to accelerate at such energies from a chain of accelerator components, starting with the ion injector, developed and build by GSI in the 90s, a component which is essential for the LHC operation with ion beams. On 25th of November "Stable beams" were declared, the long-awaited start of a measuring campaign with lead ions which will last almost a month.
In Pb-Pb collisions a quark-gluon plasma is produced, a state of matter at high temperatures or densities that existed in our early universe up to 10 microseconds in its lifetime. All four large detectors at the LHC are participating in the present data taking, in particular the ALICE detector, especially designed for the study of the quark-gluon plasma. The ALICE group at GSI is among the most active groups in the analysis of the new data.
The ALICE group at GSI shares responsibility for the operation and calibration of two important detector systems in ALICE. The Time Projection Chamber (TPC) and the Transition Radiation Detector (TRD) were designed and built with a long and dedicated contribution of the ALICE group and the Detector Laboratory of GSI. The High-Level Trigger (HLT) of ALICE, essential for the online filtering and compression of data, has also benefited from the participation of GSI. The support from the IT department, providing high-performance computer farms and data storage for the Grid and for the analyses by the German groups, is crucial.
With ALICE, a couple of hundred million collisions are expected to be registered in the coming weeks. The picture, acquired in the first minutes of the new measuring campaign, displays a typical collision with several thousand reconstructed tracks in the TPC. The first physics results are awaited very soon. The GSI scientists and PhD students have a leading contribution in the ongoing analyses, with a special focus on the transverse-momentum distribution of produced particles. This will provide the first look at the properties of the deconfined quark-gluon medium at the largest energy density ever achieved in laboratory.