by Grazia Luparello and Virginia Greco. Published: 07 July 2017

Control Room of ALICE [Credits: Grazia Luparello]

On June 28 the LHC completed the intensity ramp up phase and reached the maximum number of proton bunches in the beams (2556 bunches, with 2215 colliding in Alice), which is the nominal working condition foreseen for 2017. This year, the ALICE experiment will take data with an instantaneous luminosity of 2.6 Hz/ubarn, which corresponds to an inelastic interaction rate of about 190kHz.

During the first fills with nominal conditions, a number of tests were performed: in particular a new cluster finder algorithm for the Time Projection Chamber (TPC) in the High-Level Trigger (HLT) was validated and data were collected at different rates (from 100kHz to 800kHz) to study the performance of the TPC with the new gas mixture - and compare it to last year's.

The first week of July was dedicated to a short technical stop, during which access to the experimental cavern was allowed. The experts could thus intervene to solve some minor problems observed in the previous weeks, during the data acquisition, such as issues with the cooling system, some non-functioning electronics or cables, etc. In the meanwhile, the DCS and DAQ systems, as well as the firmware of some detectors, were updated.

The LHC is now running again at full speed (after a short intensity ramp up, with fills having less bunches: 3, 50, 600, 1300) and the ALICE experiment is collecting data at nominal conditions.

A long period of data taking, which will last until mid-September, now lies ahead. Only a four-day stop is foreseen at the end of July to allow some tests on the accelerator and a Van der Meer Scan. This scan is a special data-taking procedure in which the two beams are moved one with respect to the other in the transverse direction and it allows the measurement of a certain reference cross section, which is then used for the luminosity normalisation. The precise knowledge of this quantity is fundamental for physics analysis.

A longer interruption is planned for the end of September, when there will be first a new period of machine development, in which the accelerator experts will perform some tests in view of future developments or to improve operation, and then another technical stop.

Control Room of ALICE [Credits: Grazia Luparello]