2018 proton season coming to an end soon

Taku Gunji and Virginia Greco

The starting of the 2018 heavy-ion run is around the corner and ALICE is making sure to be ready and at its best. During the latest technical stop, a few interventions were performed in vision of the Pb-Pb run, as well as in preparation for the future upgrade.

In mid-September, the LHC experts performed another Machine Development (MD) session, which was followed by a five-day technical stop. During MD, high rate Data Acquisition (DAQ) tests were performed involving all LHC experiments and the IT department, in order to validate high-rate data transfer to and from each experiment to various Grid sites.  Along the 30 hours of testing, no cross-talk effects were observed in ALICE, which means that the other experiments activities did not interfere in our data migration.  Some technical difficulties were identified by the DAQ and Offline teams who implemented a solution to ensure full data upload capacity (10 GB/s).

Many interventions took place during the technical stop in order to improve the stability of the detector operations, especially in view of the upcoming Pb-Pb run. In addition, the firmware of the V0 detector was upgraded to allow taking simultaneously central and semi-central triggered data in lead collisions.

A number of activities for the future detector upgrade have been performed as well.  New Gas Electron Multipliers (GEM) readout (2 inner and 8 outer) chambers for the upgraded TPC were installed in the miniframe located in the forward region to ensure their stability under high particle fluxes.  A prototype of the FoCAL (Forward Calorimeter) detector, which is one of the future upgrade projects currently under discussion, was also installed in front of the A-side of the Forward Electromagnetic Calorimeters (ZEM detector) and it will take pp data until the next technical stop.

After a “mini” intensity ramp-up, at the end of September the accelerator was already back in luminosity production with 2556 bunches per beam. ALICE continued standard physics data taking at 200 kHz rate, accumulating statistics of minimum bias and rare triggered data.  The minimum bias data sample is approaching the target size, while the rare triggered data sample is a little bit behind the projections.

During this period, the setting of the TPC gating grid voltage was changed to decrease further the space charge distortions (interventions in this direction had been already performed). A Run 2 Pb-Pb equivalent flux test was also performed to ensure the running stability of the various sub-detectors for the upcoming ion run. New Run 3 Pb-Pb equivalent flux tests were conducted as well, to check the behaviour of the detector under conditions similar to those expected for runs with 50 kHz Pb-Pb collisions, which will take place after the next long shut down (LS2). In the latest of these tests, the TPC field cage, as well as the other detectors (EMCal, TRD, CPV, HMPID, PHOS, TOF), ran stably for more than 12 hours in a row, showing very good performance.

Currently (8-14 October), a special run is ongoing at low-energy and high-beta*: collisions are delivered at 450 GeV per beam, without squeezing the beam in the experiments. This configuration is required by the TOTEM and ALFA (ATLAS) experiments to measure the elastic cross-section of protons in a regime where the momentum of the protons only changes by a small amount. These measurements will add to those previously performed by TOTEM at 8 TeV and 13 TeV.

Once this special run is concluded, one week of more “nominal” pp collisions will be delivered, before entering in another short period – about one-week long – of machine development and technical stop. Then, lead-ions will finally enter the game.

Alice Matters