by Iva Raynova, Siegfried Förtsch. Published: 30 June 2016

Due to some setbacks which the LHC had to endure this year, it was decided to reduce the first technical stop (TS1) of the year from five days to 54 hours. Nevertheless most of the interventions in ALICE planned for TS1 could be executed.

Immediately after TS1 the LHC provided a fill which was dedicated to interaction rate scans in ATLAS and CMS. This was followed by three consecutive tests of the background around ALICE, ATLAS and CMS. In a controlled way vacuum experts let H2 gas into the vacuum at three defined positions from the interaction point – 164, 80, and 22 metres, respectively. Thereby a deterioration of the pressure by up to two orders of magnitude was observed. The largest contribution due to the background was observed in the AD and V0 trigger detectors when the test was performed at 22 m from the interaction point. Each of these three measurements lasted about 20 minutes. While all detectors of ALICE were involved in these measurements, the first analysis involving only the AD and V0 trigger detectors was already performed and the count rates were fitted according to the three sources of background. Consequently this test is seen to complement our knowledge on the background around IP2 since the data taken in ALICE in Run 1 were severely affected by the background. This was mainly caused by a contamination of the vacuum around the TDI injection protection collimators close to ALICE at the time.

The interaction rate in the proton-proton data taking of ALICE was recently lowered from 200 kHz to 100 kHz. This was done in order to alleviate the data storage capacity. So far roughly four petabytes of data have been collected. Furthermore, the lower interaction rate results overall in less pile-up as well as in smaller distortions in the Time Projection Chamber (TPC).

This month also saw more records set up by the LHC. Not only was the longest fill bettered to 37 hours, but also was the design luminosity of 1034 cm-2 s-1 reached at 6.5 TeV instead of 7 TeV.