by Sabyasachi Siddhanta. Published: 27 May 2011

The LHC Technical stop started on 9 May. During this period, the ALICE cavern at Point 2 was abuzz with activity. There were upgrades, interventions and maintenance taking place in ALICE. Several detectors, like the Inner Tracking System, the Time Projection Chamber, the Dimuon Spectrometer, the Time of Flight, the Transition Radiation Detector, the Electromagnetic Calorimeter and the High Momentum Particle Identification Detector carried out interventions and repair work in the cavern.

The central systems like the Data Acquisition System, Detector Control System and High Level Trigger carried out several software, hardware and firmware upgrades. These upgrades will enable several new features in these systems, thereby increasing their efficiency.

After finishing all the technical stop activities, we were ready to start. On 14 May, ALICE started with cosmic runs and collected over 1.4 million events. On 15 May, the LHC provided dedicated fills for the Van der Meer scans and length scale calibrations, which went smoothly for ALICE. On 18 May, the LHC carried out the Roman pot beam based alignment for ALPHA/TOTEM.

On 19 May, the LHC started filling for physics, with 768 bunches per beam1. After few fills with this scheme, they went ahead with filling 912 bunches per beam2. During fill 1799, with 912 bunches per beam, the initial luminosity was 8.5 x 1032 cm-2s-1, and there were more than 1014 protons per beam in collision.

At the end of this fill, a record integrated luminosity in 24 hours - of 33.33 pb-1 - was reached. The successive fills continued with the same filling scheme; with fill 1804 hitting an initial luminosity of 1 x 1033 cm-2s-1.

During this period, ALICE delivered a stable performance and collected over 240 million events.

  • 1. 72 bunches per train.
  • 2. 108 bunches per train.