by Daniele De Gruttola. Published: 30 April 2011

After the intermediate energy proton-proton run, at 2.76 TeV, performed very successfully in March - followed by a technical stop - ALICE started, in April, an important period of tests and calibrations and is now back to doing physics.

Following the technical stop some days were spent to check the stability of the subsystems, profiting of the period used by LHC to perform the scrubbing run. The cleaning of the vacuum chamber, performed using high intensity beams with small bunch spacing, took around ten days, then the machine was able to inject more than 1000 bunches, with a 50 nanoseconds spacing between the trains.

The results of the scrubbing run exceeded expectations and it was decided to use 50 nanoseconds bunch spacing, instead of 75 nanoseconds as planned at the beginning of the year, for the luminosity production.

LHC then started the intensity ramp-up phase, which reached the level of 624 bunches per beam on 28 April.

ALICE used the first week of stable beams to perform a study of the behaviour of the TPC at high interaction rate, the calibration of EMCAL (>50 million events) and Photon Spectrometer (>10 million events) and Cherenkov ring studies with High Momentum Particle Identification (~200 million events). Physics with the Muon Arm has also been performed in parallel, with more than 100 million events recorded.

The second half of the month has been witness to the instantaneous luminosity, 4.67 x 1032 cm-2s-1, not only the highest collision rate ever achieved at the LHC, but also the highest ever at a hadron collider, exceeding the largest instantaneous luminosity recorded by Tevatron at Fermilab. At the time of writing the LHC has exceeded its previous record; achieving on the 29 April a peak luminosity of 6.7 x 1032 cm-2s-1.

From 25 April ALICE is back to data taking with minimum bias trigger, ~94 million events recorded in two days with a data taking efficiency of ~92% in the first two fills, reaching ~96% in the last fill with 13 colliding bunches in ALICE.