2017 Impact factor 0.519
Historical Perspectives on Contemporary Physics

First proton–proton collisions at the LHC as observed with the ALICE detector

Figure shows the first pp collision candidate by the event display in the ALICE counting room (3D view).

On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam, allowing all LHC experiments to report first collision candidates.

284 such candidates were recorded by the ALICE experiment, allowing the events to be immediately reconstructed and analyzed. The results obtained by measuring the spatial distribution (specifically, the pseudorapidity density) of charged primary particles in the central region, were found to be consistent with previous measurements in proton-antiproton interactions at the same centre-of-mass energy at the CERN SppS collider (UA5 Collaboration, G.J. Alner et al., Z Phys. C 33 (1986), DOI 10.1007/BF01410446).

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J Schukraft, the ALICE spokesman, said: This important benchmark test illustrates also the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase.
The paper is published open access on SpringerLink.com and distributed under the Creative Commons Attribution Noncommercial License.

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Managing Editors
W. Beiglböck and F. Guerra
ISSN (Print Edition): 2102-6459
ISSN (Electronic Edition): 2102-6467

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