TY - JOUR
T1 - First proton-proton collisions at the LHC as observed with the ALICE detector
T2 - measurement of the charged-particle pseudorapidity density at root s=900 GeV
AU - Aamodt...[et al.], K.
AU - Bearden, Ian
AU - Bøggild, Hans
AU - Gaardhøje, Jens Jørgen
AU - Dalsgaard, Hans Hjersing
AU - Gulbrandsen, Kristjan Herlache
AU - Larsen, Truls Martin
AU - Christensen, Christian Holm
AU - Nygaard, Casper
AU - Nielsen, Børge Svane
AU - Søgaard, Carsten
PY - 2009/1
Y1 - 2009/1
N2 - 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. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |η|<0.5, we obtain dNch/dη=3. 10±0. 13(stat.)±0. 22(syst.) for all inelastic interactions, and dNch/dη=3.51±0. 15(stat.)±0. 25(syst.) for non-single diffractive interactions. These results are consistent with previous measurements in proton-antiproton interactions at the same centre-of-mass energy at the CERN Spp̄S collider. They also illustrate 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.
AB - 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. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |η|<0.5, we obtain dNch/dη=3. 10±0. 13(stat.)±0. 22(syst.) for all inelastic interactions, and dNch/dη=3.51±0. 15(stat.)±0. 25(syst.) for non-single diffractive interactions. These results are consistent with previous measurements in proton-antiproton interactions at the same centre-of-mass energy at the CERN Spp̄S collider. They also illustrate 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.
U2 - 10.1140/epjc/s10052-009-1227-4
DO - 10.1140/epjc/s10052-009-1227-4
M3 - Journal article
SN - 1434-6044
VL - 65
SP - 111
EP - 125
JO - The European Physical Journal C: Particles and Fields
JF - The European Physical Journal C: Particles and Fields
IS - 1-2
ER -