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

First proton--proton collisions at the LHC as observed with the ALICE detector:
measurement of the charged particle pseudorapidity density at sqrt(s) = 900 GeV</span>
Authors: ALICE Collaboration
(Submitted on 28 Nov 2009 (v1), last revised 1 Dec 2009 (this version, v2))

Abstract: 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 |eta| < 0.5, we obtain dNch/deta = 3.10 +- 0.13 (stat.) +- 0.22 (syst.) for all inelastic interactions, and dNch/deta = 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 SppS 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.

Comments: First ALICE physics publication v2: Small corrections to the text, author list and references
Subjects: High Energy Physics - Experiment (hep-ex)
Cite as: arXiv:0911.5430v2 [hep-ex]
Submission history
From: Jan Fiete Grosse-Oetringhaus [view email]
[v1] Sat, 28 Nov 2009 22:01:29 GMT (447kb,D)
<span style="color:#FF0000">[v2] Tue, 1 Dec 2009 17:56:32 GMT (506kb,D)

Download PDF

**Hidden Content: To see this hidden content your post count must be 10 or greater.**

First proton--proton collisions at the LHC as observed with the ALICE detector:
measurement of the charged particle pseudorapidity density at sqrt(s) = 900 GeV</span>
Authors: ALICE Collaboration
(Submitted on 28 Nov 2009 (v1), last revised 1 Dec 2009 (this version, v2))

Abstract: 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 |eta| < 0.5, we obtain dNch/deta = 3.10 +- 0.13 (stat.) +- 0.22 (syst.) for all inelastic interactions, and dNch/deta = 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 SppS 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.

Comments: First ALICE physics publication v2: Small corrections to the text, author list and references
Subjects: High Energy Physics - Experiment (hep-ex)
Cite as: arXiv:0911.5430v2 [hep-ex]
Submission history
From: Jan Fiete Grosse-Oetringhaus [view email]
[v1] Sat, 28 Nov 2009 22:01:29 GMT (447kb,D)
<span style="color:#FF0000">[v2] Tue, 1 Dec 2009 17:56:32 GMT (506kb,D)

Download PDF

**Hidden Content: To see this hidden content your post count must be 10 or greater.**