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Title: 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

Journal Article · · European Physical Journal. C, Particles and Fields
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  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

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 Sp$$\bar{p}$$S 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.

Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Science (SC); National Science Foundation (NSF); State of Texas; State of Ohio
Contributing Organization:
The ALICE Collaboration
Grant/Contract Number:
AC02-05CH11231; AC05-00OR22725
OSTI ID:
1511316
Alternate ID(s):
OSTI ID: 973129
Journal Information:
European Physical Journal. C, Particles and Fields, Vol. 65, Issue 1-2; ISSN 1434-6044
Publisher:
SpringerCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 135 works
Citation information provided by
Web of Science

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Underlying Event measurements in pp collisions at $ \sqrt {s} = 0.9 $ and 7 TeV with the ALICE experiment at the LHC journal July 2012
Charged particle pseudorapidity distributions in high energy $$ p{-} \bar{p} $$ or $$ p{-}p $$ collisions and the improved multi-source thermal model journal October 2012
Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC journal May 2011
Alignment of the ALICE Inner Tracking System with cosmic-ray tracks journal March 2010
Heavy-ion physics with the ALICE experiment at the CERN Large Hadron Collider journal February 2012
Hadron production in p + p , p + Pb , and Pb + Pb collisions with the hijing 2.0 model at energies available at the CERN Large Hadron Collider journal January 2011
Gluon saturation in p A collisions at energies available at the CERN Large Hadron Collider: Predictions for hadron multiplicities journal April 2012
Centrality determination of Pb-Pb collisions at s N N = 2.76 TeV with ALICE journal October 2013
Two-pion Bose-Einstein correlations in p p collisions at s = 900 GeV journal September 2010
Gluon saturation and energy dependence of hadron multiplicity in p p and A A collisions at the LHC journal June 2011
Measurement of electrons from semileptonic heavy-flavor hadron decays in p p collisions at s = 2.76 TeV journal January 2015
CGC/saturation approach for high energy soft interactions: v 2 in proton-proton collisions journal April 2016
Midrapidity Antiproton-to-Proton Ratio in p p Collisons at s = 0.9 and 7 TeV Measured by the ALICE Experiment journal August 2010
Charged-particle multiplicity measurement in proton–proton collisions at $\sqrt{s}=0.9$ and 2.36 TeV with ALICE at LHC journal June 2010
Charged-particle multiplicity measurement in proton–proton collisions at $\sqrt{s}=7$ TeV with ALICE at LHC journal June 2010
Strange particle production in proton–proton collisions at $\sqrt{s}=0.9$ $\mbox {${\rm TeV}$}$ with ALICE at the LHC: The ALICE Collaboration journal March 2011
Production of K∗(892)0 and ϕ(1020) in pp collisions at $\sqrt{s}=7\ \mathrm{TeV}$ journal October 2012
Mid-rapidity anti-baryon to baryon ratios in pp collisions at $\sqrt{s} = 0.9,\ 2.76\mbox{ and }7\mbox{ TeV}$ measured by ALICE journal July 2013
CGC/saturation approach for soft interactions at high energy: survival probability of central exclusive production journal March 2016
Charged-particle multiplicities in proton–proton collisions at $$\sqrt{s} = 0.9$$ s = 0.9 to 8 TeV journal January 2017
A CGC/saturation approach for angular correlations in proton–proton scattering journal September 2017
Evidence of Entropy Scaling in Relativistic Nucleus–Nucleus Collisions journal July 2012
Saha Institute of Nuclear Physics — Its Past and the Present journal August 2014
Transverse momentum and pseudorapidity distributions of charged hadrons in pp collisions at √s = 0.9 and 2.36 TeV text January 2010
Transverse momentum and pseudorapidity distributions of charged hadrons in pp collisions at sqrt(s) = 0.9 and 2.36 TeV text January 2010
Charged-particle multiplicity measurement in proton-proton collisions at $\sqrt{s}$ = 7 TeV with ALICE at LHC text January 2010
CGC/saturation approach for soft interactions at high energy: survival probability of the central exclusive production text January 2015
Charged-particle multiplicities in pp interactions at sqrt(s) = 900 GeV measured with the ATLAS detector at the LHC text January 2010
Charged-particle multiplicities in proton-proton collisions at $\sqrt{s}$ = 0.9 to 8 TeV text January 2015
Charged-particle distributions in $pp$ interactions at $\sqrt{s}=8$ TeV measured with the ATLAS detector text January 2016
Measuring Charged Particle Multiplicity with Early ATLAS Public Data text January 2016


Figures / Tables (9)