Charged-particle multiplicity measurement in proton–proton collisions at $\sqrt{s}=7$ TeV with ALICE at LHC

Abstract

The pseudorapidity density and multiplicity distribution of charged particles produced in proton-proton collisions at the LHC, at a centre-of-mass energy √ s = 7 TeV, were measured in the central pseudorapidity region |η| < 1. Comparisons are made with previous measurements at √ s = 0.9 TeV and 2.36 TeV. At √ s = 7 TeV, for events with at least one charged particle in |η| < 1, we obtain dN ch /dη = 6.01 ± 0.01(stat.) +0.20 −0.12 (syst.). This corresponds to an increase of 57.6% ± 0.4%(stat.) +3.6 −1.8 %(syst.) relative to collisions at 0.9 TeV, significantly higher than calculations from commonly used models. The multiplicity distribution at 7 TeV is described fairly well by the negative binomial distribution.

Connecting accelerator experiments and cosmic ray showers

“…6 righthand side). After re-tuning at 7 TeV to be compatible with CMS data [23] or ALICE data [24] on Fig. 7, the difference even at high energy in -air is less than a factor of 2.…”

“…As a consequence, the number of electromagnetic particles at ground are compared to data points from ALICE experiment [24].…”

Underlying Event measurements in pp collisions at $ \sqrt {s} = 0.9 $ and 7 TeV with the ALICE experiment at the LHC

“…Its high granularity and particle identification capabilities can be exploited for precise measurements of global event properties [18][19][20][21][22][23][24]. The central barrel covers the polar angle range 45 • −135 • (|η| < 1) and full azimuth.…”

“…The arrival time of particles in the V0A and V0C are used to reject beam-gas interactions that occur outside the nominal interaction region. A more detailed description of the online trigger can be found in [20]. An additional offline selection is made following the same criteria but considering reconstructed information instead of online trigger signals.…”

Light flavor hadron spectra at low pT and search for collective phenomena in high multiplicity pp, p–Pb and Pb–Pb collisions measured with the ALICE experiment

“…Transverse momentum distributions and their relative ratios for identified positive charged hadrons π + , K + , p at mid-rapidity in pp collisions at √ s = 7 TeV, measured by the ALICE experiment [7] at the LHC, as a function of charged particle multiplicity are obtained. The p T range goes from 0.2 GeV/c, 0.3 GeV/c and 0.5 GeV/c to 2.6 GeV/c, 1.4 GeV/c and 2.6 GeV/c for π + , K + and p respectively, significantly larger than previously reported results [8].…”