Charged particle multiplicities in p p interactions at $\sqrt{s}$ = 0.9 and 7 TeV in a diffractive limited phase-space measured with the ATLAS detector at the LHC and new PYTHIA6 tune

This note is an update to the result presented in ATLAS-CONF-2010-024, where the phase-space is restricted to ≥ 6 charged particles in order to limit the contribution due to diffraction processes. The data sample and corrections procedure are identical to the ones described in the previous CONF note except for the need of an additional correction to ac- count for the cut at six or more charged particles. These diffraction limited samples at both √s = 0.9 TeV and √s = 7 TeV are used to generate the new Monte Carlo tune AMBT1 (ATLAS Minimum Bias Tune 1) which better models the pT and charged multiplicity spectra. This is the first tuning of pythia6 to LHC data at √s = 7 TeV.