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Comment: 4 pages, 4 figures, Moriond QCD 2003 Conference
Comment: LaTeX, 12 pages, 6 tables
A sample of more than one million Ke4 decay candidates with less than one percent background contamination has been collected by the NA48/2 experiment at the CERN SPS in 2003-2004, allowing a detailed study of the decay properties. The branching ratio, inclusive of radiative Ke4gamma decays, is measured to be BR(Ke4) = (4.257 +/- 0.016_exp +/- 0.031_ext) x 10-5 with a total relative error of 0.8%. This measurement complements the study of S- and P-wave hadronic form factors by assigning absolute values to the relative hadronic form factors obtained earlier in a simultaneous analysis of the pion-pion scattering lengths conducted on the same data sample. The overall form factor normalization f_s = 5.705 +/- 0.017_exp +/- 0.031_ext is obtained with a total relative precision of 0.6%.
This paper gives a detailed description of the acquisition and trigger electronics especially designed for the V0 detector of ALICE at LHC. A short presentation of the detector itself is given before the description of the Front End Electronics (FEE) system, which is completely embedded within the LHC environment as far as acquisition (DAQ), trigger (CTP), and detector control (DCS) are concerned. It is able to detect on-line coincident events and to achieve charge (with a precision of 0.6 pC) and time measurements (with a precision of 100 ps). It deploys quite a simple architecture. It is however totally programmable and fully non-standard in discriminating events coming from Beam-Beam interaction and Beam-Gas background. Finally, raw data collected from the first LHC colliding beams illustrate the performance of the system.
Measurements of cross sections of inelastic and diffractive processes in proton--proton collisions at LHC energies were carried out with the ALICE detector. The fractions of diffractive processes in inelastic collisions were determined from a study of gaps in charged particle pseudorapidity distributions: for single diffraction (diffractive mass $M_X < 200$ GeV/$c^2$) $\sigma_{\rm SD}/\sigma_{\rm INEL} = 0.21 \pm 0.03, 0.20^{+0.07}_{-0.08}$, and $0.20^{+0.04}_{-0.07}$, respectively at centre-of-mass energies $\sqrt{s} = 0.9, 2.76$, and 7 TeV; for double diffraction (for a pseudorapidity gap $\Delta\eta > 3$) $\sigma_{\rm DD}/\sigma_{\rm INEL} = 0.11 \pm 0.03, 0.12 \pm 0.05$, and $0.12^{+0.05}_{-0.04}$, respectively at $\sqrt{s} = 0.9, 2.76$, and 7 TeV. To measure the inelastic cross section, beam properties were determined with van der...
Correlations of two charged identical kaons (Kch Kch) are measured in pp collisions at sqrt{s}=7 TeV by the ALICE experiment at the Large Hadron Collider (LHC). One-dimensional Kch Kch correlation functions are constructed in three multiplicity and four transverse momentum ranges. The Kch Kch femtoscopic source parameters R and lambda are extracted. The Kch Kch correlations show a slight increase of femtoscopic radii with increasing multiplicity and a slight decrease of radii with increasing transverse momentum. These trends are similar to the ones observed for pi pi and Ks0 Ks0 correlations in pp and heavy-ion collisions. However, the observed one dimensional correlation radii for charged kaons are larger at high multiplicities than those for pions in contrast to what was observed in heavy-ion collisions at RHIC.
In high-energy heavy-ion collisions, the correlations between the emitted particles can be used as a probe to gain insight into the charge creation mechanisms. In this article, we report the first results of such studies using the electric charge balance function in the relative pseudorapidity \Delta\eta and azimuthal angle \Delta\phi in Pb-Pb collisions at sqrt{s_{NN}} = 2.76 TeV with the ALICE detector at the Large Hadron Collider. The width of the balance function decreases with growing centrality (i.e. for more central collisions) in both projections. This centrality dependence is not reproduced by HIJING, while AMPT, a model which incorporates strings and parton rescattering, exhibits qualitative agreement with the measured correlations in \Delta\phi but fails to describe the correlations in \Delta\eta. A thermal blast wave model ...
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