Charged-particle multiplicities in pp interactions at √s = 900 GeV measured with the ATLAS detector at the LHC


The first paper published by the ATLAS Collaboration using an early LHC data. Properties of ordinary proton-proton interactions were measured at center of mass energy of √s = 900 GeV. The data are important for tuning models of soft, low momentum transfer physics. These events constitute a background to the short-distance scale physics which is the main focus of ATLAS and CMS. Understanding this background is important for full exploration of discovery potential of the LHC.

Young postdoctoral researcher Oldřich Kepka from our institute was strongly involved in the analysis and was one of the primary authors of the paper. Presented result documents that our physicists and engineers were not only active in building and operating the ATLAS detector but were involved actively as well in analyzing the data since the very beginning of the data taking.

The measured pT spectrum of charged-particle multiplicities. The ATLAS pp data (black dots) are compared to the UA1 pp data (blue open squares) and CMS NSD pp data (red triangles) at the same centre-of-mass energy.