Measurement of the inelastic pp cross section at

Abstract

The proton-proton inelastic cross section at TeV was measured with the CMS detector at the Large Hadron Collider. The analysis was performed using Zero Bias triggered events on data collected in low luminosity LHC runs. The inelastic events were detected and counted requiring an energy deposit in either of the Hadron Forward Calorimeters. Results for the visible inelastic pp cross section, corresponding to events in which at least one proton loses more than a fraction of its total momentum are presented together with the extrapolated value for the total inelastic pp cross section.

Approved plots

	Figure 1: Left: Generator level distributions for inelastic events using PYTHIA 6 tune D6T (1a), PYTHIA 8 (1c), PHOJET (1e) and the CMS full simulation model, normalized to unity over the full range. Figures 1b, 1d, 1f: Efficiency of the event selection for the above three models, for the two thresholds of the energy deposited in the HF calorimeters. The threshold at is also shown.
	Figure 2: Inelastic cross section with the selection using data sets with various pile-up values. The error bars show the statistical errors combined with the systematic errors from tower exclusion and run-by-run variations.
	Figure 3: Generator level distribution of inelastic events in the different models used for extrapolation. For illustration, the distribution is also shown after a fiducial cut similar to the requirement in data and full simulation, requiring at least one particle with at least 4 or 5 GeV total energy to hit the HF calorimeters (where the magnetic field is neglected).
	Figure 4: Figure 4a: The total inelastic cross section predicted by various models, together with the cross section with using the event selection in the present study as well as the visible cross section requiring at least 2, 3 and 4 tracks in the and range. The measured and extrapolated values from the two methods are shown by the red and black solid dots. Fig. 4b: the same, but normalized by an overall factor for each model and the measurements as well, such that the value is unity for the 4-track requirement. Fig. 4c: the same, but normalized by an overall factor for each model and the measurements as well, such that the value is unity for the requirement.
	Comparison of the pp total inelastic cross sections (red dots) and the inelastic cross section with the selection (blue squares) from CMS, ATLAS, the CMS pile-up counting, ALICE and TOTEM. The leftmost points are the results of the present measurement. The errorbars do not contain the common (3%) uncertainty of the measurement of the absolute scale of the LHC luminosity.
	The results from the present CMS inelastic cross section analysis at (red square) compared with the results from ATLAS, the CMS pile-up counting, ALICE, TOTEM and lower energy and data from PDG.

-- AnnaJuliaZsigmond - 25-Feb-2012