Measurement of the inelastic pp cross section at $\sqrt{\rm{s}} = 7 \mbox{ TeV}$


The proton-proton inelastic cross section at $\sqrt{s}=7$ 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 $\xi\sim5\times10^{-6}$ of its total momentum are presented together with the extrapolated value for the total inelastic pp cross section.

Approved plots

Figure1a.pngFigure1b.png Figure1c.pngFigure1d.png Figure1e.pngFigure1f.png Figure 1: Left: Generator level $\xi$ 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 $\xi$ 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 $\xi$ threshold at $5\times10^{-6}$ is also shown.
Figure2.png Figure 2: Inelastic cross section with the selection $\xi>5\times10^{-6}$ 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.
Figure3a.png Figure3b.png Figure3c.png Figure3d.png Figure3e.png Figure3f.png Figure 3: Generator level $\xi$ 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).
Figure4a.png Figure4b.png Figure4c.png Figure 4: Figure 4a: The total inelastic cross section predicted by various models, together with the cross section with $\xi>5\times10^{-6}$ 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 $p_T>200 \rm{ MeV}/c$ and $-2.4<\eta<2.4$ 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 $\xi>5\times10^{-6}$ requirement.
Figure5.png Comparison of the pp total inelastic cross sections (red dots) and the inelastic cross section with the $\xi>5\times 10^{-6}$ 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.
Figure6.png The results from the present CMS inelastic cross section analysis at $\sqrt{s}=7\rm{ TeV}$ (red square) compared with the results from ATLAS, the CMS pile-up counting, ALICE, TOTEM and lower energy $pp$ and $p\bar{p}$ data from PDG.

-- AnnaJuliaZsigmond - 25-Feb-2012

Topic attachments
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PDFpdf Figure1a.pdf r1 manage 11.3 K 2012-02-26 - 09:55 AnnaJuliaZsigmond  
PNGpng Figure1a.png r1 manage 79.6 K 2012-02-27 - 17:47 AnnaJuliaZsigmond  
PDFpdf Figure1b.pdf r1 manage 10.7 K 2012-02-26 - 09:56 AnnaJuliaZsigmond  
PNGpng Figure1b.png r1 manage 92.7 K 2012-02-27 - 17:48 AnnaJuliaZsigmond  
PDFpdf Figure1c.pdf r1 manage 11.4 K 2012-02-26 - 09:56 AnnaJuliaZsigmond  
PNGpng Figure1c.png r1 manage 87.8 K 2012-02-27 - 18:00 AnnaJuliaZsigmond  
PDFpdf Figure1d.pdf r1 manage 10.6 K 2012-02-26 - 09:56 AnnaJuliaZsigmond  
PNGpng Figure1d.png r1 manage 91.4 K 2012-02-27 - 17:48 AnnaJuliaZsigmond  
PDFpdf Figure1e.pdf r1 manage 11.5 K 2012-02-26 - 10:03 AnnaJuliaZsigmond  
PNGpng Figure1e.png r1 manage 86.4 K 2012-02-27 - 17:48 AnnaJuliaZsigmond  
PDFpdf Figure1f.pdf r1 manage 10.7 K 2012-02-26 - 10:03 AnnaJuliaZsigmond  
PNGpng Figure1f.png r1 manage 90.8 K 2012-02-27 - 17:48 AnnaJuliaZsigmond  
PDFpdf Figure2.pdf r1 manage 9.4 K 2012-02-26 - 10:03 AnnaJuliaZsigmond  
PNGpng Figure2.png r1 manage 26.2 K 2012-02-27 - 18:00 AnnaJuliaZsigmond  
PDFpdf Figure3a.pdf r1 manage 11.2 K 2012-02-26 - 10:03 AnnaJuliaZsigmond  
PNGpng Figure3a.png r1 manage 69.8 K 2012-02-27 - 18:00 AnnaJuliaZsigmond  
PDFpdf Figure3b.pdf r1 manage 11.0 K 2012-02-26 - 10:03 AnnaJuliaZsigmond  
PNGpng Figure3b.png r1 manage 69.6 K 2012-02-27 - 18:00 AnnaJuliaZsigmond  
PDFpdf Figure3c.pdf r1 manage 11.2 K 2012-02-26 - 10:04 AnnaJuliaZsigmond  
PNGpng Figure3c.png r1 manage 68.3 K 2012-02-27 - 18:06 AnnaJuliaZsigmond  
PDFpdf Figure3d.pdf r1 manage 11.1 K 2012-02-26 - 10:04 AnnaJuliaZsigmond  
PNGpng Figure3d.png r1 manage 68.8 K 2012-02-27 - 18:01 AnnaJuliaZsigmond  
PDFpdf Figure3e.pdf r1 manage 11.2 K 2012-02-26 - 10:04 AnnaJuliaZsigmond  
PNGpng Figure3e.png r1 manage 68.9 K 2012-02-27 - 18:01 AnnaJuliaZsigmond  
PDFpdf Figure3f.pdf r1 manage 11.3 K 2012-02-26 - 10:04 AnnaJuliaZsigmond  
PNGpng Figure3f.png r1 manage 70.4 K 2012-02-27 - 18:01 AnnaJuliaZsigmond  
PDFpdf Figure4a.pdf r1 manage 11.4 K 2012-02-26 - 10:05 AnnaJuliaZsigmond  
PNGpng Figure4a.png r1 manage 41.2 K 2012-02-27 - 18:01 AnnaJuliaZsigmond  
PDFpdf Figure4b.pdf r1 manage 11.5 K 2012-02-26 - 10:05 AnnaJuliaZsigmond  
PNGpng Figure4b.png r1 manage 41.8 K 2012-02-27 - 18:01 AnnaJuliaZsigmond  
PDFpdf Figure4c.pdf r1 manage 11.2 K 2012-02-26 - 10:05 AnnaJuliaZsigmond  
PNGpng Figure4c.png r1 manage 37.5 K 2012-02-27 - 18:02 AnnaJuliaZsigmond  
PDFpdf Figure5.pdf r2 r1 manage 13.0 K 2012-03-20 - 14:05 AnnaJuliaZsigmond  
PNGpng Figure5.png r2 r1 manage 19.1 K 2012-03-20 - 14:05 AnnaJuliaZsigmond  
PDFpdf Figure6.pdf r1 manage 19.3 K 2012-02-26 - 10:05 AnnaJuliaZsigmond  
PNGpng Figure6.png r1 manage 47.3 K 2012-02-27 - 18:02 AnnaJuliaZsigmond  
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