Measurement of the inelastic pp cross section at √s = 7 TeV with the CMS detector


A measurement is presented of the inelastic proton-proton cross section at a centre of mass energy of √s = 7 7TeV. Using the CMS detector at the LHC, the inelastic cross section is measured through two independent methods based on information from (i) forward calorimetry (for pseudorapidity 3 < |η| < 5), in collisions where at least one proton loses more than 5 10−6 of its longitudinal momentum, and (ii) the central tracker ( |η| < 2.4), in collisions containing an interaction vertex with more than 1, 2, or 3 tracks with transverse momenta pT > 200 MeV/c. The measurements cover a large fraction of the inelastic cross section for particle production over about 9 units of pseudorapidity and down to small transverse momenta. The results are compared with those of other experiments, and with models used to describe high- energy hadronic interactions.

Approved Plots from FWD-11-001 PAS ( click on plot to get .pdf )

Figure Abbreviated Caption
Paper_Fig1new.gif The normalized $\xi$ distributions for $E_{\rm{HF}} > 4$ and $E_{\rm{HF}} > 5 $ \GeV from MC simulation of inelastic pp collisions using (a) \textsc{ Pythia6}, (c) \textsc{ Pythia8}, and (e) \textsc{ Phojet}, are shown for the full range of $\xi$. The corresponding efficiencies are shown in (b), (d), and (f), respectively. The lowest value of $\xi$ used in the analysis, $\xi = 5\cdot10^{-6}$, is shown on the plots as a dashed vertical line.

Paper_Fig2new.gif Fraction of reconstructed events with more than 1 track, corrected for efficiency, measured as a function of the number of vertexes, in data (dots) and in Monte Carlo (histogram), for instantaneous bunch-crossing luminosities between 0.05~$\cdot 10^{30}$ and 0.6~$\cdot 10^{30}\; {\rm cm^{-2} \; s^{-1}}$.

Paper_Fig3new.gif Fraction of pp events with $n$ pileup vertexes, for $n$ = 0 to 8, containing more than one charged particle, as a function of instantaneous bunch-crossing luminosity. The dashed lines are the fits described in the text. The data points are plotted at the mean of the differential distribution in each bin

Paper_Fig4new.gif (a) Values of the inelastic pp cross section $\sigma_{\rm inel}$ and (b) their associated goodness of fit $\chi^2$/NDOF, obtained for each of the fits in Fig.~\ref{fig:final}, as a function of the number of pileup vertexes, in interactions with $>1$ track with $p_T>$ 200 \MeVc and abs(eta) < 2.4$. The line in (a) is the result of a fit to the 9 individual values of $\sigma_{\rm inel}$ while the dashed line in (b) indicates $\chi^2$/NDOF = 1.

Paper_Fig5new.gif The two types of CMS measurements of the inelastic pp cross section (red filled circle and squares) compared to predictions from several Monte Carlo models for different criteria, as labelled below the abscissa axis. The MC predictions have an uncertainty of $1 $ mb (not shown). Other LHC experimental results are also included for comparison.

Paper_Fig6new.gif Comparison of the measured inelastic pp cross sections with predictions of several Monte Carlo models, for different criteria, normalized to the value obtained for $>$3 tracks.

Paper_Table1.gif Values of efficiency ($\epsilon_\xi$) and contamination ($b_\xi$) for events with $\xi > 5\cdot10^{-6}$ using the selection criterion of $E_{\rm{HF}} > 5$ \GeV, obtained for three Monte Carlo models of hadronic production.

Paper_Table2.gif Mean number of collisions with $E_{\rm{HF}} > 5 $ \GeV per coincidence trigger ($\lambda$) and fraction of overlapping collisions ($f_{\rm{pu}}$) for the runs used in this analysis.

Paper_Table3.gif List of systematic sources and their effects on the value of the inelastic cross section measured using HF calorimeters. The contribution from luminosity uncertainty is kept separated.

Paper_Table4.gif List of systematic sources and their effects on the value of the inelastic cross section measured using the vertex-counting method. The percentage changes are shown for $\sigma_{\rm{inel}}(\rm{>1~track})$. The contribution from luminosity uncertainty is kept separated.

Paper_Table5.gif $\sigma_{\rm inel}$ values for interactions with $>$1, $>$2 and $>$3 charged particles, with their uncertainties from systematic sources of the method, and from luminosity.

-- NicoloCartiglia - 01-Aug-2011

Topic attachments
I Attachment History Action Size Date Who Comment
GIFgif 1_2_vtx.gif r1 manage 8.0 K 2011-08-02 - 09:39 NicoloCartiglia  
GIFgif Blind2.gif r1 manage 29.1 K 2011-08-01 - 22:26 NicoloCartiglia  
GIFgif CMS_manyVtx.gif r1 manage 162.1 K 2011-08-02 - 09:28 NicoloCartiglia  
GIFgif Data_MC_Lumibins.gif r1 manage 30.2 K 2011-08-01 - 13:22 NicoloCartiglia  
GIFgif FInal_plots_05.gif r1 manage 21.1 K 2011-08-01 - 13:28 NicoloCartiglia  
GIFgif MC_64_564.gif r1 manage 17.1 K 2011-08-01 - 22:33 NicoloCartiglia  
GIFgif MC_LumiBins.gif r1 manage 25.2 K 2011-08-02 - 09:34 NicoloCartiglia  
GIFgif MC_Sigma_chi2.gif r1 manage 10.0 K 2011-08-01 - 22:34 NicoloCartiglia  
GIFgif MC_data_64_05.gif r1 manage 26.1 K 2011-08-01 - 13:22 NicoloCartiglia  
GIFgif Paper_Fig1new.gif r1 manage 37.6 K 2012-10-14 - 00:28 NicoloCartiglia  
PDFpdf Paper_Fig1new.pdf r1 manage 86.9 K 2012-10-14 - 00:22 NicoloCartiglia  
GIFgif Paper_Fig2new.gif r1 manage 56.4 K 2012-10-14 - 00:37 NicoloCartiglia  
PDFpdf Paper_Fig2new.pdf r1 manage 27.2 K 2012-10-14 - 00:37 NicoloCartiglia  
GIFgif Paper_Fig3new.gif r1 manage 50.5 K 2012-10-14 - 00:37 NicoloCartiglia  
PDFpdf Paper_Fig3new.pdf r1 manage 28.9 K 2012-10-14 - 00:37 NicoloCartiglia  
GIFgif Paper_Fig4new.gif r1 manage 40.0 K 2012-10-14 - 00:37 NicoloCartiglia  
PDFpdf Paper_Fig4new.pdf r1 manage 16.0 K 2012-10-14 - 00:37 NicoloCartiglia  
GIFgif Paper_Fig5new.gif r1 manage 53.3 K 2012-10-14 - 00:42 NicoloCartiglia  
PDFpdf Paper_Fig5new.pdf r1 manage 16.3 K 2012-10-14 - 00:42 NicoloCartiglia  
GIFgif Paper_Fig6new.gif r1 manage 51.2 K 2012-10-14 - 00:42 NicoloCartiglia  
PDFpdf Paper_Fig6new.pdf r1 manage 15.9 K 2012-10-14 - 00:42 NicoloCartiglia  
GIFgif Paper_Table1.gif r1 manage 8.7 K 2012-10-14 - 00:49 NicoloCartiglia  
GIFgif Paper_Table2.gif r1 manage 23.8 K 2012-10-14 - 00:49 NicoloCartiglia  
GIFgif Paper_Table3.gif r1 manage 28.9 K 2012-10-14 - 00:49 NicoloCartiglia  
GIFgif Paper_Table4.gif r1 manage 26.0 K 2012-10-14 - 00:49 NicoloCartiglia  
GIFgif Paper_Table5.gif r1 manage 16.1 K 2012-10-14 - 00:49 NicoloCartiglia  
GIFgif Secondary.gif r1 manage 8.3 K 2011-08-01 - 23:08 NicoloCartiglia  
GIFgif Sigma_chi_final_65_05_2trk.gif r1 manage 9.5 K 2011-08-01 - 13:29 NicoloCartiglia  
GIFgif Tot_inel.gif r1 manage 146.0 K 2011-08-01 - 13:48 NicoloCartiglia  
GIFgif Uncor_plots_05.gif r1 manage 16.1 K 2011-08-01 - 22:28 NicoloCartiglia  
GIFgif Vtx_Eff_2_3_trk.gif r1 manage 14.2 K 2011-08-01 - 13:09 NicoloCartiglia Fig1_gif
GIFgif Vtx_vs_lumi.gif r1 manage 12.3 K 2011-08-01 - 22:24 NicoloCartiglia  
GIFgif csi.gif r1 manage 11.0 K 2011-08-01 - 14:14 NicoloCartiglia  
GIFgif data_over_MC_64_05.gif r1 manage 29.2 K 2011-08-02 - 09:33 NicoloCartiglia  
GIFgif nvertexes.gif r1 manage 11.0 K 2011-08-01 - 22:26 NicoloCartiglia  
GIFgif sigma_com_part.gif r1 manage 10.3 K 2011-08-01 - 13:34 NicoloCartiglia  
GIFgif transversecut.gif r1 manage 17.8 K 2011-08-02 - 09:28 NicoloCartiglia  
GIFgif xi_models.gif r2 r1 manage 16.6 K 2011-08-01 - 14:01 NicoloCartiglia  
Edit | Attach | Watch | Print version | History: r6 < r5 < r4 < r3 < r2 | Backlinks | Raw View | WYSIWYG | More topic actions
Topic revision: r6 - 2012-10-14 - NicoloCartiglia
    • Cern Search Icon Cern Search
    • TWiki Search Icon TWiki Search
    • Google Search Icon Google Search

    CMSPublic All webs login

This site is powered by the TWiki collaboration platform Powered by PerlCopyright & 2008-2023 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
or Ideas, requests, problems regarding TWiki? use Discourse or Send feedback