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Measurement of diffractive dissociation cross sections in pp collisions at s =7TeV

Physical Review D - Particles, Fields, Gravitation and Cosmology (2015) 92(1)
DOI: 10.1103/PhysRevD.92.012003
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Abstract

Measurements of diffractive dissociation cross sections in pp collisions at s=7TeV are presented in kinematic regions defined by the masses MX and MY of the two final-state hadronic systems separated by the largest rapidity gap in the event. Differential cross sections are measured as a function of ξX=MX2/s in the region -5.5 <0.5, dominated by single dissociation (SD), and 0.5 3, log10MX>1.1, and log10MY>1.1, a region dominated by DD. The cross sections integrated over these regions are found to be, respectively, 2.99±0.02(stat)-0.29+0.32(syst)mb, 1.18±0.02(stat)±0.13(syst)mb, and 0.58±0.01(stat)-0.11+0.13(syst)mb, and are used to extract extrapolated total SD and DD cross sections. In addition, the inclusive differential cross section, dσ/dΔηF, for events with a pseudorapidity gap adjacent to the edge of the detector, is measured over ΔηF=8.4 units of pseudorapidity. The results are compared to those of other experiments and to theoretical predictions and found compatible with slowly rising diffractive cross sections as a function of center-of-mass energy.

Figures

  • FIG. 1. Schematic diagrams of (a) nondiffractive, pp → X, and diffractive processes with (b) single dissociation, pp → Xp or pp → pY, (c) double dissociation, pp → XY, and (d) central diffraction, pp → pXp; XðYÞ represents a dissociated proton or a centrally produced hadronic system.
  • FIG. 2 (color online). Detector-level distributions of the energy of PF objects in four pseudorapidity intervals: jηPFj < 1.4, 1.4 < jηPFj < 2.6, 2.6 < jηPFj < 3.2, and jηPFj > 3.2, corresponding to the barrel, end-cap, end-cap-forward transition, and forward detector regions (columns), for five particle candidate types: charged hadrons (tracks), photons, neutral hadrons, and two types that yield electromagnetic or hadronic energy deposits in HF (rows). Electron and muon candidates constitute less than 0.1% of the PF objects reconstructed in the jηPFj < 2.6 region, and are not shown. The data are compared to the predictions of the PYTHIA 8 MBR simulation, normalized to the integrated luminosity of the data sample. The contribution of each of the generated processes is shown separately.
  • FIG. 3 (color online). Event topologies in final-state particle η space. Detector level: nondiffractive events (ND), diffractive events with a forward pseudorapidity gap on the positive (FG1) or negative (FG2) η side of the detector, or with a central pseudorapidity gap (CG). Generator level: (a) ND, pp → X, (b) SD1, pp → Xp, (d) SD2, pp → pY, and (c, e, f) DD, pp → XY, events. The empty box represents the central CMS detector (jηj ≲ 4.7), filled full boxes indicate final-state hadronic systems or a proton—the vertical thin bar at the right/left end of sketch (b)/ (d). The dotted empty boxes in (d) and (e) represent the CASTOR calorimeter (−6.6 < η < −5.2).
  • FIG. 4 (color online). Detector-level distributions for the (a) ηmax, (b) ηmin, and (c) Δη0 ¼ η0max − η0min variables measured in the minimum bias sample (with only statistical errors shown), compared to predictions of the PYTHIA 8 MBR simulation normalized to the integrated luminosity of the data sample. Contributions from each of the MC-generated processes, and simulated events with at least two overlapping interactions of any type (pileup), are shown separately. The dashed vertical lines indicate the boundaries for the ηmax < 1, ηmin > −1, and Δη0 > 3 selections.
  • FIG. 5 (color online). Simulated distributions of the dissociated mass MX at stable-particle level for the SD process in the FG2 sample at successive selection stages (trigger, minimal detector activity within BSC acceptance, ηmin > −1) for PYTHIA 8 MBR (left) and PYTHIA 8 4C (right). The MC samples are normalized to the luminosity of the data sample.
  • FIG. 6 (color online). Simulated (PYTHIA 8 MBR) event selection efficiency in the MX vs. MY plane for true DD events after (a) the trigger selection, and (b) the FG2 selection with a CASTOR tag or (c) the CG selection (Fig. 3). The regions delimited by the solid (red) lines in (b) and (c) are those of the cross section measurements; the dashed (red) box in (b) corresponds to the enlarged region for which the cross section is given (Sec. IX), assuming the same dependence onMX andMY ; the dashed (blue) line in (c) marks the region of Δη > 3.
  • FIG. 7 (color online). Two-dimensional distribution of reconstructed ξþX vs. generated ξX values for the events in the SD2 sample obtained with the PYTHIA 8 MBR simulation. The solid red line represents the condition log10ξ þ X ¼ log10ξX.
  • FIG. 8 (color online). Detector-level distributions of the reconstructed and calibrated ξX for (a) the entire FG2 sample, and the FG2 subsamples with (b) no CASTOR tag, and (c) a CASTOR tag (statistical errors only). The data are compared to the predictions of the PYTHIA 8 MBR (top three plots) and PYTHIA 8 4C (bottom three plots) simulations, which are normalized to the integrated luminosity of the data sample. The contribution of each of the generated processes is shown separately.

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APA

Khachatryan, V., Sirunyan, A. M., Tumasyan, A., Adam, W., Bergauer, T., Dragicevic, M., … Woods, N. (2015). Measurement of diffractive dissociation cross sections in pp collisions at s =7TeV. Physical Review D - Particles, Fields, Gravitation and Cosmology, 92(1). https://doi.org/10.1103/PhysRevD.92.012003

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