Measurement of pp diffraction dissociation cross sections at √s = 7 TeV at the LHC

Abstract

We present results from a measurement of the single and double diffraction dissociation cross sections in pp collisions at √s = 7 TeV using the Compact Muon Solenoid detector at the Large Hadron Collider, and compare our results to other experimental measurements and to theoretical expectations. In addition, the differantial cross section of forward rapidity gaps (dσ/dΔη^F) at √s = 7 TeV pp collisions is presented.

Figures part1

Figure	Caption
	The (a) $\eta_{max}$, (b) $\eta_{min}$ and (c) $\Delta\eta^{0} = \eta^{0}_{max}-\eta^{0}_{min}$ distributions for the minimum-bias sample, compared to predictions of the PYTHIA8-MBR simulation normalized to the luminosity of the data. Contributions from each of the generated processes are shown separately. The DD MC events are additionally scaled downwards by 15~$\%$. The dashed vertical lines represent the $\eta_{max}<1$, $\eta_{min}>-1$ and $\Delta\eta^{0}>3$ selections.
	The generator-level distributions of the dissociated mass, $M_X$, for the SD process in the SD1 sample at different selection stages for the PYTHIA8-MBR MC sample
	The generator-level distributions of the dissociated mass, $M_X$, for the SD process in the SD1 sample at different selection stages for the PYTHIA8-4C MC sample
	The generator-level efficiency (PYTHIA8-MBR), in the $M_X$ and $M_Y$ plane, for selecting truly DD events after (a) the trigger selection and (b) the SD2 or (c) the DD selections
	The detector-level distributions of the reconstructed and corrected $\xi$ for (a) the entire SD2 sample, and the SD2 subsamples with (b) no CASTOR tag and (c) a CASTOR tag. The data are compared to predictions of the PYTHIA8-MBR simulation normalized to the luminosity of the data. Contributions for each one of the generated processes are shown separately. The DD MC events are additionally scaled downwards by 15~$\%$.
	The detector-level distributions of the reconstructed and corrected $\xi$ for (a) the entire SD2 sample, and the SD2 subsamples with (b) no CASTOR tag and (c) a CASTOR tag. The data are compared to predictions of the PYTHIA8-4C simulation normalized to the luminosity of the data. Contributions for each one of the generated processes are shown separately.
	The SD (left) and DD (right) cross sections as a function of $\xi$ compared to PYTHIA6, PYTHIA8-4C and PYTHIA8-MBR MC predictions.
	The detector-level distributions of the reconstructed and corrected $\Delta\eta^{0}$ for the DD sample with central LRG. The data are compared to predictions of the PYTHIA8-MBR simulation normalized to the luminosity of the data. Contributions for each one of the generated processes are shown separately. The DD events in PYTHIA8-MBR sample are scaled downwards by 15~$\%$.
	The detector-level distributions of the reconstructed and corrected $\Delta\eta^{0}$ for the DD sample with central LRG. The data are compared to predictions of the PYTHIA8-4C simulation normalized to the luminosity of the data. Contributions for each one of the generated processes are shown separately.
	The DD cross sections as a function of $\Delta\eta$ compared to PYTHIA6, PYTHIA8-4C and PYTHIA8-MBR MC predictions.

Figures part2

Figure 12. (a) Comparison of uncorrected forward rapidity gap size (∆ηF) distribution (black points) with the different MC models (colored lines), (b) Beam background from unpaired bunches.

Figure 13. Single side BSC trigger efficiency for at least two hits (offline) in either side of the BSC. The trigger efficiency correction factors are obtained from a fit to the data. The discrepancy between the fit and the data points has a small effect on the results and is covered by the systematics.

Figure 14. Migration matrix between the truth and reconstructed ∆ηF according to PYTHIA8-MBR (ε = 0.08) for stable final state particles with pT > 200 MeV in ΙηΙ < 4.7. The plot is normalized to the unity in columns.

Figure 15. Unfolded and fully corrected differantial cross section of the forward rapidity gap size (dσ/d∆ηF) for all stable final particles with pT > 200 MeV in ΙηΙ < 4.7 are compared with the hadron level predictions of (a) PYTHIA8-MBR (ε = 0.08), (b) PYTHIA8-MBR (ε = 0.104), (c) PYTHIA8 tune 4C and (d) PYTHIA6 tune Z2star. The green band represents the total systematic uncertainty on the measurement which is obtained as the quadrature sum of the different uncertainty sources.

Figure 16. Comparison of CMS measurement (black points) with ATLAS result (blue points). The green band respresents the total systematic uncertainty of the CMS measurement and the total uncertainty of ATLAS measurement is shown with the error bars on the ATLAS points. The hadron level definitions of the two measurements are not the same. CMS measures the forward rapidity gap size in η starting from η = ±4.7 where the ATLAS limit is η = ±4.9.

Rivet Validation Plots (CMS_2015_I1356998)

• Validation plots Rivet 2.2.0: