Spires | arXiv:1201.2808 [hep-ex]
Pseudorapidity gap distributions in proton-proton collisions at $\sqrt{s} = 7$ TeV are studied using a minimum bias data sample with an integrated luminosity of 7.1 inverse microbarns. Cross sections are measured differentially in terms of $\Delta \eta_F$, the larger of the pseudorapidity regions extending to the limits of the ATLAS sensitivity, at $\eta = \pm 4.9$, in which no final state particles are produced above a transverse momentum threshold $p_\perp$ cut. The measurements span the region $0 < \Delta \eta_F < 8$ for $200 < p_T\text{ cut} < 800\;\text{MeV}$. At small $\Delta \eta_F$, the data test the reliability of hadronisation models in describing rapidity and transverse momentum fluctuations in final state particle production. The measurements at larger gap sizes are dominated by contributions from the single diffractive dissociation process ($pp \to Xp$), enhanced by double dissociation ($pp \to XY$) where the invariant mass of the lighter of the two dissociation systems satisfies $M_Y \lesssim 7\;\text{GeV}$. The resulting cross section is $\mathrm{d} \sigma / \mathrm{d} \Delta \eta_F \sim 1$ mb for $\Delta \eta_F \gtrsim 3$. The large rapidity gap data are used to constrain the value of the pomeron intercept appropriate to triple Regge models of soft diffraction. The cross section integrated over all gap sizes is compared with other LHC inelastic cross section measurements.
Spires | arXiv:1103.1816
Underlying event measurements with the ATLAS detector at the LHC at center-of-mass energies of 900 GeV and 7 TeV, using calorimeter clusters rather than charged tracks.
Spires | arXiv:1012.5104
Measurements from proton-proton collisions at centre-of-mass energies of $\sqrt{s} = 0.9$, 2.36, and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase-space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections.
Spires | arXiv:1012.0791
The underlying event measurements with the ATLAS detector at the LHC at the center of mass energies of 900 GeV and 7 TeV. The observables sensitive to the underlying event, i.e the charged particle density and charged pT sum, as well as their standard deviations and the average pT, are measured as functions of the leading track. A track pT cut of 500 MeV is applied for most observables, but the main profile plots are also shown for a lower track cut of 100 MeV, which includes much more of the soft cross-section. The angular distribution of the charged tracks with respect to the leading track is also studied, as are the correlation between mean transverse momentum and charged particle multiplicity, and the `plateau' height as a function of the leading track $|\eta|$.
Spires | Europhys.Lett. 98 (2012) 31002 | arXiv:1205.4105 | CERN-PH-EP-2012-106 | TOTEM 2012-01
The TOTEM experiment has measured the charged particle pseudorapidity density $\mathrm{d}N_\text{ch}/\mathrm{d}\eta$ in $pp$ collisions at $\sqrt{s} = 7$\,TeV for $5.3 < |\eta| < 6.4$ in events with at least one charged particle with transverse momentum above 40\;MeV/$c$ in this pseudorapidity range.
Rick Field's measurement of the underlying event in leading jet events, extended to the LHC. As usual, the leading jet of the defines an azimuthal toward/transverse/away decomposition, in this case the event is accepted within $|\eta| < 2$, as in the CDF 2008 version of the analysis. Since this isn't the Tevatron, I've chosen to use $k_\perp$ rather than midpoint jets.
Analysis for bookkeeping of the total cross section, number of generated events and the ratio of events with positive and negative weights.
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