Diffraction at the LHC

We show that the diffractive pp (and p\bar{p}) data (on \sigma_tot, d\sigma_el/dt, proton dissociation into low-mass systems, \sigma^D(low M), and high-mass dissociation, d\sigma/d(\Delta\eta)) in a wide energy range from CERN-ISR to LHC energies, may be described in a two-channel eikonal model with only one `effective' pomeron. By allowing the pomeron coupling to the diffractive eigenstates to depend on the collider energy (as is expected theoretically) we are able to explain the low value of \sigma^D(low M) measured at the LHC. We calculate the survival probability, S^2, of a rapidity gap to survive `soft rescattering'. We emphasize that the values found for S^2 are particularly sensitive to the detailed structure of the diffractive eigenstates.Comment: 20 pages, 6 figures. Version to be published in EPJC. Typos corrected in eqs.(4) and (11

Checking formalism for central exclusive production in the first LHC runs

We discuss how the early LHC data runs can provide crucial tests of the formalism used to predict the cross sections of central exclusive production.Comment: 7 pages, 6 figures; Based on a talk by A.D. Martin at the CERN - DESY Workshop "HERA and the LHC", 26 - 30 May 2008, CER

Lessons from LHC elastic and diffractive data

In the light of LHC data, we discuss the global description of all high energy elastic and diffractive data, using a one-pomeron model, but including multi-pomeron interactions. The LHC data indicate the need of a $k_t(s)$ behaviour, where $k_t$ is the gluon transverse momentum along the partonic ladder structure which describes the pomeron. We also discuss tensions in the data, as well as the $t$ dependence of the slope of $d\sigma_{el}/dt$ in the small $t$ domain.Comment: 5 pages, 3 figures, Proceedings of Diffraction 2014, Primosten, Croatia, Sept. 10-1

Partonic description of soft high energy pp interactions

We discuss how the main features of high-energy `soft' and `semihard' pp collisions may be described in terms of parton cascades and multi-Pomeron exchange. The interaction between Pomerons produces an effective infrared cutoff, k_sat, by the absorption of low k_t partons. This provides the possibility of extending the parton approach, used for `hard' processes, to also describe high-energy soft and semihard interactions. We outline a model which incorporates these features. Finally, we discuss what the most recent LHC measurements in the soft domain imply for the model.Comment: 12 pages, 5 figures. Presented at Linear Collider 2011: Understanding QCD at Linear Colliders in searching for old and new physics, 12-16 September 2011, ECT*, Trento, Ital

Information from leading neutrons at HERA

In principle, leading neutrons produced in photoproduction and deep-inelastic scattering at HERA have the potential to determine the pion structure function, the neutron absorptive cross section and the form of the pion flux. To explore this potential we compare theoretical predictions for the x_L and p_t spectra of leading neutrons, and the Q^2 dependence of the cross section, with the existing ZEUS data.Comment: 17 pages, 8 figure

Luminosity monitors at the LHC

We study the theoretical accuracy of various methods that have been proposed to measure the luminosity of the LHC pp collider, as well as for Run II of the Tevatron p barp collider. In particular we consider methods based on (i) the total and forward elastic data, (ii) lepton-pair production and (iii) W and Z production.Comment: 23 pages, Latex, 9 figure

High pTp_{T} Higgs signal for the LHC

We show that the broad transverse momentum distribution of the Higgs boson produced by WW fusion can provide a viable way to identify H --> b anti-b decays at the LHC, if particular kinematical configurations with large rapidity gaps are selected. We estimate the event rate of the signal and of the QCD b anti-b background. We also discuss Higgs boson detection via the H --> tau tau and H --> WW* decay modes