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A bstract The existence of an axion-like particle (ALP) would induce anomalous scattering of light by light. This process can be probed at the Large Hadron Collider in central exclusive production of photon pairs in proton-proton collisions by tagging the surviving protons using forward proton detectors. Using a detailed simulation, we estimate the expected bounds on the ALP-photon coupling for a wide range of masses. We show that the proposed search is competitive and complementary to other collider bounds for masses above 600 GeV, especially for resonant ALP production between 600 GeV and 2 TeV. Our results are also valid for a CP-even scalar, and the efficiency of the search is independent of the width of the ALP.

A bstract The sensitivities to the anomalous quartic gauge boson coupling γγγZ are estimated via γZ production with intact protons in the forward region at the LHC. Proton tagging proves to be a powerful tool to suppress the background, which allows consideration of the hadronic decays of the Z boson in addition to the leptonic ones. We discuss the discovery potential for an integrated luminosity of 300 fb −1 and 3000 fb −1 . The sensitivity we obtain at 300 fb −1 goes beyond the one expected from LHC bounds on the Z → γγγ decay by about three orders of magnitude. The γZ channel provides important discriminatory information with respect to the exclusive γγ channel, as many particles beyond the Standard Model (such as a radion or Kaluza Klein gravitons) predict a signal in the latter but not the former.

A bstract We present a phenomenology study on central exclusive production of W + W − boson pairs in proton-proton collisions at the Large Hadron Collider at 14 TeV using the forward proton detectors, such as the ATLAS Forward Proton or the CMS-TOTEM Precision Proton Spectrometer detectors. Final states where at least one of the W bosons decay hadronically in a large-radius jet are considered. The latter extends previous efforts that consider solely leptonic final states. A measurement of exclusive W + W − also allows us to further constrain anomalous quartic gauge boson interactions between photons and W bosons. Expected limits on anomalous quartic gauge couplings a 0 , C W associated to dimension-six effective operators are derived for the hadronic, semi-leptonic, and leptonic final states. It is found that the couplings can be probed down to one-dimensional values of a 0 W = 3.7 × 10 − 7 GeV − 2 and a C W = 9.2 × 10 − 7 GeV − 7 at 95% CL at an integrated luminosity of 300 fb − 1 by combining all final states, compared to values of about a 0 W = 4 × 10 − 6 GeV − 2 and a C W = 1 × 10 − 5 GeV − 2 at 95% CL expected for the leptonic channel alone.

A bstract We present a phenomenological analysis of events with two high transverse momentum ( p T ) jets separated by a large (pseudo-)rapidity interval void of particle activity, also known as jet-gap-jet events. In the limit where the collision energy s is much larger than any other momentum scale, the jet-gap-jet process is described in terms of perturbative pomeron exchange between partons within the Balitsky-Fadin-Kuraev-Lipatov (BFKL) limit of perturbative quantum chromodynamics (QCD). The BFKL pomeron exchange amplitudes, with resummation at the next-to-leading logarithmic approximation, have been embedded in the PYTHIA8 Monte Carlo event generator. Standard QCD dijet events are simulated at next-to-leading order in α s matched to parton showers with POWHEG+PYTHIA8. We compare our calculations to measurements by the CDF, D0, and CMS experiments at center-of-mass energies of 1.8, 7 and 13 TeV. The impact of the theoretical scales, the parton densities, final- and initial-state radiation effects, multiple parton interactions, and p T thresholds and multiplicities of the particles in the rapidity gap on the jet-gap-jet signature is studied in detail. With a strict gap definition (no particle allowed in the gap), the shapes of most distributions are well described except for the CMS azimuthal-angle distribution at 13 TeV. The survival probability is surprisingly well modelled by multiparton interactions in PYTHIA8. Without multiparton interactions, theoretical predictions based on two-channel eikonal models agree qualitatively with fits to the experimental data.

A bstract This study focuses on hard diffractive events produced in proton-proton collision at LHC exhibiting one intact proton in the final state which can be tagged by forward detectors. We report prospective results on the W boson charge asymmetry measured for such events, which allow to constrain the quark diffractive density functions in the Pomeron.

The TOTEM collaboration at the CERN LHC has measured the differential cross-section of elastic proton–proton scattering at s=8TeV in the squared four-momentum transfer range 0.2GeV2<|t|<1.9GeV2. This interval includes the structure with a diffractive minimum (“dip”) and a secondary maximum (“bump”) that has also been observed at all other LHC energies, where measurements were made. A detailed characterisation of this structure for s=8TeV yields the positions, |t|dip=(0.521±0.007)GeV2 and |t|bump=(0.695±0.026)GeV2, as well as the cross-section values, dσ/dtdip=(15.1±2.5)μb/GeV2 and dσ/dtbump=(29.7±1.8)μb/GeV2, for the dip and the bump, respectively.

The proton–proton elastic differential cross section d σ / d t has been measured by the TOTEM experiment at s = 2.76 TeV energy with β ∗ = 11 m beam optics. The Roman Pots were inserted to 13 times the transverse beam size from the beam, which allowed to measure the differential cross-section of elastic scattering in a range of the squared four-momentum transfer (| t |) from 0.36 to 0.74 GeV 2 . The differential cross-section can be described with an exponential in the | t |-range between 0.36 and 0.54 GeV 2 , followed by a diffractive minimum (dip) at | t dip | = ( 0.61 ± 0.03 ) GeV 2 and a subsequent maximum (bump). The ratio of the d σ / d t at the bump and at the dip is 1.7 ± 0.2 . When compared to the proton–antiproton measurement of the D0 experiment at s = 1.96 TeV , a significant difference can be observed. Under the condition that the effects due to the energy difference between TOTEM and D0 can be neglected, the result provides evidence for the exchange of a colourless C-odd three-gluon compound state in the t -channel of the proton–proton and proton–antiproton elastic scattering.

We show that the forward-jet measurements performed at HERA allow for a detailed study of corrections due to next-to-leading logarithms (NLL) in the Balitsky–Fadin–Kuraev–Lipatov (BFKL) approach. While the description of the dσ/dx data shows small sensitivity to NLL-BFKL corrections, these can be tested by the triple differential cross section d 3 σ/dxdk T 2 dQ 2 recently measured. These data can be successfully described using a renormalization-group improved NLL kernel, while the standard next-to-leading-order QCD or leading-logarithm BFKL approaches fail to describe the same data in the whole kinematic range. We present a detailed analysis of the NLL scheme and renormalization-scale dependences and also discuss the photon impact factors.

We discuss first the discovery of the odderon by the TOTEM and D0 collaborations. We then describe the gap between jets measurements sensitive to the high gluon density regime and the possible observation of saturation phenomenon in Pb Pb interactions. We also mention the sensitivity to beyond standard model physics and to the production of axion-like particles via photon photon interactions.

We study the single production of supersymmetric particles at Tevatron Run II which occur in the \\(2 2-body\\) processes involving R-parity violating couplings of type \\('_ijk L_i Q_j D_k^c\\). We focus on the single gaugino production which receive contributions from the resonant slepton production. We first calculate the amplitudes of the single gaugino production. Then we perform analyses of the single gaugino production based on the three charged leptons and like sign dilepton signatures. These analyses allow to probe supersymmetric particles masses beyond the present experimental limits, and many of the \\('_ijk\\) coupling constants down to values smaller than the low-energy bounds. Finally, we show that the studies of the single gaugino production offer the opportunity to reconstruct the \\( ^0_1, ^_1, _L\\) and \\( l^_L\\) masses with a good accuracy in a model independent way.