abstract

We present the first results of the new SuperChic 2 Monte Carlo event generator. This includes significant theoretical improvements and updates, most importantly, a fully differential treatment of the soft survival factor, as well as a greater number of generated processes.

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A selected set of topics in the low-\(x\) physics is discussed. Among them, recent developments in the next-to-leading corrections to the small-\(x\) nonlinear evolution with saturation, resummation of higher order corrections, forward inclusive production beyond lowest order and impact parameter dependence.

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CMS results on the multiple parton interactions measured with the leading track and the leading charged particle jet in \(pp\) collisions at different \(\sqrt {s}\) are presented. The charged particles distributions in central CMS detector and in TOTEM in inclusive sample and sample enhanced with non-diffractive interactions are shown. The single and double diffractive dissociation results are discussed. Finally, the double diffractive cross section measurement in the forward region done by TOTEM is presented.

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We present the review of the recent results on diffraction from the LHC.

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We develop a consistent approach to describe soft interactions at high energy based on the BFKL Pomeron and CGC/saturation. We build a two-channel model, in which the opacity is determined by the exchange of the dressed BFKL Pomeron. The Green function of the Pomeron is calculated in the framework of CGC/saturation approach. Having eight parameters, we obtained a good description of the experimental data at high energies (\(W\geq 0.546\) TeV).

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Updated RENORM/MBR-model predictions of diffractive, total, and total-inelastic cross sections at the LHC are presented and compared with experimental results and predictions from other models. In addition, expectations for diffraction at the upcoming LHC run at \(\sqrt s=13\) TeV are discussed.

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Due to its unique pseudorapidity coverage (\(2\lt \eta \lt 5\)) and excellent performance, the LHCb detector allows for studying soft QCD processes at large rapidities and low transverse momenta. Selected results, such as charged particle multiplicities and densities, forward energy flow and prompt charm production are briefly summarized in these proceedings. The measurements are performed using large samples of proton–proton collision data accumulated with the LHCb detector at \(\sqrt {s}=7\) TeV. The results are compared with predictions from a number of different Monte Carlo event generators providing a unique insight into particle production in the forward region at the LHC.

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We present recent measurements of elastic scattering by the TOTEM and ATLAS (ALFA) experiments.

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The quantum statistical parton distributions approach proposed more than one decade ago is revisited by considering a larger set of recent and accurate Deep Inelastic Scattering experimental results. It enables us to improve the description of the data by means of a new determination of the parton distributions. This global next-to-leading order QCD analysis leads to a good description of several structure functions, involving unpolarized parton distributions and helicity distributions, in terms of a rather small number of free parameters. There are several challenging issues. The predictions of this theoretical approach will be tested for single-jet production and charge asymmetry in \(W^{\pm }\) production in \(\bar p p\) and \(p p\) collisions up to the LHC energies, using recent data and also for forthcoming experimental results.

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The installation of forward proton detectors at the LHC will provide the possibility to observe central exclusive processes, opening a novel window on physics beyond the Standard Model. We review recent developments about the discovery potential from central exclusive light-by-light scattering. The search for this process is expected to provide bounds on a wide range of new particles, and turns out to be complementary from the new physics searches in central detectors.

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This proceeding reports a measurement of the exclusive \(\gamma \gamma \rightarrow l^+l^-\) \((l=e, \mu )\) cross section in proton–proton collisions at a center-of-mass energy of 7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of \(4.6\) fb\(^{-1}\). The measured cross section is found to be consistent with theory prediction, when proton absorptive effects due to the finite size of the proton are taken into account in the calculation.

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We compute prompt photon production in double-Pomeron exchange events in \(pp\) collisions at 13 TeV using the resolved-Pomeron-model assumptions. We make use of the proton diffractive pdf imposing specific kinematical constraints from the LHC experiments. For the hard-scattering matrix element computation, we make use of the JetPhox program. We show that NLO contributions must be taken into account in order to constraint quarks and gluons inside Pomeron.

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We present our results for exclusive \(p p \to p p \pi ^+ \pi ^-\) or \(p \bar p \to p \bar p \pi ^+ \pi ^-\) processes at high energies. We discuss the role of new additional absorption corrections in the non-resonant Lebiedowicz–Szczurek model mediated by the Pomeron and Reggeon exchanges. We discuss also the role of the \(\rho ^{0}\) and the Drell–Söding photoproduction mechanism. We compare our predictions with recent experimental results obtained by the STAR and CDF collaborations. We present predictions for the ALICE, ATLAS and CMS experiments. Differential distributions in invariant two-pion mass and two-dimensional distributions in proton–proton relative azimuthal angle and transverse momentum of one of the protons are presented.

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We discuss diffractive production of open charm and bottom mesons at the LHC. The differential cross sections for single- and central-diffractive mechanisms for \(c\bar c\) and \(b\bar b\) pair production are calculated in the framework of the Ingelman–Schlein model corrected for absorption effects. The LO gluon–gluon fusion and quark–antiquark annihilation partonic subprocesses are taken into consideration, which are calculated within standard collinear approximation. The extra corrections from Reggeon exchanges are taken into account. The hadronization of charm and bottom quarks is taken into account by means of fragmentation functions. Predictions for single- and central-diffractive production in the case of \(D\) and \(B\) mesons, as well as \(D\bar D\) pairs are presented, including detector acceptance of the ATLAS, CMS and LHCb collaborations.

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We present an overview of the options for diffraction implemented in the general-purpose event generator PYTHIA8. We review the existing model for low- and high-mass soft diffraction and present a new model for hard diffraction in \(pp\) and \({p}\bar {p}\) collisions. Both models use the Pomeron approach pioneered by Ingelman and Schlein, factorising the single diffractive cross section into a Pomeron flux and a Pomeron PDF. The model for hard diffraction is implemented as a part of the multiparton interactions framework, thereby introducing a dynamical rapidity gap survival probability that explicitly breaks factorisation.

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The diffractive dijet cross sections for photoproduction and deep inelastic scattering were studied with emphasis on studying of factorisation properties of diffractive processes. The production of isolated prompt photons in diffractive photoproduction was measured for the first time. The measurement of exclusive dijet production was compared to predictions from models based on different assumptions about the nature of diffractive exchange.

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Central Exclusive Production is a unique QCD process in which particles are produced via colourless propagators. Several results have been obtained at LHCb for the production of single charmonia, pairs of charmonia, and single bottomonia.

abstract

At the 2011 Blois Workshop, \(pp\) elastic scattering measurements at the LHC at 7 TeV were presented by the TOTEM Collaboration. They showed that our predicted \(d\sigma /dt\) in the momentum transfer region \(|t|\simeq 0.5\)–2.5 GeV\(^2\) disagreed significantly with TOTEM results. This led us to consider an extensive investigation of the large \(|t|\) \(pp\) elastic scattering that included: (i) multiple \(\omega \)-exchanges; (ii) valence quark–quark scattering via low-\(x\) gluon–gluon interactions; and (iii) the single \(\omega \)-exchange amplitude and the quark–quark scattering amplitude having opposite signs. We found a satisfactory description of the 7 TeV \(d\sigma /dt\) in the region of 0.6 GeV\(^2\lt |t|\lt 2.5\) GeV\(^2\). This result was presented by us at the Blois 2013 Workshop. However, as noted by others, there was still a significant difference between our calculated \(d\sigma /dt\) and TOTEM data in the forward direction: \(|t|\lt 0.6\) GeV\(^2\). This led us to envisage a new aspect of our \(q\bar {q}\) Condensate-Enclosed Chiral-Bag Model of the proton. In this model, the proton has a core of baryonic shell with valence quarks inside. The proton baryonic-charge core polarizes the \(q\bar {q}\) condensate cloud and creates a layer of antiquarks surrounding the baryonic core. This, in turn, leads to a layer of positive quarks at the boundary of the proton. For an antiproton, the opposite happens — a layer of negative antiquarks appears at the boundary of the antiproton. In \(pp\) forward scattering, the two polarization layers at the boundary interact giving rise to a new scattering amplitude. For \(\bar {p}p\), the same thing happens except the amplitude has the opposite sign as in D0 1.96 TeV. Our phenomenological investigation has now shown that we can describe quantitatively the \(pp\) \(d\sigma /dt\) TOTEM data at 7 TeV throughout the entire \(|t|\) range. We now predict the \(pp\) \(d\sigma /dt\) at the LHC at 13 TeV, which will test our model of the proton structure.

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HERMES and COMPASS results of DVCS and DVMP are presented. Preparations for the 2016/17 COMPASS GPD run are at full swing.

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We demonstrate that the transversity chiral-odd generalized parton distributions can be accessed through the azimuthal dependence of the \(\nu _l N \to l^- D^+ N'\) or \(\bar \nu _l N \to l^+ D^- N'\) differential cross sections, in the framework of the collinear QCD approach, where GPDs factorize from perturbatively calculable coefficient functions calculated up to the order of \(m_c/Q\).

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We reconsider the perturbative next-to-leading calculation of single inclusive hadron production in the framework of the hybrid formalism, applied to hadron production in proton–nucleus collisions. We introduce the explicit requirement that fast fluctuations in the projectile wave function which only exists for a short time are not resolved by the target. This Ioffe time cut-off also strongly affects the next-to-leading order terms.

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We study the impact factor for the photon to quark, antiquark and gluon transition within Balitsky’s shock-wave formalism. Our aim is to extend existing results beyond approximations discussed in the literature. We present our results of the real contribution, and present some intermediate results on virtual contributions for the photon to quark, antiquark transition.

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We propose a new factorization formula for forward dijet production in dilute–dense collisions which generalizes the hybrid high energy factorization to the regime of the gluon saturation. The approach uses several unintegrated gluon distributions convoluted with appropriate gauge invariant off-shell hard factors calculated in two independent ways, in particular using the color decomposition and the spinor helicty method. The new formula extrapolates the Transverse Momentum Dependent (TMD) factorization approach beyond the leading-twist and towards the small \(x\).

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We present an estimation of the contribution of double parton scattering (DPS) for jets widely separated in rapidity and for four-jet sample. In the case of four-jet production, we calculate cross section for both single-parton scattering (SPS) using the code ALPGEN as well as for DPS in LO collinear approach. The DPS contribution is calculated within the so-called factorized Ansatz and each step of DPS is calculated in the LO collinear approximation. We show that the relative (with respect to SPS dijets and to the BFKL Mueller–Navelet (MN) jets) contribution of DPS is growing at large rapidity distance between jets. The calculated differential cross sections as a function of rapidity distance between the most remote in rapidity jets are compared with recent results of LL and NLL BFKL calculations for the Mueller–Navelet jet production at \(\sqrt {s} = 7\) TeV. Our results for four-jet sample are compared with experimental data obtained recently by the CMS Collaboration and a rather good agreement is achieved. We propose to impose different cuts in order to enhance the relative DPS contribution. The relative DPS contribution increases when decreasing the lower cut on the jet transverse momenta as well as when a lower cut on the rapidity distance between the most remote jets is imposed.

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We report on our NLL BFKL studies of the Mueller–Navelet jets. We first perform a complete NLL BFKL analysis supplemented by a BLM renormalization scale fixing procedure, which is successfully compared with recent CMS data. Second, we argue for the need of a measurement of an asymmetric jet configuration in order to perform a valuable comparison with fixed order approaches. Third, we predict that the energy-momentum violation is rather tiny in the NLL BFKL approach, for an asymmetric jet configuration. Finally, we argue that the double parton scattering contribution is negligible in the kinematics of actual CMS measurements.

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The Mueller–Navelet di-jet production process represents an ultimate test field of pQCD in the high-energy limit. Several experimental analyses carried out so far are in a good agreement with theoretical predictions, based on collinear factorization and BFKL resummation of energy logarithms in the next-to-leading approximation, with the CMS experimental data at center-of-mass energy equal to 7 TeV. However, the question if the same data can be described also by fixed-order perturbative approaches has not yet been fully answered. We discuss how the use of partially asymmetric cuts in the transverse momenta of the detected jets allows to discriminate between BFKL-resummed and fixed-order predictions (the latter in the high-energy limit) in observables related with this process at the LHC.

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A summary of the jet energy calibration efforts of the ATLAS and CMS collaborations is presented. Both experiments have recorded data corresponding to an integrated luminosity of 20 \(\mathrm {fb}^{-1}\) of proton–proton collisions at a centre-of-mass energy of 8 TeV. Different procedures to handle the effects from pileup collisions are carried out. Data-driven estimations of jet energy scale and resolution are performed with balancing methods in dijet, photon+jet, \(Z\)+jet and multijet samples. Novel techniques are explored to measure the differences between jets originating from partons with different flavours. The resulting uncertainty on the jet energy scale is at the level of only a few percent.

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Different features of the jet production in \(pp\) collisions at \(\sqrt {s}=7\) TeV have been measured by the ATLAS experiment. Among them are: the dijet double-differential cross sections, upper limit of the scale for contact interaction, the flavor dijet decomposition for different light-, \(c\)-, and \(b\)-jet combinations, double-differential inclusive jet cross sections, and \(b\)-jet and light-jet shapes measured using top-quark pair events. In all cases, good agreement with the SM QCD expectations was found. The dijet analysis provided a lower limit for the compositeness scale of about 7 TeV.

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In this paper, I present the brand new results from the H1 and ZEUS collaborations on the combination of all previously published inclusive deep inelastic cross sections at HERA for neutral and charged current \(e^\pm p\) scattering for zero beam polarisation and the corresponding parton distributions functions, HERAPDF 2.0, at up to next-to-next-to-leading order (NNLO). The results also include a new precise determination at next-to-leading order (NLO) of the strong coupling constant \(\alpha _{\rm s}(M^2_Z)=0.1184\pm 0.0016\) (excluding scale uncertainties) based on a simultaneous fit to the combined inclusive cross section data and jet production data.

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Finding an accurate model of soft hadronic interactions is of great interest for the field of astroparticle physics. Most ground-based astroparticle experiments deal with air showers initiated by cosmic rays in Earth’s atmosphere, either as signal or as an important background. I discuss the importance of hadron interaction models for air shower experiments, and summarize recent tests of current models performed by the Pierre Auger Observatory, Telescope Array, and the IceCube Neutrino Observatory.

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We review our recent results for double-scattering mechanism in the exclusive \(AA \to AA \rho ^0\rho ^0\) reaction in ultrarelativistic ultraperipheral heavy-ion collisions. The cross section for single and double-\(\rho ^0\) production is calculated in the impact parameter space equivalent photon approximation. We compare the results of our calculation with the STAR and ALICE collaborations results on one \(\rho ^0(770)\) meson and four-charged-pion production.

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High-energy hadronic reactions with proton-to-neutron transitions (and vice versa) with small momentum transfer allow to study the properties of nearly on-shell pions, which cannot be accessed otherwise. We overview the recent results for such processes in deeply inelastic scattering, single- and double-leading-neutron production in \(pp\) collisions, including polarization effect. A special attention is paid to the absorption effects, which are found to be much stronger than what has been evaluated previously.

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In this paper, a brief description of three measurements sensitive to BFKL evolution effects is given: the measurement of angular correlation between forward and central jet, the measurement of Mueller–Navelet dijet angular decorrelations and the measurement of ratios of cross sections for production of jets at the CMS. The experimental results are presented as a function of the rapidity separation \(\Delta \eta \) between jets, and compared to the predictions of various Monte Carlo models and theoretical calculations.

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The interpretation of cosmic ray measurements at the highest energies is fundamentally linked with the understanding of hadronic interactions. The dependence of the air shower observables \(X_{\rm max}\) and \(N_\mu \) on certain features of hadronic interactions is discussed and the effect of some of the LHC measurements is demonstrated. The uncertainty due to the lack of accelerator data on meson interactions is stressed.

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After recalling briefly the BFKL fits to the HERA forward jet data, we describe different possibilities to probe the BFKL dynamics at hadronic colliders, namely Mueller–Navelet jet, and jet–gap–jet events. We also discuss briefly the jet veto measurement as performed by the ATLAS Collaboration at the LHC.

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We present a twist expansion of differential cross sections of the forward Drell–Yan process at the high energies. The expansion of all invariant form factors is performed assuming Golec-Biernat and Wüsthof (GBW) saturation model and the saturation scale plays the role of the hadronic scale of Operator Product Expansion (OPE). Some explicit predictions for LHC experiments are given. It is shown also how the Lam–Tung relation is broken at twist 4 what provides a sensitive probe for searching of higher twists.

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Three models for the \(|t|\)-dependence of the amplitudes in \(pp\) elastic scattering are reviewed with comparison of their similarities and differences.

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We report on the measurement of \(J/\psi \) production at very low transverse momentum (\(p_{\rm T} \lt 300\) MeV/\(c\)) in Pb–Pb collisions performed with the ALICE detector at the LHC. We find an excess in the yield of \(J/\psi \) with respect to expectations from hadronic production. Coherent photo-production of \(J/\psi \) is proposed as a plausible origin of this excess. We show the nuclear modification factor of very low-\(p_{\rm T}\) \(J/\psi \) as a function of centrality. Then, we measure the \(J/\psi \) coherent photo-production cross section in peripheral events assuming that it is the mechanism at the origin of the measured excess. It is worth noting that the observation of \(J/\psi \) coherent photo-production in Pb–Pb collisions at impact parameters smaller than twice the nuclear radius has never been observed so far and would open new theoretical challenges.

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One of the most surprising results of the first run of the Large Hadron Collider (LHC) are the similarities between events with the same multiplicity but coming from proton–proton (\(pp\)), proton–lead (\(p\)Pb) or lead–lead (PbPb) collisions at different energies. A consistent treatment of the various stages of a high energy hadronic interaction is possible and realized in the EPOS 3 event generator. Using this model, a possible origin of the v2 and v3 flow coefficient observed in \(p\)Pb and PbPb can be explained. In this paper, we will focus on the new treatment of the saturation scale in this model which is a key aspect to get proper initial conditions for the hydrodynamical calculation.