The large equivalent-photon fluxes accompanying Pb ion beams at the LHC initiate photon-photon and photo-nuclear interactions which dominate when the colliding nuclei have large impact parameter (ultra-peripheral collisions). These electromagnetically-induced processes are sensitive to the nuclear wave-function and in particular the nuclear modifications of the nucleon parton distribution...

We will report on new results concerning exclusive dilepton and diphoton production with the CMS-TOTEM Precision Proton Spectrometer (CT-PPS). For the first time, exclusive dileptons at high masses have been observed in the CMS detector while at least one or the two intact protons are measured in CT-PPS using about 10 fb-1 of data accumulated in 2016. These first results show a good...

We report the measurements of exclusive production of dihadrons, the Upsilon meson and WW pairs in proton-proton and ultra-peripherial proton-lead collisions at the LHC. The data are compared to results from other experiments and to theoretical predictions.

The cross-section for central exclusive production of J/psi and Psi(2S) mesons at 13 TeV is measured using the LHCb detector. Proton dissociative backgrounds are significant reduced compared to previous measurements through the use of forward shower counters, recently installed for Run 2. Plans for future measurements are also presented to exploit the new Run2 dataset.

The electromagnetic field of a fast moving lead ion at the LHC is an intense source of quasi-real photons. This makes it possible to study J/Psi exclusive photoproduction off protons in p-Pb collisions at the LHC. This process is sensitive to the gluon content of the target.

Using Run1 data, ALICE has measured the exclusive J/Psi photoproduction cross section for centre-of-mass energies of...

The intense photon fluxes of relativistic nuclei provide a possibility

to study photonuclear and two-photon interactions in ultra-peripheral collisions (UPC) where the nuclei do not overlap and no strong nuclear interactions occur.

Within the Vector-meson Dominance Model (VDM), the rho0 contribution prevails in the QCD photon structure function and the gamma+A -> rho0+A process in heavy-ion...

The TOTEM collaboration at the LHC has completed its analysis of the elastic, inelastic and total proton-proton cross-sections (via the optical theorem) at sqrt(s) = 2.74 TeV. The new measurement lies close in energy to the Tevatron's 1.8 TeV with its two slightly conflicting total cross-section results.

The presentation will put the new measurement in the context of completed, ongoing and...

The aim of the ATLAS Forward Proton (AFP) detector system is the measurement of protons scattered diffractively or electromagnetically at very small angles. The first arm of the system was installed last year and AFP took data in several commissioning and physics runs. The installation of the second arm is ongoing and will be completed in time for the 2017 data taking period. This will allow...

The photoproduction of isolated photons is measured using diffractive events

recorded by the ZEUS detector at HERA. Cross sections are evaluated in the

photon transverse-energy and pseudorapidity ranges $5 < E_T^{\gamma} < 15$ GeV

and $-0.7 < \eta^{\gamma} < 0.9$, inclusively and with a jet with

transverse-energy and pseudorapidity in the ranges $4 < E_T^{\rm jet} < 35$ GeV

and $-1.5 <...

Progress is reported with a phenomenological analysis in full view of chromodynamics of a plausible Bethe-Heitler-like approach to measurements of exclusive elastic and dissociative electroproduction cross sections for vector-meson (VM) “quarkonia” of different flavour, namely ?\rho(760), u ubar - d dbar, \phi(??1019) s sbar, J\psi?(3096) c cbar and \Upsilon(??9460) b bbar? . First results...

Measurements of open charm production are presented in diffractive deep inelastic scattering ($5< Q^2< 100$ GeV$^2$), based on 287 pb$^{−1}$ of H1 HERA-II data recorded at the center of mass energy sqrt(s)=319 GeV. The event topology is given by $ep\to eXY$ , where the system $X$, containing at least one $D^{∗}(2010)$ meson, is separated from a leading low-mass proton dissociative system Y by...

Ultra-Peripheral Pb-Pb collisions, in which the two nuclei pass close to each other but at an impact parameter larger than the sum of their radii, provide information about the initial state of nuclei. In particular, J/Psi production in such collisions proceeds by photon-gluon interactions, and is sensitive to the nuclear gluon distribution. The ALICE collaboration has published measurements...

We present a method to extract the photonuclear cross section for the coherent production of J/Psi off lead nuclei using peripheral and ultra-peripheral cross sections measured at the LHC. The method allows to extract the photonuclear cross section up to a centre-of-mass energy of around 500 GeV.(Corresponding to x-Bjorken of 4.5 10^-5.) Using the photonuclear cross section, and the impulse...

We investigate the energy dependence of the photo-production cross-section of vector mesons J/Psi and Upsilon on protons. In particular we are interested in the question whether the energy dependence has a description in terms of perturbative low x (i.e. BFKL) evolution or whether a successful description requires to invoke effects related to gluon saturation. To answer this question we study...

We have developed a model in which we treat photoproduction of charmonia via the color dipole approach taking into account the quantum fluctuations of the proton structure. These fluctuations are characterized by hot spots, randomly generated in the transverse plane, whose number grows with decreasing Bjorken-$x$. Our model successfully reproduces the $F_2(x,Q^2)$ data from HERA at the...

One of the striking results of the LHC has been the observation of collective behavior in high-multiplicity proton-proton and proton-nucleus collisions. These signals are similar to those that have been previously seen in collisions of heavy nuclei, and have been interpreted as a result of the hydrodynamic evolution of the produced QCD matter.

Initial state geometry is a necessary input to...

We present the first calculations for dijet production in diffractive deep-inelastic scattering (DIS) at next-to-next-to-leading order accuracy (NNLO). The calculations are based on the antenna subtraction formalism, where the hard coefficients are convoluted with available PDFs for diffractive scattering (DPDFs). Unfortunately, these DPDFs are currently available only in NLO precision.

We...

We will present two exclusive diffractive processes with NLO accuracy in the shockwave (CGC) formalism, which extends the linear BFKL picture to include high-energy saturation effects. We will detail the impact factors for the production of a forward dijet and for the production of a light neutral vector meson.

We study diffractive dijet production in lepton-nucleon scattering as a means to probe the phase space (Wigner) distribution of small-x gluons. We also discuss the experimental signature of the gluon orbital angular momentum.

A correct modelling of the underlying event in proton-proton collisions is important for the proper simulation of kinematic distributions of high-energy collisions. The ATLAS collaboration extended previous studies at 7 TeV with a leading track or jet or Z boson by a new study at 13 TeV, measuring the number and transverse-momentum sum of charged particles as a function of pseudorapidity and...

We present results on the measurement of the underlying event at 13 TeV using leading tracks, jets, and Drell-Yan processes. In addition measurements of forward-backward particle correlations and the rapidity gap fraction are presented. Finally results on charged particle multiplicity and transverse momenta distributions are shown.

We present recent results on Double Parton Scattering (DPS) studies using data collected during Run 1 and Run 2 of the LHC with the CMS experiment. Double parton scattering is investigated in several final states including vector bosons and multi-jets. Measurements of observables designed to highlight the DPS contribution are shown and compared to MC predictions from models based on multiple...

The CASTOR calorimeter at CMS measures the energy of particles emitted with pseudorapidity between -5.2 and -6.6. It has been operating since the startup of the LHC in 2009 and has taken data in pp, pPb, and PbPb collisions at various centre-of-mass energies during run 1 and run 2. In this presentation we give an overview of some important and unique results obtained with CASTOR, with emphasis...

We use spinor helicity formalism to calculate production of 3 partons of any polarization in DIS at small x. The target hadron or nucleus is treated as a classical color field from which the partons scatter. We then study the azimuthal angular correlations between the produced partons and show that it is a sensitive probe of gluon saturation at small x. We finally relate this process to Double...

We present an update of the first-ever study of 4-jet production in kt-factorization. We discuss how to supplement it with parton showers using the CASCADE Monte Carlo program and discuss the evidence for the need of contributions from Multi Parton Interactions to properly describe the data over the full phase space.

We propose to consider the production of a forward J/Psi and a backward jet at the LHC, similarly to Mueller Navelet jet production. We will present a feasibility study for our process and give predictions in the BFKL framework.

Beams of relativistic heavy ions accompanied by a large flux of equivalent photons, and photon-induced reactions are the dominant interaction mechanism in heavy-ion collisions when the colliding nuclei have transverse separation larger that the nuclear diameter. In these ultra-peripheral collisions (UPC) the photon can provide a clean probe of the partonic structure of the nucleus analogous...

Recently, a new family of observables consisting of azimuthal-angle generalised ratios was proposed in a kinematical setup that resembles the usual Mueller-Navelet jets but with an additional tagged jet in the central region of rapidity. Here, we calculate the, presumably, most relevant higher order corrections to the observables. The corrections appear to be mostly moderate giving us...

I am going to present predictions for spectra of very forward single inclusive jet production in proton-proton collisions obtained within High Energy Factorization.

The calculations are performed in HEF are compared to Pythia MC generator. The options available in Pythiia allow us to study importance of various effects like multiple interactions, hadronization.

We explicitly show that once...

We study high-energy jet production in the multi-Regge limit making use of the Monte Carlo event generator BFKLex which includes collinear improvements in the form of double-log contributions.

Imposing infrared boundary conditions transforms the complex momentum w-plane cut present into an infinite series of positive Regge poles. In addition, a cut on the negative w line remains. We find a...

A simple factorized form of high energy QCD amplitudes with gluon quantum numbers in the cross channels and negative signature is known to be broken in the next-to-next-to-leading logarithmic approximation (NNLLA). It is argued that the violation is caused by contributions of three-Reggeon cuts. The consequent need to change the scheme of derivation of the BFKL equation in the NNLLA is...

We discuss an application of formalism of Lipatov's effective action for the calculation of classical field of relativistic color charge, similarly to the done in CGC approach.

The equations of motion are solved in the LO and NLO approximation and the LO results are compared with the calculations performed in the CGC

framework. It is demonstrated that the CGC results for the classic field are...

The growth of the hadronic and nuclear scattering cross sections with energy is described by the linear BFKL

evolution equation. At very high energies, when the parton density becomes high, the hadronic cross section reaches the

unitarity limit, and the transition to high parton density is described by the non-linear BK and JIMWLK evolution

equations. These equations are currently the...

In the regime of low Bjorken x for DIS on a proton or nucleus target, one enters in the nonlinear regime of gluon saturation, where the gluons are better described as a strong coherent semi-classical field than as a collection of quasi on-shell partons. Hence, that regime lies outside the validity range of the collinear factorization, and is better described within the dipole factorization of...

Studies of correlated hadron production are an important source of information about the early stages of hadron formation, not yet understood from first principles. Although experimental high energy physics employs several semi–classical models of hadronization which describe the formation of jets with remarkable accuracy, correlation phenomena are more elusive. In this presentation, we will...

We address the general features of event-by-event fluctuations of the multiplicity of gluons produced in the scattering of a dilute hadron off a large nucleus at high energy in the fragmentation region of the dilute hadron. We relate these fluctuations to the stochasticity of the number of quanta contained in the hadron at the time of the interaction. For simplicity, we address the ideal case...

The explanation of the ridge observed in pp and pA collisions at the Large Hadron Collider constitutes one of open questions in our understanding of high-energy hadronic collisions. Apart from final-state hydrodynamic models, correlations between gluons in the wave function of the incoming hadrons, computed in the framework of the Color Glass Condensate, offer an alternative rationale to...

The inclusive production of a pair of hadrons (a “dihadron” system), having high transverse momenta and separated by a large interval of rapidity, is investigated. This process has much in common with the widely discussed Mueller-Navelet jet production and can be also used to access the BFKL dynamics at proton colliders. The first full NLA BFKL analysis for cross sections and azimuthal angle...

The forward Drell-Yan process is analysed assuming dominance of the

quark-gluon partonic channel in the asymmetric kinematic configuration

in which x of the gluon is very small. The small x logarithms in the

gluon evolution are resummend using the BFKL formalism. Effects of

the resummation are determined in all the Drell-Yan structure functions.

In particular the impact of the gluon transverse...

We study single inclusive forward hadron production in the color glass condensate formalism. The first numerical studies of this process at next-to-leading-order accuracy have led to negative cross sections at large transverse momenta. We identify the origin of this problem as an oversubtraction of the rapidity divergence into the Balitsky-Kovchegov evolution equation for the target. We then...

I discuss how the rapidity evolution of gluon transverse momentum dependent distribution

changes from nonlinear evolution at small $x\ll 1$ to linear evolution at moderate $x\sim 1$

The small-$x$ behavior of transverse-momentum-dependent (TMD) gluon distributions can be studied in the Color Glass Condensate (CGC) formalism. The cross section for forward dijet production in proton-nucleus collisions involves eight different TMD distributions, including all TMDs that have been identified in other processes so far. For each of these distributions we determine their operator...

We present results from a parton branching solution of the DGLAP

equation including color coherence (angular ordering) using LO and

NLO splitting functions. We show the difference to the standard

DGLAP evolution and present first results of a LO and NLO fit

including color coherence to precision HERA data.

We also show the resulting transverse momentum distributions.

We use transverse momentum dependent splitting functions to construct a low-x

evolution equation for gluons that takes into account the effect of non-diagonal

quark-to-gluon splittings. In order to write down a consistent equation we

resum virtual corrections coming from the gluon channel and demonstrate that

this implies a suitable regularization of the Pgq singularity, corresponding to

a...

We report the measurements of diffractive processes in proton-proton collisions at 7 and 8 TeV. Diffractive events are selected by requring the presence of rapidity gaps in the CMS detector or scattered protons reconstructed in the Roman Pots of the TOTEM experiment. The data are compared to results from other experiments and to theoretical predictions.

Parton Reggeization Approach (PRA) is a generalized scheme of kT-factorization which uses the formalism of Reggeized quarks and gluons to define gauge-invariant hard-scattering matrix elements with off-shell partons in the initial state (See Ref. [1] for more detailed discussion). The calculations in PRA are performed in the framework of Lipatov's gauge invariant effective theory for...

We review the BFKL approach for the high enegy scattering in QCD based on the gluon reggeization. The effective action and the corresponding Euler-Lagrange equations for the reggeized gluon interactions are formulated in a gauge-invariant way locally in the particle rapidities. The BFKL Pomeron is the simplest composite state of reggeized gluons. In N=4 SUSY it is dual to the reggeized...

On testing notifications - Episode 2

Inclusive four-jet events produced in proton--proton collisions at a center-of-mass energy of 7 TeV have been analyzed for the presence of hard double parton scattering collected with the ATLAS detector. The contribution of hard double parton scattering to the production of four-jet events has been extracted using an artificial neural network. The assumption was made that hard double parton...