arXiv subjects

Piotr Kotko

Publications and source records attributed to Piotr Kotko.

35 records · Page 2Linked to original sources

arXiv2019

Broadening and saturation effects in dijet azimuthal correlations in p-p and p-Pb collisions at $\mathbf{\sqrt{s_{NN}}} = $ 5.02 TeV

We demonstrate that the recent forward-forward dijet correlation data measured by the ATLAS collaboration for proton-proton and proton-lead collisions are consistent with the broadening effects due to both the gluon saturation and the resummation of large logarithms of the hard scale (the so-called Sudakov logarithms). We find that both effects are necessary to describe the experimental results.

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arXiv2019

BFKL Pomeron loop contribution in diffractive photoproduction and inclusive hadroproduction of $J/ψ$ and $Υ$

We analyze contributions to the heavy vector meson production with large transverse momentum in proton--proton and diffractive photon--proton scattering driven by an exchange of two Balitsky--Fadin--Kuraev--Lipatov Pomerons in the squared amplitudes. The Pomerons couple to a single parton and form a Pomeron loop closed by the vector meson impact factors. For the photon--proton case the diffractive cut of the Pomeron loop contributes, and for the inclusive hadroproduction one finds the loop with two cut Pomerons. We compute both of these Pomeron loop contributions and study in detail their properties. The results are then used to calculate the cross sections for diffractive $J/ψ$ photoproduction with large transverse momentum at HERA and the correlated two Pomeron contribution for inclusive $J/ψ$ and $Υ$ production cross sections at the LHC. Within a unified approach a good description of the photoproduction data is found, but correlated two Pomeron mechanism gives only a small contribution to hadroproduction of the vector mesons at the LHC.

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arXiv2019

Studying minijets and MPI with rapidity correlations

We propose and carry a detailed study of an observable sensitive to different mechanisms of minijet production. The class of observables measures how the transverse momenta of hadrons produced in association with various trigger objects are balanced as a function of rapidity. It is shown that the observables are sensitive to the model parameters relevant to the minijet production mechanisms: low-$p_{\rm T}$ cut-off regulating jet cross-section, transverse distribution of partons in protons, and parton distribution functions. We perform our test at different charge-particle multiplicities and collision energies. The MC models, which describe many features of the LHC data, are found to predict quite different results demonstrating high discriminating power of the proposed observables. We also review mechanisms and components of \sc{Herwig}, \sc{Pythia}, and \sc{Sherpa} Monte Carlo models relevant to the minijet production.

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arXiv2019

Interplay of the CGC and TMD frameworks to all orders in kinematic twist

A framework for an improved TMD (iTMD) factorization scheme at small $x$, involving off-shell perturbative subamplitudes, was recently developed as an interpolation between the TMD $k_t \ll Q$ regime and the BFKL $k_t \sim Q$ regime. In this article, we study the relation between CGC and iTMD amplitudes. We first show how the dipole-size expansion of CGC amplitudes resembles the twist expansion of a TMD amplitude. Then, by isolating kinematic twists, we prove that iTMD amplitudes are obtained with infinite kinematic twist accuracy by simply getting rid of all genuine twist contributions in a CGC amplitude. Finally we compare the amplitudes obtained via a proper kinematic twist expansion to those obtained via a more standard dilute expansion to show the relation between the iTMD framework and the dilute low $x$ framework.

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arXiv2018

PHOTON-2017 conference proceedings

This document collects the proceedings of the PHOTON 2017 conference ("International Conference on the Structure and the Interactions of the Photon", including the 22th "International Workshop on Photon-Photon Collisions", and the "International Workshop on High Energy Photon Colliders") held at CERN (Geneva) in May 2017. The latest experimental and theoretical developments on the topics of the PHOTON conference series are covered: (i) $γ\,γ$ processes in e$^+$e$^-$, proton-proton (pp) and nucleus-nucleus (AA) collisions at current and future colliders, (ii) $γ$-hadron interactions in e$^\pm$p, pp, and AA collisions, (iii) final-state photon production (including Standard Model studies and searches beyond it) in pp and AA collisions, and (iv) high-energy $γ$-ray astrophysics. These proceedings are dedicated to the memory of Maria Krawczyk.

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arXiv2016

Off-shell amplitudes as boundary integrals of analytically continued Wilson line slope

One of the methods to calculate tree-level multi-gluon scattering amplitudes is to use the Berends-Giele recursion relation involving off-shell currents or off-shell amplitudes, if working in the light cone gauge. As shown in recent works using the light-front perturbation theory, solutions to these recursions naturally collapse into gauge invariant and gauge-dependent components, at least for some helicity configurations. In this work, we show that such structure is helicity independent and emerges from analytic properties of matrix elements of Wilson line operators, where the slope of the straight gauge path is shifted in a certain complex direction. This is similar to the procedure leading to the Britto-Cachazo-Feng-Witten (BCFW) recursion, however we apply a complex shift to the Wilson line slope instead of the external momenta. While in the original BCFW procedure the boundary integrals over the complex shift vanish for certain deformations, here they are non-zero and are equal to the off-shell amplitudes. The main result can thus be summarized as follows: we derive a decomposition of a helicity-fixed off-shell current into gauge invariant component given by a matrix element of a straight Wilson line plus a reminder given by a sum of products of gauge invariant and gauge dependent quantities. We give several examples realizing this relation, including the five-point next-to-MHV helicity configuration.

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arXiv2015

Unintegrated gluon distributions for forward jets at LHC

We test several BFKL-like evolution equations for unintegrated gluon distributions against forward-central dijet production at LHC. Our study is based on fitting the evolution scenarios to the LHC data using the high energy factorization approach. Thus, as a by-product, we obtain a set of LHC-motivated unintegrated gluon distributions ready to use. We utilize this application by calculating azimuthal decorrelations for forward-central dijet production and compare with existing data.

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arXiv2014

Three jet production and gluon saturation effects in p-p and p-Pb collisions within high-energy factorization

We analyze three jet production in the central-forward and forward rapidity regions in proton-proton and proton-lead collisions at LHC energies. Our calculation relies on high-energy factorization with a single off-shell gluon obeying small x evolution equation which includes saturation. The calculations are made using two independent Monte Carlo codes implementing tree-level gauge invariant off-shell matrix elements. We calculate differential cross sections for azimuthal decorrelations and unbalanced jet transverse momenta and discuss them in the context of differences in the evolution of the unintegrated gluon densities.

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arXiv2014

Wilson lines and gauge invariant off-shell amplitudes

We study matrix elements of Fourier-transformed straight infinite Wilson lines as a way to calculate gauge invariant tree-level amplitudes with off-shell gluons. The off-shell gluons are assigned "polarization vectors" which (in the Feynman gauge) are transverse to their off-shell momenta and define the direction of the corresponding Wilson line operators. The infinite Wilson lines are first regularized to prove the correctness of the method. We have implemented the method in a computer FORM program that can calculate gluonic matrix elements of Wilson line operators automatically. In addition we formulate the Feynman rules that are convenient in certain applications, e.g. proving the Ward identities. Using both the program and the Feynman rules we calculate a few examples, in particular the matrix elements corresponding to gauge invariant $g^{*}g^{*}g^{*}g$ and $g^{*}g^{*}g^{*}g^{*}g$ processes. An immediate application of the approach is in the high energy scattering, as in a special kinematic setup our results reduce to the form directly related to Lipatov's vertices. Thus the results we present can be directly transformed into Lipatov's vertices, in particular into $RRRP$ and $RRRRP$ vertices with arbitrary "orientation" of reggeized gluons. Since the formulation itself is not restricted to high-energy scattering, we also apply the method to a decomposition of an ordinary on-shell amplitude into a set of gauge invariant objects.

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arXiv2013

Off-shell helicity amplitudes in high-energy factorization

In the Catani-Ciafaloni-Hautmann high-energy factorization approach a cross section is expressed as a convolution of unintegrated gluon densities and a gauge-invariant hard process, in which two incoming gluons are off-shell with momenta satisfying certain high-energy kinematics. We present two methods of evaluating the tree-level hard process with multiple final states. The first one assumes that only one of the gluons is off-shell and relies on the Slavnov-Taylor identities. Such asymmetric configuration of incoming gluons is phenomenologically important in small x probing by forward processes. The second method deals also with two off-shell gluons and is based on the analytic continuation of the off-shell gluons momenta to the complex space. The methods were implemented into Monte Carlo computer programs and used in phenomenological applications. The results of both methods are straightforwardly related to Lipatov's effective vertices in quasi-multi-regge kinematics.

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arXiv2012

Multi-gluon helicity amplitudes with one off-shell leg within high energy factorization

Basing on the Slavnov-Taylor identities, we derive a new prescription to obtain gauge invariant tree-level scattering amplitudes for the process g*g->Ng within high energy factorization. Using the helicity method, we check the formalism up to several final state gluons, and we present analytical formulas for the the helicity amplitudes for N=2. We also compare the method with Lipatov's effective action approach.

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arXiv2012

General Mass Scheme for Jet Production in DIS

We propose a method for calculating DIS jet production cross sections in QCD at NLO accuracy with consistent treatment of heavy quarks. The scheme relies on the dipole subtraction method for jets, which we extend to all possible initial state splittings with heavy partons, so that the Aivazis-Collins-Olness-Tung massive collinear factorization scheme (ACOT) can be applied. As a first check of the formalism we recover the ACOT result for the heavy quark structure function using a dedicated Monte Carlo program.

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arXiv2012

Fully massive Scheme for Jet Production in DIS

We present a consistent treatment of heavy quarks for jet production in DIS at NLO accuracy. The method is based on the ACOT massive factorization scheme and dipole subtraction method for jets. The last had to be however extended in order to take into account initial state splittings with heavy quarks. We constructed relevant kinematics and dipole splitting functions together with their integrals. We partially implemented the method in a MC program and checked against the known inclusive result for charm structure function.

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arXiv2010

Low-energy amplitudes in the non-local chiral quark model

We apply chiral quark model with momentum dependent quark mass to two kinds of non-perturbative objects. These are: photon Distribution Amplitudes which we calculate up to twist-4 in tensor, vector and axial channels and pion-photon Transition Distribution Amplitudes together with related form factors. Where possible we compare our results with experimental data.

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arXiv2009

Photon Distribution Amplitudes in nonlocal chiral quark model

Photon distribution amplitudes up to twist four are calculated within the nonlocal chiral quark model with a simple pole ansatz for momentum dependence of the constituent quark mass. Calculations are performed using modified electromagnetic vector current in order to satisfy Ward identities. Quark condensate and magnetic susceptibility of the QCD vacuum entering definitions of the distribution amplitudes are computed and compared with existing phenomenological estimates. Both real and off-shell photons are considered and relevant form factors are calculated. Our results are analytical up to the numerical solution of certain algebraic equation.

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arXiv2009

Soft Matrix Elements in Non-local Chiral Quark Model

Using non-local chiral quark model and currents satisfying Ward-Takahashi identities we analyze Distribution Amplitudes (DA) of photon and pion-to-photon Transition Distribution Amplitudes (TDA) in the low energy regime. Photon DA's are calculated analytically up to twist-4 and reveal several interesting features of photon structure. TDA's calculated in the present model satisfy polynomiality condition. Normalization of vector TDA is fixed by the axial anomaly. We also compute relevant form factors and compare them with existing data. Axial form factor turns out to be much lower then the vector one, what indeed is seen in the experimental data.

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arXiv2009

Pion-to-photon transition distribution amplitudes in the non-local chiral quark model

We apply the non-local chiral quark model to study vector and axial pion-to-photon transition amplitudes that are needed as a nonperturbative input to estimate the cross section of pion annihilation into the real and virtual photon. We use a simple form of the non-locality that allows to perform all calculations in the Minkowski space and guaranties polynomiality of the TDA's. We note only residual dependence on the precise form of the cut-off function, however vector TDA that is symmetric in skewedness parameter in the local quark model is no longer symmetric in the non-local case. We calculate also the transition form-factors and compare them with existing experimental parametrizations.

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