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Krzysztof Kutak

Publications and source records attributed to Krzysztof Kutak.

At least 55 records · Page 3Linked to original sources
arXiv2017

Single inclusive jet production and the nuclear modification ratio at very forward rapidity in proton-lead collisions with $\sqrt{s_{NN}}$ = 5.02 TeV

We present calculations of single inclusive jet transverse momentum and energy spectra at forward rapidity ($5.2\!<\!y\!<\!6.6$) in proton-lead collisions with $\sqrt{s_{NN}}$ = 5.02 TeV. The predictions are obtained with the KaTie Monte Carlo event generator, which allows to calculate interactions within the High Energy Factorisation framework. The tree-level matrix element results are subsequently interfaced with the CASCADE Monte Carlo event generator to account for hadronisation. The effects of the saturation of the gluon density, leading to suppression of the cross section, are investigated.

hep-ph↗
arXiv2017

Calculations with off-shell matrix elements, TMD parton densities and TMD parton showers

A new calculation using off-shell matrix elements with TMD parton densities supplemented with a newly developed initial state TMD parton shower is described. The calculation is based on the KaTie package for an automated calculation of the partonic process in high-energy factorization, making use of TMD parton densities implemented in TMDlib. The partonic events are stored in an LHE file, similar to the conventional LHE files, but now containing the transverse momenta of the initial partons. The LHE files are read in by the CASCADE package for the full TMD parton shower, final state shower and hadronization from PYTHIA where events in HEPMC format are produced. We have determined a full set of TMD parton densities and developed an initial state TMD parton shower, including all flavors following the TMD distribution. As an example of application we have calculated the azimuthal de-correlation of high pt dijets as measured at the LHC and found very good agreement with the measurement when including initial state TMD parton showers together with conventional final state parton showers and hadronization.

hep-ph↗
arXiv2017

Towards tomography of quark-gluon plasma using double inclusive forward-central jets in Pb-Pb collision

We propose a new framework, merging High Energy Factorization with final-state jet quenching effects due to interactions in a quark-gluon plasma, to compute di-jet rates at mid- and forward rapidity. It allows to consistently study the interplay of initial-state effects with medium interactions, opening the possibility for understanding the dynamics of hard probes in heavy-ion collisions and the QGP evolution in rapidity.

hep-ph↗
arXiv2017

The rapidity dependence of the average transverse momentum in p+p and p+Pb collisions - revisited

We revisit the rapidity dependence of the average transverse momentum $\left\langle p_{T}\right\rangle$ in a $pp$ and $pA$ collision, using the high energy factorization (HEF). We update previous predictions for the $\left\langle p_{T}\right\rangle$ both in central and forward rapidity region using parton densities following from extended BK and BFKL evolution equations to account for corrections of higher orders as well as one obtained by Sudakov resummation. Furthermore, we demonstrate that in the mid rapidity region the saturation based formalisms predict increase of the transversal momentum while in the forward rapidity region the $\left\langle p_{T}(y)\right\rangle$ decreases.

hep-ph↗
arXiv2017

Production of four-jets in single- and double-parton scattering within high-energy factorization

We report on a first study of 4-jet production in a high energy factorization (HEF) framework \cite{Kutak:2016mik,Kutak:2016ukc}. We include and discuss contributions from both single-parton scattering (SPS) and double-parton scattering (DPS) and compare to the measured data. The DPS HEF result is considerably smaller than the one obtained with collinear factorization. The mechanism leading to this difference is of kinematical nature. In contrast to the collinear approach, the HEF approach nicely describes the distribution of the $ΔS$ variable, which involves all four jets and their angular correlations.

hep-ph↗
arXiv2017

Single inclusive jet transverse momentum and energy spectra at very forward rapidity in proton-proton collisions with $\sqrt{s} = 7$ and 13 TeV

We present predictions of single inclusive jet transverse momentum, energy, and Feynman-$x$ spectra at forward rapidity ($5.2 < y < 6.6$) in proton-proton collisions with $\sqrt{s} = 7$ and 13 TeV. Calculations based on high-energy factorization and $k_T$-dependent parton densities are compared to simulations using the \pythia\ event generator. Effects from parton density evolution, parton shower dynamics, multi-parton interactions, and saturation of parton densities are investigated.

hep-ph↗
arXiv2017

QCD amplitudes with 2 initial spacelike legs via generalised BCFW recursion

We complete the generalisation of the BCFW recursion relation to the off-shell case, allowing for the computation of tree level scattering amplitudes for full High Energy Factorisation (HEF), i.e. with both incoming partons having a non-vanishing transverse momentum. We provide explicit results for color-ordered amplitudes with two off-shell legs in massless QCD up to 4 point, continuing the program begun in two previous papers. For the 4-fermion amplitudes, which are not BCFW-recursible, we perform a diagrammatic computation, so as to offer a complete set of expressions. We explicitly show and discuss some plots of the squared $2 \rightarrow 2$ matrix elements as functions of the differences in rapidity and azimuthal angle of the final state particles.

hep-ph↗
arXiv2016

Single and double inclusive forward jet production at the LHC at $\sqrt{s}$ = 7 and 13 TeV

We provide a description of the transverse momentum spectrum of single inclusive forward jets produced at the LHC, at the center-of-mass energies of 7 and 13 TeV, using the high energy factorization (HEF) framework. We subsequently study double inclusive forward jet production and, in particular, we calculate contributions to azimuthal angle distributions coming from double parton scattering. We also compare our results for double inclusive jet production to those obtained with the Pythia Monte Carlo generator. This comparison confirms that the HEF resummation acts like an initial state parton shower. It also points towards the need to include final state radiation effects in the HEF formalism.

hep-ph↗
arXiv2016

Search for optimal conditions for exploring double-parton scattering in four-jet production: $k_t$-factorization approach

In the present paper we discuss how to maximize the double-parton scattering (DPS) contribution in four-jet production by selecting kinematical cuts. Here both single-parton and double-parton scattering effects are calculated in the $k_T$-factorization approach, following our recent developments of relevant methods and tools. Several differential distributions are shown and discussed in the context of future searches for DPS effects, such as rapidity of jets, rapidity distance, and azimuthal correlations between jets. The dependences of the relative DPS amount is studied as function of those observables. The regions with an enhanced DPS contribution are identified. Future experimental explorations could extract more precise values of $σ_{eff}$ and its potential dependence on kinematical variables.

hep-ph↗
arXiv2016

Four-jet production in single- and double-parton scattering within high-energy factorization

We perform a first study of 4-jet production in a complete high-energy factorization (HEF) framework. We include and discuss contributions from both single-parton scattering (SPS) and double-parton scattering (DPS). The calculations are performed for kinematical situations relevant for two experimental measurements (ATLAS and CMS) at the LHC. We compare our results to those reported by the ATLAS and CMS collaborations for different sets of kinematical cuts. The results of the HEF approach are compared with their counterparts for collinear factorization. For symmetric cuts the DPS HEF result is considerably smaller than the one obtained with collinear factorization. The mechanism leading to this difference is of kinematical nature. We conclude that an analysis of inclusive 4-jet production with asymmetric $p_T$-cuts below 50 GeV would be useful to enhance the DPS contribution relative to the SPS contribution. In contrast to the collinear approach, the HEF approach nicely describes the distribution of the $ΔS$ variable, which involves all four jets and their angular correlations.

hep-ph↗
arXiv2015

Transverse-momentum-dependent quark splitting functions in $k_T$-factorization: real contributions

We calculate transverse momentum dependent quark splitting kernels $P_{gq}$ and $P_{qq}$ within $k_T$-factorization, completing earlier results which concentrated on gluon splitting functions $P_{gg}$ and $P_{qg}$. The complete set of splitting kernels is an essential requirement for the formulation of a complete set of evolution equations for transverse momentum dependent parton distribution functions and the development of corresponding parton shower algorithms.

hep-ph↗
arXiv2015

Hard scale dependent gluon density, saturation and forward-forward dijet production at the LHC

We propose a method to introduce Sudakov effects to the unintegrated gluon density promoting it to be hard scale dependent. The advantage of the approach is that it guarantees that the gluon density is positive definite and that the Sudakov effects cancel on integrated level. As a case study we apply the method to calculate angular correlations and $R_{pA}$ ratio for p+p vs. p+Pb collision in the production of forward-forward dijets.

hep-ph↗
arXiv2015

Kinematical constraint effects in the evolution equations based on angular ordering

We study effects of imposing various forms of the kinematical constraints on the full form of the CCFM equation and its non-linear extension. We find that imposing the constraint in its complete form modifies significantly way the shape of gluon density as compared to forms of the constraint used in the numerical calculations and phenomenological applications. In particular the resulting gluon density is suppressed for large values of hard scale related parameter and kT of gluon. This result might be important in description studies of jet correlations at Large Hadron Collider within CCFM approach.

hep-ph↗
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.

hep-ph↗
arXiv2014

Non-linear evolution of unintegrated gluon density at large values of coupling constant

We propose an evolution equation for unintegrated gluon densities that is valid for large values of the QCD coupling constant $\barα _s$. Our approach is based on the linear resummation model introduced by Staśto. We generalize the model including a non-linear term in the diffusive regime. The validity of the diffusive evolution at strong coupling is supported by the AdS/CFT consideration, as well as perturbative arguments. We solve the evolution equation numerically and extract the saturation scale, which we compare with the weak coupling counterpart.

hep-ph↗