arXiv subjects

Antoni Szczurek

Publications and source records attributed to Antoni Szczurek.

At least 127 records · Page 7Linked to original sources

arXiv2018

$J/ψ$-meson production within improved color evaporation model with the $k_{T}$-factorization approach for $c\bar{c}$ production

We use a new approach to color evaporation model (CEM) for quarkonium production. The production of $c\bar c$ pairs is performed within $k_T$-factorization approach using different unintegrated gluon distribution functions (UGDF) from the literature. We include all recent improvements to color evaporation model. We cannot describe simultaneously mid and forward rapidity data measured at the LHC when using the KMR UGDF with the same normalization parameter. Furthermore we get somewhat too hard distribution in $J/ψ$ transverse momentum. Correcting the standard KMR distributions for saturation effects at small values of $x$ improves $J/ψ$ rapidity distributions, while taking correction for emissions hidden in the KMR UGDF in the evaluation of $x$ values improves a bit $J/ψ$ transverse momentum distributions. The modifications improve also description of the LHCb $D$-meson data.

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arXiv2018

Production of $p\bar{p}$ pairs in UPC at the LHC

We discuss production of $p\bar{p}$ pairs in two-photon interactions in heavy-ion collisions. We present predictions for the ultraperipheral, ultrarelativistic, heavy-ion collisions (UPC) $^{208}\!Pb \, ^{208}\!Pb \to$ $^{208}\!Pb \, ^{208}\!Pb \,p \bar{p}$. The parameters of vertex form factors are adjusted to the Belle data for the $γγ\to p \bar{p}$ reaction. To described the Belle data we include the proton-exchange, the $f_2(1270)$ and $f_2(1950)$ $s$-channel exchanges, as well as the hand-bag mechanism. Then, the total cross section and several differential distributions for experimental cuts corresponding to the LHC experiments are presented. The distribution in $\mathrm{y}_{diff}$, the rapidity distance between the proton and antiproton, is particularly interesting. We find the total cross sections: 100 $μ$b for the ALICE cuts, 160 $μ$b for the ATLAS cuts, 500 $μ$b for the CMS cuts, and 104 $μ$b taking into account the LHCb cuts. This opens a possibility to study the $γγ\to p \bar{p}$ process in UPC at the LHC.

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arXiv2018

Recent theoretical results for electromagnetically induced ultraperipheral reactions of heavy ions

We briefly review our works on ultraperipheral heavy ion collisions. We discuss both $γγ$ and rescattering of hadronic photon fluctuation induced by one nucleus in the collision partner. Production of one and two leptonic and pionic and $p \bar p$ pairs is discussed as an example of photon-photon processes. The production of single vector mesons ($ρ^0$ or $J/ψ$) is an example of the second category. The double-scattering mechanisms of two $ρ^0$ meson production is discussed in addition.

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arXiv2018

Central exclusive production of $K^{+}K^{-}$ pairs in proton-proton collisions

We discuss central exclusive diffractive production of light mesons in the reactions $pp \to ppπ^{+}π^{-}$ and $pp \to ppK^{+}K^{-}$. The calculation is based on a tensor-pomeron approach. We include a purely diffractive dipion continuum, and the scalar $f_{0}(980)$, $f_{0}(1500)$, $f_{0}(1710)$ and tensor $f_{2}(1270)$, $f'_{2}(1525)$ resonances decaying into pseudoscalar meson pairs. We include also photoproduction mechanisms for the nonresonant (Drell-Söding) and the $ϕ(1020)$ resonance contributions. The theoretical results are compared with existing CDF experimental data and predictions for being carried out LHC experiments are presented. The distributions in dimeson invariant mass and in a special "glueball filter variable" including the interference effects of resonance and dimeson continuum are presented.

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arXiv2018

From $D_{s}^{\pm}$ production asymmetry at the LHC to prompt $ν_τ$ at IceCube

The description of the heavy meson production at large energies and forward rapidities at the LHC is fundamental to derive realistic predictions of the prompt atmospheric neutrino flux at the IceCube Observatory. In particular, the prompt tau neutrino flux is determined by the decay of $D_s$ mesons produced in cosmic ray - air interactions at high energies and large values of the Feynman - $x_F$ variable. Recent data from the LHCb Collaboration indicate a production asymmetry for $D_s^+$ and $D_s^-$ mesons, which cannot be explained in terms of the standard modelling of the hadronization process. In this paper we demonstrate that this asymmetry can be described assuming an asymmetric strange sea ($s(x) \ne \bar s(x)$) in the proton wave function and taking into account of the charm and strange fragmentation into $D_s$ mesons. Moreover, we show that the strange quark fragmentation contribution is dominant at large - $x_F$ ($\ge 0.3$). The prompt $ν_τ$ flux is calculated and the enhancement associated to the strange quark fragmentation contribution, disregarded in previous calculations, is estimated.

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arXiv2018

Dilepton Radiation in Heavy-Ion Collisions at Small Transverse Momentum

We study the invariant-mass distributions of dileptons produced in ultrarelativistic heavy-ion collisions at very low pair transverse momenta, $P_T\leq 0.15$ GeV. Specifically, we investigate the interplay of thermal radiation with initial photon annihilation processes, $γγ\to l^+ l^-$, triggered by the coherent electromagnetic fields of the incoming nuclei. For the thermal radiation, we employ the emission from the QGP and hadronic phases with in-medium vector spectral functions which describes the inclusive excess radiation observed over a wide range of collision energies. For the coherent photon fusion processes, whose spectrum is much softer than for thermal radiation, we employ initial fluxes from the Fourier transform of charge distributions of the colliding nuclei in the equivalent-photon approximation. We first verify that the combination of photon fusion, thermal radiation and final-state hadron decays gives a fair description of the low-$P_T$ dilepton mass spectra as recently measured by the STAR collaboration in $\sqrt{s_{NN}}$=200 GeV Au+Au collisions for different centrality classes, including experimental acceptance cuts. The coherent contribution dominates in peripheral collisions, while thermal radiation shows a markedly stronger increase with centrality. We perform similar calculations at lower collision energies ($\sqrt{s_{NN}}$=17.3 GeV) and compare to the acceptance-corrected dimuon excess spectra measured by the NA60 experiment at the CERN SPS; here, the contribution from photoproduction is subleading. We also provide predictions for the ALICE experiment at the LHC; the pertinent excitation function from SPS to LHC energies reveals a nontrivial interplay of photoproduction and thermal radiation.

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arXiv2018

Exclusive and semiexclusive production of $μ^+ μ^-$ pairs with $Δ$ isobars and other resonances in the final state and the size of absorption effects

We include $p p \to p Δ^{+} μ^{+} μ^{-}$ and $p p \to Δ^{+} Δ^{+} μ^{+} μ^{-}$ processes in addition to the standard $p p \to p p μ^{+} μ^{-}$ process both in equivalent-photon approximation (EPA) and in exact $2 \to 4$ calculations. For comparison we calculate also the continuum proton dissociation in a recently developed $k_{t}$-factorization approach to $γγ$-involved processes with parametrizations of $F_{2}$ structure function known from the literature. The calculated cross section including all the processes is considerably larger than the one measured recently by the ATLAS collaboration. We calculate absorption effects for $p p \to p p μ^{+} μ^{-}$ process in the momentum space. The final cross section with absorption effects is by 10\% larger than the one measured by the ATLAS collaboration which is difficult to explain. Several differential distributions with the ATLAS experimental cuts are presented. It is shown that the processes with electromagnetic $p \to Δ(1232)$ and $p \to N(1440)$ transitions, that have similar characteristics as the $p p \to p p μ^+ μ^-$ process, increase the cross section for $μ^+ μ^-$ production and thus can affect its theoretical interpretation when the leading baryons are not detected as is the case for the CMS and ATLAS measurements. The mechanism of dissociation into hadronic continuum is not under full control as the corresponding absorption effects are not fully understood. We present first predictions for future ATLAS experiment with the ALFA sub-detectors and discuss observables relevant for this measurement.

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arXiv2018

Towards a complete study of central exclusive production of $K^{+}K^{-}$ pairs in proton-proton collisions within the tensor Pomeron approach

We present a study of the central exclusive production of the $K^{+} K^{-}$ pairs in proton-proton collisions at high energies. We consider diffractive mechanisms including the $K^{+} K^{-}$ continuum, the dominant scalar $f_{0}(980)$, $f_{0}(1500)$, $f_{0}(1710)$ and tensor $f_{2}(1270)$, $f'_{2}(1525)$ resonances decaying into the $K^{+} K^{-}$ pairs. We include also photoproduction mechanisms for the non-resonant (Drell-Söding) and the $ϕ(1020)$ resonance contributions. The theoretical results are calculated within the tensor-pomeron approach including both pomeron and reggeon exchanges. Predictions for planned or current experiments at RHIC and LHC are presented. We discuss the influence of the experimental cuts on the integrated cross section and on various differential distributions for outgoing particles. The distributions in two-kaon invariant mass, in a special `glueball filter variable', as well as examples of angular distributions in the $K^{+}K^{-}$ rest frame are presented. We compare the $ϕ(1020)$ and continuum photoproduction contributions to the $f_{0}(980)$ and continuum diffractive contributions and discuss whether the $ϕ(1020)$ resonance could be extracted experimentally. For the determination of some model parameters we also include a discussion of $K$-nucleon scattering, in particular total cross sections, and of $ϕ(1020)$ photoproduction.

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arXiv2018

Central exclusive diffractive production of $p \bar{p}$ pairs in proton-proton collisions at high energies

We consider the central exclusive production of the $p\bar{p}$ in the continuum and via resonances in proton-proton collisions at high energies. We discuss the diffractive mechanism calculated within the tensor-pomeron approach including pomeron, odderon, and reggeon exchanges. The theoretical results are discussed in the context of existing WA102 and ISR experimental data and predictions for planned or current experiments at the RHIC and the LHC are presented. The distribution in ${\rm y}_{diff}$, the rapidity distance between proton and antiproton, is particularly interesting. We find a dip at ${\rm y}_{diff} = 0$ for the $p \bar{p}$ production, in contrast to the $π^{+}π^{-}$ and $K^{+}K^{-}$ production. We predict also the $p \bar{p}$ invariant mass distribution to be less steep than for the pairs of pseudoscalar mesons. We argue that these specific differences for the $p \bar{p}$ production with respect to the pseudoscalar meson pair production can be attributed to the proper treatment of the spin of produced particles. We discuss asymmetries that are due to the interference of $C=+1$ and $C=-1$ amplitudes of $p \bar{p}$ production. We have also calculated the cross section for the $pp \to pp Λ\overlineΛ$ reaction. Here, the cross section is smaller but the characteristic feature for $dσ/d{\rm y}_{diff}$ is predicted to be similar to $p \bar{p}$ production. The presence of resonances in the $p \bar p$ channel may destroy the dip at ${\rm y}_{diff} = 0$. This opens the possibility to study diffractively produced resonances. We discuss the observables suited for this purpose.

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arXiv2018

Production of $W^+ W^-$ pairs via $γ^γ^ \to W^+ W^-$ subprocess with photon transverse momenta

We discuss production of $W^+ W^-$ pairs in proton-proton collisions induced by two-photon fusion including, for a first time, transverse momenta of incoming photons. The unintegrated inelastic fluxes (related to proton dissociation) of photons are calculated based on modern parametrizations of deep inelastic structure functions in a broad range of their arguments ($x$ and $Q^2$). In our approach we can get separate contributions of different $W$ helicities states. Several one- and two-dimensional differential distributions are shown and discussed. The present results are compared to the results of previous calculations within collinear factorization approach. Similar results are found except of some observables such as e.g. transverse momentum of the pair of $W^+$ and $W^-$. We find large contributions to the cross section from the region of large photon virtualities. We show decomposition of the total cross section as well as invariant mass distribution into polarisation states of both W bosons. The role of the longitudinal $F_L$ structure function is quantified. Its inclusion leads to a 4-5 % decrease of the cross section, almost independent of $M_{WW}$.

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arXiv2018

$D \bar D$ asymmetry at low and high energies and possible consequences for prompt atmospheric neutrinos

We discuss the role of unfavoured light quark/antiquark to $D$ meson fragmentation. The unknown parameters of fragmentation process are adjusted to describe the asymmetry for $D^+$ and $D^-$ production measured by the LHCb. Predictions for similar asymmetry for neutral $D$ mesons are presented. The predicted asymmetry at large rapidity (or $x_F$) are very large which is related to the valence-quark contribution. As a result, prompt atmospheric neutrino flux at high neutrino energies can be much larger than for the conventional $c \to D$ fragmentation. We predict large rapidity-dependent $D^+/D^-$ and $D^0/{\bar D}^0$ asymmetries for low ($\sqrt{s} =$ 20 - 100 GeV) energies. The $q/\bar q \to D$ fragmentation leads to enhanced production of $D$ mesons at low energies. Predictions for fixed target $p+^{4}\!\textrm{He}$ collisions relevant for a fixed target LHCb experiment are discussed.

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arXiv2018

Production of $Λ_c$ baryons at the LHC within the $k_T$-factorization approach and independent parton fragmentation picture

We calculate cross section for production of $D$ mesons and $Λ_c$ baryons in proton-proton collisions at the LHC. The cross section for production of $c \bar c$ pairs is calculated within $k_T$-factorization approach with the Kimber-Martin-Ryskin unintegrated gluon distributions obtained on the basis of modern collinear gluon distribution functions. We show that our approach well describes the $D^0$, $D^+$ and $D_s$ experimental data. We try to understand recent ALICE and LHCb data for $Λ_c$ production with the $c \to Λ_c$ independent parton fragmentation approach. The Peterson fragmentation functions are used. The $f_{c \to Λ_c}$ fragmentation fraction and $\varepsilon_{c}^Λ$ parameter for $c \to Λ_c$ are varied. As a control plot we show transverse momentum distribution of different species of $D$ mesons assuming standard values of the $f_{c \to D}$ fragmentation fractions known from the literature. The fraction $f_{c \to Λ_c}$ neccessary to describe the ALICE data is much larger than the average value obtained from $e^+ e^-$ or $e p$ experiments. No drastic modification of the shape of fragmentation function is allowed by the new ALICE and LHCb data for $Λ_c$ production. We also discuss a possible dependence of the $Λ_c/ D^0$ baryon-to-meson ratio on rapidity and transverse momentum as seems observed recently by the ALICE and LHCb collaborations. Three different effects are considered: the value of $\varepsilon_c^Λ$ parameter in Peterson fragmentation function for $c \to Λ_c$, a kinematical effect related to the hadronization prescription and a possible feed-down from higher charmed-baryon excitations. It seems very difficult, if not impossible, to understand the ALICE data within the considered independent parton fragmentation scheme.

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arXiv2018

Double-parton scattering effects in $D^{0}B^{+}$ and $B^{+}B^{+}$ meson-meson pair production in proton-proton collisions at the LHC

We extend our previous studies of double-parton scattering (DPS) to simultaneous production of $c \bar c$ and $b \bar b$ and production of two pairs of $b \bar b$. The calculation is performed within factorized ansatz. Each parton scattering is calculated within $k_T$-factorization approach. The hadronization is done with the help of fragmentation functions. Production of $D$ mesons in our framework was tested in our previous works. Here we present our predictions for $B$ mesons. A good agreement is achieved with the LHCb data. We present our results for $c \bar c b \bar b$ and $b \bar b b \bar b$ final states. For completeness we compare results for double- and single-parton scattering (SPS). As for $c \bar c c \bar c$ final state also here the DPS dominates over the SPS, especially for small transverse momenta. We present several distributions and integrated cross sections with realistic cuts for simultaneous production of $D^0 B^+$ and $B^+ B^+$, suggesting future experimental studies at the LHC.

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arXiv2018

D meson production asymmetry, unfavoured fragmentation and consequences for prompt atmospheric neutrino production

We consider unfavoured light quark/antiquark to $D$ meson fragmentation. We discuss nonperturbative effects for small transverse momenta. The asymmetry for $D^+$ and $D^-$ production measured by the LHCb collaboration provides natural constraints on the parton (quark/antiquark) fragmentation functions. We find that already a fraction of $q/{\bar q} \to D$ fragmentation probability is sufficient to account for the measured asymmetry. We make predictions for similar asymmetry for neutral $D$ mesons. Large $D$-meson production asymmetries are found for large $x_F$ which is related to dominance of light quark/antiquark $q/\bar q \to D$ fragmentation over the standard $c \to D$ fragmentation. As a consequence, prompt atmospheric neutrino flux at high neutrino energies can be much larger than for the conventional $c \to D$ fragmentation. The latter can constitute a sizeable background for the cosmic neutrinos claimed to be observed recently by the IceCube Observatory. Large rapidity-dependent $D^+/D^-$ and $D^0/{\bar D}^0$ asymmetries are predicted for low ($\sqrt{s} =$ 20 - 100 GeV) energies. The $q/\bar q \to D$ fragmentation leads to enhanced production of $D$ mesons at low energies. At $\sqrt{s}$ = 20 GeV the enhancement factor with respect to the conventional contribution is larger than a factor of five. In the considered picture the large-$x_F$ $D$ mesons are produced dominantly via fragmentation of light quarks/antiquarks. Predictions for fixed target $p+^{4}\!\textrm{He}$ collisions relevant for a fixed target LHCb experiment are presented.

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arXiv2017

Prompt inclusive production of $J/ψ$, $ψ'$ and $χ_{c}$ mesons at the LHC in forward directions within the NRQCD $k_t$-factorization approach - search for the onset of gluon saturation

We discuss prompt production of $J/ψ$ mesons in proton-proton collisions at the LHC within NRQCD $k_t$-factorization approach using Kimber-Martin-Ryskin (KMR) unintegrated gluon distributions (UGDF). We include both direct color-singlet production ($g g \to J/ψg$) as well as a feed-down from $χ_c \to J/ψγ$ and $ψ' \to J/ψX$ decays. The production of the decaying mesons ($χ_c$ or $ψ'$) is also calculated within NRQCD $k_t$-factorization approach. The corresponding matrix elements for $g g \to J/ψ$ g, $g g \to ψ'g$ and $g g \to χ_c$ include parameters of the nonrelativistic space wave functions of the quarkonia at $r = 0$, which are taken from potential models in the literature. We get the ratio of the corresponding cross section ratio for $χ_c(2)$-to-$χ_c(1)$ at midrapidities much closer to experimental data than obtained in a recent analysis. Differential distributions in rapidity and transverse momentum of $J/ψ$ and $ψ'$ are calculated and compared with experimental data of the ALICE and LHCb collaborations. We discuss a possible onset of gluon saturation effects in the production of $J/ψ$ and $χ_{c}$ mesons at forward/backward rapidities. We show that it is neccessary to modify the standard KMR UGDF to describe ALICE and LHCb data. A mixed UGDF scenario was proposed. Then we can describe the experimental data for $J/ψ$ production within model uncertainties with color-singlet component only. Therefore our theoretical results leave only a relatively small room for the color-octet contributions.

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arXiv2017

From the $γγ\to p \bar{p}$ reaction to the production of $p \bar{p}$ pairs in ultraperipheral ultrarelativistic heavy-ion collisions at the LHC

In this paper we consider the production of proton-antiproton pairs in two-photon interactions in electron-positron and heavy-ion collisions. We try to understand the dependence of the total cross section on the photon-photon c.m. energy as well as corresponding angular distributions measured by the Belle Collaboration for the $γγ\to p \bar{p}$ process. To understand the Belle data we include the proton-exchange, the $f_2(1270)$ and $f_2(1950)$ $s$-channel exchanges, as well as the hand-bag mechanism. The helicity amplitudes for the $γγ\to f_{2} \to p \bar{p}$ process are written explicitly based on a Lagrangian approach. The parameters of vertex form factors are adjusted to the Belle data. Having described the angular distributions for the $γγ\to p \bar{p}$ process we present first predictions for the ultraperipheral, ultrarelativistic, heavy-ion reaction $^{208}\!Pb \, ^{208}\!Pb \to$ $^{208}\!Pb \, ^{208}\!Pb \,p \bar{p}$. Both, the total cross section and several differential distributions for experimental cuts corresponding to the ALICE, ATLAS, CMS, and LHCb experiments are presented. We find the total cross section 100 $μ$b for the ALICE cuts, 160 $μ$b for the ATLAS cuts, 500 $μ$b for the CMS cuts, and 104 $μ$b taking into account the LHCb cuts. This opens a possibility to study the $γγ\to p \bar{p}$ process at the LHC.

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arXiv2017

Production of $χ_c$ pairs in $k_T$-factorization

We calculate the production of pairs of $χ_c(J)$ mesons with all possible combinations of $J=0,1,2$. The leading order production mechanism is the crossed-channel gluon exchange in the gluon-gluon fusion reaction. The building blocks are the vertices $g^* g^* \to χ_c(J)$ for off shell gluons. We stick to the color-singlet model and calculate the gluon fusion vertices in the limit of heavy quarks with nonrelativistic motion in the bound state. These vertices are used to construct the $g^* g^* \to χ_c(J_1) χ_c(J_2)$ amplitudes. We then calculate hadron-level cross sections using the $k_T$-factorization approach. In our numerical predictions, we use the KMR-type unintegrated gluon distributions. Several differential distributions at the $pp$ center of mass energy $\sqrt{s} = 8 \, {\rm TeV}$ are shown. The salient feature of the $t$ and $u$-channel gluon exchange are the broad distributions in rapidity difference $Δy$ between $χ_c$ mesons.

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arXiv2017

$γγ\to γγ$ scattering in ultrarelativistic UPC

We discuss diphoton semi(exclusive) production in ultraperipheral lead-lead collisions at energy of $\sqrt{s_{NN}}$ = 5.5 TeV (LHC) and in proton-proton collisions at $\sqrt{s_{pp}}$ = 7 TeV (LHC) and $\sqrt{s_{pp}}$ = 100 TeV (FCC). The nuclear calculations are based on equivalent photon approximation in the impact parameter space. The cross sections for elementary $γγ\to γγ$ subprocess are calculated including three different mechanisms: box diagrams with leptons and quarks in the loops, a VDM-Regge contribution with virtual intermediate hadronic excitations of the photons and the two-gluon exchange contribution. We get relatively high cross sections in heavy ion collisions. This opens a possibility to study the light-by-light (quasi)elastic scattering at the LHC. We find that the cross section for elastic $γγ$ scattering could be measured in the lead-lead collisions for the diphoton invariant mass up to $W_{γγ} \approx$ 15 - 20 GeV. Our Standard Model predictions are compared to a recent ATLAS experimental result. We present differential distributions for PbPb$\to$PbPb$γγ$ and pp$\to$pp$γγ$ reaction.

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