arXiv subjects

Piotr Lebiedowicz

Publications and source records attributed to Piotr Lebiedowicz.

At least 55 records · Page 3Linked to original sources

arXiv2018

Tensor pomeron, vector odderon and diffractive production of meson and baryon pairs in proton-proton collisions

We review some selected results of the tensor-pomeron and vector-odderon model of soft high-energy proton-proton scattering and central exclusive production of meson and baryon pairs in proton-proton collisions. We discuss the theoretical aspects of this approach and consider the phenomenological implications in a variety of processes at high energies, comparing to existing experimental data. We consider the diffractive dipion and dikaon production including the continuum and the dominant scalar and tensor resonance contributions as well as the photoproduction processes. The theoretical results are compared with existing CDF experimental data and predictions for planned or current LHC experiments, ALICE, ATLAS, CMS, LHCb are presented.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

arXiv2017

Exclusive diffractive production of hadrons in $pp$ collisions

We discuss central exclusive diffractive dihadron production in proton-proton collisions at high energies. The calculation is based on a tensor pomeron model and the amplitudes for the processes are formulated in an effective field-theoretic approach. We include a purely diffractive dipion continuum, and the scalar and tensor resonances decaying into the $π^{+} π^{-}$ pairs as well as the photoproduction contributions ($ρ^{0}$, Drell-Söding). We discuss how two pomerons couple to tensor meson $f_{2}(1270)$ and the interference effects of the scalar and tensor resonances and the dipion continuum. The theoretical results are compared with existing CDF and CMS experimental data. We discuss also the Drell-Hiida-Deck type mechanism with centrally produced $ρ^{0}$ meson associated with a very forward/backward $πN$ system. For the $pp \to pp π^{+} π^{-} π^{+} π^{-}$ reaction we consider both the $σσ$ and $ρρ$ contributions as well as the triple Regge exchange mechanism. Predictions for planned or being carried out experiments (STAR, ALICE, ATLAS, CMS) are presented. We show the influence of the experimental cuts on the integrated cross section and on various differential distributions for outgoing particles.

hep-ph↗

arXiv2017

The role of meson exchanges in light-by-light scattering

We discuss the role of meson exchange mechanisms in $γγ\to γγ$ scattering. Several pseudoscalar ($π^0$, $η$, $η'(958)$, $η_c(1S)$, $η_c(2S)$), scalar ($f_{0}(500)$, $f_0(980)$, $a_0(980)$, $f_0(1370)$, $χ_{c0}(1P)$) and tensor ($f_2(1270)$, $a_2(1320)$, $f_2'(1525)$, $f_2(1565)$, $a_2(1700)$) mesons are taken into account. We consider not only $s$-channel but also for the first time $t$- and $u$-channel meson exchange amplitudes corrected for off-shell effects including vertex form factors. We find that, depending on not well known vertex form factors, the meson exchange amplitudes interfere among themselves and could interfere with fermion-box amplitudes and modify the resulting cross sections. The meson contributions are shown as a function of collision energy as well as angular distributions are presented. Interesting interference effects separately for light pseudoscalar, scalar and tensor meson groups are discussed. The meson exchange contributions may be potentially important in the context of a measurement performed recently in ultraperipheral collisions of heavy ions by the ATLAS collaboration. The light-by-light interactions could be studied in future in electron-positron collisions by the Belle II at SuperKEKB accelerator.

hep-ph↗

arXiv2017

Triple Regge exchange mechanisms of four-pion continuum production in the $pp \to pp π^{+}π^{-}π^{+}π^{-}$ reaction

We consider exclusive multi-peripheral production of four charged pions in proton-proton collisions at high energies with simultaneous exchange of three pomerons/reggeons. The amplitude(s) for the genuine $2 \to 6$ process are written in the Regge approach. The calculation is performed with the help of the GenEx Monte Carlo code. Some corrections at low invariant masses in the two-body subsystems are necessary for application of the Regge formalism. We estimate the corresponding cross section and present differential distributions in rapidity, transverse momenta and two- and four-pion invariant masses. The cross section and the distributions depend on the value of the cut-off parameter of a form factor correcting amplitudes for off-shellness of $t$-channel pions. Rather large cross section is found for the whole phase space ($σ\sim$ 1-5 $μ$b, including absorption corrections). Relatively large four-pion invariant masses are populated in the considered diffractive mechanism compared to other mechanisms discussed so far in the context of four-pion production. We investigate whether the triple Regge exchange processes could be identified with the existing LHC detectors. We consider the case of ATLAS and ALICE cuts. The ATLAS (or CMS) has better chances to identify the process in the region of large invariant masses $M_{4 π} > 10$ GeV. In the case of the ALICE experiment the considered mechanism competes with other mechanisms (production of $σσ$, $ρρ$ pairs or single resonances) and cannot be unambiguously identified.

hep-ph↗

arXiv2016

Central production of $ρ^{0}$ in $pp$ collisions with single proton diffractive dissociation at the LHC

We consider the $pp \to pp ρ^{0} π^{0}$ and $pp \to pn ρ^{0} π^{+}$ processes at LHC energies. Our description is based on the nonperturbative framework of tensor pomeron and tensor reggeon exchanges. We discuss the Drell-Hiida-Deck type mechanism with centrally produced $ρ^{0}$ meson associated with a very forward/backward $πN$ system. The considered processes constitute an inelastic (non-exclusive) background to the $p p \to p p ρ^0$ reaction in the case when only the centrally produced $ρ^{0}$ meson decaying into $π^{+} π^{-}$ is measured, the final state protons are not observed, and only rapidity-gap conditions are checked experimentally. We compare our results for the $γπ^{+} \to ρ^{0} π^{+}$ reaction with the experimental data obtained by the H1 collaboration at HERA. We present several differential distributions for the $pp \to pn ρ^{0} π^{+}$ reaction and estimate the size of the proton dissociative background to the exclusive $p p \to p p ρ^0$ process. The ratio of integrated cross sections for the inelastic $p p \to p N ρ^0 π$ processes, where $p N ρ^0 π$ stands for $p n ρ^0 π^{+}$ plus $p p ρ^0 π^{0}$, to the reference reaction $pp \to \ pp ρ^0$ is of order of (7--10)\%. We present also the ratios of the $ρ^0$ rapidity and transverse momentum distributions for the inelastic $p p \to p N ρ^0 π$ versus the elastic $pp \to \ pp ρ^0$ reaction. Our results may be used to investigate the $γπ\to ρ^{0} π$ process at LHC energies.

hep-ph↗

arXiv2016

New Results for Ultraperipheral Heavy Ion Collisions

We discuss diphoton semi(exclusive) production in ultraperipheral $PbPb$ collisions at energy of $\sqrt{s_{NN}}=$ 5.5 TeV (LHC). 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 (formally three-loops). We got relatively high cross sections in $PbPb$ collisions. This opens a possibility to study the $γγ\to γγ$ (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. We identify region(s) of phase space where the two-gluon exchange contribution becomes important ingredient compared to box and nonperturbative VDM-Regge mechanisms. We discuss also first results concerning production of two $e^+ e^-$ pairs in UPCs of heavy ions. We considered only double scattering mechanism.

nucl-th↗

arXiv2016

Exclusive production of two and four pions in proton-proton scattering

We consider exclusive $pp \to pp π^{+} π^{-}$ and $pp \to pp π^{+} π^{-}π^{+} π^{-}$ reactions at high energies. The calculation is based on a tensor pomeron model and the amplitudes for the processes are formulated in an effective field-theoretic approach. In the case of $pp \to pp π^{+} π^{-}$ process we consider both diffractive and photoproduction mechanisms and we include the non-resonant $π^{+}π^{-}$ continuum and the resonance $f_{0}(500)$, $f_{0}(980)$, $f_{2}(1270)$, $ρ(770)$ contributions. We discuss how two pomerons couple to tensor meson $f_{2}(1270)$ and the interference effects of resonance and dipion continuum. We find that the relative contribution of resonances $ρ(770)$, $f_2(1270)$ and dipion continuum strongly depends on the cut on proton transverse momenta. In the case of exclusive central $4 π$ production we include the contribution via the intermediate $σσ$ and $ρρ$ states. For both processes the theoretical results have been compared with the experimental data and predictions for planned or being carried out experiments (e.g. STAR, ATLAS-ALFA) are presented.

hep-ph↗

arXiv2016

Interpreting the 750 GeV diphoton signal as technipion

We discuss whether the enhancement in the diphoton final state at $M_{γγ}$ = 750 GeV, observed recently by the ATLAS and CMS Collaborations could be a neutral pseudoscalar technipion $\tildeπ^0$. We considered two distinct minimal models for the dynamical electroweak symmetry breaking. Here we concentrate only on two-flavor vector-like technicolor model and we assume that the two-photon fusion is a dominant production mechanism. We include contributions of $2 \to 1$, $2 \to 2$ and $2 \to 3$ partonic processes. All the mechanisms give similar contributions to the cross section. With the strong Yukawa (technipion-techniquark) coupling $g_{TC} \simeq 20$ we roughly obtain the measured cross section of the "signal". With such value of $g_{TC}$ we get a relatively small total decay width $Γ_{\rm tot}$. We discuss also the size of the signal at lower energies (LHC, Tevatron) for $γγ$ final states, where the enhancement was not observed. We predict a measurable cross section for neutral technipion production associated with one or two soft jets. The technipion signal is compared with the Standard Model diphoton background contributions. We observe the dominance of inelastic-inelastic $γγ$ processes. We predict the signal cross section for purely exclusive $p p \to p p γγ$ procesess at $\sqrt{s}$ = 13 TeV to be about 0.2 fb. Such a cross section would be, however, difficult to measure with the planned integrated luminosity. We conclude that in all considered cases the signal is below the background or/and below the threshold set by statistics although some tension can be seen.

hep-ph↗

arXiv2016

Light-by-light scattering in UPC at the LHC

hep-ph↗

arXiv2016

Exclusive diffractive production of $π^+ π^-$ pairs within tensor pomeron approach

We discuss exclusive central diffractive production of $π^{+} π^{-}$ in proton-(anti)proton collisions at high energies. Based on a tensor pomeron model we present results of the purely diffractive dipion continuum, the scalar $f_{0}(500)$, $f_{0}(980)$ and tensor $f_{2}(1270)$ resonances decaying into the $π^{+} π^{-}$ pairs as well as the photoproduction mechanism ($ρ^{0}$, Drell-Söding). We discuss how two pomerons couple to the tensor meson $f_{2}(1270)$ and the interference effects of resonance and dipion continuum contributions. The theoretical results are compared with existing STAR, CDF, and CMS experimental data. Predictions for planned or being carried out experiments (ALICE, ATLAS) are presented. We find that the relative contribution of resonant $f_2(1270)$ and dipion continuum strongly depend on the cut on proton transverse momenta (or four-momentum transfer squared $t_{1,2}$) which may explain some controversial observations made by different ISR experiments in the past. The cuts may play then the role of a $ππ$ resonance filter.

hep-ph↗

arXiv2016

Helicity in Proton-Proton Elastic Scattering and the Spin Structure of the Pomeron

We discuss different models for the spin structure of the nonperturbative pomeron: scalar, vector, and rank-2 symmetric tensor. The ratio of single-helicity-flip to helicity-conserving amplitudes in polarised high-energy proton-proton elastic scattering, known as the complex r_5 parameter, is calculated for these models. We compare our results to experimental data from the STAR experiment. We show that the spin-0 (scalar) pomeron model is clearly excluded by the data, while the vector pomeron is inconsistent with the rules of quantum field theory. The tensor pomeron is found to be perfectly consistent with the STAR data.

hep-ph↗

arXiv2016

Exclusive diffractive production of $π^{+}π^{-}π^{+}π^{-}$ via the intermediate $σσ$ and $ρρ$ states in proton-proton collisions within tensor pomeron approach

We present first predictions of the cross sections and differential distributions for the central exclusive reaction $pp \to pp π^{+} π^{-} π^{+} π^{-}$ being studied at RHIC and LHC. The amplitudes for the processes are formulated in terms of the tensor pomeron and tensor $f_{2 R}$ reggeon exchanges with the vertices respecting the standard crossing and charge-conjugation relations of Quantum Field Theory. The $σσ$ and $ρρ$ contributions to the $π^{+} π^{-} π^{+} π^{-}$ final state are considered focussing on their specificities. The correct inclusion of the pomeron spin structure seems crucial for the considered sequential mechanisms in particular for the $ρρ$ contribution which is treated here for the first time. The mechanism considered gives a significant contribution to the $pp \to pp π^{+} π^{-} π^{+} π^{-}$ reaction. We adjust parameters of our model to the CERN-ISR experimental data and present several predictions for the STAR, ALICE, ATLAS and CMS experiments. A measurable cross section of order of a few $μb$ is obtained including the experimental cuts relevant for the LHC experiments. We show the influence of the experimental cuts on the integrated cross section and on various differential distributions.

hep-ph↗