arXiv subjects

Piotr Lebiedowicz

Publications and source records attributed to Piotr Lebiedowicz.

At least 73 records · Page 4Linked to original sources

arXiv2016

Light-by-light scattering in ultraperipheral heavy-ion collisions at the LHC

We present cross sections for diphoton production in (semi)exclusive $PbPb$ collisions, relevant for the LHC. The calculation is based on equivalent photon approximation in the impact parameter space. The cross sections for elementary elastic scattering $γγ\to γγ$ subprocess are calculated including two mechanisms: box diagrams with leptons and quarks in the loops and a mechanism based on vector-meson dominance (VDM-Regge) model with virtual intermediate vector-like excitations of the photons. We get measureable cross sections in $PbPb$ collisions. We present many interesting differential distributions which could be measured by the ALICE, CMS or ATLAS Collaborations at the LHC. We study whether a separation of box and VDM-Regge contributions is possible. We find that the cross section for elastic $γγ$ scattering could be measured in the heavy-ion collisions for subprocess energies smaller than $W_{γγ} \approx 15-20$~GeV.

hep-ph↗

arXiv2016

Can the diphoton enhancement at 750 GeV be due to a neutral technipion?

We discuss a scenario in which the diphoton enhancement at $M_{γγ}$ = 750 GeV, observed by the ATLAS and CMS Collaborations, is a neutral technipion $\tildeπ^0$. We consider two distinct minimal models for the dynamical electroweak symmetry breaking. In a first one, two-flavor vector-like technicolor (VTC) model, we assume that the two-photon fusion is a dominant production mechanism. We include $γγ\to {\tilde π}^0$ and production of technipion associated with one or two jets. All the considered mechanisms give similar contributions. With the strong Yukawa (technipion-techniquark) coupling $g_{TC}$ = 10 - 20 we obtain the measured cross section of the "signal". With such values of $g_{TC}$ we get a relatively small $Γ_{\rm tot}$. In a second approach, one-family walking technicolor (WTC) model, the isoscalar technipion is produced dominantly via the gluon-gluon fusion. We also discuss the size of the signal at lower energies (LHC, Tevatron) for $γγ$ (VTC) and jet-jet (WTC) final states and check consistency with the existing experimental data. We predict a measurable cross section for ${\tilde π}^0$ production associated with one or two soft jets. The technipion signal in both models is compared with the SM background diphoton contributions. We observe the dominance of inelastic-inelastic processes for $γγ$ induced processes. In the VTC scenario, we predict the signal cross section for purely exclusive $p p \to p p γγ$ processes 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. In all considered cases the signal is below the background or/and below the threshold set by statistics.

hep-ph↗

arXiv2016

Light-by-light scattering in ultraperipheral PbPb collisions at the Large Hadron Collider

We calculate cross sections for diphoton production in (semi)exclusive $PbPb$ collisions, relevant for the LHC. The calculation is based on equivalent photon approximation in the impact parameter space. The cross sections for elementary $γγ\to γγ$ subprocess are calculated including two different mechanisms. We take into account box diagrams with leptons and quarks in the loops. In addition, we consider a vector-meson dominance (VDM-Regge) contribution with virtual intermediate hadronic (vector-like) excitations of the photons. We get much higher cross sections in $PbPb$ collisions than in earlier calculation from the literature. This opens a possibility to study the $γγ\to γγ$ (quasi)elastic scattering at the LHC. We present many interesting differential distributions which could be measured by the ALICE, CMS or ATLAS Collaborations at the LHC. We study whether a separation or identification of different components (boxes, VDM-Regge) is possible. We find that the cross section for elastic $γγ$ scattering could be measured in the heavy-ion collisions for subprocess energies smaller than $W_{γγ} \approx 15-20$ GeV.

nucl-th↗

arXiv2016

Central exclusive diffractive production of $π^{+}π^{-}$ continuum, scalar and tensor resonances in $pp$ and $p \bar{p}$ scattering within tensor pomeron approach

We consider central exclusive diffractive dipion production in the reactions $pp \to pp π^{+} π^{-}$ and $p\bar{p} \to p\bar{p} π^{+} π^{-}$ at high energies. We include the dipion continuum, the dominant scalar $f_{0}(500)$, $f_{0}(980)$, and tensor $f_{2}(1270)$ resonances decaying into the $π^{+} π^{-}$ pairs. The calculation is based on a tensor pomeron model and the amplitudes for the processes are formulated in terms of vertices respecting the standard crossing and charge-conjugation relations of Quantum Field Theory. The formulae for the dipion continuum and tensor meson production are given here for the first time. The theoretical results are compared with existing STAR, CDF, CMS experimental data and predictions for planned or being carried out experiments (ALICE, ATLAS) are presented. We show the influence of the experimental cuts on the integrated cross section and on various differential distributions for outgoing particles. Distributions in rapidities and transverse momenta of outgoing protons and pions as well as correlations in azimuthal angle between them are presented. We find that the relative contribution of resonant $f_2(1270)$ and dipion continuum strongly depends 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. We suggest some experimental analyses to fix model parameters related to the pomeron-pomeron-$f_{2}$ coupling.

hep-ph↗

arXiv2015

Production of charged Higgs boson pairs in the $pp \to ppH^{+}H^{-}$ reaction at the LHC and FCC

We present differential cross sections for the $pp \to ppH^{+}H^{-}$ reaction via photon-photon fusion with exact kinematics. We show predictions for $\sqrt{s}$ = 14 TeV (LHC) and at the Future Circular Collider (FCC) for $\sqrt{s}$ = 100 TeV. The integrated cross section for $\sqrt{s}$ = 14~TeV (LHC) is about 0.1~fb and about 0.9~fb at the FCC for $\sqrt{s}$ = 100~TeV when assuming $m_{H^{\pm}} = 150$~GeV. We present distributions in diHiggs boson invariant mass. The results are compared with those obtained within equivalent-photon approximation. We discuss also first calculations of cross section for exclusive diffractive pQCD mechanism with estimated limits on the $g_{hH^{+}H^{-}}$ coupling constant within 2HDM based on the LHC experimental data. The diffractive contribution is much smaller than the $γγ$ one. Absorption corrections are calculated differentially for various distributions. In general, they lead to a damping of the cross section. The damping depends on $M_{H^{+}H^{-}}$ invariant mass and on four-momentum transfers squared in the proton line. We discuss a possibility to measure the exclusive production of $H^{\pm}$ bosons.

hep-ph↗

arXiv2015

Central exclusive production of pion pairs in proton-(anti)proton collisions

We present results for exclusive $p p \to p p π^+ π^-$ or $p \bar p \to p \bar p π^+ π^-$ processes at high energies. We discuss the role of new additional absorption corrections in the non-resonant Lebiedowicz-Szczurek model mediated by the pomeron and reggeon exchanges. We discuss also the role of the $ρ^{0}$ and the Drell-Söding photoproduction mechanism. We compare our predictions with recent experimental results obtained by the STAR and CDF Collaborations. We present predictions for the ALICE, ATLAS and CMS experiments. Differential distributions in invariant two-pion mass and two-dimensional distributions in proton-proton relative azimuthal angle and transverse momentum of one of the protons are presented.

hep-ph↗

arXiv2015

Revision of absorption corrections for the $p p \to p p π^{+} π^{-}$ process

We include new additional absorption corrections into the Lebiedowicz-Szczurek (non-resonant) model for $p p \to p p π^+ π^-$ or $p \bar p \to p \bar p π^+ π^-$ processes. They are related to the $πN$ nonperturbative interaction in the final state of the reaction. The role of the absorption corrections is quantified for several differential distributions for $\sqrt{s}$ = 0.2, 1.96, 7, and 8 TeV. The new absorption corrections lead to further decrease of the cross section by about a factor of two. They change the shape of some distributions ($d σ/ dt$, $d σ/ dp_{t,p}$, $d σ/d ϕ_{pp}$) but leave almost unchanged shape of other distributions ($d σ/ dM_{ππ}$, $d σ/ dy_π$, $d σ/dp_{t,π}$, $d σ/ d ϕ_{ππ}$). The effect may have important impact on the interpretation of the recent STAR and CDF data as well as the forthcoming data of the ALICE, ATLAS + ALFA and CMS + TOTEM collaborations.

hep-ph↗

arXiv2015

Exclusive production of heavy charged Higgs boson pairs in the $p p \to p p H^+ H^-$ reaction at the LHC and a future circular collider

We calculate differential cross sections for exclusive production of heavy charged scalar, weakly interacting particles (charged Higgs bosons, charged technipions, etc.) via photon-photon exchanges in the $p p \to p p H^+ H^-$ reaction with exact $2 \to 4$ kinematics. We present distributions in rapidities, transverse momenta, and correlations in azimuthal angles between the protons and between the charged Higgs bosons. As an example, the integrated cross section for $\sqrt{s}$ = 14~TeV (LHC) is about 0.1~fb and about 0.9~fb at the Future Circular Collider (FCC) for $\sqrt{s}$ = 100~TeV when assuming $m_{H^{\pm}} = 150$~GeV. The results are compared with results obtained within standard equivalent-photon approximation known from the literature. We discuss the role of the Dirac and Pauli electromagnetic form factors of the proton. We have also performed first calculations of cross sections for the exclusive diffractive Khoze-Martin-Ryskin mechanism. We have estimated limits on the $g_{h H^+ H^-}$ coupling constant within two-Higgs dublet model based on recent experimental data from the LHC. The diffractive contribution is, however, much smaller than the $γγ$ one. The $Z γ$, $γZ$, and $ZZ$ exchanges give even smaller contributions. Absorption corrections are calculated for the first time differentially for various distributions. In general, they lead to a damping of the cross section. The damping depends on the $M_{H^{+}H^{-}}$ invariant mass and on $t$ four-momentum transfers squared. In contrast to diffractive processes, the larger the collision energy, the smaller the effect of absorption. We discuss a possibility to measure the exclusive production of two charged Higgs bosons with the help of so-called "forward proton detectors" at the LHC experiments.

hep-ph↗

arXiv2014

The $ρ^0$ and Drell-Söding contributions to central exclusive production of $π^+ π^-$ pairs in proton-proton collisions at high energies

We present a study of the central exclusive $π^{+} π^{-}$ production via the photoproduction mechanism in nucleon-nucleon collisions. The photon-pomeron/reggeon and pomeron/reggeon-photon exchanges both for the $ρ^{0}$ resonance contribution and the Drell-Söding contribution are considered. The amplitudes for the processes are formulated in terms of vertices respecting the standard crossing and charge-conjugation relations of Quantum Field Theory. The coupling parameters of tensor pomeron and reggeon exchanges are fixed based on the H1 and ZEUS experimental data for the $γp \to ρ^{0} p$ reaction. We present first predictions of this mechanism for the $pp \to pp π^{+} π^{-}$ reaction being studied at COMPASS, RHIC, Tevatron, and LHC. We show the influence of the experimental cuts on the integrated cross section and on various differential distributions for outgoing particles. Distributions in rapidities and transverse momenta of outgoing protons and pions as well as correlations in azimuthal angle between them are presented. We compare the photoproduction contribution to $π^{+} π^{-}$ distributions with double pomeron/reggeon two-pion continuum. We discuss whether the high-energy central production of $ρ^{0}$ mesons could be selected experimentally.

hep-ph↗

arXiv2014

Exclusive central diffractive production of scalar, pseudoscalar and vector mesons

We discuss exclusive central diffractive production of scalar ($f_{0}(980)$, $f_{0}(1370)$, $f_{0}(1500)$), pseudoscalar ($η$, $η'(958)$), and vector ($ρ^{0}$) mesons in proton-proton collisions. The amplitudes are formulated in terms of effective vertices required to respect standard rules of Quantum Field Theory and propagators for the exchanged pomeron and reggeons. Different pomeron-pomeron-meson tensorial (vectorial) coupling structures are possible in general. In most cases two lowest orbital angular momentum - spin couplings are necessary to describe experimental differential distributions. For the $f_{0}(980)$ and $η$ production the reggeon-pomeron, pomeron-reggeon, and reggeon-reggeon exchanges are included in addition, which seems to be necessary at relatively low energies. The theoretical results are compared with the WA102 experimental data, in order to determine the model parameters. For the $ρ^{0}$ production the photon-pomeron and pomeron-photon exchanges are considered. The coupling parameters of tensor pomeron and/or reggeon are fixed from the H1 and ZEUS experimental data of the $γp \to ρ^{0} p$ reaction. We present first predictions of this mechanism for $pp \to pp π^{+} π^{-}$ reaction being studied at COMPASS, RHIC, Tevatron, and LHC. Correlation in azimuthal angle between outgoing protons and distribution in pion rapidities at $\sqrt{s} = 7$TeV are presented. We show that high-energy central production of mesons could provide crucial information on the spin structure of the soft pomeron.

hep-ph↗

arXiv2014

Applications of the tensor pomeron model to exclusive central diffractive meson production

We discuss exclusive central diffractive production of scalar ($f_{0}(980)$, $f_{0}(1370)$, $f_{0}(1500)$), pseudoscalar ($η$, $η'(958)$), and vector ($ρ^{0}$) mesons in proton-proton collisions. We show that high-energy central production of mesons could provide crucial information on the spin structure of the soft pomeron. The amplitudes are formulated in terms of effective vertices respecting standard rules of Quantum Field Theory and propagators for the exchanged pomeron and reggeons. For the scalar and pseudoscalar meson production, in most cases, two lowest orbital angular momentum - spin couplings are necessary to describe WA102 experimental differential distributions. Different pomeron-pomeron-meson tensorial (vectorial) coupling structures are possible in general. For the $ρ^{0}$ production the photon-tensor pomeron/reggeon exchanges are considered and the coupling parameters are fixed from the H1 and ZEUS experimental data of the $γp \to ρ^{0} p$ reaction. We present first predictions of this mechanism for the $pp \to pp (ρ^{0} \to π^{+} π^{-})$ reaction being studied at COMPASS, RHIC, Tevatron, and LHC. We analyse influence of the experimental cuts on integrated cross section and various differential distributions for produced mesons.

hep-ph↗

arXiv2013

Search for technipions in exclusive production of diphotons with large invariant masses at the LHC

We focus on exclusive production of neutral technipion $\tilde π^0$ in $pp$ collisions at the LHC, i.e. on $p p \to p p \tilde π^0$ reaction. The dependence of the cross section on parameters of recently proposed vector-like Technicolor model is studied. Characteristic features of the differential distributions are discussed. For not too large technipion masses the diphoton decay channel has the dominant branching fraction. This is also the main reason for an enhanced production of neutral technipions in $γγ$-fusion reaction. We discuss potential backgrounds of the QCD and QED origin to the $p p \to p p (\tildeπ^0 \to γγ)$ process at large invariant $γγ$ masses. We conclude that compared to inclusive case the signal-to-background ratio in the considered exclusive reaction is vary favorable which thereby could serve as a good probe for Technicolor dynamics searches at the LHC.

hep-ph↗

arXiv2013

Exclusive central diffractive production of scalar and pseudoscalar mesons; tensorial vs. vectorial pomeron

We discuss consequences of the models of "tensorial pomeron" and "vectorial pomeron" for exclusive diffractive production of scalar and pseudoscalar mesons in proton-proton collisions. Diffractive production of $f_{0}(980)$, $f_{0}(1370)$, $f_{0}(1500)$, $η$, and $η'(958)$ mesons is discussed. Different pomeron-pomeron-meson tensorial coupling structures are possible in general. In most cases two lowest orbital angular momentum - spin couplings are necessary to describe experimental differential distributions. For $f_{0}(980)$ and $η$ production reggeon-pomeron, pomeron-reggeon, and reggeon-reggeon exchanges are included in addition, which seems to be necessary at relatively low energies. The theoretical results are compared with the WA102 experimental data. Correlations in azimuthal angle between outgoing protons, distributions in rapidities and transverse momenta of outgoing protons and mesons, in a special "glueball filter variable", as well as some two-dimensional distributions are presented. We discuss differences between results of the vectorial and tensorial pomeron models. We show that high-energy central production, in particular of pseudoscalar mesons, could provide crucial information on the spin structure of the soft pomeron.

hep-ph↗

arXiv2013

Exclusive diffractive photon bremsstrahlung at high energies

We discuss the $p p \to p p γ$ reaction at the LHC. We consider diffractive classical bremsstrahlung mechanisms including effects of non point-like nature of protons. In addition, we take into account (vector meson)-pomeron, photon-pion as well as photon-pomeron exchange processes for the first time in the literature. The integrated diffractive bremsstrahlung cross section ($E_γ>100$ GeV) is only of the order of $μ$b. We try to identify regions of the phase space where one of the mechanisms dominates. The classical bremsstrahlung dominates at large forward/backward photon pseudorapidities, close to the pseudorapidities of scattered protons. In contrast, the photon-pomeron (pomeron-photon) mechanism dominates at midrapidities but the related cross section is rather small. In comparison the virtual-omega--rescattering mechanism contributes at smaller angles of photons (larger photon rapidities).

hep-ph↗

arXiv2013

Diffractive mechanisms in $pp \to pp π^{0}$ reaction at high energies

We present a study of exclusive production of $π^{0}$ meson in proton-proton collisions at high energies. Both diffractive bremsstrahlung (Drell-Hiida-Deck type model), photon-photon, photon-omega and photon-odderon exchange mechanisms are included in the calculation. The $π^{0}$-bremsstrahlung contribution dominates at large (forward, backward) pion rapidities and contributes at small $π^0 p$ invariant mass and could be therefore misinterpreted as the Roper resonance $N^{*}(1440)$. Large cross sections of the order of mb are predicted. We predict strong dependence of the slope in $t$ (squared four-momentum transfer between ingoing and outgoing proton) on the mass of the supplementary excited $π^{0} p$ system. At high energy and midrapidity, the photon-photon contribution dominates over the diffractive components, however, the corresponding cross section is rather small. The photon-odderon and odderon-photon contributions are included in addition and first estimates (upper limits) of their contributions are presented. We suggest a search for the odderon contribution at midrapidity and at $p_{\perp,π^{0}} \sim$ 0.5 GeV. Our predictions are ready for verification at LHC. The bremsstrahlung mechanisms discussed here contribute also to the $pp \to p(n π^{+})$ reaction. Both channels give a sizable contribution to the low-mass single diffractive cross section and must be included in extrapolating the measured experimental single diffractive cross section.

hep-ph↗

arXiv2013

Exclusive $p p \to p p π^{0}$ reaction at high energies

The amplitudes for the $p p \to p p π^{0}$ process applicable at high energy are discussed in detail. Both diffractive bremsstrahlung (Drell-Hiida-Deck--type model), photon-photon and photon-omega exchange mechanisms are included in the calculation. Large cross sections of the order of mb are predicted. The corresponding differential cross sections in rapidities and transverse momenta of outgoing protons and pions as well as relative azimuthal angle between outgoing protons are calculated for RHIC and LHC energies. The hadronic bremsstrahlung contributions dominate at large (forward, backward) pion rapidities. The diffractive nonresonant background contributes at small $π^0 p$ invariant mass and could be therefore misinterpreted as the Roper resonance. We predict strong dependence of the slope in $t$ (squared four-momentum transfer between ingoing and outgoing proton) on the mass of the supplementary excited $π^{0}p$ system. At high energies and midrapidities, the photon-photon contribution dominates over the diffractive components, however, the corresponding cross section is rather small. The photon-odderon and odderon-photon contributions are included in addition and first estimates (upper limits) of their contributions to rapidity and transverse momentum distribution of neutral pions are presented. We suggest a search for the odderon contribution at midrapidity and at $p_{\perp,π^{0}} \sim$ 0.5 GeV. Our predictions are ready for verification at RHIC and LHC. The bremsstrahlung mechanisms discussed here contribute also to the $pp \to p(n π^{+})$ reaction. Both channels give a sizable contribution to the low-mass single diffractive cross section and must be included in extrapolating the measured experimental single diffractive cross section.

hep-ph↗

arXiv2013

QCD diffractive mechanism of exclusive $W^+W^-$ pair production at high energies

We discuss new diffractive mechanism of central exclusive production of $W^+W^-$ pairs in proton-proton collisions at the LHC. We include diagrams with intermediate virtual Higgs boson as well as quark box diagrams. Several observables related to this process are calculated. Predictions for the total cross section and differential distributions in $W$-boson rapidity and transverse momentum as well as $WW$ invariant mass are presented. We also show results for different polarization states of the final $W^{\pm}$ bosons. We compare the contribution of the $γγ\to W^+ W^-$ mechanism considered in the literature with the contribution of the diffractive mechanism through the $gg \to W^+ W^-$ subprocess for the different observables. The phase space integrated diffractive contribution when separated is only a small fraction of fb compared to 115.4 fb of the $γγ$-contribution without absorption. The latter contribution dominates at small four-momentum transfers squared in the proton lines and in a broad range of $W^+ W^-$ invariant masses. This offers a possibility of efficient searches for anomalous triple-boson ($γW W$) and quartic-boson ($γγWW$) couplings and testing models beyond the Standard Model. We discuss shortly also the $p p \to p p γγ$ process, where the box contribution is very similar to that for $W^+ W^-$ and compare our results with recent CDF data. Nice agreement has been achieved without additional free parameters.

hep-ph↗

arXiv2013

Exclusive diffractive photon bremsstrahlung at the LHC

We calculate differential distributions for the $p p \to p p γ$ reaction at the LHC energy $\sqrt{s} = 14$ TeV. We consider diffractive classical bremsstrahlung mechanisms including effects of non point-like nature of protons. In addition, we take into account (vector meson)-pomeron, photon-pion as well as photon-pomeron exchange processes for the first time in the literature. Predictions for the total cross section and several observables related to these processes e.g. differential distributions in pseudorapidities and transverse momenta of photons or protons are shown and discussed. The integrated diffractive bremsstrahlung cross section ($E_γ>100$ GeV) is only of the order of $μ$b. We try to identify regions of the phase space where one of the mechanisms dominates. The classical bremsstrahlung dominates at large forward/backward photon pseudorapidities, close to the pseudorapidities of scattered protons. In contrast, the photon-pomeron (pomeron-photon) mechanism dominates at midrapidities but the related cross section is rather small. In comparison the virtual-omega rescattering mechanism contributes at smaller angles of photons (larger photon rapidities). Photons in the forward/backward region can be measured by the Zero Degree Calorimeters (ZDCs) installed in experiments at the LHC while the midrapidity photons are difficult to measure (small cross section, small photon transverse momenta). Protons could be measured by ALFA detector (ATLAS) or TOTEM detector at CMS. The exclusivity could be checked with the help of main central detectors.

hep-ph↗