arXiv subjects

Antoni Szczurek

Publications and source records attributed to Antoni Szczurek.

At least 235 records · Page 13Linked to original sources

arXiv2014

Double-parton scattering contribution to production of jet pairs with large rapidity separation at the LHC

We discuss production of four-jet final state $pp \rightarrow j j j j X$ in proton-proton collisions at the LHC through the mechanism of double-parton scattering (DPS) in the context of jets with large rapidity separation. The DPS contributions are calculated within the so-called factorized Ansatz and each step of DPS is calculated in the LO collinear approximation. The LO pQCD calculations are shown to give a reasonably good descritption of recent CMS and ATLAS data on inclusive jet production and therefore this formalism can be used to reliably estimate the DPS effects. Relative contribution of DPS is growing at large rapidity distance between jets. This is consistent with our experience from previous studies of double-parton scattering effects in the case of open and hidden charm production. The calculated differential cross sections as a function of rapidity distance between the most remote in rapidity jets are compared with recent results of LL and NLL BFKL calculations for Mueller-Navelet (MN) jet production at $\sqrt{s} = 7$ TeV. The DPS contribution to widely rapidity separated jet production is carefully studied for the present energy $\sqrt{s}$ = 7 TeV and also at the nominal LHC energy $\sqrt{s}$ = 14 TeV and in different ranges of jet transverse momenta. The differential cross section as a function of dijet transverse momenta as well as two-dimensional ($p_{T}(y_{min})\times p_{T}(y_{max})$)-plane correlations for DPS mechanism are also presented. Some ideas how the DPS effects could be studied in the case of double dijet production are suggested.

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arXiv2014

Single-parton scattering versus double-parton scattering in the production of two $c \bar c$ pairs and charmed meson correlations at the LHC

We compare results of exact calculations of single parton scattering (SPS) and double parton scattering (DPS) for production of $c \bar c c \bar c$ and for $D$ meson correlations. The SPS calculations are performed in collinear approximation with exact matrix element for $g g \to c \bar c c \bar c$ and $q \bar q \to c \bar c c \bar c$ subprocesses. It is shown that the contribution of gluon-gluon subprocess is about factor 50 larger than that for quark-antiquark annihilation. The new results are compared with results of previous calculation with the approximate matrix element for $g g \to c \bar c c \bar c$ in the high-energy approximation. The cross section for the present exact calculation is bigger only at small invariant masses and small rapidity difference between two $c$ quarks (or two $\bar c$ antiquarks). We compare correlations in rapidities of two $c$ (or two $\bar c$) for DPS and SPS contributions. Finally we compare our predictions for $D$ mesons with recent results of the LHCb collaboration for invariant mass, rapidity distance between mesons and dimeson invariant mass. The predicted shapes are similar to the measured ones, however, some strength seems to be lacking. Our new calulations clearly confirm the dominance of DPS in the production of events with double charm.

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arXiv2013

Electromagnetic excitation of nuclei and neutron evaporation in ultrarelativistic ultraperipheral heavy ion collisions

We present a new approach for calculating electromagnetic excitation of nuclei as well as probabilities of emission and distributions of neutrons from decays of excited nuclear systems for ultrarelativistic, ultraperipheral heavy ion collisions. Excitation functions for $γ$ + Pb $\to$ Pb$^*$ are parametrized using physics-motivated components: excitation of giant resonances, quasi-deuteron absorption mechanism, excitation of nucleon resonances as well as high-energy dissociation of protons and neutrons. Neutron emission (up to 10 neutrons) from low-energy excitations of $^{208}$Pb is modelled in terms of the Hauser-Feshbach formalism. The probabilities of a given number of neutrons are calculated as a function of excitation energy in a Monte-Carlo code GEMINI. These functions are parametrized by smooth analytical functions. The results are compared to appropriate data for the $γ$ Pb $\to$ Pb$^*$ $\to$ k n reaction. As an example the approach is used for calculating electromagnetic excitation in UPC processes. Both single photon and double photon excitations are included and discussed. Topological cross sections with a given number of neutrons in forward and backward directions are calculated in the calculation at the LHC energies. Excitation functions are presented. The results of calculation are compared with SPS and more recent ALICE experimental data and good agreement is achieved.

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arXiv2013

Spectator charge splitting of directed flow in heavy ion collisions

We estimate the effect of the spectator charge on distortion of single charged pion distributions as well as on azimuthal anisotropies in heavy ion collisions. A large electromagnetic effect on directed flow $v_1$ is predicted in good agreement with existing WA98 as well as RHIC data. This effect results in a splitting of $v_1$ for positive and negative pions. Detailed analysis of this phenomenon may provide new information on the collision dynamics.

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arXiv2013

Subleading processes in production of $W^+ W^-$ pairs in proton-proton collisions

We discuss many new subleading processes for inclusive production of $W^+ W^-$ pairs not included in the literature so far. We focus on photon-photon induced processes. We include elastic-elastic, elastic-inelastic, inelastic-elastic and inelastic-inelastic contributions. The inelastic photon distributions in the proton are calculated in two different ways: naive approach used already in the literature and using photon distributions by solving special evolution equation with photon being a parton in the proton. The results strongly depend on the approach used. We calculate also contributions with resolved photons. The diffractive components have similar characteristics as the photon-photon elastic-inelastic and inelastic-elastic mechanisms. The subleading contributions are compared with the well known $q \bar q$ and $g g$ as well as with double-parton scattering contributions. Predictions for the total cross section and differential distributions in $W$- boson rapidity and transverse momentum as well as $WW$ invariant mass are presented. The $γγ$ components constitute only about 1-2 % of the inclusive $W^+ W^-$ cross section but about 10 % at large $W^{\pm}$ transverse momenta, and are even comparable to the dominant $q \bar q$ component at large $M_{WW}$, i.e. are much larger than the often celebrated $g g \to W^+ W^-$ component. Its size is comparable to double parton scattering contribution. Only elastic-elastic, elastic-inelastic and inelastic-elastic contributions could be potentially measured to verify our predictions using forward proton detectors.

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.

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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

Double-scattering mechanism in exclusive $A A \to A A ρ^0 ρ^0$ reaction at ultrarelativistic collisions

We calculate, for the first time, differential distributions for double $ρ^0$ meson production in exclusive ultraperipheral, ultrarelativistic collisions via a double scattering mechanism. The calculations are done in impact parameter space. The cross section for $γA \to ρ^0 A$ is parametrized based on an existing calculation. Smearing of $ρ^0$ masses is taken into account. The results of our calculations are compared at the RHIC energy to the contribution of the two-photon mechanism discussed previously in the literature. The cross section for the double scattering mechanism is found to be an order of magnitude larger at $M_{ρρ} <$ 2 GeV and more than two orders of magnitude at $M_{ρρ} >$ 3 GeV, than that for the photon-photon mechanism. Compared to the two-photon mechanism the double scattering mechanism populates somewhat larger $ρ^0 ρ^0$ invariant masses and larger rapidity distances between the two $ρ^0$ mesons and gives a significant contribution to the $A A \to A A π^+ π^- π^+ π^-$ reaction. Some observables related to charged pions are presented too. We compare the results of our calculation with the STAR collaboration results on four charged pion production. While the shape in invariant mass of the four-pion system is very similar to the measured one, the predicted cross section constitutes only 20% of the measured one. We discuss a possibility of identifying the double scattering mechanism at the LHC.

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arXiv2013

Charmed mesons and leptons from semileptonic decays at the LHC

We discuss production of charmed mesons as well as electrons/muons from semileptonic decays of charm and bottom mesons in proton-proton collisions at the LHC. The cross section for inclusive production of $c \bar c$ and $b \bar b$ pairs is calculated in the framework of the $k_{\perp}$-factorization approach. Here, the KMR and Jung CCFM unintegrated gluon distribution functions are used. Theoretical uncertainties of the model related to the choice of renormalization and factorization scales as well as due to the quark mass are also discussed. The hadronization of charm and bottom quarks is included within the fragmentation functions technique. Inclusive differential distributions in transverse momentum of charmed mesons are presented and compared to recent results of the ALICE collaboration. Furthermore, we also consider production of different $D \bar D$ pairs in unique kinematics of forward rapidities of the LHCb experiment. Kinematical correlations in azimuthal angle $φ_{D\bar D}$ and invariant mass $M_{D \bar D}$ distributions are presented and compared to LHCb data. Furthermore, the semileptonic decays of charm and bottom mesons are done with the help of decay functions found by fitting recent semileptonic data obtained by the CLEO and BABAR collaborations. Inclusive differential distributions in transverse momentum of leptons for several kinematical regions are presented and compared to recent results of the ALICE and CMS collaborations.

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

Diffractive production of quark-antiquark pairs

We discuss diffractive dissociation of gluons into heavy quark pairs. The particular mechanism is similar to the diffractive dissociation of virtual photons into quarks. The amplitude for the $g p \to Q \bar Q p$ is derived in the impact parameter and momentum space. The cross section for single diffractive $p p \to Q \bar Q p X$ is calculated as a convolution of the elementary cross section and gluon distribution in the proton. Integrated cross section and differential distributions in transverse momentum and rapidity of the charm and bottom quark and antiquark, etc. are calculated for the nominal LHC energy for different unintegrated gluon distributions from the literature. The ratio of the bottom-to-charm cross sections are shown and discussed as a function of several kinematical variables.

hep-ph↗

arXiv2013

Production of two $c \bar c$ pairs in double-parton scattering within $k_t$-factorization

We discuss production of two pairs of $c \bar c$ in proton-proton collisions at the LHC. Both double-parton scattering (DPS) and single-parton scattering (SPS) contributions are included in the analysis. Each step of DPS is calculated within $k_t$-factorization approach. The conditions how to identify the DPS contribution are presented. The discussed mechanism leads to the production of pairs of mesons: each containing $c$ quarks or each containing $\bar c$ antiquarks. We discuss corresponding production rates and some differential distributions for $(D^0 D^0$ + $\bar D^0 \bar D^0)$ production. Within large theoretical uncertainties the predicted DPS cross section is fairly similar to the cross section measured recently by the LHCb collaboration. The best description is obtained with the Kimber-Martin-Ryskin (KMR) unintegrated gluon distribution. The contribution of SPS, calculated in the high-energy approximation, turned out to be rather small. Finally, we emphasize significant contribution of DPS mechanism to inclusive charmed meson spectra measured recently by ALICE, ATLAS and LHCb.

hep-ph↗

arXiv2013

Diffractive dissociation of gluons into heavy quark-antiquark pairs in proton-proton collisions

We discuss diffractive dissociation of gluons into heavy quark pairs. The particular mechanism is similar to the diffractive dissociation of virtual photons into quarks, which drives diffractive deep inelastic production of charm in the low-mass diffraction, or large $β$-region. There, it can be understood, with some reservations, in terms of a valence heavy quark content of the Pomeron. The amplitude for the $g p \to Q \bar Q p$ is derived in the impact parameter and momentum space. The cross section for single diffractive $p p \to Q \bar Q p X$ is calculated as a convolution of the elementary cross section and gluon distribution in the proton. Integrated cross section and the differential distributions in e.g. transverse momentum and rapidity of the charm and bottom quark and antiquark, as well as the quark-antiquark invariant mass are calculated for the nominal LHC energy for different unintegrated gluon distributions from the literature. The ratio of the bottom-to-charm cross sections are shown and discussed as a function of several kinematical variables.

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

Spectator induced electromagnetic effect on directed flow in heavy ion collisions

We estimate the electromagnetic effect of the spectator charge on azimuthal anisotropies observed in heavy ion collisions. For peripheral Pb+Pb reactions at the top energy of the CERN Super Proton Synchrotron, $\sqrt{s_{NN}}=17.3$ GeV, we predict this effect to bring very large distortions to the observed directed flow, $v_1$, of positive and negative pions emitted close to beam rapidity. The overall magnitude of this effect is comparable to values of $v_1$ reported by the WA98 experiment. We argue that also at lower rapidities, the spectator induced electromagnetic effect may result in the splitting of values of $v_1$ observed for positive and negative pions. Such a splitting is visible in the data reported by the STAR Collaboration from the RHIC Beam Energy Scan. Both effects are sensitive to the space-time scenario assumed for pion emission. Therefore, they bring new information on the collision dynamics.

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arXiv2013

Strong and Electromagnetic Forces in Heavy Ion Collisions

The interplay between the strong and electromagnetic force in high energy nucleus-nucleus collisions was studied experimentally and theoretically in our earlier works. This effect appeared to result in very large distortions in spectra of charged pions produced in the collision. It was also found to bring new, independent information on the space-time evolution of the non-perturbative process of particle production. In this paper, we present our new results on the influence of the spectator-induced electromagnetic force on spectra of charged particles produced in two different Pb-induced reactions. For the first time, we also address the topic of p+A collisions in view of obtaining information about their centrality and nuclear break-up, both subjects being of importance in the context of the new p+A data collected at the LHC.

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arXiv2013

$π^+ π^-$ and $π^0 π^0$ pair production in photon-photon and in ultraperipheral ultrarelativistic heavy ion collisions

We discuss $γγ\to ππ$ reactions, starting from the two-pion threshold up to about $\sqrt{s_{γγ}}$ = 6 GeV. We include the dipion continuum due to pion exchange (for $π^+π^-$) and $ρ^\pm$ exchange (for $π^0π^0$) as well as the dipion $σ(600)$, $f_0(980)$ and $f_2(1270)$ s-channel resonances. We discuss also a possible contribution of less pronounced scalar resonances $f_0(1500)$ and $f_0(1710)$ as well as the tensor resonances $f'_2(1525)$, $f_2(1565)$ and $f_2(1950)$. We find that the inclusion of the spin-four $f_4(2050)$ resonant state improves the situation at $\sqrt{s_{γγ}} \approx$ 2 GeV. We estimate the relevant diphoton partial decay width to be $Γ_{f_4 \to γγ} \approx$ 0.7 keV. At higher energies, Brodsky-Lepage and hand-bag mechanisms are included in addition. We nicely describe the world data for $γγ\to ππ$ for the first time both for the total cross section and angular distributions. The cross section for the production of two-pions in ultraperipheral ultrarelativistic heavy ion collisions is calculated in the impact parameter space Equivalent Photon Approximation (EPA). We obtain the nuclear cross section of 46.7 mb for $π^+π^-$ and 8.7 mb for $π^0π^0$ at the LHC energy $\sqrt{s_{NN}} =$ 3.5 TeV and minimal cut on pion transverse momentum $p_t>$ 0.2 GeV. Differential distributions in impact parameter, dipion invariant mass, single pion and dipion rapidity, pion transverse momentum as well as pion pseudorapidity are shown. The $γγ\to π^+ π^-$ subprocess constitutes a background to $A A \to A ρ^0 (\to π^+ π^-) A$ process.

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