arXiv subjects

Antoni Szczurek

Publications and source records attributed to Antoni Szczurek.

At least 109 records · Page 6Linked to original sources

arXiv2019

Do electromagnetic effects survive in the production of lepton pairs in nucleus-nucleus collisions ?

We discuss production of $J/ψ$ and $e^+ e^-$ pairs in semicentral and peripheral collisions of heavy ions at high energies. We focus on photoproduction mechanism. We present explanation of results of the ALICE collaboration for low transverse momentum production of $J/ψ$ as well as results obtained by the STAR collaboration for $e^+ e^-$ production, also at low transverse momenta. We conclude that such effects are important also in this new corner (semi-central processes) of the phase space.

nucl-th↗

arXiv2019

Semiexclusive production of vector mesons in proton-proton collisions with electromagnetic dissociation

We calculate distributions of different vector mesons in purely exclusive ($p p \to p p V$) and semi-exclusive ($p p \to p X V$) processes with electromagnetic dissociation of a proton. The cross section for the electromagnetic dissociation is expressed through electromagnetic structure functions of the proton. We include the transverse momentum distribution of initial photons in the associated flux. Contributions of the exclusive and semi-exclusive processes are compared for different vector mesons ($V = ϕ, J/ψ, Υ$). We discuss how the relative contribution of the semi-exclusive processes depends on the mass of the vector meson as well as on different kinematical variables of the vector meson ($y$, $p_t$). The ratio of semi-exclusive to exclusive contributions are shown and compared for different mesons in different variables.

hep-ph↗

arXiv2019

Diphoton elastic scattering in UPC at smaller $W_{γγ}$

We present a study of photon-photon scattering for $W_{γγ} < 5$ GeV. We extend earlier calculations of this cross section for $W_{γγ}>$ 5 GeV into the low mass range where photoproduction of the pseudoscalar mesons $η$(548), $η^{'}(958)$ and other mesonic resonances contribute to the two-photon final states. We consider the dominant background of the two photon final state which arises from $γγ$ decays of photoproduced $π^{0} π^0$-pairs. We discuss how to reduce the background by imposing cuts on different kinematical variables. We present results for ALICE and LHCb kinematics.

nucl-th↗

arXiv2019

The ${γ^* γ^* \to η_c (1S,2S)}$ transition form factors for spacelike photons

We derive the light-front wave function (LFWF) representation of the $γ^* γ^* \to η_c(1S)\,,η_c(2S)$ transition form factor $F(Q_1^2, Q_2^2)$ for two virtual photons in the initial state. For the LFWF, we use different models obtained from the solution of the Schrödinger equation for a variety of $c \bar c$ potentials. We compare our results to the BaBar experimental data for the $η_c(1S)$ transition form factor, for one real and one virtual photon. We observe that the onset of the asymptotic behaviour is strongly delayed and discuss applicability of the collinear and/or massless limit. We present some examples of two-dimensional distributions for $F (Q_1^2,Q_2^2)$. A factorization breaking measure is proposed and factorization breaking effects are quantified and shown to be almost model independent. Factorization is shown to be strongly broken, and a scaling of the form factor as a function of $\bar Q^2 = (Q_1^2 + Q_2^2)/2$ is obtained.

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arXiv2019

Production of $J/ψ$ quarkonia in color evaporation model based on $k_{T}$-factorization

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 get poor description of the large transverse momentum distributions of $J/ψ$ with the JH-2013 CCFM-based UGDF. Here explicit inclusion of $2 \to 3$ processes considerably improves the situation. Similar effects are discussed in the context of the KMR UGDF.

hep-ph↗

arXiv2019

Enhanced production of $Λ_{c}$ in proton-proton collisions at the LHC

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. 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. Although one can agree with the ALICE data using standard estimation of model uncertainties one cannot describe simultaneously the ALICE and the LHCb data with the same set of parameters. 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. It seems very difficult, if not impossible, to understand the ALICE data within the considered independent parton fragmentation scheme.

hep-ph↗

arXiv2019

Independent quark/antiquark fragmentation to massive particles in proton-proton collisions

We critically discuss fragmentation of quark or antiquark to massive particles (mesons or baryons) in proton-proton collisions. Both heavy and light quark/antiquark fragmentations are discussed using universal $z$-dependent fragmentation functions. Different scenarios how to define the $z$ variable are considered: as a fraction of energy, momentum or light-cone momentum of the parent quark/antiquark. Also a choice of the direction of motion of hadron with respect to the parent parton must be made in the simplest approach. Energy and flavour violation is discussed for the region of small $p_t$ and/or center-of-mass $y \sim$ 0. Results of different approaches are compared. We show that at the LHC energies all schemes become consistent for $D$-meson transverse momenta larger than $2$ GeV. Relations to results from the literature are made. We present some examples for production of D mesons from light and charm quarks/antiquarks. Emission with respect to the direction of motion lowers the cross section of $D$ mesons at larger rapidities compared to the traditional approach ($y_D = y_{q/\bar q}$). As illustrated here the effect of using different prescriptions is particularly large at low energies (fixed target experiments).

hep-ph↗

arXiv2019

Production of $W^+ W^-$ and $t \bar t$ pairs via photon-photon processes in proton-proton collisions

We review our recent results for production of $W^+ W^-$ and $t {\bar t}$ pairs via photon-photon fusion. A theoretical approach is presented in short. We include transverse momenta of photons when calculating fluxes of photons. Then we discuss our results for cross section (total and differential) for $W^+ W^-$ production. Results for different parametrizations of proton structure functions are used to calculate inelastic fluxes of photons. A discussion on rapidity gap survival probability due to remnant fragmentation is presented. A similar discussion is presented for $t {\bar t}$ production.

hep-ph↗

arXiv2019

Searching for odderon in exclusive reactions: $p p \to p p p {\bar p}$, $p p \to p p ϕϕ$ and $p p \to p p ϕ$

There seem to be recently an evidence for $C =$ -1 exchanges in $p p$ and $p \bar p$ elastic scattering at high energies. The analysis there is difficult as the two processes were not measured at the same (large) energies. Here we discuss three different exclusive processes given in the title as a possible source of information for odderon exchange. A sketch of the formalism is presented for each of the reactions. We consider low energy processes measured in the past by the WA102 collaboration and try to make predictions for the LHC. We discuss possible evidences at the low energies and try to make suggestions for the LHC.

hep-ph↗

arXiv2019

Central exclusive diffractive production of $K^{+} K^{-} K^{+} K^{-}$ via the intermediate $ϕϕ$ state in proton-proton collisions

We present a study of the exclusive $pp \to pp K^{+} K^{-} K^{+} K^{-}$ reaction at high energies. We consider diffractive mechanisms with the intermediate $ϕϕ$ state with its decay into the $K^{+} K^{-} K^{+} K^{-}$ system. We include the $ϕ(1020)$ $\hat{t}/\hat{u}$-channel exchanges and the $f_{2}(2340)$ $s$-channel exchange mechanism. This $f_{2}$ state is a candidate for a tensor glueball. We discuss the possibility to use the $pp \to pp ϕϕ$ process in identifying the odderon exchange. An upper limit for the $\mathbb{P} \mathbb{O} ϕ$ coupling is extracted from the WA102 experimental data. The amplitudes for the processes are formulated within the tensor-pomeron and vector-odderon approach. We adjust parameters of our model to the WA102 data and present several predictions for the ALICE, ATLAS, CMS and LHCb experiments. Integrated cross sections of order of a few nb are obtained including the experimental cuts relevant for the LHC experiments. The distributions in the four-kaon invariant mass, rapidity distance between the two $ϕ$ mesons, special ``glueball filter variable'', proton-proton relative azimuthal angle are presented. The distribution in rapidity difference of both $ϕ$-mesons could shed light on the $f_{2}(2340) \to ϕϕ$ coupling, not known at present. We discuss the possible role of the $f_{0}(2100)$, $η(2225)$, and $X(2500)$ resonances observed in the $ϕϕ$ channel in radiative decays of $J/ψ$. Using typical kinematic cuts for LHC experiments we find from our model that the odderon-exchange contribution should be distinguishable from other contributions for large rapidity distance between the $ϕ$ mesons and in the region of large four-kaon invariant masses. At least, it should be possible to derive an upper limit on the odderon contribution in this reaction.

hep-ph↗

arXiv2019

Consistent treatment of charm production in higher-orders at tree-level within $k_T$-factorization approach

We discuss production of $c \bar c$-pairs within $k_T$-factorization approach (off-shell initial partons) with unintegrated parton distribution functions (uPDFs). We present a consistent prescription which merges the standard leading-order (LO) $k_T$-factorization calculations for this process with tree-level next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) matrix elements. For the first time we include in this framework 2 $\to$ 3 and 2 $\to$ 4 processes with extra partonic emissions for single particle distributions as well as for correlation observables. The use of the KMR uPDF leads to a good description of the existing charm ($D$-meson) data already at the leading-order. On the other hand, a new Parton-Branching (PB) uPDF strongly underestimates the same experimental data. A direct inclusion of the higher-orders at tree-level leads to an overestimation of the data, especially for the KMR uPDF. This suggests a significant double-counting. We propose a simple method how to avoid the double-counting. Our procedure leads to a much better description of the experimental data when including the higher-order contributions. Then with the KMR uPDF we get similar results (both for single particle and correlation observables) as for the standard calculations of the 2 $\to$ 2 processes. For the PB uPDF inclusion of the higher-orders considerably improves description of the experimental data. We conclude that the LO calculation with the KMR uPDF effectively includes the higher-orders which is not the case for the PB uPDF.

hep-ph↗

arXiv2019

Light-by-light scattering in ultra-peripheral heavy-ion collisions at low diphoton masses

We present a study of photon-photon scattering in the mass range $W_{γγ} < 5$ GeV. We extend earlier calculations of this cross section for $W_{γγ}>$ 5 GeV into the low mass range where photoproduction of the pseudoscalar resonances $η$, $η^{'}(958)$ contributes to two-photon final states. We present the elementary photon-photon cross section as a function of diphoton mass $M_{γγ}$ arising from lepton and quark loop diagrams, and the visible cross section obtained with the gamma-gamma decay branching fractions of the resonances $η$, $η^{'}(958)$, $η_c(1S)$, $η_c(2S)$, $χ_{c0}(1P)$. We derive the corresponding cross sections in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV by folding the elementary cross section with the heavy-ion photon fluxes. We consider the dominating background of the two-photon final state which arises from gamma decays of photoproduced $π^{0}$-pairs. Such $π^{0}$-pairs contribute to the background when only two of the four decay photons are within the experimental acceptance, while the other two photons escape undetected. We reduce this background by applying cuts on asymmetries of transverse momenta of the two photons and indicate how the background can be further suppressed using a multivariate sideband analysis. We present the cross section for the signal and the background at midrapidity $|η| <$ 0.9, and in the forward rapidity range 2.0 $< η<$ 4.5.

hep-ph↗

arXiv2019

Photon induced processes in semi-central nucleus-nucleus collisions

We calculate total and differential cross sections for $J/ψ$ photoproduction in ultrarelativistic lead-lead collisions at the LHC energy $\sqrt{s_{NN}}=2.76$ TeV. We use a simple model based on vector dominance picture and multiple scattering of the hadronic ($c \bar c$) state in a cold nucleus. In our analysis we use Glauber formulae for calculating $σ_{tot,J/ψPb}$ which is a building block of our model. For semi-central collisions a modification of the photon flux is necessary. We discuss how to effectively correct photon fluxes for geometry effects. We try to estimate the cross sections for different centrality bins and for $J/ψ$ mesons emitted in forward rapidity range ($2.5<y<4$) corresponding to the ALICE experimental results. We discuss similar analysis for dilepton production in ultrarelativistic heavy-ion collisions at very low pair transverse momenta, $P_T\leq 0.15$\,GeV. We investigate the interplay of thermal radiation with photon annihilation processes, $γγ\to l^+ l^-$, due to the coherent electromagnetic fields of the colliding nuclei. For the thermal radiation, we employ the emission from the QGP and hadronic phases with in-medium vector spectral functions. We first verify that the combination of photon fusion, thermal radiation and final-state hadron decays gives a fair description of the low-$P_T$ invariant-mass as well as $P_T$ distributions as measured recently by the STAR collaboration in $\sqrt{s_{NN}}$=200\,GeV Au+Au collisions for different centralities. The coherent contribution dominates in peripheral collisions, while thermal radiation shows a significantly stronger increase with centrality. We also provide predictions for the ALICE experiment at the LHC. The resulting excitation function reveals a nontrivial interplay of photoproduction and thermal radiation.

hep-ph↗

arXiv2019

Associated production of $χ_c$ pairs with a gluon in the collinear-factorization approach

We calculate cross section for production of $χ_c$ pairs in proton-proton collisions. The cross section for the $g g \to χ_{c J_1} χ_{c J_2}$ is considerably smaller (especially for $χ_{c 1} χ_{c 1}$ final state) than that obtained recently in the $k_T$-factorization approach. We calculate therefore next-to-leading order contributions with $χ_c$ pair and one extra associated (mini-)jet. We find these contributions to be much larger than those for the $2 \to 2$ contribution. Especially the emission of a leading gluon (carrying a large momentum fraction of one of the incoming gluons) are important. These emissions in the $k_T$-factorization approach are absorbed into the initial state unintegrated gluon distributions. A smaller contribution to the cross section comes from the production of central gluons emitted with rapidities between the $χ_c$-mesons. They do lead, however, to an enhancement of the $χ_c$-pair production at large rapidity distance between the mesons. Our present study explains the size of the cross section for the $χ_c$ pair production obtained previously in the $k_T$-factorization approach. Several differential distributions are presented.

hep-ph↗

arXiv2019

Rapidity gap survival factors caused by remnant fragmentation for $W^+ W^-$ pair production via $γ^γ^ \to W^+ W^-$ subprocess with photon transverse momenta

We calculate the cross section for $p p \to W^{+} W^-$ in the recently developed $k_{\rm T}$-factorisation approach, including transverse momenta of the virtual photons. We focus on processes with single and double proton dissociation. First we discuss the gap survival on the parton level as due to the emission of extra jet. Both the role of valence and sea contributions is discussed. The hadronisation of proton remnants is performed with {PYTHIA 8} string fragmentation model, assuming a simple quark-diquark model for proton. Highly excited remnant systems hadronise producing particles that can be vetoed in the calorimeter. We calculate associated effective gap survival factors. The gap survival factors depend on the process, mass of the remnant system and collision energy. The rapidity gap survival factor due to remnant fragmentation for double dissociative (DD) collisions ($S_{R,DD}$) is smaller than that for single dissociative (SD) process ($S_{R,SD}$). We observe the approximate factorisation $S_{R,DD} \approx (S_{R,SD})^2$, however it is expected that this property will be violated by soft rescattering effects not accounted for in this letter.

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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

New vistas in charm production

We discuss some new aspects of charm production trigerred by recent observations of the LHCb collaboration. The LHCb collaboration measured small asymmetries in production of $D^+ D^-$ mesons as well as $D_s^+ D_s^-$ mesons. Is this related to initial quark/antiquark asymmetries in the proton ? Here we discuss a scenario in which unfavored fragmentations $q/{\bar q} \to D$ and $s/{\bar s} \to D_s$ are responsible for the asymmetries. We fix the strength of such fragmentations -- transition probabilities, by adjusting to the size of the LHCb asymmetries. This has consequences for production of $D$ mesons in forward directions (large $x_F$) as well as at low energies. Large asymmetries are predicted then in these regions. We present here some of our predictions. Consequences for high-energy neutrino production in the atmosphere are discussed and quantified. The production of $Λ_c$ baryon at the LHC is disussed. Large deviations from the independent-parton fragmentation picture are found.

hep-ph↗

arXiv2018

Production of $t\bar t$ pairs via $γγ$ fusion with photon transverse momenta and proton dissociation

We discuss the production of $t\bar t$ quark-antiquark pairs in proton-proton collisions via the $γγ$ fusion mechanism. We include topologies in which both protons stay intact or one or even both of them undergo dissociation. The calculations are performed within the $k_{\rm T}$-factorisation approach, including transverse momenta of intermediate photons. Photon fluxes associated to inelastic (dissociative) processes are calculated based on modern parameterisations of proton structure functions. We find an integrated cross section of about 2.36 fb at $\sqrt{s}=$ 13 TeV for all contributions. The cross section for the fully elastic process is the smallest. Inelastic contributions are significantly reduced when a veto on outgoing jets is imposed. We present several differential distributions in rapidity and transverse momenta of single $t$ or $\bar t$ quarks/antiquarks as well as distributions in invariant mass of both the $t\bar t$ and masses of dissociated systems. A few two-dimensional distributions are presented in addition.

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