arXiv subjects
Publications and source records attributed to Antoni Szczurek.
Ultra-peripheral collisions (UPCs) involving heavy ions and protons are the energy frontier for photon-mediated interactions. UPC photons can be used for many purposes, including probing low-$x$ gluons via photoproduction of dijets and vector mesons, probes of beyond-standard-model processes, such as those enabled by light-by-light scattering, and studies of two-photon production of the Higgs.
We discuss the production mechanism of a new state, a putative fully charm tetraquark, observed recently by the LHCb at M = 6.9 GeV in the $J/ψJ/ψ$ channel. Both single parton scattering (SPS) and double parton scattering (DPS) mechanisms are considered. We calculate the distribution in the invariant mass of the four-quark system $M_{4c}$ for SPS and DPS production of $c c \bar c \bar c$ in the $k_t$-factorization approach with modern unintegrated gluon distribution functions (UGDFs). The so-calculated contribution of DPS is almost two orders of magnitude larger than the SPS one, but the tetraquark formation mechanism is unknown at present. Imposing a mass window around the resonance position we calculate the corresponding distribution in $p_{t,4c}$ -- the potential tetraquark transverse momentum. The cross section for the $J/ψJ/ψ$ continuum is calculated in addition, again including SPS (box diagrams) and DPS contributions which are of similar size. The formation probability is estimated trying to reproduce the LHCb signal-to-background ratio. The calculation of the SPS $g g \to T_{4c}(6900)$ fusion mechanism is performed in the $k_T$-factorization approach assuming different spin scenarios ($0^+$ and $0^-$). The $0^+$ assignment is preferred over the $0^-$ one by the comparison of the transverse momentum distribution of signal and background with the LHCb preliminary data assuming the SPS mechanism dominance. There is no reliable approach for the DPS formation mechanism of tetraquarks at present as this is a complicated multi-body problem.
We discuss the sensitivity of the $γγ\to τ^+ τ^-$ process in ultraperipheral Pb+Pb collisions on the anomalous magnetic ($a_τ$) and electric ($d_τ$) moments of $τ$ lepton at LHC energies. We derive the corresponding cross sections by folding the elementary cross section with the heavy-ion photon fluxes and considering semi-leptonic decays of both $τ$ leptons in the fiducial volume of ATLAS and CMS detectors. We present predictions for total and differential cross sections, and for the ratios to $γγ\to e^+ e^- (μ^+ μ^-$) process. These ratios allow to cancel theoretical and experimental uncertainties when performing precision measurement of $a_τ$ at the LHC. The expected limits on $a_τ$ with existing Pb+Pb dataset are found to be better by a factor of two comparing to current best experimental limits and can be further improved by another factor of two at High Luminosity LHC.
We investigate consequences of local energy-momentum conservation for initial eccentricity coefficients in heavy ion collisions at not too high energies relevant for CERN SPS and RHIC BES. Different models of energy density available for pion production are considered. We study dependence of eccentricity coefficients on space-time rapidity for different impact parameters. The naive formula how to define eccentricities breaks with our initial conditions and must be corrected. We predict considerable eccentricities for $ε_{1,2,3,4}$ and specific dependence on space-time rapidity as well as on impact parameter for lower energies. The effect becomes smaller at larger energies when restricting to narrow rapidity interval arround zero. Our predictions are in principle input for further hydrodynamical evolution but it is not clear whether they can be easily used. Our initial condition suggest a strong preequilibrium phase which is difficult for modelling.
We calculate inclusive cross section for $f_2(1270)$ tensor meson production via color singlet gluon-gluon fusion in the $k_t$-factorization approach with unintegrated gluon distribution functions (UGDFs). The process may be potentially interesting in the context of searches for saturation effects. The energy-momentum tensor, equivalent to helicity-2 coupling, and helicity-0 coupling are used for the $g^* g^* \to f_2(1270)$ vertex. Two somewhat different parametrizations of helicity-2 and helicity-0 tensorial structure from the literature are used in our calculations. Some parameters are extracted from $γγ\to f_2(1270) \to ππ$ reactions. Different modern UGDFs from the literature are used. The results strongly depend on the parametrization of the $g^* g^* \to f_2(1270)$ form factor. Our results for transverse momentum distributions of $f_2$ are compared to preliminary ALICE data. We can obtain agreement with the data only at larger $f_2(1270)$ transverse momenta only for some parametrizations of the $g^* g^* \to f_2(1270)$ form factor. No obvious sign of the onset of saturation is possible. At low transverse momenta one needs to include also the $ππ$ final-state rescattering. The agreement with the ALICE data can be obtained by adjusting probability of formation and survival of $f_2(1270)$ in a harsh quark-gluon and multipion environment. The pomeron-pomeron fusion mechanism is discussed in addition and results are quantified.
We discuss the role of intrinsic charm (IC) in the nucleon for forward production of $c$-quark (or $\bar c$-antiquark) in proton-proton collisions for low and high energies. The calculations are performed in collinear-factorization approach with on-shell partons, $k_T$-factorization approach with off-shell partons as well as in a hybrid approach using collinear charm distributions and unintegrated (transverse momentum dependent) gluon distributions. For the collinear-factorization approach we use matrix elements for both massless and massive charm quarks/antiquarks. The distributions in rapidity and transverse momentum of charm quark/antiquark are shown for a few different models of IC. Forward charm production is dominated by $gc$-fusion processes. The IC contribution dominates over the standard pQCD (extrinsic) $gg$-fusion mechanism of $c\bar c$-pair production at large rapidities or Feynman-$x_F$. We perform similar calculations within leading-order and next-to-leading order $k_T$-factorization approach. The $k_T$-factorization approach leads to much larger cross sections than the LO collinear approach. At high energies and large rapidities of $c$-quark or $\bar c$-antiquark one tests gluon distributions at extremely small $x$. The IC contribution has important consequences for high-energy neutrino production in the Ice-Cube experiment and can be, to some extent, tested at the LHC by the SHIP and FASER experiments by studies of the $ν_τ$ neutrino production.
We propose a new procedure for parton-to-hadron fragmentation in proton-proton collisions. The hadronization is considered in the parton-parton center-of-mass system and hadrons are assumed to be emitted in the direction of outgoing partons in that frame and then their four-momenta are transformed to the overall center-of-mass system using relevant Lorentz transformations and appropriate distributions are constructed. For heavy hadron production the energy-momentum condition is imposed. In many cases our procedure disagrees with the commonly used rule that rapidity of produced hadron is the same as rapidity of the parent parton. We illustrate the newly proposed scheme for production of $D$ mesons, $Λ_c$ baryon and $η_c$ quarkonium in leading-order approach to parton production. The transverse momentum, rapidity and Feynman-$x_F$ distributions are shown. We consider $c \to D$ and $g \to D$ as well as $c \to η_c$ and $g \to η_c$ hadronization processes. The resulting rapidity distributions are much narrower than those obtained in the traditional approach with parton-hadron rapidity equivalence. This has consequences both for mid- and forward rapidities and could have consequences for high-energy neutrino production in the Earth's atmosphere. We discuss also $c \to Λ_c^+$ and $b \to Λ_c^+$ fragmentation and find that the second mechanism could be partly responsible for the enhanced production of $Λ_c^{\pm}$ observed recently by the ALICE collaboration.
We calculate cross sections for production of axial-vector $f_1(1285)$ mesons for double-tagged measurements of the $e^+ e^- \to e^+ e^- f_1(1285)$ reaction. Different $γ^* γ^* \to f_1(1285)$ vertices from the literature are used. Both integrated cross section as well as differential distributions are calculated. Predictions for a potential measurement at Belle II are presented. Quite different results are obtained for the different vertices proposed in the literature. Future measurements at $e^+ e^-$ colliders could test and/or constrain the $γ^* γ^* \to f_1 (a_1, f_1')$ vertices and associated form factors, known to be important ingredients for calculating contributions to anomalous magnetic moment of muon and hyperfine splitting of levels of muonic atoms.
The production of the $f_{0}(980)$ meson at high energies is not well understood. We investigate two different potential mechanisms for inclusive scalar meson production in the $k_t$-factorization approach: color-singlet gluon-gluon fusion and color evaporation model. The $γ^* γ^* \to f_0(980)$ form factor(s) can be constraint from the $f_0(980)$ radiative decay width. The $g^* g^* \to f_0(980)$ form factors are obtained by a replacement of $α_{\rm{em}}$ electromagnetic coupling constant by $α_{\rm{s}}$ strong coupling constant and appropriate color factors. The form factors for the two couplings are parametrized with a function motivated by recent results for scalar quarkonia. The differential cross sections are calculated in the $k_t$-factorization approach with modern unintegrated gluon distributions. Unlike for quarkonia it seems rather difficult to describe a preliminary ALICE data for inclusive production of $f_0(980)$ exclusively by the color singlet gluon-gluon fusion mechanism. Two different scenarios for flavor structure of $f_0(980)$ are considered in this context. We consider also mechanism of fusion of quark-antiquark associated with soft gluon emission in a phenomenological color evaporation model (CEM) used sometimes for quarkonium production. Here we use $k_t$-factorization version of CEM to include higher-order contributions. In addition, for comparison we consider also NLO collinear approach with $q \bar{q} q$ and $q \bar{q} g$ color octet partonic final states. Both approaches lead to a similar result. However, very large probabilities are required to describe the preliminary ALICE data. The pomeron-pomeron fusion mechanism is also discussed and results are quantified.
We explore the possibility of observing odderon exchange in the $pp \to pp K^{+}K^{-}$ and $pp \to pp μ^{+}μ^{-}$ reactions at the LHC. We consider the central exclusive production (CEP) of the $ϕ(1020)$ resonance decaying into $K^{+} K^{-}$ and $μ^{+}μ^{-}$. We compare the purely diffractive contribution (odderon-pomeron fusion) to the photoproduction contribution (photon-pomeron fusion). The theoretical results are calculated within the tensor-pomeron and vector-odderon model for soft reactions. We include absorptive corrections at the amplitude level. In order to fix the coupling constants for the photon-pomeron fusion contribution we discuss the reactions $γp \to ωp$ and $γp \to ϕp$ including $ϕ$-$ω$ mixing. We compare our results for these reactions with the available data, especially those from HERA. Our coupling constants for the pomeron-odderon-$ϕ$ vertex are taken from an analysis of the WA102 data for the $p p \to p p ϕ$ reaction. We show that the odderon-exchange contribution significantly improves the description of the $pp$ azimuthal correlations and the $dP_{t}$ "glueball-filter variable" dependence of $ϕ$ CEP measured by WA102. To describe the low-energy data more accurately we consider also subleading processes with reggeized vector-meson exchanges. However, they do not play a significant role at the LHC. We present predictions for two possible types of measurements: at midrapidity and with forward measurement of protons (relevant for ATLAS-ALFA or CMS-TOTEM), and at forward rapidities and without measurement of protons (relevant for LHCb). We discuss the influence of experimental cuts on the integrated cross sections and on various differential distributions. With the corresponding LHC data one should be able to get a decisive answer concerning the presence of an odderon-pomeron fusion contribution in single $ϕ$ CEP.
We discuss production of $W^+ W^-$ pairs and $t \bar t$ quark-antiquark pairs in proton-proton collisions induced by two-photon fusion including transverse momenta of incoming photons. The unintegrated inelastic fluxes (related to proton dissociation) of photons are calculated based on modern parametrizations of deep inelastic structure functions in a broad range of $x$ and $Q^2$. We focus on processes with single and double proton dissociation. Highly excited remnant systems hadronise producing particles that can be vetoed in the calorimeter. We calculate associated 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 is smaller than that for single dissociative (SD) process. We observe approximate factorisation: $S_{R,DD} \approx S_{R,SD}^2$ when imposing rapidity veto. For the $W^+W^-$ final state, the remnant fragmentation leads to a taming of the cross section when the rapidity gap requirement is imposed. Also for $t \bar t$ quark-antiquark pairs such a condition reverses the hierarchy observed for the case when such condition is taken into account. Our results imply that for the production of such heavy objects as $t$ quark and $\bar t$ antiquark the virtuality of the photons attached to the dissociative system are very large ($Q^2 <$ 10$^{4}$ GeV$^2$). A similar effect is observed for the $W^+ W^-$ system.
We review our recent results for production of $η_c(1S)$ and $η_c(2S)$ in the $γ^* γ^* \to η_c(1S,2S)$ fusion and in proton-proton collisions via gluon-gluon fusion. The quarkonium wave functions are calculated by solving Schrödinger equation for different $c \bar c$ potentials. Using Terentev prescription the light-cone wave functions are obtained. The light-cone wave functions are used then to calculate $γ^* γ^* \to η_c$ transition form factors. The theoretical results are compared to the Belle experimental data for $η_c(1S)$. In addition we discuss our results for two-photon decay width. We present also results of our calculations for proton-proton collisions obtained within $k_T$-factorization approach for different unintegrated gluon distributions. The results for hadroproduction of $η_c(1S)$ are compared to the LHCb experimental data.
In this work, we present a thorough analysis of scalar $P$-wave $χ_{Q0}$, $Q=c,b$ quarkonia electromagnetic form factors for the $γ^* γ^* \to χ_{Q0}$ couplings, as well as their hadroproduction observables in $k_\perp$-factorisation using the light-front potential approach for the quarkonium wave function. The electromagnetic form factors are presented as functions of photon virtualities. We discuss the role of the Melosh spin-rotation and relativistic corrections estimated by comparing our results with those in the standard nonrelativistic QCD (NRQCD) approach. Theoretical uncertainties of our approach are found by performing the analysis with two different unintegrated gluon densities and with five distinct models of the $Q\bar Q$ interaction potentials consistent with the meson spectra. The results for the rapidity and transverse momentum distributions of $χ_{Q0}$ produced in high-energy $pp$ collisions at $\sqrt{s} = 13 \, \rm{TeV}$ are shown.
We discuss how to extract the pomeron-pomeron-$f_2(1270)$ ($\mathbb{P} \mathbb{P} f_2(1270)$) coupling within the tensor-pomeron model. The general $\mathbb{P} \mathbb{P} f_2(1270)$ coupling is a combination of seven basic couplings (tensorial structures). To study these tensorial structures we propose to measure the central-exclusive production of a $π^+ π^-$ pair in the invariant mass region of the $f_2(1270)$ meson. An analysis of angular distributions in the $π^+ π^-$ rest system, using the Collins-Soper (CS) and the Gottfried-Jackson (GJ) frames, turns out to be particularly relevant for our purpose. For both frames the $\cosθ_{π^{+}}$ and $ϕ_{π^{+}}$ distributions are discussed. We find that the azimuthal angle distributions in these frames are fairly sensitive to the choice of the $\mathbb{P} \mathbb{P} f_2$ coupling. We show results for the resonance case alone as well as when the dipion continuum is included. We show the influence of the experimental cuts on the angular distributions in the context of dedicated experimental studies at RHIC and LHC energies. Absorption corrections are included for our final distributions.
In this work, we present a thorough analysis of $η_c(1S,2S)$ quarkonia hadroproduction in $k_\perp$-factorisation in the framework of the light-front potential approach for the quarkonium wave function. The off-shell matrix elements for the $g^* g^* η_c(1S,2S)$ vertices are derived. We discuss the importance of taking into account the gluon virtualities. %We discuss the role of relativistic corrections, the Melosh spin-rotation and theoretical uncertainties by comparing our results with the standard NRQCD approach. We present the transverse momentum distributions of $η_c$ for several models of the unintegrated gluon distributions. Our calculations are performed for four distinct parameterisations for the $c\bar c$ interaction potential consistent with the meson spectra. We compare our results for $η_c(1S)$ to measurements by the LHCb collaboration and present predictions for $η_c(2S)$ production.
The centrality dependence of rapidity distributions of pions in Pb+Pb reactions can be understood by imposing local energy-momentum conservation in the longitudinal "fire-streaks" of excited matter. With no tuning nor adjustment to the experimental data, the rapidity distribution of pions produced by the fire-streak which we obtained from Pb+Pb collisions reproduces the shape of the experimental pion rapidity distribution in p+p interactions, measured by the NA49 Collaboration at the same energy. The observed difference in the absolute normalization of this distribution can be explained by the difference in the overall energy balance, induced by baryon stopping and strangeness enhancement phenomena occurring in heavy ion collisions. We estimate the latter effects using a collection of SPS experimental data on $π^\pm$, $K^\pm$, net $p$, and $n$ production in p+p and Pb+Pb reactions. Implications of the above findings are discussed.
We discuss the possibility to use the $pp \to pp ϕϕ$ process in identifying the odderon exchange. So far there is no unambiguous experimental evidence for the odderon, the charge conjugation $C = -1$ counterpart of the $C= +1$ pomeron. Last year results of the TOTEM collaboration suggest that the odderon exchange can be responsible for a disagreement of theoretical calculations and the TOTEM data for elastic proton-proton scattering. Here we present recent studies for central exclusive production (CEP) of $ϕϕ$ pairs in proton-proton collisions. We consider the pomeron-pomeron fusion to $ϕϕ$ ($\mathbb{P}\mathbb{P} \to ϕϕ$) through the continuum processes, due to the $\hat{t}$- and $\hat{u}$-channel reggeized $ϕ$-meson, photon, and odderon exchanges, as well as through the $s$-channel resonance process ($\mathbb{P}\mathbb{P} \to f_{2}(2340) \to ϕϕ$). This $f_{2}$ state is a candidate for a tensor glueball. The amplitudes for the processes are formulated within the tensor-pomeron and vector-odderon approach. Some model parameters are determined from the comparison to the WA102 experimental data. The odderon exchange is not excluded by the WA102 data for high $ϕϕ$ invariant masses. The measurement of large $M_{ϕϕ}$ or $\rm{Y_{diff}}$ events at the LHC would therefore suggest presence of the odderon exchange.
We discuss how to calculate cross sections as well as rapidity, transverse momentum and energy distributions of $ν_τ$ and ${\overline ν}_τ$ produced from the direct $D_s^{\pm} \to ν_τ/{\overline ν}_τ$ and chain $D_s^{\pm} \to τ^+/τ^- \to ν_τ/{\overline ν}_τ$ decays in $p\!+^{96}\!\mathrm{Mo}$ scattering with proton beam $E_{\mathrm{lab}}$ = 400 GeV \textit{i.e.} at $\sqrt{s}_{NN}$ = 27.4 GeV. The $τ$ decays are simulated with the help of the \textsc{Tauola} code and include multiple decay channels of $τ$ in amounts proportional to their branching ratios. In our calculations we include $D_s^{\pm}$ from charm fragmentation $c \to D_s^{+}$ and $\bar c \to D_s^-$ as well as those from subleading fragmentation of strange quarks/antiquarks $s \to D_s^-$ and $\bar s \to D_s^+$. The $s \ne \bar s$ asymmetry of the strange quark content of proton is included. The different contributions to $D_s^{\pm}$ and $ν_τ / {\overline ν}_τ$ are shown explicitly. We discuss and quantify a not discussed so far effect of asymmetries for production of $ν_τ$ and ${\overline ν}_τ$ caused by subleading fragmentation mechanism and discuss related uncertainties. A potential measurement of the asymmetry is discussed. Estimates of a number of observed $ν_τ / \overlineν_τ$ in the $ν_τ / \overlineν_τ +^{208}\!\mathrm{Pb}$ reaction, with 2m long target are given with the help of the NuWro program. We refer also to the production of the high-energy (anti)neutrinos in the atmosphere.