arXiv subjects

Antoni Szczurek

Publications and source records attributed to Antoni Szczurek.

At least 181 records · Page 10Linked to original sources

arXiv2016

Diffractive production of heavy mesons at the LHC within $k_t$ - factorization approach

We discuss diffractive production of heavy mesons at the LHC. The differential cross sections for single- and central-diffractive mechanisms for $c\bar c$ pair production are calculated in the framework of the Ingelman-Schlein model corrected for absorption effects. Here, leading-order gluon-gluon fusion and quark-antiquark anihilation partonic subprocesses are taken into consideration. Both pomeron flux factors as well as parton distributions in the pomeron are taken from the H1 Collaboration analysis of diffractive structure function and diffractive dijets at HERA. The extra corrections from subleading reggeon exchanges are also taken into consideration. In addition to standard collinear approach, for the first time the differential cross sections for the diffractive $c\bar c$ pair production are calculated in the framework of the $k_t$-factorization approach, i.e. effectively including higher-order corrections. The unintegrated (transverse momentum dependent) diffractive parton distributions in proton are calculated with the help of the Kimber-Martin-Ryskin prescription where collinear diffractive PDFs are used as input. Some correlation observables, like azimuthal angle correlation between $c$ and $\bar c$, and $c \bar c$ pair transverse momentum were obtained for the first time. The hadronization of charm quarks is taken into account by means of fragmentation function technique.

hep-ph↗

arXiv2016

From deep-inelastic structure functions to two-photon dilepton production in proton-proton collisions

We compare two different approaches used for calculating cross sections for the two-photon $p p \to l^+ l^- X$ process. In one of the approaches photon is treated as a collinear parton in the proton. In the second approach a recently proposed $k_T$-factorization method is used. In this presentation we discuss sensitivity of the results to the choice of structure function parametrization and experimental cuts in the $k_T$-factorization approach. We compare results of our calculations with recent experimental data for dilepton production and find that in most cases the contribution of the photon-photon mechanism is rather small. We discuss how to enhance the photon-photon contribution. We also compare our results to those of recent measurements of exclusive and semi-exclusive $e^+ e^-$ pair production with certain experimental data by the CMS collaboration.

hep-ph↗

arXiv2016

New single- and double-parton scattering mechanisms for double charmed meson production

We discuss charm meson-meson pair production recently observed by the LHCb Collaboration at $\sqrt{s}$ = 7 TeV in proton-proton scattering. We examine double-parton scattering (DPS) mechanisms of double $c \bar c$ production and following $cc \to D^{0}D^{0}$ hadronization as well as double $g$ and mixed $g c\bar c $ production with $gg \to D^{0}D^{0}$ and $gc \to D^{0}D^{0}$ hadronization calculated with the help of the scale-dependent KKKS08 fragmentation functions. A new single-parton scattering (SPS) mechanism of $gg$ production is also taken into consideration. Calculated differential distributions as a function of transverse momentum $p_{T}$ of one of the $D^{0}$ mesons, pair invariant mass $M_{D^{0}D^{0}}$ and azimuthal angle $φ_{D^{0}D^{0}}$ distributions are confronted with the measured ones. The manifestation of the new SPS mechanisms with $g \to D^{0}$ fragmentation within the scale-dependent fragmentation scheme change the overall picture suitable for standard scale-independent fragmentation where only DPS $cc \to D^{0}D^{0}$ mechanism is present. Some consequences of the new mechanisms are discussed

hep-ph↗

arXiv2016

Light-by-light scattering in UPC at the LHC

We discuss diphoton semi(exclusive) production in ultraperipheral $PbPb$ collisions at energy of $\sqrt{s_{NN}}=$ 5.5 TeV (LHC). The nuclear calculations are based on equivalent photon approximation in the impact parameter space. The cross sections for elementary $γγ\to γγ$ subprocess are calculated including two different mechanisms: box diagrams with leptons and quarks in the loops and a VDM-Regge contribution with virtual intermediate hadronic excitations of the photons. We got relatively high cross sections in $PbPb$ collisions ($306$ nb). This opens a possibility to study the $γγ\to γγ$ (quasi)elastic scattering at the LHC. We find that the cross section for elastic $γγ$ scattering could be measured in the lead-lead collisions for the diphoton invariant mass $W_{γγ} \approx 15-20$ GeV.

hep-ph↗

arXiv2016

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

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

hep-ph↗

arXiv2016

Searching for optimal conditions for exploration of double-parton scattering in four-jet production at the LHC

We discuss the double-parton scattering (DPS) effects in four-jet production at the LHC. A special attention is given to the optimization of kinematical conditions in order to enhance the relative contribution of DPS in four-jet sample. The calculations of single-parton and double-parton scattering components are done in the high-energy (or $k_{T}$)-factorization approach. Here we follow our recent developments of relevant methods and tools that are implemented in the AVHLIB Monte Carlo library. Several differential distributions are calculated and carefully discussed in the context of recent and future searches for DPS effects at the LHC, for both $\sqrt{s} = 7$ and $13$ TeV energies. The dependences of the relative DPS amount is studied as a function of rapidity of jets, rapidity distance, and various azimuthal correlations between jets. The regions with an enhanced DPS contribution are identified.

hep-ph↗

arXiv2016

Search for optimal conditions for exploring double-parton scattering in four-jet production: $k_t$-factorization approach

In the present paper we discuss how to maximize the double-parton scattering (DPS) contribution in four-jet production by selecting kinematical cuts. Here both single-parton and double-parton scattering effects are calculated in the $k_T$-factorization approach, following our recent developments of relevant methods and tools. Several differential distributions are shown and discussed in the context of future searches for DPS effects, such as rapidity of jets, rapidity distance, and azimuthal correlations between jets. The dependences of the relative DPS amount is studied as function of those observables. The regions with an enhanced DPS contribution are identified. Future experimental explorations could extract more precise values of $σ_{eff}$ and its potential dependence on kinematical variables.

hep-ph↗

arXiv2016

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

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

hep-ph↗

arXiv2016

Single-diffractive production of charmed mesons at the LHC within the $k_t$-factorization approach

We discuss the single diffractive production of $c \bar c$ pairs and charmed mesons at the LHC. For a first time we propose a $k_t$-factorization approach to the diffractive processes. The transverse momentum dependent diffractive parton distributions are obtained from standard (collinear) diffractive parton distributions used in the literature. In this calculation the transverse momentum of the pomeron is neglected with respect to transverse momentum of partons entering the hard process. We also perform the first evaluation of the cross sections at the LHC using the diffractive transverse momentum dependent parton distributions. The results of the new approach are compared with those of the standard collinear one. Significantly larger cross sections are obtained in the $k_t$-factorization approach where some part of higher-order effects is effectively included. The differences between corresponding differential distributions are discussed. Finally, we present a feasibility study of the process at the LHC using proton tagging technique. The analysis suggests that the measurement of single diffractive charm production is possible using ATLAS and CMS/TOTEM detectors.

hep-ph↗

arXiv2016

Two-gluon exchange contribution to elastic $γγ\to γγ$ scattering and production of two-photons in ultraperipheral ultrarelativistic heavy ion and proton-proton collisions

We discuss the two-gluon exchange contribution (formally three-loops) to elastic photon-photon scattering in the high-energy approximation. The elastic $γγ\to γγ$ amplitude is given in the impact-factor representation for all helicity configurations and finite quark masses. We discuss the importance of including the charm quark, which contribution, due to interference, can enhance the cross section considerably. We investigate the contribution to the $γγ\to γγ$ amplitude from the soft region, by studying its dependence on nonperturbative gluon mass. Helicity-flip contributions are shown to be much smaller than helicity-conserving ones. We identify region(s) of phase space where the two-gluon exchange contribution becomes important ingredient compared to box and nonperturbative VDM-Regge mechanisms considered in the literature. Consequences for the $A A \to A A γγ$ reaction are discussed. Several differential distributions are shown. A feasibility study to observe the effect of two-gluon exchange is presented. We perform a similar analysis for the $p p \to p p γγ$ reaction. Only by imposing severe cuts on $M_{γγ}$ and a narrow window on photon transverse momenta the two gluon contribution becomes comparable to the box contribution but the corresponding cross section is rather small.

hep-ph↗

arXiv2016

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

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

hep-ph↗

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

New mechanisms for double charmed meson production at the LHCb

We discuss production of $D^0 D^0$ (and ${\bar D}^0 {\bar D}^0$) pairs related to the LHCb Collaboration results for $\sqrt{s}$ = 7 TeV in proton-proton scattering. We consider double-parton scattering (DPS) mechanisms of double $c \bar c$ production and subsequent $cc \to D^{0}D^{0}$ hadronization as well as double $g$ and mixed $g c\bar c $ production with $gg \to D^{0}D^{0}$ and $gc \to D^{0}D^{0}$ hadronization calculated with the help of the scale-dependent hadronization functions of Kniehl et al. Single-parton scattering (SPS) mechanism of digluon production is also taken into account. We compare our results with several correlation observables in azimuthal angle $φ_{D^{0}D^{0}}$ between $D^{0}$ mesons or in dimeson invariant mass $M_{D^{0}D^{0}}$. The inclusion of new mechanisms with $g \to D^{0}$ fragmentation leads to larger cross sections, than when including only DPS mechanism with standard scale-independent $cc \to D^{0}D^{0}$ fragmentation functions. Some consequences of the presence of the new mechanisms are discussed. In particular a larger $σ_{eff}$ is needed to describe the LHCb data. There is a signature that $σ_{eff}$ may depend on transverse momentum of $c$ quarks and/or $\bar c$ antiquarks.

hep-ph↗

arXiv2016

Four-jet production in single- and double-parton scattering within high-energy factorization

We perform a first study of 4-jet production in a complete high-energy factorization (HEF) framework. We include and discuss contributions from both single-parton scattering (SPS) and double-parton scattering (DPS). The calculations are performed for kinematical situations relevant for two experimental measurements (ATLAS and CMS) at the LHC. We compare our results to those reported by the ATLAS and CMS collaborations for different sets of kinematical cuts. The results of the HEF approach are compared with their counterparts for collinear factorization. For symmetric cuts the DPS HEF result is considerably smaller than the one obtained with collinear factorization. The mechanism leading to this difference is of kinematical nature. We conclude that an analysis of inclusive 4-jet production with asymmetric $p_T$-cuts below 50 GeV would be useful to enhance the DPS contribution relative to the SPS contribution. In contrast to the collinear approach, the HEF approach nicely describes the distribution of the $ΔS$ variable, which involves all four jets and their angular correlations.

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

Can we obtain a "new femtoscopy" on the basis of electromagnetic effects?

We review our studies of spectator-induced electromagnetic (EM) effects on charged pion emission in ultrarelativistic heavy ion collisions. These effects are found to consist in the electromagnetic {charge splitting} of pion directed flow as well as very large distortions in spectra and ratios of produced charged particles. As it emerges from our analysis, they offer sensitivity to the actual distance $d_E$ between the pion formation zone at freeze-out and the spectator matter. As a result, this gives a new possibility of studying the space-time evolution of dense and hot matter created in the course of the collision. Having established that $d_E$ traces the longitudinal evolution of the system and therefore rapidly decreases as a function of pion rapidity, we investigate the latter finding in view of pion feed-over from intermediate resonance production. As a result we obtain a first estimate of the pion decoupling time from EM effects which we compare to existing HBT data. We conclude that spectator-induced EM interactions can serve as a new tool for studying the space-time characteristics and longitudinal evolution of the system.

nucl-th↗

arXiv2016

Low mass Drell-Yan production of lepton pairs at forward directions at the LHC: a hybrid approach

We discuss Drell-Yan production of dileptons at high energies in forward rapidity region in a hybrid high-energy approach. This approach uses unintegrated gluon distributions in one proton and collinear quark/antiquark distributions in the second proton. Corresponding momentum-space formula for the differential cross sections in high-energy approximation has been derived and will be presented. The relation to the commonly used dipole approach is discussed. We conclude and illustrate that some results of the dipole approaches are too approximate, as far as kinematics is considered, and in fact cannot be used when comparing with real experimental data. We find that the dipole formula is valid only in very forward/backward rapidity regions ($|y| >$ 5) that cannot be studied experimentally in the moment. We performed calculations of some differential cross sections for low-mass dilepton production by the LHCb and ATLAS collaborations. In distinction to most of dipole approaches, we include all of the four Drell-Yan structure functions, although the impact of interference structure functions is rather small for the relevant experimental cuts. We find that both side contributions ($g + q/\bar q$ and $q/\bar q + g$) have to be included even for the LHCb rapidity coverage which is in contradiction with what is usually done in the dipole approach. We present results for different unintegrated gluon distributions from the literature (some of them include saturation effects). We see no clear hints of saturation even at small $M_{ll}$ when comparing with the LHCb data.

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↗