arXiv subjects

Rafal Maciula

Publications and source records attributed to Rafal Maciula.

At least 19 recordsLinked to original sources

arXiv2025

Production of open and hidden charm in fixed-target experiments at the LHC

We discuss the production of $D$ mesons and $J/\psi$ quarkonia in proton-nucleus collisions in the fixed-target LHCb experiment. We consider gluon-gluon fusion within $k_t$-factorization, processes initiated by intrinsic charm in the nucleon and perturbative recombination mechanism. All the mechanisms seem to be necessary to describe the LHCb experimental data. We get an upper limit for the probability of the large-$x$ $c \bar c$ Fock component in the nucleon, which is slightly less than 1 \%. The recombination mechanism allows the description of $D^0$ and $\bar D^0$ asymmetry observed by the LHCb collaboration.\\ We also discuss the production of $J/\psi$ quarkonia, including color singlet mechanisms. We include $g^* g^* \to J/\psi g$ and $g^* g^* \to \chi_c(1^+,2^+)(\to J/\psi \gamma)$ within $k_t$-factorization approach. Different unintegrated gluon distributions from the literature are used. A reasonable agreement is achieved with some distributions from the literature.

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arXiv2024

The asymmetric intrinsic charm in the nucleon and its implications for the $D^{0}$ production in the LHCb $p\!+\!\!^{20}\!N\!e$ fixed-target experiment

Recent results indicate that charm quarks are intrinsic components of the proton wave function, and that the charm and anticharm distributions for a given value of the Bjorken - $x$ variable can be different. In this paper, we will investigate the impact of this asymmetric intrinsic charm on the production of $D^0$ and ${\bar D}^0$ mesons for fixed target $p \!+ ^{20}\!\!Ne$ collisions at the LHCb. In our calculations, we include the contribution of the gluon-gluon fusion, gluon - charm and recombination processes and assume distinct models for the treatment of the intrinsic charm component. We demonstrate that the presence of an intrinsic charm improves the description of the current data for the rapidity and transverse momentum distributions of $D$ mesons. However, such models are not able to describe the LHCb data for the $D^0$-${\bar D}^0$ asymmetry at large transverse momentum, which point out that the description of the intrinsic charm needs to be improved and/or new effects should be taken into account in the production of heavy mesons at forward rapidities in fixed - target collisions.

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arXiv2022

Far-forward production of charm mesons and neutrinos at Forward Physics Facilities at the LHC and the intrinsic charm in the proton

We discuss production of far-forward $D$ mesons/antimesons and neutrinos/antineutrinos from their semileptonic decays in pp-collisions at the LHC. We include the gluon-gluon fusion $gg \to c\bar{c}$, the intrinsic charm (IC) $gc \to gc$ as well as the recombination $gq \to Dc$ partonic mechanisms. The calculations are performed within the $k_T$-factorization approach and the hybrid model using different unintegrated parton distribution functions (uPDFs) for gluons from the literature, as well as within the collinear approach. We compare our results to the LHCb data for forward $D^{0}$-meson production at $\sqrt{s} = 13$ TeV for different rapidity bins in the interval $2 < y < 4.5$. The IC and recombination models are negligible at the LHCb kinematics. Both the mechanisms start to be crucial at larger rapidities and dominate over the standard charm production mechanisms. At high energies there are so far no experiments probing this region. We present also energy distributions for forward electron, muon and tau neutrinos to be measured at the LHC by the currently operating FASER$ν$ experiment, as well as by future experiments like FASER$\nu2$ or FLArE, proposed very recently by the Forward Physics Facility project. Again components of different mechanisms are shown separately. For all kinds of neutrinos (electron, muon, tau) the subleading contributions, i.e. the IC and/or the recombination, dominate over light meson (pion, kaon) and the standard charm production contribution driven by fusion of gluons for neutrino energies $E_ν \gtrsim 300$ GeV. For electron and muon neutrinos both the mechanisms lead to a similar production rates and their separation seems rather impossible. On the other hand, for $ν_τ + {\bar ν}_τ$ neutrino flux the recombination is further reduced making the measurement of the IC contribution very attractive.

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arXiv2022

Recombination mechanism for $D^{0}$-meson production and $D^{0}\!-\!\bar{D^{0}}$ production asymmetry in the LHCb $p\!+\!\!^{20}\!N\!e$ fixed-target experiment

We discuss production of neutral $D$ mesons in proton-proton collisions at the LHC (fixed target mode) in the framework of the BJM recombination model. We present rapidity and transverse momentum distributions of $D$ mesons and compare the recombination contribution to the dominant gluon-gluon fusion mechanism. Both the direct production, as dictated by the matrix element, and fragmentation of the associated $c$ or $\bar c$ are included. The latter mechanism generates $D$ mesons with smaller rapidities than those produced directly. We calculate the $D^0 + {\bar D^{0}}$ meson distributions relevant for fixed target $p\!+\!\!^{4}\!H\!e$ collisions at $\sqrt{s}$ = 86.6 GeV as well as for $p\!+\!\!^{20}\!N\!e$ collisions at $\sqrt{s}$ = 69 GeV. The recombination component is consistent with the LHCb data and in addition results in production asymmetry. The asymmetries in $D^{0}\!-\!\bar{D^{0}}$ production as a function of rapidity and transverse momentum are shown and the cancellation of terms for direct production and associated $c/{\bar c}$ fragmentation is discussed.

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arXiv2022

The Forward Physics Facility: Sites, Experiments, and Physics Potential

The Forward Physics Facility (FPF) is a proposal to create a cavern with the space and infrastructure to support a suite of far-forward experiments at the Large Hadron Collider during the High Luminosity era. Located along the beam collision axis and shielded from the interaction point by at least 100 m of concrete and rock, the FPF will house experiments that will detect particles outside the acceptance of the existing large LHC experiments and will observe rare and exotic processes in an extremely low-background environment. In this work, we summarize the current status of plans for the FPF, including recent progress in civil engineering in identifying promising sites for the FPF and the experiments currently envisioned to realize the FPF's physics potential. We then review the many Standard Model and new physics topics that will be advanced by the FPF, including searches for long-lived particles, probes of dark matter and dark sectors, high-statistics studies of TeV neutrinos of all three flavors, aspects of perturbative and non-perturbative QCD, and high-energy astroparticle physics.

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arXiv2022

Production of forward heavy-flavour dijets at the LHCb within $k_{T}$-factorization approach

We calculate differential cross sections for $c \bar c$- and $b \bar b$-dijet production in $pp$-scattering at $\sqrt{s} = 13$ TeV in the $k_T$-factorization and hybrid approaches with different unintegrated parton distribution functions (uPDFs). We present distributions in transverse momentum and pseudorapidity of the leading jet, rapidity difference between the jets and the dijet invariant mass. Our results are compared to recent LHCb data on forward production of heavy flavour dijets, measured recently for the first time individually for both, charm and bottom flavours. We found that an agreement between the predictions and the data within the full $k_T$-factorization is strongly related to the modelling of the large-$x$ behaviour of the gluon uPDFs which is usually not well constrained. The problem may be avoided following the hybrid factorization approach. Then a good description of the measured distributions is obtained with the Parton-Branching, the Kimber-Martin-Ryskin, the Kutak-Sapeta and the Jung setA0 CCFM gluon uPDFs. We calculate also differential distributions for the ratio of $c \bar c$ and $b \bar b$ cross sections. In all cases we obtain the ratio close to 1 which is caused by the condition on minimal jet transverse momentum ($p_{T}^{\mathrm{jet}} > 20$ GeV) introduced in the experiment, that makes the role of heavy quark mass almost negligible. The LHCb experimental ratio seems a bit larger. We discuss potentially important for the ratio effect of $c$- or $b$-quark gluon radiative corrections related to emission outside of the jet cone. The found effect seems rather small. More refine calculation requires full simulation of $c$- and $b$-jets which goes beyond of the scope of the present paper.

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arXiv2022

Impact of the LHCb $p\!+\!\!^{4}\!H\!e$ fixed-target $D^0/\bar{D^0}$ data on the intrinisic $c \bar c$ component in the nucleon

We discuss the impact of the new LHCb fixed-target $p\!+\!^{4}\!He$ data for $D^0/{\bar D}^0$ production on the intrinsic $c \bar c$ component in the nucleon wave function. Within the scenario presented here neither the traditional gluon-gluon fusion or quark-antiquark annihilation mechanisms calculated in the $k_T$-factorization approach nor their counterparts from the collinear next-to-leading order collinear framework are sufficient to describe the transverse momentum and rapidity distributions of $D^0/{\bar D}^0$ mesons. First the $c{\bar c}$-pair production within the standard frameworks is considered. Here a crucial role of the $c \to D$ hadronization effects at low energies and low transverse momenta is found and discussed, which was not analyzed in previous studies. A contribution related to intrinsic $c \bar c$ component in the nucleon wave function is included in addition. Two models of the symmetric ($c(x) = \bar c(x)$) intrinsic charm (IC) component are considered. The intrinsic charm $g^* c \to g c$ (or $g^* {\bar c} \to g {\bar c}$) contribution needs to be regularized in order to obtain a suppression of the minijet $p_{T}$ spectrum present in the phenomenological minijet model, commonly used in Monte Carlo generators. We show that in our model the regularization parameter can be obtained from the fit to the LHCb fixed-target data under consideration here. We discuss uncertainties of our calculations (scale, charm quark mass, fragmentation function) as well as set limits on the IC probability. According to our model the intrinsic charm probability $P_{IC} = 1.65\%$ allows to significantly improve description of the LHCb data but the number is rather uncertain.

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arXiv2021

Intrinsic charm in the nucleon and forward production of charm: a new constrain from IceCube Neutrino Observatory

The predictions for the atmospheric neutrino flux at high energies strongly depend on the contribution of prompt neutrinos, which are determined by the production of charmed meson in the atmosphere at very forward rapidities. Here we estimate the related cross sections taking into account the presence of an intrinsic charm (IC) component in the proton wave function. The impact on the predictions for the prompt neutrino flux is investigated assuming different values for the probability to find the IC in the nucleon.

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arXiv2021

Impact of intrinsic charm amount in the nucleon and saturation effects on the prompt atmospheric $ν_μ$ flux for IceCube

The predictions for the atmospheric neutrino flux at high energies strongly depend on the contribution of prompt neutrinos, which are determined by the production of charmed meson in the atmosphere at very forward rapidities. In this paper we estimate the related cross sections taking into account the presence of an intrinsic charm (IC) component in the proton wave function and the QCD dynamics modified by the onset of saturation effects. The impact on the predictions for the prompt neutrino flux is investigated assuming different values for the probability to find the IC in the nucleon. Comparison with the IceCube data is performed and conclusions are drawn.

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arXiv2020

Production of $ν_τ$ neutrinos and $\overlineν_tau$ antineutrinos -- elaborate calculation for a fixed target experiment SHiP

We discuss cross sections for $ν_τ$ and ${\overline ν}_τ$ production 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. 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 different contributions to $D_s^{\pm}$ and $ν_τ / {\overline ν}_τ$ production rates are shown explicitly. 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.

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arXiv2020

Intrinsic charm in the nucleon and charm production at large rapidities in collinear, hybrid and $k_T$-factorization approaches

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.

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arXiv2020

QCD predictions for open charm meson production at the LHCb in fixed-target experiment

We investigate open charm meson production in fixed-target LHCb experiment at $\sqrt{s}=86.6$ GeV in $p+^4\!\mathrm{He}$ collisions. Theoretical calculations of charm cross section are done in the framework of the $k_{T}$-factorization approach. Its application in the kinematical range never examined before is carefully discussed. We consider different schemes for the calculations relevant for different unintegrated (transverse momentum dependent) parton densities in a proton. We include in the analysis both CCFM- and DGLAP-based models of unintegrated parton distributions appropriate for the considered kinematics. Integrated as well as differential cross sections as a function of $D^{0}$ meson rapidity and transverse momentum are shown and compared with the experimental data. As a reference point, predictions of next-to-leading order collinear approach are also presented and discussed. A very good agreement between the experimental data and the $k_{T}$-factorization predictions was obtained. Both the CCFM and the DGLAP-based frameworks for parton distributions in a proton are successfully used to explain the LHCb fixed-target open charm cross section.

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arXiv2019

Production asymmetry of $ν_τ$ neutrinos and ${\overline ν}_τ$ antineutrinos from a fixed target experiment SHiP

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.

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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.

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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.

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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).

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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.

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arXiv2018

Double parton scattering effects in heavy meson production

We present results of our theoretical investigation of double-parton scattering (DPS) effects in production of heavy flavour mesons (charm and bottom). We discuss production of charm-bottom and bottom-bottom meson-meson pairs in proton-proton collisions at the LHC. The calculation of DPS mechanism is performed within factorized ansatz where each parton scattering is calculated in the framework of the $k_T$-factorization. The hadronization is done with the help of independent parton fragmentation picture. For completeness we compare results for double- and single-parton scattering (SPS). As in the case of double charm production also here the DPS dominates over the SPS, especially for small transverse momenta. We present several distributions and integrated cross sections with realistic cuts for simultaneous production of $D^0 B^+$ and $B^+ B^+$, suggesting future experimental studies at the LHCb detector.

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