A
bstract
We discuss the role of intrinsic charm (IC) in the nucleon for forward production of
c
-quark (or
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
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
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 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 M4c for SPS and DPS production of ccc¯c¯ in the kT-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 pt,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 gg→T4c(6900) fusion mechanism is performed in the kT-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 propose a new complete method, based on the Wigner distributions of photons, how to calculate differential distributions of dileptons created via photon-photon fusion in semicentral (b<2RA) AA ...collisions. The formalism is used to calculate different distributions of invariant mass, dilepton transverse momentum and acoplanarity for different regions of centrality. The results of calculation are compared with recent STAR, ALICE and ATLAS experimental data. Very good agreement with the data is achieved without free parameters and without including additional mechanisms such as a possible rescattering of leptons in the quark-gluon plasma.
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 c¯ are included. The latter mechanism generates D mesons with smaller rapidities than those produced directly. We calculate the D0+D‾0 meson distributions relevant for fixed target p+4He collisions at s = 86.6 GeV as well as for p+20Ne collisions at s = 69 GeV. The recombination component is consistent with the LHCb data and in addition results in production asymmetry. The asymmetries in D0−D0‾ production as a function of rapidity and transverse momentum are shown and the cancellation of terms for direct production and associated c/c¯ fragmentation is discussed.
A
bstract
In this work, we present a thorough analysis of
η
c
(1
S,
2
S
) quarkonia hadroproduction in
k
⊥
-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
(1
S,
2
S
) vertices are derived. We discuss the importance of taking into account the gluon virtualities. 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
c
¯
interaction potential consistent with the meson spectra. We compare our results for
η
c
(1
S
) to measurements by the LHCb collaboration and present predictions for
η
c
(2
S
) production.
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 r5 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.
We calculate inclusive cross section for f2(1270) tensor meson production via color singlet gluon-gluon fusion in the kt-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⁎→f2(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→f2(1270)→ππ reactions. Different modern UGDFs from the literature are used. The results strongly depend on the parametrization of the g⁎g⁎→f2(1270) form factor. Our results for transverse momentum distributions of f2 are compared to preliminary ALICE data. We can obtain agreement with the data only at larger f2(1270) transverse momenta only for some parametrizations of the g⁎g⁎→f2(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 f2(1270) in a harsh quark-gluon and multipion environment. The pomeron-pomeron fusion mechanism is discussed in addition and results are quantified.
We present first measurable predictions for electromagnetic (two-photon) double scattering production of two positron–electron pairs in ultraperipheral heavy-ion collisions at LHC. Measurable cross ...sections are obtained with realistic cuts on electron/positron (pseudo)rapidities and transverse momenta for the ALICE and ATLAS or CMS experiments. The predictions for total and differential cross sections are presented. We show also two-dimensional distributions in rapidities of the opposite-sign (from the same or different subcollisions) and of the same-sign (e+e+ or e−e−) electrons and in rapidity distance between them. Expected number of events are presented and discussed. Our calculations strongly suggest that relevant measurements with the help of ATLAS, CMS and ALICE detectors are possible in a near future. We show and compare energy dependence of the cross sections for one-pair and two-pair production.
We investigate whether the triple-parton scattering effects can be observed in open charm production in proton–proton collisions at the LHC. We use so-called factorized Ansatz for calculations of ...hard multiple-parton interactions. The numerical results for each parton interaction are obtained within the kT-factorization approach. Predictions for one, two and three cc¯ pairs production are given for s=7 TeV and s=13 TeV. Quite large cross sections, of the order of milibarns, for the triple-parton scattering mechanism are obtained. We suggest a measurement of three D0 or three D0¯ mesons by the LHCb Collaboration. Confronting our results with recent LHCb experimental data for single and double D0 (or D0¯) meson production we present our predictions for triple meson final state: D0D0D0 or D0¯D0¯D0¯. We present cross sections for the LHCb fiducial volume as well as distributions for D0 meson transverse momentum and three-D0 meson invariant mass. The predicted visible cross sections, including the detector acceptance, hadronization effects and c→D0 branching fraction, is of the order of a few nanobarns. The counting rates including D0→K−π+ branching fractions are given for known or expected integrated luminosities.
PDF
