Abstract
We calculate cross section for production of $D$ mesons and $\Lambda_c$ 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 obtained on the basis of modern collinear gluon distribution functions. 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 $\Lambda_c$ production with the $c \to \Lambda_c$ independent parton fragmentation approach. The Peterson fragmentation functions are used. The $f_{c \to \Lambda_c}$ fragmentation fraction and $\varepsilon_{c}^{\Lambda}$ parameter for $c \to \Lambda_c$ are varied. As a control plot we show transverse momentum distribution of different species of $D$ mesons assuming standard values of the $f_{c \to D}$ fragmentation fractions known from the literature. The fraction $f_{c \to \Lambda_c}$ neccessary to describe the ALICE data is much larger than the average value obtained from $e^+ e^-$ or $e p$ experiments. No drastic modification of the shape of fragmentation function is allowed by the new ALICE and LHCb data for $\Lambda_c$ production. We also discuss a possible dependence of the $\Lambda_c/ D^0$ baryon-to-meson ratio on rapidity and transverse momentum as seems observed recently by the ALICE and LHCb collaborations. Three different effects are considered: the value of $\varepsilon_c^{\Lambda}$ parameter in Peterson fragmentation function for $c \to \Lambda_c$, a kinematical effect related to the hadronization prescription and a possible feed-down from higher charmed-baryon excitations. It seems very difficult, if not impossible, to understand the ALICE data within the considered independent parton fragmentation scheme.
Highlights
The production of charm belongs in principle to the domain of perturbative physics
The parameter will be varied only in the case of the c → Λc transition. This choice of fragmentation function and parameters is based on our previous theoretical studies of open charm production at the LHC [8], where a detailed analysis of uncertainties related to the application of different models of fragmentation functions (FFs) was done
We have discussed the production of Λc baryons in proton-proton collisions at LHC energies
Summary
The production of charm (ccpairs) belongs in principle to the domain of perturbative physics. To describe D-meson production fragmentation functions (FFs) for c → D, quark-to-meson transitions are usually included. The evolution equation leads by construction to g → D fragmentation Such an approach gives a good description of the LHC data at large transverse momenta (pT > 2–3 GeV) but overshoots experimental data at low transverse momenta [9,15]. The evolution approach was done only for massless quarks and it may be expected that the inclusion of a mass effect would probably change the results. It is not clear how initial conditions for evolution should be included. It would be interesting to study whether the fc→Λc fragmentation fraction is consistent with those found in previous studies of eþe−, ep, and B-meson decays
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