Production of Λc baryons at the LHC within the kT -factorization approach and independent parton fragmentation picture

Abstract

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 cc 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 Λ c production with the c → Λ c independent parton fragmentation approach. The Peterson fragmentation functions are used. The f c→Λ c fragmentation fraction and ε Λ c parameter for c → Λ 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→D fragmentation fractions known from the literature.The fraction f c→Λ c neccessary to describe the ALICE data is much larger than the average value obtained from e + e − or ep experiments. No drastic modification of the shape of fragmentation function is allowed by the new ALICE and LHCb data for Λ c production. We also discuss a possible dependence of the Λ 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 ε Λ c parameter in Peterson fragmentation function for c → Λ c , a kinematical effect related to the hadronization prescription and a possible feed-down from higher charmedbaryon excitations. It seems very difficult, if not impossible, to understand the ALICE data within the considered independent parton fragmentation scheme.

Measurement of $${{\mathrm{D}}^0}$$, $${{\mathrm{D}}^+}$$, $${{\mathrm{D}}^{*+}}$$ and $${{\mathrm{D}}^+_{\mathrm{s}}}$$ production in pp collisions at $${\sqrt{{\textit{s}}}~=~5.02~{\text {TeV}}}$$ with ALICE

“…In the evaluation of the systematic uncertainties on these ratios, the sources of correlated and uncorrelated systematic effects were treated separately. In particular, the contributions of the yield [39,40], GM-VFNS(SACOT-m T ) [6], and k T -factorisation [41]. The ratios of the data to the theoretical predictions are shown in the lower part of each panel D * + and D + s mesons.…”

“…The most precise measurement of the prompt D 0 -meson production cross section is obtained using the results of the analysis without decay-vertex reconstruction in the interval 0 < p T < 1 GeV/c and those of the analysis with decayvertex reconstruction for p T > 1 GeV/c. , two calculations using the GM-VNFS framework with different prescriptions to regulate the divergences at small transverse momentum, dubbed as GM-VFNS(mod-μ R,F ) [39,40] and GM-VFNS(SACOT-m T ) [6], and a calculation based on k Tfactorisation [41]. The GM-VFNS(mod-μ R,F ) calculations were performed with a different choice of the factorisation and renormalisation scales μ F and μ R with respect to the GM-VFNS predictions of Ref.…”

“…In GM-VFNS(SACOT-m T ), the divergences of the heavy-quark PDFs and light-parton fragmentation functions at low p T are regulated by the heavyquark mass, thus allowing the calculation of the D-meson cross section down to p T = 0. Note also that the authors of the k T -factorisation calculations changed the treatment of the running strong coupling constant α S and the gluon distributions [41], with respect to the predictions shown in Ref. [27].…”

Charm-baryon production in proton-proton collisions

“…However, recent mesurements of charm-baryon production in proton-proton (pp) collisions by the ALICE collaboration at the LHC held a surprise; specifically, the cross section ratio of prompt Λ c over D 0 -mesons, Λ c /D 0 ≃ 0.54, measured at √ s = 7 GeV [17] turns out to be much larger than expected in most event generators [2,3,4,18,19], as well as in the SHM where it is ∼ 0.22 [11] based on charm-hadron states listed by the particle data group (PDG) [20]. Recent attempts [7] to reproduce these data using an independent fragmentation approach confirmed the challenge to describe the ALICE data. Measure-ments of Λ c production have also been carried out by the LHCb collaboration at forward rapidities, yielding smaller values of Λ c /D 0 ≃ 0.25 ± 0.05 in √ s = 7 TeV pp collisions [21], and ∼ 0.35 ± 0.05 in √ s NN = 5 TeV pPb collisions [22].…”

New vistas in charm production

“…Finally in this presentation we consider production of Λ c baryons. Whether the independent parton fragmentation works for Λ c baryons was discussed in [14]. In such an approach the cross section can be written as:…”